Evidence Contrary to the Accepted Diels–Alder Mechanism in the Thermal Modification of Vegetable Oil

Abstract

AbstractA fatty methyl ester product has been made using two routes. Soybean oil was thermally polymerized anaerobically without a catalyst at 330 °C and the material was then transesterified using base catalyst and methanol. Alternatively, a similar product can be obtained by heating methyl linoleate to the same temperature in a pressure reactor. The product structure was studied by NMR spectroscopy, gel permeation chromatography and mass spectrometry. It is a dimeric product which does not contain substituted cyclohexane structures. This evidence shows that the Diels–Alder reaction has not occurred under these conditions. This is in contradiction to many literature reports, but in agreement with a neglected paper from 1971. This correction has implications in both biodiesel and industrial oil products.