an infra-red spectroscopic study of some substituted 1,3-thiazolidin-4-ones
TRANSCRIPT
This article was downloaded by: [McGill University Library]On: 18 September 2013, At: 01:47Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
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AN INFRA-RED SPECTROSCOPICSTUDY OF SOME SUBSTITUTED 1,3-THIAZOLIDIN-4-ONESChristopher Richard Joseph Woolston a , John Barry Lee a &Frederick John Swinbourne aa Department of Chemistry, University of Hertfordshire,College Lane, Hatfield, Hertfordshire, AL10 9AD, UnitedKingdomPublished online: 23 Sep 2006.
To cite this article: Christopher Richard Joseph Woolston , John Barry Lee & FrederickJohn Swinbourne (1993) AN INFRA-RED SPECTROSCOPIC STUDY OF SOME SUBSTITUTED 1,3-THIAZOLIDIN-4-ONES, Phosphorus, Sulfur, and Silicon and the Related Elements, 78:1-4,223-235, DOI: 10.1080/10426509308032438
To link to this article: http://dx.doi.org/10.1080/10426509308032438
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Phosphorus, Sulfur, and Silicon, 1993, Vol. 78, pp. 223-235 Reprints available directly from the publisher Photocopying permitted by license only
0 1993 Gordon and Breach Science Publishers S.A. Printed in the United States of America
AN INFRA-RED SPECTROSCOPIC STUDY OF SOME SUBSTITUTED 193-THIAZOLIDIN-4-ONES
CHRISTOPHER RICHARD JOSEPH WOOLSTON,? JOHN BARRY LEE and FREDERICK JOHN SWINBOURNE
Department of Chemistry, University of Hertfordshire, College Lane, Hatfield, Hertfordshire, ALlO 9AD, United Kingdom
(Received July 10, 1992; in final form October 16, 1992)
The infra-red spectra of a series of 2,3-diaryl-1,3-thiazolidin-4-ones were measured and the majority of the absorption bands assigned. The value of the carbonyl stretching frequency was related to the availability of the lone pair on the nitrogen atom of the thiazolidinone ring. The effects of S-oxidation of these compounds on their spectra were examined. The spectra of 3-benzyl-2-phenyl-l,3-thiazolidin- 4-one, 3-butyl-2-phenyl-l,3-thiazolidin-4-one, 5-methyl-2,3-diphenyl-l,3-thiazolidin-4-one and 3-phe- nyl-2-thioxo-l,3-thiazolidin-4-one were also investigated.
Key words: 1,3-Thiazolidin-4-0nes; 1-oxides; 1,l-dioxides; infra-red spectroscopy.
INTRODUCTION
Despite the large number of references, listed in reviews, which discuss the ir spectra of 1,3-thiazoIidin-4-ones with doubly-bonded substituents at C(2)1-3 and a discussion of the factors affecting the carbonyl stretching frequencies of 2,3-disub- stituted and 2,3,5-trisubstituted 1,3-thiazolidin-4-ones by Vigorita and Chimirri,4 no adequate discussion of the ir spectra of the 2,3-diaryl-1,3-thiazolidin-4-ones (1) has appeared in the literature. An investigation of the spectra of these compounds was, therefore, undertaken and was then extended to include the effects of oxidation to the 1-oxides (2) and 1,l-dioxides (3). 3-Benzyl-2-phenyl-l,3-thiazolidin-4-one (4a), 3-butyl-2-phenyl-1,3-thiazolidin-4-one (4b), 5-methyl-2,3-dipheny1-l73-thia- zolidin-4-one ( lv ) and 3-phenyl-2-thioxo-l,3-thiazolidin-4-one (5) were also inves- tigated for comparison.
/~ 2 3-- \
* < 5 S c = O CH W
Z
1 s 2 so 3 so*
?Author to whom correspondence should be addressed.
