Rafiga A. Aliyeva

Ion Pairs of 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione with Cationic Surface-Active Substances as Analytical Reagent for Determination of Copper(II)

A new organic reagent, 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)сyclo-hexane-1,3-dione (H2L), was synthesized by azo coupling of diazonium salts of 2-hydroxy-3,5-disulfoaniline with dimedone. The dissociation constants of H2L were determined by potentiometric titration, being pK 1 = 5.90 ± 0.03 and pK 2 = 9.67 ± 0.04. The interaction in systems of H2L and cationic surface-active substances (CSAS), cetylpyridinium chloride (CPCl), cetylpyridinium bromide (CPBr), or cetyltrimethylammonium bromide (CTABr) was studied in the presence and absence of Cu(II). It was found that the detection limit of Cu(II) using H2L–CSAS pairs decreases in accord with the stability of associates H2L(CPCl)2 > H2L(CPBr)2 > H2L(CTABr)2 and their copper(II) complexes Cu[(HL)(CPCl)2]2 > Cu[(HL)(CPBr)2]2 > Cu[(HL)(CTABr)2]2. The effects of foreign ions and masking substances on the complexation were studied and showed that the reaction of Cu(II) with H2L in the presence of CSAS is more selective. Based on these observations, a procedure for the spectrophotometric determination of copper(II) in soils polluted by oil, seawater, igneous rock, and nickel-based alloys was developed.

Thermodynamics of Dissociation of ortho-Hydroxyphenylhydrazo-β-diketones and of Their Complexation with Copper(II) in Aqueous–Ethanol Solutions

The thermodynamics of dissociation of 3-(2-hydroxyphenylhydrazo)pentane-2,4-dione (H2L1), 5,5-dimethyl-2-(2-hydroxyphenylhydrazo)cyclohexane-1,3-dione (H2L2), 5,5-dimethyl-2-(2-hydroxy-4-nitrophenylhydrazo)cyclohexane-1,3-dione (H2L3), 1-ethoxy-2-(2-hydroxyphenylhydrazo)butane-1,3-dione (H2L4) and 1-ethoxy-2-(2-hydroxy-4-nitrophenylhydrazo)butane-1,3-dione (H2L5) and of their complexation with copper(II) was studied in aqueous–ethanol solutions by potentiometry and UV–vis spectrophotometry. It was found that the thermodynamic parameters of the proton dissociation in H2L1–5 and of their complexation with copper(II) depend on the substituents in the aromatic and β-diketone fragments of the molecules. Thus, the acidic properties of H2L increase from H2L1 to H2L5, reflecting the electron-acceptor character of the substituents, whereas all of the thermodynamic functions tend to decrease with increasing electron-withdrawing capacity of the substituents. The complexation of Cu(II) with H2L1–5 is exothermic, which is connected with the formation of two stable chelating cycles.