CHEMICAL CONSTITUTION 



xylidines was introduced by R. Kuhn and F. Weygand.22 Whereas 

 they experienced no difficulty in obtaining quantitative yields of 

 lumiflavine, the yields of riboflavine, araboflavine, etc., were only 5 

 to 10 % of the theoretical. This they attributed to the presence, not 

 of the sugar residue, but of the methyl groups. O. Kiihling and O. 

 Kaselitz,^^ in attempting to prepare alloxazines, had obtained pale 

 yellow substances containing one molecule of water more than the 

 alloxazines when the condensation was effected in neutral solution. 

 When the condensation was carried out in strongly acid solution, 

 however, good yields of alloxazines were obtained. When this method 

 was applied to the synthesis of riboflavine, with perchloric acid as the 

 condensing agent, it met with little or no success, but the use of boric 

 acid increased the yield to 95 % of the theoretical. 



References to Section 3 



1. P. EUinger and W. Koschara, Ber., 1933, 66, 141 1. 



2. R. Kuhn and T. Wagner- J auregg, ihid., 1577. 



3. R. Kuhn, H. Rudy and T. Wagner- J auregg, ihid., 1950. 



4. R. Kuhn, H. Rudy and F. Weygand, ibid., 1935, 68, 625. 



5. O. Warburg and W. Christian, Biochem. Z., 1933, 266, 377. 



6. R. Kuhn and H. Rudy, Ber., 1934, 67, 892. 



7. R. Kuhn and H. Rudy, ihid., 1298. 



8. R. Kuhn and F. Bar, ihid., 898. 



9. R. Kuhn and F. Weygand, ihid., 1409. 



10. R. Kuhn and F. Weygand, ihid., 1459. 



11. R. Kuhn, K. Reinemund and F. Weygand, ihid., 1460. 



12. R. Kuhn and K. Reinemund, ihid., 1932. 



13. R. Kuhn and H. Rudy, ihid., 1936. 1826. 



14. P. Karrer, H. Salomon, K. Schopp, E. Schlitter and H. Fritzsche, 



Helv. Chim. Acta, 1934, ^'^* loio. 



15. R. Kuhn and F. Weygand, Ber., 1934, 67, 1939. 



16. R. Kuhn and F. Weygand, ihid., 1935, 68, 166. 



17. P. Karrer, K. Schopp, F. Benz and K. Pfaehler, Helv. Chim. Acta, 



1935. 18, 69 ; Ber., 1935, 68, 216. 



18. P. Karrer, K. Schopp and F. Benz, Helv. Chim. Acta, 1935, 18, 



426. 



19. Hoffmann-la Roche, B.P. 45798^4. 



20. R. Kuhn, Naturwiss., 1935, 23, 260. 



21. H. von Euler, P. Karrer, M. Malmberg, K. Schopp, F. Benz and 



P. Frei, Helv. Chim. Acta, 1935, 18, 522 ; Svensk. Kem. Tids., 

 1935, 47, 99. 



22. R. Kuhn and F. Weygand, Ber., 1935, 68, 1282. 



23. O. Kiihling and O. Kaselitz, ihid., 1906, 39, 1324. 



139 



