Decomposition of benzoylthioureas into benzamides and thiobenzamides under solvent-free conditions using iodine-alumina as the catalyst and its mechanistic study by density functional theory

Article abstract of DOI:10.1039/c4nj02021a

The breaking down of benzoylthioureas to benzamides and thiobenzamides in a single route using iodine-alumina as the catalyst under solvent-free conditions is highlighted. Results show that when an electron donating group, such as the methyl or methoxy group, is at the para-position of the aryl group of 1, benzamide (2) is the favoured product. When an electron withdrawing group, such as the chlorine or nitro group, is at the para-position of the aryl group of 1, thiobenzamide (3) is the favoured product. From the study of the reaction mechanism, it may be postulated that the formation of benzamide is due to the migration of the aryl group, whereas the formation of thiobenzamide may be due to the migration of the phenyl group. Thus, a new method for the formation of benzamides and thiobenzamides was developed.

Full text of DOI:10.1039/c4nj02021a

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Decomposition of benzoylthioureas into
benzamides and thiobenzamides under
solvent-free conditions using iodine–alumina as
the catalyst and its mechanistic study by density
functional theory†
Cite this:DOI: 10.1039/c4nj02021a
Lokendrajit Nahakpam,a Francis A. S. Chipem,a Brajakishor S. Chingakhamb and
Warjeet S. Laitonjam*a
The breaking down of benzoylthioureas to benzamides and thiobenzamides in a single route using
iodine–alumina as the catalyst under solvent-free conditions is highlighted. Results show that when an
electron donating group, such as the methyl or methoxy group, is at the para-position of the aryl group of
1, benzamide (2) is the favoured product. When an electron withdrawing group, such as the chlorine or
nitro group, is at the para-position of the aryl group of 1, thiobenzamide (3) is the favoured product. From
the study of the reaction mechanism, it may be postulated that the formation of benzamide is due to the
migration of the aryl group, whereas the formation of thiobenzamide may be due to the migration of the
phenyl group. Thus, a new method for the formation of benzamides and thiobenzamides was developed.
Received (in Porto Alegre, Brazil)
12th November 2014,
Accepted 20th December 2014
DOI: 10.1039/c4nj02021a
www.rsc.org/njc
catalyst for various organic transformations because of its
inexpensive, non-toxic, ready availability and eco-friendly nature.12
Introduction
Amides and thioamides are important for the synthesis of various It has high tolerance to air and moisture that can be removed from
natural products as well as intermediates for the synthesis of reaction systems easily, and thus has also been explored as a useful
organic compounds.1 In general, amides can be prepared from reagent in organic synthesis.13 Molecular iodine is known to form
their corresponding ketoximes by the Beckmann rearrangement2,3 electron donor–acceptor addition complexes on reacting with
and by the coupling of carboxylic acids with amines.4,5 In most organo-sulfur compounds14 and it is thiophilic in nature.15 Recently,
cases, thioamides are prepared by the thionation of the corres- solvent-free organic synthesis using inorganic supports has become
ponding amide analogues by Lawesson’s reagent.1b,c,6 The a popular method16 and attracted immense interest as an environ-
thionation of benzamides with Lawesson’s reagent was accom- mentally benign methodology, because it often leads to high yields,
plished in refluxing chlorobenzene, which is a toxic chemical.1b clean reactions, and shorter reaction times. In continuation of our
The Beckmann rearrangement generally requires a strong acid, work on the clean conversion of thioureas into 2-(N-arylamino)
high reaction temperatures, harsh reaction conditions and results benzothiazoles under solvent free conditions,17 we herein report a
in the production of unwanted by-products.7 Several methodologies simple and efficient process for the conversion of benzoylthioureas
to check the reaction conditions, such as in a liquid phase,8 in a to benzamides and thiobenzamides using iodine–alumina as the
vapor phase,9 in supercritical water,10 and in ionic liquids,11 have catalyst without any solvent. The method (Scheme 1) is simple with
been developed. However, the drawbacks in such methods are the high yields and easy for isolation of the products from the reaction
use of toxic solvents, expensive reagents, long reaction times, low mixture.
yields and the production of considerable amounts of by-products.
