Chemical pathways of epoxidized and hydroxylated fatty acid methyl esters and triglycerides with phosphoric acid

Abstract

The polymerization pathways of epoxidized and hydroxylated triglycerides with phosphoric acid (H₃PO₄) were investigated using model reactions. Involved epoxides and diols were derived from oleic acid methyl ester, which was easily monitored by one- and two-dimensional nuclear magnetic resonance (NMR) techniques as well as electrospray ionization mass spectroscopy (ESI-MS). Phosphoric acid played two key functions: (a) as a Brønsted acid catalyst that activated the epoxide toward nucleophilic attack by the diol, thus generating ether (C–O–C) cross-linkages; and (b) as a reaction partner establishing phosphate ester linkages [(RO)₂(O)P–O–C, R = C or H]. In studies with ¹⁸O labeled diol, phosphate esters formed exclusively from H₃PO₄ and epoxide without incorporation of diol whereas diols acted as polymerization initiators in polyether formations.