Phenylosazones mechanism

Reaction with reducing sugars. For evidence on the mechanism of phenylosazone formation, see Chapman el aU ... 

The mechanisms suggested by the various authors for the formation of a glyculose phenylosazone may be broadly divided into two types the... 

In the controversy on the mechanism of osazone formation, it was found that glucose-f-t is converted into the phenylosazone and the phenyl-osotriazole without loss of tritium." This finding was taken as evidence against formation, by the Amadori rearrangement, of an intermediate having two hydrogen atoms on C-1 as in Weygand s scheme" B. 

The accepted mechanism for the formation of phenylosazones is presented in Scheme 23.2. Following initial formation of the phenylhydrazone 18 from the aldose, a double tautomerization leads to the ketone 19. The newly formed carbonyl group then condenses with a second equivalent of phenylhydrazine to give 20, which tautomerizes to 21. After 1,4-elimination of aniline to produce either 22 or 23, a third equivalent of phenylhydrazine condenses with the imine group of 22 or 23 to yield the phenylosazone 24 and ammonia. Although it may appear that... 

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