• 제목/요약/키워드: Rate Determining Step

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2,4-이니트로할로벤젠과 치환된 아닐린의 반응속도에 대한 용매효과 (제2보) (Influence of Solvents on Rates of Reactions of 2,4-Dinitro Substituted Halobenzenes with Substituted Anilines (Ⅱ))

  • 이해황;이익춘
    • 대한화학회지
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    • 제22권1호
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    • pp.7-11
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    • 1978
  • 이니트로요오도벤젠과 파라치환체 아닐린과의 반응을 아세토니트릴-메탄올 혼합용매에서 연구하였다. 행해진 반응에서의 반응속도 상수는 메탄올 용매하에서 아세토니트릴 용매에 비해 큰 값을 보였다. 실험 결과로 부터 중간체 생성 과정이 반응속도 결정 단계임을 알았으며 용매효과는 메탄올의 산소 원자와 아닐린의 수소원자 사이의 수소결합에 의한 천이상태 안정화로 설명하였다.

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Effects of Added Anions on the Reaction of Nitrous Acid with Hydrogen Peroxide

  • Park, Jong-Yoon;Choi, Eun-Jin;Park, Joon-Woo
    • Bulletin of the Korean Chemical Society
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    • 제13권1호
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    • pp.37-41
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    • 1992
  • The reactions of nitrous acid with hydrogen peroxide in acidic aqueous solution in the presence of several added anions have been studied at $0^{\circ}C$ and pH 2-4 to investigate the nucleophilic catalysis of these anions. From the dependence of reaction rates on the anion concentrations, significant catalytic effects were found for $Cl^-,\;Br^-,\;SCN^-$, in order of effect $SCN^-\;{\approx}\;Br^->Cl^-$, while no observable effect was found for ${ClO_4}^-$ and ${NO_3}^-$. These results support O-nitrosation reaction is the rate-determining step and NOX formed in the presence of an anion ($X^-$) also acts as a nitrosating agent and accelerates the overall reaction rate. The order of reactivity was found to be NOCl>NOBr>NOSCN, which is consistent with the results of N-nitrosation and S-nitrosation reactions.

A Mechanistic Study on Acyl Transfer Reactions of Aryl Substituted Benzoates Between Aryloxides

  • Ik-Hwan Um;Jae-Shin Jeon;Dong-Sook Kwon
    • Bulletin of the Korean Chemical Society
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    • 제12권4호
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    • pp.406-410
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    • 1991
  • Second order rate constants have been measured spectrophotometrically for reactions of 4-nitrophenyl substituted benzoates with various aryloxides and aryl benzoates with p-chlorophenoxide. The reactivity has exhibited significant dependences on the electronic nature of the substituent in the acyl moiety of the substrate and in the nucleophilic phenoxide, while the substituent in the leaving phenoxide has little influenced the reactivity. The Bronsted coefficient $\beta$ values so obtiained support that the present acyl transfer reaction proceeds via a stepwise mechanism in which the nucleophilic attack would be the rate-determining step. Interestingly, the magnitude of the $\betaacyl$ and $\beta$ nuc increases with increasing reactivity, implying that the reactivity selectivity principle is not operative in the present system. The failure of the reactivity selectivity principle is attributed to a change in transition state structure upon the substituent variation in the present acyl transfer reaction.

Theoretical Studies on the A2 Hydrolysis of Methyl Acetimidate

  • Ikchoon Lee;Chang Kon Kim;Bon-Su Lee
    • Bulletin of the Korean Chemical Society
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    • 제11권3호
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    • pp.194-200
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    • 1990
  • Various mechanistic aspects of the A2 hydrolysis of methyl acetimidate were explored using the MNDO method. As in thecorresponding reactions of acetamide and methyl carbamate, a proton transfer pre-equilibrium exists between the N-protonated and the O-protonated tautomers, and the subsequent hydrolysis proceeds from the more stable N-protonated form. Of the two reaction pathways, the $A_{AL}2$ path is favored in the gas phase and in concentrated acid solutions, whereas the $A_{AC}2$ path is favored in less acidic solutions with a stable cationic tetrahedral intermediate formed in the rate determining step. Negative charge development on the alkoxy oxygen in the transition state suggested a rate increase with the increase in the electron withdrawing power of the alkoxy group. Calculations on the reaction processes with AM1 indicated that MNDO is more reliable in this type of work, although AM1 is better than MNDO in reproducing hydrogen bonds.

