Problem 102 - A Complete Resource Book in Chemistry for JEE Main

Question

An alcohol and a phenol can be distinguished by their reactions with (a) Ceric ammonium nitrate (b) \(\mathrm{NaOH}\) (c) Benezene diazonium chloride (d) \(\mathrm{NaHCO}_{3}\)

Step-by-Step Solution

Answer

Phenols react with benzene diazonium chloride to form azo dyes, distinguishing them from alcohols.

Step 1: Understanding the reaction with Ceric Ammonium Nitrate

When alcohols react with ceric ammonium nitrate, a deep red color is observed due to the formation of a complex. Phenols do not give this color change because they do not form such complexes under these conditions.

Step 2: Analyzing the Reaction with NaOH

Phenols, being more acidic than alcohols, can react with NaOH to form phenoxide ions, which are soluble in water. Alcohols, which are much less acidic, do not react with NaOH to form any soluble products.

Step 3: Examining the Reaction with Benzene Diazonium Chloride

Phenols can react with benzene diazonium chloride to form azo dyes, which are brightly colored. Alcohols, on the other hand, do not react to form such dyes, allowing phenols and alcohols to be distinguished by this test.

Step 4: Considering the Reaction with NaHCO₃

Phenols do not react with NaHCO₃ because they are not strong enough acids to release CO₂ from NaHCO₃. Alcohols also do not react with NaHCO₃ for the same reason. Therefore, both phenols and alcohols remain non-reactive in this test.

Key Concepts

Ceric Ammonium Nitrate Reaction

When it comes to distinguishing between alcohols and phenols, one effective method is through the ceric ammonium nitrate reaction. Alcohols interact with ceric ammonium nitrate to produce a deep red color due to the formation of a unique complex. This color change serves as a clear indicator of the presence of an alcohol in the substance tested.

In contrast, phenols do not produce this color change. Phenols do not form the same complexes with ceric ammonium nitrate, which highlights a key chemical distinction between phenols and alcohols. This lack of reactivity makes the ceric ammonium nitrate test a straightforward way to differentiate between these two types of compounds.

To summarize:

• Alcohols → Form a deep red complex, indicating presence.
• Phenols → No color change, indicating absence of such reaction.

This simple yet effective test takes advantage of the different chemical properties and reactivities of alcohols and phenols.

Phenol Reactivity with NaOH

The reactivity of phenols with sodium hydroxide ( ext{NaOH} ) further distinguishes them from alcohols. Phenols are more acidic than alcohols, which means they can donate protons much more easily. As a result, phenols react with ext{NaOH} to form phenoxide ions. The resulting phenoxide compounds are soluble in water, offering a clear visual cue of the reaction's occurrence.

Conversely, alcohols are far less acidic, and they do not react with ext{NaOH} to any significant extent. This lack of reaction results in no significant change when alcohols are treated with ext{NaOH} , making this test another effective means to differentiate phenols from alcohols.

Key points include:

• Phenols + ext{NaOH} → Formation of water-soluble phenoxide ions.
• Alcohols + ext{NaOH} → No reaction or change observed.

This test leverages the difference in acidity between phenols and alcohols to make a clear distinction between the two.

Benzene Diazonium Chloride Test

The benzene diazonium chloride test is a distinguished technique used to identify phenols due to their unique ability to form azo dyes. When phenols react with benzene diazonium chloride, they form vibrant, brightly colored azo compounds. This vivid color change is a clear and compelling indicator of the presence of a phenol.

Alcohols, however, do not participate in such reactions and therefore, do not produce any azo dyes. This non-reactivity of alcohols in this context provides a simple yet powerful contrast with the behavior of phenols.

Important points to remember:

• Phenols → React with benzene diazonium chloride to form colored azo dyes.
• Alcohols → Do not form azo dyes, resulting in no color change.

This test exploits the difference in reactivity of phenols compared to alcohols in the presence of benzene diazonium chloride, making it an invaluable tool in distinguishing between these compounds.