Nitroxide radicals. Part XII. Decomposition of ortho-, meta-, and para-halogenophenyl t-butyl nitroxides

Abstract

The spontaneous decomposition of t-butyl p-halogenophenyl nitroxides and the hydroxylamines from which they are derived produces mainly p-benzoquinone t-butylimine N-oxide, the corresponding amine, and hydrogen halide or molecular halogen. Primary studies indicate that the rates of decomposition under comparable conditions in benzene solution increase in the order p-I < p-F < p-Cl < p-Br. Under certain conditions small quantities of amino-quinones and quinone imines have also been isolated. The principal decomposition route entails O-to-para-C coupling with subsequent homolytic fragmentation of the intermediate cyclohexadiene. The isomeric meta-bromo-and-chloro-radicals also decompose mainly in this way although O-to-ortho-C coupling also occurs, as shown by analysis of the minor products. ortho-Bromo-and chlorophenyl t-butyl nitroxides are sufficiently stable to be crystallised and analysed.