Elementary plant Biochemistry and Biotechnology (2+1)

Reaction with phenylhydrazine

• When reducing sugars are heated with phenylhydrazine at pH 4.7 a yellow precipitate is obtained. The precipitated compound is called as osazone. One molecule of reducing sugar reacts with three molecules of phenylhydrazine. D-mannose and D-fructose form same type of osazone as that of D-glucose since the configuration of C-3, C-4, C-5 and C-6 is same for all the three sugars. This reaction serves to distinguish between aldose and ketose sugars.