810 IX. THE VITAMIN E GROUP 



droquinone (XIV) is condensed with phytyl bromide (XVIII) in the pres- 

 ence of zinc chloride, rfZ-a-tocopherol (I) results. 



HOC- \h Y T' T^ ^^' 



C OH 



CHj 



ML 



HBr 



CHj 

 ^C^ ^,CH, 



HOC-' C CH^ ^^^ ^^^ cH^ 



Hck X C(CH,)3CH(CH,)3CH(CH,)3CHCH3 + 



' \^ ^0^ \h3 



CHj 



I 

 Synthesis of (//-a-Tocopheiol 



Bergel et aL^°>^^ have carried out the synthesis satisfactorily by employing 

 phj^tol : 



CH3 CH3 CH;, CHs 



I I I I 



HOCHo.CH:C(CH2)3-CH(CH.,)3-CH-(CH,).3-CH-CH,; 



in place of phytyl bromide. Smith et a/.^^ have also successfully used 

 phytadiene : 



CH3 CH3 CHa CH3 



CHaiCH.CiCHCH.CH.CHCH.CHsCHo-CHCH.CHoCHoCHCH, 



in place of the phytyl bromide. The synthesis can be accomplished with 

 the phytyl derivatives^- without the employment of catalysts. The result- 

 ing racemic a-tocopherol yields an ester with bromocamphorsulfonic acid 

 which can be resolved into the d- and /-a-tocopherol.^^-^'''^- 



For the synthesis of j3-, 7-, and 5-tocopherols, the trimethylhydroquinone 

 is replaced by p-xylohydroquinone, o-xylohy droquinone, or toluhydro- 

 quinone.^^ One of the difficulties which is encountered in these reactions is 

 the condensation of the dimetMd- or monomethylquinone with 2 molecules 

 of phytyl bromide. This side reaction does not occur with the trimethyl- 

 hydroquinone, since only one space is available on the benzene ring for the 

 condensation to take place. More by-products result when zinc chloride is 

 used as a catalyst^^ than when formic acid^- is employed. ^^'^^ Better yields 



«• F. Bergel, A. Jacob, A. R. Todd, and T. S. Work, Nature, U2, 36 (1938). 



91 F. Bergel, A. M. Copping, A. Jacob, A. R. Todd, and T. S. Work, /. Chem. Soc, 

 1938, 1382-1384. 



92 P. Karrer, H. Koenig, B. H. Ringier, and H. Salomon, Helv. Chim. Ada, 22, 1139- 

 1145 (1939). 



