• Journal of the Korean Chemical Society
• /
• v.29 no.1
• /
• pp.15-22
• /
• 1985

Kinetic studies of nucleophilic substitution reaction of substituted benzoyl cyanides and benzoyl chlorides with pyridines were conducted at 25$^{\circ}C$ in pure acetone solvent. Results showed that (ⅰ) magnitudes of $_{\rho}_S$, $_{\rho}_N$ and ${\beta}$ associated with a change of substituent in the nucleophile indicate relatively advanced bond-formation in the transition state, (ⅱ) the potential energy surface model is able to predict the reaction mechanism, but it is unable to predict the transition state variation to a more product-like transition state, where bond-formation is much more progressed than bond breaking, upon changing the leaving group to that with better leaving ability (ⅲ) the quantum mechanical model predicted the product-like transition state and slightly better leaving ability of CN- as compared with Cl-.

• Journal of the Korean Chemical Society
• /
• v.19 no.3
• /
• pp.156-162
• /
• 1975

Rates of reactions of methanesulfonyl chloride with various substituted anilines have been measured in methanol. Substituent effects in aniline are found to be linearly correlated with pKa(Bronsted relation with ${\beta}$ = 0.84) and ${\rho}$(Hammett equation with ${\rho}$ = -2.46) respectively. The results are interpreted in terms of degree of bond-formation at the transition state, which was found to have progressed relatively further. The rates for o-methylaniline deviated from the Bronsted plot established by meta and para substituted anilines because of a steric effect of ortho position in aniline. Activation parameters, ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$ have also been determined. The enthalpy of activation showed a regular variation in that electron donating substituents in the p-substituted aniline decrease ${\Delta}H^{\neq}$ and increase the negative value of ${\Delta}S^{\neq}$.

• Journal of the Korean Chemical Society
• /
• v.47 no.2
• /
• pp.137-146
• /
• 2003

3-Hydroxybenzopyran[3,2-c]-[1]-benzopyran-6,7-diones (3) and 3-methoxycarbonylcoumarin (4) were prepared via condensation of 1 with resorcinol in the presence of sodium methoxide. The chemical behavior of 3 towards acetic anhydride, alkyl halides and diazonium chloride is described. The electron impact ionization mass spectra of compounds 4,5 and 6a,b show a weak molecular ion peak and a base peak of m/z 89, m/z 280. m/z 91 and m/z 120 resulting from a cleavage fragmentation respectively. The molecular ion of compounds 3, 6b, and 7a is a base peak of m/z 280, m/z 366 and m/z 488 respectively. Compound 7a give a characteristic fragmentation pattern with a two very stable fragmentation of m/z 383 and m/z 77.

• Journal of the Korean Chemical Society
• /
• v.50 no.1
• /
• pp.46-52
• /
• 2006

studies of olefin oxidation using Al(III)-porphyrin complexes as catalyst are investigated in CH2Cl2, in which NaClO is used as terminal oxidant. Porphyrins are TPP(5,10,15,20-Tetraphenylporphyrin) and (p-X)TPP(X=CH3O, CH3, F, Cl). Olefins are styrene and (p-X)styrene (X=CH3O, CH3, Cl, Br). The values of Km and Vmax are calculated from the Michaelis-Menten equation. According to the substituents of substrate and catalyst, kinetic parameters will be measured. Investigating the correlation between the Michaelis-Menten rate parameters and the substituent constants, we were able to analyze the influence on the changes of catalytic activity or the rate determining step during the process of the formation and the dissociation of the M-oxo-olefin.

• Journal of the Korean Chemical Society
• /
• v.40 no.12
• /
• pp.733-740
• /
• 1996

The rate constants for the hydrolysis of 4'-[N-(9-acridinyl)]-1'-(N-methanesulfonyl)-3'-methoxyquinonediimide(AMQD) were determined by ultraviolet visible spectrophotometer in water at $25^{\circ}C.$ The rate equation which could be applied over wide pH ranges were obtained. On the basis of pH-rate profile, Bronsted plot, hydrolysis product analysis, general base catalysis and substituent effect, the plausible hydrolysis mechanism was proposed: Below pH 3.00, the hydrolysis reaction was proceeded by the attack of water to 4'-position of quinonoid after protonation at nitrogen of acridinyl and between pH 3.00 and 9.00, the addition of water and hydroxide occurred competitively. However, above pH 9.00, the rate constants were dependent upon only the concentration of hydroxide ion.

