• Journal of the Korean Chemical Society
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• v.25 no.4
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• pp.283-290
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• 1981

The reaction rates for the transesterification reaction were measured on the excess sucrose with the five fatty acid methyl ester systems such as methyl laurate, methyl myristate, methyl palmitate, methyl stearate and methyl oleate at temperature range of $50^{\circ}C$ to $90^{\circ}C$ in N,N-dimethylformamide solvent and potassium carbonate as a catalyst. Their activation parameters as well as rate constants were calculated from these measurements. And these reactions were found to be pseudo-first order and depended mainly on the structural changes in fatty acid residue of methyl esters. Also their reactions were found to be of enthalpy-controlled, which were disfavored in the order of methyl laurate, methyl myristate, methyl palmitate, methyl oleate and methyl stearate. Correspondingly their activation energies were 9.3, 9.9, 10.3, 10.9 and 11.1 kcal/mole, respectively.

• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.177-181
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• 2014

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for the reactions of Y-substituted-phenyl benzoates (5a-j) with potassium ethoxide (EtOK) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. [EtOK] curve upward regardless of the electronic nature of the substituent Y in the leaving group. Dissection of $k_{obsd}$ into the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOK (i.e., $k_{EtO^-}$ and $k_{EtOK}$, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated $EtO^-$. The Br${\phi}$nsted-type plots for the reactions with the dissociated $EtO^-$ and ion-paired EtOK exhibit highly scattered points with ${\beta}_{lg}$ = -$0.5{\pm}0.1$. The Hammett plots correlated with ${\sigma}^o$ constants result in excellent linear correlations, indicating that no negative charge develops on the O atom of the leaving Y-substituted-phenoxide ion in transition state. Thus, it has been concluded that the reactions with the dissociated $EtO^-$ and ion-paired EtOK proceed through a stepwise mechanism, in which departure of the leaving group occurs after the RDS, and that $K^+$ ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a four-membered cyclic TS structure.

• Journal of the Korean Chemical Society
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• v.48 no.3
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• pp.254-260
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• 2004

The reaction rates of para-substituted benzoyl chlorides ($p-CH_3$, p-H, $p-NO_2$) with pyridine have been measured employing the conductometry method in acetonitrile. The pseudo first-order and second-order rate constants were determined at various pressures and temperatures. The activation parameters (${\Delta}V{\ddagger},\;{\Delta}{\beta}{\ddagger},\;{\Delta}H{\ddagger},\;{\Delta}S{\ddagger},\;{\Delta}G{\ddagger}$) and the Hammett ${\rho}$-values are determined from the values of rate constant. The values of ${\Delta}V{\ddagger},\;{\Delta}{\beta}{\ddagger}\;and\;{\Delta}S{\ddagger}$ are all negative. The Hammett ${\rho}$-values are positive for the substrate (${\rho}_Y$) over the given pressure range. The results of kinetic studies, for the pressure and substituent changes, show that these reactions are proceeded by a typical $SN_2$reaction mechanism and its bond formation is favored with elevating pressure.

• Journal of the Korean Chemical Society
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• v.37 no.6
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• pp.577-584
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• 1993

The reaction rates of para-substituted benzoyl chlorides with substituted pyridines have been measured employing the conductometry method in acetonitrile, and pseudo-first order and second order rate constants are determined at various pressures and temperatures. The activation parameters (${\Delta}V^\neq, {\Delta}{\beta}^{\neq}, {\Delta}H^{\neq}, {\Delta}S^{\neq} {\Delta}G^{\neq}$) and the Hammett ρ-values are determined from the values of rate constants. The values of △${\Delta}V^\neq, {\Delta}{\beta}^{\neq}and {\Delta}S^{\neq}$ are all negative. The Hammett ρ-values are negative for the nucleophile (ρ$_X$), and positive for the substrate (ρ$_Y$) over the pressure range studied. The results of kinetic studies for pressure and substituent show that these reactions proceed in typical S$_N$2 reaction mechanism and in bond formation favored with elevating pressure.

• Archives of Pharmacal Research
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• v.22 no.2
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• pp.219-224
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• 1999

In our search for the anticonvulsant consitutent of Gastrodia elata repeated column chromatographies guided by activity assay led to isolation of an active compound, which was identified as gastrodin on the basis of spectral data. Brain succinic semialdehyde dehydrogenase (SSADH) was inactivated by preincubation with gastrodin in a time-dependent manner and the reaction was monitored by absorption and fluorescene spectroscopic methods. The inactivation followed pseudo-first-order kinetics with the second-rate order constant of $1.2{\times}10^{3} M^{-1} min^{-1}$. The time course of the reaction was significantly affected by the coenzyme NAD^{+}$, which affected complete protection against the loss of the catalytic activity, whereas substrate succinic semialdehyde failed to prevent the inactivation of the enzyme. It is postulated that the gastrodin is able to elevate the neurotransmitter GABA levels in central nervous system by inhibitory action on one of the GABA degradative enzymes, SSADH.

