Problem 147 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

The reaction between chlorobenzene and chloral in the presence of concentrated sulphuric acid produces: [P (PMT) 2001| (a) gammexane (b) \(p_{i} p^{\prime}\)-dichloro diphenyl trichloro ethane (c) chloropicrin (d) benzene hexachloride

Step-by-Step Solution

Answer

Option (b): p-p'-dichloro diphenyl trichloro ethane is produced.

Step 1: Understand the Reactants

Identify the reactants given in the problem. The reaction involves chlorobenzene and chloral in the presence of concentrated sulphuric acid. Chlorobenzene is a benzene ring with a chlorine atom attached, and chloral is trichloroacetaldehyde, represented as CCl₃CHO.

Step 2: Identify the Required Conditions and Catalyst

The problem specifies the presence of concentrated sulphuric acid. This acts as a catalyst for the reaction, facilitating the condensation process.

Step 3: Analyze Possible Products Based on Reactants

Consider the likely reaction products when chlorobenzene reacts with chloral (CCl₃CHO) in the presence of concentrated sulfuric acid. The known reaction between these compounds typically involves the formation of DDT (DichloroDiphenylTrichloroethane).

Step 4: Match with Given Options

Based on the possible products, match the most likely product to the options given in the question. DDT is chemically described as p-p'-dichloro diphenyl trichloro ethane, which matches option (b).

Step 5: Choose the Correct Answer

Given the analysis above, the reaction between chlorobenzene and chloral in the presence of sulfuric acid produces DDT, which corresponds to option (b): p-p'-dichloro diphenyl trichloro ethane.

Key Concepts

Chlorobenzene

Chlorobenzene is an aromatic compound featuring a benzene ring bonded to a chlorine atom. Its chemical formula is C₆H₅Cl, and it serves as a key building block in many chemical reactions.

• Chlorobenzene is colorless and has a distinctive almond-like smell.
• It is moderately soluble in water but well soluble in organic solvents such as ethanol and diethyl ether.

In organic chemistry, chlorobenzene is often used due to its ability to introduce chlorine into larger compounds effectively. This property is useful in the synthesis of various complex molecules.
Many reactions involving chlorobenzene focus on the substitution of the chlorine atom, leading to the formation of other important chemicals. In this context, the reaction with chloral is a notable example.

Chloral

Chloral, chemically known as trichloroacetaldehyde (CCl₃CHO), is an organic compound that is a key reagent in synthesis reactions.

• Chloral is a colorless liquid with a pungent smell and is highly reactive due to its functional groups.
• Its reactivity stems from the presence of three electron-withdrawing chlorine atoms bonded to the carbon adjacent to the carbonyl group.

These electron-withdrawing chlorine atoms make chloral an electronegative compound, enhancing its ability to participate in nucleophilic attacks.
Chloral is significant in the formation of substances like DDT, where it reacts with compounds containing nucleophilic substitution sites, such as chlorobenzene discussed above. This reaction is a classical example in understanding electrophilic aromatic substitution reactions.

Sulfuric Acid Catalysis

Sulfuric acid (H₂SO₄) is a powerful acid widely used as a catalyst in various organic reactions, including those involving chlorobenzene and chloral.

• As an acid catalyst, it donates protons to facilitate chemical reactions by lowering the activation energy.
• It plays a crucial role in the condensation reactions by enhancing the electrophilicity of reactive species.

In the interaction between chlorobenzene and chloral, concentrated sulfuric acid serves as a co-reagent that helps to drive the reaction towards the formation of complex organic compounds like DDT.
Its strong acidic nature helps to accelerate the reaction, ensuring a higher yield of the desired product. This catalysis method demonstrates the fundamental role of acids in modifying reaction pathways and encouraging product formation in organic chemistry.