Better understanding of the maleinization of oils using model fatty compounds: Insights from NMR, SEC, and HRMS analyses

The chemical modification of vegetable oils through maleinization reaction offers a promising route to sustainable bio-based materials for diverse industrial applications. However, the underlying mechanisms of the maleinization reaction such as the ene, Diels-Alder, and radical pathways, remain insufficiently understood, limiting process optimization and broader adoption. In this study, we employed a model compound approach using methyl oleate (C18:1), methyl linoleate (C18:2), and their corresponding triglycerides to systematically investigate the maleinization reaction with maleic anhydride (MA) under controlled conditions. Advanced analytical techniques, including nuclear magnetic resonance (NMR) spectroscopy, size-exclusion chromatography (SEC), and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were performed to elucidate reaction mechanisms, quantify product distributions (when possible), and assess structural modifications. Our results demonstrated that the ene reaction is the predominant pathway for C18:1 substrates while radical mechanisms contribute to minor products. The Diels-Alder cycloaddition is negligible under the studied conditions. The extent of maleinization increases with MA equivalents, as confirmed by quantitative 13 C NMR and FT-ICR MS analyses while SEC reveals some polymerization.