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, K_p and the distribution, K_d constants in this solvent system and the ion-pair formation constant, K_a in the water saturated organic phase. Comparison of K_d, K_p and K_a 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, K_ex and K_d from distribution data for a 1:2 (ligand:metal-cation) extraction process has been formulated and successfully applied. Good agreement is found between the K_d 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.