THE CARBOHYDRATES AND THEIR METABOLISM 233 



while the phenylhydrazine is converted to anilin and ammonia The car 

 bonyl group then reacts with another molecule of phenylhydrazine to 

 form the osazone, thus : 



CH :N . NH - C 6 H 5 CH -N . NH - C 6 H, 



l> 5 



HCOH 

 HOCH 

 HCOH 

 HCOH 



CO 



I . 

 HOCH 



-> HCOH 

 HCOH 



CH 2 OH CH,OH 



Phenylhydrazone + phenylhydra- intermediary + anilin + ammonia 



zine oxidation 



product 



C 6 H 5 



CO 



I 

 HOCH 



HCOH 

 HCOH 



C 6 H 5 



C 6 H 5 



HOCH 

 HCOH 

 HCOH 



CH 2 OH 



phenylosazone -f- water 



CH 2 OH 



Intermediary oxida- -j- phenylhydra- 

 tion product zine 



Because the second stage of the reaction is a' process of oxidation, it 

 follows that those sugars that are most easily oxidized (as d-fructose) most 

 readily form osazones. 



Aldoses and ketoses may be differentiated by means of their reaction 

 with methyl phenylhydrazine. According to Newberg, ketoses form osa- 

 zones, while aldoses reach only the hydrazone stage. The asymmetrically 

 substituted hydrazines do not act as oxidizing agents. Since the conversion 

 of hydrazone to osazone involves oxidation, the reason for this behavior 

 is evident. 



Most of the hydrazones are very soluble in water and therefore not 

 adapted for identification. Mannose, however, is a notable exception. 

 It forms a crystalline precipitate easily identifiable. The osazones are, 

 as a rule, quite insoluble in water. In order to form more specific com- 