223
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224 C. R. J. WOOLSTON, J. B. LEE and F. J. SWINBOURNE
2,3-Diaryl-1,3-thiazolidin-4-ones (1): Com- Com- pound W X Y pound W
l a H H H 11 H lb H 4-OMe H l m H lc H 4-Me H In H Id H 3-Me H l o H l e H 3-OMe H 1P H If H 4-C1 H 1q H 1g H 4-Br H l r H lb H 3-F H 1s H l i H 3-C1 H It H U H 3-Br H l u H lk H 4-CN H l v Me
x 3-NOz 4-NOz H H H H H H H H H
Y H H 4-0h 4-0me 4-Me
4-Br 3-Br
4-C1
4-COZH 3-n0z H
2,3-Diaryl-1,3-thiazolidin-4-one-l-oxides (2): Com- Com-
2a H H H O 2e H 4-CI H 0 2b H 4-OMe H 0 2f H 3-Br H 0 2c H 4-Me H O 2g H H 4-OMe 0 2d H 3-OMe H 0 2b H H 3-Br 0
pound W X Y Z pound W X Y z
2,3-Diaryl-1,3-thiazolidin-4-one-l ,l-dioxides (3): Com- pound W X Y Z 3a H H H 0, 3b H 4-Br H 0, 3c H 3-Br H 0,
4a R = Bz
4b R Bu
5
RESULTS AND DISCUSSION
Ir absorption bands characteristic of aromatic C-H out-of-plane bending (680- 900 cm-l), CH2 scissoring (1450-1470 cm-l), aromatic C=C stretching (ca. 1500 and ca. 1600 cm-l), X = O stretching (1640-1735 cm-l), aliphatic C-H stretch- ing (2830-3000 cm-') and aromatic C-H stretching (3020-3130 cm-*) were ob- served in the spectra of nearly all of the compounds investigated. In addition, an assortment of other bands was observed which characterised the functional groups in individual compounds (Tables I-IV).
Aromatic C-H Bending Bands
The arrangement of the C-H out-of-plane bending bands in the 680-900 cm-l region has often been reported as varying with substitution patterns in aromatic
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IR OF 1.3-THIAZOLIDIN-4-ONES 225
systems although the frequency ranges quoted by different authors tend to vary ~ o m e w h a t . ~ - ~ Those quoted by Williams and Fleming6 were found to be present in the spectra of most of the diary1 compounds examined although the number of bands in this region was found to be quite large owing to the presence of two aromatic rings. Tentative assignments of these bands are given in Tables I-IV although in some compounds other weaker bands were present in addition to those tabulated and in the spectra of the S-oxides one of the bands assigned to C-H bending may, in fact, have been due to C-S stretching.
Absorptions in the regions 680-720 cm-' (m-s), 730-770 cm-' (m-s) and ca. 900 cm-' (w-m) were attributed to the five adjacent hydrogens of the monosub- stituted ring.
Generally, more C-H bending bands were observed in the spectra of compounds with a meta-substituted ring than in those of compounds having a para-substituted ring. This was explained by the greater asymmetry of the meta-substituted ring, with the three adjacent and one isolated hydrogen atoms giving rise to bands at 775-810 cm-' (m-s) and 855-880 cm-' (w-m), respectively. In contrast, in the spectra of most para-substituted compounds, these bands were replaced by a single band at 830-850 cm-l (m-s) which tended to occur at a slightly lower frequency in compounds (other than the oxides) with the substituent in the N-ring than in those with it in the C-ring.
No attempt was made to identify the aromatic C-H in-plane deformations in the 950-1225 cm-l region as most of the compounds displayed many bands in this region, ranging in intensity from weak to strong. However, the aromatic C-Me in-plane bending band was identified as a medium band at 300-320 cm-' in the spectra of compounds lc, Id and 2c.
It was not possible to relate substitution patterns to the frequencies of the over- tone and combination band^^,^ at 1650-2000 cm-l as these were very weak and sometimes obscured by the carbonyl absorption.
