• Bulletin of the Korean Chemical Society
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• 제25권6호
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• pp.847-851
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• 2004

The complexation characteristics of tetramethyl (1) and tetraethyl esters (2) of p-tert-butylcalix[4]arene with alkali metal cations have been investigated by ab initio calculation. The structures of endo- or exocomplexation of the hosts in cone conformation with alkali metal ions have been optimized using HF/6-31G method followed by B3LYP/6-31G(d) single point calculation. B3LYP/6-31G(d) calculations suggest that exo-complexation efficiencies of sodium ion to the cavity of lower rim of hosts 1 and 2 are 27.1 and 25.8 kcal/mol better than that of potassium ion, respectively. The exo-complexation efficiencies of potassium ion to the cavity of lower rim of hosts 1 and 2 are 33.3 and 31.5 kcal/mol better than the endo-complexation inside the upper rim (four aromatic rings) as expected from the experimental results. B3LYP/6-31G(d) calculation of the ethyl ester 2 shows 29.5 and 30.8 kcal/mol better exo-complexation efficiency for both sodium and potassium ions than the methyl ester 1.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.487-490
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• 1991

Electrochemical studies of alkali metal cations $(Na^+, K^+, Rb^+, Cs^+)$ were performed in methanolic solutions of 18-crown-6 and tetrabutylammonium salts at dropping mercury electrodes (DME) and thin mercury film electrodes (TMFE). All the cations investigated were reduced reversibly at DME in the absence and presence of 18-crown-6, and in the latter the limiting currents were decreased and the reduction potentials shifted to the negative direction. The reduction potentials of the metal ions (0.2 mM) in the presence of the crown (10 mM) were - 2.14 $(Na^+)$, - 2.26 $(K^+)$, - 2.20 $(Rb^+) and - 2.14 $(Cs^+)$ V vs. SCE, respectively. The measured potentials were rationalized with ion recognition of the cations by the crown. Electroreduction at TMFE were highly irreversible. A new representation method of ion recognition is presented. In aqueous solutions, electroreduction of the alkali metal ions were characterized by adsorption.

• Bulletin of the Korean Chemical Society
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• 제17권9호
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• pp.840-845
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• 1996

Rate constants have been measured spectrophotometrically for the reactions of p-and m-nitrophenyl 2-thiophenecarboxylate (5a and 5b, respectively) with alkali metal ethoxides (EtO-M+) in absolute ethanol at 25.0±0.1 ℃. The reactivity of EtO-M+ exhibits dependence on the size of alkali metal ions, i.e. the reactivity of EtO-M+ toward 5a decreases in the order EtO-K+ ≥ EtO-Na+ > EtO-Li+ > EtO-, while the one toward 5b does in the order EtO-Na+ ≥ EtO-K+ > EtO-Li+ > EtO-. This result indicates that ion paired EtO-M+ is more reactive than dissociated EtO-, and alkali metal ions form complexes with the substrate more strongly at the transition state than at the ground state. The catalytic effect shown by alkali metal ions appears to be less significant in the reaction of 5 than in the corresponding reaction of 4, indicating that complexation of alkali metal ions with 5 is not as strong as the one with 4.

• Bulletin of the Korean Chemical Society
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• 제22권1호
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• pp.53-58
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• 2001

Sulfonated poly(phenylene sulfide) (SPPS) polymers were prepared by sulfonation of poly[methyl[4-(phenylthio) phenyl]sulfonium trifluoromethanesulfonate] (PPST) with fumic sulfonic acid (10% $SO_3-H_2SO_4$) and demethylation with aqueous NaOH solution. The equilibrium constants of ion exchange reactions between alkali metal cations ($Li^+,\;Na^+,\;and\;K^+$) and SPPS ion exchanger in organic solvents such as tetrahydrofuran (THF) and dioxane were measured. The equilibrium constants of ion exchange reactions increased as the polarity of the solvent increased, and the reaction temperature decreased. The equilibrium constants of the ion exchange reaction ($K_{eq}$) also increased in the order of $Li^+,\;Na^+,\;and\;K^+$. To elucidate the spontaneity of the exchange reaction in organic solvents, the enthalpy, entropy, and Gibbs free energy were calculated. The enthalpy of reaction ranged from -0.88 to -1.33 kcal/mol, entropy ranged from 1.42 to 4.41 cal/Kmol, and Gibbs free energy ranged from -1.03 to -2.55 kcal/mol. Therefore, the exchange reactions were spontaneous because the Gibbs free energies were negative. The SPPS ion exchanger and alkali metal ion bounding each other produced good ion exchange capability in organic solvents.

