Synthesis, Structure, and Chemical Properties of 1-Oxidopyridinediazonium Sulfonates

The diazotization products of 2-, 3- and 4-aminopyridine 1-oxides in the presence of p-toluene­sulfonic acid, trifluoromethanesulfonic acid, and camphorsulfonic acid have been studied by IR and NMR spectroscopy, X-ray analysis, ESI mass spectrometry (MS and MS2), and B3LYP/aug-cc-pVDZ quantum chemical calculations. The product structure and their storage stability depend on the initial aminopyridine N-oxide. 4-Aminopyridine 1-oxide gives rise to stable diazonium sulfonate, whereas 2-aminopyridine 1-oxide is converted to [1,2,3,5]oxatriazolo[5,4-a]pyridin-4-ium sulfonates. All diazotization products easily undergo transformations typical of diazonium salts. According to the B3LYP/aug-cc-pVDZ calculations, 1-oxido­pyridine-4-diazonium cation is the most stable in the series of diazonium ions derived from aminopyridines and aminopyridine 1-oxides and benzenediazonium ion.