• Journal of the Korean Chemical Society
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• v.34 no.5
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• pp.460-464
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• 1990

Proton behavior was investgated for the redox reaction of trans-[$Co(en)_2(NO_2)Cl]^+$ with aqueous Fe(II) in acidic solution by UV/vis-spectrophotometric method. The reaction order of proton is first one and the rate constant(k$_H^+$) is 6.7 ${\times}\;10^{-1}L^2/mol^2{\cdot}min$. The values of $E_a$, ${\{Delta}H^{\neq}$, ${\{Delta}S^{\neq}$ are 14.5 Kcal/mol, 13.8 Kcal/mol and -18.3e.u., respectively. As the result of analysis of kinetic data, it has been found that this reaction proceeds through inner-sphere mechanism.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.13-19
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• 1997

From the formation of the monodispersed silica particle which is a valuable for the industry by Sol-Gel process, the effects of the parameters participated in the process, the growth mechanism and the characteristics of silica particles for each rection conditions are investigated. To investigate about the formation of final silica particles, the suspension which performs the polymerization is reacted with molybdic acid, and the evolutions of TEOS and silica particle size are investigated in the reaction time ？ 새 the characteristics of molybdic acid with the suspension. From the results, a constant number of silica particle is formed at early reaction stage. Silica particles grow through the aggregation of smaller particles and nucleation is rate-limiting step for the growth of particles. In the conditions of this study, spherical silica particles are formed, [NH$_3$] and [$H_2O$] concentration increase the particle size but particle size decrease with [$H_2O$] concentration which is a certain above region. Average particle sizes are 187.4~483.3 nm and standard deviations in the average particle size are 1.7~2.9% with each experimental condition. From the BET results, specific surface area is 5.5~23.4 $m^2$/g and these values decrease with increase size. The average pore size is 50~70$\AA$.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1951-1956
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• 2011

A kinetic study is reported on nucleophilic substitution reactions of 4-nitrophenyl nicotinate 5 and isonicotinate 6 with alkali metal ethoxide EtOM (M = K, Na, and Li) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. Plots of pseudo-first-order rate constant $k_{obsd}$ vs. EtOM concentration exhibit upward curvature for the reactions of 5 and 6 with EtOK and EtONa but are almost linear for those with EtOLi. 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 shown that $k_{EtOK}$ ${\geq}$ $k_{EtONa}$ > $k_{EtO^-}$ but $k_{EtOLi}$ < $k_{EtO^-}$. It has been concluded that $K^+$ and $Na^+$ ions catalyze the reactions by increasing the electrophilicity of the carbonyl carbon atom through formation of a 4-membered cyclic transition state $TS_3$ or $TS_4$. However, $M^+$ ion catalysis has been found to be much less significant for the reactions of 5 and 6 than for the corresponding reactions of 4-nitrophenyl picolinate 4, which was reported to proceed through a 5-membered cyclic transition state $TS_2$. Although 5 and 6 are significantly more reactive than 4-nitrophenyl benzoate 3, the reactions of 5 and 6 result in smaller $k_{EtOK}/k_{EtO^-}$ ratios than those of 3. The electron-withdrawing ability of the nitrogen atom in the acyl moiety of 5 and 6 has been suggested to be responsible for the increase in reactivity and the decrease in the $k_{EtOK}/k_{EtO^-}$ ratio.

• Journal of Environmental Science International
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• v.17 no.5
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• pp.509-516
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• 2008

New functional surfactant, N,N-dimethyl-N-dodecyl-N-(2-methyl benzimidazoyl) ammonium chloride(DDBAC) having benzimidazole(BI) functional group have been synthesized and the critical micellar concentration of DDBAC measured by surface tentiometry and electric conductivity method was $8.9{\times}10^{-4}M$. Micellar effects in DDBAC functional surfactant solution on the hydrolysis of p-nitrophenylacetate(p-NPA), p-nitro-phenylpropionate(p-NPP) and p-nitrophenylvalerate(p-NPV) were observed with change of various pH (Tris-buffer). The pseudo first rate constants of hydrolysis of p-NPA, p-NPP and p-NPV in optimum concentration of DDBAC solution increase to about 160, 280 and 600 times, respectively, as compared with those of aqueous solution at pH 8.00(Tris-buffer). It is considered that benzimidazole functional moiety accelerates the reaction rates of hydrolysis because they act as nucleophile or general base. In optimum concentration of DDBAC solution, the rate constants of hydrolysis of p-NPP and p-NPV increase to about 1.5 and 3.0 times, respectively, as compared with that of p-NPA. It means that the more the carbon numbers of alkyl group of substrates, the larger the binding constants between DDBAC micelle and substrates are. To know the hydrolysis mechanism of p-NPCE(p-NPA, p-NPP and p-NPV), the deuterium kinetic isotope effects were measured in $D_2O$ solutions. Consequently the pseudo first order rate constant ratios in $H_2O$ and $D_2O$ solution, $k_{H_2O}/k_{D_2O}$, were about $2.8{\sim}3.0$ range. It means that the mechanism of hydrolysis were proceeded by nucleophile and general base attack in approximately same value.

