Electron spin resonance study of radicals derived from cyclic hydrazides

Abstract

Transient radicals derived from cyclic hydrazides (QH₂), generated by in situ photolysis of flowing aqueous solutions in the presence of either added oxidants or reductants, have been studied by e.s.r. The radicals obtained through one-electron oxidation at basic pH values have a semiquinone-type structure (Q^–˙) of the same type as certain intermediates in the chemiluminescence of luminol and other cyclic hydrazides. At acidic pH values, the conjugate acids (QH˙) of the semiquinone radicals derived from cyclic hydrazides of both phthalic and naphthalene-2,3-dicarboxylic acids were identified as the corresponding o-formyl carboxylate radicals, produced through a mechanism involving loss of dinitrogen. Reduced radicals (QH₂^–˙ and QH^2–˙) generated in aqueous solution in the presence of propan-2-ol were detected only in the case of cyclic maleohydrazide. Reactions of hydrazides with the OH˙ radical were also investigated; an OH-adduct to the CC bond of the protonated maleohydrazide was identified in the pH range 2–3.