Biocatalytic Epoxidation Pathway of Oils in Sponge-Like Ionic Liquids Toward CO₂-Derived Cyclic Carbonate Synthesis

A sustainable chemo-enzymatic synthesis of poly(cyclic carbonate)s from CO₂ and renewable oils is reported for the first time using sponge-like ionic liquids (SLILs) such as hexadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([C₁₆tma][NTf₂]) as a monophasic reaction medium. The process integrates biocatalysis and IL technologies in two sequential steps. In the first step, a lipase catalyzes the in situ formation of peracids from free-fatty acids (FFAs), such as oleic acid, using urea hydrogen peroxide (UHP) as a solid oxidant. These peracids spontaneously epoxidize the CC double bonds of FFAs (oleic or linoleic acid) and oils (e.g., soybean, linseed, fish, and triolein). Thus, high epoxide yields were achieved in the SLIL medium, reaching up to 72% for soybean oil (SBO) and 92% for triolein after 6 h at 55°C. The enzyme is isolated for subsequent reuse (up to five cycles). In the second step, the synthesis of poly(cyclic carbonate)s, from previously epoxidized oils, is carried out using different halide-based IL catalysts (e.g., tetrabutylammonium bromide, [TBA][Br]), reaching up to 54% carbonated SBO yields after 72 h at 100°C and 1 MPa CO₂. UHP is an efficient oxidant for the lipase-catalyzed epoxidation, while the urea byproduct can promote cyclic carbonate formation without the direct use of CO₂.