H. Valizadeh, M. Ahmadi / C. R. Chimie 15 (2012) 1077–1080
1079
medium in this procedure. Although the literature
4. Experimental
enumerates a number of procedures for conversion of
aldehydes to esters, the simplicity, solvent-free conditions,
and inexpensiveness of our procedure makes it a practical
alternative.
4.1. General information
All reagents were purchased from Merck Company and
used without further purification. Infrared spectra were
recorded in KBr and were determined on a Perkin Elmer FT-
IR spectrometer. 1H NMR spectra were recorded on a
Bruker Avance AC-300 MHz using TMS as internal stan-
dard. All melting points measured in open glass-capillaries
using Stuart melting point apparatus.
3. Selected spectroscopic-data
4-Cyanobenzoic acid methyl ester (2a): white solid; IR
(KBr) (
NMR (300 MHz, CDCl3):
n
max/cmÀ1): 2229 (CN), 1718 (C O), 1600 (C C); 1H
d
8.16–8.13 (d, 2H, J = 7.2 Hz),
7.76–7.74 (d, 2H, J = 7.2 Hz), 3.96 (s, 3H).
4-Cyanobenzoic acid ethyl ester (2b): white solid; IR
4.2. Preparation of 1-butyl-3-methylimidazolium azide
(KBr) (
1H NMR (300 MHz, CDCl3)
n
max/cmÀ1): 2230 (CN), 1719 (C O), 1602 (C C);
d
8.16–8.13 (d, 2H, J = 7.1 Hz),
1-Butyl-3-methylimidazolium chloride was prepared
from the reaction of N-methylimidazole with n-butylchlor-
ide at 80 8C under neat conditions. Sodium azide
(46 mmol) was added to a solution of this freshly prepared
ionic liquid (40 mmol) in dichloromethane (18 mL) and
stirred for 20 h at room temperature. The suspension was
filtered to remove the precipitated sodium chloride salt
and the organic layer was washed with water (5 Â 8 mL)
until no precipitation of AgCl occurred in aqueous phase on
addition of a concentrated AgNO3 solution. The solvent and
other volatile materials were removed from organic layer
in vacuo and the resulting ionic liquid was stirred with
activated charcoal for 12 h, after which the ionic liquid was
passed through a short alumina column(s) (acidic and/or
neutral) to give a colorless ionic liquid, which was dried at
60 8C in vacuo for 24 h or until no visible signs of water
present in the IR spectrum. Yields generally 80–85%. IR
7.76–7.74 (d, 2H, J = 7.1 Hz), 4.46–4.39 (q, 2H), 1.44–1.40
(t, 3H).
4-Cyanobenzoic acid n-propyl ester (2c): yellow solid; IR
(KBr) (
NMR (300 MHz, CDCl3):
n
max/cmÀ1): 2227 (CN), 1725 (C O), 1609 (C C); 1H
d
8.17–8.14 (d, 2H), 7.77–7.74 (d,
2H), 4.35–4.3 (t, 2H, J = 6.8 Hz), 1.85–1.78 (m, 2H), 1.07–
1.02 (t, 3H, J = 7.2 Hz).
4-Cyanobenzoic acid n-butyl ester (2d): light yellow
solid, IR (KBr) (
(C C); 1H NMR (300 MHz, CDCl3):
n
max/cmÀ1): 2232 (CN), 1719 (C O), 1611
d
8.16–8.13 (d, 2H,
J = 7.3 Hz), 7.77–7.74 (d, 2H, J = 7.3 Hz), 4.39–4.35 (t, 2H,
J = 6.8 Hz), 1.80–1.73 (m, 2H), 1.58–1.45 (m, 2H), 1.02–0.98
(t, 3H, J = 7.6 Hz).
4-Nitro-benzoic acid methyl ester (2e): light yellow
solid; IR (KBr) (
(NO2), 1608 (C C); 1H NMR (400 MHz, CDCl3):
n
max/cmÀ1): 1718 (C O), 1339 and 1519
d
8.33–
8.31 (d, 2H, J = 7.2 Hz), 8.23–8.20 (d, 2H, J = 7.2 Hz), 3.98 (s,
3H).
