BACKGROUND: The conversion of carboxylic esters to amides can be accomplished efficiently by enzymatic catalysis. Amidation of benzyl acetate with n-butyl amine was studied in non-aqueous media using immobilized lipases. RESULTS: The activities of immobilized lipases, Novozym 435, Lipozyme RM IM and Lipozyme TL IM were evaluated in the synthesis of n-butyl acetamide, among which Novozym 435 was the best. The process was optimized by studying various process parameters. Benzyl acetate conversion of 46% was achieved in 8 h for a mole ratio of 3:1 of n-butyl amine to benzyl acetate with 3.67 g L-1 Novozym 435 in toluene at 55 degrees C. A model based on an ordered bi-bi mechanism fitted the initial rate data very well and the rate constant and inhibition constants were calculated by non-linear regression analysis. The initial rate studies showed that the Michaelis constant for benzyl acetate was low indicating high affinity between the enzyme and the reactant. CONCLUSION: A novel, efficient and environmentally benign enzymatic process is reported for the synthesis of n-butyl acetamide. This method is general and can be used to synthesize analogous compounds in optically enriched form, since it is difficult to make such amides directly from carboxylic acids and amines by purely chemical means. The theoretical predictions and experimental data matched very well. (C) 2008 Society of Chemical Industry