• Proceedings of the KIEE Conference
• /
• 2000.07c
• /
• pp.1999-2001
• /
• 2000

Impulse breakdown voltage characteristics of sulphur-hexafluoride/nitrogen ($SF_{6}-N_{2}$) mixtures were presented. The applied voltages were the positive and negative lightning impulse (1.2/44${\mu}s$) and oscillating impulse ($0.4{\mu}s$/2.08MHz) voltages. The predischarge current was observed to clarify the breakdown mechanism. The electrode system was consisted of plane to plane configuration with a needle-shaped protrusion whose length and diameter are 10mm and 1mm. The measurements were carried out at the gas pressure of mixtures up to 0.5MPa with nitrogen concentrations varying from 5 to 20%. The electrical breakdown in $SF_{6}-N_{2}$ mixtures develops with steplike pulses in leader mechanism. The minimum breakdown voltages for the negative lightning and oscillating impulse voltages were higher than those for the positive.

• Applied Chemistry for Engineering
• /
• v.21 no.3
• /
• pp.278-283
• /
• 2010

The cationic polymerization of oxolane high explosives which have pendant explosive groups such as azido, nitrato and hydrazino is investigated theoretically using the semiempirical MINDO/3, MNDO and AM1 methods. The nucleophilicity and basicity of oxolane high explosives can be explained by the negative charge on oxygen atom of oxolane. The reactivity of propagation in the polymerization of oxolane can be represented by the positive charge on carbon atom and the low LUMO energy of active species of oxolane. The reaction of the oxolane high explosives in oxonium ion form to the open chain carbenium ion form is expected by computational stability energy (17.950~30.197 kcal/mol) of the oxonium ion and carbenium ion favoring the carbenium ion. The relative equilibrium concentration of cyclic oxonium ion and carbenium ion is found to be a major determinant of mechanism, owing to the rapid equilibrium of these catoinic forms. Based on calculation, in the prepolymer propagation step, $S_N1$ mechanism will be at least as fast as that for $S_N2$ mechanism.

• Archives of Pharmacal Research
• /
• v.2 no.1
• /
• pp.9-16
• /
• 1979

3-Amino-2-phenylthietane derivatives were considered as a useful tool to elusidate the mechanism of inhibiton of MAO by tranylcypromine-type inhitors. The synthesis of 3-benzoylamino-2-phenylthieetane, 3-amino-2-phenylthietane, and 3-N, N-dimentylamino-2-p-nitrophenythietane was attempted using the reaction between 1, 3 dihalogeno alkanes with alkali sulfide. When 1-pheny1-1, 3-dihalo-2-benzolaminopropane was treated with sodium sulfide, 2-pheny 1-4 benzylidene-2-oxazoline was isolated, indicating the case of elimination reaction compared to ring formation. The reaction of 1-p-nitropheny1-1, 3-dichloro-2-N, N-dimethylaminopropane with sodium sulfide gave bis (1-p-nitropheny1-2-N, N-dimethylamino-3-chloropropane)sulfide. The mechanism of reaction was discussed.

• Bulletin of the Korean Chemical Society
• /
• v.9 no.3
• /
• pp.157-160
• /
• 1988

The rates of hydrolysis of N-(benzenesulfonyl) benzimidoyl chlorides (p-H, $p-CH_3,\;p-CH_3,\;p-NO_2\;and m-NO_2$) have been measured by UV spectrometry in 60% methanol-water at $25^{\circ}C$ and a rate equation which can be applied over wide pH range was obtained. Below pH 7.00, the substituent effect on the hydrolysis rate of N-(benzenesulfonyl) benzimidoyl chloride was found to conform to the Hammett ${\sigma}$ constant with ${\rho}$ = -0.91, whereas above pH 9.00, with ${\rho}$ = 0.94. On the basis of the rate equation obtained and the effect of solvent, substituents and salt, the following reaction mechanism were proposed; below pH 7.00, the hydrolysis of N-(benzenesulfonyl) benzimidoyl chloride proceeds by $S_N1$ mechanism, however, above pH 9.00, the hydrolysis is initiated by the attack of the hydroxide ion and in the range of pH 7.00-9.00, these two reactions occur competitively.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.12
• /
• pp.1451-1456
• /
• 1999

