Thermodynamics of substituted pyrazolone VIII. Potentiometric, spectrophotometric, and conductometric studies of 4-(4-nitrophenylazo)-3-methyl-1-(2-hydroxy-3-morpholinopropan-1-yl)-2-py razolin-5-one and its metal complexes

Proton-ligand dissociation constant of 4-(4-nitrophenylazo)-3-methyl-1-(2-hydroxy-3-morpholinopropan-1-yl)-2-py razolin-5-one (NAMP) and metal-ligand stability constants of its complexes with some transition metal ions were measured potentiometrically in 0.1 M-KCl and 40 vol.\% ethanol-water. The order of stability constants was found to be K(UO22+) > K(Ce3+) > K(La3+) > K(Mn2+) < K(Co2+) <K(Ni2+) < (Cu2+) > K(Zn2+) The dissociation constant pK(1)(H) of NAMP and the stepwise stability constants log K of its complexes were determined at different temperatures (298 K, 308 K, and 318 K). The corresponding thermodynamic parameters (DeltaG, DeltaH, and DeltaS) were derived and discussed. The dissociation process is nonspontaneous, endothermic, and entropically unfavourable. The formation of the complexes was found to be spontaneous, exothermic or endothermic (depending on the metal) and entropically favourable. The stoichiometries of the complexes were determined spectrophotometrically and conductometrically and indicate the formation of n(metal): n(ligand) = 1: 1 and 1: 2 complexes.