Evidence contrary to the accepted Diels-Alder mechanism in the thermal modification of vegetable oil

A 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.