• Bulletin of the Korean Chemical Society
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• 제34권8호
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• pp.2325-2329
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• 2013

Second-order rate constants $k_N$ have been measured for reactions of benzyl 2-pyridyl thionocarbonate (4b) and t-butyl 2-pyridyl thionocarbonate (5b) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The $k_N$ values for the reactions of 4b and 5b have been compared with those reported previously for the corresponding reactions of benzyl 2-pyridyl carbonate (4a) and t-butyl 2-pyridyl carbonate (5a) to investigate the effect of changing the electrophilic center from C=O to C=S on reactivity and reaction mechanism. The thiono compound 4b is more reactive than its oxygen analogue 4a. The Br${\o}$nsted-type plots for the reactions of 4a and 4b are linear with ${\beta}_{nuc}=0.57$ and 0.37, respectively. The reactions of 4a were previously reported to proceed through a concerted mechanism, while those of 4b in this study have been concluded to proceed through a stepwise mechanism with formation of an intermediate being the rate-determining step on the basis of the ${\beta}_{nuc}$ value of 0.37. Enhanced polarizability upon changing the C=O in 4a by C=S has been suggested to be responsible for the reactivity order and the contrasting reaction mechanisms. In contrast, the reactivity of 5a and 5b is similar, but they are much less reactive than 4a and 4b. Furthermore, the reactions of 5a and 5b have been concluded to proceed through the same mechanism (i.e., a concerted mechanism) on the basis of linear Bronsted-type plots with ${\beta}_{nuc}=0.45$ or 0.47. It has been concluded that the strong steric hindrance exerted by the t-Bu in 5a and 5b causes a decrease in their reactivity and forces the reactions to proceed through a concerted mechanism.

• Bulletin of the Korean Chemical Society
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• 제30권12호
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• pp.2909-2912
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• 2009

The amines studied in this study are less reactive toward ethyl propiolate (3) in MeCN than in H$_2$O although they are 7 to 9 pK$_a$ units more basic in the aprotic solvent. The reactivity of morpholine and deuterated morpholine toward 3 is found to be identical, indicating that proton transfer occurs after rate-determining step (RDS). The fact that kinetic isotope effect is absent excludes a stepwise mechanism in which proton transfer occurs in RDS as well as a concerted mechanism in which nucleophilic attack and proton transfer occur concertedly through a 4-membered cyclic transition state (TS). Thus, the reactions have been concluded to proceed through a stepwise mechanism in which proton transfer occurs after RDS. Brønsted-type plots are linear with small ${\beta}_{nuc}$ values, i.e., ${\beta}_{nuc}$ = 0.29 in H$_2$O and ${\beta}_{nuc}$ = 0.51 in MeCN, indicating that bond formation is not advanced significantly in RDS. The small ${\beta}_{nuc}$ value also supports the conclusion drawn from the study of kinetic isotope effect.

• Korean Chemical Engineering Research
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• 제53권3호
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• pp.333-338
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• 2015

본 연구에서는 재생가스조성에 따른 건식 흡수제의 재생률, $CO_2$ 흡수능 그리고 응집 특성에 관한 연구를 실시하였다. 실험은 내경 0.05 m, 높이 0.8 m이며 석영으로 제작된 회분식 기포 유동층 반응기에서 수행되었으며 흡수제는 연속공정의 흡수반응기 후단에서 채취한 입자를 사용하였다. 반응성에 관한 연구는 재생반응 유동화 기체의 조성을 $CO_2$, $H_2O$, $N_2$의 농도를 다양하게 변화시키며 수행하였다. 실험결과 재생온도가 증가함에 따라 흡수반응 동안의 흡수능이 증가하는 경향을 나타내었으며 재생기체에 포함된 수분의 함량이 증가함에 따라 흡수능이 다소 감소하는 경향을 나타내었다. 재생반응기체로 $N_2$ 100%를 사용한 경우 흡수반응 동안의 흡수능이 가장 높게 나타났으며, ($H_2O+N_2$)를 사용한 경우, $CO_2$ 100%를 사용한 경우, ($H_2O+CO_2$)를 사용한 경우 순으로 흡수능이 감소하는 경향을 나타내었다. 또한, 응집특성에 관한 연구는 흡수제의 입자크기 변화와 흡수반응기체에 포함된 수분의 농도가 응집에 미치는 영향을 살펴보았다. 실험결과 수분함량이 높고 입자크기가 작을수록 응집입자가 많이 생성되는 것으로 나타났다.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2135-2138
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• 2014

