Extraction of Sodium and Potassium Perchlorates with Dibenzo-18-crown-6 into Various Organic Solvents.Quantitative Elucidation of Anion Effects on the Extraction-Ability and-Selectivity

摘要

The constants for overall extraction into various diluents of low dielectric constants(K_ex)and aqueous ion-pair formation(K_(MLA))of dibenzo-18-crown-6(DB18C6)-sodium and potassium perchlorate 1:1:1 complexes(MLA)were determined at 25 deg C.The K_(ex)value was analyzed by the four underlying equilibrium constants.The K_MLA values were determined by applying our established method to this DB18C6/alkali metal perchlorate extraction system.The K_M(DBi8C6)A value of the perchlorate is much greater for K~+ than for Na~+,and is much smaller than that of the picrate.The K_MLA value makes a negative contribution to the extractability of DB18C6 for MC1O_4,whereas the value of the MLA distribution-constant does a major one.The partition behavior of M(DB18C6)C1O_4 obeys the regular solution theory.However,the M(DB18C6)C1O_4 complexes in the diluent of high dipole moment somewhat undergo the dipole-dipole interaction.DB 18C6 always shows high extraction selectivity for KC1O_4 over NaClO_4,which is governed largely by the much greater K_MLA value for K~+ than for Na~+.The K~+ extraction-selectivity of DB18C6 over Na~+ for perchlorate ions is comparable to that for picrate ions.By comparing this perchlorate system with the picrate one,the anion effects on the extraction-efficiency and-selectivity of DB18C6 for Na~+ and K~+ was discussed in terms of the fundamental equilibrium constants.