Durham E-Theses
Studies on the organic chemistry of boron
Livingstone, J.G.
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Livingstone, J.G. (1961)
Studies on the organic chemistry of boron, Durham theses, Durham University.
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79
STUDIES
THE
ORGANIC
OF
ON
CHEMISTRY
BORON
BY
J . Gr« LIVINGSTONE
A d i s s e r t a t i o n s u b m i t t e d f o r t h e Degree o f D o c t o r o f
P h i l o s o p h y i n t h e Durham C o l l e g e s o f t h e
U n i v e r s i t y o f Durham.
1961
CONTENTS
Page
Acknowledgments
(1)
Memorandum
(II)
Summary
(Ill)
FART I
Introduction
Page
Organor-Derivatives o f B o r i c A c i d
I
T r i a l k y l - and T r i a r y l Boranes
8
Mixed T r i a l k y l and A r y l - A l k y l b o r a n e s
40
C y c l i c Boranes
43
B o r o n i c A c i d s and E s t e r s
46
B o r i n i c A c i d s and E s t e r s
54
Boroxines
62
A l k y l - and A r y l - D i h a l o b o r a n e s
65
D i a l k y l . and D i a r y 1 Haloboranes
72
PART I I
P r e p a r a t i o n o f Reagents
Page
Chlorodiphenylborane
78
Chlorodi-p-tolylborane
79
Chlorodi-p-bromphenylborane
79
Pluorodimesitylborane
80
-
Dimethylaminoborp^^feuLoride
(22SEPIW
)
80
Page
Diphenylphosphine
80
Di-m-tolylphosphine
81
Tri-m-tolylphosphine
81
Triphenylarsine
82
Diphenylarsine
82
Phenylphosphine
83
PART I I I
Experimental Results
Aminoboranes
Page
Aminodiphenylborane
85
Aminodimesitylborane
85
Dimethylarain o d i p h e n y l b o r a n e
86
DiTn.fttliyla.Triiriodi-p-tolyl'bora.jie
86
Dimethylaminodi-p-bromophenylborane
86
Diphenylaminodiphenylborane
88
Di-p-tolylamino:diphenylborane
89
D i p h e n y l a m i n o d i - p - t o l y l b o r a n e at
89
AMINO &I - o - t O L Y L b o » A N e .
Phosphinoboranes
Diphenyl(diethylphosphino)borane
90
D i - p - b r o r a p h e n y l ( d i e t h y l p h o s p h i n o ) b o r a n e 90
Diphenyl(diphenylphosphino)borane
91
Chlorodiphenyl(diphenylphosphino)
borane
92
Triethylammoniura c h l o r o d i p h e n y l ( d i p h e n y l p h o s p h i n o ) borane
92
Diphenyl(di-m-tolylphosphino)borane
Di-m-tolylphosphinodi-p-tolylborane
Di-p-bromphenyl(di-m-tolylphosphino)
borane
Phenyl(bis-diphenylphosphino)borane
Dichlorophenyl(phenylphosphino)borane
Phenyl(phenylphosphino)borane
Di~m-tolylphosphino( dimesityl)borane
Di-m-to-lylphosphino( b i s - b i p h e n y l ) b o r a n
Bis-diphenyl(phenylphosphino)borane
Arsinoboranes
Mphenylarsinodiphenylborane
D i p h e n y i a r s i n o ( d i - p - 1 o l y 1 ) b orane
Diphenylarsino(di-p-bromphenyl)borane
Methods o f A n a l y s i s
Boron
Phosphorus
D i p o l e Moment Measurements
Theory o f Measurements
Evaluation of Results
P h y s i c a l Measurements
Experimental
Discussion
Appendix
I n t r o d u c t i o n t o B o r i n i c Acids
Page
Experimental
139
Discussion
140
I n t r o d u c t i o n t o w h i t e phosphorus
141
Reaction w i t h Phenyllithium
142
Reaction w i t h M e t h y l l i t h i u m
144
R e a c t i o n w i t h Boron T r i c h l o r i d e
144
Discussion
145
Tables
References
Experimental
Page
139
Discussion
140
I n t r o d u c t i o n to white phosphorus
141
Reaction with Phenyllithium
142
Reaction with Methyllithium
144
R e a c t i o n w i t h Boron T r i c h l o r i d e
144
Discussion
145
Tables
References
(i)
ACKNOWLEDGEMENTS
The
a u t h o r w i s h e s t o express h i s most s i n c e r e
t h a n k s t o P r o f e s s o r G. E. Coates, M.A., D . S c , F.R.I.C.,
under whose d i r e c t i o n t h i s r e s e a r c h was c a r r i e d o u t ,
f o r h i s c o n s t a n t encouragement and e x t r e m e l y v a l u a b l e
a d v i c e , and t o Dr. G. Kohnstam and Dr. P. G l o c k l i n g f o r
t h e i r comments.
The
a u t h o r a l s o t a k e s t h i s o p p o r t u n i t y t o express,
h i s t h a n k s t o t h e Senate o f Durham U n i v e r s i t y a t w h i c h
l a b o r a t o r i e s t h i s work was c a r r i e d o u t , and t o t h e
Department o f S c i e n t i f i c
t h e award o f a g r a n t .
and I n d u s t r i a l Research f o r
(ii)
MEMORANDUM
The work i n c l u d e d i n t h i s t h e s i s was c a r r i e d
out a t t h e Durham C o l l e g e s Science L a b o r a t o r i e s i n
the U n i v e r s i t y
o f Durham between September 1958 and
September 1 9 6 1 ,
and has n o t been s u b m i t t e d f o r any
o t h e r Degree.
P a r t o f t h i s work has a l r e a d y been
the subject o f a p u b l i c a t i o n i n t h e Journal o f t h e
Chemical S o c i e t y .
A l l t h e work d e s c r i b e d i s t h e o r i g i n a l work o f
t h e a u t h o r , e x c e p t t h a t acknowledged by r e f e r e n c e .
(iii)
SUMMARY
S e v e r a l a m i n o d i a r y l b o r a n e s ( A r B NR ) have been
2
2
p r e p a r e d by t h e methods:
Ar BCl + LiNR
2
2
= Ar^B^NRg + L i C l
(l)
Ar^BCl + R NH + Bt^N = A r B NR + Et^NHCl ....
2
2
2ArMgBr + C1 B NR
2
?
= A r B NR + M g C l
2
(2)
?
2
2
(3)
+ MgBr .
2
Aminodiphenylborane (R = H, method 2 ) i s d i m e r i c and nonp o l a r i n benzene s o l u t i o n .
Experiments
w i t h m o l e c u l a r models
i n d i c a t e t h a t l a r g e r groups a t t a c h e d t o t h e n i t r o g e n
would
cause s u b s t a n t i a l s t e r i c i n t e r f e r e n c e even w i t h t h e h y d r o g e n
atoms i n o r t h o - p o s i t i o n s on t h e a r y l g r o u p s .
Similarly,
a m i n o d i r a e s i t y l b o r a n e i s monomeric.
A l l t h e o t h e r aminodiarylboranes prepared are
raonomeric
i n nitrobenzene s o l u t i o n , though o f t e n s l i g h t l y associated
i n benzene p a r t i c u l a r l y i n t h e more c o n c e n t r a t e d s o l u t i o n s .
The monomeric a m i n o d i a r y l b o r a n e s have low d i p o l e moments
whose d i r e c t i o n i s r e v e r s e d on p a s s i n g f r o m Ph B*NMe t o
2
Ph BNPh .
2
2
2
T h i s r e v e r s a l o f p o l a r i t y c o u l d be due t o t h e
e l e c t r o n r e p e l l i n g e f f e c t o f a m e t h y l g r o u p , whereas a p h e n y l
group can a c t as an e l e c t r o n a c c e p t o r i n such a system. A l l
t h e observed moments a r e c o n s i s t e n t w i t h o n l y a s m a l l o r
zero n e t p o l a r i t y f o r t h e B-N bond.
(iv)
The
r a p i d and
q u a n t i t a t i v e h y d r o l y s i s , by c o l d w a t e r ,
o f the aminoboranes was
t h e b a s i s o f a method sometimes
used f o r t h e i r a n a l y s i s , and
more i m p o r t a n t
v e n i e n t method f o r t h e p r e p a r a t i o n
f o r a most con-
of d i a r y l b o r i n i c acids.
Some t w e l v e a c i d s have been p r e p a r e d as t h e monoethanolamine
esters
( y i e l d s 51-93$) by h y d r o l y s i s , n f t h e
diarylarainor-
borane o b t a i n e d f r o m the r e a c t i o n o f a s l i g h t excess o f t b e
appropriate
Grignarrt r e a g e n t w i t h d i c h l o r o d i p h e n y l a m i n o b o r a n e .
T h i s would appear t o be t h e most c o n v e n i e n t p r e p a r a t i v e
method
f o r d i a r y l b o r i n i c acids.
P h o s p h i n o d i a r y l b o r a n e s are monomeric b u t u n l i k e
the
amino nompounds t h e y are q u i t e s t a b l e t o b o i l i n g d i l u t e
and
alkalies*
acids
However, q u a n t i t a t i v e o x i d a t i o n by aqueous
a l c o h o l i c hydrogen p e r o x i d e t o b o r i c a c i d t h e p h o s p h i n i c
and
t h e p h e n o l has
analysis.
acid
sometimes been used as a method f o r t h e i r
T h e i r d i p o l e moments are g e n e r a l l y g r e a t e r
those o f t h e c o r r e s p o n d i n g amino-compounds, and
group i s a t t h e n e g a t i v e end
of the d i p o l e .
than
the phosphino-
This s u r p r i s i n g
r e s u l t suggests t h a t phosphorus a c t s as a % donor ( t o b o r o n )
o n l y w e a k l y i f a t a l l i n these compounds, p o s s i b l y
owing t o
an u n f a v o u r a b l e r e l a t i o n between t h e " s i z e s " of b o r o n
and
phosphorus 3p-
orbitals.
2p-
(v)
Formula I a c c o u n t s i n a q u a l i t a t i v e way
not
only
f o r t h e observed d i p o l e moments, but a l s o f o r t h e
of chemical r e a c t i v i t y , since
b o t h boron and
are
(or p a r t l y so).
co-ordinatively saturated
r
lack
phosphorus
Further
— t h e i n d i c a t e d charge
between boron and
separation
phosphorus
s h o u l d r e s u l t i n B-P
stretching
f o r c e c o n s t a n t s g r e a t e r t h a n would
be e x p e c t e d f o r B-P
since
s i n g l e bonds,
t h e B-P bond would amount
t o a o-bond p o s s i b l y w i t h a s m a l l Ti-component but
some e l e c t r o s t a t i c a t t r a c t i o n i n a d d i t i o n .
t h e B-P
bond c o u l d perhaps be d e s c r i b e d
I n t h i s sense
as a
"serai-polar
double bond", t h u s a c c o u n t i n g f o r t h e r a t h e r h i g h
(1400
- 1500
B-P bond.
- 1
c m ) associated
The
frequencies
w i t h the s t r e t c h i n g of
the
reason f o r the phosphinodiarylboranes being
monomeric, when t h e s e r i e s R^B'PR^ (R = H,
a l k y l ) form
t r i m e r s , t e t r a m e r s , or p o l y m e r s , t h u s l i e s i n t h e
atom i n t h e d i a r y l b o r a n e
saturated
with
series being already
boron
coordinatively
( o r n e a r l y so) n o t by T C - b o n d i n g w i t h phosphorus
b u t by ir-bonding w i t h t h e a r y l g r o u p s .
The
a r s i n o - d e r i v a t i v e s are
s i m i l a r t o the phosphino-
(vi)
compounds but t h e y are l e s s p o l a r .
Perhaps t h e most s i g n -
i f i c a n t d i f f e r e n c e i s t h a t o x i d a t i o n w i t h aqueous a l c o h o l i c
hydrogen p e r o x i d e a f f o r d s b o r i c a c i d , a r s e n i c
appropriate
phenols
Ph B AsAr
2
2
smaller
due
to a smaller
the
e.g.
+ H,^ —
The
a c i d and
2PhOH + 2ArOH.+ H^BO^ + I^AsO^
d i p o l e moments of t h e a r s i n o b o r a n e s i s p r o b a b l y
degree o f e l e c t r o n t r a n s f e r f r o m
arsenic
t o t h e a r y l groups bound t o i t .
I t now
seems e v i d e n t
t h a t t h o u g h t h e o'-donor
of n i t r o g e n , phosphorus, and
arsenic
character
towards boron d i m i n i s h e s
i n t h a t o r d e r t h e rc-donor c h a r a c t e r
d i m i n i s h e s even more
rapidly.
The
and
phosphinoboranes Ph B ( P P h ) , Ph P ( B P h ) , (Ph B PPh)
2
(Ph B PPh)
2
have a l s o been p r e p a r e d .
2
2
They are a l l more
s e n s i t i v e t o o x i d a t i o n t h a n t h e phosphinodiarylboran.es mentioned
earlier.
P A R T
I
I N T R O D U C T
I O N
1.
A)
1.
ORGANO-DERIVATIVES OF BORIC ACID
PREPARATION OF TRIALKYL- & TRIARYL BORATES
The best known and most s t a b l e organo d e r i v a t i v e s
of b o r i c a c i d are the t r i a l k y l and t r i a r y l borates (RO)^B;
unsymmetrical e s t e r s ROB(OR') are known but they tend
2
to d i s p r o p o r t i o n a t e t o the symmetrical e s t e r s .
Indeed
d i s p r o p o r t i o n a t i o n i s a common and sometimes troublesome
f e a t u r e o f organo-boron chemistry.
1
Lappert" " i n h i s review describes s e v e r a l methods o f
p
p r e p a r a t i o n o f the borates.
Ebelmen and Bouquet , t h e
f i r s t workers t o mention orthoborates, prepared t r i m e t h y l ,
t r i e t h y l , and t r i a m y l borates by h e a t i n g the a p p r o p r i a t e
a l c o h o l w i t h boron t r i c h l o r i d e i n a sealed tube, but attempts
t o prepare t r i a l l y l and t r i b e n z y l borates were unsuccessful.
M i c h a e l i s and H i l l r i n g h a u s ^ prepared t r i a r y l borates by
the
sealed tube method a t 100° but r e c e n t l y Golclough,
4
Gerrard and Lappert
have shown t h a t h e a t i n g i s unnecessary,
t r i a r y l borates being obtained i n n e a r l y q u a n t i t a t i v e y i e l d
by the a d d i t i o n o f boron t r i c h l o r i d e ( 1 mole) t o the phenol
(3 moles) a t - 80°C i n methylene c h l o r i d e . Wiberg and S u t t 5
e r l i n i n v e s t i g a t e d the r e a c t i o n sequences i n the boron
2.
t r i c h l o r i d e - m e t h a n o l and boron t r i c h l o r i d e - e t h a n o l systems,
employing high vacuum apparatus at -80°C, and
obtained
q u a n t i t a t i v e y i e l d s of the orthoborates when the c o r r e c t
p r o p o r t i o n of reagents was used
3R0H + BC1
B(OR) +
3
3
3HC1
L a t e r l a r g e scale p r e p a r a t i o n s , by t h i s method, i n an i n e r t
solvent (pentane) a f f o r d e d the borates almost instantaneously
and i n n e a r l y q u a n t i t a t i v e y i e l d .
When about 20-100 grams
of b o r a t e , p a r t i c u l a r l y one of h i g h molecular weight, i s
r e q u i r e d the best method comprises h e a t i n g boron t r i o x i d e
w i t h the appropriate a l c o h o l i n toluene and a l l o w i n g the
condensed vapours t o percolate through anhydrous copper
sulphate i n a soxhlet e x t r a c t o r t o remove the water formed
i n the r e a c t i o n .
Trimethylborate was obtained i n good y i e l d
92% by Schechter^ when boron t r i o x i d e (2 moles) was added
to methanol (3 moles) at 35-60° and the mixture digested
1 hour a t 25°C.
2B 0
2
3
4 3CH OH •+ 3HB0 + B(OCH ) .
3
2
3
3
7
P i c t e t and Geleznoff
prepared
several t r i a r y l
and
t r i a l k y l borates by warming phenols or alcohols w i t h boron
acetate and s e p a r a t i n g the borate and a c e t i c a c i d by f r a c t ional
distillation.
3!.
Boric acid was f i r s t used t o prepare orthoborates
8
by Cohn :-
B(OH) 4 3HOH
3
B(OR) + 3H 0.
3
2
The e s t e r i f i c a t i o n was performed i n the presence of hydrogen
c h l o r i d e o r concentrated s u l p h u r i c a c i d .
Later t h i s method
was modified by use o f an i n e r t solvent such as benzene,
toluene or carbon t e t r a c h l o r i d e and removal of the water
o
as a t e r n a r y azeotrope .
1
Recently Brown, Mead and Shoaf ^ have found a general
synthesis f o r a l k y l borates by t h e r e a c t i o n between sodium
borohydride and t h e appropriate a l c o h o l i n the presence o f
one equivalent o f a c e t i c a c i d .
3R0H + NaBH + HOAC -r (RO) B + NaOAC + 4H
4
3
With t e r t i a r y alcohols higher temperatures
2
are needed t o
d r i v e o f f the l a s t mole of hydrogen and y i e l d s of about
20$ are obtained:-
2R0H • NaBH^ + HOAC
(R0) BH + NaOAC + 3^
2
and a t higher temperatures, ROH + (RO) BH ^(ROj^B + Hg.
2
Brown and co-workers also recommend the t r a n s e s t e r i f i c a t i o n o f methyl borate when other methods f a i l .
Less mention has been made o f t h e metaborates.
Schiff^"
observed t h a t t h e primary r e a c t i o n between ethanol and boron
t r i o x i d e was t h e f o r m a t i o n of methyl metaborate, the same
4
compound was also obtained from t r i e t h y l b o r a t e and
boron t r i o x i d e .
C H OH + B 0
2
5
2
B(OC H )
2
5
3
-* HOBO • C H OBO
3
2
+ B 0
2
3
5
~* 3 C H OBO
2
5
12
A c e t y l metaborate has been claimed by Dimroth
as a
product o f the p y r o l y s i s o f t e t r a c e t y l d i b o r a t e but no
d e t a i l s were given.
Goubeau and K e l l e r ^ r e p o r t e d t h a t
boron t r i o x i d e and t r i m e t h y l borate when heated i n a sealed
tube i n equimoiar p r o p o r t i o n s a f f o r d e d methyl metaborate
which was t r i m e r i c ( c r y o s c o p i c ) and t h e r e f o r e formulated
as a boroxole; i t decomposed a t 170-220°.
By o x i d a t i o n of t r i m e r i c n - b u t y l b o r o n i c anhydride w i t h
1
dry a i r Gruinmitt ^ obtained n - b u t y l metaborate which, c o n t r a r y
15
t o h i s observations, has been shown by Lappert
t o be
trimeric•
1
O'Connor and Nace ^ prepared 1-menthyl and c y c l o h e x y l
metaborates from t h e appropriate a l c o h o l and o r t h o b o r i c
a c i d , the water formed was removed by azeotropic
w i t h toluene.
ROH + H B0 -*R0B0 •* 2H 0.
3
3
2
distillation
Recently Lappert
11
1
has prepared the lower a l k y l
11
1
s
(Me, E t , Pr , P r , Bu , Bu , Bu , but n o t Bu*) metaborates
(RO.BO)^ by thermal or c a t a l y t i c decomposition
corresponding
o f the
d i a l k y l chloroboronates, (ROjgBCl, or by
heating the orthoborates w i t h boron t r i o x i d e .
The l a t t e r
method was also successful f o r preparing phenyl metaborate.
I I . PROPERTIES
( a ) PHYSICAL
Parachor and d i p o l e measurements have v e r i f i e d
planar
s t r u c t u r e s and e l e c t r o n d i f f r a c t i o n measurements on t r i methyl borate showed the BO^ c o n f i g u r a t i o n t o be planar
w i t h angles 120 ; bond distances were also measured.
I n f r a - r e d spectra o f metaborates showed strong absorp"l
1 8
t i o n bands near 720 and 735 cm- .
(b)
CHEMICAL
The borates are g e n e r a l l y e a s i l y hydrolysed by water
t o give o r t h o b o r i c a c i d and the a p p r o p r i a t e a l c o h o l ; t h e i r
important r e a c t i o n w i t h organo-metallic compounds w i l l be
mentioned i n d e t a i l l a t e r .
They are g e n e r a l l y very s t a b l e
6.
and can be heated t o q u i t e h i g h temperatures without
sign-
i f i c a n t decomposition.
They react w i t h acids, t y p i c a l products
1Q
being i n d i c a t e d by t h e f o l l o w i n g r e a c t i o n s :-
B(OC H )
3
160-180°C
+ 2B(OH)
*
B(OC H )
3
+ H S0
2
2
5
5
3C H OH + 3HB0
3
2
4
2
5
Heat
» C H HS0 + 2C H
2
5
4
2
2
+ HB0 + HgO
4
2
r
B(OC H )
2
5
3
+ H S0 *H 0
2
4
2
l H e a t t o 140-150°
y C H HS0 + B ( O H ) + ( C H ) 0
2
5
4
3
2
5
2 Addition of H 0
2
B(0C H )
2
5
3
+ H S0 + 2RC00H -» C H HS0 + B ( 0 H )
2
4
2
5
4
R = CH , n - C H , n - C H , C H
3
B(0C H )
3
+ 3HN0
B(0C H )
3
+ H P0
2
2
5
5
3
3
?
4
g
3
3C H 0N0 + B ( 0 H )
4
BP0 + 3C H 0H
2
5
4
2
2
g
3
+ 2RC00C H
2
5
5
3
5
Rapid d e a l k y l a t i o n occurs when borates c o n t a i n i n g powerful
e l e c t r o n r e l e a s i n g groups, e.g. 1 p h e n y l e t h y l borate,
w i t h hydrogen h a l i d e s : -
react
2
7.
B(OR) + 3HX
3
3RX + B(OH)
3
X = halogen
I n c o n t r a s t t o most a l k y l borates, t h e a r y l
borates
being stronger Lewis acids, g e n e r a l l y form c o o r d i n a t i o n
complexes w i t h ammonia and amines.
8
B)
1.
TRIALKYL- AND TRIARYL BORANES
PREPARATION
The r a p i d development o f organo-boron chemistry i n
the l a s t twenty years i s due t o three main f a c t o r s
a)
The use o f the v o l a t i l e t r i a l k y l s i n the study
of the e l e c t r o n i c and s t e r i c e f f e c t s which i n f l u e n c e t h e
f o r m a t i o n o f c o o r d i n a t i o n compounds.
b)
The a p p l i c a t i o n of t r i a l k y l s o f boron t o t h e
i s o m e r i s a t i o n o f o l e f i n s and the p r e p a r a t i o n o f primary
alcohols from o l e f i n s w i t h e i t h e r t e r m i n a l or non-terminal
double bonds.
c)
The use o f the t r i a l k y l s of boron as c a t a l y s t s
f o r the p o l y m e r i s a t i o n o f n e g a t i v e l y s u b s t i t u t e d v i n y l
compounds.
Compounds c o n t a i n i n g B-C bonds have been prepared by three
d i f f e r e n t types o f r e a c t i o n , these are r e a c t i o n s between
1)
another organo-metallic compound and a boron h a l i d e
or borate e s t e r .
2)
an o l e f i n and a boron hydride.
9.
3)
a hydrocarbon and a boron h a l i d e .
The l a s t of these i s g e n e r a l l y used t o prepare mono- or d i s u b s t i t u t e d boron h a l i d e s and w i l l be discussed
later.
The f i r s t r e a c t i o n i s the most successful and convenient f o r the p r e p a r a t i o n of t r i a l k y l s and t r i a r y l s of
boron e i t h e r on a l a b o r a t o r y or l a r g e scale.
The
boron
20
h a l i d e s g i v e best y i e l d s when used as t h e i r ether complexes
but a l k y l orthoborates appear t o be the most g e n e r a l l y
satisfied
reagents:
B(OMe) + 3RMgX - R^B + 3fflgX0Me
3MgX0Me + 3HC1 - l^MgClg + l^MgXg + 3Me0H
3
Where quaternary anions (BAr^~) may
be formed excess of
reagent must be avoided and t h i s i s p a r t i c u l a r l y
important
when o r g a n o - l i t h i u m compounds are used as a l k y l a t i n g
agents.
The f i r s t t r i a l k y l s were prepared by Frankland and Duppa'
i n 1859
by the a c t i o n of excess d i a l k y l zinc (methyl
and
e t h y l were used) on t r i e t h y l borate.
3R Zn i . 2B(OC H )
2
2
5
3
= 2BR • 3 Z n ( 0 C H ) .
3
2
5
3
This r e a c t i o n has not been much used since, because i t i s
apt t o become v i o l e n t and the y i e l d s are not as good as those
10:.
r e s u l t i n g from Grignard r e a c t i o n s .
However c a r e f u l c o n t r o l
of the r e a c t i o n between dimethyl zinc and boron t r i c h l o r i d e
22
has been used by Wiberg and Ruschmann
t o prepare the
unstable methyl boron c h l o r i d e s ; these products r e a d i l y
d i s p r o p o r t i o n a t e t o t r i m e t h y l b o r a n e and boron t r i c h l o r i d e .
This d i s p r o p o r t i o n a t i o n i s p a r t i c u l a r l y i n t e r e s t i n g since
2 ~\
McCusker, Ashby and Iffakowski
J
r e p o r t t h a t the e t h y l and
higher d i a l k y l b o r o n c h l o r i d e s showed no tendency t o d i s p r o p o r t i o n a t e below 170°,
even a f t e r repeated d i s t i l l a t i o n s
at atmospheric pressure.
The most s a t i s f a c t o r y a l k y l a t i n g agents f o r the
p a r a t i o n of organo-boron compounds now
pre-
appear t o be the
a l k y l s of a l u m i n i u m ^ ; no quaternary s a l t s are formed and
the f a c t t h a t many of the r e a c t i o n s r e q u i r e no solvent
or
diluent i s a p a r t i c u l a r l y a t t r a c t i v e feature f o r large
scale
preparations.
T r i e t h y l b o r a n e was
obtained by d i s t i l l a t i o n i n
SOfo
y i e l d , r e l a t i v e t o boron t r i f l u o r i d e , from the r e a c t i o n
B P 0 E t + Et ALOEt —* E t B + E t A l F
0Et
The use of amine complexes i s r a t h e r b e t t e r and y i e l d s of
3
2
3
2
3
2
2
11.
over 90$ o f t r i p r o p y l b o r a n e are obtained when a mixture
of t r i p r o p y l a l u m i n i u m and t r i e t h y l a m i n e - b o r o n t r i f l u o r i d e
i s heated t o 150-160°
n
Et N.BP + P r A l
3
Pr^B + Et^N
3
AlP^
Perhaps t h e most s a t i s f a c t o r y method i s the r e a c t i o n between
an aluminium a l k y l and a borate e s t e r , no solvent being
necessary.
A mixture o f t r i e t h y l aluminium and e t h y l o r t h o -
borate spontaneously heats t o over 100° and t r i e t h y l b o r o n
can be d i s t i l l e d o f f i n over 90% y i e l d :
B(0Et)
f Et AL = E t B -»• A L ( 0 E t )
3
3
3
3
A u s e f u l v a r i a t i o n o f t h i s method i s the p r e p a r a t i o n o f
boronic esters by t h e use of appropriate r e a c t a n t r a t i o s :
n
n
n
Et AL + 3B(OBu ) = 3 E t B ( 0 B u ) + A L ( 0 B u ) .
3
3
2
3
A l k y l metaborates also give good y i e l d s of t r i a l k y l s o f boron
when allowed t o r e a c t w i t h aluminium a l k y l s or more conv e n i e n t l y i n some instances a l k y l a l u m i n i u m sesquihalides.
The exothermic r e a c t i o n i s conveniently c a r r i e d out i n a
25
mineral o i l d i l u e n t .
3 E t A L C l + (Me0B0) = 3Et B + AL(0Me) * A L 0 * 2A1C1-J.
3
2
3
3
3
3
2
3
12.
The second general method, the a d d i t i o n of B-H
bonds t o
o l e f i n s , i s one of the most important developments i n boron
chemistry.
The r e a c t i o n between diborane and
9fi
olefins
aliphatic
97
and styrene
whereby organo-boron compounds
are formed was reported some years
ago.
