• Applied Chemistry for Engineering
• /
• v.26 no.2
• /
• pp.145-153
• /
• 2015

$Cr_2O_3/AP$ (ammonium perchlorate) energetic composites were prepared by a method of solvent/anti-solvent. XRD analysis revealed that the crystalline structure of AP in $Cr_2O_3/AP$ composites is the same as that of pure AP. SEM photomicrograph shows that an average size of cuboid $Cr_2O_3/AP$ composites is approximately $2.5{\mu}m$. TGA analysis shows that the addition of submicron $Cr_2O_3$ particles into AP lowers the HTD (high-temperature decomposition) compared to that of neat AP and the activation energy of the $Cr_2O_3/AP$ composites was calculated by the isoconversional Starlink method. Considering changes in the activation energy, the decomposition reaction mechanism of AP was suggested as follows; the decomposition with the formation of nucleation sites renders formation of porous structure in the composites up to conversion of about 0.25 and after further conversion of over 0.3, it seems that decomposition reaction vigorously takes place rather than sublimation of AP.

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

• The Korean Journal of Food And Nutrition
• /
• v.16 no.4
• /
• pp.321-327
• /
• 2003

The reaction rates of 4-ethyl pyridine with p-methyl benzylbromide have been measured by conductometry in acetonitrile, and the rate constants of these reactions are determined in accordance with various temperatures (20, 25, 30$^{\circ}C$) and pressures (1, 200, 500, 1000 bar). The rate constants increased with the higher pressure and temperature. The activation energies and activation parameter values of these reactions are calculated by determination of the rate constants the same. The activation volume, activation compressibility coefficient and the activation entropy are all negative. The result of kinetic studies for the pressure show that this reaction proceeds in typical bimolecular nucleophilic substitution reaction.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.4
• /
• pp.835-839
• /
• 2010

The rate constants of solvolyses of 2,2,2-trichloro-1,1-dimethylethyl chloroformate ($\underline{I}$) in 33 solvents can be well correlated using the extended Grunwald-Winstein equation, with incorporation of the $N_T$ solvent nucleophilicity scale and the $Y_{Cl}$ solvent ionizing scale, with sensitivities towards changes in the scale having values of $1.42\;{\pm}\;0.09$ for l and $0.39\;{\pm}\;0.05$ for m, respectively. The activation enthalpies are ${\Delta}H^{\neq}\;=\;12.3$ to $14.5\;kcal{\cdot}mol^{-1}$ and the activation entropies are -28.2 to $-35.5\;cal{\cdot}mol^{-1}{\cdot}K^{-1}$, consistent with the proposed bimolecular reaction mechanism. The kinetic solvent isotope effect of 2.14 in MeOH/MeOD is in accord with a bimolecular mechanism, probably assisted by general-base catalysis.

• Journal of the Korean Chemical Society
• /
• v.34 no.3
• /
• pp.239-247
• /
• 1990

The gas-phase S_N2$ reactions can be classified into neutral bimolecular, solvated, and ionic reactions; the neutral bimolecular reaction proceeds via retention mechanism whereas the ionic reaction produces inversion products. In the reaction of solvated nucleophile with one solvent molecule, a six-center transition state (TS) is formed and the two processes i.e., retention and inversion, are found to compete with a favored path depending on the electronic effect of the nucleophile and substituents in the substrate and on the steric requirement. In the ionic reaction, the difference in the energy barrier between the two processes reduces to a small value when the substrate methyl group is made bulky, leaving ability of the leaving group is improved and at the same time the negative charge of the nucleophile is dispersed. When the reaction center atom in the $S_N2$ reaction is changed to a larger sized second row elements, the activation barrier decreases since the steric crowding in the penta-coordinated TS is relieved. However within the same row, the barrier was found to increase as the atomic size decreased. For the boron, B, the barrier height was the least since in addition to the relatively large atomic size compared to C and N, it forms tetra-coordinated TS so that the steric crowding becomes nearly negligible.