(KBr): 2120, 1649, 1613, 1529, 1353, 1200 cmÀ1
;
1H NMR
(400 MHz, CDCl3) 1.15 (3H, t, –CH3), 1.48 (2H, m, CH2),
d
4-Nitro-benzoic acid ethyl ester (2f): light yellow solid; IR
1.80 (2H, m, CH2), 3.85 (3H, s, N–CH3), 4.01 (2H, t, –N–CH2),
7.24 (1H, d, Ar–H), 7.45 (1H, d, Ar–H), 9.21 (1H, broad, Ar–
H). 13C NMR (100 MHz, CDCl3) 12.30, 19.1, 24.4, 36.4, 38.7,
124.1, 127.0, 142.8. Anal. Calcd (%) for C8H15N5: C, 53.02; H,
8.34; N, 38.64. Found (%): C, 53.12; H, 8.36; N, 38.61.
(KBr) (
1610 (C C); 1H NMR (300 MHz, CDCl3)
n
max/cmÀ1): 1719 (C O), 1339 and 1519 (NO2),
d: 8.31–8.28 (d, 2H,
J = 7.1 Hz), 8.22–8.21 (d, 2H, J = 7.1 Hz), 4.46–4.41 (q, 2H),
1.46–1.41 (t, 3H, J = 7.2 Hz).
4-Nitro-benzoic acid n-propyl ester (2g): yellow solid; IR
(KBr) (
n
max/cmÀ1): 1719 (C O), 1341 and 1520 (NO2),
4.3. Oxidative esterification of arylaldehydes using
[bmim]N3, general procedure
1600 (C C); 1H NMR (300 MHz, CDCl3):
d
8.31–8.28 (d,
2H, J = 7.2 Hz), 8.23–8.20 (d, 2H, J = 7.2 Hz), 4.36–4.32 (t,
2H, J = 6.8 Hz), 1.86–1.79 (m, 2H), 1.07–1.02 (t, 3H,
J = 7.4 Hz).
Arylaldehyde (25 mmol) and [bmim]N3 (75 mmol) and
alcohol (75 mmol) were mixed thoroughly and stirred at
50–60 8C. The completion of reaction was monitored by
TLC using (EtOAc/petroleum ether 1:7) as eluent and the
product was isolated via preparative chromatography from
EtOAc/petroleum ether as eluent.
4-Nitro-benzoic acid isopropyl ester (2h): solid; IR (KBr)
(n
max/cmÀ1): 1719 (C O), 1345 and 1525 (NO2), 1604
(C C); 1H NMR (300 MHz, CDCl3):
d 8.30-8.27 (d, 2H,
J = 7.4 Hz), 8.22–8.19 (d, 2H, J = 7.4 Hz), 4.36–4.32 (t, 2H,
J = 6.8 Hz), 1.86–1.79 (m, 2H), 1.55 (m, 1H), 1.42–1.140 (d,
6H, J = 7.2 Hz).
Acknowledgement
4-Nitro-benzoic acid n-butyl ester (2i): light yellow solid;
IR (KBr) (
1601 (C C);1H NMR (300 MHz, CDCl3):
n
max/cmÀ1): 1719 (C O), 1343 and 1529 (NO2),
The partial financial assistance from the Research Vice
Chancellor of Azarbaijan Shahid Madani University is
gratefully acknowledged.
d
8.30–8.27 (d, 2H,
J = 7.3 Hz), 8.22–8.19 (d, 2H, J = 7.2 Hz), 4.41–4.36 (t, 2H,
J = 7.6 Hz), 1.81–1.74 (m, 2H), 1.53–1.45 (m, 2H), 1.02–0.97
(t, 3H, J = 7.8 Hz).
References
3-Nitro-benzoic acid methyl ester (2j): light yellow
n
max/cmÀ1): 1718 (C O), 1340 and 1524
[1] J. Otera, Esterification: Methods, Reactions and Applications, Wiley,
New York, 2003.
[2] R.C. Larock, Comprehensive Organic Transformations, VCH, New York,
1989.
solid; IR (KBr) (
(NO2), 1608 (C C); 1H NMR (300 MHz, CDCl3):
8.24 (d, 2H, J = 7.1 Hz), 8.22–8.18 (d, 2H, J = 7.1 Hz), 4.00
d
8.28–
(s, 3H).
[3] R. Lerebours, C. Wolf, J. Am. Chem. Soc. 128 (2006) 13052.