3-Aryl-1-benzoylthioureas with α-bromoketones in water form 2-N-benzoyl-3-arylthiazol-2(3H)-imines, not 3-aryl-l-benzoylimidazoline-2- thiones

Article abstract of DOI:10.3184/030823407X196719

The products obtained by the reaction of 1-benzoyl-3-phenylthioureaswith a-bromoketones in water in the presence of triethylamine are not imidazoline-2-thiones as reported (J. Chem. Res. 2005, 689-690); rather they are thiazol-2-imine derivatives.

Full text of DOI:10.3184/030823407X196719

1
36 RESEARCH PAPER
MARCH, 136–137
JOURNAL OF CHEMICAL RESEARCH 2007
3
2
2
-Aryl-1-benzoylthioureas with a-bromoketones in water form
-N-benzoyl-3-arylthiazol-2(3H)-imines, not 3-aryl-1-benzoylimidazoline-
-thiones
C.B. Singh, Siva Murru, Veerababurao Kavala and Bhisma K. Patel*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
The products obtained by the reaction of 1-benzoyl-3-phenylthioureas with a-bromoketones in water in the presence
of triethylamine are not imidazoline-2-thiones as reported (J. Chem. Res. 2005, 689–690); rather they are thiazol-2-
imine derivatives.
Keywords: thiazol-2-imines, imidazoline-2-thiones, reactions in water, thioureas, a-haloketones
1
Recently we have reported that the products of reaction of
benzoyl-3-phenylthioureas with bromine and acetone or other
enolisable ketone in the presence of triethylamine are thiazol-
2
-imine derivatives and not imidazoline-2-thiones as earlier
2
claimed. Experimental evidence in favour of our interpretation
included crystal structure determinations of three of the
products. The first step of the thiazolimine formation involves
the reaction of the 1-benzoyl-3-phenylthioureas with the in
situ generated a-bromoketones. We were surprised to see that
when an analogous reaction was performed in water with a
preformed a-haloketone, it was reported to give imidazoline-
3
2
-thione derivatives. Water as a reaction medium has special
effects; it is known to accelerate the reaction rates and even to
4
alter the reaction path in some cases. We were thus interested
to discover whether water has any special role in this particular
case, or whether it is just another error of identification.
Results and discussion
When 1-benzoyl-3-(4-chlorophenyl)thiourea (1a) (5 mmol)
was reacted with a-bromoacetone (5 mmol) in water (20 ml)
in the presence of triethylamine (5 mmol) and was heated at
Fig. 1 ORTEP view of compound 2a
Ar1
1
00°C for 15 minutes, according to the experimental procedure
3
S
of Wang et al., the product isolated was identical in all respects
1
13
(m.p, IR, H NMR and C NMR) to that reported by the
1
Ar2
O
Ar CO
C
N
5
-8
earlier workers. However, X-ray crystallographic analysis
N
H
N
H
(
Fig. 1) revealed the product as having the thiazolimine
Ar2
1
∆
1
skeleton (2a) analogous to those of our recent report, and not
the imidazoline-2-thione derivative as previously stated.
S
N
R
3
H O
2
+
BrCH COR
2
This is not an isolated instance of the thiazolimine skeleton
being formed in aqueous medium. When 1-benzoyl-3-
2
phenylthiourea (1b) was treated with a
 -bromoacetone under
identical conditions, the product obtained (2b) was identical
1
13
Scheme 1
in all respects (m.p., IR, H NMR and C NMR) to that
3
reported. The structure of 2b has already been confirmed as
Table
1 Thiazolimines (2) from thioureas (1) and
a-bromoketones (R = Me, Ph) in water (Scheme 1)
having the thiazolimine skeleton by X-ray crystallographic
analysis.1 Again, when 1-benzoyl-3-phenylthiourea (1b)
and 1-(3-bromobenzoyl)-3-phenylthiourea (1c) were reacted
separately with a-bromoacetophenone and a-bromoacetone,
they gave products 2c and 2d respectively. Products 2c and 2d
Thiourea
Ar1
Bromo-
ketone
Product
Ar2
R
1
13
were again found to be identical (m.p., IR, H and C NMR)
to the structures which were earlier confirmed as having
thiazolimine structures by single crystal X-ray analysis.
In conclusion, we have unambiguously proved that
the product obtained by the reaction of three 1-benzoyl-
1a
1b
Ph
Ph
Ph
4-ClC6H4
Ph
Me
Me
Ph
2a
2b
2c
2d
1
1
b
c
Ph
1
3-BrC H4
Ph
Me
6
3
-phenylthioureas with α-bromoketones in the presence
Experimental
of triethylamine in an aqueous medium are thiazolimine
derivatives, not imidazole-2-thiones as reported earlier. We
believe that all other structures reported by Wang et al. can
be expected to have thiazole and not imidazole rings.
3
IR spectra were recorded in KBr on a Nicolet Impact 410
spectrophotometer. NMR spectra were recorded in CDCl3 with
tetramethylsilane as internal standard for H NMR (400 MHz) and
3
1
13
CDCl solvent as the internal standard for C NMR (100 MHz).
3
Melting points were recorded on Buchi B-545 melting point
apparatus. Crystal data were collected with a Bruker Smart Apex-II
*
Correspondent. E-mail: patel@iitg.ernet.in
PAPER: 06/4460

JOURNAL OF CHEMICAL RESEARCH 2007 137
CCD diffractometer using graphite monochromated MoKa radiation
l = 0.71073 Å) at 298 K.
polarisation effects. Absorption corrections were applied with the
program SADABS. The structure was solved by direct methods
implemented in SHELX-9716 program and refined by full-matrix
least-squares methods on F2. All non-hydrogen atomic positions
were located in difference Fourier maps and refined anisotropically.
The hydrogen atoms were placed in their geometrically generated
positions.
(
3
-Aryl-N(2)-benzoylthiazol-2(3H)-imines (2a–d)
To a suspension of 1-benzoyl-3-arylthiourea (5 mmol) in water
20 ml) were added the a-bromocarbonyl compound (5 mmol)
(
and triethylamine (5 mmol). The mixture was heated under reflux
and the completion of reaction (45 min) was monitored by thin
layer chromatography. After cooling the crude product was filtered
B.K.P and C.B.S acknowledge the support of this research
from DST (SR/S1/OC-15/2006) New Delhi and CSIR
off and recrystallised from EtOH: H O (4:1). For single crystal
2
X-ray diffraction analysis a sample was recrystallised from EtOAc–
hexane (4:1).
0
1/1964/04/EMR-II. Thanks are due to CIF IIT Guwahati for
NMR spectra, and to DST FIST for XRD facility.
N(2)-Benzoyl-3-(4-chlorophenyl)-4-methylthiazol-2(3H)-imine
3
(
(
2
1
2a): M.p. 213–-215°C (Lit.
4-chlorophenyl)-4-methyl-1,3-dihydro-2H-imidazole-2-thione, m.p.
11–212°C). IR (KBr): 708, 797, 835, 907, 1017, 1089, 1171, 1272,
for reported 1-benzoyl-3-
Received 6 February 2007; accepted 26 February 2007
Paper 07/4460
doi:10.3184/030823407X196719
-
1 1
343, 1462, 1492, 1563, 1598 cm . H NMR (400 MHz, CDCl ):
3
References
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3
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3
1
2
3
4
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8
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PAPER: 06/4460