4.1.1.1 Synthesis of 5-(4-methylphenyl)-1H-pyrazole-3-carboxylic acid (1): 0.4 g of 4-(4-methylphenyl)-2,4-dioxobutanoic acid was dissolved in 20 mL of glacial acetic acid in a 50 mL round bottom flask. Under stirring conditions, 280 μL (3 equivalents) of hydrazine monohydrate (N2H4-H2O) was added slowly and dropwise to the solution. Immediately after the dropwise addition of hydrazine, the solution changed to a light yellow color. The reaction process was monitored by thin layer chromatography (TLC). After completion of the reaction, the reaction mixture was poured into 50 mL of water and stirred overnight. The white precipitate was collected by filtration, dried in air and recrystallized from a solvent mixture of hexane/ethanol (about 9:1) to give 0.34 g of product in 87% yield.
4.1.2.22 Synthesis of 5-(4-methoxyphenyl)-1H-pyrazole-3-carboxylic acid (22): 0.50 g of 4-(4-methoxyphenyl)-2,4-dioxobutanoic acid was used as a starting material, and 0.45 g of the product was obtained in 92% yield by following the same procedure as above. The product is a white solid with a melting point of 226-228 °C (decomposition, hexane/ethyl acetate). The molecular formula was C11H10N2O3 and the molecular weight was 218.21. ESI-MS: [M+H]+ calculated value was 219.07642, measured value was 219.07540. IR (ν, cm-1): 3309, 3249 (N-H stretching vibration), 1679 (C=O stretching vibration), 1456, 1206. 1H NMR ( 200MHz, DMSO-d6) δ (ppm): 3.77 (s, 3H, OCH3), 6.99 (d, J=8.99Hz, 2H, Ar-H), 7.09 (s, 1H, pyrazole-H), 7.76 (d, J=8.42Hz, 2H, Ar-H), 13.21 (br, COOH).13C NMR ( 50MHz, DMSO-d6) δ (ppm): 55.45 (OCH3), 104.75, 114.60, 123.70, 127.00, 140.62, 147.45, 159.57, 162.43.
