Electron paramagnetic resonance study of the reactions of the spin trap 3,5-dibromo-4-nitrosobenzenesulfonate

Using rapid-mixing, continuous-flow TiCl3-based techniques and also by means of static-sample studies involving the thermal decomposition of symmetric aliphatic azo compounds, we have characterized by electron paramagnetic resonance 22 spin adducts of 3,5-dibromo-4-nitrosobenzenesulphonate, 1, in aqueous solution at 25 °C. These spin adducts, all nitroxides, exhibit a moderately wide range of a-nitrogen and β-CH proton splitting constants, which we discuss in terms of steric and electronic effects. In connection with these studies, blank experiments showed that aqueous solutions of 1 gave no radicals when exposed to light and heat. In addition, we have studied by electron paramagnetic resonance at 25 °C static samples of aqueous solutions of 1 both by itself and in the presence of each of several acrylic and methacrylic monomers and in both the presence and absence of light. These solutions yielded radicals, namely, nitroxides, only when containing methacrylic monomers, the presence of light having no effect. These observations support the "ene" addition/oxidation mechanism of nitroxide formation.