The reaction of benzenediazonium chloride with phenol to give p-hydroxy azobenzene is which of the following type of reaction?

Question

Accepted Answer

The reaction of benzenediazonium chloride with phenol to give p-hydroxy azobenzene is an example of an electrophilic substitution reaction. Here's a detailed explanation supporting why Option 3 is correct and why the other options are incorrect:

1. **Explanation for Option 3 (Electrophilic substitution reaction):**
   - In this reaction, the benzenediazonium ion acts as an electrophile. The diazonium group is highly reactive and can easily form a bond with nucleophilic sites.
   - Phenol, which contains an electron-rich aromatic ring, acts as the nucleophile. The hydroxyl group (-OH) on phenol increases the electron density on the benzene ring, particularly at the ortho and para positions, making it more reactive towards electrophiles.
   - The reaction proceeds through the formation of a sigma complex (also known as an arenium ion), where the diazonium ion substitutes a hydrogen atom on the aromatic ring of phenol, specifically at the para position, leading to the formation of p-hydroxy azobenzene.
   - This mechanism is characteristic of electrophilic aromatic substitution reactions, where an electrophile replaces a hydrogen atom on an aromatic ring.

2. **Why Option 1 (Electrophilic addition reaction) is incorrect:**
   - Electrophilic addition reactions typically occur in alkenes and alkynes, where an electrophile adds across a carbon-carbon double or triple bond. In this case, there is no addition across a double bond; instead, there is a substitution on an aromatic ring.

3. **Why Option 2 (Nucleophilic addition reaction) is incorrect:**
   - Nucleophilic addition reactions involve a nucleophile adding to a carbon atom, typically in carbonyl compounds. This reaction does not involve the addition of a nucleophile to a carbonyl group but rather the substitution of a hydrogen atom on an aromatic ring by an electrophile.

4. **Why Option 4 (Nucleophilic substitution reaction) is incorrect:**
   - Nucleophilic substitution reactions involve the replacement of a leaving group by a nucleophile. This reaction does not involve a nucleophile replacing a leaving group on a saturated carbon atom but rather an electrophile substituting a hydrogen atom on an aromatic ring.

In conclusion, the reaction between benzenediazonium chloride and phenol to form p-hydroxy azobenzene is best described as an electrophilic substitution reaction, making Option 3 the correct choice.