• Journal of Environmental Science International
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• v.16 no.4
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• pp.393-397
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• 2007

The sonolytic decomposition of NHCs(Nitrogen Heterocyclic Compounds), such as atrazine[6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine], simazine(6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine), trietazine(6-chloro-N,N,N'-triethyl-1,3, 5-triazine-2,4-diamine), in water was investigated at a ultrasound frequency of 200kHz with an acoustic intensity of 200W under argon and air atmospheres. The concentration of NHCs decreased with irradiation, indicating pseudo-first-order kinetics. The rates were in the range $1.06{\sim}2.07({\times}10^{-2}min^{-1})$ under air and $1.30{\sim}2.59({\times}10^{-2}min^{-1})$ under argon at a concentration of $200{\mu}M$ of NHCs. The rate of hydroxyl radicals(${\bullet}{OH}$) formation from water is $19.8{\mu}M\;min^{-1}$ under argon and $14.7{\mu}M\;min^{-1}$ under air in the same sonolysis conditions. The sonolysis of NHCs is effectively inhibited, but not completely, by the addition of t-BuOH(2-methyl-2-propanol), which is known to be an efficient ${\bullet}{OH}$ radical scavenger in aqueous sonolysis. This suggests that the main decomposition of NHCs proceeds via reaction with ${\bullet}{OH}$ radical; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fenton's reagent $[Fe^{2+}]$ accelerates the decomposition. This is probably due to the regeneration of ${\bullet}{OH}$ radicals from hydrogen peroxide, which would be formed from recombination of ${\bullet}{OH}$ radicals and which may contribute a little to the decomposition.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.502-509
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• 1997

Aromatic pollutants(benzene, toluene, ethylbenzene and xylenes) were photodegraded by using a UV oxidation and the rates of degradation were investigated under various reaction conditions. Each of the solution containing 50 ppm benzene, 150 ppm ethylbenzene and 250 ppm xylenes was found UV-photodegraded over 90% in 1 hour of reaction time, wheras the only was 43 % degradation was obtained with 350 ppm toluene solution. A single component solution was more degradable than a mixed component solution and benzene was almost photodegraded at a pH 4.0, 6.4 and 10.0 after reaction time is 1 hr, ehtylbenzene was photodegraded about 92%(pH 4.0), 90%(pH 6.4) and 91%(pH 10.0), xylenes was photodegraded about 95%(pH 4.0), 90%(pH 6.4) and 92%(pH 10.0), but toluene was photodegraded about 80%(pH 4.0), 43%(pH 6.4) and 70%(pH 10.0), respectively. Kinetics studies show that the rate of decay in TOC(total organic carbon) were pseudo first-order rate except ethylbenzene, and then we could evaluate mineralization rate constants(k) of aromatics.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.171-176
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• 2003

The sonolytic decomposition of NHCs, such as atrazine［6-chloro-N-ethyl-N＇ -(1-methylethyl)-1,3,5-triazine-2,4-diamine］, simazine( 6-chloro-N,N＇ -diethyl-l ,3,5-triazine-2,4-diamine), trietazine(6-chloro-N,N,N＇-triethyl-l,3,5-triazine-2,4-diamine), in water was investigated at a ultrasound frequency of 200kHz with an acoustic intensity of 200W under argon and air atmospheres. The concentration of NHCs decreased with irradiation, indicating pseudo-first-order kinetics. The rates were in the range 1.06∼2.07 (x10/sup -3/ min/sup -1/) under air and 1.30∼2.59(x10/sup -3/ min/sup -1/)under argon at a concentration of 200μM of NHCs. The rate of hydroxyl radicals(·OH) formation from water is 19.8μM min/sup -1/ under argon and 14.7 μM min/sup -1/ under air in the same sonolysis conditions. The sonolysis of NHCs is effectively inhibited, but not completely, by the addition of t-BuOH(2-methyl-2-propanol), which is known to be an efficient ·OH radical scavenger in aqueous sonolysis. This suggests that the main decomposition of NHCs proceeds via reaction with ·OH radical; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fenton's reagent ［Fe/sup 2＋/］ accelerates the decomposition. This is probably due to the regeneration of ·OH radicals from hydrogen peroxide, which would be formed from recombination of ·OH radicals and which may contribute a little to the decomposition.

• Journal of the Korean Chemical Society
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• v.33 no.6
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• pp.651-656
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• 1989

The catalytic effects of several phase-transfer catalysts (PTC) on the liquid-liquid heterogeneous nucleophilic displacement reaction of thiocyanate on benzyl chloride have been determined. Reactions followed a pseudo-first order dependency on the benzyl chloride concentration and the observed rate constant $(k_{obsd})$ were linearly related to the concentration of catalyst and varied with variables such as reaction temperature and solvent. The sequences of catalytic activity of the displacement were $NH_4Cl$ < BTMAC < 18-crown-6 < BTEAC < PEG < TBAC < CTMAB. Enthalpies and entropies of activation associated with the displacement were 15∼20 Kcal$mo^{l-1}$, -12∼-29 eu. respectively and the reaction occurs in the interphase comprising of microemulsion.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.6
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• pp.663-669
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• 2005

The aim of this study was to investigate the ozone decay pattern for the effective application of ozone in drinking water treatment. In order to measure the ozone decomposition in water, ozone measuring instrument was developed with flow injection analysis (FIA) method. From the result of continuous residual ozone concentration in water, it was confirmed that the ozone decay pattern was divided with instantaneous ozone demand(I.D) and pseudo first-order rate($k_c$) phases, which were influenced by the variation of ozone dose. The empirical model obtained from I.D and $k_c$ values enabled us to predict the residual ozone concentration according to the reaction time, showing the high correlation between model and experimental values. The concentration of OH radical and $R__{ct}$ could be indirectly measured by OH radical probe compound. In both I.D and $k_c$ phases, the production pattern of OH radical could be observed, which was also affected by the variation of ozone dose. Finally, it was confirmed that the ozone consumption rate was varied according to the each drinking water treatment process and seasoning. Therefore, the optimum position and dosage of ozone have to be selected by considering various factors.