Question

Benzyl chloride \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl}\right)\) can be prepared from toluene by chlorination with (1) \(\mathrm{SO}_{2} \mathrm{Cl}_{2}\) (2) \(\mathrm{SOCl}_{2}\) (3) \(\mathrm{Cl}_{2}\) (4) \(\mathrm{NaOCl}\) (a) 1 and 3 (b) 1 and 4 (c) 2 and 3 (d) 4

Short answer

The correct answer is (a) 1 and 3.

Step-by-step solution

Understand the Reaction

Benzyl chloride is produced by the chlorination of the methyl group in toluene. This can occur via free radical chlorination using chlorine gas or sulfuryl chloride, which are strong chlorinating agents.

Analyze Chlorinating Agents

Evaluate each chlorinating agent:1. \(\mathrm{SO}_{2}\mathrm{Cl}_{2}\) (Sulfuryl chloride) is a chlorinating agent and can produce benzyl chloride by free radical mechanism.2. \(\mathrm{SOCl}_{2}\) (Thionyl chloride) is generally used for chlorination of alcohols, not effective for replacing a hydrogen in hydrocarbons.3. \(\mathrm{Cl}_{2}\) (Chlorine gas) effectively replaces hydrogen in hydrocarbons like toluene, especially when illuminated by light or heat.4. \(\mathrm{NaOCl}\) (Sodium hypochlorite) is a weak oxidizing agent and generally used for chlorination of water or in mild chlorinations.

Choose Correct Options

Based on the analysis:- Option (1) \(\mathrm{SO}_{2} \mathrm{Cl}_{2}\) and option (3) \(\mathrm{Cl}_{2}\) are suitable for preparing benzyl chloride by chlorination of toluene.

Finalize Correct Answer

Given the problem choices, (a) 1 and 3 is the appropriate solution since both \(\mathrm{SO}_{2} \mathrm{Cl}_{2}\) and \(\mathrm{Cl}_{2}\) can successfully chlorinate toluene to form benzyl chloride.

Key concepts

Benzyl Chloride Preparation

Benzyl chloride is an important compound that can be synthesized from toluene, a simple aromatic hydrocarbon. The process involves the substitution of one hydrogen atom in the methyl group of toluene with a chlorine atom, resulting in the formation of benzyl chloride the chemical formula \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl}\). The preparation is typically achieved through chlorination, specifically targeting the side chain methyl group.

• The use of certain chlorinating agents facilitates this replacement process.
• For instance, sulfuryl chloride (\(\mathrm{SO}_{2}\mathrm{Cl}_{2}\)) and chlorine gas (\(\mathrm{Cl}_{2}\)) are both effective agents for this conversion.

Given their high reactivity, these agents are suitable for carrying out the desired substitution in such reactions. The choice of chlorinating agents greatly influences the efficiency and outcome of the preparation process.

Free Radical Chlorination

Free radical chlorination is a chemical reaction mechanism commonly used for halogenation of hydrocarbons like toluene. This process involves three main steps: initiation, propagation, and termination, which collectively form the free radical chain mechanism.In the initiation step, free radicals are generated through the homolytic cleavage of chlorine molecules (\(\mathrm{Cl_{2}}\)). This can be induced by heat or light, particularly ultraviolet light.

• A chlorine molecule absorbs energy and splits into two chlorine atoms, each possessing an unpaired electron, making them highly reactive radicals.
• These chlorine radicals then attack the weaker C-H bonds of toluene's methyl group, forming hydrogen chloride and a benzyl radical in the propagation step.

The benzyl radical reacts with another chlorine molecule, yielding benzyl chloride and regenerating a chlorine radical. This cycle continues until the radicals are depleted or stabilized, often in the termination phase where the radicals combine to form more stable molecules. Such a mechanism is effective and preferred for the production of benzyl chloride under controlled conditions.

Chlorinating Agents for Hydrocarbons

Chlorination of hydrocarbons like toluene requires the right choice of chlorinating agents to ensure efficient substitution reactions. Different agents have varying reactivities and suitabilities, depending on the specific hydrocarbon and site of chlorination desired.**Common Chlorinating Agents Include:**

• **Chlorine Gas (\(\mathrm{Cl}_2\))**: A powerful oxidizing agent used for direct chlorination, effective especially with the presence of light or heat.
• **Sulfuryl Chloride (\(\mathrm{SO}_{2}\mathrm{Cl}_{2}\))**: It is often used for substituting hydrogen in hydrocarbons like toluene due to its effectiveness in producing radicals necessary for the free radical mechanism.
• **Sodium Hypochlorite (\(\mathrm{NaOCl}\))**: While useful in mild chlorination reactions, it is not typically effective for substituting hydrogen in hydrocarbons compared to more reactive agents like chlorine gas.
• **Thionyl Chloride (\(\mathrm{SOCl}_{2}\))**: Primarily used to chlorinate alcohols rather than hydrocarbons, and does not efficiently replace hydrogen in toluene's methyl group.

The choice of chlorinating agent significantly influences the success of the reaction and the specific substitution pattern observed in the resulting product.