• Bulletin of the Korean Chemical Society
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• v.27 no.2
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• pp.255-265
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• 2006

The oxidation of hydrazobenzene by molecular oxygen in the polar solvent methanol is catalysed by a Schiff's base complex Co(3MeOsalen) which is a synthetic oxygen carrier. The products are trans-azobenzene and water. The rate of the reaction has been studied spectrophotometrically and the rate law established. A mechanism involving a ternary complex of catalyst, hydrazobenzene and molecular oxygen has been proposed. The kinetic studies show that a ternary complex $CoL{\cdot}H_2AB{\cdot}O_2$ is involved in the rate determining step. The reactions are summarised in a catalytic cycle. The kinetic data suggest that a ternary complex involving Co(3MeOsalen), triphenyl-phosphine and molecular oxygen is catalytically acive species but at higher triphenylphosphine concentrations the catalyst becomes inactive. The destruction of the catalytic activity could be due to the catalyst becoming coordinated with triphenyl phosphine at both z axis sites of the complex e.g. Co (3MeOsalen)$(PPh_3)_2$.

• Bulletin of the Korean Chemical Society
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• v.24 no.1
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• pp.91-94
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• 2003

Kinetic studies of the reaction of O-methyl-S-phenylthiocarbonates with benzylamines in methanol at 45.0 ℃ have been carried out. The reaction proceeds by a stepwise mechanism in which the rate-determining step is the breakdown of the zwitterionic tetrahedral intermediate, $T^{\pm}$, with a hydrogen-bonded four-center type transition state (TS). These mechanistic conclusions are drawn based on (ⅰ) the large magnitude of ${\rho}_X\;and\;{\rho}_Z$, (ⅱ) the normal kinetic isotope effects $(k_H/k_D\;>\;1.0)$ involving deuterated benzylamine nucleophiles, (ⅲ) the positive sign of ${\rho}_{XZ}$ and the larger magnitude of ${\rho}_{XZ}$ than that for normal $S_N2$ processes, and lastly (ⅳ) adherence to the reactivity-selectivity principle (RSP) in all cases.

• Bulletin of the Korean Chemical Society
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• v.24 no.9
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• pp.1261-1264
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• 2003

A method for the determination of trace amount of sulfide based on the addition reaction of sulfide with methyl green at pH 7.5 and $25{\circ}C$ is described. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of the dyestuff at 637 nm by the initial rate and fixed time method. The calibration graph is linear in the range 30-1200 ppb. The theoretical limit of detection was 0.014 ppm. Seven replicate analysis of a sample solution containing 0.70 ppm sulfide gave a relative standard deviation of 1.5%. The interfering effects of various ions on sulfide determination have been reported and procedures for removal of interference have been described. The proposed method was applied successfully to the determination of sulfide in tap and wastewater samples.

• Bulletin of the Korean Chemical Society
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• v.29 no.9
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• pp.1769-1773
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• 2008

fThe kinetics and mechanism of the reactions of Y-O-aryl phenylphosphonochloridothioates with X-pyridines are investigated in acetonitrile at 35.0 ${^{\circ}C}$. The negative value of the cross-interaction constant, $\rho$XY = −0.46, indicates that the reaction proceeds by concerted $S_N2$ mechanism. The observed $k_H/k_D$ values involving d-5 pyridine ($C_5D_5N$) nucleophiles are greater than unity (1.05-1.11). The net primary deuterium kinetic isotope effects, $(k_H/k_D)_{net}$ = 1.28-1.35, excluding the increased $pK_a$ effect of d-5 pyridine are obtained. The transition state with a hydrogen bond between the leaving group Cl and the hydrogen (deuterium) atom in the C-H(D) is suggested for the studied reaction system.

• Journal of the Korean Chemical Society
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• v.57 no.2
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• pp.210-215
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• 2013

Kinetics of oxidation of indole by peroxomonosulphate (PMS) in aqueous acetonitrile medium has been investigated. The reaction follows a total second order, first order each with respect to [Indole] and [PMS]. The rate of the reaction was not affected by added [$H^+$]. Variation of ionic strength (${\mu}$) had no influence on the rate. Increase of percentage of acetonitrile decreased the rate. Absen ce of any polymerization indicated a nonradical pathway. Activation and thermodynamic parameters have bee n computed. A suitable kinetic scheme based on these observations is proposed. The reactivity of PMS towards Indole was found to be higher than that with peroxodisulphate.

• Bulletin of the Korean Chemical Society
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• v.16 no.9
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• pp.827-831
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• 1995

Kinetic studies on the reactions of five secondary acylic alkyl arenesulfonates with anilines are carried out in acetonitrile at 65.0 ℃. The magnitude of ρXZ determined (ρXZ=0.12-0.13) is slightly greater than that for the alicyclic series (ρXZ=0.11) under the same experimental condition. Ab initio MO results are found to support the slightly tighter transition state expected from the greater magnitude of ρXZ for the acyclic series. Despite the small variations, the magnitude of ρXZ and the theoretical transition state tightness remain relatively constant for the secondary carbon centers. Secondary kinetic isotope effects involving deuterated aniline nucleophiles show a successively smaller kH/kD(<1.0) value for a more sterically crowded reaction center carbon. This is in accord with the later transition state for bond-making predicted by the Bell-Evans-Polanyi principle for the more endothermic nucleophilic substitution reaction. Further support is provided by the results of the AM1 MO calculations on the reactions of secondary alkyl benzenesulfonates with chloride nucleophile.