• Journal of the Korean Chemical Society
• /
• v.39 no.6
• /
• pp.440-445
• /
• 1995

The chemical compositions and stability constants, thermodynamic parameters for the neodymium(Ⅲ) complexes of substituted benzo-1,4,7,10,13-pentaoxacyclopentadecane(B15C5) have been determined by spectrophotometry and conductometry in methanol solution at various temperatures. As substituents, CH3, Br, CHO, NO2, and 3,4-(NO2)2 were used. In methanol solution the ratios of neodymium(Ⅲ) to the ligands in the complexes are 1 : 1. The stability constants were increased in order of B15C5-3,4-(NO2)2 < B15C5-NO2 < B15C5-CHO < B15C5-Br < B15C5 < B15C5-CH3. This observation can be explained in terms of the substituent effect. The order of stability constants was dimethylsulfoxide < acetone < acetonitrile in solution and the magnitudes were found to be inversely proportional to the solvents donicities. These results could be understood in terms of solvent basicity, ligand basicity, solvation of the cation, and entropy changes of complex formation.

• Journal of the Korean Chemical Society
• /
• v.48 no.3
• /
• pp.254-260
• /
• 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.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.7
• /
• pp.1579-1582
• /
• 2009

The reaction rates of 4-X-2,6-dinitrochlorobenzenes (X = $NO_2,\;CN,\;CF_3$) with Y-substituted pyridines (Y = 3-$OCH_3,\;H,\;3-CH_3,\;4-CH_3$) in methanol-acetonitrile mixtures were measured by conductometry at 25 ${^{\circ}C}$. It was observed that the rate constant increased in the order of X = 4-$NO_2\;>\;4-CN\;>\;4-CF_3$ and the rate constant also increased in the order of Y = 4-$CH_3\;>\;3-CH_3\;>\;H\;>\;3-OCH_3$. When the solvent composition was varied, the rate constant increased in order of MeCN > 50% MeOH > MeOH. The electrophilic catalysis by methanol may be ascribed to the formation of hydrogen bonds between alcoholic hydrogen and nitrogen of pyridines in ground state. Based on the transition parameters, ${\rho}_S,\;{\rho}_N,\;{\beta}_Y,\;{\rho}_{XY}$ and solvent effects, the reaction seems to proceed via $S_N$Ar-Ad.E mechanism. We also estimated the isokinetic solvent mixtures (${\rho}_{XY}$ = 0) based on cross-interaction constants, where the substituent effects of the substrate and nucleophile are compensated.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.12
• /
• pp.2913-2917
• /
• 2009

Second-order rate constants (k$_{Nu–}$) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-i) with butane-2,3-dione monoximate ($Ox^-\;an\;\alpha$-nucleophile) and Z-substituted phenoxides in 80 mol% H$_2$O/20 mol% DMSO at 25.0${\pm}$0.1$^{\circ}C$. Hammett plots correlated with ${\sigma}^o$ and ${\sigma}^-$ constants for reactions of 1a-h with Ox$^–$ exhibit many scattered points. In contrast, the Yukawa-Tsuno plot results in a good linear correlation with ${\rho}_Y$ = 2.20 and r = 0.45, indicating that expulsion of the leaving group occurs in the rate-determining step (RDS). A stepwise mechanism with expulsion of the leaving-group being the RDS has been excluded, since Y-substituted phenoxides are less basic and better nucleofuges than Ox$^–$. Thus, the reactions have been concluded to proceed through a concerted mechanism. Ox$^–$ is over 10$^2$ times more reactive than its reference nucleophile, 4-chlorophenoxide (4-ClPhO$^–$). One might suggest that stabilization of the transition-state (TS) through intramolecular general acid/base catalysis is responsible for the ${\alpha}$-effect since such general acid/base catalysis is not possible for the corresponding reactions with 4-ClPhO$^–$. However, destabilization of the ground-state (GS) of Ox$^–$ has been concluded to be mainly responsible for the ${\alpha}$-effect found in this study on the basis of the fact that the magnitude of the ${\alpha}$-effect is independent of the nature of the substituent Y.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.12
• /
• pp.3543-3548
• /
• 2010

A kinetic study on nucleophilic displacement reactions of 2-pyridyl X-substituted benzoates 1a-e with potassium ethoxide (EtOK) in anhydrous ethanol is reported. Plots of pseudo-first-order rate constants ($k_{obsd}$) vs. $[EtOK]_o$ exhibit upward curvature. The $k_{obsd}$ value at a fixed $[EtOK]_o$ decreases steeply upon addition of 18-crown-6-ether (18C6) to the reaction mixture up to [18C6]/$[EtOK]_o$ = 1 and then remains nearly constant thereafter. In contrast, $k_{obsd}$ increases sharply upon addition of LiSCN or KSCN. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ has revealed that ion-paired EtOK is more reactive than dissociated $EtO^-$, indicating that $K^+$ ion acts as a Lewis acid catalyst. Hammett plots for the reactions of 1a-e with dissociated $EtO^-$ and ion-paired EtOK result in excellent linear correlation with $\rho$ values of 3.01 and 2.67, respectively. The $k_{EtOK}/k_{EtO^-}$ ratio increases as the substituent X in the benzoyl moiety becomes a stronger electron-donating group. $K^+$ ion has been concluded to catalyze the current reaction by stabilizing the transition state through formation of a 6-membered cyclic complex.