• Bulletin of the Korean Chemical Society
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• 제26권4호
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• pp.641-644
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• 2005

Nucleophilic addition reactions of benzylamines $(XC_6H_4CH_2NH_2)\;to\;{\beta}$-cyanostilbenes ($YC_6H_4CH=C(CN)C_6H_4$Y’) have been studied in acetonitrile at 30.0 oC. A greater degree of N-$C_{\alpha}$ bond formation (larger ${\beta}_X$) is obtained with a stronger electron-withdrawing substituent in either ${\alpha}-\;(\delta\sigma_Y\;{\gt}\;0)\;or\;{\beta}-ring\;(\delta\sigma_{Y'}\;{\gt}$ 0). A stronger charge development is observed in the TS on $C_{\beta}\;(\rho_{Y'}$= 1.06 for X=Y=H) rather than on $C_{\alpha}\;(\rho_{Y}$ = 0.62 for X=Y’H) indicating the lag in the resonance development into the activating group (CN) on $C_{\beta}$ in the transition state. Similarly, the magnitude of $\rho$$_{XY'}$(−0.72) is greater than $\rho_{XY}$ (−0.66) due to a stronger interaction of the nucleophile with $\beta$-ring than $\alpha$-ring. The positive sign of $\rho_{YY'}$correctly reflects $\pi$ bond cleavage between the two rings in the TS. Relatively large kinetic isotope effects ($k_H/k_D\;{\geq}$ 2.0) involving deuterated nucleophiles ($XC_6H_4CH_2ND_2$) suggest a four-membered cyclic TS in which concurrent N-C$_{\alpha}$ and H(D)-C$_{\beta}$ bond formation occurs.

• 대한기계학회논문집B
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• 제26권4호
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• pp.555-560
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• 2002

Numerical simulations of freely propagating flames burning stoichiometric CH$_4$/O$_2$/$N_2$mixtures are performed at atmospheric pressure in order to understand the effect of the $O_2$enrichment level on CH$_4$/Air flame. A chemical kinetic mechanism is employed, the adopted scheme involving 54 gas-phase species and 632 forward reactions. The calculated flame speeds are compared with the experiments for the flames established at several $O_2$enrichment level, the results of which is in excellent agreement. As a result of the increased $O_2$enrichment level from 0.21 to 1, the mole fraction of CO in the burred gas is increased. The flame speed and the temperature in the burned gas are also increased, but the thickness of the flame is severely shrunken in the preheat region. The maximum of the calculated EINO is obtained around 0.6 and 0.7 of the $O_2$enrichment level in cases of flames for fuel-lean mixtures.

• 대한화학회지
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• 제30권2호
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• pp.231-236
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• 1986

수소크롬산이온에 의한 $[Mo_2O_4(C_2O_4)_2(OH_2)_2]^{2-}$의 산화는 $[Mo_2O_5(C_2O_4)_2(OH_2)_2]^{2-}$를 생성한다. 수소크롬산이온과 $[Mo_2O_4(C_2O_4)_2(OH_2)_2]^{2-}$의 반응에 대한 화학양론은 ${3Mo_2}^V+2Cr^{VI}\;{\rightleftharpoons}\;{3Mo_2}_{VI}+2Cr^{III}$와 같다. 관찰된 속도상수는 $[H+]^2$에 의존한다. $Cr^{VI}$는 Cr^V$와 $Cr^{IV}$를 거쳐서 $Cr^{III}$로 일전자씩 연속적으로 변화한다. 이들 반응에 대한 상세한 메카니즘이 제시되며 이에 대해서 논의된다.

• Bulletin of the Korean Chemical Society
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• 제35권2호
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• pp.471-476
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• 2014