In recent years, molecular iodine (I2) has emerged as a useful
Results and discussion
a Department of Chemistry, Manipur University, Canchipur, Imphal - 795003,
To optimize the reaction conditions, N-2-pyridinyl-N0-benzoyl-
thiourea (1a) was used as a model substrate for the reaction
with iodine–alumina (I2–Al2O3). A few experiments were carried
Manipur, India. E-mail: warjeet@manipuruniv.ac.in, warjeet@yahoo.com;
Fax: +91-0385-2435145; Tel: +91-0385-2435093
b Institute of Bioresources & Sustainable Development, Takyelpat-795001, Imphal,
Manipur, India
out with different solvents at varied reaction temperatures and
mol% of catalyst, as illustrated in Table 1. The reaction was first
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4nj02021a
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Scheme 1 Decomposition of benzoyl thioureas, 1, into benzamides, 2, and thiobenzamides, 3.
Table 1 Optimization of the reaction conditions for the preparation of 2aa
As the optimal condition was established, the scope and
limitations of the reaction scheme were investigated on different
substituted benzoylthioureas. In a typical procedure, iodine–alumina
(20 mol%) was added to benzoylthiourea 1 (1 mmol) whereby the
reaction mixture was grounded using a motor and pestle, stirred for
30 seconds and irradiated in a microwave, MW (10–20 min, 100 W)
without any solvent to give products 2 and 3. Various substituted
benzoylthioureas were reacted with iodine–alumina (20 mol%)
under MW irradiation without any solvent, and all the reactions
proceeded smoothly and gave the corresponding N-substituted
benzamides 2a–k and thiobenzamides 3b–k in good to excellent
isolated yields (Table 2). When N-2-pyridinyl-N0-benzoylthiourea was
used as the substrate, the benzamide derivative was found to be
the only product (Table 2, entry 1). However, when N-phenyl-N0-
benzoylthiourea was reacted under the same reaction conditions, a
mixture of benzamide 2b and thiobenzamide 3b (Table 2, entry 2)
was obtained with an overall yield of 94%. Similarly, mixtures of
N-substituted benzamides (2c–k) with an overall yield of 30–96% and
thiobenzamides (3c–k) with an overall yield of 17–53% were obtained
from the corresponding thioureas (Table 2, entries 3–11).
Catalyst
Entry (mol%) Temperature (1C) Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
10
10
10
10
10
10
10
10
20
30
20
20
20
30
30
80
80
Reflux
180
100
Reflux
Reflux
Reflux
180
H2O
No reaction
H2O : CH3CN (1 : 1) No reaction
H2O No reaction
H2O : CH3CN (1 : 1) Trace
CH3CN
DMF
DMSO
Toluene
CH3CN
CH3CN
DMF
No solvent
No solvent
63
42
45
28
74
65
58
82
96
9
10
11
12
13
110
100 (MW)
a
b
N-2-Pyridinyl-N0-benzoylthiourea (1 mmol), solvent (10 mL). Isolated
yield.
Density functional calculations were also performed to study
carried out in water by stirring 1a with iodine–alumina (10 mol%) the reactions. All the structures were optimized by the hybrid
as the catalyst at room temperature. The reaction failed to give the density functional B3LYP using the segmented all-electron
desired product even when the reaction time was extended up to relativistically contracted Def2-TZVP(-df) basis set with the help
48 h (Table 1, entry 1). The desired product could not be obtained of ORCA. The calculations show that the formations of both
when water : acetonitrile (1 : 1) was used as the solvent by keeping benzamide and the thiobenzamide products with the byproducts
the same reaction conditions (Table 1, entry 2). Therefore, the same as isothiocyanate and isocyanate, respectively, are endothermic.
reaction was tried under reflux conditions with different solvents The formation of benzamide and isothiocyanate involves lower
(Table 1, entries 3–8). Only traces of the target product could be energy (Table 3). This indicates that out of the two reactions, the
obtained (Table 1, entry 4) when water : acetonitrile (1 : 1) was used. formation of the benzamide product is the thermodynamically
It was found that the yield obtained was increased (63% yield) favoured reaction although it is observed from the experimental
when acetonitrile was used alone (Table 1, entry 5) but the yield results that both products are formed except in the o-pyridinated
decreased when the reaction was carried out in other solvents starting molecule where only the energetically favoured benzamide
(Table 1, entries 6–8). To increase the yield, we looked for different product is formed.
