Question

Out of \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHClC}_{6} \mathrm{H}_{5}\), which is more easily hydrolysed by aqueous KOH.

Short answer

Benzhydryl chloride (\( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHClC}_{6} \mathrm{H}_{5} \)) is more easily hydrolysed.

Step-by-step solution

Identify the Compounds

The first compound is \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl} \), which is benzyl chloride. The second compound is \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHClC}_{6} \mathrm{H}_{5} \), known as benzhydryl chloride.

Analyze the Structural Differences

Benzyl chloride has the \(-\mathrm{CH}_2\mathrm{Cl} \) group attached to the benzene ring, while benzhydryl chloride has \(-\mathrm{CHCl}\) bonded to two benzene rings. The carbon holding the chlorine in benzhydryl chloride is tertiary, whereas it is primary in benzyl chloride.

Evaluate Hydrolysis Conditions

In aqueous KOH, hydrolysis reactions typically occur more readily with compounds that have a better leaving group and a more stable carbocation intermediate. Benzhydryl chloride, with its tertiary carbon, can form a more stable carbocation compared to benzyl chloride's primary carbon.

Determine Reactivity

Due to the stability of the carbocation in benzhydryl chloride, this compound will undergo hydrolysis more easily. The tertiary carbocation is stabilized by the resonance effect of the adjacent benzene rings.

Key concepts

Benzyl Chloride

Benzyl chloride is a chemical compound with the structural formula \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl}\). In this structure, a chlorine atom is attached to a \(-\mathrm{CH}_2\) group, which in turn, is connected to a benzene ring.
This makes the carbon housing the chlorine a primary carbon.
Benzyl chloride is known for its use in organic chemistry as an alkylating agent.

• Primary Carbon: The primary nature of the carbon means that it is bonded to only one other carbon atom, the benzene ring.
• General Reactivity: Benzyl chloride can participate in nucleophilic substitution reactions, but its primary carbon leads to less stable reaction intermediates.

This can result in slower reaction rates compared to compounds with more stable carbocation intermediates.

Benzhydryl Chloride

Benzhydryl chloride, chemically represented as \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHClC}_{6} \mathrm{H}_{5}\), is a compound where chlorine is attached to a tertiary carbon. This carbon is bonded to two benzene rings, giving significant differences compared to benzyl chloride.

• Tertiary Carbon: The tertiary carbon is central to its high reactivity as it can form a much more stable carbocation during reactions.
• Structural Characteristics: The two benzene rings offer resonance stability, facilitating a stable carbocation once chlorine leaves.

The presence of two benzene rings adjacent to the reactive center improves electron delocalization, making benzhydryl chloride more reactive in hydrolysis.

Carbocation Stability

Carbocations are positively charged ions that are intermediates in many organic reactions. Their stability significantly impacts the likelihood of a reaction occurring.

• Primary vs. Tertiary Carbocations: In general, tertiary carbocations are more stable than primary ones, as they have more alkyl groups available to donate electron density, thereby stabilizing the positive charge.
• Resonance Stabilization: For benzhydryl chloride, the tertiary carbocation benefits from resonance stabilization due to the benzene rings, further increasing its stability.

In contrast, benzyl chloride forms a less stable primary carbocation, which does not benefit from the same degree of stabilizing interactions.

Hydrolysis

Hydrolysis is a chemical reaction wherein a bond is broken by the addition of water. In the context of organic compounds, it's often used to convert halides into alcohols using a base like KOH.

• Mechanism: Typically, hydrolysis of alkyl halides proceeds via nucleophilic substitution, where a hydroxide ion attacks the carbon bonded to the halide, displacing the halide ion.
• Factors Influencing the Reaction: Compounds with more stable carbocations undergo hydrolysis more easily, as they support the intermediate formed during the reaction.

Given these principles, benzhydryl chloride, having a more stable tertiary carbocation, reacts more readily with aqueous KOH, compared to benzyl chloride.