A kinetic study is reported for the SNAr reaction of 1-Y-substituted-phenoxy-2,4-dinitrobenzenes (1a-1h) with OH- in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The second-order rate constant ($k_{OH^-}$) increases as the substituent Y in the leaving group changes from an electron-donating group (EDG) to an electronwithdrawing group (EWG). The Br${\o}$nsted-type plot for the reactions of 1a-1h is linear with ${\beta}_{lg}$ = -0.16, indicating that the reactivity of substrates 1a-1h is little affected by the leaving-group basicity. A linear Br${\o}$nsted-type plot with ${\beta}_{lg}=-0.3{\pm}0.1$ is typical for reactions reported previously to proceed through a stepwise mechanism in which formation of a Meisenheimer complex is the rate-determining step (RDS). The Hammett plot correlated with ${\sigma}_Y{^{\circ}}$ constants results in a much better correlation than that correlated with ${\sigma}_Y{^-}$constants, implyng that no negative charge is developing on the O atom of the leaving group (or expulsion of the leaving group is not advanced at all in the TS). This excludes a possibility that the $S_NAr$ reaction of 1a-1h with $OH^-$ proceeds through a concerted mechanism or via a stepwise pathway with expulsion of the leaving group being the RDS. Thus, the current reactions have been concluded to proceed through a stepwise mechanism in which expulsion of the leaving group occurs rapidly after the RDS.

• Bulletin of the Korean Chemical Society
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• 제33권4호
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• pp.1199-1203
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• 2012

Catalytic filters consisting of Ni nanoparticle and carbon fiber with different oxidation states of Ni (either metallic or oxidic) were prepared using a chemical vapor deposition process and various post-annealing steps. CO oxidation reactivity of each sample was evaluated using a batch type quartz reactor with a gas mixture of CO (500 mtorr) and $O_2$ (3 torr) at $300^{\circ}C$. Metallic and oxidic Ni showed almost the same CO oxidation reactivity. Moreover, the CO oxidation reactivity of metallic sample remained unchanged in the subsequently performed second reaction experiment. We suggested that metallic Ni transformed into oxidic state at the initial stage of the exposure to the reactant gas mixture, and Ni-oxide was catalytically active species. In addition, we found that CO oxidation reactivity of Ni-oxide surface was enhanced by increase in the $H_2O$ impurity in the reactor.

• Korean Chemical Engineering Research
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• 제45권5호
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• pp.506-514
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• 2007

합성가스 연소 매체순환식 가스연소기 적용을 위한 최적 산소공여입자를 선정하기 위해 네 가지 산소공여입자(NiO/bentonite, $NiO/LaAl_{11}O_{18}$, $Co_xO_y/CoAl_2O_4$, $NiO/NiAl_2O_4$)에 대해 환원반응기체로 모사 합성가스($H_2,\;CO2$, CO 각각 30, 10, 60%)를 사용하여 열중량 분석기(TGA)에서 환원반응특성 및 탄소침적특성을 측정 및 해석하였다. 환원반응온도가 증가함에 따라 최대전환율, 산소전달능력이 증가하였고 산소전달속도 측면에서 $900^{\circ}C$가 합성가스 연소반응에 적합한 조건으로 나타났으며 높은 환원반응온도(${\geq}800^{\circ}C$)에서는 네 가지 입자 모두에 대해 탄소침적현상이 나타나지 않았다. 네 가지 산소공여입자 중 NiO 계 산소공여입자가 CoO 계 산소공여입자에 비해 반응성이 높게 나타났으며 NiO/bentonite 입자가 산소전달속도, 탄소침적도 면에서 가장 좋은 반응성을 나타내었다. NiO/bentonite 입자에 포함된 금속산화물의 함량이 증가함에 따라 산소전달능력과 산소전달속도가 증가하는 것으로 나타나 금속산화물의 함량이 높은 산소공여입자가 매체순환식 가스연소기의 안정적인 조업에 유리한 것으로 나타났다.

• Bulletin of the Korean Chemical Society
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• 제32권spc8호
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• pp.2955-2959
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• 2011

