Problem 94 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify (a) in the following sequence of reactions. $$ \mathrm{C}_{4} \mathrm{H}_{7} \mathrm{OCl}(\mathrm{a}) \stackrel{\mathrm{NH}_{5}}{\longrightarrow} \mathrm{C}_{4} \mathrm{H}_{9} \mathrm{ON} \stackrel{\mathrm{Br}_{2}+\mathrm{NaOH}}{\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}} $$ (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COCl}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHClCHO}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{Cl}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{2} \mathrm{Cl}\)

Step-by-Step Solution

Answer

The correct compound (a) is \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COCl} \).

Step 1: Analyze Given Reaction Sequence

The reaction sequence starts with the compound \( \mathrm{C}_4 \mathrm{H}_7 \mathrm{OCl} \) and ends with the amine \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{NH}_2 \). This indicates the use of a Hoffman bromamide degradation reaction, which typically involves an amide converting to an amine, shortening the carbon chain by one carbon.

Step 2: Identify Possible Initial Compound

The initial compound \( \mathrm{C}_4 \mathrm{H}_7 \mathrm{OCl} \) could represent an acyl chloride, as their formula typically matches this given setup. We must find which option (a), (b), (c), or (d) can undergo conversion leading to correct amide and eventual amine. Looking at the options, we need an option that would easily allow chain reduction via the Hofmann bromamide degradation.

Step 3: Identify the Correct Acyl Chloride

Convert options into acyl chlorides and assess each one for continuity with reaction steps. Option (a) \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COCl} \) is an acyl chloride and can react with \( \mathrm{NH}_3 \) to produce \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CONH}_2 \). This intermediate, when subjected to \( \mathrm{Br}_2 \) and \( \mathrm{NaOH} \), aligns perfectly with the final amine product of reduced chain length. Options b, c, and d don't efficiently convert given the required reaction conditions.

Step 4: Confirm the Suitability of Option (a)

By checking the reaction sequence: \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COCl} \) ( ext{a}) with \( \mathrm{NH}_3 \) forms \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CONH}_2 \), and subsequent Hofmann degradation results in \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{NH}_2 \). This confirms (a) as the only formula matching the reaction scheme.

Key Concepts

Acyl Chloride Chemistry

Acyl chlorides are a crucial component in organic chemistry, specifically in the formation of amides and subsequent chemical transformations. They are part of a larger category of acyl compounds. These compounds feature a chlorine atom bonded to an acyl group. The general formula is \(\mathrm{RCOCl}\), where \(\mathrm{R}\) represents an alkyl or aryl group. These compounds are highly reactive due to the presence of the electron-withdrawing chlorine atom, which makes the acyl group more susceptible to nucleophilic attack.

In the context of the exercise, the given compound \(\mathrm{C}_4 \mathrm{H}_7 \mathrm{OCl}\) is identified as an acyl chloride, specifically, \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COCl}\). This reactivity is what makes it an ideal candidate for further transformations, such as forming amides with ammonia, and then engaging in Hofmann Bromamide Degradation to yield amines. Acyl chlorides are often used in synthetic pathways due to their ability to easily form esters, amides, and other key organic molecules. This makes them a linchpin in various transformations and synthetic sequences.

Amide to Amine Conversion

Amide to amine conversion is a fundamental transformation in organic chemistry, allowing for the alteration of functional groups in a controlled manner. This transformation is prominently featured in the Hofmann Bromamide Degradation reaction. The initial step involves the reaction of acyl chloride with ammonia, \(\mathrm{NH}_3\), to yield an amide. For instance, reacting \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COCl}\) with ammonia results in the formation of \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CONH}_2\).

During the Hofmann degradation process, this amide is subjected to bromine (\(\mathrm{Br}_2\)) and a strong base like sodium hydroxide (\(\mathrm{NaOH}\)). The reaction mechanism involves the formation of an isocyanate intermediate, which hydrolyzes to give the primary amine. This conversion not only changes the functional group but also shortens the carbon chain by one carbon atom, turning the \( \mathrm{C}_4 \mathrm{H}_7 \mathrm{OCl} \) starting material effectively into \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{NH}_2\). This outcome is crucial for applications where amine residues are desired, such as in pharmaceuticals and materials chemistry.

Carbon Chain Reduction

Carbon chain reduction is an essential technique in organic chemistry that allows chemists to modify or shorten carbon chain lengths within molecules. In the exercise, this is illustrated through the Hofmann Bromamide Degradation reaction, which involves the conversion of an amide to an amine, while systemically reducing the carbon chain by one unit. This type of reduction occurs because, within the reaction, an alkyl group is removed during the formation of the primary amine.

This aspect of transformation is crucial because it permits the conversion of complex, longer-chain molecules into more manageable, specific products like \(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{NH}_2\). By engaging in the Hofmann process, chemists can strategically reduce carbon backbones, enabling further transformations or direct applications in synthetic chemistry. Each reduction opens pathways for the creation of various smaller and often more reactive species, important for drug synthesis and the production of bespoke organic compounds. The sequence of these reactions embedded in the process highlights the practical utility of such conversions.

Organic Chemistry Reactions

Organic chemistry is a vast and intricate field, primarily concerned with the study of carbon-containing compounds. Various types of reactions take place in organic chemistry, facilitating the transformation of molecules in both industrial and laboratory settings. Among these, the Hofmann Bromamide Degradation exemplifies a reaction that is both necessary and utilitarian.

Organic reactions can generally be classified into categories such as substitution, addition, elimination, and rearrangement reactions. Hofmann degradation is a type of rearrangement reaction, where the migration of an acyl group occurs in the presence of bromine and a strong base. This rearrangement is key in the conversion from amide to amine, demonstrating how rearrangement reactions are used to alter functional groups and molecular structures.

• Substitution reactions: Involve one atom or group replacing another in a molecule.
• Addition reactions: Two or more molecules combine to form a larger molecule.
• Elimination reactions: Components of a molecule are removed, forming a new bond.
• Rearrangement reactions: The structural reorganization of a molecule’s constituents.

This classification allows chemists to predict products and tailor syntheses to achieve desired outcomes, demonstrating the structured complexity and utility of organic chemistry.