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

• Korean Chemical Engineering Research
• /
• v.46 no.4
• /
• pp.739-746
• /
• 2008

The aim of this study is finding the optimal design parameters and the optimal operation variables of a reactive distillation column. Different from steady state optimization, dynamic optimization makes it possible considering operation ability as well as design problems at process design step. For performing dynamic optimization, dynamic simulation should be done first. If dynamic simulation is already finished, dynamic optimization can be performed with less effort than that of dynamic simulation.Reactive distillation systems involving reaction and separation in a single unit have the potential to reduce capital and operating costs, particularly when reaction have conversion constraint or when azeotropes exist making conventional separation difficult and expensive. This study here present work on the continuous distillation process, the homogeneous catalyzed esterification of methanol and acetic acid, the synthesis of methyl acetate. Based on an equilibrium stage model of a reactive distillation column a dynamic optimization problem was formulated and solved. And the results were verified by performing dynamic simulation and showing the variation of conversion and purity as the variation of the operation variables. As the results of dynamic optimization, this study found optimal feed ratio, reflux ratio and reboiler duty of this system. And as this study applied it to dynamic simulations the dynamic characteristics of a reactive distillation column are showed under optimal operating condition.

• Journal of the Korean Chemical Society
• /
• v.38 no.1
• /
• pp.61-68
• /
• 1994

The intramolecular formal iron-catalyzed [4+2] cycloaddition reaction of acetylenic dienes to produce bicyclic products has been investigated. These reactions proceeded, competing via intramolecular carbocyclization and bimolecular cycloaddition. However, the iron-catalyzed bicyclic carbocyclization of 4,4-dimethyl-3-(tert-butyldimethylsiloxy)-1-phenyl-6,8-decadien-1-yne(11) yielded exclusively bicyclic diene product(yield 78.1%). From this result, we found that the substrate containing a dimethyl substitutent at the 4,4-position helped to promote the intramolecular reaction, which is stable to the iron catalyzed conditions.

• Macromolecular Research
• /
• v.8 no.4
• /
• pp.147-152
• /
• 2000

The activity of periodic acid as an initiator for the polymerization of acrylamide in aqueous medium was investigated. The rate of polymerization was found to be proportional to the monomer concentration to the 1.5th power in the range of 1.41-5.64 mol/L. The reaction order to the periodic acid concentration was 0.49, which indicated a bimolecular mechanism for the termination reaction in the range of 0.5-4.0$\times$10$\^$-2/ mol/L. Propagation rate increased with raising the temperature according to an Arrhenius expression resulting in the exhibition of an apparent activation energy of 87.8 kJ/mol in the temperature range of 60-80$\^{C}$. The addition of hydroquinone as a radical scavenger stopped the polymerization of acrylamide initiated by periodic acid. These results support that the polymerization proceeds via a radical chain mechanism .

• Bulletin of the Korean Chemical Society
• /
• v.26 no.8
• /
• pp.1241-1245
• /
• 2005

Solvolyses of trifluoromethanesulfonyl chloride (TFMSC) in water and in aqueous binary mixtures of acetone, ethanol and methanol are investigated at 25, 35 and 45 ${^{\circ}C}$. The Grunwald-Winstein plot of first-order rate constants for the solvolytic reaction of TFMSC with YCl (based on 2-adamantyl chloride) shows marked dispersions into three separate curves for three aqueous mixtures. The extended Grunwald-Winstein plots for the solvolysis of TFMSC show better correlation. The large negative ${\Delta}S^{\neq}$ and relatively small positive ${\Delta}H^{\neq}$ reveals that the solvolytic reaction proceeds via a typical bimolecular reaction mechanism. The l and m values determined in various solvents are consistent with the proposed mechanism of the general base catalysis $S_AN/S_N2$reaction mechanism for TFMSC solvolyses based on mass law and stoichiometric solvation effect studies.