JOURNAL OF CHEMICAL RESEARCH 2012 211
Table 2 Oxidative desulfurisation of thiobenzamides to ben-
N-Methyl-p-toluamide (2b): Solid, m.p. 145–146 °C (lit.28 143–
145 °C). 1H NMR (500 MHz, CDCl3): δ 7.67 (d, J = 8.0 Hz, 2H), 7.22
(d, J = 8.0 Hz, 2H), 6.30 (bs, 1H), 3.00 (s, 3H), 2.39 (s, 3H) ppm. IR
(KBr): 3338, 1633, 1549, 1508, 1303, 835, 752 cm–1.
zamidesa
4-Bromo-N-methylbenzamide (2c): Solid, m.p. 163–164 °C (lit.29
1
163–164 °C). H NMR (500 MHz, CDCl3): δ 7.65–7.63 (m, 2H),
7.58–7.55 (m, 2H), 6.28 (bs, 1H), 3.00 (s, 3H) ppm. IR (KBr): 3344,
2932, 1639, 1550, 1483, 1322, 839, 750 cm–1.
N, N-Dimethylbenzamide (2d): Solid, m.p. 44–46 °C (lit.30 43–
45 °C). H NMR (500 MHz, CDCl3):31 δ 7.43–7.38 (m, 5H), 3.10
1
Entry
Ar, R1, R2
Yield/%b
(s, 3H), 3.01 (s, 3H) ppm. IR (KBr): 3465, 2934, 1625, 1340, 1087,
736 cm–1.
89 (2a)
N-Isopropylbenzamide (2e): Solid, m.p. 98–100 °C (lit.32 99–
100 °C). 1H NMR (500 MHz, CDCl3): δ 7.77–7.75 (m, 2H), 7.51–7.48
(m, 1H), 7.44–7.41 (m, 2H), 5.98 (bs, 1H), 4.35–4.26 (m, 1H), 1.28 (s,
3H), 1.27 (s, 3H) ppm. IR (KBr): 3299, 2972, 1632, 1535, 698 cm–1.
N-Cyclohexylbenzamide (2f): Solid, m.p. 145–146 °C (lit.1 144 °C).
1H NMR (500 MHz, CDCl3): δ 7.77–7.75 (m, 2H), 7.51–7.48 (m, 1H),
7.44–7.41 (m, 2H), 6.02 (bs, 1H), 4.03–3.95 (m, 1H), 2.06–2.03 (m,
2H), 1.79–1.75 (m, 2H), 1.69–1.65 (m, 1H), 1.49–1.39 (m, 2H), 1.30–
1.20 (m, 3H) ppm. IR (KBr): 3315, 2935, 2853, 1627, 1578, 1533,
1330, 693 cm–1.
1
2
3
4
5
6
7
8
9
Ph, CH3, H (1a)
4-MeC6H4, CH3, H (1b)
4-BrC6H4, CH3, H (1c)
Ph, CH3, CH3 (1d)
Ph, CH(CH3)2, H (1e)
Ph, C6H11, H (1f)
78 (2b)
79 (2c)
71 (2d)
91 (2e)
79 (2f)
84 (2g)
96 (2h)
86 (2i)
85 (2j)
70 (2k)
Null
Ph, Ph, H (1g)
Ph, 4-MeC6H4, H (1h)
Ph, 4-ClC6H4, H (1i)
4-MeC6H4, Ph, H (1j)
4-ClC6H4, Ph, H (1k)
C6H5CH2, CH3, H (1l)
10
11
12
N-Phenylbenzamide (2g): Solid, m.p. 161–162 °C (lit.1 161–163 °C).
