• Title/Summary/Keyword: Hammett reaction constant (${\rho}$)

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Kinetics on the Reaction of 1-Adamantyl Fluoroformate with Substituted Pyridines (치환 피리딘류와 1-Adamantyl Fluoroformate의 반응에 대한 속도론적 연구)

  • Park, Byoung Chun;Park, Soo Hyun;Kyong, Jin Burm;Kim, Chang Bae
    • Journal of the Korean Chemical Society
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    • v.43 no.4
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    • pp.456-460
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    • 1999
  • Rates of 1-adamantyl fluoroformate with substituted pyridines ($3-CH_3,\;4-CH_3,\;H,\;3-Cl,\;3,4-(CH_3)_2,\;3,5-(CH_3)_2$) in methanol have been measured by conductometric method at various temperatures and concentrations. The activation parameters (${\Delta}H^{\neq},\;{\Delta}S^{\neq}$) and Hammett reaction constant (${\rho}$) or Bronsted coefficient (${\beta}$) were evaluated from rate constants. The activation entropies are large and negative, and the activation enthalpies are small and positive. The Hammett reaction constant (${\rho}$) and Bronsted coefficient (${\beta}$) values were -4.15 and 0.63, respectively. From the above results, it may be concluded that this reaction proceeds to a concerted displacement mechanism in methanol.

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Kinetic Study on the Oxidation Reaction of Substituted Benzyl Alcohols by Cr(VI)-Heterocyclic Complex (2,2'-Bipyridinium Dichromate) (크롬(VI)-헤테로고리 착물(2,2'-Bipyridinium Dichromate)에 의한 치환 벤질 알코올류의 산화반응에 대한 속도론적 연구)

  • Kim, Young Sik;Park, Young Cho
    • Applied Chemistry for Engineering
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    • v.23 no.2
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    • pp.241-246
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    • 2012
  • Cr(VI)-heterocyclic complex (2,2'-bipyridinium dichromate) was synthesized by the reaction between of 2,2'-bipyridine and chromium trioxide in $H_2O$, and characterized by IR and ICP. The oxidation of benzyl alcohol using 2,2'-bipyridinium dichromate in various solvents showed that the reactivity increased with the increase of the dielectric constant, in the order: cyclohexene < chloroform < acetone < N,N-dimethylformamide. In the presence of DMF solvent with acidic catalyst such as $H_2SO_4$ solution, 2,2'-bipyridinium dichromate oxidized the benzyl alcohol and its derivatives (p-$p-OCH_3$, $m-CH_3$, H, $m-OCH_3$, m-Cl, $m-NO_2$). Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant was -0.66 (303 K). The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

Kinetics and Mechanism of the Pyridinolysis of O,O-Dimethyl S-Aryl Phosphorothioates in Dimethyl Sulfoxide

  • Barai, Hasi Rani;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • v.32 no.7
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    • pp.2339-2344
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    • 2011
  • Kinetic studies for the reactions of O,O-dimethyl Z-S-aryl phosphorothioates with X-pyridines have been carried out in dimethyl sulfoxide at 85.0 $^{\circ}C$. The Hammett and Br$\"{o}$nsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H, while those for substituent Z variations in the leaving groups are linear. The negative sign of the cross-interaction constant (${\rho}_{XZ}$) implies that the reaction proceeds through a concerted mechanism for both the strongly and weakly basic pyridines. The magnitude of ${\rho}_{XZ}$ (= -0.35) for the strongly basic pyridines is greater than that (${\rho}_{XZ}$ = -0.15) for the weakly basic pyridines, indicating a change of the nucleophilic attacking direction from frontside for the strongly basic pyridines to backside for the weakly basic pyridines. The early transition state is proposed on the basis of the absence of positive deviations from both the Hammett and Br$\"{o}$nsted plots for the strong ${\pi}$-acceptor, X = 4-Ac, and small values of ${\rho}_{XZ}$ and ${\beta}_X$.

