Thermodynamics of substituted pyrazolone IX: potentiometric, spectrophotometric and conductometeric studies of 4-(4-chlorophenylazo)-3-methyl-1-{[}2-hydroxy-3-morphilinopropane 1-yl]-2-pyrazolin-5-one and its metal complexes

The dissociation constants of 4-(4-chlorophenylazo)-3-methyl-1-{[}2-hydroxy-3-morphilinopropane-1-yl]- 2-pyrazolin-5-one (CAMP) has been determined potentiometrically in 0.1 M KCl and 40\% (v/v) ethanol-water mixture. The stepwise stability constants of the formed complexes of Mn2+, Co2+, Ni2+, Cu2+, Zn2+, La3+, Ce3+ and UO22+ with CAMP have been determined. The stability of the formed complexes were found as follows: UO22+ > Ce3+ > La3+ > Mn2+ < Co2+ < Ni2+ < Cu2+ > Zn2+ The thermodynamic parameters (DeltaG, DeltaH and DeltaS) for CAMP and its complexes were evaluated and discussed. The dissociation process is non-spontaneous, endothermic and entropically unfavourable. The formation of the complexes have been found to be spontaneous, exothermic or endothermic (depending on the metal) and entropically favourable. The stoichiometries of these complexes were determined spectrophotometrically and conductometrically and indicated the formation of 1:1 and 1:2 (metal:ligand) complexes. (C) 2001 Elsevier Science B.V. All rights reserved.