Indian Journal of Chemical Technology
Vol. 7, September 2000, pp. 230-235
Conversion of anilines to their oligomers by copper hexacyanoferrate(II)
T an veer Alam", Priti Gairolah, Hina Tarannum", Kamaluddin h & M N V Ravi Kurnarh
"Department of Chemi stry, KLDA V Degree College, Roorkee 247 667, India
hDe partment of Chemi stry, Uni versit y of Roorkee, Roorkee 247 667, India
Received 18 }anum)' 1999; accepted 20 June 2000
Aniline, p-toluidine and p-chlo roaniline have been oxidi zed by copper hexacyanoferrate(l l). The reaction was
appreciable in basic med ium. The result an t oxidation products deposited on cop per hexacya noferrate (II ) surface are reddi sh
brown in colour. The oxidation products have been characterized by GC-MS and IR spectroscopy. Fro m the spectral studies,
the oxidatio n product of aniline ha s been identifi ed as tetramer, while th at of p-toluidine and p-chloroaniline are trimer and
dimer, respectively.
During the course of chemical evolution, cyanide ions
were abundant in nature. Cyanide ion is smal ler in
si ze and is considered as a strong li gand due to the
presence of triple bond. It shows basic, ambidentate
c haracte ristics and forms a variety of complexes with
transition metal ions 1.2. Metal hexacyanoferrate(II)
mostly insoluble in water, could have played an
78 ·
6
.
Important
ro Ie as a dsorbe nr' - an d .ton exc hanger · 111
the course of chemical evol ution .
Reactions between amines and clays have bee n
9 11
studied by a number of workers - • Hasegawa carried
out spectroscopic studies on the coloured products
12 13
obtained by the reaction of clays with amines ' .
Apart from these studies, reports were avai lable on
14 17
the reaction with be nzidine and anilines - . Studies
on th e interaction of aromatic amines with metal
hexacyanoferrates(ll)
and
its
rel evance
in
evo lut ionary context , can hardl y be seen in lite rature.
During the inte raction stu dies of aromatic amines wi th
copper hex acyanoferratc(II), it was observed that
aniline, p-to lui c.Jine and p-chloroaniline react wi th
copper hexacya noferrate(Il) and gave co loured
products.
In thi s pape r studi es on the interact ion of aniline, pto luidine
and
p-chloroaniline
with
copper
hex acyanofe n·atc(ll) ha ve been re ported . A tentati ve
mechani sm invol ved in the formation of col o ured
products is a lso proposed.
a solution of potassium ferroc yanide ( 167 mL, 0 . I M)
was slowly added to the copper ch loride solution (500
mL, 0 . 1 M) under stirring conditions . The reaction
mixture was then heated at 60°C on a water bath for
2-3 h and allowed to stand for 24 h at roo m
temperature. The precipitate obtained was filtered and
washed th oroughly with distilled water and dried in
an ove n at 60°C. The dri ed produc t was ground and
1.97
..
17. 72
~
c
0
Q
~
"
0:
2.50
Experimental Procedure
Preparation of copper hexacmnoferrate (/I)Copper hcxacya noferrate(II) was pre pared by th e
7
fo ll owing meth od reported by Kourim et al. In bri e f,
" For correspondence
Timq(rr Jtn )~
Fig. 1-Gas chromatogram o f an iii ne products
ALAM eta/.: CONV ERSIO N OF AN ILIN ES TO OLI GOMERS
23 1
80
60
m/z
-- ~
Fig. 2-M ass spectrum of anil ine product
1.98
30.12
3.12
Fi g. 3-Gas chromatogram of p-toluidine product s
sieved to I 00 mesh size . T he purity o f copper
hexacyanoferrate(IT) was checked by comparin g Xray data of th e compl ex. The rela tive inte ns ity data
and interplanne r spacing, d, were in good agreeme nt
with reported va lues 18 .
Oxidation
of
amines
by
copper
hexa cyanoferrat e( //)- Oxidation of ani I in e, ptoluidine and p -c hloroaniline was carri ed out by
adding buffered amine solution ( I 0 mL, I o·' M) to 0 . 1
g of copper hexacyan oferrate(IT) each time . The
required alkal ine pH 7-9, of the reac tion medium is
maintained usi ng borax buffer. T he suspension s were
shaken using Expo Shaker initially for I h a nd then
allowed to equilibrate wi th intermittent shakin g at
fixed ti me intervals . Redd ish brown coloured products
were depos ited on the surface of copper
hexacyanofe rrate( II) w ithin 72 h. T hese coloured
products were e xtracted with the he lp of be nzene. The
co loured products soluble in benzene or acetone were
separated with separatin g funne l and
were
concentrated for GC-MS and JR studi es .