A kinetic study on aminolysis of 2-chloro-4-nitrophenyl X-substituted-benzoates (2a-k) in 80 mol % $H_2O/_20mol%$ DMSO at $25.0^{\circ}C$ is reported. The Br${\emptyset}$nsted-type plot for the reactions of 2-chloro-4-nitrophenyl benzoate (2g) with a series of cyclic secondary amines curves downward (e.g., ${\beta}_1=0.25$, ${\beta}_2=0.85$ and $pK_a^o=10.3$), which is typical of reactions reported to proceed through a stepwise mechanism with a change in ratedetermining step (RDS). The Hammett plot for the reactions of 2a-k with piperidine consists of two intersecting straight lines, while the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with ${\rho}_X=1.15$ and r = 0.59. Thus, it has been concluded that the nonlinear Hammett plot is not due to a change in RDS but is caused by stabilization of substrates through resonance interactions between the electron-donating substituent and the C=O bond. Substrates possessing a substituent at the 2-position of the leaving aryloxide deviate negatively from the curved Br${\emptyset}$nsted-type plot for the reactions of Y-substituted-phenyl benzoates (3a-i), implying that the steric hindrance exerted by the substituent at the 2-position is an important factor which governs the reactivity of Y-substituted-phenyl benzoates.

• 대한화학회지
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• 제28권3호
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• pp.155-162
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• 1984

메탄올-아세토니트릴 혼합용매계에서 파라치환된 브롬화 벤질 및 요오드화 벤질과 아닐린 치환체 사이의 친핵성 치환반응을 35.0$^{\circ}$C에서 연구하였다. Hammett관계식, Bronsted 관계식을 이용하여 반응 선택성 파라미터인$ {\rho}_N,\;{\rho}_C$ 및 ${\beta}$값을 구했으며 분광용매화 관계식의 계수 a, s 등을 구했다. 분광용매화 관계식의 계수 a, s 및 a/s값으로부터 혼합용매의 ${\pi}^{sat}$효과가 본 반응에 크게 작용함을 알았다. PES 모형을 적용하여 본 반응이 dissociative $S_N$2메카니즘으로 진행됨을 알 수 있었으며 이탈기 효과의 논의에는 PES모형이 실험결과와 잘 일치하지 않음을 알 수 있었다. 양자역학적 해석방법을 이용하여 본 반응의 전이상태 변화를 논의했으며 실험결과와 잘 일치함을 알 수 있었다.

• 대한화학회지
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• 제32권3호
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• pp.227-232
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• 1988

$Hg^{2+}$촉매 존재하에서 cis-amminechlorobis(ethylenediamine)cobalt(III)의 Cl이 $H_2O$로 치환되는 반응을 전자흡수 스펙트라로 속도론적 연구를 하였다. 그 결과 $cis-[Co(en)_2(NH_3)Cl]^{2+}$에 대해서 각각 1차인 총괄반응이 2차반응이다. 활성화 파라메타인 ${\Delta}H^{\neq}$와 ${\Delta}S^{\neq}$는 각각 12.9 kcal/mol, -19.3 e.u 이고 $Hg^{2+}$에 의한 반응속도상수는 $1.65{\times}10^{-2}l/mol.sec$가 됨을 알았다. 이러한 속도 자료로부터 본 반응계의 Cl이 $H_2O$로 치환되는 반응은 촉매인 $Hg^{2+}$가 관여하는 Id 메카니즘을 제안하였다.

• Journal of Microbiology and Biotechnology
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• 제27권2호
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• pp.297-305
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• 2017

The use of peroxidase in the nitration of phenols is gaining interest as compared with traditional chemical reactions. We investigated the kinetic characteristics of phenol nitration catalyzed by horseradish peroxidase (HRP) in an aqueous-organic biphasic system using n-butanol as the organic solvent and ${NO_2}^-$ and $H_2O_2$ as substrates. The reaction rate was mainly controlled by the reaction kinetics in the aqueous phase when appropriate agitation was used to enhance mass transfer in the biphasic system. The initial velocity of the reaction increased with increasing HRP concentration. Additionally, an increase in the substrate concentrations of phenol (0-2 mM in organic phase) or $H_2O_2$ (0-0.1 mM in aqueous phase) enhanced the nitration efficiency catalyzed by HRP. In contrast, high concentrations of organic solvent decreased the kinetic parameter $V_{max}/K_m$. No inhibition of enzyme activity was observed when the concentrations of phenol and $H_2O_2$ were at or below 10 mM and 0.1 mM, respectively. On the basis of the peroxidase catalytic mechanism, a double-substrate ping-pong kinetic model was established. The kinetic parameters were ${K_m}^{H_2O_2}=1.09mM$, ${K_m}^{PhOH}=9.45mM$, and $V_{max}=0.196mM/min$. The proposed model was well fit to the data obtained from additional independent experiments under the suggested optimal synthesis conditions. The kinetic model developed in this paper lays a foundation for further comprehensive study of enzymatic nitration kinetics.

