Ionic Liquid-Strengthened Immobilized Rhizomucor miehei Lipase for Catalytic Esterification of Itaconic Acid in Aqueous Media

Dimethyl itaconate (DI), a promising biomass-derived intermediate, cannot be synthesized from itaconic acid (IA) in organisms due to the lack of metabolic pathways. It is necessary to develop a green and high-efficiency method to synthesis DI from IA. In this study, DI was, for the first time, produced from IA in an aqueous medium by an ionic liquid-strengthened enzymatic method. We found that when pretreated by the ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate abmim][PF6]), the pH tolerance range of the lipase shrunk and the hydrolysis activity of it was greatly inhibited, while its esterification activity was not. Moreover, when the [bmim] [PF6]-treated immobilized Rhizomucor miehei lipase (RML, SO mg/mL) was employed in a reaction containing IA/methanol at a molar ratio of 1:30 and methanol/water in a volume ratio of 1:10 at 30 degrees C after 24 h, a 64.3% yield and 73.2% selectivity of DI was obtained. The results of HPLC and GC-MS revealed that in addition to the main product DI, other side products including acetic acid, propionic acid, and itaconic acid cyclolactone were also generated, which indicates that the RML-catalyzed esterification of IA and methanol has various side reactions, such as lactonization and self-decomposition of IA.