1H NMR (500 MHz, CDCl3): δ 7.99 (bs, 1H), 7.88 (d, J = 7.5 Hz, 2H),
7.66 (d, J = 8.0 Hz, 2H), 7.55 (t, J = 7.5 Hz, 1H), 7.48 (t, J = 7.5 Hz,
2H), 7.37 (t, J = 8.0 Hz, 2H), 7.17 (t, J = 7.3 Hz, 1H) ppm. IR (KBr):
3344, 2924, 1656, 1599, 1534, 1438, 751, 691 cm–1.
a Reactions were carried out on a 0.5 mmol scale at 50 °C, TBHP
(0.7 mmol, 70% in water), 10 mol% catalyst for 3h.
b Isolation yields.
N-(p-Tolyl)benzamide (2h): Solid, m.p. 158–159 °C (lit.1 158–159 °C).
1H NMR (500 MHz, CDCl3): δ 7.94 (bs,1H), 7.87 (d, J = 7.5 Hz, 2H),
7.55–7.53 (m, 3H), 7.47 (t, J = 7.8 Hz, 2H), 7.17 (d, J = 8.0 Hz, 2H),
2.35 (s, 3H) ppm. IR (KBr): 3310, 2924, 1648, 1510, 1320, 813,
695 cm–1.
Table 3 Oxidative desulfurisation of thioamides to 1,2,4-
thiadiazolesa
N-(4-Chlorophenyl)benzamide (2i): Solid, m.p. 196–197 °C (lit.33
192–194 °C). 1H NMR (500 MHz, CDCl3): δ 7.88–7.87 (m, 2H), 7.83
(bs, 1H), 7.63–7.61 (m, 2H), 7.60–7.57 (m, 1H), 7.53–7.50 (m, 2H),
7.36–7.35 (m, 2H) ppm. IR (KBr): 3350, 1655, 1519, 1493, 1399,
825, 719 cm–1.
4-Methyl-N-phenylbenzamide (2j): Solid, m.p. 145–146 °C (lit.33
145–147 °C). H NMR (500 MHz, CDCl3): δ 7.91 (bs, 1H), 7.78 (d,
1
Entry
Ar
Yield/%b
J = 8.5 Hz, 2H), 7.66 (d, J = 8.0 Hz, 2H), 7.39–7.36 (m, 2H), 7.29–
7.27 (m, 2H), 7.17–7.14 (m, 1H), 2.43 (s, 3H) ppm. IR(KBr): 3449,
2924, 1650, 1524, 1439, 1321, 747, 689 cm–1.
1
2
3
4
5
6
Ph, 1m
4-CH3OC6H4, 1n
4-FC6H4, 1o
3-CH3C6H4, 1p
3-ClC6H4, 1q
2-thienyl, 1r
79, 3m
90, 3n
56, 3o
63, 3p
78, 3q
78, 3r
4-Chloro-N-phenylbenzamide (2k): Solid, m.p. 201–203 °C (lit.33
191–193 °C). 1H NMR (500 MHz, CDCl3): δ 7.83 (d, J = 8.0 Hz, 2H),
7.77 (bs, 1H), 7.64 (d, J = 7.5 Hz, 2H), 7.48 (d, J=8.0 Hz, 2H), 7.40 (t,
J = 7.5 Hz, 2H), 7.19 (t, J = 7.5 Hz, 1H) ppm. IR(KBr): 3353, 2924,
1639, 1550, 1483, 1322, 839, 750 cm–1.
a Reactions were carried out on a 0.5 mmol scale at r.t., TBHP
(0.7 mmol, 70% in water), 10 mol% catalyst for 0.5h.
b Isolation yields.
3,5-Diphenyl-1,2,4-thiadiazole (3m): Solid, m.p. 89–90 °C (lit.9
91–91.5 °C). 1H NMR (500 MHz, CDCl3): δ 8.43–8.40 (m, 2H),
8.09–8.07 (m, 2H), 7.58–7.49 (m, 6H) ppm. IR (KBr): 1477, 1440,
1330, 760, 707, 682 cm–1.
3,5-Bis(4-methoxyphenyl)-1,2,4-thiadiazole (3n): Solid, m.p. 140–
141 °C (lit.9 139–139.5 °C). 1H NMR (500 MHz, CDCl3): δ 8.35–8.32
(m, 2H), 8.00–7.98(m, 2H), 7.03–7.00 (m, 4H), 3.90 (s, 6H) ppm. IR
(KBr): 2937, 1608, 1476, 1252, 1168, 834, 747 cm–1.