The successful development of these r e a c t i o n s as u s e f u l
l a b o r a t o r y methods r e s u l t e d from improvements i n processes
f o r the p r e p a r a t i o n of diborane (by adding a s o l u t i o n of
sodium borohydride
i n 2,5,8-trioxanonane
(CH^OCHgCHg)
also known as d i e t h y l e n e g l y c o l dimethyl ether or 'diglyme
1
t o a s o l u t i o n of b o r o n t r i f l u o r i d e - e t h e r complex i n the same
solvent)
2 7 a
3WaBH + 4BF^
4
2B Hg + 3NaBF
2
4
and from the discovery t h a t the a d d i t i o n of diborane t o
o l e f i n s i s s t r o n g l y catalysed by ethers.
Good y i e l d s of boron t r i a l k y l s are also obtained when
triethylamine-borane (Et^N.BH^) i s heated w i t h o l e f i n s at
200°.
25
The p r e p a r a t i o n of organo-boron compounds by
B-H
a d d i t i o n t o o l e f i n s does not n e c e s s a r i l y i n v o l v e the p r e p a r a t i o n of diborane.
One recent method depends on the
13.
f o r m a t i o n of diborane or some other a c t i v e B-H compound
from sodium borohydride and a l i t t l e aluminium c h l o r i d e
and i t s use on s i t u .
For example, t r i - n - p e n t y l b o r o n has
been prepared by adding 1-pentene (0.5 mole) t o a s t i r r e d
s o l u t i o n of sodium borohydride (0.25 mole) and
c h l o r i d e (0.084 mole) i n diglyme (250 c . c ) .
aluminium
When s t i r r i n g
had been continued three hours a t room temperature
and one
hour on a steam bath, solvent was pumped from the cooled
r e a c t i o n m i x t u r e , and t r i - n - p e n t y l b o r a n e c o l l e c t e d on 88$
o
27b
y i e l d a t 94-95 /2 mm.-
More recent work has shown the
r e a c t i o n t o work e q u a l l y w e l l u s i n g more e a s i l y obtainable
ethers ( d i e t h y l e t h e r , t e t r a h y d r o f u r a n , and t r i g l y m e ) d i f f e r e n t hydride sources and s e v e r a l other Lewis a c i d s .
The a d d i t i o n of B-H bonds t o t e r m i n a l o l e f i n s i s f a s t e r
than a d d i t i o n t o non t e r m i n a l o l e f i n s , and treatment of a
mixture o f 1 - and 2-pentene w i t h a d e f i c i e n c y of diborane
r e s u l t s i n the s e l e c t i v e conversion of the t e r m i n a l o l e f i n
into tri-n-pentylborane.
The a d d i t i o n of diborane t o 2-
pentene gives a mixture of products, since o x i d a t i o n of the
r e s u l t i n g t r i a l k y l b o r a n e y i e l d s a roughly 2:1 mixture o f 2-
14
and 3-pentanol:
28b
H
Pr
11
CH:CH
B
^ ^ n ^
2
2°2 95# n-C H OH
OH5
i;L
B,JL
EtCH:CHCH
3
H
^°5 ll^3
B
-^-^63$ Pr
OH—
11
CHOHCH + 37$ EtgCHOH
3
Various attempts a t the p r e p a r a t i o n o f mixed t r i a l k y l b o r a n e s
RRgB, have shown t h a t these compounds tend t o d i s p r o p o r t i o n a t e
and, more p a r t i c u l a r l y , t o isomerise i n the sense t h a t compounds
are favoured i n which chain branching i s absent or r e l a t i v e l y
remote from the boron atom.
I f the mixed alkylboranes
resulting
1
from the r e a c t i o n o f diborane w i t h 2-pentene are b o i l e d i n d i glyme' f o r f o u r hours, they are converted i n t o t r i - n - p e n t y l
boron since o x i d a t i o n w i t h a l k a l i n e hydrogen peroxide a f f o r d s
1-pentanol:
B„H
EtCHrCHCH, - ^ - X
EtCH CHCH
EtCH'CHCH
T73
0
3
B
/
n-C H OH
5
1:L
l 8 4 / 4 ]Lours
H^O,
,
2 2
(n-Cj^^B
V
0HNot only does t h i s r e a c t i o n provide a method f o r o b t a i n i n g
primary a l c o h o l s from non-terminal o l e f i n s , but i t s scope has
15.
been extended by t h e discovery t h a t t h e r e a c t i o n i s
reversible.
A t r i a l k y l b o r a n e whose a l k y l chains are three
or more carbon atoms long r e v e r s i b l y d i s s o c i a t e s
when heated:
2(RCH CH ) B * (RCH CH ) BH-BH(CH CH R) + 2CH :CHR
2
2
3
2
2
2
2
2
2
2
Consequently a d d i t i o n of a less v o l a t i l e longer chain o l e f i n
OA
pQ
w i l l displace a more v o l a t i l e shorter chain o l e f i n . *
( D i - s e c - b u t y l ) t-butyl-borane has been prepared by McCusker,
Hennion and Rutkowski and was found t o be stable t o d i s o 29
proportionation
or re-arrangement below 60.
An important d i s t i n c t i o n between a l k y l b o r o n
and a l k y l -
aluminium compounds i s t h a t t h e former r e a c t w i t h both
terminal/'olefins ( c o n t a i n i n g C:CH group).
2
The a d d i t i o n
of o l e f i n s t o t r i a l k y l b o r a n e s i s catalysed by small amounts
of t r i a l k y l a l u m i n i u m . ^
Both boron 31 and aluminium32 hydrides react w i t h
acetylenes by c i s a d d i t i o n , and t h i s provides an important
route t o c i s o l e f i n s
R
H
R
H
\ /
HOAC
\S
Q
RC:CR
+
B H
2
2
6
6
'
d l
W
0°
*
g
^
/ \
R
B/
J
/ \
R
H
16.
This r e a c t i o n which has teen c a l l e d the hydroboration
r e a c t i o n , i s not s a t i s f a c t o r y when a p p l i e d t o t e r m i n a l
acetylenes since complete r e d u c t i o n occurs by a d d i t i o n o f
two B-H bonds.
This d i f f i c u l t y has been overcome by the
use o f a less r e a c t i v e B-H compound ( P r ^ H M e )
BH, i t s e l f
2
prepared from diborane and 2-methyl-2-butene:
n
(P^CHMe^BH • Bu C*CH
n
Bu CH: CHB( CHMePr )
2
HOAC
n
Bu CH:CH
2
H„0
n
Bu CHO.
The hydroboration of c y c l i c o l e f i n s r e s u l t s i n s t e r e o specifie cis hydration.
For example i f diborane i s passed
i n t o a s o l u t i o n of 1-methylcyclopentene i n t e t r a h y d r o f a r a n
f o r two hours a t 0° and the r e a c t i o n mixture hydrolysed and
oxidised w i t h a l k a l i n e hydrogen peroxide, trans-2-methylcyclopentanol i s obtained i n 85$ y i e l d w i t h only about 2$
cis
impurity.^
O
CH •}
-CH
!
13X„
17
The Long and Dollimore
m o d i f i e d Grignard method has
proved t h e most successful i n p r e p a r i n g the t r i a r y l b o r a n e s .
A l l o f them are a i r s e n s i t i v e ( r e q u i r i n g work under n i t r o g e n )
and t h i s , coupled w i t h t h e i r r e l a t i v e l y low v o l a t i l i t y , can make
t h e i r s e p a r a t i o n from r e a c t i o n mixtures d i f f i c u l t .
3CgH MgBr+BP .0(0 H ) -»(C H ) B+l-5MgP + l - 5 M B r
5
3
2
5
2
6
5
3
2
g
2
+ (C R" ) 0.
2
5
2
Further r e a c t i o n can occur w i t h excess Grignard t o give
t e t r a p h e n y l b o r a t e anions.
(CgH ) B • C H MgBr
5
3
6
MgBr"*
5
BtCgH^
7
This p r o p e r t y has proved u s e f u l i n preparing small amounts
of pure t r i p h e n y l b o r a n e .
A f t e r h y d r o l y s i s and removal of mag-
nesium as carbonate, trimethylamine hydrochloride i s added t o
the s o l u t i o n c o n t a i n i n g t e t r a p h e n y l b o r a t e ions when ( C H )
3
B(CgH(j)^
3
NH
™ i s p r e c i p i t a t e d and t h i s decomposes when heated i n
a stream o f n i t r o g e n a t 200?
(CH ) ftH
3
3
B(C H )
6
5
4
"
( C H ) N + CgHg + ( C g H ^ B
3
The t r i p h e n y l b o r a n e i s d i s t i l l e d
3
i n vacuum a f t e r the benzene
and trimethylamine have been swept away; the y i e l d (from t e t r a phenylborate) i s about 90$.
A new method f o r the p r e p a r a t i o n of t r i p h e n y l b o r a n e makes
18.
use o f the r e a c t i o n between benzene (present i n excess)
and diethylborane E t ^ Bg
a t 180° under p r e s s u r e d
I I . PROPERTIES
(a)
PHYSICAL
Molecular weight measurements^ (cryoscopic i n benzene)
of s e v e r a l t r i a r y l b o r a n e s have shown them t o be monomeric.
Stock and Z e i d l e r ^ showed the methyl and e t h y l homologues
t o be monomeric (vapour d e n s i t y ) and Bamford, L e v i and
•37
Newitt
a r r i v e d a t s i m i l a r conclusions
(methyl, i s o - p r o p y l ,
n - p r o p y l ) by e v a l u a t i o n o f Trouton's constant.
The f o r c e
constants o f trimethylborane c a l c u l a t e d by Goubeau
from
Raman and u l t r a - v i o l e t spectra would suggest t h a t resonance
of the type found i n the boron h a l i d e s was u n l i k e l y , _i.£.
the B-C bonds are e s s e n t i a l l y s i n g l e .
(b)
CHEMICAL
Generally h y d r o l y t i c a l l y s t a b l e i n a c i d , a l k a l i n e , o r
n e u t r a l s o l u t i o n , t h e t r i a l k y l b o r a n e s are q u i t e s t a b l e except
i n the presence of o x i d i s i n g agents, (thus they r e q u i r e an
i n e r t atmosphere f o r t h e i r m a n i p u l a t i o n ) .
19.
Trimethylborane, though s t a b l e t o water under
o r d i n a r y c o n d i t i o n s , i s slowly (7 hours) hydrolysed
at 180° w i t h loss o f one methyl group.
S t i l l more
r e s i s t a n t t o hydrogen sulphide i t reacts a t 280° g i v i n g
boron sulphide, *
B S
2
3
+- CH
280°
18D°
4
K S + Me B * H 0
* Me B0H + CH
4
2
3
2
2
4
T r i a l l y l b o r a n e i s most unusual i n i t s ease of hydrolysis.
40
and r e a c t i o n w i t h b u t a n o l ;
(CH :CH CH ) B + H 0 -> (CHg-.CH CH )B(0H)
2
2
3
2
2
n
n
(CH :CH CH ) B + Bu 0H
2
2
2
CH :CH C H B ( 0 B )
3
2
2
U
2
T r i a r y l b o r a n e s are not s e n s i t i v e t o water but t r i p h e n y l borane reacts w i t h a l c o h o l t o give e t h y l diphenylborate.
( C H ) B * EtOH
g
5
3
(C H ) BOEt • CgHg.
6
5
2
The chemical r e a c t i v i t y o f t h e t r i a l k y l - and t r i a r y l
boranes may be accounted f o r by t h e i r very powerful
Lewis
a c i d p r o p e r t i e s and so as h i g h l y r e a c t i v e e l e c t r o p h i l e s
many o f t h e i r r e a c t i o n s , a t l e a s t i n the i n i t i a l stages,
probably i n v o l v e c o o r d i n a t i o n .
20.
(i)
OXIDATION
The lower t r i a l k y l b o r a n e s are spontaneously
inflammable
but t h e i r pyrophoric character decreases as the size o f t h e
hydrocarbon group increases.
The t r i a r y l b o r a n e s are much
less e a s i l y o x i d i s e d , tri-e<-naphthylborane being s t a b l e
i n a i r but t h i s i s probably due t o slowness o f a t t a c k by
oxygen on account of s t e r i c
hindrance.
1
C o n t r o l l e d oxidation^" " o f t h e lower t r i a l k y l b o r a n e s
leads t o t h e f o r m a t i o n of e s t e r s o f a l k y l b o r i n i c a c i d s ,
e.g.
2 Bu
n
3
B * 0
2
2 Bu
n
11
2
BOBu
That t h e primary ( o r a t l e a s t an e a r l y ) step i n t h e r e a c t i o n
i s t h e f o r m a t i o n o f a peroxide has been confirmed i n t h e
case o f t r i m e t h y l b o r a n e
. At pressures below t h e explosion
l i m i t Me B00Me i s obtained; t h i s explosive substance i s
2
reduced t o methyl d i m e t h y l b o r i n a t e by sodium i o d i d e a t -78°C
I n a sealed tube a t room temperature i t rearranges t o give
about 90$ dimethyl methylboronate.
MeB(OMe),,.
The o x i d a t i o n o f organo-boron compounds w i t h a l k a l i n e
( o r a l c o h o l i c a l k a l i n e ) hydrogen peroxide smoothly breaks
the B-C bonds, w i t h q u a n t i t a t i v e f o r m a t i o n o f an a l c o h o l
21.
and a b o r i c a c i d .
This i s a general r e a c t i o n o f a n a l y t i c a l
importance.
(ii)
REACTIONS WITH HALOGENS AND HYDROGEN HALIDES
The lower t r i a l k y l s o f boron inflame i n c h l o r i n e o r
bromine, but t r i p r o p y l b o r a n e reacts smoothly w i t h i o d i n e
at about 150°, g i v i n g
Pr*B + 1
iododipropylborane:
n
2
Pr BI + PA
The corresponding c h l o r i d e and bromide have been obtained
by the a c t i o n o f antimony t r i c h l o r i d e ( o r SbBr^) on t h e
iodidef^
When hydrogen c h l o r i d e i s bubbled i n t o t r i b u t y l b o r a n e
at 110° d i b u t y l b o r o n c h l o r i d e (b.p. 173°) i s formed almost
44.
quantitatively .
Bu^B + HC1 -* B u
n
BC1 + C H
4
10
Further r e a c t i o n w i t h hydrogen c h l o r i d e takes place between
180° and 210°, but mixtures o f products r e s u l t .
(iii)
REACTIONS WITH ALKALI METALS AND THEIR HYDRIDES
T r i a l k y l b o r a n e s r e a c t w i t h a l k a l i metals o r t h e i r
amides i n l i q u i d ammonia ( e s s e n t i a l l y ammonia c o o r d i n a t i o n
compounds are formed):-
22.
R^B -v NH M* (R B-NH )~ + $ H
3
3
2
2
R^B-NH-j+M
2 B'NH + NaNH —? Na*(R BNH )~ «• NH
3
3
2
3
2
3
These s a l t s can be c r y s t a l l i s e d from ether, but are only
s l i g h t l y soluble i n benzene and are i n s o l u b l e i n l i g h t
petroleum. S i m i l a r compounds are formed i n ethylamine
45
s o l u t i o n , e.g.
Me B'NH Et
3
2
Li
L i * (Me-jB-NHEt)" + ^Hg
I n the absence of ammonia, t r i - n - b u t y l b o r a n e i n ether
s o l u t i o n very s l o w l y develops a colour on standing i n
contact w i t h l i q u i d sodium/potassium a l l o y , but no compound
has been i s o l a t e d . I n c o n t r a s t t h e t r i a r y l b o r a n e s form
w e l l defined adducts w i t h a l k a l i metals.
Although s t e r i c e f f e c t s l a r g e l y o f f s e t t h e enhanced
acceptor p r o p e r t i e s o f the more e l e c t r o n e g a t i v e a r y l groups,
strong acceptor p r o p e r t i e s are s t i l l evidenced i n t h e i r
r e a c t i o n s w i t h the a l k a l i metals
Ar^B •* Na
Ar-jB* Na*
46
The r e s u l t i n g compounds
which are prepared i n ether
23
s o l u t i o n w i t h r i g o r o u s exclusion of moisture,
oxygen
and even carbon d i o x i d e , are n e c e s s a r i l y r a d i c a l s ( i f
monomeric). The t r i p h e n y l b o r a n e
anion-radical i s i s o -
e l e c t r o n i c w i t h the t r i p h e n y l m e t h y l n e u t r a l r a d i c a l , and
i n f a c t the colours of the two s e r i e s are s i m i l a r ,
Triphenylborane-sodium reacts w i t h t r i p h e n y l m e t h y l
w i t h the f o r m a t i o n of the t r i p h e n y l m e t h y l
,
+
Ph B "toa + Ph C*
3
anion,:
Ph B + Ph^C~Na*.
3
3
A b r i l l i a n t red compound r e s u l t s from t r i p h e n y l m e t h y l
t r i p h e n y l b o r a n e ; t h i s may
(Ph B-CPh )*.
3
w e l l be a r a d i c a l of c o n s t i t u t i o n
There i s some e v i d e n c e ^ t h a t
3
sodium i s dimeric ( Ph B«BPh
3
and
a
3
triphenylborane-
Na"*"*) since i t i s d i a 2
magnetic*
The
conductance of these compounds i n ether s o l u t i o n
i s very small, i n d i c a t i n g extensive
ion-association.
Tri-o^-naphthylborane can add successively
one atom
of sodium t o give the brown-yellow compound (0-^11^)
( o r i t s dimer) and then a second t o give the deep v i o l e t
(C H )
1 0
7
+
3
B=Na +.
48
2
Studies on the molecular weights of s o l u t i o n s of the
a d d i t i o n compounds, and on t h e i r magnetic s u s c e p t i b i l i t i e s ,
24
have shown a marked dependence of t h e p o s i t i o n of t h e
monomer-dimer e q u i l i b r i a on ( a ) t h e aromatic groups
bonded t o boron, and (/b )\ t h e s o l v e n t . 49
^ The tendency
t o form monomeric anions (which, however, e x i s t as i o n p a i r s ) increases w i t h the degree of s t e r i c hindrance
about t h e boron, i n t h e order:
phenyl < 1-naphthyl < 2-naphthyl <• m e s i t y l
The e f f e c t of t e t r a h y d r o f a r a n i n d i s s o l v i n g s o d i u m - t r i 1-naphthyl ~ borane as the green monomeric form, i n
c o n t r a s t t o d i e t h y l ether d i s s o l v i n g i t as the orange
dimeric form has been a t t r i b u t e d t o t h e s t r o n g e r donor
character of t e t r a h y d r o f a r a n r e s u l t i n g i n a B-0 covalent
bond
(1-C H )3*B~- 0 ( C H ) }
10
7
2
4
+
Na .
The t r i a r y l b o r a n e - a l k a l i metal3 compounds are v e r y
r e a c t i v e ; i o d i n e i n ether i s immediately d e c o l o r i s e d
2 Ph B Na* + I
3
2
= 2 Ph^B + 2NaI
The r e a c t i o n w i t h methanol gives a boron hydride
50
derivative:
2Ph B~Na+ + MeOH - Na* j~Ph B-0Me~| ~ * Na+ j~Ph BH ~ J "
3
3
3
25-
Trimethylborane
reacts w i t h l i t h i u m aluminium hydride
at room temperature (24 hours) t o form dimethyl aluminium
hydride^
1
LiAIH
+ Me-jB
4
LiBH^Me + Me AlH
2
52
Recently Wiley and co-workers
have shown t r i e t h y l -
borane t o form an a d d i t i o n compound w i t h sodium h y d r i d e .
Sodium ( o r l i t h i u m ) t r i p h e n y l b o r o h y d r i d e can be
obtained by the d i r e c t a d d i t i o n ( i n e t h e r ) o f t r i p h e n y l b o r a n e
53.54
to sodium o r l i t h i u m hydride, though a b e t t e r method
'
i s t o add, say, L i H t o Ph^B and heat a t 180° u n t i l the melt
solidifies.
They are moderately r e a d i l y hydrolysed by water,
but v i g o r o u s l y evolve hydrogen w i t h acids,
Na £ph BHj" + H 0* = Na* + Ph^B + H + H 0.
+
3
(iv)
3
2
2
REDUCING PROPERTIES
The f o l l o w i n g examples o f r e a c t i o n s w i t h a l c o h o l s ,
aldehydes, ketones and c a r b o x y l i c acids show the reducing
p r o p e r t i e s o f the t r i a l k y l b o r a n e s .
B(C H )
3
+ RCHO
B(C H )
3
+ RCH OH -» ( C H )
B(C H )
3
t RCOOH -* ( C 5 ^ 2
2
2
2
5
5
5
(C H )
2
5
2
2
H
2
2
5
BOCHg R + C H
2
BOCH R + C H
2
B
4
2
0
0
C
R
+
2
H
°2 6
g
26.
Using these r e a c t i o n s , Meerwein, Hinz, Majart and
55
Sonke
prepared boronous esters and also d i a l k y l b o r o n i t e s .
T r i a r y l b o r a n e s r e a c t w i t h alcohols t o form b o r i n i c
esters.
(C H )
6
(v)
5
3
B + C H OH -* ( C H )
2
5
6
5
2
BOC H + CgHg
2
5
REACTIONS WITH ALKALIS
T r i a r y l b o r a n e s react w i t h a l k a l i s t o form complexes
c o n t a i n i n g f o u r - covalent boron.
A compound which c r y s t a l -
l i s e d w i t h water or a l c o h o l was obtained by D. L. Fowler
56
and C. A. Kraus'
from t r i p h e n y l b o r a n e w i t h t e t r a m e t h y l
ammonium hydroxide i n a l c o h o l i c s o l u t i o n .
Ph B + ( O H ) to -* ( 0 H ) n I
Ph,BOH 1
3
3
4
3
4
Fusion o f triphenylborane w i t h a l k a l i - m e t a l hydroxide
+
gives t h e sodium s a l t Na j^Ph^BOlTJ"* which c r y s t a l l i s e s w i t h
solvent o f c r y s t a l l i s a t i o n from ether.
Although s o l u b l e
i n water the s a l t hydrolyses and a c e t i c a c i d causes
immediate p r e c i p i t a t i o n o f t r i p h e n y l b o r a n e .
A similar
compound, Na* j~Ph BCN~l ~, prepared by G. W i t t i g and P.
57
3
Raff,
i s more stable t o acids and i s n e u t r a l i n aqueous
solution.
The l i t h i u m , sodium, potassium and ammonium
s a l t s are soluble i n water, t h e rubidium s a l t i s s l i g h t l y
27.
soluble and the ceasium s a l t i s i n s o l u b l e .
1:1 Complexes
between t r i p h e n y l b o r a n e and sodamide and t e t r a - n - b u t y l
ammonium hydroxide were confirmed by C. A. Kraus and W. WV
58
Hawes.
I n the former case, the e l e c t r i c a l c o n d u c t i v i t y
and the d i s s o c i a t i o n constant were measured, and i n the
l a t t e r t h e p o l a r i s a t i o n curve.
accurately
T r i - ot-naphthylborane was
t i t r a t e d i n a l c o h o l i c S o l u t i o n o f sodium meth-
oxide, ethoxide, or isopropoxide, using phenolphthaiein
as i n d i c a t o r .
+
( 0 H ) B + Na OGH "
1 0
(vi)
7
3
3
Na*j~
59
(C H ) BOCH
10
7
3
AMINE COMPLEXES
The v o l a t i l e t r i a l k y l b o r a n e s , being Lewis acids, are
s t r o n g l y e l e c t r o p h i l i c and t h i s p r o p e r t y makes them u s e f u l
i n the study of t h e e l e c t r o n i c and s t e r i c e f f e c t s i n f l u e n c i n g
coordination
compounds.
The most e x t e n s i v e l y
studied
compounds are the 1:1 complexes between ammonia or amines
and the t r i a l k y l b o r a n e s (and the t r i a r y l b o r a n e s ) .
These
are prepared by i n t e r a c t i o n a t low temperatures i n e q u i molar p r o p o r t i o n s
o f f under vacuum.
or excess base, the excess being pumped
I n cases where complex f o r m a t i o n has
f a i l e d s t e r i c hindrance has g e n e r a l l y
been the cause.
28.
Trimethylborane
can conveniently be stored and a l s o
p u r i f i e d using i t s s o l i d complex w i t h trimethylamine
(CH )
3
B«H ( C H ) .
3
3
3
Pure t r i m e t h y l b o r a n e i s regenerated w i t h hydrogen
chloride a f t e r resublimation
(CH )
3
3
B«N ( C H )
3
3
+ HC1 —» ( C H ) B + ( C H ) NHC1
3
3
3
3
T r i e t h y l b o r a n e has also been p u r i f i e d by i t s amine
complex by the same workers, H. C. Brown and R. B.
Johannesen^ T r i a r y l b o r a n e s l i k e t r i a l k y l b o r a n e s do n o t
coordinate t o ethers or other oxygen donors but form a
number of 1:1 complexes w i t h ammonia and amines.
So great
i s the s t e r i c s t r a i n i n these c o o r d i n a t i o n compounds t h a t
ammonia the l e a s t s t e r i c a l l y hindered donor forms t h e most
stable compounds.
With t r i - c x - n a p h t h y l b o r o n , which can
e x i s t i n two isomeric forms ( r o t a t i o n about B-C bonds)
the order o f donor s t r e n g t h o f the methylamines i s
NH 7 CH NH ^ ( C H )
3
3
2
3
2
NH * ( C H )
3
3
N, ammonia forms a s t a b l e
compound y e t trimethylamine does n o t combine.
(vii)
COMPLEXES WITH ORGANO-METALLIC COMPOUNDS
Trimethylborane
reacts w i t h e t h y l - l i t h i u m i n benzene
s o l u t i o n t o form a c r y s t a l l i n e compound L i B ( C H ) C H ^ ,
3
which would normally be regarded as a s a l t L i
+
3
2
B(CH?Kc H
3 3 25
29.
hence i t s s o l u b i l i t y i n benzene, a s u i t a b l e solvent f o r
c r y s t a l l i s a t i o n i s remarkable.
H. I . Schlesinger
and
H. C. Brown*'"'" r e p o r t e d t h a t the compound d i s s o l v e s i n
water t o give a c l e a r s o l u t i o n but w i t h i n a few seconds
a gas i s evolved.
A s i m i l a r compound LiB(CH-j) was
pre-
4
pared from m e t h y l - l i t h i u m and t r i m e t h y l b o r a n e by D.
Hurd.
T.
L i t h i u m t e t r a p h e n y l b o r a t e formed by the r e a c t i o n
of p h e n y l - l i t h i u m w i t h an ether s o l u t i o n of t r i p h e n y l b o r o n
was prepared by G. W i t t i g , C. Keicher, A. Ruckert and
P. R a f f . ^
The s a l t , more s t a b l e than the a l k y l s a l t s ,
i s s t a b l e t o water and i s decomposed by acids only a t
or more.
80°
I t c r y s t a l l i s e s from ether as L i ( B P h ) 8 E t 0 ,
4
the ether being l o s t i n h i g h vacuum.
2
The sodium s a l t i s
best prepared by adding excess sodium c h l o r i d e t o the
product of the r e a c t i o n between boron t r i f l u o r i d e
and
excess phenyl magnesium bromide ( a f t e r p r e c i p i t a t i o n of
magnesium as carbonate).
I t i s now a v a l u a b l e a n a l y t i c a l
reagent p a r t i c u l a r l y f o r potassium, rubidium, and caesium
as the s a l t s of these c a t i o n s are p r a c t i c a l l y i n s o l u b l e
i n water.
Several other c a t i o n s form t e t r a p h e n y l b o r a t e s
whose i n s o l u b i l i t y renders them s u i t a b l e f o r gravimetric.
a n a l y s i s , e.g
[ph P] [BPh ]
4
4
[<30(CO )H ]
4
[BPh 1
4
30.
Mixed complexes are w e l l e s t a b l i s h e d ; the compound
L i ^Ph CSCB(Ph)^| was prepared by G. W i t t i g and P.
Raff
who warmed t r i p h e n y l b o r a n e and l i t h i u m phenyl-
a c e t y l i d e and then cooled t o -80°G.
The complex
generates phenylacetylene w i t h acids and w i t h aqueous
i o d i n e gave p h e n y l e t h i n y l i o d i d e .
