Acetic Anhydride → N-Acetyl-3-nitrobenzamide

A solution of 3-nitrophenylcarboxamide (2 g) in 125 ml of dry methylene chloride was cooled to 0° C. and mixed with 1.25 ml of acetic anhydride and 2.1 g of 4-N,N-dimethylaminopyridine. The reaction mixture was warmed to room temperature and stirred for 1 hour. Additional amounts of 4-N,N-dimethylaminopyridine (809 mg) and acetic anhydride (1.25 ml) were added to the reaction mixture and stirring was continued overnight. The reaction mixture was diluted with 300 ml of methylene chloride and was washed with 60 ml of 5% citric acid solution. The organic extracts were dried, concentrated in vacuo, and the residue was chromatographed on silica gel (chloroform-methanol, 97:3 v/v) to yield 500 mg of the title compound in pure form.