432
TEORETICHESKAYA
21 700 c m - i , w h i l e the c o r r e s p o n d i n g v a l u e s f o r p s o r a l e n e a r e 6000 and 21 600 c m -1. T a b l e 2 g i v e s t h e
t r a n s i t i o n e n e r g i e s A E and Xma x c a l c u l a t e d v i a v0 =
= 5300 c m -1, fl0 = 21 700 c m -1 f o r the c o u m a r i n s and
~0 = 6000 c m -1, fl0 = 21 600 c m -~ f o r t h e f u r o c o u m a r i n s ; F i g s . 1 and 2 s h o w t h e s p e c t r a in c y c l o h e x a n e
and a l c o h o l , * w i t h the t h e o r e t i c a l s p e c t r a i n d i c a t e d by
l i n e s at t h e b o t t o m . T h e Hiickel a p p r o x i m a t i o n g i v e s a
g e n e r a l l y s a t i s f a c t o r y p r e d i c t i o n of t h e m a i n b a n d s ,
t h e a g r e e m e n t b e i n g b e t t e r f o r the end b a n d s t h a n f o r
the m i d d l e o n e s . * *
A l t h o u g h the i n t e n s i t y c a l c u l a t i o n s f o r c o u m a r i n and
p s o r a l e n e s h o w t h a t a l l the t r a n s i t i o n s a r e a l I o w e d t h e
a c t u a l v a l u e s ( T a b l e 3) do not a g r e e w i t h e x p e r i m e n t .
T h i s is not u n e x p e c t e d and is a r e s u l t of the a s s u m p t i o n s m a d e in the c a l c u l a t i o n s .
We a r e i n d e b t e d to A. V. T u t k e v i c h f o r p r o v i d i n g
the p r o g r a m f o r the c a l c u l a t i o n s and to N. P. G a m b a r y a n f o r d i s c u s s i o n of s e v e r a l a s p e c t s .
I EKSPERIMENTAL'NAYA
KHIMIYA
REFERENCES
1~ G~ V. P i g u l e v s k i i and G. A. K u z n e t s o v a , ZhOKh,
24, 2174, 1954.
2o R. H. Goodwin a n d B. M. P o l l o k , A r c h . B i o c h e m . B i o p h y s . , 49, 1, 1954.
3. C. R. J a c o b s o n , K. R. B r o w e r , and E. D.
A m s t u t z , J . O r g . C h e m . , 18, 1117, 1953.
4. B. K. G a n g u l i a n d P. B a g e h i , J . O r g . C h e m . ,
21, 1415, 1956.
5. K. Sen and P. B a g c h i , J . O r g . C h e m . , 24, 316,
1959.
6. M. E. P e r e l ' s o n , A. V. T u t k e v i c h , Yu. N.
S h e i n k e r , and N. P. G a m b a r y a n , T E K h , [ T h e o r e t i c a l
a n d E x p e r i m e n t a l C h e m i s t r y ] , 2, 575, 1966.
7. E. S t r e i t w e t s e r , T h e o r y of M o l e c u l a r O r b i t a l s
[ R u s s i a n t r a n s l a t i o n ] , M o s c o w , " M i r , " 202, 1965.
8. H. H. J a f f e and M. O r c h i n , T h e o r y and A p p l i c a t i o n of U l t r a v i o l e t S p e c t r o s c o p y , N . Y . - L o n d o n ,
113, 124, 1962.
14 S e p t e m b e r 1966
* S p e c t r a r e c o r d e d w i t h an S F - 4 s p e c t r o p h o t o m e t e r .
**It s h o u l d be r e m e m b e r e d t h a t o v e r l a p of the b a n d s
c a n c a u s e the m a x i m a to b e d i s p l a c e d .
All-Union Medicinal Plants
Research Institute;
Orzhonikidze All-Union
C h e m i c a l and P h a r m a c e u t i c a l
Research Institute, Moscow
K I N E T I C S O F I S O T O P E E X C H A N G E B E T W E E N HC1 A N D D B r IN L I Q U I D
NITROGEN AND OXYGEN
G. S. D e n i s o v and E. V. R y l ' t s e v
Teoretieheskaya
i Eksperimental'naya
Khimiya,
Vol. 3, No. 5, pp. 7 0 1 - 7 0 5 , 1967
Not m u c h is known a b o u t h y d r o g e n i s o t o p e e x c h a n g e
w h e n the p r o t o n s a r e l i n k e d to a t o m s w i t h n o n b o n d i n g
e l e c t r o n p a i r s . NMR p r o v i d e s c o n s i d e r a b l e s c o p e f o r
r e s e a r c h in t h i s a r e a [ 1 - 4 ] , but a l m o s t a l l p a p e r s on
t h i s d e a l w i t h p u r e l i q u i d s o r b i n a r y m i x t u r e s of t h e s e ,
w h e r e a s , a s r e g a r d s m e c h a n i s m s , it is of m o s t i n t e r e s t to e x a m i n e p r o c e s s e s in v a p o r s o r in s o l u t i o n
in s o l v e n t s f r e e f r o m a c t i v e h y d r o g e n . S t u d i e s of e x c h a n g e at low t e m p e r a t u r e s s h o u l d a l s o p r o v i d e u s e ful e v i d e n c e .