Solvolyses of α-methoxy-α-(trifluoromethyl)phenylacetyl chloride in H₂O, D₂O, CH₃OD, 50% D₂O-CH₃OD, and in aqueous binary mixtures of acetone, dioxane, ethanol and methanol are investigated at 25.0℃. The Grunwald-Winstein plots of first-order rate constants for α-methoxy- α-(trifluoromethyl)phenylacetyl chloride with $Y_{Cl}$ show a dispersion phenomenon. Solvent nucleophilicity N has been shown to give considerable im-provement when it is added as an 1N term to the original Grunwald-Winstein for the solvolyses of α-methoxy- α-(trifluoromethyl)phenylacetyl chloride. The dispersions in the Grunwald-Winstein correlations in the present studies are caused by solvent nucleophilicity. The magnitude of l and m values associated with a change of solvent composition predicts the associative $S_N2$ transition state. The kinetic solvent isotope effects determined in deuterated water and methanol are consistent with the proposed mechanism of the general base catalyzed associative $S_N2$ or $S_AN$ mechanism for the of α-methoxy- α-(trifluoromethyl)phenylacetyl chloride.

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

• Bulletin of the Korean Chemical Society
• /
• v.32 no.12
• /
• pp.4361-4365
• /
• 2011

The nucleophilic substitution reactions of bis(N,N-dimethylamino) phosphinic chloride (3) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $65.0^{\circ}C$. The anilinolysis rate of 3 is rather slow to be rationalized by the conventional stereoelectronic effects. The magnitudes of ${\rho}_X$ (= -6.42) and ${\beta}_X$ (= 2.27) values are exceptionally great. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are secondary inverse ($k_H/k_D$ = 0.69-0.96). A concerted $S_N2$ mechanism involving a backside attack is proposed on the basis of secondary inverse DKIEs and the variation trend of the $k_H/k_D$ values with X. The anilinolyses of six phosphinic chlorides in MeCN are briefly reviewed by means of DKIEs, steric effects of the two ligands, positive charge of the reaction center phosphorus atom, and selectivity parameters to obtain systematic information on phosphoryl transfer reaction mechanism.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.10
• /
• pp.3293-3297
• /
• 2012

The solvolysis rate constants of 5-nitro-2-furoyl chloride (5-$NO_2(C_4H_2O)$-2-COCl, 1) in 27 different solvents are well correlated with the extended Grunwald-Winstein equation, using the $N_T$ solvent nucleophilicity scale and YCl solvent ionizing scale, with sensitivity values of $1.20{\pm}0.05$ and $0.37{\pm}0.02$ for l and m, respectively. The activation enthalpies (${\Delta}H^{\neq}$) were 5.63 to $13.0kcal{\cdot}mol^{-1}$ and the activation entropies (${\Delta}S^{\neq}$) were -25.9 to $-43.4cal{\cdot}mol^{-1}{\cdot}K^{-1}$, which is consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effect (SKIE, $k_{MeOH}/k_{MeOD}$) of 2.65 was also in accord with the $S_N2$ mechanism and was possibly assisted using a general-base catalysis. The product selectivity (S) for solvolysis of 1 in alcohol/water mixtures was 1.2 to 11, which is also consistent with the proposed bimolecular reaction mechanism.

• Journal of the Korean Chemical Society
• /
• v.35 no.6
• /
• pp.673-679
• /
• 1991

The electrochemical reduction of N-tert-butylbenzothiazole-2-sulfenamide (TBBS; vulcanization accelerator) was investigated by direct current, differential pulse polarography, cyclic voltammetry and controlled potential coulometry. The electrode reduction of TBBS proceeded E-C-E-C reaction mechanism by four electrons transfer at irreversible one wave (-2.31 volts vs. Ag/0.1M AgN$O_3$ in AN). As the results of controlled potential electrolysis, mercaptobenzothiazole (MBT), benzothiazole disulfide (MBT dimer) and extricated sulfur were products which followed by cleavage of the sulfenamide (-S-N=) bond. Upon the basis of products analysis and polarogram interpretation with pH variable, electrochemical reaction mechanism was suggested.

• Journal of Photoscience
• /
• v.12 no.1
• /
• pp.51-54
• /
• 2005

The electronic excitationenergy quenching of 2, 5-diphenyl-1, 3, 4-oxadiazole (PPD) by Carbon tetrachloride ($CCl_4$) in different solvents viz, n-hexane, n-heptane, toluene, benzene, cyclohexane, 1, 4- dioxane has been carried out at room temperature to understand the role of quenching mechanism. The Stern-Volmer plots have been found to be linear. As probability of quenching per encounter 'p' is less than unity, and the activation energy for quenching '$E_a$' is greater than the activation energy of diffusion '$E_d$', it is inferred that the fluorescence quenching mechanism is not due to material diffusion alone.