• Bulletin of the Korean Chemical Society
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• v.19 no.3
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• pp.349-353
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• 1998

Solvolysis rates of substituted 2-aryl-1,1-dimethylethyl bromides (1) were determined in a variety of solvents such as aqueous mixtures of ethanol, acetone, 2,2,2-trifluoroethanol, and also mixtures of ethanol and TFE at 25 ℃, 35 ℃, and 45 ℃. The solvent effects were analyzed in terms of Winstein-Grunwald equation. The solvent effects of 1-4-MeO failed to give a single linear correlation against either Y or YCl (YBr), but exhibited a wide split pattern which could not be related to the solvent nucleophilicity. On the other hand 1-4-CH3 and 1-H gave a fairly good linearity. In the case of 1-4-MeO, a fairly good linearity was observed against YΔ defined from the solvolysis of 4-methoxyneophyl tosylate. It is assumed that resonance interaction between reaction site and aryl-π-system operates to give charge delocalization regardless of the different solvolysis mechanisms. The Hammett-Brown treatment of the solvolytic rate constant of compounds 1 was obtained non-linear two separated lines of - 1.06 to - 1.46, suggesting of mechanistic changeover from kc-ks to kΔ on going from electron-withdrawing to electron-donating substituents as a basis of 4-CH3 group.

• Analytical Science and Technology
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• v.9 no.3
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• pp.292-301
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• 1996

The synthesis of poly(ether)tailed bipyridine complex as redox reaction probes has advanced attempts to interpret very slow diffusion and heterogeneous electron transfer. Diffusion coefficients as low as $1.5{\times}10^{-15}cm^2/s$ have been observed for the oxidation of neat $Co(bpy(ppgm)_2)_{3^-}(ClO_4)_2$ with $LiClO_4$ electrolyte. Heterogeneous electron transfer rate constants of materials were found to vary with diffusion coefficient. The decrease in k as the diffusion coefficient decreases was actually caused by the decreasing D. Diffusion coefficient for compound of strong ion pairing anion($ClO{_4}^-$) was much smaller than the diffusion coefficient for compound of weak ion pairing anion($CF_3COO^-$).

• Bulletin of the Korean Chemical Society
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• v.29 no.1
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• pp.191-196
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• 2008

Kinetic studies of the reactions of a-bromoacetanilides [YC6H4NHC(=O)CH2Br] with substituted benzylamines (XC6H4CH2NH2) have been carried out in dimethyl sulfoxide at 35.0 oC. The Hammett plots for substituent (Y) variations in the substrate (log kN vs. sY) are biphasic concave upwards/downwards with breaks at Y = 4-Cl (sY = 0.23). The Hammett coefficients rY and the cross-interaction constant rXY (= +0.16) are positive for sY 0.23, while the rY values are positive/negative [rY > 0 for X = (4-MeO and 4-Me) and rY < 0 for X = (H, 4-Cl and 3-Cl)] and the rXY (= -1.51) value is negative for sY ³ 0.23. Based on these and other results, the benzylaminolyses of a-bromoacetanilides are proposed to proceed through rate-limiting expulsion of the bromide leaving group from a zwitterionic tetrahedral intermediate, T, with a bridged transition state for s Y 0.23, while the reaction proceeds through concerted mechanism with an enolate-like TS in which the nucleophile attacks the a-carbon for s Y ³ 0.23.