Triphenylborane and
p-dimethylaminophenyllithium a f f o r d e d a complex from
65
which G. W i t t i g and W. Herwig
i s o l a t e d an i n t e r e s t i n g
" z w i t t e r i o n " m.p. 337°-339° a f t e r conversion t o the
potassium s a l t and h e a t i n g w i t h methyl i o d i d e i n acetone.
Mel
[
M
e
H
2 <
)>
B P h
+
3
Prolonged h e a t i n g o f the complexes i n aqueous c e l l o s o l v e
r e s u l t e d i n decomposition.
G. A. Razuvaev and T. G.
B r i l k i n a ^ found t h a t benzene, phenol and d i p h e n y l b o r i n i c
acid were obtained from sodium or potassium t e t r a p h e n y l boronates.
Mixed complexes also reacted.
K |BPh J -* CgHg + C H 0H + PhgBOH
4
g
NH ^-C H BPh J
4
10
7
3
5
-s, C H
8
«. BPh NH
3C H
g
+ PhB(0H) .
10
10
3
3
2
31
Mixed a r a l k y l complexes were r e c e n t l y obtained
from a l k y l l i t h i u m (methyl, e t h y l ) compounds and t r i arylboranes (phenyl,cx-naphthyl).
Lithium methyltri—
borane decomposed on exposure t o a i r and f r e s h aqueous
s o l u t i o n s gave no v i s i b l e evidence o f r e a c t i o n s w i t h
potassium or ammonium s a l t s ; prolonged
standing, however,
caused p r e c i p i t a t i o n o f ammonium tetraphenylborane.
(viii)
INTERNAL COORDINATION COMPOUNDS
When t r i v a l e n t boron i s bonded t o an atom* o f donor
2
character by t r i g o n a l Sp bonds i t i s possibles f o r the
covalency o f the boron t o increase from three t o f o u r
by i n t e r n a l c o o r d i n a t i o n .
methyl
Thus, f o r example i n aminodi-
borane the boron atom assumes a s i m i l a r e l e c t r o n i c
c o n f i g u r a t i o n t o t h a t o f the carbon atoms i n ethylene.
-
+•
Me B-NH — 9 Me B - NH
Coordination s a t u r a t i o n can also be achieved by
2
2
2
2
a s s o c i a t i o n , u s u a l l y d i m e r i s a t i o n , and J. Goubeau and
67
R. L i n k
have obtained the above compound i n two d i f f e r e n t
forms a monomeric gas (b.p. 1°) and c o l o u r l e s s c r y s t a l s
(m.p. 9°).
32.
Me B
2
=
NH
Me «B
NH2
BMe2
a r e v e r s i b l e e q u i l i b r i u m i s observed i n the gas phase
at room temperature.
The nature of t h e atoms or groups
attached t o t h e boron or n i t r o g e n determine which form
of c o o r d i n a t i o n s a t u r a t i o n occurs.
When r e l a t i v e l y
e l e c t r o p o s i t i v e groups are bound t o boron double bonding
i s favoured, e.g. Me BNMe i s m o n o m e r i c ^ ' ^ and t h e B-N
70 x
2
2
f o r c e constant ( f r o m i t s Raman spectrum
B - N double bond(Me N) B,
2
3
71
) indicates a
S i m i l a r l y trisdimethylaminoboron,
methoxy dimethylboron ( M e B 0 M e )
2
methyl borate (MeO)^B are a l l monomeric.
6 9 , 7 2
and
The degree o f
c o o r d i n a t i v e s a t u r a t i o n i s n a t u r a l l y g r e a t e s t i n the t r i o x y or amino- compounds, and t h i s i s r e f l e c t e d i n a considerable
d i m u n i t i o n of r e a c t i v i t y .
71
I n compounds l i k e Cl B-NMe
2
i s achieved by d i m e r i s a t i o n .
2
coordinative saturation
Double bonding (B - N) i s
e v i d e n t l y much weakened by t h e B-Cl, and t h i s substance can
be obtained i n two forms; the v e r y r e a c t i v e l i q u i d monomer
slowly changes i n t o a remarkable, u n r e a c t i v e s o l i d dimer.
The dimer s t a b l e t o hot acids, i s converted back t o t h e
33.
monomer on v a p o r i s a t i o n .
The monomer i s v i o l e n t l y
hydrolysed
by c o l d water
2 Cl B-NMe
2
^
2
C1 ~BC^
^>B~C1
2
2
N
+ Me
2
Reactions between boron t r i c h l o r i d e ( o r BBr^) and
secondary amines w i t h r e l a t i v e l y bulky a l k y l or c y c l o a l k y l
groups give aminoboron h a l i d e s which remain monomeric, e.g.
1
Pr NBCl , B u ^ B C l .
2
2
2
I n c o n t r a s t , p i p e r i d i n o - and morpholino- boron d i 73
c h l o r i d e g r a d u a l l y form dimers:
/
\
y
B
ci
s
/
\
C 1
.B 2 /
B
2
ci
\
2
The B o r a z i n e s , another s e r i e s of c y c l i c
internal
c o o r d i n a t i o n compounds, have been the s u b j e c t of a r e c e n t
74
review.
Since the p r e p a r a t i o n of t h e parent compound
b o r a z i n e , B^N^Hg, b . p . 5 3 ° by A. S t o c k
7 5
i n 1 9 2 6 the
chemistry of t h i s c l a s s of compounds has been g r e a t l y
extended.
The compound was o r i g i n a l l y obtained by the
thermal decomposition of the diborane-diammonia complex
34.
B H .2NH
2
6
3
(now formulated as NHyBH'-NH^BH").
The planar
e s s e n t i a l l y aromatic s t r u c t u r e of borazine
has been confirmed by v a r i o u s
electron
76
d i f f r a c t i o n and s p e c t r o s c o p i c
studies.
The
main d i s t i n c t i o n from the u s u a l aromatic r i n g
i s the a l t e r n a t i n g e l e c t r o n d e n s i t y r e s u l t i n g
from the d i f f e r e n t e l e c t r o n e g a t i v i t i e s of the
boron and n i t r o g e n atoms.
Though borazine i t s e l f
slowly
decomposes a t room temperature, many of i t s d e r i v a t i v e s
w i t h a r y l or a l k y l groups s u b s t i t u t e d f o r hydrogen ( e i t h e r
on the boron or n i t r o g e n atoms) a r e s t a b l e when kept a t
room temperature and some d e r i v a t i v e s have been
studied
as part of r e s e a r c h programmes aimed a t m a t e r i a l s r e s i s t a n t
to high temperatures.
S e v e r a l new methods have been devised f o r the p r e 77
p a r a t i o n of b o r a z i n e , one of which i s the r e a c t i o n
3 LiBH
4
+ 3 NH C1
4
=
(NH-BH) * 9 H
3
2
+ 3 LiCl.
R e a c t i o n of l i t h i u m borohydride w i t h methylammonium
chloride s i m i l a r l y affords
3 LiBH
4
N-trimethylborazine:
+ 3 MeNH Cl = (MeN-BH) + 9 H
3
3
2
+ .3 L i C l
35.
Another method f o r the p r e p a r a t i o n of borazine i s
the r e d u c t i o n of B - t r i c h l o r o b o r a z i n e w i t h sodium borohydride
i n t r i e t h y l e n e g l y c o l dimethyl ether ( 2 , 3 , 8 , 1 1 - t e t r a 78
oxadecane)I
B - t r i c h l o r o b o r a z i n e i s now
relatively easily
prepared
from ammonium c h l o r i d e and boron t r i c h l o r i d e mixed w i t h
pumice soaked i n c o b a l t n i t r a t e s o l u t i o n , d r i e d and reduced.
B C 1
NH 01
4
1 N n
3
1
or
HN
/
^
C1B
2 6 -2
4
1
BCl
\
NrA HH ^VCJ I ^
N a B H
NH
/
HN
\
NH
HB
/
BH
\
/
N
N
H
H
B - t r i a l k y b o r a z i n e s are best prepared
80
of trialkylborane-ammine complexes:
by the p y r o l y s i s
330°
Me.B'NH.
3
3
>
20atm.
(MeB-NH), + CH,
3
4
N - s u b s t i t u t e d borazines a l r e a d y mentioned above can
a l s o be obtained by the r e d u c t i o n of the B - t r i c h l o r o - N 81
t r i a l k y l ( o r a r y l ) borazines w i t h l i t h i u m aluminium hydrideV
36.
C1B„
BOl
HB.
iH
R
R
Since the B - t r i c h l o r o - N - s u b s t i t u t e d borazines are
f a i r l y r e a d i l y a c c e s s i b l e from boron t r i c h l o r i d e and the
appropriate amine hydrochloride B-N s u b s t i t u t e d borazines
are a l s o r e a d i l y prepared from the B - t r i c h l o r o compounds
Op
and Grignard or organo l i t h i u m reagents,
or by F r i e d e l -
Q •J
Craft
arylation.
A somewhat remarkable development has been the
p r e p a r a t i o n B-N s u b s t i t u t e d borazines by the a c t i o n of
Grignard and organo-lithium reagents, not on B C 1 compounds
81
but on the B-H compounds.
BH
B^
X
H
B
\
^
n
R
BH
m
R'Li
f
^
( o r R'MgBr)
ii
R
B
\
N
R
i
/
N
R
R
^iH(orHMgBr)
i
B R
I t i s p o s s i b l e to prepare borazines w i t h one, two, or
a l l t h r e e B-H groups s u b s t i t u t e d .
Borazines a r e much more c h e m i c a l l y r e a c t i v e than
37.
analogous benzene compounds.
Borazine i t s e l f adds water,
methanol, a l k y l i o d i d e s and hydrogen h a l i d e s , the n e g a t i v e
p a r t s of these reagents becoming attached to boron.
BH
BHC1
\H
I
I
HB.
BH
*y
\H
I
I
HC1B
N
H
_
9
^BHCl
Nf
H,
2
y
m
^1
"
B^
1
\H
I
I
C1B.
BC1
NH
[
B-trichloroborazine.
The h y d r o l y t i c s e n s i t i v i t y i s c o n s i d e r a b l y a f f e c t e d
by the s u b s t i t u e n t s e.g. B-tripheny-N-trimethylborazine
i s r e l a t i v e l y e a s i l y hydrolysed w h i l s t B-trimethyl-Ntriphenyl
borazine i s r e s i s t a n t .
The h i g h l y s u b s t i t u t e d b o r a z i n e s . e.g. hexamethylborazine m.p.99, b.p.221°, a r e g e n e r a l l y substances of
f a i r l y high thermal s t a b i l i t y .
R a p i d l y developing
i s the chemistry of a s e r i e s of
i n t e r n a l c y c l i c c o o r d i n a t i o n compounds i n which each boron
atom i s bonded t o two phosphorus ( o r a r s e n i c ) atoms or
vice versa.
These compounds a r e g e n e r a l l y t h e r m a l l y s t a b l e
and r e s i s t a n t t o chemical a t t a c k and these p r o p e r t i e s have
d i r e c t e d a t t e n t i o n t o the p o s s i b l e development of l i n e a r
polymers of these g e n e r a l t y p e s .
38
R e a c t i o n between dimethylphosphine and bromodiraethylborane i n the presence of 1 mol. t r i e t h y l a m i n e
g i v e s the f u l l y methylated phosphinoborane:
Me PH 4 Me BBr •+ Et^N
2
2
Me P
PMe
2
2
+ Et NHBr
3
Me B^
BMe
2
/
2
0
0
X
r
Me
2
T h i s compound m.p. 333-334? i s r e s i s t a n t
h y d r o l y s i s below 300?
u n s t a b l e , but Me PBH
2
2
to acid
I n c o n t r a s t , H PBMe i s r a t h e r
2
2
from Me^H-BH^ a t 150? forms
84
e x c e p t i o n a l l y s t a b l e c y c l i c t r i m e r s and t e t r a m e r s .
Dimethylphosphinoborane polymers (Me PH«BH ).
2
2
n
have
been obtained w i t h n about 80 by the p y r o l y s i s of MegPH'BH^
i n the presence of an amine ( e . g . t r i e t h y l a m i n e ) as a c h a i n
end b l o c k i n g group.
These polymers melt a t c a . , 170° but
at t h i s temperature sometimes rearrange t o form the thermo85
dynamically more s t a b l e c y c l i c t r i m e r s and t e t r a m e r s .
86
The only a r s e n i c analogues so f a r d e s c r i b e d ,
( M e A s B H ) , m.p. 49.7 - 50.6? and (Me AsBH )^ m.p. 149.5 2
2
3
2
2
150.5? a r e d e c i d e d l y l e s s s t a b l e both t h e r m a l l y and t o
hydrolysis.
and Me B H , i
4
2
2
7
The sulphur compound? MeSBMe , from MeSH
2
s
monomeric and e a s i l y
hydrolysed
39.
( c . f . Me BOMe).
2
S e v e r a l phosphinoboranes have r e c e n t l y been prepared
by two g e n e r a l methods,
'
^ by r e d u c t i o n of d i a l k y l
( o r d i a r y l ) chlorophosphines or o x y c h l o r i d e s i n ethylene
g l y c o l dimethyl e t h e r or •diglyme
e.g.
P h P C l + NaBH
2
Me POCl
2
4
NaBH^
1
w i t h sodium borohydride
(Ph PBH )
2
2
3
(Me PBH )
2
2
2
(PhHP-BH K and ( E t J P B H ) , have a l s o been mentioned.
0
0
40.
C)
MIXED TRIALKYL AND ARYL-ALKYLBORANES
D i - i s o b u t y l - t - b u t y l b o r a n e has been prepared from
d i - i s o b u t y l f l u o r o b o r a n e (BUgBF) and t-butylmagnesium
bromide and by f o u r other methods?
0
As a l r e a d y mentioned
i t may be d i s t i l l e d without d i s p r o p o r t i o n a t i o n or r e a r r a n g e ment provided the b o i l i n g point does not exceed 60°, o t h e r wise Bu^B i s formed.
I t seems t h a t not more than two t -
b u t y l groups may be attached t o the same boron atom, and
then only when the remaining group i s unbranched.
m
d i - t - b u t y l b o r a n e , b,p. Al l°/l'7
n-Butyl-
mm and n - p e n t y l - d i - t -
butylborane, b.p# 42*5 - 42»7°/0 5 mm.,
have been prepared,
the f i r s t from boron t r i f l u o r i d e and t-butylmagnesium
c h l o r i d e i n e t h e r c o n t a i n i n g a l a r g e excess of 1-butene;
both compounds rearrange r a p i d l y when heated,
g i v i n g a 2:1 mixture of Bu^jB and (n-C^H^J^B.
(n-C^H^jBulB
37
I t has a l s o been p o s s i b l e to prepare n - a m y l - i s o b u t y l t-butylborane, b.p. 43*5 - 44°/0*5 mm.,
w i t h three d i f f e r e n t
a l k y l groups; i t gave the c o r r e c t a l c o h o l s i n equal amounts
92
when o x i d i s e d w i t h a l k a l i n e hydrogen peroxide.
q "i
M i k h a i l o v and Shchegoleva^
J
have prepared mixed
tri-
a l k y l b o r a n e s by the a d d i t i o n of organo-lithium compounds
41.
i n e t h e r to n - b u t y l - d i - n - b u t y l b o r o n i t e i n the same
s o l v e n t a t -70°C, e.g.
pAi
n
+ (Bu ) B0Bu
n
Bu^BPr
2
11
b.p. 76-80°/9 mm.
The d i s c o v e r y t h a t the c o o r d i n a t i o n complex t - b u t y l borane-trimethylamine r e a c t s u n u s u a l l y r a p i d l y w i t h o l e f i n s
at 50-60° has provided
an improved route t o t - b u t y l d i -
94
alkylboranes^
Bi^BHgBMe^ ••• 2CH :CHEt = B u S u ^ B + NMe ^
2
The exchange of r a d i c a l s
R B f R*B
^
3
R R*B + RR B
2
2
does not take p l a c e a t an a p p r e c i a b l e r a t e below 100°,
u n l e s s R isec-branched ( e . g . P r , Bu ). The exchange i s ,
however, s t r o n g l y c a t a l y s e d by t r a c e s of t r i a l k y l a l u r a i n i u i t i
through the formation
R
R
Al
3
/
R
intermediates:
R'
y
R.B + R,A1
3
of bridged
,B
N
s \ ,
R
R R A l + RR B.
2
0
2
0
R
96
Dimethylbromoborane^
r e a c t s w i t h v i n y l sodium and
p r o p e n y l l i t h i u m to form two mixed t r i a l k y l b o r a n e s which
42
r e a d i l y d i s p r o p o r t i o n a t e e.g.
2 Me B CH:CHR
2
-» Me^B
*
MeB(CH:CHR)
2
Mixed t r i a r y l b o r a n e s have only r e c e n t l y "been prepared.
Disproportionation
i s suppressed
by working w i t h amine
( u s u a l l y p y r i d i n e ) complexes but once prejared the mixed
arylboranes
are r e l a t i v e l y s t a b l e t o d i s p r o p o r t i o n a t i o n .
There i s evidence t h a t organo-lithium,
Grignard
reagents
and other e l e c t r o n d i f i c i e n t compounds c a t a l y s e t h i s kind
of d i s p r o p o r t i o n a t i o n , so the e s s e n t i a l point would appear
to be c o o r d i n a t i v e s a t u r a t i o n of the boron during the
p r e p a r a t i v e stages i n v o l v i n g such reagents.
p-Tolyllithium
and the p y r i d i n e complex B u ^ B P ^ p y y i e l d s p-GH^CgH^BPhgpy
m.p. 156-158°.
The p y r i d i n e can be removed by the a c t i o n
Oif aqueous a c i d , e t h e r e a l hydrogen c h l o r i d e , or p i c r i c a c i d
i n benzene.
These methods have y i e l d e d the mixed a r y l s
p-CH C H BPh , b.p. 170-173°/3 mm., ( l - C
3
6
4
2
1 ( )
H ) B P h , m.p.
7
2
146-148°, b.p. 230-240°/2 mm., and ( 1 - C H ) B C H 0 C H ,
1 0
7
2
6
4
3
97
b.p. 197-199°/0-08 mm.,
Torsell?
8
obtained
O-CH-jCgR^BPhg b.p. 167-9°/3 mm.,
and (0-CH CgH ) BPh from diphenylchloroborane and p h e n y l 3
4
2
difluoroborane r e s p e c t i v e l y w i t h the c o r r e c t
proportions
43.
of o-tolylmagnesium bromide.
CYCLIC-BQRANES
Attempts t o prepare a r a l k y l b o r a n e s such as PhBMeg
have given only d i s p r o p o r t i o n a t i o n products,
Ph^B + Me^B.
i n this
case
T h i s ready d i s p r o p o r t i o n a t i o n has been
a s c r i b e d t o the formation of r e l a t i v e l y low energy
bridged
dimers s i m i l a r t o those formed by aluminium a l k y l s :
Ph
\
Me
/
B
1
Me
+
Me
Ph
Me
Me
I
\.' \ /
B
5*
)B
)B
/ Me
\ /
\
Ph
Me
Ph
Me
X
/
m
e
Ph
Me
\
\
Me
B
+•
B^
/ \
\
Me Ph
Me
A l i c y c l i c boranes should t h e r e f o r e be s t a b l e t o d i s p r o p o r t i o n a t i o n and t h i s was confirmed by t h e p r e p a r a t i o n of
( a ) and ( b ) from phenyldifluoroborane
qq
and 1 , 5 - d i l i t h i o p e n t a n e : "
Ph
and 1 , 4 - d i l i t h i o b u t a n e
Ph
B u t y l analogues were unexpectedly obtained
i n attempts t o
prepare BUgBCCHg^B Bu!J ( n - 4 or 5) from d i - n - b u t y l c h l o r o borane and tetramethylene - (and pentamethylene-) dimagnesium
bromide
44.
2Bu^BCl * BrMg(CH ) MgBr
2
Bu B( CHg ) BBUg + 2MgBrCl
n
2
n
I
CH
(CH )
X
y
9
2
BBu
n
+• Bu*B
on 2
Diboron t e t r a c h l o r i d e and ethylene form the compound
ClgB CH
2
CH BC1 » which adds two moles of t r i e t h y l a m i n e ,
2
1 0 1
2
and whose s t r u c t u r e has been confirmed by x-ray d i f f r a c t i o n
102
The c h l o r i n e atoms i n t h i s have been r e p l a c e d by methoxy (by
methanol) or by methyl.
C1 BCH CH BC1
2
2
2
2
+ 2Me Zn -* Me BCH CH BMe
2
2
Slow p y r o l y s i s of Me BCH CH BMe
2
2
2
2
2
2
+ 2ZnCl
2
2
a t .100 r e s u l t s i n the
formation of much trimethylborane and of v a r i o u s v o l a t i l e
and polymeric products t o which the f o l l o w i n g s t r u c t u r e s
were a s s i g n e d :.103
MeB^
C
2
/
^BMe
B
C
V
H
^; 2 4—
H
2 4
C
B
H
2 4
•B—CgHj— B —
L Me
Me J
-CI*
2"4
B-
•B
\
/
H
°2 4
n
45.
The r e a c t i o n , a l r e a d y mentioned,
between
t-butylborane-trimethylamine and o l e f i n s provides a
neat method of p r e p a r i n g c y c l i c boranes:
CH
CH :CH.CH:CH
2
2
^BHgKMe^B^B^
\H
2
- CH
2
|
2
- CH
(60$).
2
These compounds appear t o deserve f u r t h e r study.
46.
BORONIC ACIDS AND ESTERS
1.
PREPARATION
U n t i l very r e c e n t l y the main use of the e s t e r s
was as p r e c u r s o r s
to the a c i d s and so a t t e n t i o n w i l l ,
he concentrated on the a c i d s , s p e c i a l methods f o r the
e s t e r s being mentioned i n a f i n a l
sub-section.
The more important methods f o r the p r e p a r a t i o n
of
boronic a c i d s and e s t e r s have depended on one of the
f o l l o w i n g procedures: ( 1 ) the o x i d a t i o n
borane to a boronic e s t e r followed
of a t r i a l k y l -
by h y d r o l y s i s to obtain
the a c i d ; ( 2 ) the a d d i t i o n of a m e t a l l i c a l k y l or a r y l
to a t r i a l k y l borate and the h y d r o l y s i s of the boronic
e s t e r thus formed; ( 3 ) the a d d i t i o n of a m e t a l l i c a l k y l
or a r y l to a boron t r i h a l i d e to obtain the a l k y l - or
arylboron
d i h a l i d e which on h y d r o l y s i s g i v e s the boronic
a c i d or on a l c o h o l y s i s the e s t e r ,
(a)
OXIDATION OF TRIALKYLBORONS
S e v e r a l a l k y l b o r o n i c a c i d s have been prepared by
a l l o w i n g t r i a l k y l b o r a n e s to stand
f l a s k s and then h y d r o l y s i n g
i n l o o s e l y stoppered
104
the products.
Prankland
105
and Duppa
^ obtained d i e t h y l ethylboronate by the con-
t r o l l e d oxidation
of t r i e t h y l b o r a n e ; h y d r o l y s i s of t h e
47.
e s t e r afforded e t h y l b o r o n i c a c i d .
2H 0
— ^
9
B(C H )
2
(b)
5
3
• 0
2
-» C H B ( O C H )
2
5
2
5
2
C H B(OH)
2
5
* 2C H OH
2
2
5
METAL ALKYLS OR ARYLS ON TRIALKYL BORATES
P h e n y l - and m - t o l y l b o r o n i c a c i d s and some of t h e i r
a l k y l e s t e r s were prepared when Khotinsky and Melamed
added e t h e r e a l s o l u t i o n s of t r i a l k y l borates (methyl,
e t h y l , n-propyl, i s o - b u t y l , i s o - a m y l ) t o t h e arylmagnesium
bromides a t 0°C.
2H 0
— %
P
B(OR)
3
+ ArMgBr
ArB(OR)
2
ArB(OH)
2
A d d i t i o n of t h e appropriate Grignard reagent to an
e t h e r e a l s o l u t i o n of t r i - n - b u t y l borate cooled t o - SO°C
107
has been used e x t e n s i v e l y to prepare a r y l b o r o n i c a c i d s
as w e l l as a l i p h a t i c (primary, secondary, and t e r t i a r y )
TO ft
alkyl acids.
P. B. B r i n d l e y , W. Gerrard and M. P. Lappert
have shown f o r d i - n - b u t y l n-butylboronate t h a t employing
n - b u t y l l i t h i u m i n s t e a d of the Grignard reagent improved
the y i e l d by some 50 p e r cent, but u s i n g p h e n y l l i t h i u m i n
p l a c e of phenylmagnesium bromide decreased the y i e l d , only
about 3 6 per cent of phenylboronic a c i d being
(c)
obtained.
METAL ALKYLS OR ARYLS ON BORON HALIDES
M i c h a e l i s and Becker^"^ heated boron t r i c h l o r i d e and
48.
diphenyl^-mercury i n a s e a l e d tube f o r 1 hour a t 180°- 200°C
and thus obtained phenylboron
d i c h l o r i d e which hydrolysed
or a l c o h o l y s e d w i t h v i g o u r to give phenylboronic a c i d
d i e t h y l phenylo-boronate, r e s p e c t i v e l y .
and
Several arylboronic
a c i d s have been prepared u s i n g t h i s method^^"
Hg(Ar)
2
+ 2BC1
-* 2 A r B C l
3
t+
2
Boron t r i b r o m i d e has advantages
2ArB(0H)
2
over the t r i c h l o r i d e
i n t h a t r e f l u x c o n d i t i o n s can be used, i n s t e a d of the
112
p r e s s u r e v e s s e l , and the r e a c t i o n i s more r a p i d .
The most
s u c c e s s f u l m o d i f i c a t i o n i n v o l v e d the a d d i t i o n of the d i e t h y l
e t h e r a t e of boron t r i b r o m i d e to the a l k y l - ^ " ^ or a r y l - " ^ ^
Grignard reagent i n e t h e r a t 0°C, and h y d r o l y s i s of the
a l k y l - or a r y l b o r o n d i f l u o r i d e s to a f f o r d the boronic a c i d s .
(d)
OTHER METHODS FOR BORONIC ACIDS
115
S c h l e s i n g e r , F l o d i n and Burg
J
have prepared methyl-
boronic a c i d by the h y d r o l y s i s of symmetrical d i m e t h y l d i borane.
(CH BH )
3
2
2
+ 2H 0 -» 2CH
2
3
B(0H)
2
+ 2H 2
E t h y l - and n-propylboronic a c i d s were formed when monoa l k y l ^ d i b o r a n e s , RB H^, were hydrolysed.
2
Amino-boronic a c i d s have been obtained by r e d u c t i o n of
the corresponding n i t r o a c i d s , u s i n g e i t h e r
hydrogenation
49
i n the presence o f p l a t i n u m 117 o r f r e s h l y p r e c i p i t a t e d
118
f e r r o u s hydroxide.
By o x i d a t i o n of d i - n - p r o p y l b o r i n i c
a c i d , formed by the h y d r o l y s i s o f di-n-propylboron oxide,
HQ
some n-propylboronic a c i d was obtained. ^ The o x i d a t i o n
of d i a r y l b o r i n i c acids by halogens ( c h l o r i n e , bromine)
120
a f f o r d e d t h e corresponding boronic a c i d s .
Ar BOH * H 0 + X
2
2
g
-> 2ArB(0H) -v H I f ArX
2
Paraphenylene d i b o r o n i c acid, (OH) BCgH^B(OH) , and
s e v e r a l esters have been prepared from methyl or b u t y l
borate and paraphenylenedimagnesium bromide i n t e t r a h y d r o 121
2
2
f u r a n o r by the use o f paraphenylene d i l i t h i u m .
(e)
SPECIAL METHODS FOR BORONIC ESTERS
A number o f a l k y l esters of a r y l b o r o n i c acids have
been prepared i n n e a r l y q u a n t i t a t i v e y i e l d s from the approp r i a t e boronic a c i d and a l c o h o l , the water of e s t e r i f i c a t i o n
being removed by r e f l u x i n g through a Soxhlet e x t r a c t o r o f
anhydrous copper sulphate (methyl e s t e r s ) , o r by azeotropic
d i s t i l l a t i o n w i t h excess o f t h e a l c o h o l ( n - p r o p y l and
n - b u t y l e s t e r s ) , or by azeotropic d i s t i l l a t i o n w i t h excess
122
of the a l c o h o l and benzene ( e t h y l e s t e r s ) .
