To a stirred solution of 3,4-dicyano-1H-pyrazole (45 g, 185 mmol) in ethanol (150 mL) was added hydrazine hydrochloride (12.67 g, 185 mmol) and the reaction mixture was stirred at room temperature overnight. Upon completion of the reaction, the volatile solvent was removed by rotary evaporator under reduced pressure. The crude product was dissolved in water and extracted with ethyl acetate (3 x 50 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The resulting crude product was purified by an ISCO automated fast chromatography system using ethyl acetate and hexane as eluents to afford diethyl 1H-pyrazole-3,4-dicarboxylate (21.00 g, 97 mmol, 52.4% yield). Mass spectrum (electrospray ionization): m/z = 211 [M-H]+; 1H NMR (300 MHz, CDCl3) δ ppm 8.22 (s, 1H), 4.48 (q, J = 7.11 Hz, 2H), 4.36 (q, J = 7.18 Hz, 2H), 1.33-1.49 (m, 6H).
![Butanedioic acid, 2-[(dimethylamino)methylene]-3-oxo-, 1,4-diethyl ester](/CAS/20210111/GIF/130187-88-1.gif)
