494 THE TOCOPHEROLS 



The course of oxidation of the tocopherols in autoxidizing fats depends 

 on the nature of the fat. In animal fats (containing added a-tocopherol) 

 and in vegetable fats, where tocopherols occur naturally, tocoquinones 

 were the immediate products, but the chroman-5 , 6-quinone appeared only 

 in vegetable fats.^^^ The red quinone appears to have its origin in 7,8-di- 

 methyltocol (7),"" in which position 5 is occupied by H. This is more 

 readily oxidized than a methyl group, but when pure a-tocoquinone is 

 gently heated in methanol containing traces of synergistic acids, such as 

 phosphoric, sulfuric, tartaric, and others, chroman-5 , 6-quinone is formed 

 along with other unidentified oxidation products of the nature of quinones."^ 

 At the same time some a-tocopherylquinone is converted to a-tocopherol, 

 as demonstrated by antioxygenic and biological activity and by absorption 

 spectrum. This is a kind of dismutation, as if the acids catalyzed the dis- 

 placement of the 5-methyl group. This behavior is consistent with the 

 more rapid production of the red quinone from 7-tocopherol by the action 

 of silver nitrate^^ and may ultimately contribute to an understanding of 

 the unsolved kinetic problem of synergism of ascorbic, phosphoric, and 

 other polyhydroxy acids with tocopherols."^-"" Further oxidation products 

 have been"'' and doubtless remain to be discovered and identified, along 

 with dimers, but it is doubtful that any of them beyond tocopherylquinone 

 will prove to play a role in biological processes. 



By analogy with simpler quinols, the transitory existence of a semi- 

 quinone or free radical could be assumed. Proof of this was provided by 

 the ingenious ■ technique used by Michaelis and Wollman."^ A solution of 

 tocopherol in suitable organic solvents and brought to the temperature of 

 liquid air assumed the consistency of glass. When this was irradiated with 

 ultraviolet light, it developed an orange-red color and absorption bands not 

 characteristic of the quinone. Both the color and the absorption bands dis- 

 appeared when the temperature was slightly elevated. Recently, fresh evi- 

 dence for the existence of the free radical of tocopherol has been obtained 

 in the author's laboratory."^ Univalent oxidation does not involve the 

 opening of the ring, and if the formation of this semiquinone is not con- 

 cerned in the biological action of tocopherol, it certainly finds its place in 

 any explanation of the antioxygenic action of tocopherols in vitro. 



1 C. Golumbic, Oil & Soap 20, 105 (1943). 



2 C. E. Swift, G. E. Mann, and G. S. Fisher, Oil & Soap 21, 317 (1944). 



3 A. Issidorides, J. Am. Chem. Soc. 73, 5146 (1951). 



* C. Golumbic and H. A. Mattill, /. A7n. Chem. Soc. 63, 1279 (1941). ■ 



6 C. Golumbic, Oil & Soap 19, 181 (1942); 23, 184 (1946). * 



6 V. P. Calkins, /. Am. Chem. Soc. 69, 384 (1947). 



7 W. John and W. Emte, Z. phxjsiol. Chem. 268, 85 (1941). 



8 L. Michaelis and S. II. Wollman, Science 109, 313 (1949); Biochim. et Biophys. 

 Actai, 156 (1950). 



119 G. E. Inglett, Unpublished data. 