Many other
esters o f phenylboronic acid have also been prepared by t h i s
50.
123
me thodT
A m o d i f i c a t i o n was t o use the phenylboronic
124
anhydride i n s t e a d of t h e a c i d .
ArB(0H) -v 2R0H
^
ArB(0R)
(CgH BO) + 6R0H
5=^
3C H B(OR) + 3H" 0.
2
5
3
6
2H 0
2
2
5
2
2
Good y i e l d s (60-90 per cent) o f esters o f a r y l b o r o n i c acids
w i t h c e r t a i n p o l y h y d r i c alcohols have been prepared by simply
125
mixing the two components, whereupon the e s t e r s p r e c i p i t a t e d .
This method i s l i m i t e d i n i t s a p p l i c a t i o n t o those compounds
where t h e esters are l e s s s o l u b l e than e i t h e r of t h e i r parent
acids or a l c o h o l s .
Alcoholysis. o f boronates was a good method f o r p r e p a r i n g
esters of higher molecular weight from those o f lower molecular
weight and the n - b u t y l
s e c - b u t y l , i s o - b u t y l and octan-2-yl
P
esters of phenylboronic acid were prepared from d i e t h y l phenylboronate by r e a c t i o n w i t h the a p p r o p r i a t e a l c o h o l .
ArB(0R) f 2R'0H
^*
ArB(0R') * 2R0H
Tetramethoxysilane and methyldibromoborane a f f o r d e d d i m e t h y l
127
me t h y l b o r o n a t e
2
Si(0Me )
3
2
4
+ MeBBr
II.
(a)
MeB(0Me) + ( M e 0 ) S i B r
2
2
2
2
PROPERTIES
PHYSICAL
128
129
Alkyl—
and a r y l —
boronic acids are monomeric
y
51.
(cryoscopic i n nitrobenzene) although s l i g h t a s s o c i a t i o n
occurs i n benzene s o l u t i o n .
The d i s s o c i a t i o n constants of many boronic a c i d s ,
mainly aromatic have been measured and i t i s i n t e r e s t i n g
t o note t h a t phenylboronic a c i d i s three times as s t r o n g
as b o r i c a c i d ^ " ^
(b)
(i)
CHEMICAL
ACIDIC PROPERTIES
Boronic acids r e a d i l y form anhydrides and e s t e r s .
R e l a t i v e l y few s a l t s have been described although phenylboronic a c i d formed both a sodium and a calcium s a l t when
t r e a t e d w i t h the a p p r o p r i a t e hydroxide^"^"
n-Butylboronic
acid formed a hydrated sodium s a l t when t r e a t e d w i t h very
1^2
concentrated sodium hydroxide.
A r y l b o r o n i c acids are e a s i l y deboronated w i t h water
at elevated temperatures, or more r a p i d l y w i t h acids or
( p r e f e r a b l y ) bases}"^
C H B(OH) + H 0 -» CgHg * B(OH) ,
6
5
2
2
3
I n c o n t r a s t the deboronation of a l k y l b o r o n i c acids i s
rather d i f f i c u l t .
(ii)
BORON-CARBON CLEAVAGE REACTIONS
A l k y l b o r o n i c acids are r e a d i l y a u t o x i d i s e d i n d r y a i r
52.
1
t o the a l c o h o l and b o r i c a c i d ^ but the a r y l acids are
quite stable.
Both a l k y l - and a r y l - b o r o n i c acids are q u a n t i t a t i v e l y
o x i d i s e d t o o r t h o b o r i c a c i d by hydrogen peroxide; use has
been made of t h i s i n e s t i m a t i n g the'boron content o f such
135
compounds.
Phenylboronic a c i d i s decomposed by halogens under
q u i t e m i l d c o n d i t i o n s , i n aqueous s o l u t i o n ^ * *
PhB(OH) + B r
2
2
+ H 0 = PhBr + HBr + H B 0
2
3
3
and by mercuric h a l i d e s conveniently mercuric c h l o r i d e i n
sodium c h l o r i d e s o l u t i o n ,
PhB(OH) 4. H g C l
2
2
+ H 0 = PhHgCl
2
HC1 * H B0 .
3
3
This r e a c t i o n has also been used i n q u a n t i t a t i v e a n a l y t i c a l
137
procedures.
A r y l b o r o n i c acids are best c h a r a c t e r i s e d as
138
diethanolamine esters
(e.g.a) o r as the p y r i d i n e complexes
-
of the corresponding boroxines"* ^' (e.g.b)
ym
0^
2
PhB- NH
/
\
OC
.CH
CH
2
o
—
OcHcN-BPh
5 5 \
0 —
BPh
0
/
BPh
2
( a ) m.p. 214-215°
( b ) m.p. 154-156
1
53.
The boronic esters are g e n e r a l l y e a s i l y hydrolysed.
C y c l i c esters are somewhat more s t a b l e , but a s u b s t a n t i a l
resistance
t o h y d r o l y s i s only develops when the boron i s
coordinatively
saturated.
54
F.
1.
BORINIC ACIDS AND ESTERS
PREPARATION
The b o r i n i c acids have g e n e r a l l y been prepared by
h y d r o l y s i s methods using h a l i d e s , e s t e r s , or borines.
Diphenylborinic
a c i d , the f i r s t b o r i n i c a c i d t o be p r e -
pared, was obtained by the h y d r o l y s i s of diphenylboron
c h l o r i d e which was obtained
i n low y i e l d from the r e a c t i o n
of diphenyl mercury w i t h phenylboron d i c h l o r i d e . ^ " ^ ' ^ ^
R-0
(C H )
6
5
2
Hg + PhBCl -> Ph BCl
2
2
PhgBOH
A number of d i a r y l b o r i n i c acids have been prepared by
the r e a c t i o n of 2 moles of a r y l Grignard reagent w i t h
1
1 mole of t r i - i s o - b u t y l b o r a t e , o r t r i - n - b u t y l b o r a t e , " " ^ "
and y i e l d s v a r i e d w i t h c o n d i t i o n s , p a r t i c u l a r l y temperature
14-4and order of a d d i t i o n . Recently M i k h a i l o r and Vaver
I K orf v i e i d s )
0
have prepared several d i a r y l b o r i n i c a c i d s
v
'
J
by
the a c t i o n of arylmagnesium bromide on t r i - i s o - b u t y l b o r a t e
i n ether a t -60°C.
ArMgBr •»- (iso-BuO)^B -»• Ar BOH
2
(ArBO)^ + iso-BuOH
H^BO^ MgBr .
The h y d r o l y s i s of b o r i n i c esters obtained by various
2
55.
14-5
methods has been e x t e n s i v e l y used t o prepare d i a r y l 1
dialkyl- ^
6
1
and mixed a l k y l a r y l b o r i n i c acids (CgH^CH-jBOH)
The h y d r o l y s i s o f s u i t a b l e methyldiboranes ( d i - ,
tri-
and t e t r a - ) , such t h a t two methyl groups were attached t o
14-8
the boron atom gave d i m e t h y l b o r i n i c acid
and s i m i l a r l y
14.Q
the e t h y l - and p r o p y l - homologues were obtained.
Recently T. P. Povlock and W. T. l i p p i n c o t t
1 5 0
have
reported a new synthesis of a r y l b o r i n i c acids (62$ y i e l d s )
from aromatic Grignard reagents (mole r a t i o 9:1) and t r i methoxyboroxine a t 25°C.
The three main methods of p r e p a r i n g b o r i n i c esters
u t i l i s e ( 1 ) t r i a l k y l - and t r i a r y l b o r a n e s , ( 2 ) i n t e r a c t i o n
of orthoborates or boronic e s t e r s w i t h organometallie
compounds or ( 3 ) t h e e s t e r i f i c a t i o n of b o r i n i c acids,
anhydrides, or d i a l k y l - or d i a r y l b o r o n c h l o r i d e s ,
(l)
T r i a l k y l b o r a n e s and T r i a r y l b o r a n e s .
B o r i n i c esters were f i r s t prepared by the r e a c t i o n
of t r i e t h y l b o r a n e w i t h c e r t a i n aldehydes (CCl^CHO, CgH^CHO
\
151
p-ClCgH^CHO) or w i t h the corresponding a l c o h o l s .
B ( C H ) + RCHO -» ( C H ) BOCH R *
2
5
B(C H )
2
5
3
3
2
5
2
+ RCH OH -+ ( C H )
2
2
5
2
2
BOCHgR + CgHg
56.
Triphenylborane reacted w i t h a l c o h o l t o form e t h y l
diphenylborinate:
Ph-jB -K EtOH = Ph BOEt + CgHg
2
The
2-aminoethyl esters of both d i p h e n y l b o r i n i c
and di-of-naphthylborinic acids were prepared i n an
analogous manner, from the appropriate
t r i a r y l b o r a n e and
152
ethanolamine, by heating i n b o i l i n g benzene.
However
w i t h methanol and the t r i a r y l b o r a n e the r e a c t i o n was more
complex; the <x-naphthyl compound a f f o r d e d naphthalene
and t r i m e t h y l borate, w h i l s t w i t h triphenylborane
and
a l a r g e excess of methanol phenyl d i p h e n y l b o r o n i t e , ( ^ 5 ^ ) 2
BOCgH^, was i s o l a t e d as an ammonia complex.
Triethylborane
reacted w i t h c a r b o x y l i c acids t o give
15 3
aryl diethylboronites.
B ( C H ) + RCOOH -* (0 H ) BOOCR + C 6 '
H
2
Oxidation
5
3
2
5
2
2
of t r i a l k y l b o r a n e s t o produce b o r i n a t e s has
154-
been mentioned e a r l i e r .
(2)
Organometallic Compounds
The
a d d i t i o n of 2 moles of allylmagnesium bromide t o
155
1 mole of t r i m e t h y l borate affibrded methyl d i a l l y l b o r o n i t e ;
156
by s i m i l a r r e a c t i o n n - b u t y l d i - n - o c t y l b o r o n i t e was obtained.
57.
The b u t y l esters of d i p h e n y l b o r i n i c
by t h i s method:
2 ArMgBr + B ( O C H - i )
4
9
3
acid were also prepared
-* Ar BOC H -i
2
4
g
D i a l k y l arylboronates react w i t h arylmagnesium bromides
157
t o produce mixed boronites
Ar
B0R
Ar'MgBr + ArB(OR)
Ar
n - O c t y l l i t h i u m reacted w i t h t r i - n - b u t y l borate t o give n - b u t y l
158
2^
9
c
di-n-octylboronite.
J
Both n - b u t y l - and n - p r o p y l l i t h i u m w i t h d i i s o b u t y l phenylboronate gave mixed b o r o n i t e s .
R
LiR ••- C H B ( O C H - i )
E s t e r i f i c a t i o n methods
6
(3)
5
4
g
2
C
6 5^ > B O C 4 H 9 - i
H
+ LiOR
D i - n - b u t y l b o r i n i c anhydride heated w i t h 1-butanol y i e l d e d
the
0
ester^
( C H ) B 0 + 2C H OH
4
The
g
2
2
4
g
2 ( 0 ^ ) ^ 0 ^
+ H0
2
a d d i t i o n of 2-amino-2=methyl-l-propanol of an aqueous
e t h a n o l i c s o l u t i o n of the mixed <x-naphthyl-phenylborinic
a c i d , obtained by h y d r o l y s i s of the 2-aminoethyl ester w i t h
a concentrated e t h e r e a l s o l u t i o n of hydrogen c h l o r i d e , gave
the appropriate
0;0'
ester.
- D i b e n z y l d i l i t h i u m and t r i - n - b u t y l borate reacted
58.
t o give a product which on h y d r o l y s i s and e s t e r i f i c a t i o n
1
w i t h e t h a n o l i c ethanolamine a f f o r d e d t h e ester:" "^
CH2 " CH2 v X \
n
l
u n
2
Mixed n - b u t y l b o r o n i t e s were prepared s i m i l a r l y , using
d i - n - b u t y l phenyl- ( o r ©<_naphthyl) boronate andc*-naphthyl
( o r phenyl) magnesium bromide,
*
0
Mixed n-propyl d i a r y l -
b o r o n i t e s were also prepared from mixed d i a r y l b o r i n i c
acids,
obtained i n s i t u , by e s t e r i f i c a t i o n w i t h 1-propanol, t h e water
produced being removed as an azeotrope w i t h excess of the
alcohol?"^
A r y l b o r o n i c acid d i a l k y l esters r e a t w i t h a l k y l
c
magnesium bromide i n mole r a t i o 1:1 a t -65° t o -60° t o form
165
esters of a r y l - a l k y l b o r i n i c a c i d s ,
i f t h e Grignard reagent
i 3 added i n mole r a t i o 2 s l t o t h e boronic e s t e r , d i s p r o p o r t i o n a t i o n occurs w i t h f o r m a t i o n of t r i - a l k y l b o r a n e s and t r i a r y l boranes.
II
(1)
PROPERTIES
PHYSICAL
Pew p h y s i c a l p r o p e r t i e s of the b o r i n i c acids have
so f a r been determined and even t h e reported
boiling
59.
p o i n t s may w e l l be those o f the anhydrides.
The values f o r the l a t e n t heat o f v a p o r i s a t i o n and
Trouton's constant f o r methyl dimethyboronite have been
obtained, and i t s molecular weight showed i t t o be monomeric^^
D i p h e n y l b o r i n i c a c i d was also shown t o be mono167
meric (cryoscopic i n camphor).
(2)
CHEMICAL
The d i a l k y l - and d i a r y l b o r i n i c acids are very weak
acids, they r e a d i l y form anhydrides and can e a s i l y be
esterified.
D i p h e n y l b o r i n i c a c i d was s a i d not t o form
168
salts with alkalis.
Several b o r i n i c acids have been q u a n t i t a t i v e l y o x i d i s e d
16°
f i r s t t o boronic acids and subsequently t o o r t h o b o r i c a c i d ,
J
by c h l o r i n e , bromine or hydrogen peroxide,
Ar BOH + Y
2
2
* H 0 -* ArB(OH)
ArB(OH) 4- Y
2
2
2
2
ArY + HY
+ H 0 -* B(OH) * ArY + HY
2
3
Y = C I , Br or OH.
When di-<x-naphthylborinic acid was heated f o r 6 hours
at 120-130°C, naphthalene.was obtained as a sublimate and
170
a residue of (X-naphthylboronic anhydride remained.
Similar
cleavage was e f f e c t e d by h e a t i n g the a c i d w i t h an aqueous
60.
171
e t h a n o l i c s o l u t i o n of 2-(diraethylamino) ethanol.
3(o(-C H ) BOH
3 C H • (o<-C H B0)
10
o<-C H
10
7
2
1Q
8
10
7
3
7
rBOH + H 0
C Hg * C H B ( 0 H )
2
10
6
5
2
H
°6 5
Boronic esters are g e n e r a l l y e a s i l y o x i d i s e d ( r e q u i r i n g
work under n i t r o g e n ) .
Hydrolysis of t h e b o r i n i c esters
has already been mentioned.
aminoethyl diphenylboronite
The r e l a t i v e s t a b i l i t y o f 2towards both o x i d a t i o n and
h y d r o l y s i s ( i t can be r e c r y s t a l l i s e d from water) has l e d
172
t o t h e suggestion t h a t i t s s t r u c t u r e i s as shown.
H
°6 5
C
H
6 5
\ CH,
/
N•
H,
-CH,
Such c h e l a t i o n has also been suggested t o account f o r the
i n a b i l i t y f o r both t h i s e s t e r and i t s cy-naphthyl analog t o
17}
undergo a l c o h o l y s i s r e a c t i o n s .
2-Aminoethyl ptf-naphthyl phenylboronite
reacted w i t h
e t h a n o l i c hydrogen peroxide and w i t h aqueous zinc c h l o r i d e
61
t o give crt-naphthol and naphthalene, r e s p e c t i v e l y ^ ^
Amine complexes of several a r y l b o r i n i c acids have been
175
used as a method f o r p u r i f y i n g the acids.
Methyl d i -
methylboronite formed a 1:1 complex (m.p. 51-52°C) w i t h
dimethylamine. Phenyl d i p h e n y l b o r o n i t e formed a 1:1
176
complex w i t h ammonia
and a s i m i l a r complex formed
177
i s o b u t y l diphenylboronite s l o w l y evolved ammonia".
62.
BOROXINES
1.
PREPARATION
The c y c l i c anhydrides o f boronic acids are commonly
known as boroxines, o f e m p i r i c a l formula (BOR)^, R being
an a r y l or a l k y l
group.
U n t i l r e c e n t l y the a l k y l boroxines were normally
~L7ft
prepared by dehydration o f a l k y l b o r o n i c acids
whilst
179
a r y l boroxines were obtained by h e a t i n g the acids.
Recently an azeotropic d i s t i l l a t i o n process f o r the
dehydration o f l a r g e amounts o f organo-boronic acids has
been used t o prepare a l k y l b o r o x i n e s , some of them h i t h e r t o
unknown.
The most convenient p r e p a r a t i v e method f o r
normal a l k y l b o r o x i n e s i s the r e a c t i o n between t r i a l k y l lfil
boranes and anhydrous b o r i c oxide.
BR
0
R.B 4- B„0
RB
0
For example h e a t i n g equimolar q u a n t i t i e s o f t r i - n - b u t y l borane and b o r i c oxide a t r e f l u x (200°) f o r 40 hours and
vacuum d i s t i l l a t i o n o f the product gives almost 70$ y i e l d
63*
of t r i - n - b u t y l b o r o x i n e .
T r i - e t h y l , -n-propyl, - i s o b u t y l ,
- c y c l o h e x y l and -phenylboroxines have been prepared by
t h i s method but i s o m e r i s a t i o n can occur i n t h i s r e a c t i o n .
T r i - n - b u t y l b o r o x i n e r e s u l t s from t r i - s - b u t y l b o r a n e and b o r i c
oxide.
II.
(a)
PROPERTIES
PHYSICAL
Molecular weight measurements (cryoscopic i n nitrobenzene)
on a r y l - and a l k y l - boroxines
show them t o be t r i m e r i c .
E l e c t r o n d i f f r a c t i o n measurements on t r i - m e t h y l b o r o x i n e are
i n agreement w i t h a planar six-membered r i n g w i t h methyl
groups bonded, i n the plane o f the r i n g , t o boron.
18 ^
Bond
distances and angles were determined.
(b)
CHEMICAL
I n c o n t r a s t t o d i a l k y l - s i l i c o n oxides the boroxines show
no tendency t o form higher c y c l i c or l i n e a r polymers.
They
are r e a d i l y hydrated t o the a c i d s ^ " ^ and r e a c t w i t h alcohols^®^
(RBO)^ -»• 3 H 0
2
m
3RB(OH)
2
(RBO) + 6R»OH - 3RB(OR') + 3 H 0 .
3
2
2
T r i - a l k y l and - a r y l boroxines form 1:1 c o o r d i n a t i o n
64,
complexes, those between t r i a r y l b o r o x i n e s and p y r i d i n e
being s u i t a b l e f o r i d e n t i f i c a t i o n purposes.
The
t r i a l k y l b o r o x i n e s are slowly oxidised by atmospheric
oxygen.
T r i - n - b u t y l b o r o x i n e y i e l d s n-butyldichloroborane
and di-n-butylchloroborane on treatment w i t h aluminium
chloride
and the mixed t r i a l k y l b o r a n e BuBMe^ i s said
t o be formed w i t h t r i m e t h y l a l u m i n i u m or methylaluminium
• •
188
sesqui-xodide
AlCl.
Me,A1
BuBCl + BuBCl <s
BU-JB^O-J —^=-> BuBMe
2
2
65.
ALKYL- AND ARYL- DIHALOBORANES
1.
PREPARATION
I n view o f t h e i r importance t o t h e research t o
be described, t h e boron h a l i d e s are reviewed i n more
d e t a i l than the other compounds.
S u b s t i t u t e d dihaloboranes are g e n e r a l l y prepared
by one of the f o l l o w i n g r e a c t i o n s :
(a)
REACTIONS WITH ORGANO-METALLIC COMPOUNDS
Dimethyl zinc was r e p o r t e d t o r e a c t w i t h boron
t r i c h l o r i d e t o give methyldichloroborane and d i m e t h y l 190
chloroborane 189 but t h e r e a c t i o n could n o t be confirmed*J
2(CH ) 2n * 3 B C 1
3
2
3
(CH^BCl
4-
2CH,BC1
2
*- ZnClg
Reaction between t r i a l k y l a l u m i n i u m compounds and
boron h a l i d e s has been used t o prepare s e v e r a l a l k y l dihaloboranes
1 9 1
'
1 9 2 .
Several a r y l d i c h l o r o b o r a n e s have been obtained from
the r e a c t i o n between boron t r i c h l o r i d e and t h e a p p r o p r i a t e
19 "\
d i - a r y l mercury compound.
Ar Hg + BC1
ArHgCl + ArBClg.
2
3
Phenyldifluoroborane and p - t o l y l d i f l u o r o b o r a n e have
66
been prepared by d i r e c t d i s t i l l a t i o n from the r e a c t i o n
between boron t r i f l u o r i d e - e t h e r complex and the Grignard
194- 1Q5
reagent i n ether. ^*- -?
Z,
X
J
Boron t r i c h l o r i d e heated w i t h 2-chlorovinylmercuric
c h l o r i d e i n kerosine i n a sealed tube f o r 2 hours a t 50°C
( o r a l l o w i n g the mixture t o stand f o r 12 hours a t room
temperature) gave t h e d i c h l o r i d e ^ ^
Phenyldichloroborane can now be prepared i n good
197
y i e l d s from boron t r i c h l o r i d e and t e t r a p h e n y l t i n i n
benzene
Ph Sn + 4BC1
4
3
4PhBCl + SnCl .
2
4
t h e r e s t i l l appears t o be some doubt about the mechanism
198
of the r e a c t i o n *
The new method f o r making PhBClg from benzene and
boron t r i c h l o r i d e may make t h i s the most convenient r o u t e
nqq
t o phenylboronic a c i d . *
The p r e p a r a t i o n of boronic (and b o r i n i c ) esters by
r e a c t i o n between o l e f i n s and l e s s than 1 mol. diborane i s
at present being d e v e l o p e d ? ^
( b ) TRIALKYLBORANES
Hydrogen c h l o r i d e bubbled i n t o t r i - n - b u t y l b o r a n e a t
110°, i n the presence of aluminium c h l o r i d e , has been used
67.
t o prepare n - b u t y l d i c h l o r o b o r a n e ,
RJB + HC1 -» R BC1
0
5
d
HC1
>
A1C1
201
RBC1, + RH.
d
3
Trimethylborane r e a c t s w i t h boron t r i c h l o r i d e t o give
202
m e t h y l d i c h l o r o b o r a n e ^ Me^B + 2BC1^-* 3MeBCl
2
(c)
BORONIC AND BORINIC ACIDS AND DERIVATIVES
The r a p i d r e a c t i o n , a t atmospheric pressure, between
t r i a l k y l b o r o x i n e s and boron t r i c h l o r i d e i s t h e most con203
venient method f o r the p r e p a r a t i o n of a l k y l d i e h l o r o b o r a n e s .
(RBO) + 2BC1 = 3RBG1 -»
3
3
2
* °y
2
Slow d i s p r o p o r t i o n a t i o n of t h e d i a l k y l c h l o r o b o r a n e s a t
temperatures above 180° and take o f f of t h e more v o l a t i l e
RBOl.^ a t t h e t o p of t h e column has also been u s e d . ^ ^
The r e a c t i o n between t r i - o r g a n o b o r o x i n e s and boron
t r i f l u o r i d e or t r i c h l o r i d e has been claimed as a general
method f o r the p r e p a r a t i o n o f organo s u b s t i t u t e d d i h a l o boranes.
*
The y i e l d s o f d i f l u o r o b o r a n e s are g e n e r a l l y
much lower than those o f dichloroboranes.
Phenyldichloroborane, f o r example, i s best prepared
by t h e dropwise a d d i t i o n of l i q u i d boron t r i c h l o r i d e
(cooled
t o -39°C) t o t r i p h e n y l b o r o x i n e i n methylene c h l o r i d e cooled
to -80°C.
207
68
(d)
OTHER METHODS
n - B u t y l d i f l u o r o b o r a n e has been prepared by s a t u r a t i n g
?nft
di-n-butylboronate w i t h boron t r i f l u o r i d e .
Phenyldichloro-
borane was s i m i l a r l y prepared, the accompanying d i c h l o r o b o r o n i t e being e i t h e r unstable ( i f secondary a l k y l ) or
decomposed by a t r a c e amount o f f e r r i c c h l o r i d e , t o f a c i l i t a t e
separation.209
RB(0R') + 2BP
2
RBP + 2R'0 BFg.
3
2
Triphenylboroxine when heated, w i t h phosphorus p e n t a c h l o r i d e ,
under r e f l u x (120-130°) f o r 24 hours gives p h e n y l d i c h l o r o 210
borane.
Recently a r y l d i f l u o r o b o r a n e s have been obtained by
the a c t i o n of antimony t r i f l u o r i d e and s i m i l a r f l u o r i n a t i n g
agents on the corresponding
211
eratures.
II.
(a)
d i c h l o r o compounds a t low temp-
PROPERTIES
PHYSICAL
A l k y l - and a r y l - dihaloboranes
density
2 1 2
'
2 1 3
'
2 1 4 -
are monomeric (vapour
and cryoscopic i n c h l o r o f o r m
216
E l e c t r o n d i f f r a c t i o n measurements
2 1 5
).
on m e t h y l d i f l u o r o -
borane have shown molecule t o be planar and s i m i l a r i n con-
69.
f i g u r a t i o n t o boron t r i f l u o r i d e .
(b)
CHEMICAL
Methyldichloroborane
217
easily
i s said to disproportionate
whereas the a l k y l - d i c h l o r o (and d i f l u o r o ) boranes
( e t h y l t o h e x y l ) are q u i t e s t a b l e t o d i s p r o p o r t i o n a t i o n up
to
0
170 .
2 1 8
Alkyldihaloboranes are pyrophoric the c h l o r o compounds
being more so than the f l u o r o compounds.
I t is interesting
to note t h a t the pyrophoric nature i s not dependent on
v o l a t i l i t y since n - b u t y l d i f l u o r o b o r a n e can be r a p ^ l y poured
i n a i r whereas the secondary and t e r t i a r y compounds are
spontaneously
inflammable.
I t has been suggested t h a t hyper
conjugation may account f o r the unexpectedly
reduced e l e c t r o
p h i l i c character of the boron i n s t r a i g h t chain compounds,~~
P
R
I
c
H
—
H
CI
=^
B;
ci
R—
4-
c
CI
-
B
H
C o n t r i b u t i o n s from q u i n o i d s t r u c t u r e s may
CI
account f o r
the l a c k of pyrophoric nature i n aryldihaloboranes.
Alkyldihaloboranes form 1:1 complexes w i t h ethers the
B-0 bond being stronger i n the c h l o r o - than i n the f l u o r o -
70
compounds.
n-Amyldifluoroborane- ether complex completely
d i s s o c i a t e s on f r a c t i o n a l d i s t i l l a t i o n whereas n - b u t y l d i 220
chloroborane- ether decomposes,
6
n
Et 0 - Bu BCl
2
n
2
-» EtCl + (EtO)tfu BCl.
221 r~
h
Phenyldichloroborane r e a c t s w i t h most ethers
F 2°
and (C1CH 0H ) 0 do not r e a c t j a t h i g h temperatures, a l k y l
2
2
2
c h l o r i d e s are produced e x c l u s i v e l y from the more e l e c t r o n
r e l e a s i n g group i n a mixed e t h e r , as w e l l as an a l k y l - or
a r y l - phenylchloroboronite
IL
Ph
.01
^ 0 : + PhBCl,-* . B
R'
^0' C 1
R
N
R'
P h
X
?<ci
R
+
CI
* PhB^
OR
+ Cl
OR
RC1 + PhBCl(0R)s
Phenyldichloroborane w i t h hydrogen i o d i d e and i o d i n e
pop
gives a phenyldiiodoborane hydrogen i o d i d e complex PhBI .2HI.
2
A l k y l - and aryl-dihaloboranes form s t a b l e 1:1 complexes w i t h
amines, those w i t h p y r i d i n e ( p a r t i c u l a r l y a r y l s ) are u s e f u l
for identification purposes.