reaction conditions. Increasing the catalytic amount from 10 to
The plausible mechanism for the formation of benzamides
20 mol% resulted in the increase of the yield. To our delight, the and thiobenzamides is shown in Scheme 2. To understand the
starting materials disappeared and desired product, N-(pyridin-2- mechanistic pathway, the two most probable iodide intermediates
yl)benzamide 2a, was formed in good yield (74% yield) (Table 1, A and B, formed after the reaction with molecular iodine (I2)
entry 9), and there was little difference in the yield on increasing molecule, were considered (Scheme 2 and Table 4). The I–I bond
the catalytic amount from 20 to 30 mol% (Table 1, entry 10). When in molecular iodine is often known to be perturbed by thiones and
the reaction was performed under solvent-free conditions at 110 1C form iodides.14a The formation of the iodide intermediate through
with 20 mol% of the catalyst, the yield was found to be 82% the oxygen atom is ruled out because of its relatively high energy
(entry 12). We carried out the reaction under microwave irradiation compared to those of intermediates A and B (ESI†). To the best of
(10 min, 100 W) without any solvent and it was found that the our knowledge, examples of the O–I bond formation of molecular
product was obtained in good yield (96%) (entry 13). Thus, the iodine with ketones are not found in the previous reports. The
reaction of benzoylthioureas with iodine–alumina (20 mol%) under results show that the intermediate (A) has the lowest energy, which
microwave (MW) irradiation without any solvent was found to be indicates that it is the most probable intermediate. The results
the optimized reaction conditions.
further show that for all the reactions theoretically considered, the
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Table 2 Synthesis of N-substituted benzamides–thiobenzamides from N-aryl-N0-benzoylthioureasa
Product (%)
Entry
1
Ar
2
3
Time (min)
10
Yieldb (%)
96c
2
10
94
3
4
5
20
18
15
85
82
88
6
7
8
18
20
15
78
80
84
9
20
78
10
20
16
76
82
11
a
b
c
Aryl substituent. Overall yield of the mixture. Absolute yield of 2a.
intermediate (A) has the lowest energy, except for the p-chlorinated strength of different bonds were considered based on the Mayer
molecule, which indicates that it is the most probable intermediate. bond order,18 which indicates the number of electron pairs that
To study the possibility of breaking the molecular backbone, the constitute a bond. When considering the backbone structure,
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Table 3 Relative energy and energy of reaction of the products
Table 4 Relative energies of different intermediates for the parent and
p-chlorinated molecules
Product
Relative energy (kcal)
Energy of reaction (kcal)
Unsubstituted
benzoylthiourea
p-Chlorinated
benzoylthiourea
o-Pyridine
2a
3a
0
2.16
9.25
11.42
Relative
energy
Relative
energy
Intermediate (kcal)
Unsubstituted benzoylthiourea
Structure
Intermediate (kcal)
2b
3b
0
1.56
5.17
6.73
A
B
0.0
0.5
A_p-Cl
B_p-Cl
0.2
0.0
o-Methyl
2c
3c
0
1.90
5.56
7.46
p-Methyl
2d
3d
0
1.45
5.27
6.72
p-Chloro
2g
3g
0
1.68
5.21
6.89
product (Table 3). The formation of benzamide occurs through the
intermediate A by the migration of the aryl group as the C1–N2
bond order is the least in intermediate A (Scheme 2).
C1–N2 has the least Mayer bond order in intermediate A while
C5–C6 has the least bond order in the intermediate B (Table 5).
In case of the p-chlorinated molecule, which has an electron
withdrawing substituent at the para-position of the aryl group,
the intermediate B is the energetically most favored intermediate.
This indicates that the migration of the phenyl group in p-chlori-
nated molecule to attack the thiocarbonyl carbon is the favored
step, as shown in Scheme 2, which on further rearrangement gives
the product thiobenzamide (3g). The proposed steps are supported
by the experimental results where the thiobenzamide is the major
product (Table 2). The probable reason for the formation of an
appreciable amount of the benzamide product (2g), although it is
not the favored step mechanistically, could be that the benzamide
product is thermodynamically more stable than the thiobenzamide
For other substituted molecules also, C5–C6 has the least
bond order in the intermediate B, as mentioned earlier. This
explains that the formation of the thiobenzamide product is
due to the migration of the phenyl group following similar
steps as in the p-chlorinated molecule. However, when the
electron withdrawing p-chlorinated aryl group is replaced by
the p-methylated aryl group, the benzamide product (2d) is the
major one. The reason for the reaction in this case could be that
the formation of the benzamide product is preferred by breaking
the C1–N2 bond in intermediate A than the mechanistically
favored step by breaking the C5–C6 bond in intermediate B (as in
the p-chlorinated molecule). This is so because the intermediate
A has lower energy than B. It is also interesting to note that when
the electron donating group methyl is at the ortho-position in the
Scheme 2 Proposed mechanism for the formation of benzamides and thiobenzamides.
