Tollen’s reagent reacts with _
A aldehydes only
B aldehydes and alpha-hydroxy ketones
C alcohols
D amines
E carboxylic acids
The correct answer and explanation is:
The correct answer is B: aldehydes and alpha-hydroxy ketones.
Tollen’s reagent, which contains a solution of silver nitrate (AgNO₃) in ammonia (NH₃), is primarily used to detect the presence of aldehydes. When aldehydes are present, they are oxidized by Tollen’s reagent, reducing the silver ions (Ag⁺) to metallic silver. This reaction results in the formation of a silver mirror on the sides of the test tube, which is characteristic of the reaction.
However, Tollen’s reagent can also react with alpha-hydroxy ketones, compounds that contain both a ketone group and a hydroxyl group attached to the carbon adjacent to the carbonyl group. In this case, the hydroxy group’s presence makes the carbonyl carbon more reactive, allowing the reaction with Tollen’s reagent, similar to aldehydes. The reaction mechanism involves oxidation of the aldehyde group or the alpha-hydroxy ketone into a carboxylate, which reduces silver ions to silver metal.
Tollen’s reagent does not react with alcohols (choice C), amines (choice D), or carboxylic acids (choice E). Alcohols lack the carbonyl group required for oxidation in this test, making them unreactive with Tollen’s reagent. Amines and carboxylic acids do not have the necessary functional groups to facilitate the reduction of silver ions, so they do not show a positive reaction with Tollen’s reagent either.
Therefore, the key groups that react with Tollen’s reagent are aldehydes and alpha-hydroxy ketones because of their ability to undergo oxidation while reducing the silver ions to metallic silver.