CH, and CH, Deformation Bands
Bands associated with the symmetrical deformation of the thiazolidinone CH2 group (scissoring) were observed with, usually, medium intensity in the 1450- 1470 cm-' range. Two CH, scissoring bands were observed in the spectra of compounds 4a and 4b, both of which have more than one CH, group. For most of the compounds examined there seemed to be no overlap of the CH, scissoring bands with the aromatic C=C stretching bands discussed below except, possibly, with the weak band in the 1430-1465 cm-' region which has been reported elsewhere5 but whose presence could not be positively demonstrated in the spectra discussed here.
Asymmetrical deformation of the CH, group of methyl and methoxy compounds was observed as the medium band in the 1410-1455 cm-' region. Neither the symmetrical CH3 deformation band nor the CH, rocking band could be identified since the regions in which these bands usually occur (1370-1390 cm-' and 720- 810 cm-l, respectively) were obscured by the presence of other bands. The band at 1310 cm-l (m-s) in the spectrum of compound 4b may have been due to CH, wagging. It seemed likely that the band at ca. 1220 cm-' (m) in the spectra of most of the compounds apart from the oxides was due to twisting of the CH, group.
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TA
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TA
BL
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b In
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a-eF
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see
Tabl
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.
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str.
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1201
11,
b 0
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str.
535m
C- i-p
def
. 102
5111
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m C
--(r
c st
r. 1
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m
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1070
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str.
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lu
i;; m
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IR OF 1,3-THIAZOLIDIN-4-ONES 229
Taylor gives a similar assignment for the band at 1205-1210 cm-l (m) which occurs in the spectra of certain 2-substituted 1,3-thiazolidin-4-0nes.~
Aromatic C=C Stretching Bands
In the spectra of many of the compounds the aromatic C%C stretching bands were observed as two pairs of narrow bands at ca. 1500 cm-I and ca. 1600 cm-I resulting from four skeletal vibrations of the aromatic rings. In most cases, the lower fre- quency pair of bands was the stronger and for each pair the more intense band was usually the one of higher frequency. In a number of cases more than four bands were observed and in others one or more bands were broadened or split into a narrow doublet of bands. This was to be expected in a system with more than one aromatic ring; indeed it was surprising that the spectra of so many of the compounds showed just the four main bands. In several spectra, including that of compound la, only the main two bands at ca. 1500 cm-l and ca. 1600 cm-' were observed and in others some of the bands were probably concealed by other ab- sorptions such as the asymmetrical NO, stretching band of the nitro compounds or the >C=O stretching band.
> C=O Stretching Bands
For all of the compounds the >C=O stretching band was observed as a very strong band in the 1640-1735 cm-l region.
Two bands were observed in the spectrum of compound It with its two carbonyl groups. As the usual >C==O stretching frequency range for aromatic carboxylic acids is 1680-1700 it seemed likely that the higher frequency, stronger carbonyl absorption at 1692 cm-I was due to the carbonyl of the COOH group. This would also be in accord with the fact that acid >C=O absorptions are often somewhat more intense than those due to amides.
V c=o
1690
1680
1670
1660
1
."T" , - 0 . 4 -0 .2 0.0 0.2 0.4 0.6 0.8
Hammet t 's 0 constant
FIGURE 1 Graph of carbonyl stretching frequency, v,,, against Hammett's (T constant for com- pounds with a substituent in the N-aryl ring. (Compounds In and Is were omitted in calculating the line of best fit.)