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Table 5 Mayer bond order for selected bonds for the parent and the p-
chlorinated molecules
used for column chromatography. The completion of the reac-
tions was monitored by TLC using silica gel 60 F254 (0.25 mm).
The melting points were recorded using a Buchi M-560 melting
point apparatus and are uncorrected.
Mayer bond order
Intermediates
C1–N2
N2–C3
C3–N4
N4–C5
C5–C6
General procedure for the synthesis of N-substituted
benzamides (2) and thiobenzamides (3) from benzoylthioureas
(1)
Unsubstituted benzoylthiourea
A
B
0.9092
1.1027
1.1663
1.8061
1.5143
0.9953
1.3996
1.1750
0.9238
0.9085
p-Chlorinated benzoylthiourea
Iodine–alumina (0.71 mmol of iodine adsorbed using 1.8 g of
neutral alumina, i.e. 20 mol%) was added to N-substituted-N0-
benzoylthioureas (1 mmol) and the mixture was ground thor-
oughly using a motor and pestle. The mixture was stirred for
30 s until they were mixed thoroughly. The reaction mixture
was then irradiated without any solvent in a microwave for 10–
20 min at 100 1C using the irradiation power of 100 W. The
reaction progress was monitored by TLC. After the reaction was
complete, the mixture was allowed to cool to room temperature
and then poured into cold water. The product was purified by
silica gel column chromatography (EtOAc–hexane) to give the
corresponding amide. The structures of the products 2b,19a–d,21
2c,19e,22 2d,19f,22 2f,19g 2g,19f 2h,19h,23 2i,19i 2j,19e 2k,19j,24 3b,25
3d,26 3f,27 3g,28 3h,29 3i,1b 3j 1b and 3k 1b were confirmed by
A_p-Cl
B_p-Cl
0.9138
1.1197
1.1550
1.7945
1.5238
1.0017
1.3918
1.1714
0.9254
0.9103
aryl group, the intermediate A, which has lowest energy, has the
lowest bond order at C5–C6 bond. This makes the breaking
of the C1–N2 bond in intermediate A less probable, thus
rendering the formation of the thiobenzamide product (3c) the
major product. A similar result is obtained in the o-pyridinated
molecule.
Conclusion
In conclusion, we have developed a new process for the
preparation of amides and thioamides from benzoyl thioureas
under solvent free conditions precluding the use of any additional
Lewis or Brønsted acids as a cocatalyst, toxic organic solvents, and
without producing any significant corrosive waste. This versatile
synthetic method is expected to find valuable applications in
various areas, particularly as intermediates for the synthesis of
heterocyclic compounds. The DFT studies showed that the for-
mation of benzamide was due to the migration of the aryl group (in
intermediate A), whereas the formation of thiobenzamide may be
due to the migration of the phenyl group (in intermediate B). It was
found that the formation of the benzamide product is the
thermodynamically favoured reaction, although it is observed
from the experimental results that both products are formed,
except in N-2-pyridinyl-N0-benzoylthiourea where only the energeti-
cally favoured benzamide product is formed. We have developed a
new method for the formation of benzamides and thiobenzamides,
which were generally derived by the thionation of benzamides with
Lawesson’s reagent.
1
comparison of their mps, TLC, IR, H NMR and 13C NMR data
with authentic samples obtained commercially or prepared by
previously reported methods. The residue of the catalyst was
washed with water and dried under vacuum to afford the
catalyst, which was used in subsequent runs.
