Extraction of silver (I) by calixarene amine derivatives: The medium effect on the stoichiometry of the phase transfer extraction process
Distribution experiments involving silver (I) perchlorate in the mutually saturated water–dichloromethane solvent system at 298.15 K were carried out. The data were used to calculate the partition, Kp and the distribution, Kd constants in this solvent system and the ion-pair formation constant, Ka in the water saturated organic phase. Comparison of Kd , Kp and Ka values with corresponding data in the water–nitrobenzene solvent system clearly reflect the medium effect on these parameters. Distribution data in the presence of various calix(4)arene amine derivatives were measured. These data show that in the water–dichloromethane solvent system the stoichiometry of the extraction process (1 : 2; ligand : metal-cation) has been altered relative to that in water–nitrobenzene (1 : 1). This is corroborated by conductometric titrations of silver (I) and these macrocycles in water saturated dichloromethane. An equation for the derivation of the extraction constant, Kex and Kd from distribution data for a 1 : 2 (ligand : metal-cation) extraction process has been formulated and successfully applied. Good agreement is found between the Kd values derived from distribution data in the absence and in the presence of the macrocycle. The individual steps which contribute to the overall extraction of silver (I) from water to dichloromethane are discussed. Final conclusions are given.