Revista de Ciências Químicas

A simple, highly sensitive and selective spectrophotometric procedure was developed for the determination of copper(II) ions. The procedure is based on the reaction at pH 4-7 between the newly synthesized Girard T derivative N-{[(phenylamino)thioxo methyl] hydrazino carbonyl methyl}trimethyl ammonium chloride (PTHAC) and Cu(II) to form an intense green Cu(II):PTHAC (1:1) complex that floats quantitatively with oleic acid (HOL) surfactant. The different analytical factors affecting the flotation and determination processes were examined viz. pH, temperature, concentration of metal, ligand and HOL, etc. The Cu-PTHAC complexes were characterized by elemental analysis, infrared, mass and electronic spectral studies. The formed Cu(II)-PTHAC complex shows a constant and maximum absorbance at 650 nm in the aqueous and scum layers. Beers’ law is obeyed over the concentration rang 0.1-6 mg l-1 with a detection limit of 0.03 mg l-1 and molar absorptivities (at λmax 650 nm) of 0.27×104 and 0.20×105 l mol-1cm-1 in aqueous and surfactant layers, respectively. Sandell’s sensitivity is calculated to be 3.2×10-3 μg cm2 and the relative standard deviation (n=5) is <3.72%. The suggested procedure has been successfully applied to the analysis of copper in different natural waters and ore samples. Moreover, the flotation mechanism is recommended based on some physical and chemical studies of the solid complex isolated from the aqueous and scum layers.

Synthetic methods for the preparation of phosphinic derivatives (esters and amides) are summarized. The basic method is, when phosphinic chlorides are reacted with alcohols or amines. These reactions take place under mild conditions, but utilize expensive chlorides, need a solvent, and a base has to be added to remove the HCl formed. On conventional heating, the phosphinic acids resist undergoing derivatizations by nucleophiles. However, on microwave (MW) irradiation, the phosphinic acids could be esterified by alcohols. The direct esterification does not require an extra solvent, it is atomic efficient, but needs a relatively higher temperature. The similar amidations were reluctant. Phosphinic acids may also be esterified by alkylation that may be promoted by combined phase transfer catalysis and MW irradiation. It is also possible to convert the phosphinic acids by different reagents (e.g. by the T3P reactant) to a more reactive intermediate that is ready to react with alcohols or amines. Other methods, such as preparation by the Arbuzov reaction or by fragmentation-related phosphorylation are also discussed.