Ammonolysis of carboxylic esters catalyzed by lipases - Synthesis of fatty acid amides

Lipases (triacyl glycerol hydrolase, EC 3.1.1.3) are stable and rugged enzymes that act? often enantioselectively, on a wide variety of nonnatural reactants. The exploitation of their characteristic features has become an essential part of the synthetic repertoire.(1) We(2) and others(3) recently reported that ammonia acts as an unnatural acyl acceptor (ammonolysis). Carboxylic esters are converted to the corresponding carboxylic amides in essentially quantitative yield in an exothermic and, hence, irreversible reaction. The lipase from Candida antarctica(4) (B type, Novozym 435) emerged from the initial investigations(2) as the catalyst of choice. We wished to extend lipase-catalyzed ammonolysis to the synthesis of fatty acid amides; these are now industrially produced from the fatty acids by a reaction with anhydrous ammonia at approximately 200 degrees C and 345-690 kPa and are primarily used for their lubricating and surfactant properties.(5) A low-temperature enzymatic process would seem advantageous for the synthesis of pure fatty acid amides, particularly the thermally unstable unsaturated ones that, inter alia, dominate the market for refined fatty acid amides. In the present paper, we report the synthesis of fatty acid amides from lipids as well as from the fatty acids by a one-pot procedure.