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Boletín de la Sociedad Chilena de Química

versão impressa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.46 n.1 Concepción mar. 2001

http://dx.doi.org/10.4067/S0366-16442001000100015 

FURTHER STUDIES ON THE SOLVENT EXTRACTION OF
COPPER (II) WITH DITHIOCARBOXYLATE DERIVATIVES
OF PYRAZOL

CLAUDIO LOPEZ, PATRICIO PONCE, AURORA MOLINARI
AND ALFONSO OLIVA*

Instituto de Química, Universidad Católica de Valparaíso, Avenida Brasil 2950,
Valparaíso, Chile.
(Received: October 4, 1999 - Accepted: October 30, 2000)

ABSTRACT

The solvent extraction behaviour of Cu(II), with 4-alkyldithiocarboxylate derivatives of pyrazol (HDTC ; alkyl = benzyl, allyl, n-hexadecyl , n-octadecyl) was studied as a function of pH. Cu(II) is efficiently extracted ( ³ 80% ) in the pH range studied. In all cases the extracted specie was found to be Cu(DTC)2.

KEYWORDS: Solvent extraction, Cu (II) extraction, pyrazoles, 1-phenyl-3,5-dioxopyrazolidine, alkyldithiocarboxylates.

RESUMEN

Se ha estudiado la extracción por solvente de Cu(II) con 4-alquilditio-carboxilatos derivados de pirazol (HDTC; alquil = bencil, alil, n-hexadecil, n-octadecil) en función del pH) Cu(II) es extraído eficientemente (³ 80% ) en el rango de pH estudiado y en todos los casos se ha encontrado que la especie extraída a la fase orgánica es del tipo Cu(DTC)2.

PALABRAS CLAVES: Extracción por solvente, extracción de Cu(II), pirazoles, 1-fenil-3,5-dioxopirazolidina, alquilditiocarboxilatos.

INTRODUCTION

As a part of a program on the synthesis and study of extractive properties of five membered heterocyclic ketones with an alkyldithiocarboxylate group at the a position1-3), in a previous paper we have reported the synthesis of 4-alkyldithiocarboxylate-3,5-dihydroxy-1-phenylpyrazoles ( HDTC : 1a R = n-butyl; 1b R = n-dodecyl ; 1c R = benzyl ; 1d R = allyl ; 1e R = n-hexadecyl ; 1f R = n-octadecyl ). The synthesis was done by the reaction of 3-hydroxy-1-phenyl-2-pyrazolin-5-one with sodium acetate in DMF, carbon disulfide and the appropiate alkyl bromide or chloride 4). The dienolic structure of all compounds was assigned on the basis of 1H and 13C NMR data and chemical shifts reported in related structures 1-3,5).

The extraction behaviour of copper(II) from acid solutions (pH 0-6) was studied with dithiocarboxylates 1a and 1b in chloroform, and the extracted specie was found to be Cu(DTC)2. Also copper (II) was selectively and quantitatively extracted from a mixture with iron(III) present in an acidic lixiviation solution of a mineral composed of enargite (Cu3AsS4) and pyrite(FeS2) 6) . Furthermore, the extraction eficiency of this compounds was compared with the commercially available LIX 984 N extractant of copper(II). Now, we wish to report further studies on the extraction of copper (II) with this kind of complexing agent 1c-f.

EXPERIMENTAL

Chemical

All chemicals were of reagent grade quality and purchased from commercial sources. Alkyldithiocarboxylate derivatives were prepared according to previously described procedure4) .

Solvent extraction procedure

In the solvent extraction studies, chloroform and chloroform / Escaid 1:1 were used as the organic phase together with diluted aqueous stock solution of Cu(II) 0.025 M and KNO3 1.0 M. A constant ionic strength of aproximately 0.1 M was kept during the extraction process. The concentration of the metal ion in the aqueous phase before and after the extraction was evaluated by titration with 0.1M EDTA solution 7) or spectrophotometrically8).

10 mL of an aqueous phase prepared by mixing 4.0 mL of 0.025 M of Cu(II) stock solution, 1.0 mL of KNO3 1 M, 5.0 mL of distilled water and the desired pH was adjusted by addition of HCl or NH3 solution of variable concentration. After the addition of 10.0 mL of a 0.02 M chloroformic solution of the extractant, the mixture was mechanically stirred 1 h. This was following by separation of the organic phase and the concentration of the remaining metal ion in the aqueous phase was evaluated with EDTA 0.1 M or spectrophotometrically. The concentration of the complex in the organic phase was calculated from the difference between the metal ion concentration before and after the extraction. These concentrations were used to calculated the distribution ratio Kd and the extraction constant Kex.

RESULTS AND DISCUSSION

The ligands used in this study are represented by the general structure 1. They were prepared by a previously reported method of synthesis and fully characterized by elemental analysis, mass spectrometry and 1H / 13C NMR spectroscopy 4).


Solvent extraction of copper (II).

The extraction behaviour of Cu(II) as a function of pH was studied with 0.02M chloroform solutions of ligands 1c-f. Due to the long of the alkyl chain R, a higher solubility in less polar hydrocarbon solvents was observed with 1e-f and it was possible to employ also chloroform mixed with Escaid (industrial hydrocarbon solvent) in a 1:1 ratio as organic phase in this study. As is observed in Figure 1, these ligands extract Cu (II) with a 80-100% eficiency in a single step (pH 0-6) and this behaviour is similar to the observed with 1a and 1b previously reported 6). With 1e and 1f, these studies were extended to pH 8-10.


The slope analysis, based on the examination of the logaritmic variation of the distribution coeficient Kd (defined as the concentration of the metal ion in the organic phase divided by the concentration of metal ion in the aqueous phase) vs. a concentration variable, is a traditional and effective means to obtain information about the number of ligands molecules in the extracted complex and also about the equilibrium constant Kex9,10). Using this analysis, the extraction mechanism is grafically investigated by plotting log Kd as a function of log [ligand] in the organic phase at a fixed pH value of the aqueous phase . The number of ligand molecules in the extracted complex is given by the slope and from the intercept, Kex value can be calculated. In all cases, slopes close to 2 were obtained in our studies (Table 2 and Figure 2), confirming that the main equilibrium in the extraction process is represented by the equation6) :


In conclusion, the alkyldithiocarboxylate derivatives of pyrazol 1c-f are efficient extractants of Cu(II) in the pH range of 0-6 or higher. Of particulary importance is the result obtained with 1c, where the extraction was always 100%. Chloroformic solutions of the complex with this ligand are green colored and is possible to study the conditions for a new spectrophotometric method in the quantitative determination of Cu(II) in strong acidic aqueous solution, taking into account that most of the available methods work at pH 4 or higher. Studies in this sense, are currently in progress.

ACKNOWLEDGEMENTS

The authors acknowledge financial support from the Dirección General de Investigación , Universidad Católica de Valparaíso (DGI 125.772-96)

REFERENCES

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