Second-order rate constants for nucleophilic substitution reactions of 2,4-dinitrophenyl benzenesulfonate 1a with a series of alicyclic secondary amines in MeCN have been measured spectrophotometrically and compared with those reported previously for the corresponding reactions performed in aqueous medium to investigate the effect of medium on reactivity and reaction mechanism. The amines employed in this study are found to be more reactive in the aprotic solvent than in $H_2O$. The reactions of 1a in MeCN result in a linear Br${\o}$nsted-type plot with ${\beta}_{nuc}$ = 0.58, which contrasts to the curved Br${\o}$nsted-type plot reported previously for the corresponding reactions performed in the aqueous medium (i.e., ${\beta}_2$ = 0.86 and ${\beta}_1$ = 0.38). Accordingly, it has been concluded that the reaction mechanism changes from a stepwise mechanism to a concerted pathway upon changing the medium from $H_2O$ to MeCN. Reactions of Y-substituted phenyl benzenesulfonates 1a-c with piperidine in MeCN result in a linear Br${\o}$nsted-type plot with ${\beta}_{lg}$ = -1.31, indicating that expulsion of the leaving group is significantly more advanced than bond formation in the transition state. The trigonal bipyramidal intermediate ($TBPy^{\pm}$) proposed previously for the reactions in $H_2O$ would be highly unstable in MeCN due to strong repulsion between the negative charge in $TBPy^{\pm}$ and the negative dipole end of MeCN. Thus, destabilization of $TBPy^{\pm}$ in MeCN has been concluded to change the reaction mechanism from a stepwise mechanism to a concerted pathway.

• 한국응용과학기술학회지
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• 제30권2호
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• pp.297-304
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• 2013

Free-radical copolymerization of glycidyl methacrylate(GMA) and N-phthalimidoethyl acrylate(NPEA) were carried out at $60^{\circ}C$ in dimethylformamide(DMF) solution in the presence of benzoylperoxide(BPO) at low conversion. The polymers were characterized by IR and $^1H$-NMR. The compositions of the copolymer was analyzed by ultra violet(UV/Vis) spectrophotometry. The reactivity ratios of the monomer was determined by the application of Fineman-Ross(FR) and Kelen-T$\ddot{u}$d$\ddot{o}$s(KT) methods. The monomer reactivity ratios of the system and Alfrey-Price's resonance effect(Q) and polar effect(e) value for NIEA were determined as follow. The reactivity ratios of the monomer obtained from FR and KT are found to be $r_1$=0.87, $r_2$=0.98 and $r_1$=0.88, $r_2$=0.99 respectively. The Q and e values of poly(GMA-co-NPEM) calculated from $r_1$ and $r_2$ was Q= 1.31, e=0.75 respectively.

• Bulletin of the Korean Chemical Society
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• 제32권3호
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• pp.988-992
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• 2011

$CO_2$ adsorption on mineral sorbents has a potential to sequester $CO_2$. This study used a density functional theory (DFT) study of $CO_2$ adsorption on barium oxide (BaO) in the presence of $H_2O$ to determine the role of $H_2O$ on the $CO_2$ adsorption properties on the ($2{\times}2$; $11.05\;{\AA}{\times}11.05\;{\AA}$) BaO (100) surface because BaO shows a high reactivity for $CO_2$ adsorption and the gas mixture of power plants generally contains $CO_2$ and $H_2O$. We investigated the adsorption properties (e.g., adsorption energies and geometries) of a single $CO_2$ molecule, a single $H_2O$ molecule on the surface to achieve molecular structures and molecular reaction mechanisms. In order to evaluate the coordinative effect of $H_2O$ molecules, this study also carried out the adsorption of a pair of $H_2O$ molecules, which was strongly bounded to neighboring (-1.91 eV) oxygen sites and distant sites (-1.86 eV), and two molecules ($CO_2$ and $H_2O$), which were also firmly bounded to neighboring sites (-2.32 eV) and distant sites (-2.23 eV). The quantum mechanical calculations show that $H_2O$ molecule does not influence on the chemisorption of $CO_2$ on the BaO surface, producing a stable carbonate due to the strong interaction between the $CO_2$ molecule and the BaO surface, resulting from the high charge transfer (-0.76 e).

• 환경위생공학
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• 제18권2호
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• pp.52-59
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• 2003

This study was progressed in photocatalysis of VOCs using $UV/TiO_2$ which was a benign process environmentally. The experiments were peformed to know photodegradation characteristics as crystalline structure of $TiO_2$ which had anatase, rutile and P-25 (anatase : rutile = 70 : 30). The main purpose of this study was to identify photocatalytic characteristics as inlet concentration of reactants, $H_2O$, and residence time. The inlet concentration of VOCs was changed 50, 100 and 200 ppmv, and amount of $H_2O$ was changed 0, 500 and $1000{\;}mg/m^3$, respectively. The deep conversion was increased as the inlet concentration decreased, and the amount of $H_2O$ increased. The deep conversion of benzene had the highest value at $1000{\;}mg/m^3${\;}H_2O$ and 50 ppmv of inlet concentration. The reactivity of reactants was decreased in order benzene > toluene > m-xylene. Also, the photocatalytic deep conversion was increased as residence time increased, because the contact time between reactants and catalyst was increased. In this study, intermediates had not found by GC/MSD analysis. Therefore, the reactants were completely converted to $H_2O{\;}and{\;}CO_2$.