• Bulletin of the Korean Chemical Society
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• 제22권7호
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• pp.673-677
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• 2001

Pseudo-first-order rate constants have been measured spectrophotometrically for the reactions of 8-(5-nitroquinolyl) 3-furoate with alkali metal ethoxides in anhydrous ethanol. The plot of kobs vs the concentration of alkali metal ethox ides is linear for the reactions performed in the presence of a complexing agent, 18-crown-6 ether, but exhibits upward curvatures for the corresponding reactions performed in the absence of the complexing agent, indicating that the alkali metal ions in this study behave as catalysts. Second-order rate constants were determined for the reactions with dissociated free ethoxide (kEtO-) and with ion paired alkali metal ethoxides (kEtO-M + ) from ion pairing treatments. The magnitude of catalytic effect (kEtO-M + /kEtO-) was found to be 1.7, 3.4 and 2.5 for the reaction of 8-(5-nitroquinolyl) 3-furoate, while 1.4, 3.6 and 4.2 for that of 4-nitrophenyl 2-furoate, 1.8, 3.7 and 2.4 for that of 8-(5-nitroquinolyl) benzoate, and 2.0, 9.8 and 9.3 for that of 8-(5-nitroquinolyl) 2-furoate with EtO- Li+ , EtO- Na+ and EtO- K+ , respectively. A 5-membered chelation at the leaving group is suggested to be responsible for the catalytic effect shown by alkali metal ions.

• Bulletin of the Korean Chemical Society
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• 제22권8호
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• pp.883-888
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• 2001

We describe an ion-surface scattering apparatus newly developed to investigate the reactive scattering process of low-energy alkali-metal ions at surfaces. The apparatus consists of an alkali-metal ion gun that is rotatable by 360°, a quadrupole mass spectrometer (QMS) with an ion energy analyzer, a sample manipulator with a heating-and-cooling stage, and an ultrahigh vacuum (UHV) chamber that houses these components. Preliminary experimental results obtained from the apparatus are presented on angular and energy distributions of the ions scattered from clean Pt(111) and water-adsorbed Pt surfaces.

• Bulletin of the Korean Chemical Society
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• 제22권7호
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• pp.669-672
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• 2001

Pseudo-first-order rate constants have been measured spectrophotometrically for the title reactions. The plot of kobs vs the concentration of alkali metal ethoxides is linear for the reactions performed in the presence of complexing age nt, 18-crown-6 ether, but curved upwardly for the corresponding reactions performed in the absence of the complexing agent, indicating that the alkali metal ions studied in this study behave as a catalyst. The catalytic effect was found to increase in the order Li+ << K+ ${\leq}$ Na+. Second-order rate constants were determined for the reactions with dissociated free ethoxide (kEtO-) and with ion paired alkali metal ethoxides (kEtO-M+ ) from ion pairing treatments. The magnitude of catalytic effect (kEtO-M+/kEtO-) was found to be 2.3, 9.5 and 8.7 for the reaction of 8-(5-nitroquinolyl) 2-furoate, while 1.4, 3.6 and 4.2 for that of 4-nitrophenyl 2-furoate, indicating that the catalytic effect is larger in the reaction of the former substrate than in that of the latter one. The larger catalytic effect was attributed to two possible complexing sites with alkali metal ions in the former substrate.

• Bulletin of the Korean Chemical Society
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• 제32권5호
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• pp.1685-1691
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• 2011

The molecular structures of thiacalix[4]biscrown-5 (1) and p-tert-butylthiacalix[4]biscrown-5 (2) and their alkali-metal-ion complexes were optimized using the DFT BLYP/6-31G(d) and mPW1PW91/6-31G(d,p) (hybrid HF-DF) calculations. The total electronic energies, the normal vibrational modes, and the Gibbs free energies of the mono- and di-topic complexes of each host with the sodium and potassium ions were analyzed. The $K^+$-complexes exhibited relatively stronger binding efficiencies than $Na^+$-complexes for both the monoand di-topic complexes of 1 and 2 comparing the efficiencies of the sodium and potassium complexes with an anisole and phenol. The mPW1PW91/6-31G(d,p) calculated distances between the oxygen atoms and the alkali metal ions were reported in the alkali-metal-ion complexes ($1{\cdot}Na^+$, $1{\cdot}2Na^+$, $1{\cdot}K^+$, $1{\cdot}2K^+$, $2{\cdot}Na^+$, $2{\cdot}Na^+$, $2{\cdot}K^+$, $2{\cdot}2K^+$). The BLYP/6-31G(d) calculated IR spectra of the host 1 and its mono-topic alkali-metal-ion complexes are compared.

• Bulletin of the Korean Chemical Society
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• 제29권3호
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• pp.541-545
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• 2008

Stable molecular isomers were calculated for the azobenzene crown ether p-tert-butylcalix[4]arene (1) in the host and their alkali-metal-ion complexes. The structures of two distinct isomers (cis and trans) have been optimized using DFT B3LYP/6-31G(d,p) method. Trans isomer of 1 is found to be 11.69 kcal/mol more stable than cis analogue. For two different kinds of complexation mode, the alkali-metal-cation in the crown-ether moiety (exo) has much better complexation efficiency than in the benzene-rings (endo) pocket for both isomers of 1. Sodium ion has much better complexation efficiency than potassium ion in all kinds of complexation mode with host 1. The Na+ complexation efficiency of the trans-complex (1) in the exo-binding mode is 8.24 kcal/mol better than cis-exo analogue.