Sw f ace area measurement-B .E.T. me th od was
used to determin e the suti -ace area o f copper
hexacy an oferrate(II) . In thi s technique, th e surface
a rea is determined by phy sica l ad sorpti on of N 2 at its
boi lin g point. Valu e of surface area of copper
1
hexacyanoferrate (II) is fou nd to be 444.7 m 2g- •
Characterization-Analyses
of
the
reaction
products were performed on a Shi mad zu gas
c hromatograph coupled d irect ly to a S hi mad zu QP 2000 quad ru po le mass spectrome ter system.
Infrared spectra of ox id ati on produ c ts have been
recorded on KBr pe ll ets usin g Perkin - E lme r F TIR
seri es-1 600 spectroph oto me ter.
Results and Discussion
19
Se ve ral authors -22 ha ve shown that aromatic
mol ecules give rise to oli go me ric or polymeri c
compounds on clay surface. It may be reasonable to
assume that anilines behave simil arly on the surface
232
INDI AN 1. CHEM. TECHNOL. , SEPTEM BER 2000
100
91
;,!
20
u
~
"~c
100
<
J~,~J:J;~;·~h~~Qtll,;lc;L~Ll6r1-,-2rio' -. -r'2~0' 'z~_u,T ~
.
--.--r-,
J17
60
40
20
Fi g. 4- Mass
1.92
~ pcc trum
of p -to lui dine prod uct
29.48
·r
I LN - o - -Nll
¢_¢
Oll" l llt'u,fe(CNIJ
·211".-l c'
l!N - o - -NH
Cydic Tetramr:r
Tt me ( mm}~
Sch eme - l
Fig. 5-Gas chro matogra m of p -chlo roanil inc produ cts
of metal hexacyanoferrate (II). Reac tio ns of aniline,
p-tolui dine and p-chl oroanil ine with copper
hexacya noferrate (II) were studied over a wide pH
range (7-9). It was found that reaction of all th e three
ammes with copper hexacyanoferrate(TI) was
appreciab le only in alkali ne med ium (p H - 8). In
acidic medi um, no noticeab le reacti on too k place.
Further, the reaction when carri ed out in basic
medium, the desired prod ucts were fo rmed wi th in 72
h, whereas it took about 30 days in case of neu tral
soluti on.
ALAM el a/.: CONVERSION OF AN ILINES TO OLIGOMERS
233
127
100BO-
&0
BO -
GO
4020
I
:;!oI
I
l~D I
I
I
Jo
I
I
I
420
I
I
I
I
440
I
I
'
I
460
I
50 0
m/z~
Fig. 6-Mass spectrum of p-chloroanilinc product
0 "l•<<"'·)
c_F'\
·1\'H l ~~~'
~
- ~U.-2c
P.,-~
C _j=\_N•• ~ li •.C o:\H
_
ct-Q-~"H, o" 'i:~;:<("''.J, cJO~NOcl
Nitrcnc
Nitrene
1
I
II
CloN~JI: oCI ~";;,'~";:'''"'· 1 ct-Q-1\H- "HOC!