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TA
BL
E I1
2a
2b
zc
M
2e
Zf
2g
Zh
Infr
a-re
d sp
ectr
a of
the
1-o
xide
s
Aro
mat
ic C
-H
out-
of-p
lane
ben
ding
C
HS
Al c
-H
Com
- as
ym
>w
st
r in
O
ther
A1
Ar
C-H
>S
-O
b d
poun
d a
def
CH
2 sc
Ar
db s
tr
str
OM
e C
-Hst
r st
r st
r
69O
m-s,
710
w-m
, 14
55~-
m
149O
m-s
, 16
80vs
29
10w
-m,
303O
vw
1065
s
68O
m-s
, 750
s, 85
Om
-s
1430
w-m
14
50m
14
85s,
1490
s, 17
08vs
28
30w
-m
2925
w-m
, 30
70w
-m
1050
vs
7551
11, 9
OOw
1595
m
2945
w-m
9Mhu
-m
690m
-s, 7
Wm
, 83
5s
1415
~-m
14
55m
74
Om
, 755
s, 77
0111
-s, 8%
or
91
0w-m
7701
11, 8
95w
-m
7m
, 76
0m.
875w
79
5w-m
14
45~-
m
1460
w-m
700s
, 760
s, 77
Om
-s,
850s
14
6511
1
690m
-s, 7
00s,
87h-
m
8OO
m-s,
14
6011
1 91
Dw
75om
, 770
s; 81
om
!Wow
-m
6901
11,
7OOm
-s,
84O
m-s
72
0111
,7651
11,
8%
1440
m-s
14
55m
-s
7ooS
, 720
111-s
, 87
5w-m
77
5s, 7
95m
14
6011
1-s
900w
-m
1505
s, 15
75m
-s,
1595
111,
1610
111-s
s, 1
595m
-se
14
90
~,~
15
1011
1- 16
96vs
15W
s, 15
9Om
, 16
96vs
16
00m
-s,
1610
111-s
m, 1
600s
1495
, 15
75m
-s,
1595
s
149O
m-s
, 15
05vs
, 15
80w
-n1,
~ 16
05m
1575
m-s
, 158
5111-s
15OO
vs, 1
585~
- 17
04vs
1475
111-s
, 17
06vs
1465
m?,
16
98vs
1480
s, 15
oOm
, 16
86vs
2950
~-m
2930
m,
3070
w-m
10
5Ovs
29
9511
1
284O
w 29
40w
-m,
306O
w 1
mv
s
2930
m.
3075
m
106o
Vs
293o
m
3060
111-
s 10
60vs
2960
w-m
299o
m
2830
w-m
29
10m
-s,
3040
w-m
10
5Ovs
29
9511
1
2910
m-s
, 30
7511
1 10
60vs
29
40m
-s,
2980
m
0
33
? 9 L m m
rn ii a
a-eF
or m
eani
ngs o
f foo
tnot
es se
e T
able
Ia.
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Com
- po
und
Oth
er a
bsor
ptio
ns
Com
- po
und
Oth
er a
bsor
ptio
ns
2a
-
2e
4701
11 o
r 490
m C
4I
str &
rin
g de
f. 11
00s X
-sen
sitiv
e ba
nd.
2h
5101
11 o
r 53
0m C
-0-C
i-p
def
. 102
0s sy
m C
--ct
C
str.
1260
s asy
m
2f
-
C+C
str.
2g
51
0111
or
550m
C-0
-C
i-p
def.
1030
s sym
Ca
st
r. 1
24O
vs as
ym
2c
3001
11 o
r 32
0111
Ar
C-M
e i-p
ben
. C
a
str.
2d
505w
-m o
r 55
Ow
C-0
-C
i-p d
ef m
aski
ng s
ym C
a
str.
1265
s 2h
-
asym
C-0
-C
str.
TA
BL
E I11
Infr
a-re
d sp
ectr
a of
the
1,l-dioxides
E A
r e
Aro
mat
ic C
-H
out-o
f-pl
ane
bend
ing
Com
- >
C=O
A
l C-
H C-
H c
b d
poun
d a
CH
2 sc
Ar
db st
r st
r st
r st
r
3a
690111
, 70
0m-s
, 730
w-
1455
111
1500
m-s
: 16
OOm
16
92vs
28
50w
-m, 2
930m
-s,
3M
h-m
2 K E g 3
m, 7
55m
-s, 8
95w
or
3000
m
905w
3b
69
0s, 7
45m
-s, 8
90w
83
0111
14
55~
-m
1485
s: 15
85m
-s
1700
vs
2930
111,
2995
w-m
30
60~
-m
3c
685s
, 695
s, 7
40s,
775m
-s, 7
95111,
1460
111
148O
m-s
, 150
0s,
1698
vs, 1
716v
s 29
30s.
