• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2483-2487
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• 2010

Pseudo-first-order rate constants ($k_{obsd}$) were measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl picolinate (6) with alkali metal ethoxides (EtOM, $M^+\;=\;K^+$, $Na^+$ and $Li^+$) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOM] exhibits upward curvature regardless of the nature of $M^+$ ions. However, the plot for the reaction of 6 with EtOK is linear with significantly decreased $k_{obsd}$ values when 18-crown-6-ether (18C6, a complexing agent for $K^+$ ion) is added in the reaction medium. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that ion-paired EtOM is 3~17 times more reactive than dissociated $EtO^-$. The reaction has been proposed to proceed through a 5-membered cyclic transition state, in which $M^+$ ion increases the electrophilicity of the reaction site. Interestingly, $Na^+$ ion exhibits the largest catalytic effect. The presence of a nitrogen atom in the pyridine moiety of 6 has been suggested to be responsible for the high $Na^+$ ion selectivity.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1506-1510
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• 2014

A kinetic study on nucleophilic substitution reaction of 5-nitro-8-quinolyl picolinate (6) with alkali-metal ethoxides (EtOM; M = K, Na, and Li) in anhydrous ethanol is reported. The plot of $k_{obsd}$ vs. [EtOM] curves upward in the absence of crown ethers but is linear with significantly decreased reactivity in the presence of crown ethers. Dissection of $k_{obsd}$ into $k_{EtO}$- and $k_{EtOM}$ (i.e., the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that the ion-paired EtOM is significantly more reactive than the dissociated $EtO^-$ (e.g., $k_{EtOM}/k_{EtO^-}$ = 33.4-141). This indicates that the reaction of 6 is catalyzed by $M^+$ ions in the order $Na^+$ > $Li^+$ > $K^+$ and the catalytic effect disappears in the presence of a proper crown ether. Picolinate ester 6 is much more reactive and is more strongly catalyzed by $M^+$ ions than 5-nitro-8-quinolyl benzoate (5). It has been concluded that $M^+$ ions catalyze the reaction of 6 by increasing electrophilicity of the reaction center through a cyclic transition state, which is structurally not possible for the reaction of 5.

• 한국토양환경학회지
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• 제1권2호
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• pp.43-50
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• 1996

The adsorption charateristics of lead(II) ions on Aspergillus niger and Rhizopus arrhizus were investigated. Adsorption amount of A. niger and R. arrhizus was about 95 mg/g and 25 mg/g, respectively. These biomass was approached to adsorption equilibrium within reaction time of 1hr because of their high reactivity. The uptake of lead ion by A. niger was less sensitivity than it by R. arrhizus on the inhibition effect of alkali metals and the decreasing ratio of uptake of lead ion of A. niger and R. arrhizus by inhibition effect of alkali metals was 37% and 50%, respectively. In pre-treatment on these biomass, NaOH treatment was contributed high adsorption capacity to these biomass. Then, adsorption amount of A. niger and R. allhizus was increased about 25 mg/g and 10 mg/g, respectively. In isotherm for the adsorption of lead ion based on Freundlich equation, 1/n value of A. niger and R. ar고izus was calculated the range of 0.28-0.56 and 0.44-0.67, respectively.

• Bulletin of the Korean Chemical Society
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• 제22권6호
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• pp.559-564
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• 2001

A method for calculating the main characteristics of a potentiometric titration curve in a carboxylic ion exchanger has been investigated. The potentiometric titration curves of simple electrolyte and ion exchangers (polyelectrolytes) showed a great difference between them. The acidity parameters of the ion exchangers, the thermodynamic constant (pK0), apparent equilibrium constant (K), and correction for the apparent equilibrium constant (b), were introduced and used to express the characteristics of the carboxylic ion exchanger. A characteristic equation related to the acidity parameters of the ion exchangers systems was derived. A fibrous carboxylic cation exchanger was used and potentiometric titration curves at different concentrations of the supporting electrolyte were obtained . To prove the validity of the characteristic equation, the concentration of the supporting electroyte was varied. In the present study, good agreement between the data points and the fitted curves was found in all the cases. The g (number of moles of alkali to 1 g of ion exchanger) of carboxylic ion exchanger was calculated from the concentration of supporting electrolyte (C), pH of the solution, and degree of neutralization of ion exchanger (x).

