Me. Moustafa et Sa. Shama, Metal chelates of cerium(III), thorium(IV) and dioxouranium(VI) with some heterocyclic azo dyes; Potentiometric and spectrophotometric studies, ANAL LETTER, 33(8), 2000, pp. 1635-1644
The stepwise formation constants of Ce3+, Th4+ and UO22+ complexes with fou
r azo compounds based on 1-phenyl-2,3-dimethylpyrazoline-5-one nucleus name
ly, 4-phenylazo- (2-hydroxy,5-x) 1-phenyl-2,3-dimethyl-pyrazoline-5-one, wh
ere x = H (I), OH (II), COOH (III) and NH2 (IV) have been determined potent
iometrically at different temperatures and ionic strengths in 30% (v/v) eth
anol-water solutions, then the thermodynamic parameters are calculated.
Negative values of both Delta H and Delta G are obtained indicating the exo
thermic and spontaneous nature of complexation reactions, whereas positive
values of Delta S show that entropy consideration favor complex formation.
The study at different ionic strengths shows that an increase in the latter
causes a decrease in the pK values. The azo compounds are also tested as n
ew reagents for the spectrophotometric determination of Ce3+, Th4+ and UO22
+ ions in synthetic and natural solutions by extensive investigation of the
optimum conditions favoring the formation of colored complexes.