When phenol reacts with ammonium sulfite in the presence of ammonia, it undergoes a chemical reaction known as the Bucherer reaction. This reaction results in the formation of 4-aminophenol, also known as p-aminophenol.

The reaction mechanism involves the initial nucleophilic attack of the sulfite ion (SO3^2-) on the phenol ring, followed by the addition of ammonia to form an intermediate product. This intermediate then undergoes a rearrangement to give p-aminophenol. The presence of ammonia in the reaction mixture is essential for the formation of the intermediate and the subsequent rearrangement.

The overall reaction can be represented as follows:

Phenol + Ammonium sulfite + Ammonia → p-Aminophenol + Ammonium sulfate

This reaction is commonly used in the synthesis of p-aminophenol, which is an important intermediate in the production of various dyes, pharmaceuticals, and photographic developers.