The present solvents were chosen as being highly
t r a n s p a r e n t in the i n f r a r e d [5], so, e v e n though the
h y d r o g e n h a l i d e s h a v e s o l u b i l i t i e s of o n l y 10 -4 to 10 -3
M, t h e a b s o r p t i o n s p e c t r a of HCI and D B r s h o u l d be
a c c e s s i b l e w i t h l a y e r s of u s a b l e t h i c k n e s s . T h e p r o c e s s e s m a y be f o l l o w e d b y r e f e r e n c e to the i n t e n s i t i e s
of the u(HCI), ,(HBr),
tions of time.
u(DCI),
~(DBr)bands
as func-
EXPERIMENTAL
W e used an IKS-12 spectrometer with an LiF prism and OAP-I
Golay detector. The spectral slit width was 7-8 crn -I. The solutions
of HCI and DBr were prepared by mixing the solid halide with the
solvent and allowing the mixture to stand for several hours with
periodic stirring, followed by filtration. The first measurements were
made with the ceil described in [5]. A layer 8 cm thick was inadequate to reveal the absorption band of DBr in saturated solution, so a
simple double-pass cell was made, which raised the effective path
length to 40 cm (Fig. 1). This cell was based on a glass dewar having
at the bottom a steel concave spherical mirror of radius of curvature
20 cm. Entry of water into the solution (which causes strong scattering and also a broad band at 2900-3200 cm -I) was prevented by a
10 Pm teflon film, which does not absorb in the region of interest.
A 35 cm path showed u(DBr) as a peak at about 1830 cm -I., u(HCI)
was much stronger and could be detected at smaller thicknesses. Addition of pure solvent did not affect the intensity, so Beer's law applies
at the concentrations used. The signal was affected by the displacement of the image of the source along the axis when the layer thickness was altered from 7 to 40 cm. The saturated solutions of HC1 and
T H E O R E T I C A L AND E X P E R I M E N T A L CHEMISTRY
DBr (isotopic ~ibundanceof D in the latter about 90%) in liquid nitrogen were mixed in roughly a 1:10 ratio, and the spectrum over the
range covering u(HC1), v(HBr), v(DC1), u(DBr)was recorded for
several hours; the liquid level changed by only 3-4 cm in 5 hr.
RESULTS AND DISCUSSION
The a b s o r p t i o n b a n d s of DBr, DC1, a n d HCI lie
c l e a r of the s o l v e n t a b s o r p t i o n , but v(HBr) lies in a
region where n i t r o g e n a b s o r b s weakly (Fig. 2). The
c o n d i t i o n s of o b s e r v a t i o n a r e l e s s f a v o r a b l e with iiquid
oxygen; Fig. 3 shows that all the b a n d s a r e o v e r l a p p e d
to s o m e extent by a b s o r p t i o n due to the oxygen o r to
i m p u r i t i e s ip it [51. However, it was p o s s i b l e to m a k e
q u a n t i t a t i v e m e a s u r e m e n t s on v(HC1) and v(DC1).
The s t r e n g t h s of the b a n d s v(HC1), u(DBr), and
u(HBr) did not a l t e r i m m e d i a t e l y after m i x i n g , while
v(DC1) was a b s e n t . Within 5 - 1 0 h r t h e r e w e r e a p p r e c i able f a i l s in v(DBr) and v(HC1), while v(DC1) appeared,
and the s t r e n g t h of v(HBr) i n c r e a s e d .
1
5
433
t00~C~
'
.....
