312 



RIBOFLAVIN 



mation of a leuco compound. *2''' ^ The colorless dihydroriboflavin is reoxi- 

 dized easily to riboflavin by air. Stronger catalytic hydrogenation of flavins 

 yields octahydroflavins, which are easily oxidized in alkaline solution by 

 air to the corresponding hexahydroflavins.^^ 



R 



N CO 



Hexahydroflavin 



Three intermediate compounds have been obtained in the crystaUine 

 state by stepwise reduction of riboflavin to leucoriboflavin. They consist 

 of molecular compounds of reduced and unreduced and radical-like inter- 

 mediate molecules.^*' ^^ In verdoflavin 1 mole of riboflavin and 1 mole of 

 monohydroriboflavin (with a free valence) are associated; chloroflavin is 

 probably partly free monohydroriboflavin and partly a quinhydrone, 

 formed of riboflavin and leucoriboflavin; rhodofiavin contains the hydro- 

 chlorides of leucoriboflavin and monohydroriboflavin: 



R 



I 



N 



N 



Consumption 

 of moles 



oxygen upon 

 oxidation 



\ 



N CO 



Flavin (yellow) 



CO 



I 

 NH 



*s P. Karrer and R. Ostwald, Rec. trav. chini. 57, 500 (1938). 

 ^6 R. Kuhn and R. Strobele, Ber. 70, 747, 753 (1937). 



