Kinetics of oxidation of benzenediols by (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(III) in aqueous acidic media

Abstract

The kinetics of the oxidation of hydroquinone (H2Q), catechol (H2cat) and substituted catechols with nickel(III) macrocycle [NiL1]3+ (L1 = 1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) has been studied spectrophotometrically in aqueous perchloric acid in the presence of sulfate. Over the pH range 1–2.6, and at higher sulfate concentration 0.05 < [SO4 2−] < 0.2 mol dm−3, the decomposition of [NiIIIL1] in the oxidation of benzenediols via [NiIIIL1(OH)(H2O)] is small. With hydroquinone, the rate constant is almost independent of the hydrogen ion concentration and with catechols, the involvement of catechol anion (Hcat−) has been considered. The rate constants for cross reactions are discussed in terms of the Marcus relationship.