STRUCTURE OF THE TOCOPHEROLS 



807 



products on pyrolysis or chromic acid oxidation. The aromatic portion of 

 the chroman ring accounts for the nucleus of duroquinone ; the 3 methyls in 

 the above compound represent groups present as such on the a-tocopherol 

 molecules. The fourth methyl group originates from the — CH2 group in 

 position 4. Both diacetyl and dimethylmaleic anhydride also represent 

 fragments of the aromatic ring; a rupture occurs between positions 6,7 and 

 8,9 in the first case, and between positions 5,6 and 9,10 in the second case. 

 Acetone (V) obviously originates from the isopropyl group at the end of the 

 side chain. The origin of the C2i lactone, Cig ketone, and Cie acid repre- 

 sents the side chain with 5, 2, and additional carbons, respectively. 



John and co-workers*^ also proved that a chroman rather than a coumaran 

 structure obtains in the ring portion of the molecule. This could be de- 

 duced from the fact that, on careful oxidation with silver nitrate*^ or ferric 

 chloride, a yellow quinone, tocopheiylquinone (XI), originates.*^-*® This 

 can be reduced to a hydroquinone (XII), the so-called "tocopheiylquinol." 

 One can readily esterify the 2 phenolic groups so formed. An attempt to 

 esterify the third hydroxyl group indicated great resistance to this reac- 

 tion; moreover, it could not be oxidized to a ketone. This is taken as 

 proof that the alcoholic group is a tertiary one, as would be the case if the 

 ring were a chroman ring. Had it been a coumaran ring, the third hy- 

 droxyl would have been a secondaiy alcohol group. On this basis, the 

 chroman ring is assumed for the cyclic part of a-tocopherol, rather than the 

 coumaran ring. 



I 



CH3 



HOC 



CHj 



CH, 



H3CC, 



XI 



H3CC. C HOC-C,sH„ 



\ / \ \ 

 C OH CH. 



CH, 



XE 



(2) ^-Tocopherol 



/3-Tocopherol is 5,8-dimethyltocol. It has an empirical formula of 

 C28H4g02, which indicates that it contains one less methyl group than does 

 a-tocopherol. The structure assigned to it is shown here (XIII). 



CH, 

 HOC C CH, 



CH, 



CH, 



CH, 



HC. 



. ^C C-CHjCHjCHjCHCHjCHjCHjCHCHjCHjCHjCHCH, 



C \h, ^^^ 



CH, ' xm: 



