The synthesis of D,L-alpha-tocopherol in supercritical carbon dioxide or nitrous oxide by condensation of trimethylhydroquinone (TMHQ) with isophytol (IP) in the presence of various Bronsted or Lewis acids, especially an imide or its metal salts, as catalysts is described. The product is obtained in high yield. The method represents an interesting alternative to existing processes. A quasi-reaction mechanism is being proposed together with kinetics, which are needed for the reactor analysis and design. (C) 2000 Elsevier Science B.V. All rights reserved.