Lewis-acid catalyzed synthesis and characterization of novel castor fatty acid-based cyclic carbonates

Abstract

Novel bio-based cyclic carbonates were synthesised from ricinoleic acid by intra molecular rearrangement of an epoxy carbonate ester with Lewis acids. The first step was the carbonate interchange reaction between methyl ricinoleate and dialkyl carbonates followed by epoxidation using the performic acid method to get methyl 8-(3-(2-(methoxy carbonyloxy)octyl)oxiran-2-yl)octanoate (3a) and methyl 8-(3-(2-(ethoxycarbonyloxy)octyl)oxiran-2-yl)octanoate (3b). These products on treatment with Lewis acids (Sc(OTf)₃, Yb(OTf)₃ and ZnBr₂) formed a mixture of inseparable five and six membered cyclic carbonates through a spiroorthocarbonate (SOC) intermediate by intramolecular rearrangement. Whereas, BF₃·OEt₂ and AlCl₃ formed only SOC. All the newly synthesized compounds were characterized by ¹H NMR, ¹³C NMR, ESI-MS, GC-MS (EI), HRMS, FT-IR and studied by thermogravimetric analysis (TGA). This is the first report on the preparation of castor fatty acid based cyclic carbonates without the use of carbon dioxide.