Microwave assisted solvent-free synthesis of n-butyl propionate by immobilized lipase as catalyst

Operational simplicity, solvent free media, potential reusability of catalyst and wide functional group tolerance are the advantages for solvent free synthesis under microwave irradiation technique. In the current work, n-butyl propionate was synthesized by esterification of propionic acid with n-butanol using different immobilized enzymes under microwave irradiation vis--vis conventional heating. Commercially available lipases such as Lypozyme RM IM, Lypozyme TLIM and Novozym 435 (Candida antarctica lipase B) were screened for n-butyl propionate synthesis from propionic acid and n-butanol for which Novozym 435 showed the best catalytic activity. n-Butyl propionate is widely used in flavour, painting, enamels, appliance coating and similar processes. In 8 h 92% conversion was achieved at 60 degrees C with 1:12 mol ratio of propionic acid to n-butanol under microwave irradiation. Systematic studies were done to understand mechanism and kinetics of reaction. By studying the Lineweaver-Burk plots it was found that the lines were intersecting at a point, showing that the reaction follows ternary complex mechanism with inhibition by n-butanol.