~ + "
:i'~ --
''
t;'---
1800
2200
2600
3000 cm-I
Fig. 2. T r a n s m i s s i o n of liquid n i t r o g e n c o n t a i n i n g d i s s o l v e d HC1, HBr, DC1, and DBr
(effective l a y e r t h i c k n e s s 38 cm).
c o n v e n i e n t than A if the r e c o r d i n g conditions a r e s t a n d a r d i z e d . The c o n c e n t r a t i o n s of HBr and DC1 in liquid
n i t r o g e n w e r e deduced f r o m the i n t e g r a l a b s o r p t i o n
c o e f f i c i e n t s in CC14 at r o o m t e m p e r a t u r e [8]. As Air '~
is i n v a r i a n t u n d e r isotope s u b s t i t u t i o n for u n p e r t u r b e d
d i a t o m i c m o l e c u l e s [10], we c a n use AHB r to c a l c u l a t e
ADB r. In fact, A / v 2 c h a n g e s only 10% [8] between HC1
and DC1 in CCI~. T a k i n g the r a t i o of the A / v 2 for HBr
and DBr as b e i n g as for HC1 and DC1 d i s s o l v e d in CC14,
we get the A for DBr in CC14 as 2200, which was used
for the s o l u t i o n s in liquid n i t r o g e n and oxygen. The
HC1 c o n c e n t r a t i o n in the k i n e t i c t e s t s was 0 . 2 - 0 . 3 raM,
while the total c o n t e n t of both isotopic f o r m s of hydrogen
b r o m i d e was 0 . 0 5 - 0 . 1 M.
The c o n c e n t r a t i o n of each c o m p o n e n t tends expon e n t i a l l y to its e q u i l i b r i u m value [11]. The exponent
r < 10 -4 sec -1, so, if the r e a c t i o n is a s s u m e d b i m o l e c u l a r , the u p p e r l i m i t to the rate c o n s t a n t can be
d e t e r m i n e d at 77 ~ and 90 ~ K,
r
k77~= [HCI] + [DBr] + {HBrI <
< 0.1 / / m o l e 9 see
Fig. 1. D o u b l e - p a s s cell: i - l i g h t s o u r c e , P - - p r i s m ,
D - - d e w a r , M - - s p h e r i c a l m i r r o r , K - - h o l d e r with teflon film, O O ' - - l i q u i d level, fl and f 2 - - i n t e r m e d i a t e
i m a g e s of s o u r c e , 1 - 4 ) m i r r o r s in i l l u m i n a t i o n s y s tem.
The r e s u l t s give u p p e r l i m i t s for the exchange r a t e
c o n s t a n t s at 77 and 90 ~ K. The c o n c e n t r a t i o n s w e r e
deduced f r o m p u b l i s h e d v a l u e s for the i n t e g r a l a b s o r p tion c o e f f i c i e n t s A of v(HC1), v(HBr), and v(DC1); that
for v(HC1) in the v a p o r s t a t e at r o o m t e m p e r a t u r e is
3000 / / m o l e 9 c m 2 [6] but in a m i x t u r e with n i t r o g e n
u n d e r high p r e s s u r e at - 8 0 ~ C it is 4500 [7], the c o e f f i c i e n t i n c r e a s i n g with the n i t r o g e n p r e s s u r e and as
the t e m p e r a t u r e is r e d u c e d . In CC14 at room t e m p e r a t u r e , the value is 7500 [8], while in c r y s t a l l i n e HC1 it
is 22 500 [9]. F o r HC1 d i s s o l v e d in t h e s e liquids we
took A = 7500, which c a n n o t differ f r o m the t r u e value
by m o r e than a f a c t o r two. This value was u s e d to
d e t e r m i n e the HC1 c o n c e n t r a t i o n s in l i q u i d n i t r o g e n
from
c = 2.3
l
S lg~o/I)dv
HCI and DBr in CC14 at r o o m t e m p e r a t u r e come to
e q u i l i b r i u m in l e s s than 5 sec, so
ks00o> l02 / / m o l e 9 sec.
T h e s e r e s u l t s i n d i c a t e (Fig. 4) that E a > 1.5 k c a l /
/mole.
100
"N""N~7
I
o
kl 1
i
IBDO
2DO0
2200
2,~Oa
2600
2800
3000 cm-1
Fig. 3. 1) T r a n s m i s s i o n of liquid oxygen
(effective l a y e r t h i c k n e s s 12 cm); 2) t r a n s m i s s i o n of liquid oxygen c o n t a i n i n g d i s s o l v e d
HC1, HBr, DC1, and DBr (effective l a y e r
t h i c k n e s s 40 cm).
A
S p e c t r a of s o l u t i o n s with c o n c e n t r a t i o n s m e a s u r e d in
this way w e r e used to d e t e r m i n e the a b s o r p t i o n c o e f f i c i e n t at the peak of the v(HC1) band, which is m o r e
The a c t i v a t i o n e n e r g y for v i s c o u s flow of liquid
n i t r o g e n , as deduced f r o m E y r i n g ' s f o r m u l a [12] v i a
data on the t e m p e r a t u r e d e p e n d e n c e of the v i s c o s i t y
[13] and d e n s i t y [14], is 0.66 k c a l / m o l e ; F r e n k e l [15]
434
TEORETICHESKAYA I EKSPERIMENTAL'NAYA KHIMIYA
gives the s i m i l a r value of 0.47 k c a l / m o l e , and both
a r e much less than the above lower l i m i t for E a. T h e r e
is t h e r e f o r e little doubt that this is a r e a s o n a b l e e s t i m a t e of the true value.