Two-Step 소결법을 통한 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 무연 압전 세라믹의 밀도 및 압전 특성 향상 (Enhancement of Density and Piezoelectric Properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Lead-Free Piezoelectric Ceramics through Two-Step Sintering Method)

  • 유일열;박상현;최성희;조경훈
    • 한국재료학회지
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    • 제34권2호
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    • pp.116-124
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    • 2024
  • In this study, we investigated the microstructure and piezoelectric properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS-BNKZ) ceramics based on one-step and two-step sintering processes. One-step sintering led to significant abnormal grain (AG) growth at temperatures above 1,085 ℃. With increasing sintering temperature, piezoelectric and dielectric properties were enhanced, resulting in a high d33 = 506 pC/N for one-step specimen sintered at 1,100 ℃ (one-step 1,100 ℃ specimen). However, for one-step 1,115 ℃ specimen, a slight decrease in d33 was observed, emphasizing the importance of a high tetragonal (T) phase fraction for superior piezoelectric properties. Achieving a relative density above 84 % for samples sintered by the one-step sintering process was challenging. Conversely, two-step sintering significantly improved the relative density of KNNS-BNKZ ceramics up to 96 %, attributed to the control of AG nucleation in the first step and grain growth rate control in the second step. The quantity of AG nucleation was affected by the duration of the first step, determining the final microstructure. Despite having a lower T phase fraction than that of the one-step 1,100 ℃ specimen, the two-step specimen exhibited higher piezoelectric coefficients (d33 = 574 pC/N and kp = 0.5) than those of the one-step 1,100 ℃ specimen due to its higher relative density. Performance evaluation of magnetoelectric composite devices composed of one-step and two-step specimens showed that despite having a higher g33, the magnetoelectric composite with the one-step 1,100 ℃ specimen exhibited the lowest magnetoelectric voltage coefficient, due to its lowest kp. This study highlights the essential role of phase fraction and relative density in enhancing the performance of piezoelectric materials and devices, showcasing the effectiveness of the two-step sintering process for controlling the microstructure of ceramic materials containing volatile elements.

색도물질과 옥살산의 오존분해를 위한 고효율 Jet Loop 반응기의 적용 (Application of High-performance Jet Loop Reactor for the Decolorization of Reactive black 5 and Mineralization of Oxalic Acid by Ozone)

  • 변석종;;;조순행;윤제용;김수명
    • 한국물환경학회지
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    • 제20권1호
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    • pp.78-85
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    • 2004
  • As an ozone contactor, we newly adopted HJLR (High-performance Jet Loop Reactor) for the decolorization of Reactive black 5 and the mineralization of oxalic acid, which has been applied exclusively in biological wastewater treatments and well-known for high oxygen transfer characteristics. The ozonation efficiency for organic removals and ozone utilization depending on the mass transfer rate were compared to those of Stirred bubble column reactor, which was controlled by varing energy input in the HJLR and Stirred bubble column reactor. The results were as follows; first, the decolorization rate of Reactive black 5 in the HJLR reactor was nearly proportional to the increasing $k_La$. When the $k_La$ was increased by 25 % from $13.0hr^{-1}$ to $16.4hr^{-1}$, 30 % of the k' (apparent reaction rate constant) was increased from 0.1966 to $0.2665min^{-1}$ (Stirred bubble column; from 0.1790 to $0.2564min^{-1}$). Ozone transfer was found to be a rate-determining step in decolorizing Reactive black 5, which was supported by that no residual ozone was detected in all of the experiments. Second, the mineralization of oxalic acid was not always proportional to the increasing $k_La$ in the RJLR reactor. The rate-determining step for this reaction was OH(OH radical) production with ozone transfer, because residual ozone was always detected during the ozonation of oxalic acid in contrast with Reactive black 5. This result indicates that the increase of $k_La$ in the HJLR reactor is beneficial only when there are in ozone transfer limited regions. In addition, regardless of $k_La$, the mineralization of oxalic acid was nearly accomplished within 60 minutes. It was interpreted as that the longer staying of residual ozone by whirling liquid in the HJLR reactor contributed to an high ozone utilization(83-94%), producing more OR radicals.

철 촉매를 이용한 Fischer-Tropsch 합성 반응과 수성 가스 전환 반응에 대한 반응 속도 연구 (Kinetic Study of the Fischer-Tropsch Synthesis and Water Gas Shift Reactions over a Precipitated Iron Catalyst)

  • 양정일;천동현;박지찬;정헌
    • Korean Chemical Engineering Research
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    • 제50권2호
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    • pp.358-364
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    • 2012
  • 철 촉매를 이용한 Fischer-Tropsch 합성 반응과 수성 가스 전환 반응에 대한 반응 메커니즘과 반응 속도식을 5 채널 고정층 반응기를 이용하여 조사하였다. 실험 조건은, 반응물 합성가스 $H_2$/CO 비 0.5~2, 반응물 공급 유량 60~80 ml/min, 반응 온도 $255{\sim}275^{\circ}C$로서 반응 압력은 1.5 MPa을 유지하였다. F-T 합성 반응의 반응 속도식($r_{FT}$)은 반응 속도 결정 단계로서 분자로 흡착된 CO와 기상의 수소 분자와의 반응을 바탕으로 하는 Eley-Rideal 반응 메카니즘을 통해 계산되었고, WGS 반응의 반응 속도식($r_{WGS}$)은 formate 중간체 생성 반응을 반응 속도 결정 단계로 가정하여 결정되었다. 실험 결과, F-T 합성 반응의 반응 속도식과 WGS 반응의 반응 속도식은 각각 탄화수소 생성과 $CO_2$ 생성에 대한 반응 속도 실험값을 잘 모사하였고, 또한 power law에 근거한 CO 전환 반응에 대한 반응 속도식도 실험값과 잘 일치하였다. 이처럼, 각각의 반응 메카니즘을 바탕으로 도출된 반응 속도식($r_{FT}$, $r_{WGS}$, $-r_{CO}$)은 실험값과 여러 가지 기존 문헌에서 보고된 반응 속도식 모델과 잘 일치하였다.

