Location: Bio-oils Research Unit
Title: Evidence contrary to the accepted Diels-Alder mechanism in the thermal modification of vegetable oil Authors
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 27, 2011
Publication Date: May 23, 2012
Repository URL: http://handle.nal.usda.gov/10113/54496
Citation: Arca, M., Sharma, B.K., Price, N.P.J., Perez, J.M., Doll, K.M. 2012. Evidence contrary to the accepted Diels-Alder mechanism in the thermal modification of vegetable oil. Journal of the American Oil Chemists' Society. 89:987-994. Interpretive Summary: Heating soybean oil or other vegetable oils in a process called heat-bodying is a decades old process which has been used on products such as inks, lubricants and coatings. However, despite many years of work, the actual chemistry behind this process is still not understood, and new developments are slow to occur. In this work, we have used modern methods to attempt to understand this process, and discovered that the reported mechanism of reaction is wrong. This knowledge is the first step which may lead to improvements in the method necessary to produce more effective materials. This research will benefit those formulators wishing to take advantage of what bio-based materials can offer.
Technical Abstract: A transesterified oleochemical product has been made using two routes. Soybean oil was thermally polymerized anaerobically at 330 deg 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. From this evidence, it is shown 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 vegetable oil industrial products as well as in potential concerns of biodiesel stability under oxygen free conditions.