Question

In the reaction of glucose with hydroxyl amine and glucose with hydrogen cyanide how was it conuded that glucose has only one carbonyl group ?

Answer 1

Glucose reacts with HCN to give a cyanohydrin, or with a schiffs base to give an oxime. This shows the presence of a carbonyl group.

To prove the presence of -CHO group:

When glucose reacts with hydroxylamine, oxime is formed and cyanohydrins are formed on the addition of hydrogen cyanide to it. This reaction can confirm the presence of carbonyl group in glucose. And also on the reaction of glucose with a mild oxidising agent like bromine water, the glucose gets oxidised to carboxylic acid containing six carbon atoms. This indicates that the carbonyl group is present (as an aldehyde group).