Page 50 - PG 504-theoretical notes-phyto-1-2024-2025..

Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

Reaction with Phenylhdrazine (Osazone formation):

• The carbonyl group of an aldose reacts with phenylhydrazine to give a yellow

crystalline phenyl osazone. Osazones are positive with red. Sugars.

• Aldose and ketose react with excess of phenylhydrazine (1:3) in aqueous

acetic acid to form osazone, aniline and ammonia. The hydrazone is first

formed by the first mole of phenylhydrazine, and then oxidized by the

second mole at C-2 to give the osone hydrazone, aniline and ammonia.

Finally, the third mole of phenylhydrazine reacts with the osone hydrazone

to give the osazone.

• Formation of osazone destroys the asymmetry at C-2; therefore glucose,

mannose and fructose produce the same osazone.

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