N-(Pyridin-2-yl)benzamide (2a)
White solid (190 mg, 96%); mp 79–81 1C (lit.20 80–83 1C); IR
(nmax, KBr) 3217, 3022, 1674, 1527, 1435, 1308, 777 cmꢀ1
;
1H NMR (300 MHz, CDCl3) dH 9.06 (br s, 1H), 8.41 (1H, d, J =
8.4 Hz), 8.17 (1H, d, J = 4.5 Hz), 7.94–7.92 (2H, m), 7.78–7.73
(1H, m), 7.59–7.46 (3H, m), 7.06–7.02 (1H, m); 13C NMR
(75 MHz, CDCl3) dC 165.9, 151.6, 147.8, 138.5, 134.3, 128.8,
127.2, 119.9, 114.2. Mass (m/z) 198, anal. calcd for C12H10N2O:
C, 72.71%, H 5.08%, N, 14.13%. Found: C, 72.76%, H, 5.16%,
N, 14.39%.
N-Phenylbenzamide (2b)
White solid (115 mg, 59%); mp 162–164 1C (lit.19 163–164 1C);
IR (nmax, KBr) 3344, 3053, 1656, 1535, 1323, 752, 690 cmꢀ1
;
1H NMR (400 MHz, CDCl3) dH 7.88–7.86 (3H, m), 7.66–7.55
(3H, m), 7.53–7.27 (3H, m), 7.18–7.14 (2H, m); 13C NMR
(100 MHz, CDCl3) dC 165.9, 137.9, 135.0, 129.0, 128.7, 127.1,
Experimental section
General information
All of the reagents were of commercial grade and purified 124.5, 120.3. Mass (m/z) 197, anal. calcd for C13H11NO: C,
according to the established procedures. NMR spectra were 79.19%, H 5.58%, N, 7.12%. Found: C, 79.27%, H, 5.47%,
recorded using 300 MHz and 400 MHz spectrometers using N, 7.23%.
CDCl3 as the solvent. 1H NMR and 13C NMR chemical shifts
are given in d (parts per million) relative to tetramethylsilane
N-(o-Tolyl)benzamide (2c)
(0 ppm). IR spectra were recorded in KBr discs using a Shimadzu White solid (67.5 mg, 32%); mp 140–142 1C (lit.19 143–144 1C);
FT-IR-8400 spectrometer. Elemental analyses (C, H and N) were IR (nmax, KBr) 3247, 3058, 1651, 1487, 1310, 747 cmꢀ1; 1H NMR
carried out using a Perkin-Elmer 2400 analytical instrument. All (300 MHz, CDCl3) dH 9.81 (br s, 1H), 8.09 (2H, d, J = 7.2 Hz), 7.64
microwave (MW) irradiation reactions were carried out using a (1H, t, J = 7.5 Hz), 7.52 (2H, t, J = 7.8 Hz), 7.28–7.23 (3H, m), 7.12
Microwave synthesis system (Monowave 300 Anton Paar) instru- (1H, t, J = 6.9 Hz), 2.42 (3H, s); 13C NMR (75 MHz, CDCl3) dC
ment at 100 W output power. Silica gel (60–120 mesh size) was 168.7, 135.7, 133.4, 132.1, 130.4, 128.9, 128.3, 127.9, 126.6,
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124.5, 18.1. Mass (m/z) 211. Anal. calcd for C14H13NO: C, N-(4-Methoxyphenyl)benzamide (2k)
White solid (116 mg, 51%); mp 152–155 1C (lit.21 147–157 1C);
IR (nmax, KBr) 3328, 3055, 2835, 1665, 1523, 1276, 850,
79.62%, H 6.16%, N, 6.64%. Found: C, 79.85%, H, 6.28%,
N, 6.51%.
798 cmꢀ1 1H NMR (300 MHz, CDCl3) dH 7.72–6.90 (9H, m),
;
3.94 (3H, s, OCH3); 13C NMR (75 MHz, CDCl3) dC 165.2, 157.6,
138.2, 129.1, 128.9, 124.4, 121.6, 116.4, 55.8. Mass (m/z) 227.
Anal. calcd for C14H13NO2: C, 74.00%, H 5.73%, N, 6.17%.
Found: C, 74.13%, H, 5.68%, N, 6.10%.
