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 QH2–˙) 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.