Kinetic Studies for the Reactions of Pyridine with Benzoylchlorides under High Pressure and High Vacuum (고압 및 고진공에서의 피리딘과 벤조일클로라이드류의 반응에 관한 속도론적 연구)

  • Kim, Se-Kyong
    • Journal of the Korean Chemical Society
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    • v.48 no.3
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    • pp.254-260
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    • 2004
  • The reaction rates of para-substituted benzoyl chlorides ($p-CH_3$, p-H, $p-NO_2$) with pyridine have been measured employing the conductometry method in acetonitrile. The pseudo first-order and second-order rate constants were determined at various pressures and temperatures. The activation parameters (${\Delta}V{\ddagger},\;{\Delta}{\beta}{\ddagger},\;{\Delta}H{\ddagger},\;{\Delta}S{\ddagger},\;{\Delta}G{\ddagger}$) and the Hammett ${\rho}$-values are determined from the values of rate constant. The values of ${\Delta}V{\ddagger},\;{\Delta}{\beta}{\ddagger}\;and\;{\Delta}S{\ddagger}$ are all negative. The Hammett ${\rho}$-values are positive for the substrate (${\rho}_Y$) over the given pressure range. The results of kinetic studies, for the pressure and substituent changes, show that these reactions are proceeded by a typical $SN_2$reaction mechanism and its bond formation is favored with elevating pressure.

A Study for Mechanism and Oxidation Reaction of Substituted Benzyl Alcohols by 2,2'-Bipyridinium Chlorochromate (2,2'-Bipyridinium Chlorochromate에 의한 치환 벤질 알코올류의 산화반응과 메카니즘에 관한 연구)

  • Kim, Young-Sik;Park, Young-Cho
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.7
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    • pp.3252-3260
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    • 2012
  • 2,2'-Bipyridinium chlorochromate[$C_{10}H_8N_2HCrO_3Cl$] was synthesized by the reaction of 2,2'- bipyridine with chromium(VI) trioxide in 6M HCl. The structure was characterized by IR and ICP analysis. The oxidation of benzyl alcohol using 2,2'-bipyridinium chlorochromate in various solvents showed that the reactivity increased with the increase in the order of the dielectric constant(${\varepsilon}$), in the order: cyclohexene< chloroform$p-CH_3$, H, m-Br, $m-NO_2$) in N,N'-dimethylformamide. Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.64(303K). The oxidation reactivity of alcohols can be a useful factor to study about physical properties such as thermal stability, when the polysilsesquioxane solution is ready for an applying coating agent. The observed experimental data was used to rationalized the hydride ion transfer in the rate-determining step.

A Study for Kinetics and Oxidation Reaction of Substituted Benzyl Alcohols using Cr(VI)-Heterocyclic Complex(Cr(VI)-Isoquinoline) (Cr(VI)-헤테로고리 착물(Cr(VI)-Isoquinoline)를 이용한 치환 벤질 알코올류의 산화반응과 속도론에 관한 연구)

  • Park, Young-Cho;Kim, Young-Sik
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.11
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    • pp.6000-6007
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    • 2013
  • Cr(VI)-heterocyclic complex[Cr(VI)-isoquinoline] was synthesized by the reaction between of heterocyclic compound(isoquinoline) and chromium trioxide, and characterized by IR and ICP analysis. The oxidation of benzyl alcohol using Cr(VI)-isoquinoline in various solvents showed that the reactivity increased with the increase of the dielectric constant(${\varepsilon}$), in the order : cyclohexene$CH_3$, m-Br, m-$NO_2$). Electron- donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.69(308K). The observed experimental data have been ratiolized. The hydride ion transfer causes the prior formation of a chromate ester in the rate-determining step.

A Study for Kinetics and Oxidation Reaction of Alcohols by Cr(VI)-4-(Dimethylamino)pyridine (크롬(VI)-4-(Dimethylamino)pyridine에 의한 알코올류의 산화반응과 반응속도에 관한 연구)

  • Kim, Young-Sik;Park, Young-Cho;Kim, Young Jun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.1
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    • pp.499-505
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    • 2013
  • Cr(VI)-4-(dimethylamino)pyridine[4-(dimethylamino)pyridinium chlorochromate] was synthesized by the reaction of 4-(dimethylamino)pyridine with chromium trioxide in 6M-HCl, and characterized by IR, ICP. The oxidation of benzyl alcohol using 4-(dimethylamino)pyridinium chlorochromate in various solvents showed that the reactivity increased with the increase of the dielectric constant(${\varepsilon}$), in the order: cyclohexene$H_2SO_4$ solution), 4-(dimethylamino)pyridinium chlorochromate oxidized benzyl alcohol and its derivatives(p-$OCH_3$, m-$CH_3$, H, m-$OCH_3$, m-Cl, m-$NO_2$) smoothly in DMF. Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.68(303K). The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

