The determination of ionization constants of some pyrazole carboxylic acids by potentiometric method in ethanol-water mixtures

In this study, stoichiometric ionization constants of pyrazole carboxylic acids (4- benzoyl-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-benzoyl-1-(4- nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1,5-diphenyl-1Hpyrazole- 3-carboxylic acid, 4-(ethoxycarbonyl)-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3- carboxylic acid, 4-(ethoxycarbonyl)-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid) were determined in several ethanol-water mixtures of 50, 60, 70 % ethanol (v/v) by potentiometric titration method. Using the potentiometric titration data, ionization constants were calculated by the aid of BEST computer programme. Titrations were performed in an ionic strength of 0,1 M NaCl at 25±0,1°C by using ORION 960 automatic titrator in nitrogen atmosphere. Furthermore, the structural effect and solvent effect on the acidity of pyrazole carboxylic acids were discussed. Key Words: Ethanol-water mixtures, ionization constants, potentiometry, pyrazole carboxylic acid, solvent effect, titrimetry.