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) \((\mathrm{CH}_3)_2\mathrm{NH}+\mathrm{CH}_3\mathrm{COOH}\)

Step 1: Identify the Structure of the Compound

The compound given is \((\mathrm{CH}_{3})_{2} \mathrm{NCOCH}_{3}\). This is an amide with a dimethylamine and an acetyl group attached to the nitrogen atom. In chemical terms, it is N,N-dimethylacetamide.

Step 2: Understand Hydrolysis with Acid

When an amide like N,N-dimethylacetamide is refluxed with an acid, it undergoes hydrolysis. The amide bond is cleaved, resulting in the formation of a carboxylic acid and an amine.

Step 3: Determine the Products

For N,N-dimethylacetamide, the likely products of hydrolysis are acetic acid and dimethylamine. This is due to the cleavage of the C-N bond in the amide. Thus, the products are \(\mathrm{CH}_3\mathrm{COOH}\) (acetic acid) and \((\mathrm{CH}_3)_2\mathrm{NH}\) (dimethylamine).

Step 4: Select the Correct Option

Comparing the expected hydrolysis products, \((\mathrm{CH}_3)_2\mathrm{NH}\) and \(\mathrm{CH}_3\mathrm{COOH}\), to the given options, it matches option (d): \((\mathrm{CH}_3)_2\mathrm{NH}+\mathrm{CH}_3\mathrm{COOH}\).

Key Concepts

N,N-dimethylacetamide

N,N-dimethylacetamide, often abbreviated as DMAc, is a specific type of amide. It features two methyl groups attached to the nitrogen atom, along with an acetyl group. This compound is notably used as a solvent in the chemical industry due to its excellent polarity and ability to dissolve a range of compounds.
One of its primary characteristics is its chemical stability, yet it can undergo hydrolysis under certain conditions.
When subjected to acidic conditions, N,N-dimethylacetamide can break down into simpler compounds. Understanding its structure, with the presence of a carbonyl group adjacent to the nitrogen, helps in predicting its reactivity, especially its susceptibility to hydrolysis. By identifying its structural elements, students can anticipate the types of interactions it may undergo.

Carboxylic Acid Formation

Carboxylic acids are a core functional group in organic chemistry. They feature a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group, designated as COOH. During the hydrolysis of amides, such as N,N-dimethylacetamide, carboxylic acids are common products.
The hydrolysis reaction involves breaking the molecule's amide bond in the presence of an acid or base. When an amide undergoes acid-catalyzed hydrolysis, the amide link breaks to form a carboxylic acid and an amine.
This process is crucial because it allows the transformation of amides into more reactive and functional organic acids, useful in many synthetic pathways.

• Acid catalysis increases the reaction rate by protonating the amide oxygen.
• Water acts as a nucleophile, attacking the carbonyl carbon.

The hydrolysis of N,N-dimethylacetamide in an acidic environment leads to the formation of acetic acid, a simple and widely encountered carboxylic acid.

Dimethylamine Production

Dimethylamine is one of the products obtained from the hydrolysis of N,N-dimethylacetamide. This compound is an organic amine that features two methyl groups attached to a nitrogen atom, justifying its classification as a secondary amine.
Amines like dimethylamine are characterized by their basicity, which makes them reactive in many organic transformations.
During the hydrolytic process, the amide bond in N,N-dimethylacetamide breaks, releasing dimethylamine as the nitrogen-containing product:

• The non-protonated nitrogen of the original amide retains its methyl groups, forming dimethylamine.
• Its basic nature results from the lone pair of electrons on the nitrogen atom, making it a good nucleophile.

Dimethylamine has a variety of applications, including in the production of agrochemicals, pharmaceuticals, and as a catalyst in some chemical reactions.