Mechanistic Insights Into the Methoxycarbonylation of Technical Grade Oleochemicals: Catalytical and Structural Analysis of Conjugated Fatty Acid Methyl Esters

Abstract

This study examines the valorization of vegetable oils through Pd-catalyzed methoxycarbonylation. It investigates the inhibitory effects of polyunsaturated fatty acid methyl esters (PU-FAME) on catalyst activity, which are frequently reported in academic literature. A particular focus lies on the isomerization of polyunsaturated FAME into conjugated species. In light of the formation of a stable Pd-allyl complex with polyunsaturated compounds, an investigation of the isomerization products was conducted. NMR and GC analyses demonstrated that isomerization results in the conjugation of double bonds and their relocation toward the ω-end of the carbon chain. The isomerization results in a thermodynamic distribution of isomerization products for mono- and polyunsaturated FAME. The formation of conjugated substrates was confirmed by structural analysis, and oxidative cleavage techniques were employed to determine the precise distribution of double bond positions. The findings offer insight into how conjugated PU-FAME inhibit methoxycarbonylation, thereby limiting the valorization of vegetable oils.

Practical Applications: This study provides further insights into the homogeneous catalyzed formation of conjugated methyl linoleate using a palladium catalyst. Combining different analytic techniques and chemical modification provides a novel approach for determining double bond positions in fatty acids. Furthermore, these findings may facilitate the design of new catalysts for the methoxycarbonylation process, thereby preventing the formation of conjugated intermediates. This could result in an efficient conversion of technical-grade oils. Additionally, the production of a diverse range of isomers for subsequent functionalization is demonstrated.