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S. Keshipour, A. Shaabani
selectivity of the reaction [22]. Other strategies toward the synthesis of amides
include the utilization of azides as amine equivalents in the modified Staudinger
reaction [23], hydrative amide syntheses with alkynes [24], and the thio acid/ester
ligation method [25]. Transition-metal-catalyzed carbonylation of alkenes [26],
alkynes [27], and haloarenes [28] with amines have also been employed for the
synthesis of amides. Finally, the direct utilization of aldehydes and alcohols under
oxidative conditions with amines can also serve as an attractive entry to amides [29–32].
In continuation of our efforts to introduce new and efficient strategies for various
aerobic organic transformations [33–37], here we report a new route including
‘‘aerobic hydrolysis of nitriles’’ promoted by Co(II)/Zn in the absence of strong
acids and bases.
Experimental
General
All reagents were purchased from Aldrich or Merck and used without further
purification. Melting points were measured on an Electrothermal 9,200 apparatus.
Identification and quantification were carried out on a Varian model 3,600 gas
chromatograph (Varian Iberica, Madrid, Spain) equipped with a split/splitless
capillary injection port and flame ionization detector (FID).
Typical procedure for the preparation of benzamide from phenylcyanide
in the presence of oxygen
The reaction was carried out in a 100-mL stainless steel autoclave. Phenylcyanide
(0.10 g, 1.00 mmol) was added to a mixture of ethylenediamine (0.12 g, 2.00 mmol),
CoCl2Á6H2O (0.24 g, 1.00 mmol) and Zn (0.07 g, 1.00 mmol) and the vessel was
placed in an autoclave. For some of the reactions that were carried out in solvent,
5 mL of solvent was also added. The autoclave was pressurized to 5.00 atm with O2.
The mixture was stirred in a preheated oil bath at 120 °C for 12 h. Then, the reaction
mixture was cooled to room temperature and the product was purified by column
chromatography on silica gel using n-hexane:CH2Cl2 (1:1) to give the benzamide
1
(88 % yield). Mp 125–127 °C; H NMR (CDCl3, 300 MHz) d = 6.26 (2H, br s,
NH2), 7.43-7.54 (3H, m, CH-Ar), 7.83 (2H, d, 3JHH = 7.6 Hz, CH-Ar).
Typical procedure for the preparation of benzamide from phenylcyanide using
H2O2
To a stirred solution of phenylcyanide (0.10 g, 1.00 mmol) in 10 mL H2O2 (30 %),
ethylenediamine (0.12 g, 2.00 mmol), CoCl2Á6H2O (0.24 g, 1.00 mmol) and Zn
(0.07 g, 1.00 mmol) were added and the vessel was stirred under appropriate
conditions (refluxing or at room temperature). After completion of the reaction, the
product was extracted from the mixture using CH2Cl2 (3 9 5 mL) and analyzed
with GC.
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