2 2 3
'
2 2 4
'
2 2 5
Reduction of phenyldichloroborane w i t h l i t h i u m aluminium
22
hydride i n the presence of p y r i d i n e gives PhBH py. ^
2
If
71
p y r i d i n e i s absent triphenylborane and diborane are obtained,
probably by d i s p r o p o r t i o n a t i o n
3PhBH
2
Ph B
B H .
3
2
Diphenyl diborane ( P h B H )
2
2
g
m.p. 85° has also been
obtained from triphenylborane and diborane a t 80° and 2*2 atm.,
228
pressure.
72
DIALKYL AND DIARYL HALOBORANES
1.
PREPARATION
The d i a l k y l - and d i a r y l - haloboranes have been prepared
by methods s i m i l a r t o those used f o r the d i h a l i d e s .
(a)
ORGANOMETALLIC COMPOUNDS
Diphenylbromoborane i s obtained from diphenyl mercury
229
and boron t r i b r o m i d e
2Ph Hg + BBr^
2PhHgBr +- PhgBBr
2
Phenyldichloroborane
reacts w i t h diphenyl merciairy t o give
2 30
diphenylchloroborane.
PhBCl
Ph Hg
2
PhKgCl -v PhgBCl
2
B i s ( 2 - c h l o r o v i n y l - ) m e r c u r y and boron t r i c h l o r i d e when heated
2 31
under r e f l u x i n benzene give the boron monochloride.
(b)
TRIALKYLBORANES AND AMINODIALKYLBORANES
D i a l k y l c h l o r o b o r a n e s are now q u i t e accessible since they
are prepared i n e x c e l l e n t y i e l d by bubbling boron t r i c h l o r i d e
i n t o the appropriate t r i a l k y l b o r a n e a t 160? The e q u i l i b r i u m
2R BC1^ RBC1 + R^B l i e s f a r t o the l e f t , a t l e a s t a t temp2
2
2
eratures up t o 180°. ^
2
73.
The r e a c t i o n between t r i a l k y l b o r a n e s and hydrogen
233
h a l i d e s has been used t o prepare several d i a l k y l h a l o b o r a n e s ,
R B + HX
R BC1 + RH
3
2
Tri-n-propylborane and i o d i n e at 140°
2 34.
iodoborane
12 + Pr^B
Pr^BI +
give d i - n - p r o p y l
n
other products i n c l u d i n g P r B I
2
Antimony t r i c h l o r i d e and t r i b r o m i d e on the i o d o - compound
give the d i - n - p r o p y l c h l o r o - and bromo- borane but antimony
t r i f l u o r i d e and other f l u o r i n a t i n g agents f a i l e d t o produce
the fluoroborane.
100°for
n-Pr„BI + SbCl.
*
*
2 hours
Pr^BCl
J
100°
Pr^BI 4- SbBr.
>
*
2 hours
J
d
Pr*BBr
d
2 35
T r i - n - b u t y l b o r a n e and bromine give di-n-butylbromoborane.
Dimethylchloroborane was obtained from (dimethylamino) d i )orai and excess hydrogen c h l o r i d e reacted at 20°C f o r
methylborane
236
2 hours
(Me) BNHMe • HC1
2
(Me^BCl.NHgMe
HC1
5*
Me BCl
2
+MeNH .HCl
2
74
(c)
BORONIC AND BORINIC ACIDS AND DERIVATIVES
Diphenylchloro
(and bromo) borane have r e c e n t l y been
prepared by the r e a c t i o n a t -80°C between d i p h e n y l b o r i n i c
2 37
anhydride and t h e appropriate boron h a l i d e .
( P h B ) 0 •»• BX^
2
2 Ph BX + BOX
2
2
The r e a c t i o n between diphenylboronitea and phosphorus
pentahalides has been used t o prepare diphenyl-chloro
(and broroo) b o r a n e .
Ph B0R + PX
2
5
2 2
-v Ph BX + RX + POX^
2
Y i e l d s from these r e a c t i o n s were r a t h e r low due t o appreciable
d i s s o c i a t i o n of t h e pentahalides a t t h e n e c e s s a r i l y h i g h
temperatures.
II.
(a)
PROPERTIES
PHYSICAL
240
241
242
Dimethyldiethyland d i p r o p y l chloroboranes
were found t o be monomeric i n t h e vapour phase and t h e
Trouton constant f o r the n - p r o p y l - compound was obtained.
D e n s i t i e s , r e f r a c t i v e i n d i c e s and i n f r a - r e d spectra o f many
4
d i a l k y l h a l o b o r a n e s have been obtained? "
(b)
3
CHEMICAL
Dialkylhaloboranes
are r e s i s t a n t t o d i s p r o p o r t i o n a t i o n
75.
up t o 170 , however a t higher temperatures the e q u i l i b r i u m
2R BCl5* RBC1 •* R-jB, though f a r t o t h e l e f t does e x i s t ,
2
2
and c a r e f u l take o f f o f the more v o l a t i l e
alkyldichloroborane
24
at atmospheric pressure leads t o complete d i s p r o p o r t i o n a t i o n .
I t appears t h a t t h e mechanism f o r the d i s p r o p o r t i o n a t i o n i s
s i m i l a r t o t h a t o f t h e t r i a l k y l b o r a n e s , a dimeric
intermediate
i s formed by the overlapping o f halogen o r b i t a l s w i t h unoccupied boron p - o r b i t a l s , the a l k y l d i h a l o b o r a n e produced
r a p i d l y reacts w i t h excess t r i a l k y l b o r a n e so t h a t the d i a l k y l haloborane i s produced e x c l u s i v e l y .
Several d i a l k y l - and d i a r y l - haloboranes have been
characterised by h y d r o l y s i s t o the corresponding acids or
245
anhydrides,
Ph„BCl + H«0
-* [ p h B j
2
2HC1
2
n
Bu«BCl f H„0 -» Bu-BOH
f HCl
The
halides r e a d i l y undergo a l c o h o l y s i s .
n
Ph BBr + Bu 0H
2
1
-» PhgBOBu + HBr.
Reduction o f dibutylchloroborane
24
i n ether ** w i t h
sodium-potassium a l l o y , gives a coloured s o l u t i o n
something equivalent
1
t o d i b u t y l b o r o n ' which
containing
disproportionates
76.
on evaporation of the ether i n t o t r i b u t y l b o r a n e and a glassy
residue ( B u B ) which evolves hydrogen on h y d r o l y s i s .
n
. BC1 •*• K
IBU^B]
2
~»
Bu^B +
BuB
n
Reduction w i t h 2 mols. of metal leads t o an a l k a l i
metal
d i b u t y l b o r i d e which forms dibutylmethylborane on treatment
w i t h methyl
iodide.
_
B u p C l + 2K
Mel
f Bu^BMe
-» BupK
No r e a c t i o n was observed when diphenylbromoborane stood
0 '"^47
over sodium wire i n pentane f o r 50 hours a t 20 C.
248
Diphenylchloroborane
and secondary amines
react i n
ether t o give s o l i d s of the type Ph,,B - NR
2
Ph BCl + Et NH
2
2
Ph BNEt
2
2
+ HC1
Ph BNEt m.p. 36-37°, b.p. 159°-l62°/ll mm., and Ph BN(CH )
2
2
2
2
5
m.p. 65-66° b.p. 200-203°/l9 mm., were obtained.
Several d i a r y l h a l o b o r a n e s have been reacted w i t h p y r i d i n e
249
t o produce s t a b l e complexes.
Compounds of the general type (PhpBX) are s t a b l e t o
ethers f o r as long as 2 hours a t 20°C, but experiments a t
250
higher temperatures have not y e t been attempted.
77.
Diphenylchloroborane undergoes an unusual r e a c t i o n
w i t h aluminium
c h l o r i d e i n e t h y l methyl ketone, whereby
diphenylboronium PhgB", ions seem to be formed.
of s i l v e r p e r c h l o r a t e
Addition
to a s o l u t i o n of diphenylchloroborane
i n nitrobenzene causes immediate p r e c i p i t a t i o n of s i l v e r
c h l o r i d e , and the s o l u t i o n contains
diphenylboronium
251
perchlorate.
P h B C l + AgClO^ -» AgCl
Ph B C10^
+
2
2
I f the r e a c t i o n i s c a r r i e d out i n nitromethane,
and
b i p y r i d y l added a f t e r removal of s i l v e r c h l o r i d e , the
c r y s t a l l i n e compound 2,2'-bipyridyldiphenylboronium p e r 252
chlorate c r y s t a l l i s e s :
dipy
P h B C l + AgC10
2
+
4
Ph B C10
2
-
r
»
4
Idipy
BPhJ
C10~.
Although e s t e r s of b o r i n i c a c i d s are r e a d i l y hydrolysed
the e s t e r ( a ) m.p. 74—75° ( q u a n t i t a t i v e l y from P h B C l and
2
e t h y l a c e t o - a c e t a t e ) , i s v e r y r e s i s t a n t to h y d r o l y s i s .
0 —
2
\
C
OEt
/
0
0 — OHj
0
2
\
C—
OEt
/
0
0 —
CH,
I t i a both conjugated and c o o r d i n a t i v e l y saturated?
PART I I
PREPARATION OP REAGENTS
78.
The p r e p a r a t i o n of chlorodiphenylborane
(GgH^) BC1
2
Trimethoxyboroxine (87g., 0*5 mole) i n d r y ether
(900 c.c.) was s l o w l y added (2 hours) t o phenylmagnesium
bromide (4-75 mole) i n t h e same solvent (3000 c.c.)
while
the temperature was maintained between 24° and 26°. A f t e r
adding a l l the boroxine
and s t i r r i n g f o r a f u r t h e r 2 hours
the r e a c t i o n mixture was hydrolysed
(465 c.c. i n 11. o f w a t e r ) .
with hydrochloric acid
The ether l a y e r was then sep-
arated, washed three times w i t h water, and d i s t i l l e d t o low
bulk.
The remainder o f t h e ether was evaporated from t h e
y e l l o w o i l y a c i d on a water bath.
The a c i d was heated (20 mins) w i t h 250 c.c. o f water
on a steam bath t o remove any boronic a c i d , and then separated, dissolved i n ether (400 c.c.) and t h e monoethanolamine ester of t h e a c i d (202g., 8856 m.p. 188°- 89°) was prec i p i t a t e d on t h e a d d i t i o n of monoethanolamine ( 9 1 c.o.) i n
water (400 c.c. )
2
^
Hydrolysis o f t h e ester i n a ^^^50 s o l u t i o n o f acetone
and methanol w i t h h y d r o c h l o r i c a c i d (95 c.c.) and s u f f i c i e n t
water t o separate t h e l a y e r s (500 c.c.) a f f o r d e d t h e pure
a c i d which was separated d i s s o l v e d i n ether (400 c.c.) and
d r i e d (anhyd. MgSO^).
A f t e r removal of t h e ether, t h e a c i d
was pumped (0«006 mm.) f o r 3 hours on a water bath a t 100?
79.
when i t s o l i d i f i e d forming the anhydride ( c r y s t a l l i s e d
from pentane m.p. 116-116*5 , 110g.,)
Chlorodiplienylborane (m.p. 21-5-22? b.p. 80°-82°/
0»05 mms., 65g., 83*5^) was obtained by the r e a c t i o n between
d i p h e n y l b o r i n i c anhydride and boron t r i c h l o r i d e i n methylene
c h l o r i d e , a s p r e v i o u s l y d e s c r i b e d by Gerrard, Lappert,
Dandgoanker and A b e l I '
B e t t e r y i e l d s than those d e s c r i b e d
were obtained by vacuum d i s t i l l i n g d i r e c t l y from the s o l i d
g e l of boron o x y c h l o r i d e .
OMe
B
°|
MeOB.^
°
9 PhMgBr -9- Ph BOMgBr
2
> PhgBOH
^BOMe
Ph B0H <e— Ph
I
o
NH2
d
CH
HOCH CH NH
2
2
BCl,
[ P h B ] ,0
2
Ph BCl
2
C h l o r o d i - p - t o l y l b o r a n e (CH^CgH^JgBCl (m.p. 64° b.p. 110113/o•! mm I8*2g., 76*4$) and Chlorodi-p-bromphenylborane
( B r C H ) B C l , (m.p. 79-80°, b.p. 1 8 4 ° - 7 % . I ^
6
4
2
23-5g.,
y i e l d 64$) were s i m i l a r l y prepared from trimethoxyboroxine
and the appropriate Grignard reagent.
2
2
80.
The p r e p a r a t i o n of f l u o r o d i m e s i t y l b o r a n e (2,4,6,CH2CgH ) BF.
2
2
Boron t r i f l u o r i d e - e t h e r a t e (10'6g., 0*075 mole) was
slowly added t o mesitylmagnesium bromide (0-24 mole) pre258
pared by the method described by Brown and Dodson.
The
r e a c t i o n mixture was r e f l u x e d (2 hours) and then l e f t t o
s e t t l e overnight.
The yellow-orange upper l a y e r was
sep-
arated ( N ) and a f t e r removal of solvent a f f o r d e d on vacuum
2
d i s t i l l a t i o n f l u o r o d i m e s i t y l b o r a n e (m.p. 76°-77° sealed tube
b.p. 130-2°/ .5 mm 16-8g., y i e l d 84$)
0
The p r e p a r a t i o n o f dimethylamino boron d i c h l o r i d e
Dimethylaminoboron d i c h l o r i d e (b.p. 50-54°/o,0 mm 94g.,
76$) was
I t was
prepared by the method described by J. P. Brown?"^
found by vapour phase chromatography t h a t even a f t e r
two c a r e f u l f r a c t i o n a t i o n s the f i n a l product contained a con
s i d e r a b l e amount of benzene,
The p r e p a r a t i o n of diphenylphosphine
The p r e p a r a t i o n of diphenylphosphine from t r i p h e n y l p h o s
phine and l i t h i u m shot i n t e t r a h y d r o f u r a n has already been
9 fin
described.
However increased y i e l d s of the
diphenylphos-
phine were obtained by using sodium wire i n s t e a d of l i t h i u m
shot and deaerated a c i d f o r h y d r o l y s i s .
Ph P + 2Na
3
PhNa 4- PhgPNa
PluPH
H0
Freshly cut sodium wire (10g.,) was pressed(N ) i n t o
2
2
81.
a s o l u t i o n of triphenylphosphine (52»6g., 0*2 mole) i n
dry t e t r a h y d r o f u r a n (250 c . c ) .
The s o l u t i o n r a p i d l y "became
deep red i n colour and i t slowly became q u i t e warm.
s t i r r i n g the r e a c t i o n mixture (2 hours) i t was
w i t h d i l u t e h y d r o c h l o r i c a c i d t o pH 7-7*5.
After
hydrolysed
Tetrahydrofuran
was removed by d i s t i l l a t i o n and vacuum d i s t i l l a t i o n a f f o r d e d
diphenylphosphine (110-112°/2 mm.
26-4g., 71%)
The p r e p a r a t i o n of di-m-tolylphosphine
Pure di-m-tolylphosphine
not described was
hitherto
prepared by the method described by
261
Gilman and D. Wittenberg
phosphine.
(b,p. 102°-4°/o.l mm.)
H.
f o r the p r e p a r a t i o n of d i p h e n y l -
The t r i - m - t o l y l p h o s p h i n e was
prepared as des-
c r i b e d below.
The
i n f r a spectrum of the phosphine a colotirless a i r
s e n s i t i v e l i q u i d showed the s t r o n g P-H
absorption a t 4*33 u.
O x i d a t i o n w i t h aqueous a l c o h o l i c hydrogen peroxide
afforded
d i - m - t o l y l p h o s p h i n i c a c i d (m.p. 169°)•
The p r e p a r a t i o n of t r i - m - t o l y l p h o s p h i n e
Phosphorus t r i c h l o r i d e (65 c.c. 0*73 mole) i n dry
ether (200 c.c.) was
slowly added (Ng) t o m - t o l y l magnesium
bromide (2*9 mole) i n the same solvent ( 1 1 ) .
f i n a l a d d i t i o n of h a l i d e the s o l u t i o n was
and then c a r e f u l l y hydrolysed
a f t e r the
r e f l u x e d ( 1 hour)
w i t h deaerated d i l u t e hydro-
82.
c h l o r i c a c i d ( f i n a l pH 7-7*5).
The ether l a y e r was
separated, d r i e d (anhydrous magnesium sulphate) and
d i s t i l l e d t o low b u l k before f i n a l l y pumping d r y . Crys t a l l i s a t i o n ( c h a r c o a l ) from ethanol a f f o r d e d t r i - m - t o l y l phosphine (m.p. 104°, 121g., 49*2$).
The p r e p a r a t i o n o f t r i p h e n y l a r s i n e
Anhydrous arsenic t r i c h l o r i d e (126 c.c., 1*5 mole)
i n d r y ether (350 c.c.) was s l o w l y added ( N ) t o phenyl2
magnesium bromide (5 mole) i n t h e same solvent ( 3 1 . ) . A f t e r
the f i n a l a d d i t i o n of h a l i d e t h e r e a c t i o n mixture was
r e f l u x e d (£ hour) and c a r e f u l l y hydrolysed w i t h d i l u t e
hydrochloric acid,
The ether l a y e r was separated, d r i e d
(anhydrous magnesium sulphate) and concentrated before
being pumped d r y . C r y s t a l l i s a t i o n from ethanol ( c h a r c o a l )
a f f o r d e d l a r g e white c r y s t a l s of t r i p h e n y l a r s i n e (m.p. 5960°, 370g., y i e l d 8 l # ) .
The p r e p a r a t i o n o f d i p h e n y l a r s i n e
Diphenylarsine (b.p. 120°-22°/l.O mm, 55*2g., y i e l d
68»2$) was prepared by the method described by W. Kuchen
and H. Buchwald
from t r i p h e n y l a r s i n e and l i t h i u m shot
i n t e t r a h y d r o f u r a n . Higher y i e l d s of a r s i n e were obtained
by u s i n g deaerated d i l u t e h y d r o c h l o r i c acid f o r h y d r o l y s i s .
83
The p r e p a r a t i o n o f phenylphosphine
Phenylphosphine (b.p. 40°/9-10 mms 30*2g., y i e l d 61$)
was obtained from phenyldichlorphosphine
( 8 0 g . ) and l i t h i u m
f
aluminium hydride (10g.,) as described by W. Kuchen and H.
Buchwald.
I t was found t h a t increased y i e l d s were
obtained when t h e white p r e c i p i t a t e formed a f t e r h y d r o l y s i s
was e x t r a c t e d again w i t h hot ether, a f t e r decanting o f f the
original
solution.
PART
III
EXPERIMENTAL RESULTS
84.
Microanalyses
(C,H, and halogen) are by Mr. A. Wiper
and Miss V. Conway, and i n f r a r e d spectra are measured by
Mr. L. Chadwick and Miss D. A. Chapman of these l a b o r a t o r i e s .
Combustion analyses o f t e n presented the d i f f i c u l t i e s ,
f a m i l i a r w i t h organo-boron compounds, due t o the r e t e n t i o n
of carbon as boron carbide i n combustion residues, l e a d i n g
t o e r r a t i c carbon r e s u l t s .
More r e p r o d u c i b l e r e s u l t s were
g e n e r a l l y obtained when smaller samples were b u r n t , and
when t h e residue a f t e r combustion was heated w i t h an oxygen
enriched flame.
Compounds were i n several instances i d e n t i f i e d
by
q u a n t i t a t i v e h y d r o l y s i s ( f o r amino-) or o x i d a t i o n r e a c t i o n s
( f o r phosphino- and a r s i n o - d e r i v a t i v e s ) .
Cryoscopic
constants were determined u s i n g biphenyl
f o r benzene and j 3 - n i t r o t o i u e n e f o r nitrobenzene.
Except i n t h e case of one compound
(PhgB N H ) »
2
2
f o r which r e f r a c t i v i t i e s were measured over a range o f wavel e n g t h s , r e f r a c t i v i t i e s were measured a t 6620A
0
(Jena
i n t e r f e r e n c e f i l t e r ) and atom p o l a r i s a t i o n s were taken as
IQfo
of these r e f r a c t i v i t i e s .
Dipole moments were measured i n benzene s o l u t i o n ,
t o t a l p o l a r i z a t i o n s being derived by H a l v e r s t a d t and
Kumler's
method.
I n s p i t e o f the apparent a s s o c i a t i o n
85.
of many o f the compounds s t u d i e d , as suggested by cryoscopic
measurements, d i e l e c t r i c constant - weight f r a c t i o n p l o t s
were always very n e a r l y l i n e a r .
I n fra red spectra were measured w i t h a Grubb-Parsons
GS2A g r a t i n g
spectrometer.
Aminodiphenylborane
(Ph B NHg^
2
Chlorodiphenylborane (10g., 0*05 mole) i n d r y ether
(100 c.c.) was s a t u r a t e d w i t h ammonia a t room temperature
and t r i e t h y l a m i n e (5*lg.» 0*05 mole) i n ether (50 c.c.)
was s l o w l y added.
The r e a c t i o n mixture was b o i l e d w i t h
r e f l u x ( 1 h o u r ) , cooled, and f i l t e r e d under n i t r o g e n from
triethylamine hydrochloride.
The f i l t r a t e was pumped
dry and the c o l o u r l e s s product c r y s t a l l i s e d from benzene,
m.p. 129-130°(3-6g., 43%) (Pound: C, 79-4; H, 6-7 C
H
1 2
i2
B N
r e q u i r e s C, 79*9; H, 6-6%)
Aminodimesitylborane (2,4,6,CH^CgH ) BNH
2
2
2
D i m e s i t y l f l u o r o b o r a n e (6g., 0*224 mole) i n ether was
slowly added t o excess ammonia i n the same solvent (50 c.c.)
cooled t o -60°C.
An immediate p r e c i p i t a t e of d i m e s i t y l
fluoroborane-ammonia complex (m.p. 144°-5°) a s observed.
W
The f i n a l r e a c t i o n mixture was r e f l u x e d (48 hours) and t h e
p r e c i p i t a t e slowly r e d i s s o l v e d and ammonium f l u o r i d e (0»4g.,)
86.
was p r e c i p i t a t e d . Pumping o f f solvent a f f o r d e d aminodimesitylborane ( c r y s t a l l i s e d from pet., ether, m.p. 118°20° 5'5g., y i e l d 92-6$)
Pound Ms B, 93'4, 93*5$, NH 5*96,
2
2
5*92$ C H BN r e q u i r e s MsgB 94*1%, NH fcO#
18
24
2
Dimethylaminodiphenylborane,
Ph B»NMe
2
2
To a s o l u t i o n o f monomeric dimethylamino
dichloroborane
(3*2g., 0*025 mole) i n benzene (50 c.c.) was slowly added
phenylmagnesium bromide (0-05 mole) i n ether.
The r e a c t i o n
mixture was pumped dry, t o remove the ether since magnesium
h a l i d e - ether complexes are s o l u b l e i n organic
solvents,
and the organic product was e x t r a c t e d w i t h hot benzene.
Vacuum d i s t i l l a t i o n o f the e x t r a c t yielded^ a c l e a r
c o l o u r l e s s , a i r s e n s i t i v e l i q u i d product, b.p. 102-104°/
0*05 mm. ( 4 - l g . , 81$) (Pound: 0, 80-8; H, 8-0.
C H
1 4
1 6
BN
r e q u i r e s C, 80»4; H, 7'6%)
Dimethylamino d i - p - t o l y l b o r a n e , (p-CH^CgH.^) B«NMe , b.p.
2
2
110-112°/0-04-0-05 mm. (4"5g., 76$) Pounds C, 80-0; H, 8«6.
G
H
16 20
B N
r
e
<
l
u
i
r
e
s
c
» 81*1; H, 8*4$.
By h y d r o l y s i s , found:
(p_-CH C H ) B, 81-8; 80-5; Me N, 18*8, 18-3. C H BN r e q u i r e s
3
6
4
2
2
l6
2Q
(p_-CH C H ) B, 81-5; Me N, 18-6%) and
3
6
4
2
2
Dimethylamino di-p-bromophenylborane, (p-BrCgH ) B"NMe ,
4
2
2
m.p. 39-40° from benzene-hexane ( 4 - l g 44$) (Pound: C, 46*6;
H, 3'7; Br 43-9- C H B B r N r e q u i r e s C, 45-8; H, 3-8; Br,
u
1 4
2
87.
43*7$) were s i m i l a r l y prepared using £-tolyl- and p_-bromphenylmagnesium bromide r e s p e c t i v e l y .
88.
Diphenylaminodiphenylborane
Pb^B NPh
(Method
2
1.)
L i t h i u m diphenylamide («051 moles) i n dry ether was
slowly added t o an e q u i v a l e n t q u a n t i t y of c h l o r o - d i p h e n y l borane i n the same solvent a t -60°C.
The r e a c t i o n m i x t u r e
was allowed t o warm t o room temperature, f i l t e r e d
under
n i t r o g e n , and the white product which r e s u l t e d from pumping
solvent from the f i l t r a t e was crystal3.ised from benzene,
l l * 9 g . , m.p.
C
H
24 20
B N
r
e
c
148-150 (66%) (Pound: C, 85*8; H, 6-1; B, 3*14'
l
u
i
r
e
s
c
6
» 8 *4; H, 6*0; B, 3*26%).
0*l86g. was
warmed w i t h aqueous acetone f o r a few minutes, and a s l i g h t
excess of ethanolamine was added.
The r e a c t i o n mixture was
poured i n t o water, the s o l i d c o l l e c t e d , pumped dry and sublimed i n vacuo.
The sublimate, 0«093g.» m.p.
56°,
was
identified (infra-red
spectrum) as diphenylamine, and the
residue 0*132g., m.p.
l88°-9°, was s i m i l a r l y i d e n t i f i e d
a3
the ethanolamine ester of d i p h e n y l b o r i n i c a c i d . C^H^QBN
r e q u i r e s 0*096g, and 0*128g, r e s p e c t i v e l y .
(Method
2.)
Freshly p u r i f i e d diphenylamine (8*5g, 0*05 moles i n
benzene was added t o a s o l u t i o n c o n t a i n i n g e q u i v a l e n t amounts
of t r i e t h y l a m i n e (9*1 mis.,) and chlorodiphenylborane (lOg.)
i n the same s o l v e n t .
The r e a c t i o n mixture was b o i l e d w i t h
89.
r e f l u x (30 min.), f i l t e r e d under n i t r o g e n from t r i ethylamine h y d r o c h l o r i d e (6*2g.) m.p. 255-6? and the
f i l t r a t e concentrated t o c r y s t a l l i s a t i o n ( l l ' l g .
61$).
The i n f r a spectrum o f the product was i d e n t i c a l w i t h t h a t
of the m a t e r i a l prepared by method ( 1 ) .
Di-p-tolylaminodiphenylborane,
[Ph B'N( CgH^jD-CH^g]» tn.p.
2
130-132° ( f r o m a benzene-hexane m i x t u r e )
H, 6*5.
found:
[Pound: C, 85•3;
C H BN r e q u i r e s C, 86«3; H, 6»8%.
2g
24
Ph B, 45*9; (p_-CH C H ) N 54-9.
2
3
6
4
2
By h y d r o l y s i s ,
C^H^BN r e q u i r e s
PhpB, 45*8? (pj-CH^CgH^^N 54*2%] was prepared by methods
(1) 53% and (2) 57%.
Diphenylaminodi-p-tolylborane [(^-CH^CgH^) B«NPh ].
p
2
This was prepared by method ( 2 ) and the white product was
c r y s t a l l i s e d from benzene-hexane (5*9g.» 67%), m.p. 72-73°
[Pound: C, 89'9; H, 7-0.
C H BN r e q u i r e s C, 89'1; H, 7*0%.
26
24
By h y d r o l y s i s , found: (p_-CH CgH ) B , 53'8, 53-7; Ph N, 46*8,
3
46'4.
4
2
2
C H BN r e q u i r e s (jo-CH C H ) B, 53'4? Ph N, 46-6%].
2g
24
3
6
4
2
2
Aminodi-o-tolylborane, (o-CH CgH ) B»NH - This was prepared
3
4
i n ether s o l u t i o n by method ( 2 ) .
2
2
A f t e r f i l t r a t i o n ( N ) from
?
t r i e t h y l a m i n e h y d r o c h l o r i d e , the product was obtained by vacuum
d i s t i l l a t i o n (67*2% b.p, 86°-88°/ 3o"mm. [By h y d r o l y s i s , found:
3
c
H
(o-CH CgH ) B, 91-9%? NH , 7«6%, 7»4%; i 4 i B N r e q u i r e s
3
4
2
2
( o - 0 H c H ) B , 92-3%; NH , 7-7%.]
