Analytical Sciences

Evaluation of the Hydrophilic Properties of Crown Ether-ion-pair Complexes with Alkali Metal Picrates by Their Distribution into Less-polar Diluents

Yoshihiro KUDO, Shoichi KATSUTA, and Yasuyuki TAKEDA

Graduate School of Science, Chiba University, Chiba 263-8522, Japan

Cohesive energy densities (C_w,MLA/J cm^-3) for ion-pair complexes (MLA: M⁺ = Li⁺ to Cs+; w: water) with six crown ethers (L), such as 18-crown-6 ether (18C6), benzo-18C6, and dibenzo-24-crown-8 one, and A^- = picrate were calculated at 298 K by a procedure that uses either (i) an equation rearranged from that underlying log K_D,MLA-vs.-log K_D,L plots or (ii) intercepts of their plots and from both procedures. Here, K_D,MLA and K_D,L denote the distribution constants of MLA and L from w into a diluent, respectively. As additional MLA, Na(18C6)(2,4-dinitrophenolate) and Na(18C6)(2,6-dinitrophenolate) were employed for the present C_w,MLA calculation. The C_w,MLA values calculated from the two procedures agreed well, and they were proportional to the log(K_D,MLA)^-1 values. From the log K_D,MLA values for dinitrophenolates and previously-reported values for Na(18C6)A, the hydrophobic property of some pairing anions, A^-, was ordered as F₃CCO₂^- < ReO₄^- < MnO₄^- < 2,4-dinitrophenolate < 2,6-dinitrophenolate < picrate, and then discussed based on a relation with the log K_ex values, where K_ex shows the extraction constant (mol^-2 dm⁶ unit) for Na(18C6)A into 1,2-dichloroethane.

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