The Chemistry of Vitamin E. Iii. Permanganate Oxidation of Alpha Tocopherol.

By oxidizing alpha tocopherol with chromic anhydride in acetic acid solution, a lactone C21H4002 was obtained. The origin of such a lactone is easily explicable on the theory that alpha tocopherol contains a chromane ring; if alpha tocopherol contained a coumarane ring, a beta hydroxy acid would be expected. Karrer and his co-workers,2 by treating pseudo cumo hydroquinone with phytyl bromide, obtained a synthetic product which apparently is a mixture of alpha tocopherol and its C-2 epimer. Karrer believed that this reaction would yield a coumarane rather than a chromane, and he suggested that Fernholz's gamma lactone arose by rearrangement in acid solution. As example of this rearrangement he referred to work by Pospjechoff,'3 Raichstein4 and Braun,'5 where beta hydroxy acids on distillation over 20 per cent. H2SO4 were converted to the gamma lactones. As further support for the chromane structure, alpha tocopherol was oxidized in acetone solution with neutral permanganate. No difficulty was experienced in isolating in good yield the C21H4002 lactone in the form of the benzyl thiuronium salt of its hydroxy acid. On admixture with the corresponding salt obtained by the chromic acid oxidation of alpha tocopherol, there was no depression of the melting point. Experimental:-1.0 mg of alpha tocopheryl allophanate was saponified in the usual way. To the free tocopherol, in 50 cc of acetone, was added slowly with mechanical stirring 1.87 gm (6 moles) of potassium permanganate. The first 900 mg were rapidly decolorized; then it became necessary to warm the solution slightly. When all the permanganate had been added, the solution was refluxed until the permanganate was entirely reduced.