Complex formation constants of six crown ethers, benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, dibenzo-18-crown-6, dibenzo-21-crown-7, and dibenzo-24-crown-8 (B12C4, B15C5, B18C6, DB18C6, DB21C7, and DB24C8, respectively) with alkali and alkaline earth metal cations have been measured in aqueous solutions by capillary zone electrophoresis. The procedure involved the measurement of change in the electrophoretic mobility of the ligands upon increasing the metal ion concentration in the carrier electrolyte solution. A substantial increase in apparent electrophoretic mobility was observed for the crown ethers with increasing concentrations of the metal ions. The variations in increased electrophoretic mobility were attributed to the different stability of the complexes formed between the cations and the crown ether. The complex formation constants obtained with alkali metal cations were in the orders of: K+ > Na+ > Rb+ > Cs+ (B18C6), K+ > Na+ > Rb+ > Cs+ (DB18C6), Rb+ > Cs+ > K+ (DB21C7), and Rb+ > Cs+ (DB24C8); while with alkaline earth metal cations it was: Ba2+ > Sr2+ > Ca2+ (B18C6) and Ba2+ > Sr2+ (DB18C6). All the ligands examined showed no change in their apparent electrophoretic mobility upon changing Li+ and Mg2+ concentrations, indicating less reactivity with the cations. From the results obtained in this study, the electrophoretic method was proved to be preferable for analyzing the reactivity of the crown ethers and the selectivity toward metal cations.

Extensive studies have been carried out on the concentrated salt effects on the solvolysis reaction rates of aliphatic halides and related compounds (RX) in acetone-water mixed solvents. In 90 vol% acetone-10 vol% water solution, the pseudo-first-order rate constant (k/s ؊1 ) of a typical S N 1 substrate, tert-butyl chloride, at 50 ЊC was increased exponentially by the addition of M ؉ ClO 4 ؊ (M ؉ ‫؍‬ Li ؉ , Na ؉ : up to 4.0 mol dm ؊3 ) and M 2؉ (ClO 4 ؊ ) 2 (M 2؉ ‫؍‬ Mg 2؉ , Ba 2؉ : up to 2.0 mol dm ؊3 ); the extent of the cation effects increased as Na ؉ р р р Li ؉ < Mg 2؉ р р р Ba 2؉ . However, the addition of Et 4 NClO 4 (up to 1.0 mol dm ؊3 ) decreased the solvolysis rate substantially. In 50 vol% acetone-water solution, the effects of the metal perchlorates on the solvolysis rates of 1-adamantyl chloride at 50 ЊC increased as Na ؉ < Li ؉ < Ba 2؉ < Mg 2؉ . Addition of >1.0 mol dm ؊3 Et 4 NBr decreased the solvolysis rate markedly, whereas it was increased slightly by lower Et 4 NBr concentrations. The positive effects of metal ions for typical S N 1 substrates were explained by the change of solvent structure and by a "chemical" interaction between the anions from the substrates (R ؉ -X ؊ ) and M ؉ or M 2؉ in the presence of very concentrated salts; the negative effects of nonmetallic salts should have been brought about by the decrease in activity of H 2 O. The solvolysis rate of 2-adamantyl tosylate (C 10 H 15 OTs) in 50 vol% acetone-water solution at 50 ЊC was also increased exponentially by the addition of LiClO 4 , whereas those of typical S N 2 substrates, methyl tosylate (CH 3 OTs) and ethyl bromide, were decreased by the addition of LiClO 4 . On the other hand, for isopropyl bromide and benzyl chloride, the solvolysis rates were not changed by the addition of LiClO 4 . A good linearity was observed between the increase in log (k/s ؊1 ) in the presence of 1.0 mol dm ؊3 LiClO 4 and the m-values of the substrates (by Grunwald-Winstein). It is proposed that one could simply distinguish S N 1 from S N 2 reactions merely by observing a substantial increase in the solvolysis rate constant at 1.0 mol dm ؊3 LiClO 4 in aqueous mixed solvents. The salt effects on the solvolysis rates of sulfonyl chlorides in 50% acetone-water at 35 ЊC were very different from those for substrates with carbocations as reaction intermediates.Over many years, a number of studies have been performed to account for the salt effects on solvolysis reactions, 1 however, no theory has been successful in explaining comprehensively the effects of very high salt concentrations (у1.0 mol dm Ϫ3 ) on solvolysis reactions. Previously, 2 we explained quantitatively the concentrated salt effects on the solvolysis rates of aliphatic halides and related compounds in a protic MeOH-H 2 O solvent. The salt effects were examined at higher salt concentrations which approached the solubility limits of salts. We proposed that under such high salt concentrations, the structures due to hydrogen bonding of the solvents are destroyed beyond theoretical evalu...

The solvolysis rates of aliphatic halides and related compounds (RX) were determined in an 80 vol% MeOH–20 vol% H2O solvent in the presence of very highly concentrated salts (0.25—5.0 mol dm−3) at 25—75 °C. For typical SN1 substrates, such as 1-adamantyl bromide and t-butyl chloride, the pseudo-first-order reaction rates (k/s−1) increased exponentially with increasing concentration of LiClO4, NaClO4, Mg(ClO4)2, and Ba(ClO4)2. The cation effects increased as Na+ &lt; Li+ &lt; Ba2+ ≤ Mg2+. A nonmetallic salt, Et4NBr, caused the k/s−1 value for 1-adamantly bromide to be slightly increased at lower concentrations ( &lt; 1.0 mol dm−3), but to be greatly decreased at higher salt concentrations ( ≥ 2.0 mol dm−3). The large positive effects of metal perchlorates were explained by a change in the solvent structure and the formation of “stable” carbocations through a “chemical” interaction between X− (Cl−, Br−, or I−) and M+ (Li+, Na+) or M2+ (Mg2+, Ba2+) in the “modified” solvent. On the other hand, for SN1–SN2 intermediates, the solvolysis reaction rates were decreased by a decrease in the activity of the solvent containing a large amount of salts. The apparent rate constant (“k/s−1”) for isopropyl bromide at 75 °C remained an almost constant value in the presence of 0—5.0 mol dm−3 LiClO4. The rate constant for ethyl bromide was decreased substantially by the addition of the alkali metal and alkaline-earth metal perchlorates. A good linearity was observed between log (k1/k0) and the m values for RX by Grunwald and Winstein, where k1 and k0 are the solvolysis rates in the presence of 1.0 mol dm−3 LiClO4 and in the absence of the salt, respectively. Upon the solvolysis of neophyl chloride (1-chloro-2-methyl-2-phenylpropane), the change in the reaction scheme (e.g., methyl shift) was suspected during the increase in the LiClO4 or Ba(ClO4)2 concentration.

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