Question

The compound formed on heating chlorobenzene with chloral in the presence of concentrated sulphuric acid is [2004] (a) gammexane (b) DDT (c) freon (d) hexachloroethane

Short answer

The compound is DDT (option b).

Step-by-step solution

Identify the Reaction Components

To solve this problem, start by identifying the reactants in the provided reaction. Chlorobenzene and chloral are being reacted in the presence of concentrated sulphuric acid. This combination is key in forming a well-known compound.

Recall the Reaction

The combination of chlorobenzene and chloral in the presence of concentrated sulfuric acid leads to the DDT synthesis. This reaction is known after the organic chemical DDT (Dichloro-Diphenyl-Trichloroethane). It's a famous historical pesticide.

Establish the Correct Product

Based on the previous step, recognize that the compound formed is DDT. It's a chlorinated hydrocarbon known for its use in agriculture and pest control.

Confirm the Correct Answer

Review the options and verify that the compound we identified, which is formed from this reaction, matches one of them. Option (b) DDT matches the expected product.

Key concepts

Chlorobenzene

Chlorobenzene is an aromatic organic compound with the chemical formula \(C_6H_5Cl\). It consists of a benzene ring with one chlorine atom substituted for one hydrogen atom. This substitution significantly affects the chemical reactions and properties of the compound.
Chlorobenzene is a colorless, flammable liquid that has a distinct almond-like odor. It is heavier than water and slightly soluble in it. Chlorobenzene is relatively unreactive due to the stability of the benzene ring, making reactions slower unless high temperatures or catalysts are utilized.
Some key points about chlorobenzene include:

• It is used in the production of other chemicals like phenol and aniline.
• Historically, it has been employed as a solvent or an intermediate in the synthesis of DDT.
• It's less reactive than other halobenzenes due to the resonance stabilization of the benzene ring.

Chloral

Chloral, or trichloroacetaldehyde, is a chemical compound with the formula \(CCl_3CHO\). It possesses a very high reactivity due to the presence of three chlorine atoms and an aldehyde group. This reactivity makes it a valuable intermediate in various organic reactions.
Chloral is a colorless oily liquid that has a pungent odor similar to that of other chlorine-containing chemicals. It dissolves in water to form chloral hydrate, an important compound historically used as a sedative and hypnotic.
Here are a few noteworthy aspects of chloral:

• In chemical reactions, chloral acts as an electrophile due to the electron-withdrawing effects of the chlorine atoms.
• It reacts with aromatic compounds like chlorobenzene to form more complex structures.
• The compound played a significant role in pharmaceutics before its primary usage shifted to industrial applications.

DDT Synthesis

DDT (Dichloro-Diphenyl-Trichloroethane) synthesis is a famous organic chemistry reaction known for producing a powerful insecticide. The synthesis involves reacting chlorobenzene with chloral in the presence of concentrated sulfuric acid.
The mechanism begins with the protonation of chloral by sulfuric acid, turning the chloral molecule into a more reactive species. This reacts with chlorobenzene and results in the formation of DDT, a reaction that primarily occurs under acidic conditions provided by the sulfuric acid catalyst.
DDT was once extremely popular in agriculture and pest control for its effectiveness. However, due to environmental concerns and its persistence in ecosystems, its use has drastically declined.
Key aspects of DDT synthesis include:

• It requires an acidic environment, typically provided by a catalyst like sulfuric acid, to proceed effectively.
• The resulting DDT is a chlorinated hydrocarbon, which contributes to its chemical stability and persistence in the environment.
• Although effective in pest control, the environmental ramifications of DDT led to stricter regulations and bans in many countries.

Sulphuric Acid Catalyst

Sulphuric acid (\(H_2SO_4\)) is a powerful acid and an essential component in numerous chemical reactions as a catalyst. Its primary role in the DDT synthesis process is to facilitate the conversion of reactants into the final product by providing the necessary acidic environment.
As a catalyst, sulphuric acid does not get consumed in the reaction. Instead, it accelerates the reaction rate by lowering the activation energy, making the reaction more efficient.
Specific applications of sulphuric acid include:

• It acts as a dehydrating agent in some reactions.
• It protonates compounds, making them more reactive, which is crucial in organic syntheses like DDT production.
• It is widely used in various industries, ranging from chemical manufacturing to petroleum refining.

Sulphuric acid’s utility as a catalyst showcases its vital role in advancing numerous chemical processes, both industrial and academic.