Problem 72 - A Complete Resource Book in Chemistry for JEE Main

Question

The work of concentration. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in esterification process is as (a) dehydrating agent and catalyst (b) dehydrating agent (c) hydrolyzing agent (d) catalyst

Step-by-Step Solution

Answer

(a) dehydrating agent and catalyst

Step 1: Understanding Esterification

Esterification is a chemical reaction that forms an ester as the main product. Specifically, it involves reacting an acid with an alcohol, typically in the presence of a strong acid to facilitate the reaction.

Step 2: Role of Sulfuric Acid

In esterification, sulfuric acid (\(\mathrm{H}_2 \mathrm{SO}_4\)) is used. The acid has dual roles: it acts both as a catalyst to speed up the reaction and as a dehydrating agent, helping to remove water formed during the reaction.

Step 3: Analyzing the Options

Given the roles \(\mathrm{H}_2 \mathrm{SO}_4\) plays in esterification—catalyst and dehydrating agent—the correct answer must include both functions. This eliminates options (b), (c), and (d).

Step 4: Concluding the Correct Answer

Option (a) mentions both functions: 'dehydrating agent and catalyst.' This accurately reflects the roles of sulfuric acid in the esterification process.

Key Concepts

Sulfuric Acid

Sulfuric acid, with the chemical formula \(\mathrm{H}_2 \mathrm{SO}_4\), is a highly corrosive and dense liquid. It is an important compound in the chemical industry, known for its strong acidic and oxidizing properties. In the esterification process, sulfuric acid plays a crucial role.

Firstly, it helps to protonate the carbonyl group of the acid. This action makes the carbonyl carbon more electrophilic, encouraging the nucleophilic attack by the alcohol. This step is important for forming the ester bond.

However, this isn't the only role of sulfuric acid. It also influences the reaction as a dehydrating agent, helping to remove water that forms during the process. Thus, maintaining the forward direction of the equilibrium reaction.

Catalyst

A catalyst is a substance that increases the rate of a chemical reaction without being consumed or permanently altered itself. In the esterification reaction, sulfuric acid acts as a catalyst, specifically a proton donor catalyst.

Here's how it works:

• Sulfuric acid donates a proton to the acid involved in the esterification.
• This creates a positively charged intermediate, increasing the reaction rate.
• Although sulfuric acid speeds up the reaction, it remains unchanged at the end of the reaction.

This catalytic function is vital for practical synthesis, as it allows the reaction to occur under milder conditions and in a reasonable timeframe, enhancing overall efficiency.

Dehydrating Agent

A dehydrating agent is a substance that removes water from another compound. This is an essential function in many chemical reactions, including esterification.

In esterification, after the initial reaction, water is formed as a byproduct. The presence of water can drive the equilibrium of the reaction backward, towards the reactants, thus slowing down the formation of the ester.

Sulfuric acid's function as a dehydrating agent is to remove this water, essentially "pulling" the reaction forward to favor ester formation. This ensures that the reaction proceeds efficiently and to completion, resulting in a higher yield of the desired ester product. By doing so, sulfuric acid not only speeds up the reaction but also shifts the equilibrium towards the products, emphasizing its dual role.