II. CHEMISTRY 



317 



solution.*"' *' The 3,4-xylidine-N-D-riboside formed is catalytically reduced 

 without isolation of the reaction product prior to hydrogenation.*- Karrer 

 and Meerwein*^ have shown that coupling with phenyldiazonium salt gives 

 the corresponding azo dye, with a yield of 92 % of the theoretical amount. 

 The reduction to (2-amino-4,o-dimethyIphonyl)-D-l'-ribamine can be per- 

 fomied with 85 % of the theoretical yield. ''^ 



O 



HsC 



NHs 



H3C 



I 



+ D-ribose 



OH OH OH 



H3C NH— C— C— C— C— CH2 



H H H H 



+H, 



H3C 



H3C 



NHCHaCCHOH) 3CH2OH 



r 



A 



+C6H5N2C1 , 



H3C 

 H3C 



H3C 



NHCHsCCHOH) 3CH2OH 



+H, 



N=N— CsHo 

 H3C 



\/\/ 



NHCHzCCHOH) 3CH2OH 



H3C 



NH2 



This method can be used for industrial preparation of riboflavin. The 

 yield obtained is very high, 38 % calculated for ribose. The method is limited 

 to the synthesis of 6 , 7-substituted flavins, because only rn, p-disubstituted 

 aniline derivatives couple with diazonium salts in the orlho position. 



«» P. Karrer el al., Helv. Chim. Acta 18, 1485 (1035) ; W. A. VVisansky and S. Aiisl)acli(>r, 



J. Am. Chem. Soc. 63, 2532 (1941). 

 «' R. Kuhn and L. Birkhofer, Ber. 71, 621 (1938). 



" Hoffman-La Roche, Inc., U. S. Pat. 2,477,560 (Aug. 2, 1949) (('..1. 44, 169 (1951)]. 

 " P. Karrer and H. Meervvein. Helv. Chim. Acta 18, 1130 (1935); 19, 264 (1936). 

 " P. Karrer, Helv. Chim. Acta 30, 2101 (1947). 



