Solvent effect upon ion-pair extraction of different sodium dyes using some crown ethers

Liquid-liquid extractive-spectrophotometric studies of sodium ion complexes of 18-crown-6(18C6), dibenzo-18-crown-6(DB18C6), 15-crown-5(15C5), and 12- crown-4(12C4) and anionic dyes [4-(2-pyridylazo)-resorcinol monosodium salt monohydrate (PAR), Eriochrom Black T (EBT), and methyl orange (MOR)] and s odium picrate (PICRAT) as the counter ion are described. The overall extrac tion equilibrium constants for the 1 : 1 complexes of the above crown ether s with sodium dyes between different organic solvents and water have been d etermined at 25 degrees C. They were conducted in various solvent-water sys tems maintaining an identical initial cation concentration in water, [M-0()](w), and macrocyclic ligand concentration in the organic phase, [L-0](org ), so that in all extractions [M-0(+)](w) : [L-0](org) ratios were 1 : 1, 1 : 10, 1 : 20, 1 : 50, and 1 : 62.5. An ion association complex formed betw een the sodium-crown ether complex ion and a dye anion was extracted into t he organic solvent, and then the dye concentration of the separated aqueous phase was measured with an ultraviolet-visible spectrophotometer. PAR was the best associated dye with all crown ethers sodium-dyes and the extracted dye occurs as the ion-pair complex. Methylene chloride was found to be bet ter than other extractive solvents used in this study.