Reduction of Trifluoromethyl-containing 4-Nitroso- and 4-Arylazopyrazoles as a Method for 4-Amino-3-trifluoromethylpyrazoles Synthesis

Abstract— The processes of 4-nitroso-3-trifluoromethylpyrazoles reduction under various conditions were studied. It was found that their reduction with zinc in acetic acid results in the formation of 4-aminopyrazole in a mixture with 4-bisazo- and 4-bisazoxypyrazoles. The optimal method for the synthesis of 4-amino-3-trifluoromethylpyrazoles consists in the 5–6 h hydrogenation of 4-nitrosopyrazoles under pressure (p 10 atm) in the presence of a Pd/C catalyst at 50°С in ethanol. It was shown that 4-arylazopyrazoles can be used for the synthesis of 4-aminopyrazoles by catalytic hydrogenation reactions.