Simple sugars undergo reaction with phenyl hydrazine, PhNHNH2, to yield crystalline derivatives called osazones. The reaction is a hit complex however, as shown by the fact that glucose and fructose yield the same osazone.

(a) Draw the structure of a third sugar that yields the same osazone as glucose and fructose.

(b) Using glucose as the example, the first step in osazone formation is reaction of the sugar with phenyl hydrazine to yield an imine called a phenyl-hydrazone. Draw the structure of the product.

(c) The second and third steps in osazone formation are tautomerization of the phenyl hydrazone to give an enol, followed by elimination of aniline to give a keto imine. Draw the structures of both the enol tautomer and the keto imine.

(d) 1hc final step is reaction of the keto imine with 2 equivalents of phenyl hydrazine to yield the osazone plus ammonia. Propose a mechanism for thisstep.

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H N-NHP. CHO CH2он C=N-NHPH Н C=0 но -н но- но- 3 equiv 3 equiv PHNHNH2 PHNHNH2 H- -OH Н- -он H- -HO- -он H- Н- Н- HO- -он ČH2OH ČH2OH CH-он + NH3 PHNH2 2 H20 D-Glucose D-Fructose