Electrosynthesis of 4-bromosubstituted pyrazole and its derivatives

Electrosynthesis of 4-bromosubstituted pyrazole and its derivatives was carried out by bromination of initial pyrazoles on Pt anode in NaBr aqueous solutions under the conditions of diaphragm galvanostatic electrolysis. A donor substituent (Me or Et) in pyrazole ring was shown to promote to the bromination process, while an acceptor substituent (NO 2 or COOH) does not produce a significant effect to this process. Thus, the yield of 4-bromosubstituted derivatives from bromination of 3,5-dimethylpyrazole, 1,5-dimethylpyrazole, 3-nitropyrazole, pyrazole-3(5)-carboxylic acid, 1-methylpyrazole-3-carboxylic acid, 1-methylpyrazole-5-carboxylic acid, 1-ethylpyrazole-5-carboxylic acid, and 1-methylpyrazole-3,5-dicarboxylic acid amounted 70, 94, 88, 89, 84, 78, 89, and 84%, respectively.