Enzymatic aminolysis of lactones in aqueous miniemulsion: Catalysis through a novel pathway

Lipase-catalyzed aminolysis of lactones under aqueous conditions usually leads to the hydrolysis of the ester bond with only a minor content of the corresponding amide. However, the aminolysis of pentadecanolide (PD) and hexadecanolide (HD), respectively, with oleylamine (OA) in aqueous miniemulsion under optimized conditions (temperature, concentration of enzyme, reaction time) yields >90% amide. Kinetic investigations performed with OA and PD reveal that the lipase catalyzes a novel reaction pathway, i.e., the hydrolysis of a lactone followed by the amidation requiring 30 min and 8 days reaction time, respectively. The demands of a high amount of lipase as well as the long reaction time are caused by the low reactivity of the carboxylic group and the formation of salt with the amine. Similar reactions were performed with PD and other amines such as dodecyl, decyl, octyl, benzyl and hexyl amine resulting the analogous amide compounds.