3
6
4
2
2
6
90.
Diphenyl(diethylphosphine)borane,
Ph B.PEt
2
2
n - B u t y l l i t h i u m (0»025 mole) i n d r y benzene (50 c.c.)
was s l o w l y added t o a s o l u t i o n o f diethylphosphine (2*3g..
0-025 mole) i n the same solvent a t room temperature.
Suf-
f i c i e n t t e t r a h y d r o f u r a n (30 c.c.) was added t o d i s s o l v e
the pale y e l l o w p r e c i p i t a t e ( L i P E t ) , and t o the s o l u t i o n
2
was s l o w l y added chlorodiphenylborane (5g., 0*025 mole)
i n benzene (50 c . c . ) , and the y e l l o w orange colour s l o w l y
disappeared.
mixture.
Water (100 c.c.) was added t o the r e a c t i o n
The benzene l a y e r when separated, d r i e d (MgSO^)
and pumped d r y , gave a c o l o u r l e s s ppduct, m.p. 192° from
benzene (5-3g., 84%) (Pound: C, 75«8; H, 7-9; B, 4-4; P,
12.0. C H BP r e q u i r e s G, 75-6; H= 7-9; B, 4 0 5 ; P, 11*8%).
16
20
M-p-bromphenyl(diethylphosphino)borane,
(p-BrCgH^) B.PEt )
2
2
This was s i m i l a r l y prepared from c h l o r o (di-p-bromphenyl)borane, and c r y s t a l l i s e d from benzene-hexane, m.p.
202? 4-8g., 49% (Pound: C, 45-9; H, 4-3: Br, 38-1.
C
1 6
H
l 8
BBr P r e q u i r e s C, 46-5; H, 4-4; B, 38*9%)
2
A d d i t i o n of methyl i o d i d e t o a s o l u t i o n of the phosphinoborane i n benzene gave an immediate white p r e c i p i t a t e
of methiodide, m.p. 310-312° (decomp.) (Pound: I ,
23*3.
C H B B r l P requires I ,
1 7
2 l
2
22*9%).
23*1,
91.
Diphenyl(diphenylphosphino)borane,
[Ph B*PPh 3
2
2
Chlorodiphenylborane (5g) i n dry benzene (50 c.c.)
was added a t room temperature t o a mixture o f d i p h e n y l phosphine (4*2g 0*025 mole) and t r i e t h y l a m i n e (2*5g., 0*025
mole) i n benzene (50 c . c . ) .
P a r t of the r e s u l t i n g t h i c k
white p r e c i p i t a t e was d i s s o l v e d by the a d d i t i o n of water,
and the r e s t was separated by f i l t r a t i o n , washed s e v e r a l times
w i t h e t h e r , pumped d r y , and the phosphinoborane c o l l e c t e d i by
3
;
s u b l i m a t i o n (240°/l0~ mm., 5 4g., 61%)
H, 5*6,
[Pound: C, 78-9;
C H BP r e q u i r e s C, 82*3; H, 5'7%
24
2Q
0•1906g.,] warmed
w i t h aqueous a l c o h o l i c hydrogen peroxide, phenol separated;
by steam d i s t i l l a t i o n and converted t o the tribromo d e r i v a t i v e ,
y i e l d e d tribromophenol, m.p. 95°=6°, 0*348g. C ^H BP r e q u i r e s
2
0»359g.
20
Diphenyl phosphinic a c i d (m.p. 195°-6°) was i s o l a t e d ,
but not q u a n t i t a t i v e l y from the steam d i s t i l l a t i o n r e s i d u e .
This compound was also prepared by method ( 1 )
Ph
Ph
PNa
Ph
Ph
+ C1B
Ph
+
B
Ph
Ph
NaCl
Ph
A deep red s o l u t i o n of the sodium d e r i v a t i v e o f d i phenylphosphine
(0*025 mole) i n d r y 2,5 dioxahexane (50 c.c.)
92.
was s l o w l y added t o a s o l u t i o n of chlorodiphenylborane
(5g.,
0'025 mole) i n the same solvent (50 c.c.) a t -60°C.
The s o l u t i o n was i n s t a n t l y decolourised and a white p r e c i p i t a t e was formed.
A f t e r treatment w i t h
de-aerated
water (50 c.c.) and several washings w i t h ether, the i n f r a
red spectrum o f the w a t e r - i n s o l u b l e s o l i d product showed
the presence of P-H bonds.
Vacuum s u b l i m a t i o n of the
s o l i d product a f f o r d e d d i p h e n y l (diphenylphosphino) borane
3
(240°/lO~ mm., 4-5g., 51*)
Chlorodiphenyl(diphenylphosphine)borane,
BClPh PHPhp
2
Diphenyiphosphine (4«2g., 0«025 mole) i n d r y benzene
(25 c.c.) was s l o w l y added t o chlorodiphenylborane (5g.»
0*025 mole) i n benzene (20 c.e.).
The white
crystalline
and very hygroscopic adduct (7-3g., 75*), m.p. 83-85? was
H
c o l l e c t e d by f i l t r a t i o n . (Pound: CI, 9*04, 9-08, C 4 2 1
2
BC1 P r e q u i r e s CI, 9*18*)
Triethylammonium chlorodiphenyl( diphenylpho:sphino)borate
Et^NH"*" BClPh PPh~
2
-
Diphenylphosphine
(42g., 0-025
mole) i n d r y benzene (25 c.c.) was added dropwise t o a
mixture of chlorodiphenylborane (5g.,) and t r i e t h y l a m i n e
(2»5g.) i n benzene (25 c . c . ) .
The c o l o u r l e s s s a l t
immediately
p r e c i p i t a t e d was c o l l e c t e d by f i l t r a t i o n (9«3g., 77* m.p.
152-3°). (Pound: C, 72-4; H, 7-7, B, 3-71, C I , 6-9, Et.N,
93.
19'8. C H BC1NP r e q u i r e s C, 73*5; H, 7'4," B, 3*24;
30
36
CI, 7-1; Et-jN, 20-1%).
Diphenyl(di-m-tolylphosphino)borane,
Pb^B P( CgH^m-CH^Jr,
A deep red s o l u t i o n o f t h e sodium d e r i v a t i v e of di-mt o l y l p h o s p h i n e (4'2g., 0*02 mole), prepared by adding f r e s h l y
pressed sodium wire against a c u r r e n t o f n i t r o g e n i n t o a
s o l u t i o n of t h e phosphine i n t e t r a h y d r o f u r a n (20 c . c ) , was
added t o an equivalent amount of chlorodiphenylborane (4g.)
i n d i e t h y l ether (20 c.c.) a t room temperature.
was immediately
cipitated.
The s o l u t i o n
decolourised and sodium c h l o r i d e was p r e -
Most of the solvent was then removed by pumping
the r e a c t i o n m i x t u r e , and the residue was e x t r a c t e d w i t h
hot benzene.
Evaporation
of t h e benzene s o l u t i o n gave the
c o l o u r l e s s phosphinoborane ( 5 ' l g . , 67%), m.p. 123-4°- (Pound;
C, 81'9; H, 6'3; G H BP r e q u i r e s G, 82-4,- H, 6*4%,)
26
24
Di-m-tolylphosphinodi-p-tolylborane,
m-CH )
3
(jo-CH^CgH^ ),,B«P (CgH^#
m.p. 257-8° (from benzene-hexane, 5 4g., 67%) (Found:
2
C, 80.9» H, 6*9, C gH BP r e q u i r e s C, 82.8? H, 6-9%)and
2
2g
Di-p-bromophenyldi-m-tolylphosphinoborane, (p-BrCgH^) B'P
2
C
H
CH
( 6 4—~ 3^2
m ,
* P
#
281° (from benzene-hexane 7«05, 66%)
("Pound: C, 60*2; H, 4*1; Br, 30.1. C gH BBr P r e q u i r e s C, 58-1
2
22
2
H, 4»lj Br,29-9%)were s i m i l a r l y prepared from the sodium
94.
d e r i v a t i v e of di-m-tolylphosphine and the a p p r o p r i a t e
chlorodiarylborane.
Phenyl( bis-dlphenylphosphino.)borane,
Dichlorophenylborane
PhB(PPhr>)
2
( 4 g . , ca. , 0»025 mole m.p.
5*1°2
5*5° p r e v i o u s l y described as a l i q u i d b.p. 62/11 m m s ) ^ i n
dry benzene (30 c-c.) wa,s slowly added t o a mixture o f t r i ethylamine (5«lg-, 0.Q5 mole) and diphenylphosphine
0«05 mole) i n the same solvent (50 c.c.) a t room
(9*3g»»
temperature.
The r e a t i o n mixture was r e f l u x e d (24 hours) t o ensure
c
complete dehydrohalogenation
before removal of the amine
hydrochloride (m.p. 255°-6°) by f i l t r a t i o n ( N ) .
2
A white
s o l i d and a small amount o f y e l l o w s o l i d p r e c i p i t a t e d when
the s o l u t i o n was pumped t o low b u l k .
The white s o l i d ( m.p.
143-49*2g., y i e l d 78%) was c r y s t a l l i s e d from benzene/hexane
solution.
(Pound by o x i d a t i o n PhB 17*5%, PhgP 79'8%, C^QH^
BP r e q u i r e s PhB 18»0%, Ph P 80«9%.)
2
Prolonged h e a t i n g of the c o l o u r l e s s monomer (see Table
2) i n benzene a f f o r d e d more of t h e y e l l o w i n v o l a t i l e
polymeric
s o l i d (m.p. 120°-32°) (Found by o x i d a t i o n PhB 16*0%, Ph P
?
79*9% C
3()
H B P r e q u i r e s PhB 18-0% Ph B 80«9%}
25
?
The y e l l o w s o l i d contained no halogen and v/as i n s o l u b l e
i n hydrocarbon, a l c o h o l i c , k e t o n i c and ether s o l v e n t s .
95.
B o t h s o l i d s were u n a f f e c t e d by b o i l i n g d i l u t e a c i d s
or a l k a l i .
D i c h l o r o p h e n y l ( phenylphoaphino )bora.ne,
BCl Ph«PH Ph
?
2
D i c h l o r o p h e n y l b o r a n e ( 4 ' 0 g , c a . , 0*025 mole) i n d r y
hexane ( 2 0 c.c.) was s l o w l y added t o an e q u i m o l a r q u a n t i t y
o f phenylphosphine
crystalline
( 2 * 8 g . ) i n t h e same s o l v e n t .
f
The w h i t e
and e x t r e m e l y h y g r o s c o p i c adduct was c o l l e c t e d
by f i l t r a t i o n ( N ) i n a Schlenk t u b e , washed w i t h s o l v e n t
2
and pumped d r y ( 6 * 4 .
s
74*8$ m*p* 62-64° s e a l e d t u b e ) (Found:
CI 26-5, 26-8$, C H B C 1 P r e q u i r e s 0 1 2 6 * 4 % ) .
1?
1?
2
P h e n y l ( p h e n y l p h o s p h i n o ) b o r a n e , (PhB*PPh)
Phenylphosphine
2
( l l g . , 0*1 mole) was heated t o r e f l u x
(6 h o u r s ) w i t h an e q u i m o l a r q u a n t i t y o f d i c h i o r o p h e n y l b o r a n e
(15'9g.») u n t i l e v o l u t i o n o f hydrogen c h l o r i d e had ceased.
Vacuum d i s t i l l a t i o n a f f o r d e d t h e c o l o u r l e s s f u m i n g l i q u i d
3
PhPH-BClPh ( 1 0 - l l g . , b.p. 98-100°/10" nun) (Pound: CI 15'7,
16-1$, PhB ( b y h y d r o l y s i s ) 38.2$ C^H-^BClP r e q u i r e s C I
15*4$ PhB,38'1#) and a y e l l o w - r e d g l a s s y s o l i d r e s i d u e w h i c h
was e x t r a c t e d w i t h h o t benzene and f i l t e r e d . )
The benzene s o l u t i o n a f f o r d e d t h e w h i t e dimer ( s e e
Table 2) (PhB-PPh)
2
(m.p. 89°-91°, 3'6g.,) (pound by o x i d a t i o n
PhB, 44-7; PhP, 55 '6$ C H B P r e q u i r e s PhB, 44*8; PhP, 5 5 * 2 $ ) .
12
1Q
96.
The i n v o l a t i l e y e l l o w i s h r e s i d u e ( l l - 1 2 g . , m.p.
168°-175°) was most p r o b a b l y a polymer c o n t a i n i n g "B-Cl
end groups.
(Potmd 01 1*3#
Ph
9
Ph
PhP 50*5$, PhB 42'8$)
Ph
Ph
I
CI
B
B
Ph
Gl
n
(The v a l u e o f n = 15s20)
D i - m - t o l y l p h o s p h i n o ( d i - m e s i i t y l )borane
(pCH^GgH^)r,»
( 2,4, 6, CFUCgB^^BP
The sodium d e r i v a t i v e of" d i - m - t o l y l p h o s p h i n e
(0*025 mole) i n t e t r a h y d r o g u r a n ( 5 0 c.c.) was s l o w l y added
t o d i m e s i t y l f l u o r o b c r a n e ( 6 * 7 g . j 0*025 m o l e ) i n t h e same
volume o f s o l v e n t a t -30°C.
After allowing the reaction
m i x t u r e t o s l o w l y come t o room t e m p e r a t u r e
anri r e f l u x i n g
( 1 h o u r ) i t was f i l t e r e d (N^) f r o m t h e w h i t e i n s o l u b l e
products.
Sodium f l u o r i d e was removed by washing t h e p r e -
c i p i t a t e s e v e r a l t i m e s w i t h w a t e r and t h e i n s o l u b l e compound
was washed s e v e r a l t i m e s w i t h e t h e r a.nd pumped d r y .
The
t e t r a h y d r o f u r a n s o l u t i o n was pumped d r y and a f f o r d e d a f u r t h e r
(l»2g.) o f t h e compound ( 5 * 4 g . , y i e l d 47$ m.p.
(Found:
264-5°).
C, 81«5; H, 8*2; C^H^BP r e q u i r e s C, 82*6; H, 7*9.)
97
(By o x i d a t i o n ( 2 , 4 , 6 , C H C H )
3
45'2# C H B P r e q u i r e s
32
C H )
6
5
36
6
2
2
B, 55-3%; ( m - C H C H )
3
6
5
2
P,
( 2 , 4 , 6 , C H C H ) B, 55•3%; (m-GH
3
6
2
2
P, 45-7^.)
2
A f t e r o x i d a t i o n w i t h aqueous a l c o h o l i c hydrogen p e r o x i d e
t h e m e s i t o l was s e p a r a t e d f r o m d i - m - t o l y l p h o s p h i n i c
acid
by t r e a t m e n t w i t h sodium c a r b o n a t e s o l u t i o n and e x t r a c t i o n
w i t h ether.
The compound was i n s o l u b l e i n e t h e r s ,
carbons, ketones, a l c o h o l s ,
hydro-
and c h l o r o f o r m and c a r b o n t e t r a -
chloride.
A t t e m p t s t o p r e p a r e t h e compound by t h e t r i e t h y l a m i n e
method f a i l e d b o t h i n b o i l i n g benzene and x y l e n e
Di-m-»tolylphosphino-( b i s - b i p h e n y l ) b o r a n e ,
(m-GH,CgH )
4
2
(
solutions.
)
BP
2
( 2 . 3 4 g . , 46$ y i e l d m.p. 7 7 ° - 7 8 ° ) was p r e p a r e d
by t h e t r i e t h y l a m i n e method i n benzene s o l u t i o n .
The i n s o l u b l e
compound was s e p a r a t e d f r o m t r i e t h y l a m i n e h y d r o c h l o r i d e
by
s e v e r a l washings w i t h w a t e r , washed w i t h e t h e r and pumped
dry.
The compound was i n s o l u b l e
t r i e d above. (Found:
(Pound:
C, 86-0; H, 6*0.
G
H
6 4 2 »
)
solvents
0,85*8 ; H , 5 « g ; C g H B P
requires
3
fi
38
32
( m - C H C H J P , AO-lf).
6
2
32
By o x i d a t i o n (4-C H C H.) B, 58*6$; (m-CH
6"5 6 4'2
39-9$; C H B P r e q u i r e s
P
3
i n the organic
R
fi
9
U-CgHgCgH^gB, 59-9$;
98.
Bis-diphenyl(phenylphosphino)borane
[(Ph B) PPh]
2
2
C h l o r o d i p h e n y l b o r a n e ( 1 0 g . , 0*05 mole) i n d r y x y l e n e
(50 c . c . ) was s l o w l y added t o a m i x t u r e o f t r i e t h y l a m i n e
(6*5 c.c. O 0 5 m o l e ) and p h e n y l p h o s p h i n e (2*6 c.c. 0*025
mole) i n t h e same s o l v e n t ( 5 0 c . c . ) . The r e a c t i o n m i x t u r e
was r e f l u x e d (24- h o u r s ) t o ensure complete dehydrohalogenation.
A f t e r f i l t r a t i o n (N,,), t h e s o l u t i o n was pumped
t o low b u l k and a f f o r d e d a w h i t e s o l i d w h i c h c r y s t a l l i s e d
f r o m benzene/hexane s o l u t i o n (m.p. 148-50°) [Found: C, 81*8;
H, 5*6,
C H B P r e q u i r e s C, 82«2; H, 5*7#, found by
3 Q
2 5
2
o x i d a t i o n PhP, 24*2$; PhgB, 75'1$
24-7#; Ph B, 75'3%].
2
H
B
°30 25 2
P
re
Te
V*l *
p
hP»
99
Diphenylarsinodiphenylborane, [Ph As*BPh 3. 2
2
D i p h e n y l a r s i n e ( 5 * 8 g . , 0*025 mole) was c o n v e r t e d
into
i t s sodium d e r i v a t i v e by r e a c t i o n w i t h excess sodium w i r e
i n t e t r a h y d r o f u r a n (50 c.c.) a t room t e m p e r a t u r e .
The
r u b y r e d s o l u t i o n was decanted ( N ) f r o m excess sodium
2
and was s l o w l y added t o c h l o r o d i p h e n y l b o r a n e
( 5 g . , 0*025
mole) i n t e t r a h y d r o f u r a n (50 c.c.) a t -60°, t h e r e d c o l o u r
being immediately discharged.
The r e a c t i o n m i x t u r e was
a l l o w e d t o warm t o room t e m p e r a t u r e , f i l t e r e d
(Ng) f r o m
p r e c i p i t a t e d sodium c h l o r i d e , and t h e f i l t r a t e was pumped
dry.
The r e s i d u e c r y s t a l l i s e d f r o m benzene, gave t h e
c o l o u r l e s s arsinoborane
0, 72*6; H, 5-1=
( 5 ' 8 g . , 5 7 % ) . m.p. 202-204° [ F o u n d :
C H A s B r e q u i r e s 0, 7 3 l ; H, 5 * 1 % .
e
2 4
2 0
0*0944g. were b o i l e d (10 m i n s ) w i t h aqueous
hydrogen p e r o x i d e .
alcoholic
P h e n o l s e p a r a t e d by steam
distillation
was c o n v e r t e d t o t r i b r o m p h e n o l , 0*2966g.; C ^ H ^ A s B r e q u i r e s
0*3190g.
The aqueous r e s i d u e was b o i l e d f o r a few m i n u t e s
w i t h a t r a c e o f p l a t i n u m b l a c k t o remove excess p e r o x i d e ,
filtered,
and b o r i c and a r s e n i c a c i d s e s t i m a t e d v o l u m e t r i c a l l i y
[(Found: B, 3*61; As, 18*6.
C H
24
2()
A s B r e q u i r e s B, 3*68;
As 1 9 * 0 % ) ] .
The same compound ( i d e n t i c a l by mixed m.p. and by
100.
i n f r a r e d s p e c t r u m ) was o b t a i n e d
t r i e t h y l a m i n e method.
i n 67% y i e l d by t h e
A s m a l l amount o f r e d i n s o l u b l e
m a t e r i a l c o n t a i n i n g boron, a r s e n i c and p h e n y l groups was
also i s o l a t e d but not i d e n t i f i e d .
G H
C
H
D i p h e n y l a r s i n o ( d i - p - t o l y l ) b o r a n e , [ ( p . ~ 3 g 4 . ) 2 B'AsPhg)]
(7'3g.
f
69%), m.p. 2 2 4 - 2 2 5 ° ( f r o m benzene-hexane) [ F o u n d :
C, 7 3 ' 6 ; H, 5*6.
CggH^AsB r e q u i r e s C, 74-0; H, 5'7%) and
d i p h e n y l a r s i n o ( d i - p - b r o m p h e n y l ) b o r a n e , [(p-BrCgH^) B»AsPh )]
2
#
(7 5g.,
2
67%), m.p. 2 4 4 - 2 4 5 ° ( f r o m benzene-hexane) [ F o u n d :
C, 5 2 « 3 ; H, 3 ' 4 .
C H As B Br
2 4
l 8
2
r e q u i r e s C, 52-2; H, 3'3%)
were b o t h p r e p a r e d f r o m t h e sodium d e r i v a t i v e o f d i p h e n y l a r s i n e and t h e a p p r o p r i a t e
chlorodiarylboranes.
101.
Boron A n a l y s i s
Boron was
d e t e r m i n e d by t h e method d e s c r i b e d by
274.
D. E. Powler and C. A. Kraus.
A q u a n t i t y o f sample ( c o n t a i n i n g 0»02-0«03g., o f
b o r o n ) was
sulphuric
c o m p l e t e l y degraded by warming w i t h c o n c e n t r a t e d
a c i d ( 5 c.c.,) i n a two-necked f l a s k .
After
c o o l i n g , d r y ( d i s t i l l a t i o n f r o m magnesium) methanol (40
was
s l o w l y added f r o m a d r o p p i n g f u n n e l .
m i x t u r e was
was
The
c.c.
reaction
r e f l u x e d (15 m i n s ) and t h e n t h e m e t h y l b o r a t e
distilled
t h r o u g h a s h o r t column and t h e f i r s t t h r e e
10 c.c., f r a c t i o n s were c o l l e c t e d and mixed w i t h an
volume o f w a t e r .
The b o r i c a c i d was
titrated
with
r
sodium h y d r o x i d e m
t h e presence o f m a n n i t o l .
equal
N
-j-^
N
[ 1 c.c.
^
NaOH s 0-0011g B ] .
Phosphorus A n a l y s i s
A weighed amount o f sample ( c o n t a i n i n g ca., 0'02g.,
o f phosphorus) was
heated a t 500° (3-4 h o u r s ) w i t h excess
sodium p e r o x i d e i n a bomb.
was
A f t e r cooling the s o l i d residue
e x t r a c t e d w i t h b o i l i n g w a t e r and f i l t e r e d
from
carbon.
Ammonium n i t r a t e ( 1 0 g . , ) and c o n c e n t r a t e d n i t r i c a c i d (5 c.c
were added t o t h e s o l u t i o n w h i c h was warmed t o 35°
t h e ammonium molybdate r e a g e n t
Phosphorus was
(50 c.c.,) was
t h e n d e t e r m i n e d by t h e t i t r i m e r i c
7
d e s c r i b e d by V o g e l . ^ ^
before
added.
procedure
102.
DIPOLE MOMENT MEASUREMENTS
1.
Theory o f D i p o l e Moment Measurements
266
I t was p o i n t e d out by Faraday
t h a t the
molecules
o f a d i e l e c t r i c when p l a c e d i n an e l e c t r i c f i e l d become
' p o l a r i s e d ' i . e . a s e p a r a t i o n o f charge t a k e s p l a c e .
end o f t h e m o l e c u l e
One
a c q u i r e s a s m a l l p o s i t i v e charge, t h e
o t h e r a n e g a t i v e charge o f e q u a l magnitude.
Mathematical
treatment o f t h i s statement
d e r i v a t i o n o f t h e C l a u s i u s and M o s o t t i law
ii±
i =
£ - 2
d
l e d t o the
'
p
(i)
where p i s t h e s p e c i f i c p o l a r i s a t i o n , d i s t h e d e n s i t y
and d t h e d i e l e c t r i c c o n s t a n t o f t h e
substance.
For a number o f m a t e r i a l s o f low d i e l e c t r i c
p remains c o n s t a n t d e s p i t e changes i n t e m p e r a t u r e
constant
and p r e s -
s u r e , and i s a l m o s t t h e same f o r t h e l i q u i d o r s o l i d
states.
269
I t was shown by M a x w e l l
t h a t f o r such m a t e r i a l s
the d i e l e c t r i c constant i s r e l a t e d t o the r e f r a c t i v e index
n f o r t h e same f r e q u e n c y o f r a d i a t i o n by
»
2
-eer
(2)
10'3.
where # i s t h e magnetic
permeability of the material.
As 0 i s almost e q u a l t o u n i t y f o r a l l except f e r r o magnetic
substances
then i f t h e values of the r e f r a c t i v e
i n d e x o b t a i n e d i n t h e v i s i b l e r e g i o n o f t h e spectrum a r e
e x t r a p o l a t e d t o t h e wavelength a t which t h e d i e l e c t r i c
c o n s t a n t i s measured ( v i r t u a l l y i n f i n i t e w a v e l e n g t h )
£=
n
2
then
(3)
For substances
o f h i g h d i e l e c t r i c c o n s t a n t £ i s almost
2
i n v a r i a b l y greater than n
270
?71
n - 1
I t was shown by L o r e n z "
and L o r e n t z
that ^
ri
- 2
2
1
= r where r i s a c o n s t a n t , independent
as t h e s p e c i f i c r e f r a c t i o n .
1
—
d
o f t e m p e r a t u r e , known
The p r o d u c t o f t h e m o l e c u l a r
w e i g h t M and t h e s p e c i f i c r e f r a c t i o n i s known as t h e m o l e c u l a r
refraction
R.
R
-
n
n
2
2
- 1
- 2
M
d
(4)
Molecular r e f r a c t i o n s are a d d i t i v e , w i t h i n c e r t a i n
limits,
and by a l l o c a t i o n o f c e r t a i n v a l u e s t o c e r t a i n atoms and
bonds, m o l e c u l a r r e f r a c t i o n s may be c o m p i l e d .
Molecular
p o l a r i s a t i o n P o b t a i n e d by m u l t i p l y i n g t h e s p e c i f i c
polar-
i s a t i o n by t h e m o l e c u l a r w e i g h t would a l s o be expected t o
mi.
be a d d i t i v e .
for
I t i s f o u n d however t h a t P i s o n l y
additive
2
compounds o f low d i e l e c t r i c c o n s t a n t where £
=
n .
272 27 3
Debye
'
indicated
e x p l a i n e d by assuming
t h a t t h i s b e h a v i o u r c o u l d be
t h a t a l t h o u g h a m o l e c u l e as a whole
i s n e u t r a l t h e c e n t r e s o f p o s i t i v e and n e g a t i v e charge
do
n o t u s u a l l y c o i n c i d e and t h e m o l e c u l e has a permanent
d o u b l e t o r d i p o l e w h i c h tends t o o r i e n t a t e
electric field
frequency).
itself
i n an
o f r e l a t i v e l y low i n t e n s i t y , ( i . e . r a d i o
Thus t h e m o l e c u l e shows p o l a r i s a t i o n by
orient
a t i o n b e s i d e s charge d i s p l a c e m e n t .
I n d e e d i t would be f o r t u i t o u s i f any m o l e c u l e o t h e r
t h a n a s y m m e t r i c a l one d i d n o t have some n e t permanent d.ip o l e due t o t h e v a r i a t i o n i n e l e c t r o n e g a t i v i t y o f t h e atoms
of the molecule.
The magnitude
o f t h e e l e c t r o n i c charge 4*8 x 10~^e.s.u
—8
and d i s t a n c e s between s m a l l atoms 1 t o 2 x 10"
cms.
I tis
found t h a t d i p o l e moments o f most m o l e c u l e s l i e between 0
and 9 x 1 0 "
1 8
e.s.u. o r 0-9
Debye.
1 8
( 1 Debye = 1 x 1 0 ~ e . s
A f u r t h e r c o n t r i b u t i o n t o t h e t o t a l p o l a r i s a t i o n o f a molec u l e i s t h a t due t o t h e r e l a t i v e d i s p l a c e m e n t o f t h e atoms
o f t h e m o l e c u l e i n an e l e c t r i c
field.