Kinetics of the KOH Catalyzed-Methanolysis for Biodiesel Production from Fat of Tra Catfish

  • Huong, Le Thi Thanh;Tan, Phan Minh;Hoa, Tran Thi Viet;Lee, Soo
    • 한국응용과학기술학회지
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    • 제25권4호
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    • pp.418-428
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    • 2008
  • Transesterification of fat of Tra catfish with methanol in the presence of the KOH catalyst yields fatty acid methyl esters (FAME) and glycerol (GL). The effects of the reaction temperature and reaction time on rate constants and kinetic order were investigated. Three regions were observed. In the initial stage, the immiscibility of the Tra fat and methanol limited the reaction rate, hence this region was controlled by the mass transfer. Subsequent to this region, produced FAME like a co-solvent made the reaction mixture homogeneous, therefore the conversion rate increased rapidly so it was controlled by the kinetic parameters of the reaction until the equilibrium was approached in the final slow region. A second-order kinetic mechanism was proposed involving second regions for the forward reaction. The rate determining step for the overall KOH catalyzed-methanolysis of Tra fat was the conversion of triglycerides (TG) to diglycerides (DG). This rate constant was increased from 0.003 to $0.019min^{-1}$ when the reaction temperature was increased from 35 to $60^{\circ}C$. Its calculated activation energy was 14.379 ($kcal.mol^{-1}$).

회분식 오존 공정에서 페놀의 분해 속도에 관한 연구 (A Study on the Decomposition Rate of Phenol in the Batch Type Ozonation)

  • 안재동;강동수
    • 한국환경보건학회지
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    • 제23권4호
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    • pp.127-132
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    • 1997
  • The characteristics of the ozone treatments of phenol were studied in a laboratory scale wastewater treatment system. The ozone treatment of wastewater was carried out in a batch-type reactor. The initial pH of wastewater(7-10), volumetric flow rate(1-2l/min) and ozone concentration(20~30 mg/l) of aerating gas were considereal as experimental variables in the ozone treatment. Phenol was decomposed easily by the ozone in a batch treatment, where the rate determining step was the COD removal that is decomposition of intermediates formed by the ozonation of phenol. Phenol decomposition and COD removal could be expressed by the first order reaction for the phenol concentration and COD, respectively. Rate constants of phenol decomposition and COD removal increased with the initial pH, volumetric flow rate and ozone concentration of aeration gas. Under the present experimental condition, their relationships could be given by for the phenol decomposition $k'=4.46\times 10^{-9}[pH]_o ^{3.94}[O_3]^{1.42}Q_{O3}^{1.57}$ for the COD removal $k=2.46\times 10^{-10}[pH]_o ^{5.19}[O_3]^{1.15}Q_{O3}^{1.19}$

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산소에 의한 바나듐 (III) 이온의 산화반응에 대한 $O^{18}$ 동위원소 연구 (Tracer Study Using $H_2O^{18}$ on the Oxidation of Vanadium (III) by Molecular Oxygen)

  • 김명자;최동식
    • 대한화학회지
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    • 제18권4호
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    • pp.259-266
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    • 1974
  • 과염소산 수용액 중에서 바나듐(III)이온이 산소에 의해 산화되는 반응에 대해서 pH 범위1∼3에 걸쳐 $H_2O^{18}$을 이용한 동위원소 실험을 행했다. 반응속도식$-\frac{d[V(III)]}{dt}=k_1\frac{[O_2][V(III)]}{[H^+]}$가 성립되는 높은 히드로늄이온 농도(pH<∼2)에서는 반응생성물 $VO^{2+}$이온의 산소가 모두 산소분자에서 유래된다는 결과를 얻었다. 반면 $-\frac{d[V(III)]}{dt}=K_2\frac{[O_2][V(III)]^2}{[Ht]^2}$의 속도식이 성립하는 pH>∼2 범위에서의 추적자 실험은 바나딜이온의 산소의 50%가 산소분자에서 온다는 결과를 주었다. 반응속도론의 결과 화학량론적 결정과 아울러 동위원소 실험결과를 고려하면 다음과 같은 반응 메카니즘을 제안할 수 있다.$$V^{3+}\rightleftarrows VOH^{2+} + H+, 2VOH^{2+}\rightleftarrowsV_2(OH)_2^{4+}$$$$ 낮은\PH:\ VOH^{2+}+O_2 \rightarrow V(O_2)OH^{2+}, V(O_2)OH^{2+}+VOH^{2+}\rightarrow 2VO^{2+}+H_2O_2$$$$ 높은\PH:\V2(OH)_2^{4+}+O_2\rightarrow2VO^{2+}+H_2O_2, V_2(OH)_2^{4+}+H_2O_2\rightarrow2VO^{2+}+2H_2O$$

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