A Study for Kinetics and Oxidation Reaction of Substituted Benzyl Alcohols Using (C10H8N2H)2Cr2O7 ((C10H8N2H)2Cr2O7를 이용한 치환 벤질 알코올류의 산화반응과 반응속도에 관한 연구)

  • Park, Young Cho;Kim, Young Sik;Kim, Soo Jong
    • Applied Chemistry for Engineering
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    • v.28 no.5
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    • pp.597-600
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    • 2017
  • $(C_{10}H_8N_2H)_2Cr_2O_7$ was synthesized by reacting 4,4'-bipyridine and chromium (VI) trioxide. The structure of the product was characterized with FT-IR (infrared spectroscopy) and elemental analysis. The oxidation of benzyl alcohol using $(C_{10}H_8N_2H)_2Cr_2O_7$ in various solvents showed that the reactivity increased with the increase of the solvent dielectric constant, in the order of DMF (N,N'-dimethylformamide) > acetone > chloroform > cyclohexane. In the presence of DMF, an acidic catalyst such as $H_2SO_4$ $(C_{10}H_8N_2H)_2Cr_2O_7$ oxidized benzyl alcohol (H) and its derivatives ($p-OCH_3$, $m-CH_3$, $m-OCH_3$, m-Cl, $m-NO_2$). Electron donating substituents accelerated the reaction rate, whereas electron acceptor groups retarded the reaction rate. Hammett reaction constant (${\rho}$) was -0.70 (308 K). The observed experimental data were used to rationalize the hydride ion transfer in the rate determining step.

Kinetics and Mechanism of the Pyridinolysis of Aryl Ethyl Chlorothiophosphates in Acetonitrile

  • Adhikary, Keshab Kumar;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • v.32 no.11
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    • pp.3947-3951
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    • 2011
  • The nucleophilic substitution reactions of Y-aryl ethyl chlorothiophosphates with X-pyridines are studied kinetically in acetonitrile at $55.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Me. The substituents of X = 4-CN and 4-Ac show great positive deviations from both the Hammett and Bronsted plots. The Hammett plots for substituent Y variations in the substrates exhibit biphasic concave upwards with a minimum point at Y = H. The obtained values of the cross-interaction constants (${\rho}_{XY}$) are all in spite of the biphasic free energy correlations for both substituent X and Y variations, since the ${\rho}_X$values with both the strongly and weakly basic pyridines are almost constant. A stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed where the distance between X and Y does not vary from the intermediate to the second transition state. A frontside attack is proposed with the strongly basic pyridines based on the considerably great magnitudes of ${\rho}_X$ and ${\beta}_X$ values and a backside attack is proposed with the weakly basic pyridines based on the relatively small magnitudes of ${\rho}_X$ and ${\beta}_X$. The positive deviations of the two strong ${\pi}$-acceptor parasubstituents, X = 4-Ac and 4-CN, from both the Hammett and Bronsted plots are rationalized by the great extents of bond formation and breaking.

Kinetic Studies on the Reaction of Benzyl m-Nitrobenzenesulfonate with N,N-Dimethylanilines (벤질 m-술폰산니트로벤젠과 N,N-디메틸아닐린類와의 反應에 關한 反應速度論的 硏究)

  • Yoh Soo-Dong;Lee Mu-Sang
    • Journal of the Korean Chemical Society
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    • v.23 no.1
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    • pp.37-41
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    • 1979
  • The kinetics of the reaction of benzyl m-nitrobenzenesulfonate with m-and p-substituted N,N-dimethylanilines in acetone have been investigated by an electric conductivity method. The effects of substituents on the reactivity of N,N-dimethylaniline and the existence of linear free energy relationship were discussed. The rate constants k were in the range 2.55∼487 $10^{-4}l{\cdot}mol^{-l}{\cdot}sec^{-1} (35^{\circ}C)$ and increased with the electron donating ability of substituents. In the present reaction, the Hammett plot was correlated with ${\sigma}$ substituent constant, especially using the new ${\sigma}$ value of 0.35 in p-MeO and it's ${\rho}$ value was found to be -1.37. r value for the reaction was very large than the value obtained in the reaction of benzyl bromide. $Br{\"{o}}nsted$ linear relationship was shown between rate constant and basicites except for p-MeO resulted from solvent effect. From the Bronsted plot, this reaction was suggested that the cleavage of the C${\cdot}{\cdot}{\cdot}$O bond in the $S_N2$ transition state proceed the bond formation.

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