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

The correct answer is (d) \((\mathrm{CH}_{3})_{2} \mathrm{NH} + \mathrm{CH}_{3} \mathrm{COOH}\).

Step 1: Understand the structure of the compound

The given compound is \((\mathrm{CH}_{3})_{2} \mathrm{NCOCH}_{3}\). It is an amide with two methyl groups attached to the nitrogen atom, and an acetyl group \(-COCH_{3}\) attached to the nitrogen.

Step 2: Identify the reaction conditions

The problem states that the compound undergoes refluxing with an acid. Refluxing typically involves heating the compound along with an acid, which can result in hydrolysis.

Step 3: Predict the likely reaction

Under acidic conditions, amides typically undergo hydrolysis to produce carboxylic acids and amines. The hydrolysis would break the C-N bond in the amide.

Step 4: Determine the products of hydrolysis

The initial structure \((\mathrm{CH}_{3})_{2} \mathrm{NCOCH}_{3}\) under acidic hydrolysis would break down into \(\left(\mathrm{CH}_{3}\right)_{2}\mathrm{NH}\) (dimethylamine) and \(\mathrm{CH}_{3}\mathrm{COOH}\) (acetic acid).

Step 5: Match the resultant products to the options

Among the given options, (d) \((\mathrm{CH}_{3})_{2} \mathrm{NH} + \mathrm{CH}_{3}\mathrm{COOH}\) correctly describes the products of the hydrolysis reaction.

Key Concepts

Reflux

Reflux is a widely used laboratory technique in chemical reactions and is crucial for facilitating reactions that require prolonged heating. The process involves heating a mixture while continuously condensing the vapor back into liquid, allowing the reaction to occur at a constant temperature without evaporating the solvents.
In the context of amide hydrolysis, reflux helps maintain the temperature required for breaking the amide bonds without the loss of volatile components. This is particularly important as many organic reactions need extended periods of heating to adequately break stable bonds, like those found in amide groups.

• The process ensures that the reaction is effective and efficient.
• It prevents loss of material and increases the reaction's efficacy.
• It allows reactions to carry on without interruption, which is crucial for completing the hydrolysis.

Dimethylamine

Dimethylamine, represented as \((CH_{3})_{2}NH\), is a secondary amine and one of the products of the hydrolysis of the amide in the given chemical reaction. It is characterized by two methyl groups attached to a nitrogen atom, giving it its distinct chemical behavior and properties.
This compound is basic in nature, making it reactive in many organic synthesis reactions. Being a small and volatile molecule, dimethylamine is soluble in water and other solvents, which makes it easier to isolate during purification after the reaction.

• It plays a role in the formation of various pharmaceuticals and agricultural chemicals.
• In industry, it's used in making solvents, rubber, and resins.
• It demonstrates typical amine properties like participating in nucleophilic substitution reactions.

Acetic Acid

Acetic acid, with the chemical formula \(CH_{3}COOH\), is the simplest carboxylic acid and a common product in organic reactions, such as amide hydrolysis. As a key product in this reaction, understanding its properties is essential.
Known for its pungent smell and sour taste, acetic acid is a weak acid but quite influential in chemical reactions, acting as both a reactant and a solvent. It is completely miscible with water and many other polar and non-polar solvents, enhancing its utility in chemical processes.

• It serves as a precursor in synthesizing various compounds, including esters and polymers.
• It can act as an acid catalyst in reactions requiring an acidic medium.
• Acetic acid's reactivity and physical properties make it a staple in laboratory and industrial settings.

Chemical Reaction Mechanism

A chemical reaction mechanism provides insight into the step-by-step process by which reactants are transformed into products, emphasizing the importance of understanding these pathways in predicting and manipulating the outcomes of reactions.
In the hydrolysis of amides, the mechanism often entails breaking the C-N bond to yield a carboxylic acid and an amine. This is typically facilitated under acidic conditions, enhancing the reaction by providing protons that help weaken and break the bonds.
Understanding the mechanism of this particular amide hydrolysis involves recognizing that given adequate thermal energy (provided often by reflux), the acid catalyst donates a proton to stabilize intermediate forms, leading to the cleavage of the bond.

• This understanding helps in optimizing conditions for the desired products.
• Knowing the mechanism allows chemists to predict side reactions and address them before they occur.
• It is crucial for designing new reactions and pathways in organic synthesis.