Regioselective Synthesis of Palm-Based Sorbitol Esters as Biobased Surfactant by Lipase from Thermomyces lanuginosus in Nonaqueous Media

This paper describes the regioselective production of palm-based sorbitol monoesters via esterification catalyzed by Lipozyme^® TL IM (Thermomyces lanuginosus lipase adsorbed onto silica gel, Novozymes, Inc., Franklington, NC, USA). Effects of various reaction parameters including types of solvent, substrate molar ratio, molecular sieve and lipase concentration, temperature, reaction time, and fatty acid chain length were investigated. Approximately 76% conversion of sorbitol to sorbitol esters was achieved within 24 h under optimal conditions: sorbitol (0.4 M), fatty acid (0.8 M), 20 wt% Lipozyme^® TL IM in 100 mL tert-butanol at 55 °C for 24 h in the presence of 25 wt% 3 Å molecular sieve as water absorbent. The reactions were conducted in an orbital incubator shaker at a shaking rate of 200 rpm. Lipozyme^® TL IM was highly regioselective, esterifying exclusively at sorbitol's primary hydroxyl groups, producing 1-O- and 6-O-sorbitol monoesters. The biocatalyst also exhibited substrate selectivity toward shorter chain acyl donors, with caprylic acid exhibiting the highest conversion of sorbitol. In addition, Lipozyme^® TL IM was reused up to four successive reaction cycles without significant loss of activity. The biocatalytic process reported in this paper is a one-step process to produce biobased surfactants that does not involve the use of toxic or expensive solvents that are commonly employed for derivatization of sugars, or pre-derivatization of the substrates molecules.