• Journal of the Korean Chemical Society
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• v.36 no.4
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• pp.589-597
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• 1992

The rate constants of hydrolysis of phenyl-N-benzoylchlorothioformimidates were determined by UV spectrophotometry in 30% (v/v) aqueous dioxane at $25^{\circ}C$. On the basis of rate equation, general base catalysis, solvent effect, substituent effect, thermodynamic parameters, frontier orbital interaction and hydrolysis product analysis, it may be concluded that the hydrolysis of phenyl-N-benzoylchlorothioformimidates proceeds through $S_N1$ mechanism via azocarbocation intermidiate below pH 10.0, while above pH 10.00 the hydrolysis proceeds through nucleophilic addition-elimination ($Ad_{N-E}$) mechanism. In the range of pH from 10.0 to 11.0 these two reaction occur competitively.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.179-182
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• 2011

Second-order rate constants ($k_{OH^-}$) have been measured spectrophotometrically for reactions of Y-substituted phenyl phenyl thionocarbonates (4a-i) with $OH^-$ in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The $k_{OH^-}$ values for the reactions of 4a-i have been compared with those reported previously for the corresponding reactions of Y-substituted phenyl phenyl carbonates (3a-i) to investigate the effect of changing the electrophilic center from C=O to C=S on reactivity and mechanism. Thionocarbonates 4a-i are less reactive than the corresponding carbonates 3a-i although 4a-i are expected to be more reactive than 3a-i. The Bronsted-type plot for reactions of 4a-i is linear with $\beta_{lg}$ = -0.33, a typical $\beta_{lg}$ value for reactions reported to proceed through a stepwise mechanism with formation of an intermediate being the rate-determining step (RDS). Furthermore, the Hammett plot correlated with $\sigma^o$ constants results in much better linearity than that correlated with $\sigma^-$ constants, indicating that expulsion of the leaving group is not advanced in the RDS. Thus, alkaline hydrolysis of 4a-i has been concluded to proceed through a stepwise mechanism with formation of an intermediate being RDS, which is in contrast to the forced concerted mechanism reported for the corresponding reactions of 3a-i. Enhanced stability of the intermediate upon modification of the electrophilic center from C=O to C=S has been concluded to be responsible for the contrasting mechanisms.

• Journal of the Korean Chemical Society
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• v.38 no.5
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• pp.366-371
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• 1994

The kinetics of the hydrolysis of 5,6-dihydro-1,4-thiazine derivatives was investigated by ultraviolet spectrophotometry in $H_2O$ at 25$^{\circ}C$. A rate equation which can be applied over a wide pH range was obtained. The substituent effects on the hydrolysis of 5,6-dihydro-1,4-thiazine derivatives were studied and the rate of hydrolysis was shown to be accelerated by electron donating groups. Final product of the hydrolysis was 2-(N-acetylaminoethylthio)-acetoacetanilide enol from Judging from the results of the rate equation, general base effect, activation parameters and final products, the hydrolysis of 5,6-dihydro-1,4-thiazine derivatives seemed to be initiated by the neutral $H_2O$ molecule which does not dissociate at pH below 10.0, but proceeded by the hydroxide ion at pH above 11.0, and those two reactions occurred competively at pH 10.0∼11.0 range. On the basis of these findings a plausible mechanism for the hydrolysis of 5,6-dihydro-1,4-thiazine derivative was proposed.

• Journal of the Korean Chemical Society
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• v.43 no.5
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• pp.505-510
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• 1999

$TiO_2$ powders were prepared via hydrolysis of titanium n-butoxide in n-butanol and hydrolysis mechanism of titanium n-butoxide was studied using UV-Vis spectrometer. Hydrolysis reactions were controlled to proceed to pseudo-first order reaction in the presence of excess water. The phases of $TiO_2$ powders, prepared under the these conditions, were identified by XRD and reaction rates were calculated by Gugggenheim method. Prepared powders were noncrystalline states in their initial stage of formation but transformed to crystalline rutile structure by heating. Reaction mechanism of titanium n-butoxide was proposed as Interchange-Associative(Ia) mechanism, based on the data of n-value and termodynamic parameters which were determined from the rate constants.

