Polyhalogeno-aromatic compounds. Part XXI. A novel reagent system for the N-oxidation of weakly basic N-heteroaromatic compounds

A mixture of concentrated sulphuric acid, an organic acid, and hydrogen peroxide converts many polyhalogenated-N-heteroaromatic compounds into their N-oxides in good yield. The scope and limitations as well as the mode of action of this reagent are discussed. The use of a mixture of hydrogen peroxide and polyphosphoric acid for N-oxidation of certain polyhalogeno-N-heteroaromatic compounds is also described. An example of nucleophilic substitution in the pentachloropyridinium ion is reported.