• 대한화학회지
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• 제37권9호
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• pp.820-825
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• 1993

새로운 HDBPDA 이온교환체, {(4,5) : (13,14)-dibenzo-6,9,12-trioxa-3,15,21-triazabicyclo[15.3.l]heneicosa-(1,17,19)(18,20,21) triene ion exchanger: HDBPDA ion exchanger}의 이온교환용량은 3.8 meq/g이었다. 그리고 이 이온교환체에 대한 알칼리 및 알칼리토금속 이온들의 분포계수를 물과, 여러 농도의 염산용액중에서 측정하였다. 금속이온들의 분포계수는 염산농도의 영향을 거의 받지 않았으나, 대체적으로 염산의 농도가 감소할수록 점진적으로 약간 증가하는 경향을 보였다. 그리고 물속에서의 분포계수가 가장 컸다. HDBPDA 이온교환체를 사용하여 알칼리 및 알칼리토금속 이온들을 컬럼이온교환크로마토그래피로 분리하였으며, 이때 용리액으로 물을 사용하였다. 또한 알칼리 및 알칼리토금속 이온들의 분포계수는 그들 이온들의 이온반경이 증가함에 따라 증가하였다.

• Bulletin of the Korean Chemical Society
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• 제15권8호
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• pp.654-658
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• 1994

Rate constants have been measured spectrophotometrically for the nucleophilic substitution reactions of p-and m-nitrophenyl 2-furoates (4 and 5, respectively) with alkali metal ethoxides ($EtO^-M^+$) in absolute ethanol at 25$^{\circ}$C. The reactivity of $EtO^-M^+$ toward 4 is in the order $EtO^-K^+$ > $EtO^-Na^+$> $EtO^-Li^+$ > $EtO^-K^+$+ 18-crown-6 ether. This is further confirmed by an ion pairing treatment method. The present result indicates that (1) ion paired $EtO^-M^+$ is more reactive than dissociated $EtO^-$ ; (2) the alkali metal ions ($K^+,\;Na^+,\;Li^+$) behave as a catalyst; (3) the catalytic effect increases with increasing the size of the metal ion. A similar result has been obtained for the reaction of 5, however, the catalytic effects shown by the metal ions are more significant in the reaction of 5 than in that of 4.

• Bulletin of the Korean Chemical Society
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• 제18권7호
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• pp.749-754
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• 1997

Rate constants have been measured spectrophotometrically for the reactions of alkali metal ethoxides (EtOM) with S-p-nitrophenyl 2-thiofuroate (1b) and 2-thiophenethiocarboxylate (2b) in absolute ethanol at 25.0±0.1 ℃. 1b is observed to be more reactive than 2b toward all the EtOM studied. The reactivity of EtOM is in the order EtOK > EtONa > EtO- > EtOLi for both substrates, indicating that K+ and Na+ behave as a catalyst while Li+ acts as an inhibitor in the present system. Equilibrium association constants of alkali metal ions with the transition state (KaTS) have been calculated from the known equilibrium association constants of alkali metal ion with ethoxide ion (Ka) and the rate constants for the reactions of EtOM with 1b and 2b. The catalytic effect (KaTS/Ka) is larger for the reaction of 1b than 2b, and decreases with decreasing the size of the alkali metal ions. Formation of 5-membered chelation at the transition state appears to be responsible for the catalytic effect.

• 분석과학
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• 제6권3호
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• pp.261-265
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• 1993

새로운 DBPDA이온교체, {(4,5):(13,14)-dibenzo-6, 9, 12-trioxa-3, 15, 21-triazabicyclo [15.3.1] heneicosa-1(21), 17, 19-triene-2, 16-dione : DBPDA 이온교환체}의 이온교환용량은 4.2meq/g이었다. 그리고 이 이온교환체에 대한 알칼리 및 알칼리 토금속 이온들의 분배계수를 여러 농도의 염산용액 중에서 측정하였다. 또한 DBPDA 이온교환체를 사용하여 알칼리 및 알칼리 토금속 이온들을 이온교환 컬럼 크로마토그라피로 분리하였다. 이러한 결과로부터 알칼리 및 알칼리 토금속 이온들의 분배계수에 미치는 용액의 pH와 금속 이온들의 이온반경 효과를 고찰하였다.

• Bulletin of the Korean Chemical Society
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• 제30권9호
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• pp.1996-2000
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• 2009

Alkali metal salts were introduced to enhance the ionization efficiency of glucose and maltooligoses in electrospray ionization-mass spectrometry (ESI-MS). A mixture of the same moles of glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose was used. Salts of lithium, sodium, potassium, and cesium were employed as the cationizing agent. The ionization efficiency varied with the alkali metal cation types as well as the analyte sizes. Ion abundance distribution of the [M+$cation]^+$ ions of the carbohydrates varied with the fragmentor voltage. The maximum ion abundance at low fragmentor voltage was observed at maltose, while the maximum ion abundance at high fragmentor voltage shifted to maltotriose or maltotetraose for Na, K, and Cs. Variation of the ionization efficiency was explained with the hydrated cation size and the binding energy of the analyte and alkali metal cation.