Nitrogen as Leaving Group: Dediazoniations of Aromatic Diazonium Ions

On heating, aromatic diazonium salts eliminate nitrogen by two fundamentally different mechanistic pathways, i.e. heterolysis and homolysis. Among these pathways a series of variants are known, giving rise to a whole variety of mechanisms. This article considers the effect of specific solvation, apparently characteristic of diazonium ions, by various solvents (fluorinated alcohols, methanol, water, dimethyl sulfoxide, pyridine, and hexamethylphosphoric triamide) on the mechanism. Apart from the donor properties of the solvent, the oxidation potential and the presence of additives play a major role in determining what reaction type will predominate.