N-(p-Tolyl)benzamide (2d)
White solid (132 mg, 63%); mp 153–155 1C (lit.19 156–157 1C);
IR (nmax, KBr) 3266, 3054, 1658, 1345, 688 cmꢀ1 1H NMR
;
(300 MHz, CDCl3) dH 8.06 (3H, d, J = 7.2 Hz), 7.72 (1H, d, J =
8.1 Hz), 7.60–7.44 (4H, m), 7.15 (1H, t, J = 7.8 Hz), 7.02 (1H, s),
2.32 (3H, s); 13C NMR (75 MHz, CDCl3) dC 166.2, 136.0, 133.0,
132.2, 131.6, 128.9, 128.4, 128.2, 126.2, 125.5, 124.4, 21.3. Mass
(m/z) 211. Anal. calcd for C14H13NO: C, 79.62%, H 6.16%, N,
6.64%. Found: C, 79.85%, H, 6.28%, N, 6.51%.
N-Phenylbenzothioamide (3b)
Yellow solid (74 mg, 35%); mp 101–104 1C (lit.22 102 1C);
IR (nmax, KBr) 3210, 3034, 1551, 1238, 698 cmꢀ1 1H NMR
;
(400 MHz, CDCl3) dH 7.86 (br s, 1H), 7.42–7.10 (10H, m); 13C
NMR (100 MHz, CDCl3) dC 179.8, 136.9, 129.6, 128.9, 127.1,
125.3, 119.9. Mass (m/z) 213. Anal. calcd for C13H11NS: C,
73.20%, H 5.20%, N, 6.57%. Found: C, 73.58%, H, 5.46%,
N, 6.82%.
N-(2,4-Dimethylphenyl)benzamide (2e)
White solid (124 mg, 55%); mp 170–173 1C; IR (nmax, KBr) 3268,
3024, 1647, 1520, 1310, 818 cmꢀ1; 1H NMR (400 MHz, CDCl3) dH
7.92 (br s, 1H), 7.88–7.58 (2H, m), 7.57–7.52 (3H, m), 7.50
(1H, s), 7.27–7.06 (2H, m), 2.33 (3H, s), 2.31 (3H, s); 13C NMR
(100 MHz, CDCl3) dC 165.2, 142.9, 133.8, 131.8, 131.2, 128.9,
127.6, 127.0, 21.8, 17.6. Mass (m/z) 225. Anal. calcd for
N-(o-Tolyl)benzothioamide (3c)
White solid (121.5 mg, 53%); mp 150–152 1C; IR (nmax, KBr)
3331, 3148, 1526, 1236, 766 cmꢀ1; 1H NMR (400 MHz, CDCl3) dH
7.96 (br s, 1H), 7.90–7.69 (2H, m), 7.55–7.50 (2H, m), 7.28–7.11
(5H, m); 13C NMR (100 MHz, CDCl3) dC 182.5, 135.2, 131.2,
128.4, 127.8, 127.0, 17.8. Mass (m/z) 227. Anal. calcd for
C
15H15NO: C, 79.97%, H 6.71%, N, 6.22%. Found: C, 79.99%,
H, 6.67%, N, 6.29%.
C
14H13NS: C, 73.97%, H 5.76%, N, 6.16%. Found: C, 73.76%,
N-(m-Tolyl)benzamide (2f)
H, 5.57%, N, 6.02%.
White solid (118 mg, 56%); mp 124–125 1C (lit.19 117–118 1C);
N-(2,4-Dimethylphenyl)benzothioamide (3e)
IR (nmax, KBr) 3270, 3059, 2915, 1650, 1537, 1308, 781 cmꢀ1
;
1H NMR (300 MHz, CDCl3) dH 7.87 (2H, d, J = 6.7 Hz), 7.79
(1H, br s), 7.58–7.49 (4H, m), 7.46–7.23 (2H, m), 6.98 (1H, d, J =
7.1 Hz); 13C NMR (75 MHz, CDCl3) dC 165.8, 136.4, 135.2, 133.7,
131.7, 131.3, 129.8, 128.8, 126.6, 124.3, 21.6. Mass (m/z) 211.
Anal. calcd for C14H13NO: C, 79.62%, H 6.16%, N, 6.64%.
Found: C, 79.85%, H, 6.28%, N, 6.51%.
White solid (80 mg, 33%); mp 142–144 1C; IR (nmax, KBr) 3198,
1
3023, 1553, 1219, 1146, 808 cmꢀ1; H NMR (400 MHz, CDCl3)
dH 8.08 (br s, 1H), 7.43–7.21 (4H, m), 7.08–7.03 (4H, m), 2.47
(3H, s), 2.26 (3H, s); 13C NMR (100 MHz, CDCl3) dC 181.3, 138.0,
135.2, 131.9, 127.9, 127.7, 21.1, 17.9. Mass (m/z) 241. Anal. calcd
for C15H15NS: C, 74.65%, H 6.26%, N, 5.80%. Found: C, 74.43%,
H, 6.06%, N, 5.66%.
