The general procedure for the synthesis of dimethyl 1H-pyrazole-3,5-dicarboxylate from methanol and 3,5-pyrazoledicarboxylic acid was as follows: 31.7 g (0.203 mol) of 3,5-pyrazoledicarboxylic acid was mixed with 125 mL of methanol and the mixture was saturated with gaseous HCl. The reaction mixture was heated to reflux for 3 hours and subsequently left to stand overnight at room temperature. After completion of the reaction, the precipitate was collected by filtration and washed with methanol. A final 23.5 g (63% yield) of white crystalline product with a melting point of 142-143 °C was obtained. The structure of the product was confirmed by IR spectroscopy, and the main absorption peaks were 3105 cm-1 (broad peak, NH stretching vibration), 1710 cm-1 (strong peak, C=O stretching vibration), and 1240 cm-1 (strong peak, C-O-C stretching vibration).1H NMR spectroscopic data were as follows: δ 3.82 (single peak, 6H, CH3), δ 6.36 (single peak, 1H, pyrazolyl ring 4-H), δ 14.5 (single peak, 1H, pyrazolyl ring 4-H), and δ 14.5 (single peak, 1H). 4-H), δ 14.43 (single peak, 1H, NH).