• 한국생물공학회:학술대회논문집
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• 2005.10a
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• pp.530-534
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• 2005

This work was a method that used an acid hydrolysis for increasing the efficacy of decreasing alcohol concentration from Hovenia dulcis extract. The best pH was 2.0 to obtain a maximum alcohol dehydrogenase activity at fixed reaction temperature and time. At pH 2.0, reaction temperature $80^{\circ}C$ and reaction time 4hr gave the highest activity which was 124% of control. The bioactive compound, (+)-dihydromyricetin, content increased to 30% after acid hydrolysis. This is very simple and efficient method to increase the efficacy of decreasing alcohol concentration from Hovenia dulcis extract. The mechanism that increase the efficiency of alcohol decrease be examined through hydrolysis.

• Journal of the Korean Chemical Society
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• v.19 no.2
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• pp.123-129
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• 1975

The rate constants of the hydrolysis of phenylvinylsulfone were determined by ultraviolet spectrophotometry at various pH and a rate equation which can be applied over wide pH range was obtained. The reaction mechanism of hydrolysis of phenylvinylsulfone and especially the catalytic contribution of hydroxide ion which did not study carefully before in acidic media, can be fully explained by the rate equation obtained. The rate equation reveals that: below pH 7, the reaction is initiated by the addition of water molecule to phenylvinylsulfone. At above pH 9, the overall rate constant is only dependent upon the concentration of hydroxide ion.

• YAKHAK HOEJI
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• v.16 no.4
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• pp.155-161
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• 1972

The hydrolysis of phenobarbital is decelerated in alkaline solution by betacyclodextrin. The betacyclodextrin inhibits the degradation of phenobarbital up to 1.5 fold in the system containing 1% betacyclodextrin. The degradation mechanism in systems containing betacyclodextrin is the same that in system without complexing agent, although the rate constants are different. The pH dependence of the hydrolysis rate deceleration is compared with the ionization percent of betacyclodextrin. The results indicate that a direct relationship does not exist between the ionization of betacyclodextrin. It seems reasonable therefore that the phenobarbital undergoes a stable complex with betacyclodextrin and complex formation would provide a better shield for the phenobarbital from hydroxyl ion attack.

• Bulletin of the Korean Chemical Society
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• v.29 no.12
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• pp.2477-2481
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• 2008

• Microbiology and Biotechnology Letters
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• v.18 no.3
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• pp.260-267
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• 1990

The mechanism of enzymatic hydrolysis of raw corn starch by the purified glucoamylase and a - amylase in an agitated bead reaction system was studied by investigating the changes of sugar profiles produced by each enzyme, the granular structure of raw corn starch, the amount of enzyme adsorption on residual starch, and the amylose content in residual raw starch. The sugar profiles produced by the action of exo-type glucoamylase or endo-type $\alpha$ -amylase in an agitated bead system were not recognizably differed with those produced in reaction system without bead. Without enzyme the intergenic microcrystalline structure of starch granule was not changed by the simple mechanical impact of solid media, but it was cleaved. However, starch granule was fragment into large number of small particles by the synergistic action of enzyme and attrition-milling media, identified to be the major saccharification enhancing mechanism along with the increased amount of enzyme adsorption. The amylose content decreased more readily in an agitated bead reaction system, especially by $\alpha$ -amylase.

• Journal of Environmental Science International
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• v.5 no.5
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• pp.579-583
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• 1996

This study is involved to develop new catalysts to decompose plastics, detergents and surfactants containing synthetic peptide bonds. As the first year research, the catalytic-hydrolysis of amide bond in copper complex was accomplished. The hydrolysis reaction in aqueous solution was monitored by UV/VIS spectroscopy. As the pH of the solution Is increased and the temperature is raised, the reaction rate increases. The reaction rate is observed as the first order kinetic behavior for the copper complex. The metal catalyzed hydrolysis mechanism is proposed cia metal-hydroxide in the pH region of 5.5 to 6.3. The results of characterization of the catalytic reaction mechanism can be applied to develop new catalysts for peptide bond degradation in further research.