3ooO
m-s
3060
111
7501
11, 9
00m
81
0m
1580
111,
1595
m-s
"-eF
or m
eani
ngs
of f
ootn
otes
see
Tab
le I
a.
e 0
CA
>so
, >s
o,
Com
- SY
m as
ym
poun
d st
r st
r -
SO2 s
c X
-sen
sitiv
e ba
nd
3a
1130
s. 11
4511
1-s
1325
s, 13
40s
54Sm
or
5701
11
3h
1125
s, 1
135s
13
45vs
56
0111
-s 10
70s
3c
112O
s, 11
4Ovs
13
15vs
, 133
5vs
545m
-s o
r 55
5s
1075
11-s
N
w c
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N
(cl
N
0
P
c
TA
BL
E I
V
Infr
a-re
d sp
ectra
of
com
poun
ds l
v, 4
a, 4b
and
5 ~
~ ~~
~ ~
CH
3 A
r A
r C-
H
asym
C
H2
CH2
>C
==
A1
C-H
C-
H O
ther
C
ompo
und
0-0-
p be
na
def
sc
tw?
Ar
db st
r St
r st
r St
r ab
sorp
tions
lv (W
= M
e,
690m
-s,
710m
, 76
0m-s
, X
= Y
= H
) 4a
69
51x1
, 70
5s,
735w
-m,
4b
710s
. 735
s, 90
0w-m
5 68
55,7
50m
-s,
8801
11
89O
vw o
r 91
5w
755m
, 89S
w
dFor
mea
ning
s of
foo
tnot
es s
ee T
able
Ia.
~ ~~
~~~~
~ ~
1445
m
1455
111
1495
s, 15
9011
1-s
1674
vs
2930
111
3030
111,
3070
111
1455
w-m
, 12
20w
-m
1495
111,
1605
~-m
16
71vs
29
20~
-m
3020
w-m
14
60~
-m
1470
111-s
m
aske
d)
wag
? 14
35s
1450
111-
s, 12
2511
1-s
1500
m (
othe
r ba
nd
1664
vs
2865
m-s
, 292
% 2
955s
30
30w
-m
1310
111-s
C
HI
1450
111
mas
ked
1480
w-m
, 14
9011
1-s,
1734
vs
2910
w-m
, 296
0m
3050
~-m
12
15 - 1
235v
s 15
80~
-m
>C
=S
str?
r
m
rn
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IR OF 1,3-THIAZOLIDIN-4-ONES 233
The splitting of the carbonyl band in the spectra of compounds lk and lq may have been due to conformational effects.
An approximately linear relationship was found between the >C=O stretching frequency (vk0) and Hammett's (+ constant for compounds with a substituent in the N-phenyl group ( r = 0.816; n = 9). Omitting compounds In and 1s gave the improved relationship, ve0 = 2 2 . 1 8 ~ + 1672.5 ( r = 0.943; n = 7) (Figure 1). It was not possible to explain the anomalously low carbonyl stretching frequencies of In and 1s. Although, in the former case, it was tempting to invoke intermolecular hydrogen bonding as part of the explanation, since this was also present for It which correlated well, it seemed likely that other factors were also important.
The above mentioned correlation appeared to suggest that the value of the >C-0 stretching frequency was, to some extent, governed by competition for the N lone pair, with increasing electron withdrawal by the substituent in the N-phenyl group being accompanied by increases in >C=O stretching frequency.