• 한국재료학회지
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• 제27권3호
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• pp.166-171
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• 2017

Removal of phosphate from environmental water has become more important to prevent eutrophication. In the present study, sorption behavior of phosphate onto magnesite was investigated under different conditions. The optimum pH of phosphate adsorption was determined to be 6.0. The adsorption capacity was found to decrease with increasing temperature, which indicates that a low temperature was beneficial for phosphate adsorption. The sorption capacity for phosphate was found to be 10.2 mg/g at an initial concentration of 100 mg/L and a dose of 2 g/L. The first order kinetic equation and Freundlich isotherm model fit the data well. Phosphate adsorption on magnesite was explained by electrostatic attraction and weak physical interactions.

• Korean Chemical Engineering Research
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• 제57권5호
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• pp.679-686
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• 2019

수용액으로부터 활성탄에 대한 아닐린 블루의 흡착 평형, 동역학 및 열역학적 특성을 초기농도, 접촉시간과 온도를 흡착변수로 하여 조사하였다. 아닐린 블루의 등온흡착은 Langmuir, Freundlich, Redlich-Peterson, Temkin 및 Dubinin-Radushkevich 모델을 통해 해석하였다. Langmuir 모델이 다른 모델들 보다 등온 데이터에 더 잘 맞았다. 평가된 Langmuir 분리계수($R_L=0.036{\sim}0.068$)는 활성탄에 의한 아닐린 블루의 흡착 공정이 효과적인 처리방법이 될 수 있음을 나타냈다. 흡착속도상수는 유사일차속도 모델, 유사이차속도 모델 및 입자내 확산 모델에 적용하여 구하였다. 활성탄에 대한 아닐린 블루의 흡착속도실험 결과는 유사이차 반응속도식에 잘 따랐다. 흡착 메카니즘은 입자내 확산 모델에 의해 경막 확산과 입자내 확산의 두 단계로 평가되었다. 흡착공정에 대한 깁스 자유에너지, 엔탈피 및 엔트로피 변화와 같은 열역학 파라미터들이 평가되었다. 엔탈피 변화(48.49 kJ/mol)은 흡착공정이 물리흡착이고 흡열반응임을 알려주었다. 깁스 자유 에너지는 온도가 올라갈수록 감소하였기 때문에 흡착반응은 온도가 올라갈수록 자발성이 더 높아졌다. 등량흡착열은 흡착제 표면의 에너지 불균일성 때문에 흡착제와 흡착질 사이에 상호작용이 있음을 나타내었다.

• Bulletin of the Korean Chemical Society
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• 제34권4호
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• pp.1115-1119
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• 2013

A kinetic study is reported for nucleophilic substitution reactions of benzyl 2-pyridyl thionocarbonate (5b) and t-butyl 2-pyridyl thionocarbonate (6b) with a series of alicyclic secondary amines in $H_2O$ at $25.0^{\circ}C$. General-base catalysis, which has often been reported to occur for aminolysis of esters possessing a C=S electrophilic center, is absent for the reactions of 5b and 6b. The Br${\o}$nsted-type plots for the reactions of 5b and 6b are linear with ${\beta}_{nuc}$ = 0.29 and 0.43, respectively, indicating that the reactions of 5b proceed through a stepwise mechanism with formation of a zwitterionic tetrahedral intermediate ($T^{\pm}$) being the rate-determining step while those of 6b proceed through a concerted mechanism. The reactivity of 5b and 6b is similar to that of their oxygen analogues (i.e., benzyl 2-pyridyl carbonate 5a and t-butyl 2-pyridyl carbonate 6a, respectively), indicating that the effect of modification of the electrophilic center from C=O to C=S (i.e., from 5a to 5b and from 6a to 6b) on reactivity is insignificant. In contrast, 6b is much less reactive than 5b, indicating that the replacement of the $PhCH_2$ in 5b by the t-Bu in 6b results in a significant decrease in reactivity as well as a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway). It has been concluded that the contrasting reactivity and reaction mechanism for the reactions of 5b and 6b are not due to the electronic effects of $PhCH_2$ and t-Bu but are caused by the large steric hindrance exerted by the bulky t-Bu in 6b.