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)

Abstract

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.

Keywords:

• Azo derivatives of β-diketones
• Copper complexes
• 5,5-Dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo) cyclohexane-1,3-dione
• Nickel-based alloys analysis
• Seawater igneous rock
• Soils polluted by oil

This work has been partially supported by the Foundation for Science and Technology (FCT), Portugal, and its PPCDT (FEDER funded), and “Science 2007” programs. K. T. Mahmudov and M. N. Kopylovich express gratitude to the FCT for their post-doctoral fellowship and working contract. The authors also acknowledge the Portuguese NMR Network (IST-UTL Center) for providing access to the NMR facility.

Notes

*No interference.