• Journal of the Korean Applied Science and Technology
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• v.13 no.1
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• pp.107-113
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• 1996

Fluorenylidene chalcone derivatives were synthesized by condensation. The structure of these compounds were ascertained by means of UV, melting point, IR and $^1H-NMR$ spectra. The nucleophilic addition reaction kinetics of Thioglycolic acid to fluorenylidene chalcone was investigate by UV in 20% $dioxane-H_2O$ at $25^{\circ}C$. The rate equation which were applied over a wide $pH1.0{\sim}13.0$ range. On the basis of general base catalysis and confirmation of addition reaction product, the nucleophilic addtion reaction kinetics of thioglycolic acid to fluorenylidene chalcone were measured by the pH change. From the result of the above caption, a plausible nucleophilic addition reaction mechanism of thioglycolic acid to fluorenylidene chalcone was proposed. These compounds may be used as the starting materials for the preparation of the engineering plastics or the germicide.

• Journal of the Korean Chemical Society
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• v.34 no.5
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• pp.483-489
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• 1990

The rate of hydrolysis of insecticidal 2-chloro-l-(2,4,5-trichlorophenyl)-vinyldimethylphosphate(Gardona) have been investigated in 25${\%}$ aqueous methanol. Studies at varying pH suggest that the hydrolysis of Gardona proceeds through the bimolecular (Ad$_{N-E}$) mechanism involving the transition state and carbanion intermediate as evidenced by solvent effect (m < 0.4, n < 0.7, [m] ${\ll}$ [l](associative SN$_2$ type)), thermodynamic parameters (${\{Delta}S^{\neq}$ = -27∼-32 e.u. & ${\{Delta}H^{\neq}$ = 13∼18 Kcal/mole), hydrolysis rate equation (k = k$_A+_B$ [OH-]), general base catalysis and hydrolysis product analysis, respectively.

• Journal of the Korean Chemical Society
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• v.44 no.2
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• pp.120-126
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• 2000

The rate constants for the hydrolysis of 2-phenyl-4H,5H-3-methyl-3-thiazolinium perchlorate(PTP) derivatives were detemined by the use of ultraviolet visible spectrophotometer in water. The rate equations which could be applied over a wide pH ranges were obtained. On the basis of rate equation, hydrolysis product analysis, general base catalysis, and substituent effect, a plausible mechanism of the hydrolysis is proposed: Below pH 4.0, the reaction is initiated by addition of water, while above pH 9.0, Michael type nucleophilic addition takes place. In the pH range of $4.5{\sim}8.0$, these two reactions appear to occur competitively.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3293-3297
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• 2012

The solvolysis rate constants of 5-nitro-2-furoyl chloride (5-$NO_2(C_4H_2O)$-2-COCl, 1) in 27 different solvents are well correlated with the extended Grunwald-Winstein equation, using the $N_T$ solvent nucleophilicity scale and YCl solvent ionizing scale, with sensitivity values of $1.20{\pm}0.05$ and $0.37{\pm}0.02$ for l and m, respectively. The activation enthalpies (${\Delta}H^{\neq}$) were 5.63 to $13.0kcal{\cdot}mol^{-1}$ and the activation entropies (${\Delta}S^{\neq}$) were -25.9 to $-43.4cal{\cdot}mol^{-1}{\cdot}K^{-1}$, which is consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effect (SKIE, $k_{MeOH}/k_{MeOD}$) of 2.65 was also in accord with the $S_N2$ mechanism and was possibly assisted using a general-base catalysis. The product selectivity (S) for solvolysis of 1 in alcohol/water mixtures was 1.2 to 11, which is also consistent with the proposed bimolecular reaction mechanism.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2023-2028
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• 2013

A kinetic study is reported for the nucleophilic substitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5k) with piperidine in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. [piperidine] for the reactions of substrates possessing a strong electron-withdrawing group (EWG) in the leaving group (i.e., 5a-5i) are linear and pass through the origin. In contrast, the plots for the reactions of substrates bearing a weak EWG or no substituent (i.e., 5j or 5k) curve upward, indicating that the electronic nature of the substituent Y in the leaving group governs the reaction mechanism. Thus, it has been suggested that the reactions of 5a-5i proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate (i.e., $T^{\pm}$) while those of 5j and 5k proceed through a stepwise mechanism with two intermediates (i.e., $T^{\pm}$ and its deprotonated form $T^-$). The slope of the Br${\o}$nsted-type plot for the second-order rate constants (i.e., $k_N$ or $Kk_2$) changes from -0.41 to -1.89 as the leaving-group basicity increases, indicating that a change in the rate-determining step (RDS) occurs. The reactions of 5a-5k with piperidine result in larger $k_1$ values than the corresponding reactions with ethylamine.

