A. Khalafi-Nezhad et al. / Tetrahedron Letters 46 (2005) 6879–6882
6881
Table 2. Effect of various solvents on the amidation reaction of
benzoic acid
on silica gel using n-hexane–ethyl acetate (1:1) to obtain
a pure product.
Entry
Solvent
t (min)
Yielda (%)
1
2
3
4
5
6
MeCN
CH2Cl2
Et2O
DMF
EtOAc
Me2CO
60
60
60
60
60
60
40
20
10
5
2
5
Acknowledgements
We acknowledge Shiraz University and Shiraz Univer-
sity of Technology research councils for the partial sup-
port of this work. We also would like to thank Mr. H.
Sajedian Fard for running NMR spectra.
a Isolated yields.
References and notes
In another study, the reaction was examined in several
solvents to compare the reaction times and yields in
both solution and solvent-free conditions. Therefore,
to a solution of benzoic acid (1 mmol), ammonium chlo-
ride (2 mmol) and tosyl chloride (1 mmol) in different
solvents (10 ml) was added triethylamine (4 mmol).
Lower yields were obtained and longer reaction times
were needed in all cases. The results are depicted in
Table 2.
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3. General procedure
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In a test tube, filled with a well ground mixture of car-
boxylic acid (1 mmol) silica-supported ammonium salt
(2 equiv) and TsCl (1 equiv) was added 0.4 g of triethyl-
amine and mixed by a spatula. After 1 min, the reaction
mixture was added to 50 mL ethyl acetate, filtered and
the filtrate was washed with 0.02 N solution of HCl
(2 · 50 mL). The aqueous layer was extracted twice with
ethyl acetate (25 mL). The combined organic layers were
dried over anhydrous MgSO4 and evaporated. The
crude product was purified by column chromatography