• 폴리머
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• 제24권6호
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• pp.802-809
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• 2000

Poly(L-glutamic acid) (PLGA)와 PVA 블렌드막을 제조한 후, ethanol 수용액중에서 막증의 polypeptide 사슬의 2차구조 전이거동에 미치는 용매조성 및 대이온종의 영향과 알칼리 금속 이온 (Li, na, K, Cs)에 대한 투과특성을 조사하였다. 막중 PLG 알칼리 금속염의 helix 형성거동에 있어 대이온 선택성은 Li>Na>K>Cs의 순으로 관찰되었고, 이와 같은 특이성은 탈용매화 에너지와 정전에너지의 감소에 따른 고분자 하전기와 대이온과의 contact ion-pair 형성에 의한 것으로 설명하였다. 또한 PLGA/PVA 블렌드막의 ethanol 수용액 중에서의 알칼리 금속이온의 투과거동을 살펴보면, ethanol 농도가 점차 증가함에 따라 K, Cs의 경우는 투고도가 증가한, Li, Na의 경우에는 감소하였다. K, Cs 이온의 경우 대이온과 염소이온간의 ion-pair (M$^{+}{\cdot}$Cl$^{-}$)형성에 의한 Donnan배제효과의 감소와 중성염 형태로의 분배량 증가때문인 것으로, Li, Na 이온의 경우 막중의 coil-helix 구조전이에 따른 자유체적의 감소와 고분자 하전기와의 상호작용이 증가하여 확산성이 크게 감소하였기 때문인 것으로 생각된다.

• 한국염색가공학회지
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• 제6권4호
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• pp.72-76
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• 1994

The permselectivity of alkali metal chlorides through silk fibroin membrane was investigated at $25^{\circ}C$: The Permeability coefficients were found to increase in a sequence of LiCl < NaCl < KCl < CsCl. This sequence was explained by considering the partition and the hydrophilic membrane. The dependence of the permeability on the salts concentration was interpreted by means of TMS theory. The ionic mobility ratio of alkali metal chlorides through this membrane decreased with the increase of the Stokes radius. The Effectiveness of the charged density was found to depend on the ionic species. The greater the Stokes radius the larger the effective charge density of membrane.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.549-554
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• 2001

It is possible for concrete using sea sand to contain chloride ion as well as cation such as Na$^{+}$and $K^{+}$ during mixing process. It is known that some cations such as Na$^{+}$and $K^{+}$ remain in pore solution without binding In this study, therefore, we intend to inspect the behavior of cations in cement paste as well as NaCl, CaCl$_2$ and KCI through analysis of pore solution extracted from cement paste with high pressure vessel. As a result, increase of alkali ions by adding sea sand and admixtures to the fresh concrete means use of the cement contained high alkali contents. In this case, alkali ions in pore solution can decrease durability of cement products causing alkali-aggregate reaction or accelerated carbonation. So it needs to be studied.studied.

• Bulletin of the Korean Chemical Society
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• 제12권1호
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• pp.93-97
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• 1991

Rate constants have been measured spectrophotometrically for the reactions of alkali metal ethoxides with 4-nitrophenyl benzoate, S-4-nitrophenyl thiobenzoate and 4-nitrophenyl thionbenzoate in ethanol at 25$^{\circ}$C. Substitution of S for O in the leaving group has not affected reactivity significantly, while the effect of the similar replacement in the acyl group has led to rate decrease by a factor of 10, although pronounced rate enhancements have been expected for both systems. The replacement of O by a polarizable S has also influenced the reactivity of the esters toward alkali metal ethoxides, i.e. the reactivity decreases as the size of the metal ion decreases. The alkali metal ions have showed inhibition effect instead of catalytic effect which would have been expected for the present system. The effect of replaced sulfur atom on the reactivity for the present system is attributed to the nature of hard and soft acids and bases.

• 한국세라믹학회지
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• 제44권11호
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• pp.633-638
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• 2007

The setting time of alkali activated slag cement tends to be much faster than ordinary Portland cement, and its compressive strength had been higher from the 1 day but became lower than that of the cement on the 28 days. According to the results of the surface observation, weight loss, compressed strength, and erosion depth tests on the sulphuric acid solution. It has been drawn that alkali activated slag cement has a higher sulphate resistance than ordinary Portland cement, and in particular, the alkali activated slag cement added 5 wt% alumina cement has little deterioration on the sulphuric acid solution. The reason why the alkali activated slag cement has higher sulphate resistance than other hardened cement pastes is that it has no $Ca(OH)_2$ reactive to sulphate ion, and there is little $CaSO_4{\cdot}2H_2O$ production causing volume expansion, unlike other pastes. And it is supposed that $Al(OH)_3$ hydrates with high sulphate resistance, which is produced by adding the alumina cement increases the sulfate resistance.

• 대한화학회지
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• 제50권1호
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• pp.7-13
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• 2006

모양의 캘릭스[4]아릴에스터 호스트(1)와 그것의 알칼리 금속 양이온과의 착물에 대하여 이론적인 적외선 흡수 스펙트럼들이 계산되었다. 진동 스펙트럼들은 RHF/6-31G 방법으로 최적화 된 후에 얻어졌다. 1+Na+ 착물의 여러 가지 C-O와 C=O 신축 운동들의 특징적인 진동수들은 C2v 형태의 분자 모양을 입증하여 주는 데에 반하여, 1+K+ 착물의 구조는 C4v에 가깝다는 것을 보여 주었다. 호스트 분자(1)와 1+Na+ 착물에 대한 이론적인 결과와 실험 스펙트럼들을 비교하였을 때, 계산된 진동수들이 실험 데이터와 잘 일치하는 것을 알 수 있었다.