In line with this suggestion, a large increase in >C==O stretching frequency compared with the average value of the diary1 compounds was observed for com- pound 5. This compound showed the highest >C==O stretching frequency of all the compounds examined (1734 cm-l) and this was readily explained by the pres- ence of the electron-withdrawing thioxo group which competes strongly for the N lone pair (I). Replacement of the N-aryl group by a benzyl or butyl group (com- pounds 4a and 4b, respectively) and, hence, removal of any competition for the N lone pair, resulted in >C=O stretching frequencies (1671 and 1664 cm-l, re- spectively) fairly similar to that of the parent compound (la) (1670 cm-l). These findings are in reasonable accord with those of Vigorita and Chimirri who reported similar results for a varied selection of 2,3,5-trisubstituted 1,3-thiazolidin-4-0nes.~
J
C-H Stretching Bands
Aliphatic and aromatic C-H stretching bands were observed as weak to medium bands in the 2830-3000 cm-' and 3020-3130 cm-l regions, respectively, the latter bands generally being somewhat weaker than the former. In all but one of the methoxy compounds, the band at 2830-2840 cm-l (w-m) was identified as C-H stretching in the methyl group.
Other Absorption Bands
In the spectra of the 1-oxides (Table II), the >SO stretching band was observed as a very strong absorption at 1050-1065 cm-l. Since no obvious splitting of this band was observed, this, together with evidence from NMR,'O seemed to indicate that only one isomer was present.
The spectra of the 1,l-dioxides (Table 111) showed medium to strong absorptions due to >SO2 symmetrical stretching at 1120-1145 cm-l and due to >SO2 asym- metrical stretching at 1315-1345 cm-'. Most of these absorptions were split into
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234 C. R. J. WOOLSTON, J. B. LEE and F. J. SWINBOURNE
two bands. The asymmetrical stretching bands were slightly stronger than the symmetrical stretching bands in accordance with their larger fluctuating dipoles. In addition to these stretching bands, a variable intensity band at 545-570 cm-' in the spectra of the dioxides appeared to result from >SO, scissoring.
The spectra of the nitro compounds showed bands due to symmetrical and asym- metrical -NO2 stretching at ca. 1350 cm-l (vs) and ca. 1520 c h - l (vs), respec- tively, C-NO2 stretching at ca. 870 cm-I (m-s) and NO, in-plane bending at ca. 540 cm-l (w-m).
Symmetrical and asymmetrical C-0-C stretching of the Ar-0-Me group of the methoxy compounds were observed as, usually, strong bands at 1020- 1055 cm-l and 1230- 1265 cm-', respectively, the asymmetrical band being the stronger. In addition, in-plane deformation of the C-0-C group generally gave a medium intensity band at 505-550 cm-'.
Evidence for intermolecular hydrogen bonding was seen in the spectra of com- pounds In and It. In the case of the former compound, the OH stretching band was seen at the low value of 3120 cm-I as a broad, medium intensity band, both the low frequency and the width of which indicated the presence of intermolecular association. The broad, medium band with peaks at 1225 and 1240 cm-I (and, possibly, the strong band at 1270 cm-') was probably caused by stretching of the C-OH bond and the medium band at 1360 cm-l by OH deformation. (Socrates" lists both of these bands as combinations of the C-OH stretch and the OH de- formation).
For compound It the OH stretching band at ca. 2500-ca. 3100 cm-l (m) showed the presence of extensive hydrogen bonding, evidence for dimerisation being pro- vided both by the position of this band and by the presence of an 0-H . - * * 0 out- of-plane deformation band at 950 cm-l (w-m, b). The exceptionally low tlc Rf value and partition coefficient of this compound which we found in other experi- ments yet to be reported can, therefore, be explained in terms of the strong in- termolecular hydrogen bonding present between the carboxyl group and the silica or water.
Although somewhat weaker than usual, it seemed likely that the weak to medium 545 cm-I band in the spectrum of compound It was produced by C 0 2 rocking. A weak band with peaks at 615 and 620 cm-l was characteristic of CO, bending in a para-substituted carboxylic acid.
