• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2448-2452
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• 2014

Second-order rate constants ($k_N$) have been measured spectrophotometrically for $S_NAr$ reactions of Y-substituted-phenoxy-2,4-dinitrobenzenes (1a-1g) with hydrazine and glycylglycine in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. Hydrazine is 14.6-23.4 times more reactive than glycylglycine. The magnitude of the ${\alpha}$-effect increases linearly as the substituent Y becomes a stronger electron-withdrawing group (EWG). The Br${\o}$nsted-type plots for the reactions with hydrazine and glycylglycine are linear with ${\beta}_{lg}=-0.21$ and -0.14, respectively, which is typical for reactions reported previously to proceed through a stepwise mechanism with expulsion of the leaving group occurring after rate-determining step (RDS). The Hammett plots correlated with ${\sigma}^{\circ}$ constants result in much better linear correlations than ${\sigma}^-$ constants, indicating that expulsion of the leaving group is not advanced in the transition state (TS). The reaction of 1a-1g with hydrazine has been proposed to proceed through a five-membered cyclic intermediate ($T_{III}$), which is structurally not possible for the reaction with glycylglycine. Stabilization of the intermediate $T_{III}$ through intramolecular H-bonding interaction has been suggested as an origin of the ${\alpha}$-effect exhibited by hydrazine.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2410-2414
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• 2014

A kinetic study is reported on nucleophilic substitution reactions of Y-substituted-phenyl picolinates (7a-7h) with a series of cyclic secondary amines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. Comparison of the kinetic results with those reported previously for the corresponding reactions of Y-substituted-phenyl benzoates (1a-1f) reveals that 7a-7h are significantly more reactive than 1a-1f. The Br${\o}$nsted-type plot for the aminolysis of 4-nitrophenyl picolinate (7a) is linear with ${\beta}_{nuc}=0.78$, which is typical for reactions proceeding through a stepwise mechanism with expulsion of the leaving group being the rate-determining step. The Br${\o}$nsted-type plots for the piperidinolysis of 7a-7h and 1a-1f are also linear with ${\beta}_{lg}=-1.04$ and -1.39, respectively, indicating that the more reactive 7a-7h are less selective than the less reactive 1a-1f to the leaving-group basicity. One might suggest that the enhanced reactivity of 7a-7h is due to the inductive effect exerted by the electronegative N atom in the picolinyl moiety, while the decreased selectivity of the more reactive substrates is in accord with the reactivity-selectivity principle. However, the nature of intermediate (e.g., a stabilized cyclic intermediate through the intramolecular H-bonding interaction for the reactions of 7a-7h, which is structurally not possible for the reactions of 1a-1f) is also responsible for the enhanced reactivity with a decreased selectivity.

• Applied Chemistry for Engineering
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• v.28 no.6
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• pp.626-631
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• 2017

Transparent plastic substrates require an improvement in properties such as surface hardness and thermal stability for optical applications. In this study, UV-curable organic/inorganic hybrids were synthesized to improve those properties. In order to make the optimum dispersion of inorganic component into the organic matrix, an in situ synthetic method was applied based on sol-gel reaction. Dispersion of the inorganic component in the organic urethane acrylate matrix was improved by using a proper combination of sol-gel reaction and fast UV-curing resulting in the formation of the transparent coating layer. Various alkoxy silanes were employed to vary both the degree of curing and coating properties of UV-curable organic/inorganic hybrids. UV-cured organic/inorganic hybrid coatings showed an improved surface hardness and thermal resistance depending on the content of inorganic component.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.68-71
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• 2003

The performance of the Direct Methanol Fuel Cell (DMFC) using multi-layer electrode, which prepared by various anode catalysts and Nafion membranes, was studied for reducing the amount of the metal catalyst loaded in the MEA system. The amount of the catalyst used in this experiment was $3-4 mg/cm^2$ in cathode and $1-2 mg/cm^2$ in anode, respectively. The best performance was to be $230 mS/cm^2$ of MEA3 at $90^{\circ}C$ and 2 bar in this experiment. However, the overall performance of the DMFC was maintained almost the same compared to the general commercial catalyst systems.

• Parasites, Hosts and Diseases
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• v.33 no.1
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• pp.55-60
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• 1995

To observe the production of IgA in Balb/c mice with neodiplostomiasis, 20 mice were infected with each 200 metacercariae of Neoniplostomum seoulenis. Sera and the duodenums were obtained 3, 7, 14, 28 days post-infection (PI) from five mice each group Neodipeostomum specific IgA in serum by the enzyme-linked immunosorbent assay increased from 7 days PI and persisted till 28 days PI. Immunohistochemistry for lgA was done with sections of the duodenum. The IgA-positive reaction was generally seen in the lamina propria and submucosa. Some of epithelial cells were positive at 7 and 14 days PI. The present finding showed that Neodiplostomun specific IgA antibody increased in serum and that there was local reaction of IgA in the mucosa and submucosa of the duodenum but not directly related with worm expulsion.

