Question

This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. A compound (A) gives red colour with ceric ammonium nitrate. (A) on mild oxidation gives (B) which restores the pink colour of Schiff's reagent. (A) is (a) aldehyde (b) primary alcohol (c) secondary alcohol (d) alkyl bromide

Short answer

Answer: Compound (A) is a primary alcohol.

Step-by-step solution

Reactions with Ceric Ammonium Nitrate

Ceric ammonium nitrate (CAN) is an oxidizing agent that reacts with alcohols, particularly primary and secondary ones, to form corresponding carbonyl compounds (aldehydes or ketones). Aldehydes and alkyl bromides do not give a red colour with ceric ammonium nitrate. Since compound (A) gives a red colour with ceric ammonium nitrate, it could be either a primary alcohol or a secondary alcohol.

Reactions with Schiff's Reagent

Schiff's reagent is used to detect aldehydes. It is a colourless solution that turns pink in the presence of aldehydes. Ketones do not react with Schiff's reagent. Since compound (B) restores the pink colour of Schiff's reagent, it must be an aldehyde.

Oxidation from Compound (A) to Compound (B)

Since Compound (A) undergoes mild oxidation to form an aldehyde (compound B), it must be a primary alcohol. Primary alcohols can be oxidized to aldehydes by mild oxidizing agents, such as the reaction with ceric ammonium nitrate. Compound (A) is a primary alcohol, which oxidizes to an aldehyde (B) that restores the pink colour of Schiff's reagent.

Choosing the correct option

Based on the reactions and the information given in the problem, compound (A) is a primary alcohol. Therefore, the correct option among the given choices is: (a) aldehyde (b) primary alcohol (c) secondary alcohol (d) alkyl bromide The answer is (b) primary alcohol.

Key concepts

Reaction with Ceric Ammonium Nitrate

When dealing with ceric ammonium nitrate (CAN) in organic chemistry, particularly for IIT JEE preparation, it is crucial to understand its behavior as an oxidizing agent. Ceric ammonium nitrate is often used to test for the presence of alcohols.

When an alcohol, specifically a primary or secondary alcohol, reacts with ceric ammonium nitrate, it typically produces a distinct red color. This color change indicates the alcohol's presence as ceric ammonium nitrate helps oxidize the alcohol to its corresponding carbonyl compound.

For example:

• Primary alcohol can be converted into an aldehyde.
• Secondary alcohol can be oxidized into a ketone.

This red color does not appear with aldehydes or alkyl bromides. Hence, if a compound exhibits a red color when exposed to CAN, it is very likely to be an alcohol, aiding in the identification process in organic reactions.

Oxidation Reactions

Oxidation reactions are a central concept in organic chemistry used to modify the functional groups in a molecule. In the context of the exercise, we are focusing on the oxidation of alcohols using mild oxidizing agents.

Primary alcohols, when subjected to mild oxidation, will typically transform into aldehydes. This process can use different oxidizing agents, including ceric ammonium nitrate, which helps in the gentle conversion without pushing the reaction into further oxidation stages.

Here's the typical pathway:

• Primary alcohol + mild oxidizing agent (e.g., CAN) → Aldehyde

This controlled reaction demonstrates the selective nature of oxidizing processes for specific functional groups, making it important for synthesis and analysis in organic chemistry.

Schiff's Reagent Test

Schiff's reagent is a specialized laboratory test primarily used to detect the presence of aldehydes. This reagent remains colorless until it encounters an aldehyde group, at which point it turns pink, serving as a qualitative test for aldehydes in organic compound analysis.

This test is part of identifying unknown compounds in exercises such as the IIT JEE organic chemistry problems. It's essential to differentiate between similar groups, such as aldehydes and ketones.

• Only aldehydes will restore the pink color when Schiff's reagent is applied.
• Ketones do not cause a color change with Schiff's reagent.

In our previous exercise, once the primary alcohol (A) was oxidized to an aldehyde (B), this aldehyde successfully restored the pink color with Schiff’s reagent further confirming the presence and successful conversion of the compound to an aldehyde.