• Bulletin of the Korean Chemical Society
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• 제19권2호
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• pp.147-150
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• 1998

• Bulletin of the Korean Chemical Society
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• 제29권1호
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• pp.117-121
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• 2008

Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for nucleophilic substitution reactions of 5-nitro-8-quinolyl benzoate (5) with alkali metal ethoxides, EtO?M+ (M+ = Li+, Na+ and K+) in anhydrous ethanol (EtOH) at 25.0 0.1 C. The plots of kobsd vs. [EtO?M+] exhibit upward curvatures, while the corresponding plots for the reactions of 5 with EtO?Na+ and EtO?K+ in the presence of complexing agents, 15-crown-5-ether and 18-crown-6-ether are linear with rate retardation. The reactions of 5 with EtO?Na+ and EtO?Li+ result in significant rate enhancements on additions of Na+ClO4, indicating that the M+ ions behave as a catalyst. The dissociated EtO and ion-paired EtOM+ have been proposed to react with 5. The second-order rate constants for the reactions with EtO (kEtO) and EtOM+ (kEtOM+) have been calculated from ion-pairing treatments. The kEtO and kEtOM+ values decrease in the order kEtONa+ > kEtOK+ > kEtOLi+ > kEtO, indicating that ion-paired EtOM+ species are more reactive than the dissociated EtO ion, and Na+ ion exhibits the largest catalytic effect. The M+ ions in this study form stronger complex with the transition state than with the ground state. Coordination of the M+ ions with the O and N atoms in the leaving group of 5 has been suggested to be responsible for the catalytic effect shown by the alkali metal ions in this study.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2438-2442
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• 2014

A kinetic study is reported for $S_NAr$ reaction of 1-fluoro-2,4-dinitrobenzene (5a) and 1-chloro-2,4-dinitrobenzene (5b) with alkali-metal ethoxides (EtOM, M = Li, Na, K and 18-crown-6-ether complexed K) in anhydrous ethanol. The second-order rate constant increases in the order $k_{EtOLi}$ < $k_{EtO^-}$ < $k_{EtONa}$ < $k_{EtOK}$ < $k_{EtOK/18C6}$ for the reaction of 5a and $k_{EtOLi}$ < $k_{EtONa}$ < $k_{EtO^-$ < $k_{EtOK}$ < $k_{EtOK/18C6}$ for that of 5b. This indicates that $M^+$ ion behaves as a catalyst or an inhibitor depending on the size of $M^+$ ion and the nature of the leaving group ($F^-$ vs. $Cl^-$). Substrate 5a is more reactive than 5b, although the $F^-$ in 5a is ca. $10pK_a$ units more basic than the $Cl^-$ in 5b, indicating that the reaction proceeds through a Meisenheimer complex in which expulsion of the leaving group occurs after the rate-determining step (RDS). $M^+$ ion would catalyze the reaction by increasing either the nucleofugality of the leaving group through a four-membered cyclic transition state or the electrophilicity of the reaction center through a ${\pi}$-complex. However, the enhanced nucleofugality would be ineffective for the current reaction, since expulsion of the leaving group occurs after the RDS. Thus, it has been concluded that $M^+$ ion catalyzes the reaction by increasing the electrophilicity of the reaction center through a ${\pi}$-complex between $M^+$ ion and the ${\pi}$-electrons in the benzene ring.

• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3321-3330
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• 2012

The complexation characteristics of mixed [2 + 2'] calix[4]aryl derivatives (3 and 4) with alkali metal cations were investigated by the mPW1PW91 (hybrid HF-DF) calculation method. The total electronic and Gibbs free energies of the various complexes (cone, partial-cone, 1,2-alternate, and 1,3-alternate) of sodium and potassium cations with 3 and 4 were analyzed and compared. The structures of the endo- or exo-complexes of the alkali metal cation with the host 3 were optimized using the mPW1PW91/6-31G(d) method, followed by mPW1PW91/6-311+G(d) calculations. The structures of the endo- or exo-complexes of the alkali metal cation with the host 4 were optimized using the mPW1PW91/6-31G(d,p) method. The mPW1PW91 calculated relative energies of the various conformations of the free hosts (3 and 4) suggest that the cone conformers of 3 and 4 are the most stable. The mPW1PW91calculations also suggest that the complexation efficiencies of the sodium ion with hosts 3 and 4 are about 24 and 27 kcal/mol better than those of the potassium ion, respectively. These trends are in good agreement with the experimental results. The exo-complexation efficiencies of the sodium ion toward the conformers of hosts 3 and 4 are roughly 14 and 17 kcal/mol better than those for the endo-$Na^+$-complexes of 3 and 4, respectively. The exo-complexation of the cone isomer of 3 with cation could be confirmed by the differences of the diagnostic C=O bands in the free host and its complex's IR spectra.

• Bulletin of the Korean Chemical Society
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• 제31권2호
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• pp.303-308
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• 2010

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl benzoate (5a), 4-nitrophenyl 4-methoxybenzoate (5b), and 4-nitrophenyl 4-hydroxybenzoate (5c) with alkali metal ethoxides, $EtO^-M^+$ ($M^+=Li^+$, $Na^+$ and $K^+$) in anhydrous ethanol (EtOH) at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. [$EtO^-M^+$] exhibit upward curvatures in all cases, indicating that $M^+$ ions catalyze the reactions and ionpaired $EtO^-M^+$ species are more reactive than dissociated $EtO^-$. Second-order rate constants for reactions with dissociated $EtO^-$ and ion-paired $EtO^-M^+$ (i.e., $k_{EtO^-}$ and $k_{EtO^-M^+}$, respectively) have been calculated from ion-pair treatment for the reactions of 5a and 5b. However, such ion-pair treatment has failed to determine $k_{EtO^-}$ and $k_{EtO^-M^+}$ values for the reactions of 5c. It has been concluded that reactions of 5a and 5b are catalyzed by one metal ion, which increases electrophilicity of the reaction center through coordination on the carbonyl oxygen. In contrast, reactions of 5c have been suggested to involve two metal ions, i.e., the one coordinated on the carbonyl oxygen increases the electrophilicity of the reaction center while the other one associated on the phenoxy oxygen decreases the charge repulsion between the anionic reagents (i.e., $EtO^-$ and deprotonated 5c). It has been found that the rate equation derived from the mechanism involving two metal ions fits nicely to the kinetic results obtained for the reactions of 5c.

• Bulletin of the Korean Chemical Society
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• 제31권2호
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• pp.453-456
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• 2010

The structural and energetic preferences of thiacalix[4]biscrown-5 with and without alkali metal ions ($Na^+$, $K^+$, $Rb^+$, and $Cs^+$) have been theoretically investigated for the first time using molecular dynamic (MD) simulations and density functional theory (MPWB1K/6-31G(d)//B3LYP/6-31G(d)) methods. The formation of the metal ion complex by the host is mainly driven by the electrostatic attraction between crown-5 oxygens and a cation together with the minor contribution of the cation-$\pi$ interaction between two facing phenyl rings around the cation. The computed binding energies and the atomic charge distribution analysis for the metal binding complexes indicate the selectivity toward a potassium ion. The theoretical results herein explain the experimentally observed extractability order by this host towards various alkali metal ions. The physical nature and the driving forces for cation recognition by this host are discussed in detail.