I f a m o l e c u l e c o n t a i n s p o l a r bonds so t h a t t h e atoms
105
c a r r y d i f f e r e n t e f f e c t i v e charges t h e n t h e n u c l e i a r e
displaced
w i t h r e s p e c t t o one a n o t h e r and t h i s produces
an i n d u c e d d i p o l e t h e e f f e c t o f w h i c h i s superimposed on
t h e permanent d i p o l e i f p r e s e n t and t h e d i p o l e due t o t h e
displacement of t h e electrons
w i t h respect t o the nucleus.
T h i s t y p e o f p o l a r i s a t i o n i s known as atom p o l a r i s a t i o n
and
t o g e t h e r w i t h o r i e n t a t i o n p o l a r i s a t i o n (due t o o r i e n t i n g
o f permanent d i p o l e s )
and e l e c t r o n p o l a r i s a t i o n ( t h a t due
t o displacement o f e l e c t r o n s )
goes t o make up t h e t o t a l
polarisation.
Thus
T o t a l P o l a r i s a t i o n (TP) = Atom P o l a r i s a t i o n (AP) +
O r i e n t a t i o n P o l a r i s a t i o n (OP)
•f E l e c t r o n
Polarisation
(EP)
(5)
For m o l e c u l e s w i t h no permanent d i p o l e and no atom
p o l a r i s a t i o n t h e t o t a l p o l a r i s a t i o n i s t h e same as t h e
e l e c t r o n p o l a r i s a t i o n o r TP = EP, and i s i d e n t i c a l w i t h R
i f t h e v a l u e o f n i s .obtained by e x t r a p o l a t i o n t o i n f i n i t e
wavelength.
As t h e v a l u e s o f R o b t a i n e d f o r i n f i n i t e wave-
l e n g t h u s u a l l y o n l y d i f f e r by 1 o r 2 c.c. f r o m t h o s e o b t a i n e d
a t v i s i b l e f r e q u e n c i e s , o f t e n no c o r r e c t i o n f o r t h e d i f f e r e n c e
i s made i n d i p o l e moment c a l c u l a t i o n s .
106.
The
molecule
C l a u s i u s and M o s o t t i t h e o r y c o n s i d e r s each
as a sphere o f d i e l e c t r i c and assumes t h a t f o r
small displacements
the
i n d u c e d moment m i s p r o p o r t i o n a l
i.e.
y i s
o f e l e c t r o n s w i t h respect t o the nucleus
m =
t o t h e f i e l d F.
(6)
YF
c a l l e d t h e p o l a r i s a b i l i t y o f t h e molecule
t o t h e moment i n d u c e d by a f i e l d
The
of u n i t
and i s e q u a l
strength.
t r e a t m e n t g i v e s an e q u a t i o n f o r t h e m o l e c u l a r
p o l a r i s a t i o n known as d i s t o r t i o n p o l a r i s a t i o n , P =
^
TINY
where N i s Avogadro's number.
The
Debye t r e a t m e n t w h i c h i s concerned w i t h a molecule
w i t h a permanent d i p o l e 2i i n c l i n e d a t an a n g l e t o an e l e c t r i c
f i e l d F g i v e s an e x p r e s s i o n f o r th« m o l e c u l a r
orientation
polarisation
OP = 3
%
N
N,
(7)
3kT
where k i s Boltzraann's c o n s t a n t and T i s t h e a b s o l u t e
temperature.
Thus t h e t o t a l p o l a r i s a t i o n i s g i v e n by
TP = i
3
n
N
( v
)
+
3kT
(8)
^ it Ny r e p r e s e n t s t h e p o l a r i s a t i o n a m o l e c u l e would
have i n t h e absence o f a permanent d i p o l e
be d i v i d e d
isation.
; i
and t h i s
up i n t o atom p o l a r i s a t i o n and e l e c t r o n
may
polar-
Prom e q u a t i o n ( 7 ) :
=/9kT
As a l l d i p o l e
O.P.
=
0-012812
/oP.T
moment measurements were c a r r i e d o u t a t
25°» t h i s can be f u r t h e r reduced t o
p. = 0-2212
J OP.
(9)
108.
II
EVALUATION OP RESULTS
The e x p r e s s i o n f o r t h e p o l a r i s a t i o n o f a s o l u t i o n ,
due t o D e b y e
2 7 7 , 2 7 8
is:-
P = P.f. + P f
9
1
1
2
0
2
where P-p P , f-p f »
2
M
£ - 1
= £
i
£ - 2
a
r
e
2
l
f
l
+
M
f
2 2
^
"the t o t a l p o l a r i s a t i o n s
Ha.lverstadt and Kumler
of densities
fractions.
U
;
d
mole f r a c t i o n s o f s o l v e n t and s o l u t e
279
instead
(1)
and
respectively.
^ used s p e c i f i c volumes
and w e i g h t f r a c t i o n s i n s t e a d
o f mole
By assuming t h a t t h e s p e c i f i c volume and d i -
e l e c t r i c c o n s t a n t o f t h e s o l u t i o n are l i n e a r f u n c t i o n s
the weight f r a c t i o n ( i * e * £
=
a + aw
2
and
of
v = b + |3w where
2
a and b a r e t h e d i e l e c t r i c c o n s t a n t and s p e c i f i c volume
of t h e s o l v e n t ,
w
2
i s the weight f r a c t i o n of the s o l u t e ) ,
t h e y d e r i v e d an e x p r e s s i o n f o r t h e t o t a l s p B c i f i c
polar-
i s a t i o n a t i n f i n i t e d i l u t i o n o f t h e s o l u t e p_2.
3CLV-.
P
?
42
=
^—p
(^+2)^
+
£,
-
t
+ 2
—
±
1
(v
By p l o t t i n g £ a g a i n s t w
x
+ p)
(2)
X
2
and v a g a i n s t w , a and P
2
may be e v a l u a t e d .
I n a s i m i l a r manner t h e e l e c t r o n
polarisation
Ep
2
109.
c a n be e x p r e s s e d
as
2
n.1 - 1
bvn., v
+
Ep
(n*
+
2)
(v
x
+ p)
(3)
2
2
Ti
+ 2
where t h e a s s u m p t i o n i s made t h a t n = n-^ + yw^ where n ^
i s the r e f r a c t i v e
i n d e x of t h e s o l v e n t .
To o b t a i n d i p o l e moments by measurements on s o l u t i o n s
the d i e l e c t r i c
constant,
refractive
i n d e x and d e n s i t y o f
a number o f s o l u t i o n s must be d e t e r m i n e d .
£, v , and n a g a i n s t W2» o b t a i n i n g
g r a p h s , and f i t t i n g
By p l o t t i n g
a,fi, and y f r o m t h e
them i n t h e e q i i a t i o n s t h e n t h e t o t a l
p o l a r i s a t i o n and e l e c t r o n p o l a r i s a t i o n o f t h e compound
b e i n g s t u d i e d may be
obtained*
At low c o n c e n t r a t i o n s
(w <£. 0*02) t h e p l o t s a r e u s u a l l y
PRO
close to l i n e a r
be o b t a i n e d
and l i n e a r p l o t s o f n a g a i n s t w^ may
at s t i l l
higher
concentrations.
110.
III.
1.
PHYSICAL MEASUREMENTS
D i e l e c t r i c Constant
Measurements
Benzene was used as s o l v e n t
d i e l e c t r i c constants o f a i r
i n a l l cases and t h e
and benzene (fi-g) were
assumed t o be 1*0006 and 2«2727 r e s p e c t i v e l y .
The
p r i n c i p l e used was t h e measurement o f t h e change
i n c a p a c i t a n c e w h i c h o c c u r r e d when t h e d i e l e c t r i c
of a
condenser was charged.
2ft"L
The
condenser was a c e l l .
the d i e l e c t r i c o f which
c o u l d be changed e a s i l y by b l o w i n g o u t w i t h n i t r o g e n and
replacing with the required
liquids.
I f £ ^ i s t h e d i e l e c t r i c c o n s t a n t o f t h e s o l u t i o n and
C-^, Cg. and C-^ are t h e c a p a c i t a n c e s o f t h e c e l l f i l l e d
with
a i r , benzene and s o l u t i o n r e s p e c t i v e l y , t h e n p r o v i d e d t h e
lead capacitances remain
t3
3
constant
1
)
(
(1)
111.
C
- C-L
2
=
69*05
calibrated
pfs, was measured by connecting an
N.P.L.
condenser i n p a r a l l e l with the c e l l and f i n d i n g
the necessary change i n capacitance to restore balance
when the d i e l e c t r i c was changed from a i r t o benzene.
C
=
2
-
C was the change i n capacitance measured on M, and
since 1 i s the reading on the condenser i n cms, and the
capacitance change per cm was 3*38 pfs, then from equation
(1)
3-38 1
+ 1
1*2721
+1-0006
69*05
3-38&1
X
1-2721
69-05
a =
de
dw
=
3-38 x 1-2721 d l
69*05
dw
0-6227 Q
dw
J3 - I
—
i s the slope of the graph obtained by p l o t t i n g the
dw
reading on the calibrated
condenser against weight f r a c t i o n .
A heterodyne beat capacitance meter similar to that
pop
designed by Sutton and H i l l
was used t o measure the
capacitance change i n the c e l l .
units.
This consisted of two
The lower one was p r i n c i p a l l y a beat frequency
generator made up of two similar radio frequency o s c i l l a t o r s
112.
5
one of fixed frequency f (approximately 10 c.p.s.) and
Q
one of variable frequency f ^ incorporating the measuring
system.
Also i n the lower u n i t were the requisite c i r c u i t s
f o r mixing, demodulating, and beat frequency a m p l i f i c a t i o n .
The two o s c i l l a t o r s were made as nearly i d e n t i c a l as possible
so that any disturbances, e.g. fluctuations i n temperature
or supply voltage, affected both equally.
The upper u n i t contained a power pack, an audio f r e quency o s c i l l a t o r , and a cathode ray tube.
l a t o r w i t h frequency f
2
The audio o s c i l -
of about 1,000 c.p.s. could be
varied by a coarse and a f i n e control t o allow accurate
adjustment.
The X plates of the cathode ray tube carried
the output from the beat frequency o s c i l l a t o r and the Y
plates that of the audio frequency o s c i l l a t o r .
Several
adjustments were necessary t o increase the s t a b i l i t y of the
system.
The c e l l was a modified form of the Sayce B r i s c o e * ^
type with plates of platinum burnt onto the glass instead
of deposited s i l v e r .
This made the c e l l much more robust
and allowed washing out w i t h strong acid i f necessary.
capacitance was approximately 50 p.f.s.
The
The 25°C thermostat
i n which the c e l l was immersed was f i l l e d with transformer
o i l t o reduce stray capacitances.
113
Procedure
The cathode ray tube was used to obtain the nee essary
relationship between the output frequency of the beat
frequency generator and that of the audio frequency o s c i l lator.
As i t was possible to obtain two i d e n t i c a l beat
frequencies, one with f >
and one w i t h f^> f
Q
taken always to work with f > f ^ .
Q
care was
By varying P the output
from the beat frequency generator was tuned to give a figure
eight on the cathode ray tube corresponding to f
Q
- f ^ = 2fg
t h i s r a t i o prevented any l i k e l i h o o d of the o s c i l l a t o r s
p u l l i n g and was used as a balance point i n a l l measurements.
The c e l l was washed out twice and then f i l l e d with dry
benzene, the benaene used i n washing out being expelled by
a stream of nitrogen.
The c e l l and contents were allowed
to come to thermal equilibrium (10 mins) and F (see f i g 1)
was adjusted u n t i l the figure eight appeared on the cathode
ray tube.
D and M were then switched i n and by adjustment
the f i g u r e eight was again obtained. These last two operations
were repeated since s l i g h t variance i n the capacitance i n
the c i r c u i t containing P and the c e l l appeared to cause
changes i n the frequency of the c i r c u i t containing F, D and
M, and vice-versa. When a steady figure eight was obtained
on both sides of the switch the reading on M was noted.
FIG.
X
114.
The benzene was then blown out with dry nitrogen and
the c e l l washed out and f i l l e d with the solution under
test.
The process of adjustment was repeated but t h i s time
only F and M were adjusted so that the change i n capacitance
could be read o f f on M.
The zero reading ( i . e . the reading w i t h the c e l l , f i l l e d
with benzene) was checked a f t e r each solution, as i t occasi o n a l l y showed a tendency t o d r i f t during a set of measurements.
(2) Specific Volume Measurements
A Sprengel type pyknometer of approx., 4 c.c. capacity
f i t t e d with ground glass caps to prevent evaporation was
^lsed.
I t was calibrated by P. S, Dixon.
were made at
A l l measurements
25°0.
Volume of pyknometer =
4*1521 c.c.
Specific volume
4*1521 =
Wg
=
v
where Wg i s the weight of s o l u t i o n i n the pyknometer
(3W
v
d
2
4 -1521
Wg
dw 2
4-1521
Wg
(2)
115
Thus
i s the slope of the graph of specific volume against
weight f r a c t i o n .
Procedure
The dry pyknometer was f i l l e d and placed i n a 25°C
thermostat ( f o r 15 mins).
The meniscus of the l i q u i d was
adjusted t o the graduation mark by applying a piece of
f i l t e r paper t o the t i p of the opposite limb and the pyknometer was removed from the thermostat, dried and the caps
put i n place.
I t was hung on the balance (20 mins) t o
allow t o come t o hygrometric equilibrium w i t h the atmosphere
and then weighed'.
(3)
Refractive Index Measurements
A P u l f r i c h refractoiaeter w i t h a divided c e l l was used,
and i t was enclosed i n a 25°C a i r thermostat, which consisted
!
1
of a large box (2'x 2 x 2 ) f i t t e d w i t h a glove and a
terylene window through which one could take readings and
see t o make adjustments without opening the box.
The box was heated by an e l e c t r i c a l sheet heater placed
d i r e c t l y i n f r o n t of a fan.
The temperature was controlled
by an a/c bridge thermoregulator w i t h a platinum resistance
thermometer as the arm of the bridge inside the box, thus
giving a quick response t o temperature f l u c t u a t i o n s .
A 500 watt projector lamp especially set up w i t h a
116.
convex lens system to give a strong p a r a l l e l beam together
with six interference f i l t e r s (Jenear Glasswork Schott and
Gen.) was used as a l i g h t source.
The f i l t e r s were checked
by determining the r e f r a c t i v i t i e s of benzene with the redi
and blue lines of the hydrogen lamp and the sodium D l i n e s .
The red f i l t e r ( A. max = 6620°A) was normally used f o r the
measurements.
For the centrosymmetric compound (PhgBNHg^
r e f r a c t i v e indices were measured at several wavelengths to
allow an estimation of the electron polarisation at i n f i n i t e
wavelength to be made.
Procedure
The solution was placed i n one side of the divided c e l l
and a sample of pure dry benzene i n the other. A polythene
cap was placed on the c e l l t o prevent evaporation, and the
l i q u i d s allowed to come to thermal equilibrium (20 mins).
The e x t i n c t i o n angles were read o f f from the refractometer
and the difference obtained.
As differences rather than
absolute r e f r a c t i v i t i e s were of primary importance, t h i s
technique minimised any errors which might be caused by
temperature f l u c t u a t i o n s .
The relationship between the
e x t i n c t i o n angle and the r e f r a c t i v e index of the solution
was given by
r
n = Sin A /N - Sin"B
Sin B + Cos A Sin B
117.
where A wag the r e f r a c t i v e angle of the prism
B the angle of emergence and
N the r e f r a c t i v e index of the prism.
The graph of extinction angle against r e f r a c t i v e
index showed a l i n e a r relationship making computation
of
n values r e l a t i v e l y simple.
I t was found t h a t : -
1 min., of arc = 1087 x 10"
A plot ofA n against w gave ^
7
from 7090 to 5893
which corresponds to y i n
equation 11(3).
(4)
Total
Polarisation
=
Prom equation 11(2) i . e . Pg
3aV-,
£-,-1
-—+ — = — (v-^+B)
(c 2)
2
1 +
v
x
= 1*1447
£
x
= 2-2727
Then P - 0-1881 a + 0-2979 (1-1447+B)
(3)
?
(5)
Electron Polarisation
p
Prom equation 11(3) i . e . Ep =
2
+ —=
(v-^+B)
(n-^+2)
(n +2)
2
2
x
v-j^ = 1-1447
n-|_ = 1-4979 ( f o r sodium D l i n e )
Then:
Ep = 0-5712 + 0-2932 (1-1447 + P)
2
Y
[ f o r = 5985°A] (4)
118.
For
A = 7 0 9 0 , E.p. = 6-5744Y + 0 - 2 8 9 4 ( 1 - 1 4 4 7 + P )
2
K = 6 6 2 0 , E.p.
= 0-5734Y
+ 0-2906 ( 1 - 1 4 4 7 + P )
A = 5910, E . p .
= 0-5712Y
+ 0-2931 (1-1447 + P )
2
2
A. = 5 4 4 0 , E.p.
+ 0-2952 ( 1 - 1 4 4 7 + P )
= 0-5694Y
2
* = 4 7 8 0 , E.p.
= 0-5656Y
+ 0-2997 ( 1 - 1 4 4 7 + P )
*• = 4 3 4 0 , E.p.
= 0-5618Y
+ 0-3041 (1-1447 + P )
2
2
Values of E.p. at i n f i n i t e wavelength were obtained by
2
assuming that the values obtained f o r various values o f ^ f i t t e d
a simple equation of the form
E.p. = A +
r,
?
K
The E.p» values were plotted against
2
was extrapolated t o ^
and the curve obtained
= 0. This gave a value f o r A which was
taken as E.p» at i n f i n i t e wavelength.
2
EXPERIMENTAL
Dipole Moment Measurement f o r Ph BNPh
5
0
A Typical Series of Results
weight of f l a s k
45*4805 48-7943 34*1301
22-7729
weight of f l a s k + compd
45-5597 48-9070 34-3009
23-0099
Weight of f l a s k + compd + benzene
63-4216 71-1250 57-5594
43-0825
weight of compd
weight of compd + benzene
weight f r a c t i o n
0-0792
0-1077
0-1708
0-2370
17-8619 22-2180 23-2585
20-0726
0-04434 0-04847 0-07343 0-1178
119.
Density
weight of pyknometer + solution 23*2983 23*2992 23-3008 23*3068
weight of pyknometer
19*6648 19*6648 19*6648 19*6648
3*6335
3*6344
3*6360 3*6420
1*1427 1*1425
1*1420 1*1401
zero cms
2*459
2*459
2*459
2*459
solution reading
2*406
2*387
2*366
2*083
Ac. (cms)
0*053
0*072
0-093
0*476
weight of solution
4 < 1 5 2 1
Specific volume (
)
(wt of soln)
Dielectric
Refractivity
K 6620
12*20
change i n angle
An x 1 0
6
13*00
2•00
2 * 30
14*20
4•00
=
fw
Y=^
7•20
0*2166 0-2924 0*4332 0*7798
a = 0*06227 x |£ (from Graph 1) = 0*06227 x 10*7
p
17*50
=
" °'3100 (from Graph 2)
=0*0816 (from Graph 3)
Tp = 332-8 [ 0 * l 8 8 l a + 0*2979(1*1447 + P ) ]
2
= 332*8 [0*1251 + 0*2979(0*6827)]
= 108*3 c.c.
120
Ep = 332*8 (0-5734 x 0*0816 + -2906 x -6827)
2
= 84*9 c.c.
Ap = 8-49 c.c.
0p = 108*3 - 93*4 = 14*9 c.c.
2
2
u = 0*2212 y i 4 * 9
(2,4,6,CH C H ) BNH
3
6
2
2
= 0-9 D
2
g
AC (cms)
weight fractions
specific v o l .
an x 10
0*218
0-06764
1-1421
0*3790
0*11771
1*1417
0*6678
0*16980
1*1401
0*8664
0*27334
1*1395
0*9747
0-342
0-383
0*421
a = 0-9771,
Tp = 119-1 c.c.
2
0 = - 0-1264,
Y = 0*0799
Ep = 90-5 c.c.
2
Ap = 9*1 c.c.
2
Ph BNMe
2
2
0-06962
1*1479
0*1408
0-101
0-08814
1*1468
0*1507
0*119
0-17861
1*1461
0-6678
0*190
0-27374
1-1457
1-7508
0*260
Y= 0*07810
p= - 0-1225,
a = 4-331,
Tp = 233*9 c.c. Ep = 155-7 c.c. Ap = 15*6 c.c.
2
2
?
121.
(p-BrCgH ) BNMe
4
2
2
0*05181
1*1419
0-4512
0-452
0*07484
1*1410
0-6859
0-495
0-09573
1-1402
0-8844
0*985
0*10731
1*1393
0*9025
1*153
a = 6-119
Tp = 548*3 c.c.
?
(p-CH C H ) BNMe
3
6
4
2
p= - 0-3 3
Y= 0-08031
Ep = 323*3 c.c.
Ap = 32*3 c.c.
2
2
2
0-05211
1-1476
0-1444
0-083
0-08586
1-1464
0«3791
0-124
0-14311
1-1454
0-5957
0-192
0-23910
1-1442
0-7942
0-282
a = 0*9762
|3 = - 0-2901
Tp = 103-9 c.c. Ep = 71-9 c.c.
2
2
Ph BN(C H p-CH )
2
6
4
3
v= 0*0785
Ap =7-2 c.c.
2
2
0-03171
1-1431
0-2166
0-033
0-07026
1-1426
0-6661
0-071
0-09552
1-1417
1-0462
0-106
0-13774
1-1411
1-3711
0-140
a = 0-9504
Tp = 234*4 c.c.
5
p= - 0-5170
Y= 0-04740
Ep = 165*8 c.c.
Ap =16-6 c.c.
5
9
122.
Ph BNH
2
2
0-05010
1-1433
0-3533
0-0310
0-07575
1-1417
0-5448
0-0417
0-11487
1-1405
0-8664
0-0594
0-13667
1-1401
1-1047
0-0602
p = - 0- 2298
a = 2-047
Y = 0-0552 (a
4340
_1_
*2
5308
0-0596
108 • 3
4780
4376
0-0588
106-7
5440
3380
0-0574
105 -3
5910
2863
0-0594
104-6
6620
2282
0-0557
103-9
7090
1989
0*0527
103*1
k
Ep (c.
Y
2
Absolute Ep (when ~- = Q \= oO) = 100-3 c . C .
0
y
A
c.
2
,°. Absolute Ap = 0 p - Ep = 119 *9 c.c. - 100-3 c.c.
2
Ph BPEt
2
2
2
2
specific v o l
An x 10
0-05254
0-07158
1-1427
0-030
1-1424
0-9379
1-1187
0-11536
1-1422
1-2744
0-107
0-18076
1-1418
1-4536
0-131
weight f r a c t i o n
6
AC( cms)
0-084
a = 0-4905,
3 = - 0-3109
Tp = 92*8 c.c.
Ep = 68*0 c.c.
2
(p-BrC H ) B PEt
6
4
2
2
Y= 0.0402
Ap = 6-8 c.c
?
2
0-03178
1*1433
0-2171
0-041
0»07139
1-1429
0-6709
0-081
0-09566
1-1420
1-0512
0-126
0-14704
1-1416
1*3822
0-158
a = 0-7447,
0 = - 0-2911
Tp = 162-5 c.c.
2
Ph B P(C H m-CH )
2
6
4
3
Ep = 132-4 c.c.
2
y = 0-0895
Ap = 13*2 c.c
2
2
0*03689
1*1424
0*2888
0*277
0-06143
1-1420
0-5415
0-307
0-06930
1-1411
0-7761
0-424
0-11759
1*1399
1*3176
0-528
a = 2*7103,
p = - 0*3244,
TP = 472*6 c.c.
2
Ep = 321*7 c.c.
2
(p_-CH C H ) B P(C H m-CH )
3
6
4
2
6
4
3
7= 0*06221
Ap = 32*2 c.
?
2
0*03386
1-1458
0*4657
0-460
0*06214
1-1425
0-5632
0-558
0« 07148
1- 1407
0*6981
0*609
0*09936
1*1398
0*8113
0-872
a = 29*42
p
Tp = 313*8 c.c.
Ep
2
(p-BrC H ) ,B P(C H m-CH )
2
2
6
4
2
6
4
3
- 0*4080
125*6 c.c.
Y= 0*1663
Ap =12*6 c
2
0*08095
1*1427
0*2274
0*106
0*09894
1*1401
0-5848
0*111
0 *11742
1*1396
0*6422
0*147
0*13411
1*1382
0-79H
0-199
a = 4*531,
Tp = 174*1 c.c.
9
0
Ep
2
- 0-3721
144-9 c.c.
Y= 0*0665
Ap = 14-5 c
2
Ph B*AsPh,
0
0*02687
1*1432
0*1354
0*091
0*04-685
1 -1425
0*4115
0-111
0*05724
1-1420
0*5307
0-119
0*09996
1-1401
0*8881
0*174
a = 0*9431
p= - 0-3076
Tp = 168*2,
Ep = 117*2 c.c.
2
2
y= 0-0503
Ap = 11*7 c.
2
(p-0H^C H ) B AsPhg
6
4
2
0*05855
1-1424
0*2383
0-280
0*08084
1*1401
0-4440
0-405
0*12035
1-1396
0-6498
0-508
0-14371
1*1378
0*6972
0*638
a = 2»097
p = - 0-4201
Tp = 257*5 c.c.
2
(p-BrCgH^) BAsPh
2
Ep = 129*7 c.c.
2
=
Y
0-0865
Ap = 13*0 c.
2
2
0*03195
1*1448
0*0433
0*084
0*05145
1*1424
0*1625
0*097
0*07429
1*1409
0*2709
0*124
0*11322
1*1391
0*3046
0*137
a = 4*327
Tp = 173*1 c.c.
2
p = - 0-3649
Ep = 148*7 c.c.
5
Y = 0*04907
Ap = 14*9 c.
P
DISCUSSION
126.
Compounds i n which an atom o f acceptor character
i s c o v a l e n t l y bound t o one o f donor character can achieve
c o - o r d i n a t i o n s a t u r a t i o n e i t h e r by the f o r m a t i o n o f a
double bond or by a s s o c i a t i o n .
The f i r s t s i t u a t i o n i s
e x e m p l i f i e d by dimethylamino ( d i m e t h y l ) borane, Me B - NMe ,
2
?
since the f o r c e constant o f the B-N bond i s appropriate f o r
285
a double bond.
S i m i l a r l y the f o r c e constant of the B-N
bonds i n trisdimethylaminoborane,
(Me N) B ±
2
3
3
5.5 IQ->
X
dyne cm""'*' which i s appropriate f o r bonds o f order
Valency expansion by the f o r m a t i o n o f a f o u r t h sigraa b o n d ^ ^
occurs i n the dimeric forms o f the c h l o r i d e s , e.g. (MeNBClp) ,
2
a.nd i n the much s t u d i e d phosphinoboranes i n which c y c l i c
t r i m f i r s (Me PBMe )^
2
are found.
2
tetramers (MegPBH^ and polymers
No monomeric phosphino- or arsinoboranes app.ear
t o have been described, w i t h the possible exception o f
289
2Q0
PH *BMe and Pl^P-BH-j.
y j
2
2
The absence o f any general r u l e which might be used
t o p r e d i c t whether a compound o f t h i s type would be monomeric
( and presumably c o n t a i n a p a r t i a l double bond ) or associated
suggested the need t o o b t a i n f u r t h e r data concerning ( a )
circumstances i n which aminoboranes are associated and ( b )
the p o s s i b l e existence of monomeric phosphino- and a r s i n o boranes.
127
Aminoboranes - Unsubstituted aminoborane 291 appears t o
be polymeric, ( H B « N H ) , and unstable.
2
2
The extent o f
n
a s s o c i a t i o n decreases as hydrogen i s s u b s t i t u t e d by a l k y l
groups: thus N-methylaminoborane i s t r i r a e r i c (HgB'NHMe)^
92
and r e v e r s i b l e monomer-dimer e q u i l i b r i a may be r e a l i s e d w i t h
H B-NMe ?
2
2
93
MeHB»NMe ?
2
94
Me B«NHMe
295
2
96
and Me B-NH ? A l l
2
2
9
known t e t r a s u b s t i t u t e d aminoboranes appear t o be monomeric? ^
R e l a t i v e l y few B-arylaminoboranes have been s t u d i e d ,
but
raethylaminodiphenylborane,
Ph B«NHMe, slowly changes
pqft
2
from monomer t o dimer a t room temperature; ^
a l l others
described are monomeric.
