The general procedure for the synthesis of 1-methyl-1H-1,2,4-triazole-5-carboxylic acid from 1-methyl-1,2,4-triazole and carbon dioxide was as follows: to a stirred solution of 1-methyl-1,2,4-triazole (2.0 g, 24.0 mmol) in tetrahydrofuran (THF, 20 mL) was added slowly and dropwise at -78 °C n-butyllithium (19 mL, 12.0 mmol) and stirring was continued at this temperature for 2 hours. Subsequently, solid carbon dioxide (2 g) was added to the reaction system and stirred at -78 °C for 1 hour. The reaction mixture was gradually warmed to room temperature and stirring was continued for 16 hours. After confirming complete consumption of the feedstock by thin layer chromatography (TLC) monitoring, the reaction was quenched with deionized water (3 mL) and the resulting solid product was collected by filtration. The solid was purified by grinding with a solvent mixture of diethyl ether/n-pentane (10 mL/10 mL). Finally, the resulting white solid was dried under vacuum to afford the target compound 1-methyl-1H-1,2,4-triazole-5-carboxylic acid (Int-J, 2.0 g, 65.7% yield). The structure of the product was confirmed by 1H-NMR (500 MHz, DMSO-d6) and LCMS: 1H-NMR δ 7.70 (s, 1H), 4.01 (s, 3H); LCMS m/z: 128.3 [M+H]+.
