Identify the major product formed in the following reaction:

Step-by-step solution

The given reactant is phthalic acid (benzene-1,2-dicarboxylic acid). The reagent P₂O₅ (phosphorus pentoxide) acts as a strong dehydrating agent. When phthalic acid is heated with P₂O₅ , it undergoes intramolecular dehydration. A molecule of water ( H₂O ) is eliminated from the two adjacent carboxylic acid ( -COOH ) groups. This elimination leads to the formation of a five-membered cyclic anhydride ring fused to the benzene ring. The resulting major product is phthalic anhydride. The structure of phthalic anhydride