In the spectrum of compound l k the k N stretching band occurred as a medium to strong absorption at 2220 cm-I. In addition, other characteristic bands were seen at 400 cm-' (w) and 555 cm-I (m-s). Socrates indicates that the former band results from in-plane bending of the C - C N bond and the latter band from a combination of in-plane C%N deformation and an out-of-plane deformation of the aromatic ring.12
It seemed likely that the very strong band with peaks at 1215 and 1235 cm-l in the spectrum of compound 5 was the >C=S stretching band. However, because of the very wide range over which >C=S stretching absorptions can occur, this assignment remained questionable.
In the spectra of most of the C1 and Br compounds a sharp X-sensitive band5 was observed at 1065-1100 cm-l (m-s). Although it was not possible to identify positively this band in the spectrum of compound lh, the sharp band at 1210 cm-l (m-s) seemed a likely candidate.
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IR OF 1,3-THIAZOLIDIN-4-ONES 235
The band produced by C-halogen stretching in combination with ring defor- mation was seen as a medium to strong band at 535 cm-l in the spectrum of compound l h and as a medium band in the 450-490 cm-l region in the spectra of several of the chlorine compounds.
EXPERIMENTAL
Compounds la-lu, 2, 3 and 4 were prepared and their identities confirmed as described by us previ- o ~ s l y . ' ~ Compound l v was prepared in a similar way to compounds la - lu except that 2-mercaptopro- panoic acid was used in place of mercaptoethanoic acid.
Compound 5 was prepared by adding mercaptoethanoic acid (0.1 mol) to a solution of phenyl isothiocyanate (0.1 mol) in methanol (100 ml) and warming the mixture to 45°C for 5 min. Cooling and partial evaporation of the resulting solution yielded yellow crystals which were recrystallised to constant melting point from methanol.
Infra-red spectra were obtained using a Pye-Unicam SP3-300 spectrophotometer calibrated against polystyrene at 1601 cm-'. The samples were examined as KBr wafers. Carbonyl stretching frequencies were recorded to -t_ 1 cm-', other frequencies below 2000 cm- to ? 5 cm-' and those over 2000 cm-' to 2 10 cm-'.
ACKNOWLEDGEMENTS
We wish to express our thanks to Dr. W. A. Thomas of Roche Products Ltd., Welwyn Garden City, Hertfordshire for his continued interest in our work and to Dr. A. Krohn, also of Roche Products Ltd., for allowing us to use the statistical program which he had written for use with BBC computers.
REFERENCES
1. 2. 3. 4. 5.
6.
7.
8. 9.
10.
11. 12.
F. C. Brown, Chem. Rev., 61, 463 (1961). G. R. Newkome and A. Nayak, Adv. Heterocycl. Chem., 25, 83 (1979). S. P. Singh, S. S. Parmar, K. Raman and V. I. Stenberg, Chem. Rev., 81, 175 (1981). M. G. Vigorita and A. Chimirri, Ann. Chim. (Roma), 61, (12), 843 (1971). G. Socrates, Infrared Characteristic Group Frequencies (John Wiley and Sons, Chichester, 1980), ch. 11. D. H. Williams and I. Fleming, Spectroscopic Methods in Organic Chemistry (McGraw-Hill Book Co. (UK) Ltd., London, 1980), p. 62. D. W. Brown, A. J. Floyd and M. Sainsbury, Organic Spectroscopy (John Wiley and Sons, Chich- ester, 1988), p. 37. P. J. Taylor, Spectrochim. Acta, 26A, 165 (1970). Reference 5, p. 58. C. R. J . Woolston, J. B. Lee, F. J. Swinbourne and W. A. Thomas, Mag. Res. in Chem., 30, 1075 (1992). Reference 5 , pp. 46-48. Reference 5, p. 39.
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