Stoichiometry and kinetics of the reaction between manganese(III) and hydroquinone in acid perchlorate solution

Abstract

The stopped-flow method has been used to investigate the kinetics of the rapid reaction between manganese(III) and hydroquinone in aqueous perchlorate solution at 25°. The sole oxidation product was p-benzoquinone using spectrophotometric analysis, and the stoichiometry of the reaction corresponded to 2Mn(III)+ p-C₆H₄(OH)₂→ 2Mn(II)+ p-C₆H₄O₂+ 2H⁺. The reaction rate was first-order in each reactant, and was independent of variations in [Mn(III)]₀, [p-hydroquinone]₀, [Mn(II)], total ionic strength, [NaClO₄], [NaNO₃] and the presence of oxygen, at fixed acidity. Variation of acidity in the range [HClO₄]= 0.60–3.60 M was used to determine the rate constants k₁= 0.48 × 10⁴ M^–1 sec^–1 and k₁′= 3.28 × 10⁴ M^–1 sec^–1 for reaction of Mn³⁺_aq and MnOH²⁺_aq with the hydroquinone molecule, respectively.