Naphthalene can sublime directly to vapour upon heating, but benzoic acid do not. Related Theory When benzoic acid is heated in presence of a strong dehydrating agent like P2O5 or H2SOf it forms benzoic anhydride. 2C6H5COOHBaOl5⟶(C6H5CO)2O+H2O Caution Naphthalene is volatile and benzoic acid is non-volatile due to the formation of dimer via hydrogen bonding (intermolecular).