Relationship of mineralization of amino naphthalene sulfonic acids by Fenton oxidation and frontier molecular orbital energies

• The frontier molecular orbital theory was applied to explain the oxidation.
• Initial rates of TOC reduction and oxalic acid production related to EHOMO and χ.
• The NH4+ production related to the electron density on the α-carbon atom of –NH2.
• The electron withdrawing effect of –SO3H groups affected the oxidation significantly.

Six amino naphthalene sulfonic acids including mono-, di- and tri-sulfonic acid compounds were studied to find the relationship between the reactivity of this kind of compounds in Fenton oxidation process and energies of the frontier molecular orbital. It was found that the initial rates of TOC reduction and oxalic acid production correlated strongly to the frontier molecular orbital energies and can be estimated by EHOMO and the absolute electronegativity (χ). The cleavage of –SO3H and –NH2 groups to produce SO42− and NH4+ species was dependent on the electron density distribution on the –SO3H moiety and the α-carbon atom connecting the –NH2 moiety. The electron withdrawing effect of the –SO3H groups influenced the mineralization of naphthalene sulfonic acids significantly. The naphthalene sulfonic acid with more –SO3H groups was more recalcitrant to the Fenton oxidation.