Study in Oxidative Reaction of Polyunsaturated Fatty Acid Esters with Nuclear Magnetic Resonance Spectroscopy

Secondary ozonides (1,2,4-trioxolanes) formed from ozone reacting with unsaturated fatty acid esters in vegetable oils are the main active components of ozonated oils. When fatty acid chains contain multiple double bonds, the reaction pathway remains unclear. Two-dimensional nuclear magnetic resonance (2D NMR) effectively addresses the issue of signal overlap encountered in one-dimensional NMR (1D NMR) analysis of complex systems. In this study, methyl linoleate was employed as a model compound, and trilinolein was used for validation. The reaction products of both compounds with ozone were systematically analyzed using both 1D and 2D NMR techniques to elucidate product distribution across different stages of the ozonation process. Results indicate that, in the presence of multiple double bonds, ozone preferentially reacts with one of the double bonds, leading to the formation of an intermediate composed of 1,2,4-trioxolane and the unreacted carbon–carbon double bond along the fatty acid chain, followed by further ozonation of the remaining double bond to yield a bis(1,2,4-trioxolane) structure. The application of 2D NMR successfully resolved the characteristic peaks of the intermediates and final products, thereby confirming the proposed reaction pathway. This approach plays a crucial role in enhancing quality control in the preparation of ozonated oils.