EPR study of the arylnitro anion radicals formed in the reaction between some aminoarenes, sodium nitrite and ascorbate

Abstract

By EPR spectroscopy it was shown that stable free radicals are formed at room temperature in :reaction mixtures containing sodium nitrite and aminoarenes such as 4-aminobenzoic acid, sulfanilic acid, 3,5dimethoxyaniline 3,4,5-trimethoxyaniline, 3,5-dibromo-4-aminobenzenesulfonic acid, aminobenzene, 4fluoroaniline or 4-methoxybenzenediazonium ions together with ascorbic acid when first dissolved in water followed by the addition of NaOH to an alkaline pH. The radicals appeared without any previous irradiation with UV light. The EPR spectra exhibited an interaction of the unpaired electron with one nitrogen nucleus and the hydrogen nuclei of the parent aminoarenes. By use of [¹⁵N]nitrite it was found that the nitrogen atom of the radicals was derived from the nitrite ion. It is suggested that the radicals are arylnitro anion radicals ArNO₂˙^–. The reaction involves the formation of aryldiazonium ions ArNN (acidic conditions) in the reaction with nitrite, followed by their reduction to aryl radicals Ar˙ in the reaction (alkaline conditions) with ascorbic acid. The radicals Ar˙ combine with nitrite ions to give the observed arylnitro anion radicals ArNO₂˙^–.