Photooxidation of Some Aromatic Sulfonic Acids with Alkaline Hypochlorite

Abstract

Abstract Photochemical oxidation of aromatic sulfonic acids such as p-cumenesulfonic, 2-mesitylenesulfonic, 1- and 2-naphthalenesulfonic acids with aqueous sodium hypochlorite has been studied. Addition of a large excess of alkali enhances the decomposition of sulfonic acids remarkably. p-Cumenesulfonic and 2-mesitylenesulfonic acids are oxidized faster than 1- and 2-naphthalenesulfonic acids. The photooxidation of sulfonic acids with an equimolar amount of hypochlorite gives intermediary oxidation products involving desulfonation to parent hydrocarbons, aromatic hydroxylation, side-chain oxidation, and ring cleavage; e.g., p-cumenesulfonic acid gives cumene, 2- and 4-isopropylphenol and 2-phenyl-2-propanol; 1- and 2-naphthalenesulfonic acids give phthalic anhydride. Light-absorbing aromatic sulfonic acids sensitize the decomposition of hypochlorite ion leading to hydroxyl radical, which reacts mainly with ground state sulfonic acid to give radical intermediates. The photooxidation may also involve direct C–S bond fission of sulfonic acids.