• Bulletin of the Korean Chemical Society
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• v.13 no.4
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• pp.395-398
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• 1992

Rate of solvolysis of dansyl chloride in aqueous binary mixtures of acetone, methanol and ethanol are reported. Kinetic solvent isotope effects in methanol and product selectivities in alcohol-water mixtures are also reported. Kinetic data are interpreted with the Grunwald-Winstein and Kivinen equations. The value of $k_{CH3OH}/k_{CH3OD}=1.76$ suggests that a general have catalyzed and/or an $S_AN$ pathway is operative in methanol, a less polar solvent. Rate-rate profiles for solvolysis of dansyl chloride in the aqueous binary media indicate a change in reaction channel from $S_AN$ (in less polar media) to $S_N2$ (in more polar media) mechanism.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.1939-1945
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• 2009

Kinetic investigations on the oxidation of pyrazine and four 2-substituted pyrazines viz., 2-methylpyrazine, 2-ethylpyrazine, 2-methoxypyrazine and 2-aminopyrazine by bromamine-B (BAB) to the respective N-oxides have been studied in HCl$O_4$ medium at 303 K. The reactions show identical kinetics being first-order each in $[BAB]_o\;and\;[pyrazine]_o$, and a fractional- order dependence on $[H^+]$. Effect of ionic strength of the medium and addition of benzenesulfonamide or halide ions showed no significant effect on the reaction rate. The dielectric effect is positive. The solvent isotope effect was studied using $D_2$O. The reaction has been studied at different temperatures and activation parameters for the composite reaction have been evaluated from the Arrhenius plots. The reaction showed 1:1 stoichiometry and the oxidation products of pyrazines were characterized as their respective N-oxides. Under comparable experimental conditions, the oxidation rate of pyrazines increased in the order: 2-aminopyrazine > 2-methoxypyrazine > 2-ethylpyrazine > 2-methylpyrazine > pyrazine. The rates correlate with the Hammett $\sigma$ relationship and the reaction constant $\rho$ was found to be -0.8, indicating that electron donating centres enhance the rate of reaction. An isokinetic temperature of $\beta$ = 333 K, indicated that the reaction was enthalpy controlled. A mechanism consistent with the experimental results has been proposed in which the rate determining step is the formation of an intermediate complex between the substrate and the diprotonated species of the oxidant. The related rate law in consistent with observed results has been deduced.

• Journal of Microbiology and Biotechnology
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• v.17 no.11
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• pp.1789-1796
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• 2007

A ${\beta}$-glucosidase with the molecular mass of 160,000 Da was purified to homogeneity from cell extract of a cellulolytic bacterium, Cellulomonas uda CS1-1. The kinetic parameters ($K_m$ and $V_{max}$) of the enzyme were determined with pNP-cellooligosccharides (DP 1-5) and cellobiose. The molecular orbital theoretical studies on the cellulolytic reactivity between the pNP-cellooligosaccharides as substrate (S) molecules and the purified ${\beta}$-glucosidase (E) were conducted by applying the frontier molecular orbital (FMO) interaction theory. The results of the FMO interaction between E and S molecules verified that the first stage of the reaction was induced by exocyclic cleavage, which occurred in an electrophilic reaction based on a strong charge-controlled reaction between the highest occupied molecular orbital (HOMO) energy of the S molecule and the lowest occupied molecular orbital (LUMO) energy of the hydronium ion ($H_3O^+$), more than endocyclic cleavage, whereas a nucleophilic substitution reaction was induced by an orbital-controlled reaction between the LUMO energy of the oxonium ion ($SH^+$) protonated to the S molecule and the HOMO energy of the $H_2O_2$ molecule. A hypothetic reaction route was proposed with the experimental results in which the enzymatic acid-catalyst hydrolysis reaction of E and S molecules would be progressed via $SN_1$ and $SN_2$ reactions. In addition, the quantitative structure-activity relationships (QSARs) between these kinetic parameters showed that $K_m$ has a significant correlation with hydrophobicity (logP), and specific activity has with dipole moment, respectively.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.219-222
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• 2004

Removal characteristics of Mn and Co was studied from the contaminated solutions via surface reaction with various calcium carbonate (calcite). Synthetic calcium carbonates which has different surface morphology as well as surface areas were prepared by a spontaneous precipitation method and used. Mn and Co removal behavior by the different solid surface demonstrate characteristic sorption behaviors depend on the type of calcite used, such as surface area or surface morphology. Calcium carbonate crystals (mostly calcite) which exhibit complicated surface morphology (c-type) shows strong sorption affinity for Mn and Co removal via sorption than on the a-type or b-type calcite crystals of less complicated surfaces. The applicability of two kinetic models, the pseudo-first-order kinetic equation and the Elovich kinetic model was examined on these sorption behavior. Elovich kinetic model was found more suitable to explain the very early stage adsorption kinetics, while the pseudo-first-order kinetic equation was successfully fitted for the adsorption kinetics after 50 hours.