General procedure for the synthesis of ethyl 4-nitropyrazole-3-carboxylate from ethanol and 4-nitropyrazole-3-carboxylic acid: 4-nitro-1H-pyrazole-3-carboxylic acid (2.5 g, 15.9 mmol) was dissolved in hydrochloric acid solution (38.3 mL, 1.25 M) in ethanol, followed by refluxing the mixture overnight. Upon completion of the reaction, all volatiles were removed by evaporation to afford the white solid product ethyl 4-nitropyrazole-3-carboxylate (2.9 g, 98% yield), which could be used in subsequent reactions without further purification. Results of mass spectrometry analysis: M = 186.1 (M + H)+.
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