Kinetic strategies for selective preparation of amides from diethanolamine have been designed using Novozym 435 lipase as a biocatalyst. Two different routes, direct acylation and transacylation, have been optimized. In n-hexane, the reaction is more selective for formation of the amide by direct acylation, while in dioxane, the O-acylation reaction is highly favored. However, the initial rates of direct acylation and transacylation are both higher in dioxane than in n-hexane because of the low solubilities of both diethanolamine and its corresponding ion-pair complex with the fatty acid.At 30degreesC, the high viscosities of mixtures of diethanolamine with fatty acids limit the extent of reaction and the corresponding yields of the amide. This effect is greater in n-hexane in which the viscosity (5.52 cSt) was four times greater than dioxane. An increase in temperature to 60 degreesC increases the conversion and decreases the viscosity of the n-hexane solution to 0.8-0.9 cSt.At 60degreesC when equimolar amounts of reactants are employed, the transacylation route produces both higher conversions (71-77 mol%) and greater selectivities to the amide (74-94%) than the direct acylation reaction (69-74 mol% conversion and 76-86% selectivity). For both synthesis routes, the volumetric productivity of the reactor is restricted for reactant concentrations above 0.8 M.At 60 degreesC, conversions via the direct acylation reaction can be increased to 92 and 80 mol% in dioxane and n-hexane, respectively. These conversions require using a two-fold excess of diethanolamine. The resultant selectivities are 98 and 100%, respectively. (C) 2003 Elsevier Inc. All rights reserved.