Oxidative N—N coupling of N-alkyl-3-aminopyrazoles to azopyrazoles in aqueous solutions of NaOCl and NaOBr

Abstract

The influence of the structures of N-alkyl-3-aminopyrazoles on their transformation into azopyrazoles on treatment with sodium hypohalogenites was studied. The reaction of 3-aminopyrazoles unsubstituted at position 4 containing donor substituents with neutral solutions of sodium hypohalogenites leads to mixtures of 3,3′-azopyrazoles (yields 1–40%) and 4,4′-dihalo-3,3′-azopyrazoles (yields 20–79%). In this case, generation of 3,3′-azopyrazoles is favored by the addition of NaOH to the reaction mixture. The N—N coupling of aminopyrazoles with acceptor substituents in the aromatic ring results in the selective formation of 3,3′-azopyrazoles even in neutral media. The reactions of 4-substituted 3-aminopyrazoles with NaOBr afford only 3,3′-azopyrazoles. The regularities of occurrence of all the above processes are discussed.