• Analytical Science and Technology
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• v.13 no.1
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• pp.41-48
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• 2000

A biosensor for the determination of hydrogen peroxide was constructed by immobilizing of porcine small instestinal tissue in a plain carbon paste, and the effect of varying the $H_2O_2$ concentration and pH on the rate of catalytic reaction was evaluated. For the mathematical simplicity, no mediator was added. Electrochemical properties and the maximal rate could be derived from the quantitative analysis of the observed phenomena related to the electrode reaction. Also, pH dependence of the Michaelis constant enabled to calculate various thermodynamic parameters and subsequently to design a electrochemical method to determine the optimum pH of enzyme.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.3
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• pp.323-330
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• 2008

The study presents the results of 1,4-dioxane degradation using zero valent (Fe$^0$) or Fe$^{2+}$ ions with and without UV. During the reaction, the change of [Fe$^{2+}$] and [Fe$^{2+}$]/[Fe(t)], the concentration ratio of ferrous ion to total iron ion in solution was measured. Less than 10% degradation of 1,4-dioxane was observed by UV-only, Fe$^0$-only, and Fe$^{2+}$-only conditions, and also the changes of [Fe$^{2+}$] and [Fe$^{2+}$]/[Fe(t)] were minimal in each reaction. However, the oxidation of Fe$^0$ was enhanced with the irradiation of UV by approximately 25% and the improvement of 1,4-dioxane degradation was observed. Fenton reaction ($Fe^{2+}+H_2O_2$) showed higher degradation efficiency of 1,4-dioxane until 90 min, which of the degradation was stopped after that time. In the reaction of Fe$^{2+}$ and UV, the ratio of [Fe$^{2+}$]/[Fe(t)] decreased then slowly increased after a certain time indicating the reduction of Fe3+ to Fe$^{2+}$. In case of Fe$^0$ in the presence of UV, the first-order rate constant was found to be 1.84$\times$10$^{-3}$ min$^{-1}$ until 90 min, and then changed to 9.33$\times$10$^{-3}$ min$^{-1}$ when the oxidation of Fe$^{2+}$ mainly occurred. In this case [Fe$^{2+}$]/[Fe(t)] kept decreasing for the reaction. However, the addition of perchlortae (ClO$_4^-$) in the reaction of Fe$^0$ and UV induced the continuous increase of [Fe$^{2+}$]/[Fe(t)] ratio. The results mean the primary degradation factor of 1,4-dioxane is the oxidation by the radicals generated from the redox reaction between Fe$^{2+}$ and Fe$^{3+}$. Also, both UV and ClO$_4^-$ played the role inducing the reduction of Fe$^{3+}$, which is important to degrade 1,4-dioxane by enhancing the generation of radicals.

• Journal of the Korean Chemical Society
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• v.36 no.6
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• pp.894-905
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• 1992

Dioxygen binding and homogeneous catalytic oxidation of hydrazobenzene were investigated by employing tetradentate Schiff base Cobalt(II) complexes such as Co(II)(SED)$(Py)_2$, Co(II)(SOPD)$(Py)_2$ and Co(II)(SND)$(Py)_2$ in saturated oxygen methanol solvent. The major product of hydrazobenzene ($H_2$AB) oxidation by catalysts of superoxo type [Co(III)(SED)(Py)$O_2$] and [Co(III)(SOPD)(Py)$O_2$] complexes are trans-azobenzene (t-AB) and rate constants k for oxidation reaction was 7.692 ${\times}$ $10^{-2}$ M/sec for [Co(III)(SED)(Py)$O_2$] and 5.076 ${\times}$ $10^{-2}$ M/sec for [Co(III)(SOPD)(Py)$O_2$]. But cis-azobenzene (c-AB) are obtained as a major product with ${\mu}$-peroxo type [Co(III)(SED)(Py)]$_2O_2$ catalyst, and rate constant k is 1.266 ${\times}$ $10^{-2}$ M/sec. The rate constants of oxidation reaction has been studied spectrophotometrically and the rate law established. A mechanism involving a intermediate activated complexes of catalyst, hydrazobenzene and oxygen has been proposed. $H_2$AB + Co(II)(Schiff base)$(Py)_2$ + $O_2$ ${\rightleftharpoons}_{MeOH}^K$ Co(III)(Schiff base)(Py)$O_2$${\cdot}$$H_2$AB + Py $\longrightarrow^k$ Co(II)(Schiff base)$(Py)_2$ + t-AB + $H_2O_2$(Scchiff base : SED and SOPD). $H_2$AB + 2Co(II)(SND)$(Py)_2$ + $O_2$ ${\rightleftharpoons}_{MeOH}^K$ [Co(III)(SND)(Py)]$_2O_2$${\cdot}$H_2$AB + 2Py ${\longrightarrow}^k$ (Co(II)(SND)$(Py)_2$ + c-AB + $H_2O_2$.