Reactivities of hydrogen peroxide and the hydroperoxide ion towards 3,4-benzotropolone-1′,2′-quinone anions

Abstract

Rate constants and activation parameters have been obtained for the reactions of hydrogen peroxide and the hydroperoxide ion at the 4′-positions of 3′-substituted 3,4-benzotropolone-1′,2′-quinone monoanions. The hydroperoxide ion is shown to be 7–10 times as reactive as the peroxide molecule. Comparison of these figures with those previously obtained for the similar reactions of the purpurogalloquinone dianion shows that charge repulsions between substrate and reagent ions determine which of the peroxide species is the more reactive, and suggests that entropy factors exert decisive control of the reactivity of the hydroperoxide ion in these reactions. Comparison of rate constants for peroxide decomposition of the isomeric 3′- and 4′-methyl-3,4-benzotropolone-1′,2′-quinones shows that the 4′-methyl isomer is the more reactive: this is attributed to activation of the 3′-position by conjugation with the tropolone carbonyl group.