.'p
:
9
-46
-h8
-50
-5Z
t
r
W /~
Fig. 4. Estimation of the lower
l i m i t to the activation e n e r g y for
hydrogen exchange in HC1 +DBr.
The r e s u l t E a > 1.5 k c a l / m o l e gives some indication of the r a t e - l i m i t i n g step. It has been shown [16]
from the g e n e r a l l y accepted m e c h a n i s m [17] that, if
this step is decay of a hydrogen-bonded complex in
which proton exchange occurs [18], then the t e m p e r a ture dependence of the rate constant will be d e t e r m i n e d
by the f a c t o r exp(6/RT), in which 5 is the activation
energy for formation of that complex. This 6 should
be a l m o s t zero; it can h a r d l y be g r e a t e r than the 5
for formation of a complex of d o n o r - a c c e p t o r type,
and it is known [19] that the activation energy for the
reaction of BF 3 with amines is zero. Moreover, h y d r o gen-bonded complexes a r e f o r m e d r a p i d l y [20] in
solid solutions in nitrogen and argon at 30~
~ K, so
the exchange HC1 + DBr is slow by c o m p a r i s o n . Hence
Ea > 5, and so the assumption of [16] is not valid.
M e a s u r e m e n t of E a by NMR [2] a g r e e s with this r e sult. It may well be that the exchange rate in HC1 +
+ DBr is governed by synchronous p a s s a g e of the
protons through the potential b a r r i e r s e p a r a t i n g the
two m i n i m a on the p o t e n t i a l - e n e r g y curve for the
hydrogen bond.
2o E. K r a k o w e r and L. W. Reeves, T r a n s . F a r .
Soc., 59, 2528, 1963.
3. Z. Luz, D. Gill, and S. Meiboom, J. Chem.
P h y s . , 30, 1540, 1959.
4. S. F o r s e n and R. A. Hoffman, J. Chem. P h y s . ,
39, 2892, 1963.
5. M. O. Bulanin and Yu. V. P e t e r s o n , Opt. i
s p e k t r . , 16, 987, 1964.
6. Wo C. Benedict, R. Herman, G. E. Moore,
and S. Silverman, J. Chem. P h y s . , 26, 1671, 1957.
7. Hal Vu, J. Res. Centre Nat. Res. Sei., 53,
313, 1960.
8. D. N. Shehepkin, Opt. i s p e k t r . , 19, 709,
1965.
9. H. B. F r i e d r i c h and W. B. Person, J. Chem.
P h y s . , 39, 811, 1963.
10. D. H. Whiffen, T r a n s . F a r . Soc., 54, 327,
1958.
11. S. Z. Roginskii, T h e o r e t i c a l P r i n c i p l e s of
Isotope Methods of Studying Chemical Reactions [in
Russian], I z d - v o AN SSSR, 1956.
12. S. Glasstone, K. Laidler, and H. Eyring,
T h e o r y of Rate P r o c e s s e s [Russian translation], IL,
1948.
13. S FSrster, Cryogenics, 3, 177, 1963.
14. M. P. Malkov, I.B. Danilov, A. G. Zel'dovich,
and A. B. Fradkov, Handbook on the Technical Physics of Cryogenics [in Russian], Gosenergoizdat,
71, 1963.
15. Ya. I. Frenkel, The Kinetic Theory of Liquids;
Selected Works [in Russian], vol. 3, [zd-vo AN SSSR,
213, 1959.
16. P. Huyskens and Th. Zeegers-Huyskens,
Bull.
Soc, chim. Belg., 70, 511, 1961.
17. A. I. Brodskii, Isotope C h e m i s t r y [in Russian],
I z d - v o AN SSSR, 1957.
18. G. P. Miklukhin, Isotopes in Organic C h e m i s t r y
[in Russian], I z d - v o AN UkrSSR, 1961.
19. G. B. Kistiakowsky and R. Williams, J. Chem.
P h y s . , 23, 334, 1955.
20. G. C. P i m e n t e l , Hydrogen bonding, ed. D.
Hadzi and H. W. Thompson, P e r g a m o n P r e s s , 414,
1959.
REFERENCES
1. W. G. P a t t e r s o n , Canad. J. Chem., 41, 714,
2472, 2477, 1963.
15 July 1965
Physics Research Institute,
Leningrad University