Aminodiphenylborane was prepared from ammonia and
chlorodiphenylborane i n the presence of t r i e t h y l a m i n e ,
Ph BCl + NH^ + NEt^ = £ (Ph B-NH ) + E t ^ H C l
2
2
2
2
and i s dimeric ( c r y o s c o p i c a l l y i n benzene and n i t r o b e n z e n e ) .
The most l i k e l y s t r u c t u r e ( I ) i s eentrosymmetric, and t h e
observed e l e c t r i c p o l a r i s a t i o n i s i n agreement w i t h t h i s .
The t o t a l p o l a r i s a t i o n , measured i n benzene s o l u t i o n a t 25?
was 119*9 c.c.
The e l e c t r o n p o l a r i s a t i o n , measured a t s i x
wavelengths and e x t r a p o l a t e d
t o i n f i n i t e wavelength, was
100*3 c.c. and t h e d i f f e r e n c e , 19-6 c.c., i s about the
expected value o f the atom p o l a r i s a t i o n i n c o - o r d i n a t i o n
128
compounds c o n t a i n i n g balanced d i p o l e s (e.g. the atom
p o l a r i s a t i o n s o f t r a n s (R^P) PdAr
2
2
complexes are u s u a l l y
2
about 20 c . c . ) . ^ The d i p o l e moment of ( I ) i s t h e r e f o r e
zero.
NH
Ph„ B
BPh
NH
2
(I)
Thus the only dimeric aminodiarylboranes are those
c o n t a i n i n g NH or NHCH^ groups.
2
Experiments w i t h molecular
models i n d i c a t e t h a t any l a r g e r groups attached t o the
n i t r o g e n would cause s u b s t a n t i a l s t e r i c i n t e r f e r e n c e even
w i t h the hydrogen atoms i n ortho p o s i t i o n s on the a r y l
groups.
A l l the other aminodiarylboranes prepared i n t h i s
i n v e s t i g a t i o n were monomeric i n nitrobenzene s o l u t i o n ,
though o f t e n s l i g h t l y associated i n benzene p a r t i c u l a r l y
i n the more concentrated s o l u t i o n s .
The aminodiarylboranes, Ar^BNR^, were prepared by t h r e e
methods:
Ar BCl + L1NR = Ar^B^NRg + L i C l
(l)
2
Ar BCl + R NH + Et^N = Ar^B'NRj + Et^NHCl
2
(2)
2
2ArMgBr + ClgB'NRg = Ar B-NR + MgGl
2
2
2
+ MgBr
2
(3)
129.
Method ( 3 ) was p a r t i c u l a r l y
of dimethylaminoboranes^
s u i t a b l e f o r the p r e p a r a t i o n
00
The u l t r a - v i o l e t spectrum of diphenylaminodiphenylborane i s s i m i l a r i n general appearance t o t h a t of t e t r a phenylethylene^^" ( b o t h measured i n cyclohexane), a b s o r p t i o n
maxima and e x t i n c t i o n c o e f f i c i e n t s being at 282 mu (18,200)
and 312 mu (14,000) r e s p e c t i v e l y .
The i n f r a red spectra of these two compounds are n e a r l y
i d e n t i c a l , the main d i f f e r e n c e s being the s p l i t t i n g of the
31'*
C sir - H out-of-plane deformation bands ( a l r e a d y r e p o r t e d ,
J
and observed i n a l l the diarylboranes used i n t h i s i n v e s t i g a t i o n ) and the very strong band at 1372 cm~^ i n the r e g i o n
314i n which B-N
t o B-N
absorptions are commonly found.
The band due
absorption was always s t r o n g and e a s i l y recognised
i n aminoboranes, and i t s frequency i n the v a r i o u s compounds
examined i s given i n Table 1, which also summarizes d i p o l e
moments and degrees of a s s o c i a t i o n i n benzene and i n n i t r o benzene.
The aminoboranes l i s t e d i n Table 1 are a l l . r e a d i l y
hydrolysed by c o l d water; t h i s i s a general p r o p e r t y of aminoboranes and was the basis of a method sometimes used f o r
t h e i r analysis.
The B-N
frequencies of a l l but the f i r s t compound i n
Table 1 f a l l w i t h i n the range 1.330-1530^
eleven other aminoboranes.
02
reported f o r
A v a r i a t i o n i n these frequencies
130,
has g e n e r a l l y been i n t e r p r e t e d as mainly due t o a change
i n the m u l t i p l i c i t y o f the B-N bond, so the h i g h frequency
(1552) observed i n the case of the diraeric compound ( I ) ,
i n which the B-N bonds must s u r e l y be s i n g l e , may a t f i r s t
s i g h t appear remarkably high.
However, v i b r a t i o n a l modes
due t o the s t r e t c h i n g o f B-N bonds i n a r i n g can scarcely
be expected t o be c l o s e l y comparable t o those due t o an
i s o l a t e d B-N bond i n a monomeric compound.
Although the t e t r a m e t h y l compound Me B NMe contains
2
2
a double bond, the l a r g e dipolie moment expected from the
+
formula Me^B = NMe i s e v i d e n t l y very considerably reduced
2
by unsymmetrical e l e c t r o n sharing i n the sense B-s^N owing
t o the e l e c t r o n e g a t i v i t y d i f f e r e n c e between boron and n i t r o gen.
The observed d i p o l e moment^^ i s only 1*40 + 0«03D
(1*47 + 0»06D i n Me B«NH ).
2
2
Both Ph BNMe and Ph B-NPh
2
2
2
2
have such small d i p o l e moments (1*6 and 1»0D) t h a t i t i s not
obvious which end o f the molecule i s p o s i t i v e .
Examination
of p - t o l y l d e r i v a t i v e s shows t h a t the N-methyl compounds
have p o l a r i t i e s of d i f f e r e n t s i g n from those o f the N - a r y l
compounds:
Ph B^NMe
2
2
and Ph B^NPh
2
2
This r e v e r s a l o f p o l a r i t y could be due t o the e l e c t r o n
r e p e l l i n g e f f e c t o f a methyl group, whereas a phenyl group
131.
can a c t as an e l e c t r o n a t t r a c t o r i n such a system.
The
change i n moment, however, i s r a t h e r l a r g e ( jx = 2»6D f o r
the two compounds j u s t mentioned).
A l l the observed moments
are c o n s i s t e n t w i t h the B-N bond having a small or zero
net p o l a r i t y .
Phosphinoboranes.
v i o u s l y mentioned
The only monomeric phosphinoboranes preare the not very w e l l c h a r a c t e r i s e d com-
pound Me,,B PH^, which was described as being s e n s i t i v e t o
h y d r o l y s i s , methanolysis and s l o w l y forming a polymer i n
ether s o l u t i o n 304 and more r e c e n t l y triphenylphosphinoborane
3 0 5
which was found t o be i n s e n s i t i v e t o water d i l u t e acids or
alkalies.
I n c o n t r a s t t o the t r i - t e t r a - and polymeric
i
.
t
phosphinoboranes of the type R B«PR (R = H or a l k y l , R
2
2
=
a l k y l or a r y l ) , a l l the phosphinodiarylboranes prepared i n
t h i s i n v e s t i g a t i o n are monomeric.
Unlike the aminoboranes,
the monomeric phosphinodiarylboranes are r e l a t i v e l y r e s i s t a n t
to hydrolysis.
The diarylphosphino compounds are also un-
a f f e c t e d by a i r .
Diphenyl(diphenylphosphino)borane (Ph^B'PPh,^) was prepared by method ( 2 ) , chlorodiphenylborane being added t o an
equimolar mixture of diphenylphosphine and t r i e t h y l a m i n e .
A d d i t i o n of diphenylphosphine t o the other r e a c t a n t s gives
the s a l t ( E t N H )
3
+
(Ph BCl
2
PPh )7
2
and diphenylphosphine and
132
chlorodiphenylborane alone give a t h i r d compound Ph BCl p
PHPh .
S i m i l a r products were obtained from
2
and dichlorophenylborane.
phenylphosphine
Diphenyl(diphenylphosphino)borane
i s not only i n s o l u b l e i n and undecomposed by water but i s
so s p a r i n g l y s o l u b l e i n organic solvents t h a t n e i t h e r i t s
molecular weight nor i t s dipolemoment was measured.
I t is
presumed t o be monomeric or capable o f r e v e r s i b l e d i s s o c i a t i o n
i n t o monomer since i t could be sublimed (240°) i n vacuum
(dimer or t r i m e r would c o n t a i n 8 or 12 phenyl groups).
To a l t e r symmetry and o b t a i n more s o l u b l e compounds
d e r i v a t i v e s o f di-m-tolylphosphine were prepared by a modif i c a t i o n of r e a c t i o n ( l ) i n which the sodium d e r i v a t i v e o f
di-m-tolylphosphine i n t e t r a h y d r o f u r a n was added t o c h l o r o diphenylborane i n the same solvent
T H P
(m-CH C H ) PH + Na
3
6
4
2
*
+
Na (m-CH C H ) P~ + £ H
3
6
4
2
2
PhgBCl
Ph B.P(C H m-CH ) ^
A l l the m - t o l y l d e r i v a t i v e s but two had adequate s o l u b i l i t y
2
6
4
3
2
both f o r molecular weight measurement i n nitrobenzene and
d i p o l e moment measurement i n benzene ( i n which they are
sparingly soluble.)
133.
The diarylphosphinoboranes prepared are l i s t e d i n
Table 2.
The i n f r a red spectra of the phosphorus compounds
were very s i m i l a r t o those of t h e i r n i t r o g e n analogues, and
i n a l l but [ t h e compounds PhP(BPh ) , PhBPPh, and PhB(PPh )
2
2
2
i n which several s t r o n g bands appeared i n t h e r e g i o n (1450 1550 cm ^ ) ] i t was easy t o d i s t i n g u i s h the s t r o n g band
almost c e r t a i n l y associated w i t h s t r e t c h i n g o f the B-P bond.
1
Since these bands (1400 - 1500 cm"'') are a t higher frequencies
than those of the B-N bands i n most of the aminoboranes
s t u d i e d , i n s p i t e of t h e mass o f a phosphorus being g r e a t e r
than t h a t o f a n i t r o g e n atom, the boron-phosphorus bonds i n
the monomeric phosphinoboranes would appear t o have pronounced double bond character*
The monomeric phosphinoboranes might t h e r e f o r e be
expected t o have pronounced p o l a r character, as i n d i c a t e d
by t h e c o o r d i n a t i o n formula ( 1 1 )
—a
1-
Ar B=PR
2
2
(11)
Moreover, since boron and phosphorus ( and arsenic ) have
much t h e same e l e c t r o n e g a t i v i t i e s ( i n the range 1*9 - 2*1,
however computed), t h e moment i n d i c a t e d i n ( l l ) should n o t
be reduced by bond p o l a r i s a t i o n as i n the aminoboranes ( t h e
e l e c t r o n e g a t i v i t y o f n i t r o g e n being about 3 ) .
134.
I n f a c t , i n s p e c t i o n of Table 2, bearing i n mind the
e f f e c t of methyl and bromo s u b s t i t u e n t s on d i p o l e moments,
shows t h a t the moments of the phosphinoboranes are l a r g e r
than those of the corresponding aminoboranes, and t h a t the
phosphino group i s at the negative end of the d i p o l e (111)
-i—r»-
A r B - PR
?
2
(111)
Prom Table 2 the d i p o l e moment of
( H I , Ar = R « Ph.) must be about 2.5D,
t h a t of (111, Ar = Ph, R = E t ) being about 1.ID and i n the
same d i r e c t i o n .
This s u r p r i s i n g r e s u l t suggests t h a t phosphorus i s
a c t i n g as a weak % donor ( t o boron) i n these compounds,
p o s s i b l y due t o an unfavourable r e l a t i o n between the 'sizes'
of B2p_ and. P3p_ o r b i t a l s .
I n a l l the d i a r y Ibora/nes some
e l e c t r o n f l o w i s t o be expected
from the a r y l group t o the
vacant boron 2p_ o r b i t a l , and i n Ph B«PEt t h i s could account
2
2
f o r the greater p a r t of the observed d i p o l e .
Good evidence
f o r such e f f e c t s can be seen by considering the d i f f e r e n c e
(0.64D) between the moments of n-amyl dichloroborane
phenyldichloroborane
(see f i g . , I V ) .
and
The increased moment
n-amyldifluoroborane
1.64
of the l a t t e r must be
n-amyldichloro-
1«55
t o considerable p o l a r i s a t i o n
n-hexyldifluoro-
1*61
of the Ph-B
+
due
-
bond (Ph.-r-. B).
135.
n-hexyldichloro-
1'55
The l a r g e moment (1«97D) f o r
phenyldifluoro-
1'90
chlorodiphenylborane
phenyldichloro-
2*19
two such "bonds seems t o con-
p-tolyldifluoro-
2*48
f i r m these e f f e c t s , and the
p-tolyldichloro-
2*68
relatively
[Fig. IV]
with
low moment (l'66D)
f o r dimesitylfluoroborane
where the a r y l groups are almost c e r t a i n l y
makes t h e i r presence almost d e f i n i t e .
i n d i f f e r e n t planes
Though t h e boron atom
i n a d i a r y l ( d i e t h y l p h o s p h i n o ) b o r a n e could thus be regarded as
c o o r d i n a t i v e l y s a t u r a t e d , or p a r t l y so, the phosphorus i s n o t ,
and i n f a c t the d i e t h y l phosphino compounds add methyl i o d i d e
+
B'PEt Mej I .
t o form phosphonium s a l t s [Ar
Ar^B'PEtJWe
2
2
I n Ph^B'PPhp and r e l a t e d compounds the s t i l l l a r g e r
moments would be due i n e f f e c t , t o conjugation both between
boron and a r y l and phosphorus and a r y l as shown i n the r e s onance formula ( I V )
+
+
x
B-P
(IV)
Thus f o r m u l a t i o n accounts i n a q u a l i t a t i v e way n o t only
f o r the observed d i p o l e moments, but also f o r the l a c k o f
chemical r e a c t i v i t y since both boron and phosphorus are co-
136.
o r d i n a t i v e l y saturated ( o r p a r t l y so).
Further, the
charge separation between boron and phosphorus i n d i c a t e d
i n ( I V ) should r e s u l t i n B-P f o r c e constants g r e a t e r than
would be expected f o r B-P s i n g l e bonds, since the B-P
bond would amount t o a o* bond p o s s i b l y w i t h a small n component but w i t h some e l e c t r o s t a t i c a t t r a c t i o n i n a d d i t i o n .
The r e l a t i v e importance of s t r u c t u r e s analogous t o
( I V ) i n t h e aminoboranes i s almost c e r t a i n l y much less since
boron and n i t r o g e n achieve c o - o r d i n a t i v e s a t u r a t i o n by
f o r m a t i o n of a B = N double bond.
The reason f o r the phosphinodiarylboranes
being mono-
meric, when the s e r i e s RgB-PRj (R = H, a l k y l ) form t r i m e r s ,
tetramers or polymers, thus l i e s i n the boron atom i n t h e
d i a r y l b o r a n e s e r i e s being already c o - o r d i n a t i v e l y saturated
( o r n e a r l y so) n o t by Ti-bonding w i t h phosphorus but by nbonding w i t h the a r y l groups.
Arsinoboranes - These were prepared from the c h l o r o d i a r y l borane and the sodium s a l t of t h e d i a r y l a r s i n e i n t e t r a hydrofuran; they are l i s t e d i n Table ( 3 ) . I n f r a r e d spectra
again resembled those of t h e n i t r o g e n and phosphorus compounds, but the t e t r a p h e n y l compound PhgB*AsP.h2 was cons i d e r a b l y more soluble i n organic solvents than i t s phosphorus analogue.
The d i a r y l a r s i n o b o r a n e s resembled t h e
137.
phosphino analogues i n t h e i r r e s i s t a n c e t o water and d i l u t e
acids o r a l k a l i e s a t 100°, but d i f f e r e d i n t h e i r q u a n t i a t i v e and a n a l y t i c a l l y u s e f u l r e a c t i o n w i t h aqueous a l c o h o l i c hydrogen peroxide a t room temperature:
Ph B PAr
2
Ph B AsAr
2
+ H 0
2
2
2
+ H 0
2
—
2
2
—
2PhOH + H B0^ + Ar P0 H
3
2
2
2PhOH + 2ArOH + H^BO.^ + H^AsO^
The B-As a b s o r p t i o n bands are a t r a t h e r lower frequencies
than those o f B-P bands i n analogues compounds, and i n the
same r e g i o n as B-N bands.
The a r s i n o group i s , as i n the phosphinoboranes, t h e
negative end o f the d i p o l e , the moments being r a t h e r l e s s .
I t i s concluded t h a t the e l e c t r o n i c s i t u a t i o n i n the a r s i n o boranes resembles t h a t i n the phosphinoboranes, the smaller
moments o f the former being due t o a smaller degree of e l e c t r o n
t r a n s f e r from arsenic t o the a r y l groups bound t o i t .
Though the o~-donor character o f n i t r o g e n , phosphorus
and arsenic towards boron diminishes i n the order N P As, i t
seems t h a t the itr-donor character diminishes even more r a p i d l y .
.APPENDIX
138.
INTRODUCTION I
U n t i l r e c e n t l y moat b o r i n i c acids were prepared by
307 a h n
the a c t i o n of a Grignard reagent on an a l k y l borate
» i«-»
Letsinger who has r e c e n t l y r e v i v e d i n t e r e s t i n these com£ X
u
308
pounds i n a d d i t i o n t o preparing
s o l i d d e r i v a t i v e s has p r e 309
pared the f i r s t mixed b o r i n i c acids, and t h e f i r s t
borinic acid.
tricyclic
3 1 0
Good y i e l d s o f d i - b u t y l b o r i n i c acids have r e c e n t l y been
311
reported by Lappert and co-workers from the r e a c t i o n ( B u B ) 0 + BF -9 Bu B0H
2
2
3
2
312
T. P. Povlock and W. T. L i p p i n c o t t have prepared
several
b o r i n i c acids as t h e i r amino-ethyl esters (21-63$ y i e l d s )
by r e a c t i o n o f trimethoxyboroxine and an aromatic Grignard
reagent.
The q u a n t i t a t i v e h y d r o l y s i s o f aminodiarylboranes t o
produce the amine and the a r y l b o r i n i c acid (described
earlier
i n t h i s t h e s i s ) has l e d t o the i n v e s t i g a t i o n o f t h i s r e a c t i o n
as a p r e p a r a t i v e method f o r d i a r y l b o r i n i c a c i d s .
Several acids have been prepared and i s o l a t e d as t h e i r
araino-ethyl esters i n goad y i e l d s (51-93$).
139.
EXPERIMENTAL
General Procedure
Phenylmagnesium bromide (0.25 mole) i n d r y ether was
306
slowly added t o dichlorodiphenylaminoborane
i n benzene (100 c.c.) and a f t e r r e f l u x i n g
r e a c t i o n mixture was hydrolysed w i t h d i l u t e
(0*1 mole)
hour) t h e
hydrochloric
acid t o pH 6-7, f i l t e r e d and the l a y e r s separated.
The
organic l a y e r was pumped dry and then e x t r a c t e d w i t h h o t
water (50 c.c.) on a steam bath t o remove any boronic
acid.
The b o r i n i c a c i d , a yellow o i l , was separated dissolved i n
ether (50 c.c.) and monoethanolamine (22 c.c.) i n an equal
volume o f water was added w i t h vigorous s t i r r i n g .
The p r e c i p i t a t e d ester was c r y s t a l l i s e d f r e e of d i p h e n y l amine from ethanol (m.p. 188°-9°).
The ester was dissolved i n a s o l u t i o n (100 c.c.) o f
equal volumes o f acetone and methanol and hydrolysed w i t h
h y d r o c h l o r i c acid (12-5 c.c. cone, acid i n 100 c.c. w a t e r ) .
A f t e r shaking w i t h ether (100 c . c . ) , the organic l a y e r was
separated, d r i e d (Anhydrous MgSO^) and pumped d r y and a f f o r d e d
d i p h e n y l b o r i n i c a c i d ( 1 6 * l g . , y i e l d 88$), see Table 4
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140.
NOTES
(1)
Only when r e q u i r e d
f o r f u r t h e r work, or b e t t e r charac-
t e r i s a t i o n were the pure acids i s o l a t e d .
(2)
A f t e r d i f f i c u l t y i n p r e c i p i t a t i n g the monoethanolamine
ester o f d i - p - t o l y l b o r i n i c a c i d , i t was found t h a t the e s t e r s
were best p r e c i p i t a t e d from hear n e u t r a l
(3)
solutions.
The esters I I , V I I I , X and X I were more soluble
normal i n ether and pumping the ether s o l u t i o n dry
than
followed
by c r y s t a l l i s a t i o n from ethanol gave increased y i e l d s o f these
esters.
DISCUSSION
The
h i g h y i e l d s (51-93$>) of e s t e r s a.n.d the use o f only
a s l i g h t excess (5=10$) of Grignard reagent i n d i c a t e t h a t the
hydrolysis
of aminodiarylboranes i s the most convenient method
of preparing pure d i a r y l b o r i n i c a c i d s .
The
v a r i a t i o n i n y i e l d s shows no r e l a t i o n s h i p between
the e l e c t r o n e g a t i v i t y of the a r y l groups and the y i e l d o f
acid obtained, though the lower y i e l d s o f compounds IV, V I ,
V I I and V I I I suggest the importance o f s t e r i c f a c t o r s .
r e f l u x i n g i n these l a t t e r reactions
y i e l d s of these acids.
Longer
would probably give b e t t e r
141.
INTRODUCTION
I f white phosphorus "P^" has an a v a i l a b l e lone p a i r
of e l e c t r o n s a t each corner o f the t e t r a h e d r a l molecule,
i t would be expected t o behave as a strong donor.
This
substance i s c e r t a i n l y a powerful reducing agent, and i t
i s adequately soluble i n dry benzene.
These f a c t s suggest t h a t i t s r e a c t i o n s w i t h boron
t r i c h l o r i d e and s i m i l a r acceptors, and w i t h organo l i t h i u m
compounds, would be of i n t e r e s t .
The only work so f a r
313
described i n the l i t e r a t u r e i s by H. Moissan
who r e p o r t s
a vigorous r e a c t i o n between boron t r i i o d i d e and yellow phosphorus .
142.
REACTION OF WHITE PHOSPHORUS WITH PHENYLLITHIUM
4PhLi + P
4
~
2Ph - P - PPh
Li
Li
P h e n y l l i t h i u m (0*32 moles) i n ether was addled t o a
s o l u t i o n o f f r e s h l y d i s t i l l e d white phosphorus (9*9g. 0»32 moles
P^) i n benzene (200 c.c.) a t a r a t e s u f f i c i e n t t o g e n t l y
the r e a c t i o n mixture.
two
reflux
The deep red s o l u t i o n was separated i n t o
parts.
Part I
A f t e r c a r e f u l h y d r o l y s i s w i t h deaerated d i l u t e
hydrochloric
acid t o pH 6-7, the organic l a y e r was separated ( N ) pumped dry
?
and a f t e r b o i l i n g w i t h aqueous hydrogen peroxide (3 c.c. of 100
volumes i n 50 c.c. of water) a f f o r d e d on coo^ij.ng phenyl phosphorite
acid m.p. 158°-59° (2'8g. y i e l d 55*1%), a f t e r f i l t r a t i o n of the
hot s o l u t i o n from an i n s o l u b l e white s o l i d ( c . a . , 4g.).
The
white s o l i d was n o t i d e n t i f i e d although i t was shown, t o c o n t a i n
phosphorus and phenyl groups.
I n f r a spectroscopy i n d i c a t e d the presence o f Ph-P, P = 0
and P - 0 - P bonds.
The s o l i d was i n s o l u b l e i n organic
water and d i l u t e a l k a l i and soluble i n d i l u t e h y d r o c h l o r i c
solvents,
acid.
H„0
Ph
P
P
Ph
2PhP0yL + unknown s o l i d
t
H„0
Li
Li
143.
Part I I
Methyl c h l o r i d e (c.a., 0*32 moles) was slowly
via
bubbled
a flow-meter i n t o the deep red s o l u t i o n (N^) cooled t o
c.a., - 10°, u n t i l
i t became c o l o u r l e s s .
After
filtration
( N ) from p r e c i p i t a t e d l i t h i u m c h l o r i d e the f i l t r a t e was
2
pumped d r y and then b o i l e d (30 mins.) w i t h aqueous a l k a l i n e
a l c o h o l i c hydrogen peroxide (4 c.c. of 100 volumes i n 50 c.c.
of 2N NaOH and 50 c.c. of a l c o h o l ) .
Dilute hydrochloric
acid
was added t o adjust the pH 6-7, and the s o l u t i o n was extracted
w i t h ether.
A f t e r pumping dry the ether e x t r a c t and c r y s t a l l i
a t i o n from aqueous a l c o h o l phenylmethylphosphinic acid in.p.
134°-5° was i s o l a t e d and i d e n t i f i e d by i n f r a red spectroscopy
and mixed m e l t i n g p o i n t , (?*6g, y i e l d 53*1$),
MeCl
Ph—P — P — ? h
I
Li
5
Ph—?—F—?h
I
I
Li
H 0
* i. 2Ph
Me
+2Li"
9
u
P — OH
I
Me
cf
Me
144.
REACTION OF WHITE PHOSPHORUS WITH METHYLLITHIUM
M e t h y l l i t h i u m (0»2 moles) i n dry ether (300 c.c.) was
slowly added (room temperature) t o a s o l u t i o n o f white phosphorus (6»3g.» 0*2 moles P^) i n "benzene (300 c.c.) and the
r e a c t i o n mixture was s t i r r e d ( 3 nours).
Methyl c h l o r i d e was then slowly bubbled i n t o the r e d brown s o l u t i o n u n t i l i t i u s t tu.rned white (c.a.. 0^2 moles
were added).
A f t e r f i l t r a t i o n (N^), the s o l u t i o n was con-
centrated and a s u r p r i s i n g l y v o l a t i l e product (b.p. 25°-28°)
d i s t i l l e d w i t h the s o l v e n t .
A d d i t i o n of methyl i o d i d e t o t h e
d i s t i l l a t e a f f o r d e d an immediate white c r y s t a l l i n e s o l i d (m.p.
310°
decomp,) which was n o t i d e n t i f i e d .
The i n f r a - r e d spectrum
of t h i s compound showed t h e presence of CH^-P and weak P-H
absorptions.
REACTION OF WHITE PHOSPHORUS WITH BORON TRICHLORIDE
Boron t r i c h l o r i d e (12g.) i n benzene (100 c.c.) a t 6° was
slowly added (N^) t o a s o l u t i o n of white phosphorus (3«lg.>
0*1 mole) i n the same volume o f solvent a t 4°. A f t e r s t i r r i n g
the r e a c t i o n mixture ( 3 h o u r s ) , d i s t i l l a t i o n a f f o r d e d unreacted;
boron t r i c h l o r i d e and white phosphorus (3*0g.).
145.
DISCISSION
Sinofi white phosphorus did n o t rea-ot w i t h boron
tri-
c h l o r i d e which i s q u i t e a. strong acceptor, f u r t h e r reaction?
s
were n o t attempted.
I t seems possible t h a t h y b r i d i s a t i o n i n
phosphorus i s such t h a t there are no a v a i l a b l e lone p a i r s ,
a p o s s i b i l i t y being s t r a i n e d p-bonding w i t h some d e l o c a l i s e d
bonding.
The r e a c t i o n w i t h p h e n y l l i t h i u m may be a most convenien
method o f preparing
aromatic biphosphines,
RG1
4PhLi + P„ —
4
Ph - P - P- Ph
Ph - P - P - Ph
I
I
I
I
(R=We)
' '
Li L i
R
R
1
1
w l
A
. „,
O T
+
tflilUl
lVtc;
The o x i d a t i o n product phenylmethylphosphinic acid was
i s o l a t e d i n reasonable y i e l d (53*1%)•
The r e a c t i o n w i t h
m e t h y l l i t h i u m was not f u l l y i n v e s t i g a t e d , but f u r t h e r i n v e s t
i g a t i o n o f these and r e l a t e d r e a c t i o n s i s now i n progress.
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