Question

76. Sucrose doesn’t respond to Tollen’s test. But it gives a positive result after boiling with conc. $\mathrm{HCl}$. It is due to the

• A. cleavage of glycosidic linkage
• B. formation of glycosidic linkage
• C. formation of a compound containing carboxylic acid group
• D. isomerisation to glucose units

Answer 1

The correct option is A

cleavage of glycosidic linkage

Explanation:

• Tollen's reagent is an ammonical Silver nitrate $\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\mathrm{OH}\right]$ solution.
• Tollen’s test is shown by reducing sugars that contain a free aldehyde group but in Sucrose $\left({\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}\right)$ there is no free aldehyde group.
• But when Sucrose reacts with concentrated Hydrochloric acid $\left(\mathrm{HCl}\right)$, the glycosidic bond will break and the aldehyde group becomes free and can give positive Tollen’s test.
• The structure of sucrose is:

• Sucrose doesn’t respond to Tollen’s test. But it gives a positive result after boiling with concentrated $\mathrm{HCl}$. It is due to the cleavage of the glycosidic linkage.
• Hence, option (A) is the correct answer.