3,5-Bis(4-fluorophenyl)-1,2,4-thiadiazole (3o): Solid, m.p. 185–
186 °C (lit.34 185–186 °C). 1H NMR (500 MHz, CDCl3): δ 8.40–8.37
(m, 2H), 8.07–8.04 (m, 2H), 7.25–7.17 (m, 4H) ppm. IR (KBr): 2925,
1599, 1475, 1233, 833, 744 cm–1.
Experimental
Column chromatography was carried out on silica gel (200–300
mesh). H NMR spectra was recorded on Bruker AMX-500 MHz
1
instrument and the chemical shifts were reported in parts per million
(δ) relative to internal standard TMS (0 ppm) for CDCl3. The peak
patterns are indicated as follows: s, singlet; d, doublet; t, triplet; m,
multiplet. The coupling constants, J, are reported in Hertz (Hz). IR
spectra were determined on a Brucker Tensor 27 spectrometer. Melting
points were uncorrected. All reagents were weighed and handled in air
at room temperature and all reactions were performed without
exclusion of air or moisture.
3,5-Bis(3-methylphenyl)-1,2,4-thiadiazole (3p): Solid, m.p. 56–
1
57 °C (lit.9 55–57 °C). H NMR (500 MHz, CDCl3): δ 8.24 (s, 1H),
8.21 (d, J = 7.5 Hz, 1H), 7.90 (s, 1H), 7.86 (d, J = 7.5 Hz, 1H), 7.44–
7.39 (m, 2H), 7.37(d, J = 7.5 Hz, 1H), 7.32 (d, J = 7.5 Hz, 1H), 2.48
(s, 6H) ppm. IR (KBr): 2918, 1480, 1310, 800, 732 cm–1.
Amide (2a–k) or thiadiazole (3m–r); general procedure
TBHP (0.7 mmol), CuBr (10 mol%) was added to a stirred suspension
of thioamide (1, 0.5 mmol) in 1,2-dichloroethane (1 mL), at 50 °C or
room temperature. The mixture was stirred for the time indicated in
Tables 2 and 3. After completion of the reaction, 1,2-dichloroethane
was removed under reduced pressure. The residue obtained was
purified through silica gel using petroleum ether/ethyl acetate (10:1–
2:1) as an eluent.
3,5-Bis(3-chlorophenyl)-1,2,4-thiadiazole (3q): Solid, m.p.35 130–
1
131 °C (lit. 128–128.5 °C). H NMR (500 MHz, CDCl3): δ 8.40 (s,
1H), 8.29–8.27 (m, 1H), 8.08 (s, 1H), 7.91–7.90 (m, 1H), 7.55–7.53
(m, 1H), 7.50–7.44 (m, 3H) ppm. IR (KBr): 2925, 1467, 1304, 1004,
793, 731 cm–1.
3,5-Bis(2-thiophene)-1,2,4-thiadiazole (3r): Solid, m.p. 92–94 °C
(lit.36 84–86 °C). 1H NMR (500 MHz, CDCl3):37 δ 7.95–7.94 (m, 1H),
7.71–7.70 (m, 1H), 7.60–7.59 (m, 1H), 7.48–7.47 (m, 1H), 7.19–7.15
(m, 2H) ppm. IR (KBr): 1540, 1465, 1414, 1312, 839, 709 cm–1.
N-Methylbenzamide (2a): Solid, m.p. 77–78 °C (lit.28 75–77 °C).
1H NMR (500 MHz, CDCl3): δ 7.78–7.62 (m, 2H), 7.50–7.47 (m, 1H),
7.43–7.40 (m, 2H), 6.42 (bs, 1H), 3.00 (s, 3H) ppm. IR (KBr): 3328,
1638, 1578, 1553, 698 cm–1.