4, 4"·dichioroazobenzene
'-------···--S~hemc-
Scheme- 2
Characterization-Fi g. I shows c hromatogra m of
aniline products. o btained by the react ion of copper
hexacyanofe rrate(Il). Two peaks were found wi th
retenti on times (R.T. ) of 2 .60 and 17.72 min . Peak
with retenti on time 2.60 min was for starting mate rial
i.e . ani line, whereas, 17.72 m in corres ponds to main
ox id ation product. GC-MS anal ys is of the peak with
3_ _ _ _ _ _ _ _
j
R.T. "" 17.72 min showed a compound with mol ar
mass mlz. "" 364 ( I 00 %) and resembles to tetramer of
ani line (Fig. 2). Some o ther high mass peaks observed
m the fragme ntation pattern were 351 (8.4% ),
2~5( 15.4% ), 272 (28 .0o/r ), 260( I 0 . 1% ), l 81 ( 14.8%)
,md 93(4.7 %). The observed masses are in accordance
with the fragmentat ion pattem of proposed aniline
tetramer by electron bombardment that takes pl ace in
the ion source of the mass spectrometer. No reaction
prod uct was fo und when alkaline buffered an il in e
so lutions
were
kep t
w ithout
copper
hexacyanoferrate(II) even after 240 h. Thi s shows th at
anilines do not interact with buffer. From th e infrared
stu d ies, sin gle N-H stretchin g of med ium intensity is
o bserved at 3407 e m·' . A band at 151 6 em·' is due to
the presence of 8 N-H . Sharp hand of ary l vC-N is
INDIAN J. CHEM. TECHNOL. , SEPTEMBER 2000
234
1
1
found at 1363 cm· and a band around 827 cm- shows
the p-substitution in benzene ring. On the basis of
mass spectra and IR studies, the most probable
23
structure and tentative mechanism are proposed
(Scheme-l) .
Tetramer of aniline is formed through nitrene
intermediate. Nitrene formation involved two-proton
and two-electron transfer reaction. Cu(II) changes to
Cu(I) state during the process which is also a stable
24
state . Further, this electron deficient specie being
attacked by another aniline molecule in the presence
of OH- ions give rise to a dimer and the process
co ntinues till the formation of a tetramer.
The oxidation product of p-toluidine gave two well
defined and well
separated peaks 111 gas
chromatogram with R.T. of 3.12 and 30.12 min
(Fig.3). Mass spectrum of the peak \-vith R.T. at 30.12
min showed molar mass mlz = 317( 100% ), which
corresponds to trimer of p-toluidine (Fig. 4) . Some
high mass fragments observed were 300(42%),
284(13 .3%), 226(7.7 %), 209(20.8 %), 11 5(17.5 %),
107 (2 1.7%), 91(59.5 %) and at 77(49.1 %). Above
fragment masses resembled with possible fragment s
of a trimer. Peak with R.T. of 3. 12 min corresponded
139(1.3%), 127(100%) ,
1 11(8 .~ % ) ,
92(29.1 %) and
75( 10.3 %).
Infrared spectrum of p-chloroaniline oxidati on
product showed a well defined and very sharp peaks
at 1596, 1445, 1422 cm-
1
due to -N=N- bond .
Probable structure and tentative mechanism is given
in Scheme 3.
Conclusions
It is observed that Cu 2[Fe(CN) 6] reacts with al l the
p-toluidine
and
pthree
anilines
(anil ine,
ch loroani line) to give a coloured product. Aniline was
found to polymerize to a cyclic tetramer, whereas, ptoluidine and p-chloroaniline afforded their trimer and
dimer, respectivel y. It is important to note th at these
reactions occurred only in alkaline medium at pH 7-9.
Copper which is in its oxidation state (II) in
Cu 2 [Fe(CN)6] possibly changes to another stable
oxidation state 2-l (I).
Acknowledgement
One of the authors (Tanveer Alam) is thankful to
the University Grants Commission , New Delhi , for
fin ancia l support.
to the starti ng material , i.e. p-tolu idine.
IR spectrum of trimer showed a symmetri c vN-H
bands at 3276 cm-1 and antisymmetric vN-H at 3370
1
cm- indicati ng th e presence of amin e group.8N-H
band is fou nd at 1621 cm-1 and vC-N at 1360 cm- 1,
1
C-H st retchin gs at 2928 and 2858 cm- are also seen
1
in the spectrum . Band at 804 cm- shows that the psubstitution is a benzene rin g. Tentative mechanism
involved and possible structure of trimer product is
shown in Scheme 2.
Reaction products of p-chloroanili ne were
separated on gas chromatograph (Fig. 5). T wo maj or
peaks were found in gas chromatogram. Peak with
retention time 3.87 min corresponded to starting
material i.e . p-chloroaniline, whereas, the second peak
with retention time of 29.48 min corresponded to the
main oxidation product. A clear peak on GC-MS
correspond in g to peak with retention time 29.48 min .
showed rnolar mass m/z = 251 (24.2%) for a dimer of
p-chloroaniline (Fig. 6) . Other fragmentation products
of a dimer were observed at mlz 216(1 1.1% ),
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