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How many phenylhydrazine molecules are required to react with one glucose molecule to form an osazone?

1. 1
2. 2
3. 3
4. 4

Correct answer: 3

Solution

Glucose reacts with three molecules of phenylhydrazine to form the osazone: one condenses at C1, a second oxidizes C2 to a carbonyl (being reduced to aniline and ammonia), and a third condenses at C2. Hence three molecules are required, not two.

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