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

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 center dot OEt2 and AlCl3 formed only SOC. All the newly synthesized compounds were characterized by H-1 NMR, C-13 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.