662
Z. Karimi-Jaberi, B. Pooladian
Table 2 Comparison of results using B(HSO4)3 with other catalysts for synthesis of symmetrical bisamides
Entry
Conditions
Time
Yield/%
Reference
1
2
3
4
5
6
CF3SO3H (0.04 equiv.), CH2Cl2, 46 °C
p-TSA (0.1 mmol), solvent-free, 100 °C
H3BO3 (0.3 mmol), toluene, reflux
0.25–48 h
1 h
67–99
85–99
38–92
44–94
67–91
83–96
[13]
[16]
16–70 h
15–40 h
10–360 min
15–45 s
[17]
Phosphotungstic acid (0.3 mmol), toluene, 110 °C
SiO2–BaCl2 (0.025 g), solvent-free, 100 °C
B(HSO4)3 (0.015 g), solvent-free, 100 °C
[18]
[19]
This work
Experimental
concentrated and allowed to yield the desired product as
white crystals.
All chemicals were commercially available and used
without further purification. Melting points were deter-
mined in open capillary tubes. IR measurements were
carried out using KBr pellets on a Shimadzu FTIR spec-
trometer. 1H (400 MHz) and 13C (100 MHz) NMR spectra
were recorded on a Bruker Avance 400 spectrometer in
DMSO-d6 as a solvent. The elemental analysis was per-
formed with an Elementar Analysensysteme GmbH
VarioEL CHNS mode. The progress of reactions was fol-
lowed with thin-layer chromatography (TLC) using silica
gel 60 GF245 precoated sheets 20 9 20 cm, layer thickness
0.2 mm (E-Merck) and were visualized by UV light at
254 nm wavelength.
N,N0-(2-Methoxyphenylmethylene)dibenzamide
(3c, C22H20N2O3)
White crystals; IR (KBr): vꢀ = 3,296, 2,926, 1,647, 1,511,
1
1,484, 1,050, 649 cm-1; H NMR (400 MHz, DMSO-d6):
d = 3.83 (3H, s, CH3), 6.98 (1H, t, J = 7.6 Hz, CH), 7.05
(1H, d, J = 8.4 Hz, ArH), 7.19–7.20 (m, 1H, ArH), 7.31–
7.56 (m, 8H, ArH), 7.92 (4H, d, J = 7.2 Hz, ArH), 8.89
(2H, d, J = 2 Hz, 2 NH) ppm; 13C NMR (100 MHz,
DMSO-d6): d = 55.6, 56.1, 111.5, 120.4, 128.0, 128.3,
128.6, 129.6, 131.8, 134.5, 134.6, 157.3, 165.8 ppm.
N,N0-(3-Methylphenylmethylene)dibenzamide
(3e, C22H20N2O2)
White crystals; IR (KBr): vꢀ = 3,286, 3,028, 1,653, 1,549,
Preparation of tris(hydrogensulfato)boron [B(HSO4)3]
1,484, 707 cm-1 1H NMR (400 MHz, DMSO-d6):
;
d = 3.38 (3H, s, CH3), 7.04 (1H, t, J = 7.6 Hz, CH),
7.14 (1H, s, ArH), 7.28–7.59 (9H, m, ArH), 7.94 (4H, d,
J = 7.6 Hz, ArH), 9.02 (2H, d, J = 7.6 Hz, 2 NH) ppm;
13C NMR (100 MHz, DMSO-d6): d = 21.6, 59.1, 124.1,
127.5, 128.0, 128.7, 128.8, 129.0, 132.0, 134.3, 137.8,
140.7, 165.9 ppm.
A 50 cm3 suction flask was equipped with a constant
pressure dropping funnel. The gas outlet was connected to
a vacuum system through an adsorbing solution (water) and
an alkali trap. Boric acid (1.55 g, 25 mmol) was charged in
the flask and 8.74 g chlorosulfonic acid (ca. 5 cm3,
75 mmol) was added dropwise over a period of 1 h at room
temperature. HCl evolved immediately. After completion
of the addition, the mixture was shaken for 1 h, while the
residual HCl was eliminated by suction. Then the mixture
was washed with diethyl ether to remove the unreacted
chlorosulfonic acid. Finally, 7.0 g of a grayish solid
N,N0-(4-Bromophenylmethylene)dibenzamide
(3g, C21H17BrN2O2)
White crystals; IR (KBr): vꢀ = 3,265, 2,923, 1,649, 1,543,
1,506, 720 cm-1
;
1H NMR (400 MHz, DMSO-d6):
d = 6.99 (1H, t, J = 7.6 Hz, CH), 7.44–7.61 (10H, m,
ArH), 7.93 (4H, d, J = 7.2 Hz, ArH), 9.07 (2H, d,
J = 7.2 Hz, 2 NH) ppm; 13C NMR (100 MHz, DMSO-
d6): d = 58.9, 121.3, 128.0, 128.8, 129.3, 131.6, 132.1,
134.1, 140.1, 166.1 ppm.
1
material was obtained (93 % yield). H NMR (400 MHz,
acetone-d6): d = 12.22 ppm [27, 28].
General procedure for the preparation of symmetrical
bisamides 3a–3z
N,N0-(2,6-Dichlorophenylmethylene)dibenzamide
(3o, C21H16Cl2N2O2)
Aldehyde (1 mmol), amide (2 mmol), B(HSO4)3 (0.05
mmol), and 0.006 g silica gel were mixed and the mixture
was stirred and heated in an oil bath at 100 °C for appro-
priate time. Completion of the reaction was indicated
by TLC. After the reaction was completed, ethanol was
added and the heterogeneous catalyst was isolated from
the reaction mixture by simple filtration. The filtrate was
White crystals; IR (KBr): vꢀ = 3,269, 2,943, 1,640, 1,534,
1,510, 715 cm-1
;
1H NMR (400 MHz, DMSO-d6):
d = 7.37 (1H, t, J = 8 Hz, CH), 7.47–7.58 (10H, m,
ArH), 7.92 (3H, d, J = 7.2 Hz, ArH), 9.07 (2H, d,
J = 6.0 Hz, 2 NH) ppm; 13C NMR (100 MHz, DMSO-
d6): d = 58.6, 128.1, 128.7, 130.6, 132.0, 134.1, 134.2,
134.4, 135.4, 166.0 ppm.
123