The synthesis of 5-amino-4-arylazo-3-methyl-1H-pyrazoles and 5-aryl-3-methylpyrazole[3,4-e][1,2,3,4]tetrazines

AlCl3-catalyzed coupling of 3-amino-5-methyl-1H-pyrazole in water with different aryldiazonium compounds yielded 5-amino-4-arylazo-3-methyl-1H-pyrazole derivatives in high yield; subsequent diazotization and cyclization realised the 5-aryl-3-methylpyrazole[3,4-e][1,2,3,4]tetrazine derivatives. The structure of these novel, hetarylazo dyes was confirmed by UV–vis, FT-IR, and 1H NMR spectroscopic techniques and elemental analysis. Optimal preparation conditions for 5-amino-4-phenylazo-3-methyl-1H-pyrazole were determined with respect to the effects of the AlCl3-catalyst, pH and temperature; the reaction mechanism of formation of the 5-aryl-3-methylpyrazole[3,4-e][1,2,3,4]tetrazines is discussed and the colours of the aminopyrazoles and pyrazolo-tetrazine dyes in a range of solvents are also discussed.