Problem 74 - A Complete Resource Book in Chemistry for JEE Main

Question

An organic compound ' \(\mathrm{X}\) ' with a molecular formula \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\) when reacts with excess of methyl magnesium chloride following by acidification gives an alcohol ' \(\mathrm{Y}\) ' only, when this alcohol ' \(\mathrm{Y}\) ' is oxidized with \(\mathrm{NaOCl}\) followed by acidification, acidic acid is formed. Here the compound ' \(\mathrm{X}\) ' is (a) Propyl methanoate (b) Isopropyl methanoate (c) Ethyl ethanoate (d) Both (a) and (b)

Step-by-Step Solution

Answer

Compound 'X' is ethyl ethanoate (c).

Step 1: Understand the Problem

We are given a compound 'X' with formula \( \mathrm{C}_4 \mathrm{H}_8 \mathrm{O}_2 \) that reacts with methyl magnesium chloride to form an alcohol 'Y'. When 'Y' is oxidized, it forms acetic acid. We need to identify the compound 'X' from the given options.

Step 2: Analyze the Reaction with Grignard Reagent

The reaction between \( \mathrm{C}_4 \mathrm{H}_8 \mathrm{O}_2 \) and methyl magnesium chloride suggests that 'X' is likely an ester. When an ester reacts with a Grignard reagent like methyl magnesium chloride (\(\mathrm{CH}_3\mathrm{MgCl}\)), it typically forms a tertiary alcohol after hydrolysis.

Step 3: Understand the Formation of Alcohol 'Y'

Since the alcohol 'Y' results from the reaction of 'X' with excess methyl magnesium chloride, 'Y' must be a tertiary alcohol with a base structure that can be oxidized to acetic acid.

Step 4: Connect the Oxidation Step

Acetic acid is \( \mathrm{CH}_3\mathrm{COOH} \). The oxidative product of alcohol 'Y' leading to acetic acid indicates that 'Y' must have a portion that forms acetyl group \( \mathrm{CH}_3\mathrm{CO} \) upon oxidation.

Step 5: Identify the Compound 'X'

Esters such as ethyl ethanoate when reacted with excess methyl magnesium chloride give tert-butanol or an alcohol that upon oxidation provides acetic acid. This matches with ethyl ethanoate, which reacts as:\[ \mathrm{C}_2\mathrm{H}_5\mathrm{COOCH}_3 \] (Ethyl Ethanoate) to form tertiary alcohols when reacted with \(\mathrm{CH}_3\mathrm{MgCl}\).

Step 6: Verify the Choices Given

Among the given options, ethyl ethanoate fits the described reactions perfectly since it can react with the Grignard reagent to form an alcohol that can eventually produce acetic acid upon oxidation with NaOCl and acidification.

Key Concepts

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds and their structures, properties, and reactions. It forms the basis for understanding countless chemical processes, especially those related to living organisms. Organic compounds, like the one in this exercise, are often classified by functional groups which are specific arrangements of atoms that dictate the chemical behavior of the molecule.
In this problem, the compound 'X' with the formula \( \mathrm{C}_4 \mathrm{H}_8 \mathrm{O}_2 \) is being investigated. This formula hints at an ester due to the presence of both oxygen atoms in a typical ester structure \( \text{R}-\mathrm{COO}-\text{R}' \). Esters are vital in organic chemistry since they react uniquely with different reagents, making them useful in synthetic chemistry.
Understanding organic chemistry allows us to predict and manipulate chemical reactions to achieve desired results, such as synthesizing new compounds or transforming one compound into another.

Ester Hydrolysis

Ester hydrolysis is a reaction where an ester is broken down into its corresponding alcohol and carboxylic acid components. This can occur under acidic or basic conditions and is a key reaction in organic chemistry.
In acidic conditions, the ester reacts with water in the presence of an acid to produce the acid and the alcohol. In basic conditions, also known as saponification, the ester reacts with a hydroxide ion to form a carboxylate ion and an alcohol.
In our exercise, the ester \( \text{X} \) undergoes hydrolysis when it reacts with the Grignard reagent, methyl magnesium chloride \( \mathrm{CH}_3\mathrm{MgCl} \), in excess, followed by acidification. This results in the formation of a tertiary alcohol, 'Y'.

• The Grignard reagent is a powerful nucleophile, meaning it seeks out positive centers to donate electrons.
• It adds to the carbonyl carbon, breaking the ester into an alcohol after subsequent hydrolysis.

Oxidation of Alcohols

The oxidation of alcohols is a common transformation in organic chemistry, where an alcohol is converted into a carbonyl compound. This is achieved by using oxidizing agents, which vary in strength and properties.
In this exercise, the alcohol 'Y' produced from ester 'X' undergoes oxidation. This is achieved by using sodium hypochlorite \( \mathrm{NaOCl} \), a common household bleach and also an oxidizing agent.
This process can take a primary alcohol to an aldehyde and further to a carboxylic acid, but in the case of 'Y', a tertiary alcohol, it directly forms acetic acid. Tertiary alcohols often resist oxidation under mild conditions, but with appropriate reagents, they can undergo rearrangement and form carboxylic acids through oxidative cleavage.

• The condition is that the tertiary alcohol has the potential to break down and rearrange into a structure that can further be oxidized to form acetic acid \( \mathrm{CH}_3\mathrm{COOH} \).
• This is a classic example of using specific reagents and conditions to achieve desired chemical transformations, highlighting the power of organic synthesis.