Synthesis
3-Methyl-5-nitrothiazole (0.18 mol) was dissolved in concentrated H2SO4 (300 mL) and Na2Cr2O7-2H2O (53 ) was added to the mixture.
g, 0.27
mol) was added dropwise to this solution and the temperature was maintained at 60-65C. The reaction mixture was kept at this temperature for 8 h. The reaction mixture was poured into ice (1 kg) and extracted with ethyl acetate (3 x 250 mL). The organic layer was washed with water, dried with MgSO4, the solvent was removed in vacuo and the residue was recrystallized from H2O to give 3-nitropyrazole-5-carboxylic acid in a yield of 25 g (88%).
