Problem 45 - A Complete Resource Book in Chemistry for JEE Main

Question

When benzenediazonium chloride is treated with water, the compound formed is (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\)

Step-by-Step Solution

Answer

(b) \(C_6H_5OH\).

Step 1: Identify Reactants and Products

The question involves benzenediazonium chloride. Recognize the chemical formula for benzenediazonium chloride as \(C_6H_5N_2Cl\). When this compound reacts with water, a substitution reaction occurs.

Step 2: Consider the Mechanism

Understand that benzenediazonium ion decomposes in water to form phenol \((C_6H_5OH)\). This reaction involves the replacement of the diazonium group with a hydroxyl group, thus forming phenol as the primary product.

Step 3: Analyze Possible Products

Examine each option: (a) Benzoic acid (\(C_6H_5COOH\)), but benzoic acid is not formed in this reaction. (b) Phenol (\(C_6H_5OH\)), which is a typical product in this reaction. (c) Benzene (\(C_6H_6\)), is formed by reduction. (d) Aniline (\(C_6H_5NH_2\)), is the starting material for diazonium salts, not a product.

Step 4: Select the Correct Option

Based on the analysis, the compound formed when benzenediazonium chloride is treated with water is \(C_6H_5OH\), which corresponds to choice (b).

Key Concepts

Diazonium Compounds

Diazonium compounds are a fascinating category of organic molecules characterized by their unique functional group, the diazonium group \(N_2^+X^-\). These compounds often contain an aromatic ring, such as benzene, attached to the diazonium group. A well-known example is benzenediazonium chloride, represented as \(C_6H_5N_2Cl\).

The diazonium group is highly reactive and can undergo various chemical transformations. This makes diazonium compounds valuable intermediates in organic synthesis. They are essential in the preparation of azo dyes, as well as in various substitution and coupling reactions.

• Diazonium salts are typically formed from anilines \((C_6H_5NH_2)\), through reaction with nitrous acid.
• They are often used because they can be easily converted into a multitude of other functional groups.

Understanding diazonium compounds lays the foundation for comprehending many complex reactions in organic chemistry, particularly involving aromatic compounds.

Substitution Reaction

A substitution reaction is a type of chemical reaction where an atom or a group of atoms in a molecule is replaced by another atom or group of atoms. In the context of diazonium compounds, the diazonium group \(N_2^+\) can be substituted by other groups, such as hydroxyl \(OH^-\), to yield different products.

In the reaction involving benzenediazonium chloride \(C_6H_5N_2Cl\), water acts as the substituting reagent. The diazonium group is replaced by a hydroxyl group, producing phenol \(C_6H_5OH\). This reaction showcases the utility of diazonium salts in organic chemistry. They allow for the transformation of functional groups through simple substitution processes. Key points include:

• Substitution reactions can be influenced by temperature and pH.
• They often involve nucleophiles like \(OH^-\) displacing leaving groups such as \(N_2\).

Recognizing the nature of substitution reactions helps in predicting the outcomes of chemical processes involving diazonium compounds.

Phenol Formation

Phenol formation is a significant biochemical and industrial process. It involves the conversion of organic precursors to phenol \(C_6H_5OH\), which is an important compound in its own right. In the case of the benzenediazonium chloride reaction, phenol is formed as a result of the substitution reaction with water.

Phenol is not only crucial for academic studies but also for industrial applications. It serves as a precursor for plastics, pharmaceuticals, and other synthetic materials.

• Phenols have antiseptic properties and are used in the production of detergents and synthetic resins.
• The production of phenol from diazonium salts is an excellent demonstration of the controlled formation of functional aromatic compounds.

The formation of phenol highlights both the versatility and the utility of diazonium compounds in chemical synthesis and practical applications.