• Journal of Life Science
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• v.18 no.8
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• pp.1036-1041
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• 2008

Methenyltetrahydrofolate synthetase extract was obtained from mouse liver and purified via $30{\sim}70%$ ammonium sulfate fractionation, Fast Q anion exchange and phenyl agarose chromatography. HPLC gel chromatography and SDS-polyacrylamide electrophoresis experiments showed that the enzyme is a monomer with molecular weight of 23 kDa. Optimum temperature and pH were $35^{\circ}C$ and 6.5, respectively. The enzyme was chemically modified only by tetranitromethane and 1-ethyl-3- (3-dimethyl aminopropyl)-carbodiimide (EDC), indicating that tyrosine and carboxylate are in the active site. pH studies showed that 2 tyrosines are involved in the binding of the substrates and a carboxylate in catalysis. Therefore, the chemical mechanism of the enzyme is likely that 2 tyrosines bind to ATP and 5-formylTHFand a carboxylate acts as a general base.

• Applied Biological Chemistry
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• v.37 no.2
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• pp.124-129
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• 1994

The rate of hydrolysis of insecticidal $O,O-diethyl-{\alpha}-cyanobenzylideneamino-oxyphosphorothioate\;(Volaton^{\circledR})$ has been studied in 25% (v/v) aqueous dioxane. On the basis of solvent effect (pH 6.0; m=0.21, n=1.55, pH 12.0; m=0.42, n=3.14 & $|m|{\ll}|l|$), general base catalysis, hydrolysis product analysis, calculation of molecular orbital (MO) and rate equation, it may be concluded that the hydrolysis of Volaton proceeds through the $A_{AC}2$ mechanism via trigonal bipyramidal $(sp^3d^2)$ intermediate below pH 7.0, while above pH 9.0 the hydrolysis proceeds through the $B_{AC}2$ mechanism. Hydrolysis reactivity of Volaton depends on positive charge strength $(p{\gg}{\alpha}C_2)$ rather than steric hindrance. In the range between pH 7.0 and pH 9.0, these two reactions occur competitively.

• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.51-56
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• 2014

The solvolysis rate constants of 2,4-dimethoxybenzenesulfonyl chloride (1) in 30 different solvents are well correlated with the extended Grunwald-Winstein equation, using the $N_T$ solvent nucleophilicity scale and $Y_{Cl}$ solvent ionizing scale, with sensitivity values of $0.93{\pm}0.14$ and $0.65{\pm}0.06$ for l and m, respectively. These l and m values can be considered to support a $S_N2$ reaction pathway. The activation enthalpies (${\Delta}H^{\neq}$) were 12.4 to $14.6kcal{\cdot}mol^{-1}$ and the activation entropies (${\Delta}S^{\neq}$) were -15.5 to -$32.3kcal{\cdot}mol^{-1}{\cdot}K^{-1}$, which is consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effects (SKIE) were 1.74 to 1.86, which is also in accord with the $S_N2$ mechanism and was possibly assisted using a general-base catalysis. The values of product selectivity (S) for solvolyses of 1 in alcohol/water mixtures was 0.57 to 6.5, which is also consistent with the proposed bimolecular reaction mechanism. Third-order rate constants, $k_{ww}$ and $k_{aa}$, were calculated from the rate constants ($k_{obs}$), together with $k_{aw}$ and $k_{wa}$ calculated from the intercept and slope of the plot of 1/S vs. [water]/[alcohol]. The calculated rate constants, $k_{calc}$ ($k_{ww}$, $k_{aw}$, $k_{wa}$ and $k_{aa}$), are in satisfactory agreement with the experimental values, supporting the stoichiometric solvation effect analysis.

• Journal of the Korean Chemical Society
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• v.37 no.12
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• pp.1060-1067
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• 1993

A series of New N-[1-(benzotriazol-1-yl)-X-substituted benzyl]-Y-substituted aniline derivaties (S) have been synthesized. And the rate of hydrolysis was investigated kinetically in 25% (v/v) aqueous methanol at 25$^{\circ}C$. On the basis of rate equations, solvent effect $m {\ll} 1,\; n \leq 3\; and\; m {\ll} l$), salt effect, general base catalysis, substituent effect (${\rho}_{xy}$ > > 0), and hydrolysis products analysis, it may be concluded that the hydrolysis of N-[1-(benzotriazol-1-yl)benzyl]aniline proceeds the "A-$S_N2$" mechanism below pH 12.0, while above pH 13.0, the hydrolysis proceeds through a typical "$S_N2$" mechanism.

• Journal of the Korean Chemical Society
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• v.36 no.4
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• pp.589-597
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• 1992

The rate constants of hydrolysis of phenyl-N-benzoylchlorothioformimidates were determined by UV spectrophotometry in 30% (v/v) aqueous dioxane at $25^{\circ}C$. On the basis of rate equation, general base catalysis, solvent effect, substituent effect, thermodynamic parameters, frontier orbital interaction and hydrolysis product analysis, it may be concluded that the hydrolysis of phenyl-N-benzoylchlorothioformimidates proceeds through $S_N1$ mechanism via azocarbocation intermidiate below pH 10.0, while above pH 10.00 the hydrolysis proceeds through nucleophilic addition-elimination ($Ad_{N-E}$) mechanism. In the range of pH from 10.0 to 11.0 these two reaction occur competitively.