Selective extraction of alkali metal ions from bittern using picrate anion and crown ethers as ligand: An experimental and theoretical study

Dibenzo-2 1-crown-7 (DB2IC7) and dibenzo-24-crown-8 (DB24C8) have been used to extract the metal ions (Na+. K+. Mg2+ and Ca2+) present in bittern, schoenite and in an artificial solution containing equimolar amount of the above mentioned metal ions. Ion chromatographic study of the organic extract shows that DB21 C7 extracts potassium with hi gh selectivity, whereas DB24C8 extracts comparable amount of potassium and sodium. The extraction equilibrium constants (Ke) for potassium and sodium with both the ligands have been evaluated spectrophotometrically by two-phase (waterdichloromethane) extraction process. For DB2IC7, K. value for potassium is 4.5x10 M 2. which is 6.3x 102 time higher than that of sodium, whereas DB24C8 shows K. values 3.3xl04 and 2.4x10 M 2 for potassium and sod ium, respecti vely. Molecular mechanics calculations have been performed to examine the selectivity of the cations. In the gas phase calculations, DB21 C7 and DB24C8 are found to be selective towards the sodi um ion . However, K+ is preferred by DB21 C7 in the aqueous solution, which is in qualitative agreement with our experimental results.