Stabilities in Water and Transfer Activity Coefficients from Water to Nonaqueous Solvents of Benzo-18-crown-6–Metal Ion Complexes

Abstract

Formation constants in water of 1:1 benzo-18-crown-6 (B18C6)–metal ion complexes and the B18C6 solubility in water were determined at 25 °C by conductometry or potentiometry with ion-selective electrodes and spectrophotometry, respectively. The selectivity sequences of B18C6 for metal ions in water are Pb2+>Ba2+>Sr2+>Ag+>K+>Tl+>Na+>Rb+. In each case of alkali and alkaline earth metal ions, the more closely a metal ion fits into the B18C6 cavity, the more stable is the B18C6–metal ion complex. Although the solvation power of water for an alkali metal ion is not the largest of all solvents, the formation constant of a given B18C6–alkali metal ion complex in water is by far the smallest of all solvents. The transfer activity coefficients (γ) from water to nonaqueous solvents of the B18C6–metal ion complexes were then calculated from the formation constants of the B18C6 complexes, γ values of B18C6 (obtained from solubilities of B18C6), and γ values of the uncomplexed metal ions. The γ value of B18C6 is larger than those of B18C6–alkali metal ion complexes. This shows that when B18C6 forms a complex with an alkali metal ion, the B18C6 complex becomes more soluble in nonaqueous solvents than in water, compared with uncomplexed B18C6.

Solvent Extraction of Alkali Metal (Li - Cs) Picrates with 18-Crown-6 into Various Diluents. Elucidation of Fundamental Equilibria which Govern the Extraction-Ability and -Selectivity

“…For the M(18C6)A complexes and the diluents used in this study, Eq. (14) shows that the larger is the δ o value or the smaller the V o value, the greater is the log K D, MLA value. 17 18 The order of decreasing log K D,MLA value of B18C6 for the diluents is almost the same as that of 18C6 (Tables 3 and 4 For B18C6, the δ MLA values of Na, K, and Rb are identical; the V MLA -value order is Rb > Na ≥ K. From Eq.…”

On the Interfacial Potential Differences for the Extraction of Alkaline- Earth Metal Picrates by 18-Crown-6 Ether Derivatives into Nitrobenzene

“…The individual distribution constants (K D,ML ) of ML 2+ into the NB phase can be evaluated from the other thermodynamic cycle, [15], respectively, and these values at 298 K were available from references; log K M18C6 = 0.48 for M = Ca, 2.72 for Sr and 3.87 for Ba [4]; log K MB18C6 = 0.48 for M = Ca, 2.41 for Sr and 2.90 for Ba [21,22]; log K D,L = −1.00 [18] for L = 18C6 and 1.57 [20] for B18C6. Using the logarithmic form of the above equation, we obtained log K D,M18C6 = 0.8 8 for M = Ca, −0.1 7 for Sr and −0.9 9 for Ba and log K D,MB18C6 = 2.6 2 for M = Ca, 1.4 4 for Sr and 1.6 1 for Ba.…”

On an Expression of Extraction Constants without the Interfacial Equilibrium-Potential Differences for the Extraction of Univalent and Divalent Metal Picrates by Crown Ethers into 1,2-Dichloroethane and Nitrobenzene

“…, in water at 298 K} values were 0.48 for the Ca-18C6 [18] and -B18C6 [19] systems, 2.72 [20] for Sr-18C6, 3.87 [20] for Ba-18C6, 2.41 [15] for Sr-B18C6 and 2.90 [13] for Ba-B18C6. Also, S D,Pic log 0.05 K = [11] (into NB), logK D,18C6 = −1.00 [21] and logK D,B18C6 = 1.57 [17] (into NB) at 298 K were used for calculation.…”