N-(4-Chlorophenyl)benzamide (2g)
N-(4-Chlorophenyl)benzothioamide (3g)
White solid (69 mg, 30%); mp 202–204 1C (lit.19 199–200 1C); IR
Yellow solid (124 mg, 50%); mp 160–162 1C (lit.23 149 1C); IR
(nmax, KBr) 3248, 3055, 1665, 1532, 1317, 798 cmꢀ1 1H NMR
;
(nmax, KBr) 3211, 3020, 1593, 1537, 1249, 823 cmꢀ1 1H NMR
;
(300 MHz, CDCl3) dH 10.61 (br s, 1H), 7.93–7.88 (2H, m), 7.70–
7.64 (3H, m), 7.58–7.53 (2H, m), 7.38 (2H, d, J = 8.94 Hz); 13C
NMR (75 MHz, CDCl3) dC 167.0, 136.2, 133.9, 132.3, 131.5,
129.3, 129.1, 127.5, 125.5, 124.6. Mass (m/z) 231. Anal. calcd for
(300 MHz, CDCl3) dH 9.12 (br s, 1H), 7.89 (2H, d, J = 7.35 Hz),
7.70–7.64 (3H, m), 7.58–7.53 (2H, m), 7.38 (2H, d, J = 8.73 Hz);
13C NMR (75 MHz, CDCl3) dC 178.5, 133.9, 132.2, 131.5, 129.3,
129.0, 127.5, 125.3. Mass (m/z) 247. Anal. calcd for C13H10ClNS:
C, 63.02%, H 4.07%, N, 5.65%. Found: C, 63.16%, H, 4.13%,
N, 5.83%.
C
13H10ClNO: C, 67.53%, H 4.33%, N, 6.06%. Found: C, 67.49%,
H, 4.38%, N, 6.13%.
N-(4-Nitrophenyl)benzamide (2h)
N-(4-Methoxyphenyl)benzothioamide (3k)
Yellow solid (85 mg, 35%); mp 200–202 1C (lit.20 198–199 1C); Yellow solid (75 mg, 31%); mp 127–129 1C (lit.24 131–133 1C); IR
IR (nmax, KBr) 3338, 3024, 1656, 1573, 1517, 1306, 1253, 845, (nmax, KBr) 3335, 3064, 2845, 1573, 1242, 750 cmꢀ1
;
1H NMR
790 cmꢀ1; H NMR (400 MHz, CDCl3) dH 9.46 (br s, 1H), 8.05– (300 MHz, CDCl3) dH 7.67 (br s, 1H), 7.54–7.52 (2H, m), 7.37–
8.02 (2H, m), 7.67–7.64 (3H, m), 7.63–7.51 (2H, m), 7.39–7.26 7.27 (2H, m), 7.22–7.14 (2H, m), 7.11–6.94 (3H, m), 3.94 (3H, s,
(2H, m); 13C NMR (100 MHz, CDCl3) dC 165.4, 151.6, 137.2, OCH3); 13C NMR (75 MHz, CDCl3) dC 184.6, 157.6, 147.2, 142.9,
133.4, 132.1, 129.0, 128.9, 127.8, 124.4, 120.5. Mass (m/z) 242. 127.4, 124.1, 122.5, 121.9, 121.3, 117.4, 117.3, 55.8. Mass (m/z)
Anal. calcd for C13H10N2O3: C, 64.46%, H 4.13%, N, 11.57%. 243. Anal. calcd for C14H13NOS: C, 69.14%, H 5.35%, N, 5.76%.
1
Found: C, 64.57%, H, 4.20%, N, 11.43%.
Found: C, 69.19%, H, 5.28%, N, 5.83%.
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Acknowledgements
One of the authors Lokendrajit N. is grateful to UGC, New
Delhi, for the financial support under the scheme of UGC-BSR
Research Fellowship in Science (vide order no. F.4-1/2006(BSR)/
7-230/2009(BSR)). The authors also acknowledge Gauhati Uni-
versity, IIT Guwahati and IISc Bangalore for H NMR and 13C
1
NMR spectral data.
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