Problem 130 - A Complete Resource Book in Chemistry for JEE Main

Question

The refluxing of \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NCOCH}_{3}\) with acid gives (a) \(2 \mathrm{CH}_{3} \mathrm{OH}+\mathrm{CH}_{3} \mathrm{CONH}_{2}\) (b) \(2 \mathrm{CH}_{3} \mathrm{NH}_{2}+\mathrm{CH}_{3} \mathrm{COOH}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NCOOH}+\mathrm{CH}_{4}\) (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}+\mathrm{CH}_{3} \mathrm{COOH}\)

Step-by-Step Solution

Answer

(d) \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH} + \mathrm{CH}_{3} \mathrm{COOH} \)

Step 1: Understanding the Reaction

We need to determine the products formed when the compound \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NCOCH}_{3} \) is refluxed with acid. This compound is a N,N-dimethylacetamide, an amide, and we are looking for its hydrolysis products in acidic conditions.

Step 2: Acid-Catalyzed Hydrolysis of Amide

Under acidic conditions, an amide undergoes hydrolysis, breaking the \( \mathrm{C}-\mathrm{N} \) bond and forming a carboxylic acid and an amine. For \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NCOCH}_{3} \), the hydrolysis will yield \( \mathrm{CH}_{3} \mathrm{COOH} \) (acetic acid) and \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH} \) (dimethylamine).

Step 3: Identifying the Correct Reaction Products

Compare the products from the given options to see which matches the hydrolysis products we identified: \( \mathrm{CH}_{3} \mathrm{COOH} \) and \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH} \). The correct option is (d), as it lists the products as \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH} \) and \( \mathrm{CH}_{3} \mathrm{COOH} \).

Step 4: Verification

Briefly compare all possible answer options against the reaction mechanism explored. Given \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NCOCH}_{3} \) hydrolyzes to \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH} \) and \( \mathrm{CH}_{3} \mathrm{COOH} \) with an acid, option (d) is confirmed correct.

Key Concepts

N,N-dimethylacetamide

N,N-dimethylacetamide is a common organic solvent known by its formula \( (\mathrm{CH}_3)_2\mathrm{NCOCH}_3 \). It's an amide, which means it has a carbonyl group \( \mathrm{C}=\mathrm{O} \) attached to a nitrogen atom. This compound is particularly notable for its ability to dissolve a wide range of organic and inorganic compounds.
This versatility makes it valuable in different chemical reactions and industrial processes.
In the case of hydrolysis, N,N-dimethylacetamide serves as the starting material. Like most amides, under acidic conditions, it undergoes a chemical reaction where the nitrogen-carbon bond breaks.
This bond cleavage is crucial for forming the hydrolysis products, including carboxylic acids and amines. Understanding how N,N-dimethylacetamide behaves in chemical reactions aids in anticipating the outcomes of processes that involve it.

Carboxylic Acid Formation

Carboxylic acid formation is a key outcome of the hydrolysis of amides.
When an amide undergoes hydrolysis, under acidic conditions, it results in the formation of a carboxylic acid and an amine.
This reaction specifically involves breaking the \( \mathrm{C}-\mathrm{N} \) bond present in the amide group.

• The carbon atom from the carbonyl group (\( \mathrm{C}=\mathrm{O} \)) gets oxidized.
• It then forms a new bond with a hydroxyl group (\( \mathrm{OH} \)).

The product in question here is acetic acid, \( \mathrm{CH}_3\mathrm{COOH} \), one of the simplest carboxylic acids.
Acetic acid is not just a product of laboratory reactions but also a significant industrial chemical.
Understanding how carboxylic acids form helps predict the outcomes of many organic reactions, especially those involving esters and amides.

Amine Formation

Amine formation during the acid-catalyzed hydrolysis of amides is an essential concept to grasp.
An amine results after the \( \mathrm{C}-\mathrm{N} \) bond breaks in the amide under acidic conditions.
In this exercise, dimethylamine, \( (\mathrm{CH}_3)_2\mathrm{NH} \), is the produced amine.

• Amines are characterized by their nitrogen atom bonded to hydrogen atoms and/or organic groups (alkyl or aryl groups).
• They are derived from ammonia (\( \mathrm{NH}_3 \)) by replacement of one or more hydrogen atoms.

Dimethylamine is a secondary amine, meaning its nitrogen is bonded to two methyl groups rather than hydrogen atoms alone.
This reaction illustrates a fundamental organic transformation, one that is used in synthesizing pharmaceuticals and other complex molecules.
Knowing the process and results of amine formation is crucial for understanding broader concepts in organic chemistry.