Problem 38 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following react with \(\mathrm{NaOH}\) to produce an acid and an alcohol? (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) (b) \(\mathrm{HCHO}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\)

Step-by-Step Solution

Answer

None of the options react with NaOH to produce an acid and an alcohol.

Step 1: Identify the Reaction

Sodium hydroxide (NaOH) is a strong base, and it typically reacts with certain organic compounds under specific conditions. However, NaOH reacts with esters to produce an acid and an alcohol. This reaction is known as saponification. In this context, we need to find which option contains an ester, since esters will react with NaOH in this way.

Step 2: Analyze Each Compound

Let's examine each option: (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) is acetic acid, which is a carboxylic acid, not an ester.(b) \(\mathrm{HCHO}\) is formaldehyde, an aldehyde rather than an ester.(c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) is benzoic acid, also a carboxylic acid, not an ester.(d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\) is propionic acid, another carboxylic acid, not an ester.

Step 3: Look for Esters

Upon analyzing the options, we see that none of them is an ester. Since NaOH specifically reacts with esters to produce an acid and alcohol, and none of the options is an ester, there will be no reaction producing an acid and an alcohol with any listed compound.

Key Concepts

Esters

Esters are a type of organic compound known for their distinct fruity odors and are commonly used in perfumes and flavorings. They are derived from carboxylic acids and alcohols. Imagine an ester as a puzzle piece that fits perfectly between an alcohol and an acid.

An ester can be represented by the general formula \[ \text{RCOOR'} \]where R and R' are hydrocarbon chains. The reaction to form an ester is called esterification, where a carboxylic acid and an alcohol combine, releasing water:

\[ \text{RCOOH} + \text{R'OH} \rightarrow \text{RCOOR'} + \text{H}_2\text{O} \]

Esters can undergo a reaction known as saponification, particularly in the presence of a strong base like sodium hydroxide (NaOH), leading to the production of an alcohol and the salt of the corresponding carboxylic acid. This is an important reaction, especially in the production of soaps and detergents. The saponification process is as follows:

\[ \text{RCOOR'} + \text{NaOH} \rightarrow \text{RCOONa} + \text{R'OH} \]

In summary, for a substance to undergo saponification with NaOH, it must be an ester.

Carboxylic acids

Carboxylic acids are a group of organic compounds characterized by having a carboxyl group (-COOH). They are known for their acidic properties due to the presence of the hydrogen atom in the carboxyl group.

Carboxylic acids do not react with sodium hydroxide to form esters like in saponification; instead, they typically form salts and water. This neutralization reaction can be portrayed as:

\[ \text{RCOOH} + \text{NaOH} \rightarrow \text{RCOONa} + \text{H}_2\text{O} \]

Here are a few characteristics of carboxylic acids:

• They are usually weak acids.
• They can donate a hydrogen ion (H⁺) due to the polar nature of the carboxyl group.
• Their strength depends on the substituents attached to the carbon chain.

In the problem provided, options (a), (c), and (d) describe different carboxylic acids. These compounds, being acids themselves, do not undergo saponification with NaOH to produce an alcohol and a separate acid. Instead, they form their respective sodium salts.

Sodium hydroxide reactions

Sodium hydroxide (NaOH) is a versatile, strong base used in various chemical reactions. It is known for its ability to react with acidic components to form salts and water in a neutralization reaction.One of the key reactions of NaOH is with esters, which leads to the phenomenon of saponification. This involves breaking the ester bond to produce a carboxylate salt and an alcohol. As previously mentioned, this reaction is significant in soap making. Here's a simple illustration of the saponification reaction:\[ \text{RCOOR'} + \text{NaOH} \rightarrow \text{RCOONa} + \text{R'OH} \]In this equation:

• \(\text{RCOOR'}\) represents an ester.
• \(\text{NaOH}\) is our base.
• The result is \(\text{RCOONa}\) (a salt of the acid) and \(\text{R'OH}\) (an alcohol).

Conversely, if NaOH reacts with carboxylic acids, it neutralizes them to form sodium salts (not esters), as highlighted in the solution. This showcases the specificity of NaOH’s reactivity: forming different products based on the type of functional group present in the compound it reacts with.