Reactivity of 4-R-1,2,4-triazoline-3,5-diones towards nitrone spin-traps: spectral study of the reaction with 5,5-dimethylpyrroline-N-oxide

Abstract

Previous studies of the reactivity of 4-R-1,3,4-triazoline-3,5-diones (R = CH₃, C₆H₅) have shown that, when 5,5-dimethylpyrroline-N-oxide (DMPO) is used as a spin-trap, a thermal reaction between the dione and the spin-trap occurs, leading to the same spin-adduct as by proper spin-trapping. Therefore, the reaction between two 4-R-triazolinediones (RTAD) with DMPO was investigated by combined spectral methods, including UV–Visible, FT-IR, ¹H and ¹³C NMR and EPR spectroscopy. The results were rationalised in terms of a reaction sequence in which the spin-adduct is formed via a modified version of the Forrester–Hepburn mechanism and the rate determining step is the oxidation of the spin-adduct by RTAD, leading to the final product.