• Applied Chemistry for Engineering
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• v.8 no.6
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• pp.881-885
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• 1997

The solubilizing capacity of GL-12, LAS, SLES aqueous solutions and that of mixed surfactant systems were studied using sudan III, which is oil-siluble dye. The solubilizing capacity of mixed surfactant systems was greatly influenced by the mixing ratios. Generally, the solubilizing capacity increased as the composition of GL-12 in the mixed systems increased. From the effect of NaCl on the solubilizing capacity, it was found that the solubilizate is located near the palisade layer in the GL-12/LAS system, and the solubilizate is located inside the micellar core in the GL-12/SLES mixed system. These differences in the location of slubilizate inside micelles result from the difference of molecular structure between LAS and SLES.

• Applied Chemistry for Engineering
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• v.9 no.4
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• pp.481-485
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• 1998

Hydrated aluminum sulfate, an inorganic polymer, was synthesized from kaolin in $H_2SO_4$ solution using microwave energy. The maximum rates of alumina extracted from calcined kaolin were 72.8% in a conventional process ($80^{\circ}C$, 1M, and 180min) and 99.9% in a microwave process ($90^{\circ}C$, 1M, and 60 min). Compared with the conventional one, the hydrated aluminum sulfate synthesized under the microwave process had layer structure consisting of plate-shaped large grains. After synthesis and then calcination at $1100^{\circ}C$, both products on conventional and microwave processes were ${\gamma}-Al_2O_3$ with agglomerated powders of spherical shape. The specific area of the products in conventional and microwave processes were 113.5 and $106.6m^2/g$, and their average grain sizes were 46.5 an $26.3{\mu}m$, respectively.

• Bulletin of the Korean Chemical Society
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• v.31 no.1
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• pp.75-81
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• 2010

The reaction of N,N-diethyl carbamates of 1H-[1,2,3]triazolo[4,5-b]pyridin-1-ol (4-HOAt) 7, 3H-[1,2,3]triazolo[4,5-b]pyridin-3-ol (7-HOAt) 8, 1H-benzo[d][1,2,3]triazol-1-ol (HOBt) 9, 6-chloro-1H-benzo[d][1,2,3]triazol-1-ol (Cl-HOBt) 10, 6-(trifluoromethyl)-1H-benzo[d][1,2,3]triazol-1-ol ($CF_3$-HOBt) 11, and 6-nitro-1H-benzo[d][1,2,3]triazol-1-ol ($NO_2$-HOBt) 12 with morpholine and piperidine in $CH_3CN$ underwent acyl nucleophilic substitution to give the corresponding carboxamide derivatives. The reactants and products were identified by elemental analysis, IR and NMR. We measured the kinetics of these reactions spectrophotometrically in $CH_3CN$ at a range of temperatures. The rates of morpholinolysis and piperidinolysis were found to fit the Hammett equation and correlated with $\sigma$-Hammett values. The values were 1.44 - 1.21 for morpholinolysis and 1.95 - 1.72 for piperidinolysis depending on the temperature. The $Br{\phi}$nsted-type plot was linear with a $\beta_lg = -0.49 \pm 0.02$ and $-0.67 \pm 0.03$. The kinetic data and structure-reactivity relationships indicate that the reaction of 9-12 with amines proceeds by a concerted mechanism. The deviation from linearity of the correlation ${\Delta}H^#$ vs. ${\Delta}S^#$ and plot of $logk_{pip}$ vs. $logk_{morph}$ and $Br{\phi}$nsted-type correlation indicate that the reactions of amines with carbamates 7 and 8 is attributed to the electronic nature of their leaving groups.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2393-2397
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• 2009

Second-order rate constants ($k_{HOO}$‒) have been measured spectrophotometrically for nucleophilic substitution reactions of Y-substituted phenyl benzenesulfonates (1a-g) with $HOO^-$ ion in $H_2O$ at $25.0\;{\pm}\;0.1\;{^{\circ}C}$. The Br$\phi$nsted-type plot is linear with ${\beta}_{lg}$ = ‒0.73. The Hammett plot correlated with with ${\sigma}^-$ constants results in much better linearity than ${\sigma}^o$ constants, indicating that expulsion of the leaving group occurs in the rate-determining step (RDS) either in a stepwise mechanism or in a concerted pathway. However, a stepwise mechanism in which departure of the leaving group occurs in the RDS has been excluded since $HOO^-$ ion is more basic and a poorer leaving group than the leaving Y-substituted phenoxide ions. Thus, the reactions of 1a-g with $HOO^-$ ion have been concluded to proceed through a concerted mechanism. The $\alpha$-nucleophile $HOO^-$ ion is more reactive than its reference nucleophile $OH^-$ ion although the former is ca. 4 p$K_a$ units less basic than the latter (i.e., the $\alpha$-effect). TS stabilization through intramolecular H-bonding interaction has been suggested to be irresponsible for the $\alpha$-effect shown by $HOO^-$ ion, since the magnitude of the $\alpha$-effect is independent of the electronic nature of substituent Y in the leaving group. GS destabilization through desolvation of $HOO^-$ ion has been concluded to be responsible for the $\alpha$-effect found in the this study.

• 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.