• Journal of the Korean Chemical Society
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• v.35 no.2
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• pp.158-164
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• 1991

The reduction mechanism at a mercury electrode of o-cresolphthalexon(OCP) in strongly alkaline supporting electrolytes has been investigated by several electrochemical techniques. The radical formed after first one electron reduction uptake, dimerizes. The result of cyclic voltammetric investigation demonstrated the reversible nature of the electron transfer and standard rate constant was $3.27{\times}10^{-2}$ cm/sec. The apparent irreversible behavior of the second wave is a result of the existence of a fast protonation following the second electron transfer. At low concentration of OCP(< $1{\times}10^{-4}$M), cathodic current were remarkably adsorptive properties. Prolonged electrolysis was carried out at controlled potential of -1.85V, original violet color of the solution becames progressively weaker, and then colorless solution. The final product of an exhaustive electrolysis is electro-inactive. The appearence of four steps may be explained by the fact that the reduction of OCP elucidated ECEC mechanism.

• Journal of the Korean GEO-environmental Society
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• v.13 no.9
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• pp.69-74
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• 2012

This study investigated the TNT decomposition by the treatment of alkaline hydrolysis. To obtain this objecitive, spectrum shift characteristics, pH effect, kinetics, and product analysis were examined during the alkaline hydrolysis by means of hydroxide ions. At pH = 12, an aqueous solution of TNT was changed into yellow-brown coloring, in which its absorbances were newly increased in a range of wavelength 400-600 nm. From the kinetic data, pseudo-first-order rate constant in a excess of hydroxide ion, in contrast to TNT concentration, was $0.0022min^{-1}$, which means that the reaction rate between TNT and hydroxide ion can be very slow, and that 1,047 min is necessary to achieve a 90% reduction of the initial TNT. In products analyses, nitrite ions and formic acid were mainly produced by the alkaline hydrolysis, nitrate ions and oxalic acid as minor products were generated.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.327-327
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• 2012

사파이어는 우수한 광학적, 물리적, 화학적 특성을 가지고 있는 물질 중의 하나이며, 청색 발광특성을 나타내는 GaN와 격자상수, 열팽창 계수가 가장 유사할 뿐만 아니라 가격도 상대적으로 저렴하기 때문에 GaN 성장을 위한 기판으로 사용될 수 있다. 실제로 사파이어는 프로젝터와 전자파 장치, 군사용 장비 등 다양한 분야에 응용되고 있으며, 발광 다이오드(LED)를 위한 기판으로 활용됨으로써 그 수요가 급격히 증가하고 있다. 그러나 사파이어 결정의 성장 중에 생길 수 있는 전위(dislocation)와 적층결함(stacking fault) 등의 결정 결함들은 결정 내에 존재하여 역학적, 전기적 성질에 큰 영향을 미칠 수 있다. 특히 사파이어가 청색 발광소자의 기판으로 사용되는 경우, 사파이어 기판 내부의 결정 결함은 증착되는 박막 특성에 영향을 미치게 된다. 따라서 사파이어의 보다 나은 응용을 위해서는 결정 결함에 대한 평가기술과 결함의 형성 메커니즘 등에 대한 이해가 필요하다. 특히, 결함의 정량적 평가 기술의 개발은 사파이어의 상용화에 중요한 핵심요소 중 하나이다. 결정을 산이나 염기 등을 이용하여 화학적 식각을 하게 되면 분자나 원자 간의 결합이 약한 부분이나 높은 에너지 상태에 있는 부분부터 반응을 하게 되는데, 이러한 반응을 통해 결정의 표면에 형성되는 것을 에치 피트(etch pit)라고 한다. 일반적으로 결정 내에 존재하는 전위는 높은 에너지 상태이므로, 이러한 에치 피트는 전위와 관련되어 있다. 따라서 사파이어 결정과 같은 결정질 물질은 표면의 식각을 통하여 관찰되는 에치 피트 등의 형상이나 반응성 등을 평가하여 결정 특성을 연구할 수 있다. 본 연구는 화학적 식각법으로 사파이어 결정의 특성을 평가하기 위하여 진행하였다. 사파이어 결정의 식각을 위하여 다양한 산-염기 용액들이 사용되었다. 식각 용액의 종류에 따른 사파이어 결정의 식각거동을 연구하고, 표면에 나타나는 형상을 연구하여 사파이어 결정의 구조적 특성을 파악하였다. 특히, 에치 피트 형성거동의 시간 및 온도 의존성에 관한 연구를 진행하였다.

• The Korean Journal of Pesticide Science
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• v.6 no.3
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• pp.218-223
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• 2002

The rate of hydrolysis of insecticide, O,O-diethyl-O-(1-phenyl-3-trifluoromethylpyrazol-5-yl)phosphorothioate (Flupyrazofos) have been investigated in 25% (v/v) aqueous dioxane (${\mu}=0.1M$) at $45^{\circ}C$. The hydrolysis mechanism of flupyrazofos proceeds through the specific acid ($A_{AC}2$) catalysis below pH 4.0, specific base ($B_{AC}2$) catalysis above pH 11.0 and general acid & base ($B_{AC}2$) catalysis between pH 5.0 and pH 10.0 via trigonal-bipyramidal ($d^2sp^3$) intermediate as evidence by solvent effect ($|m|{\ll}|{\ell}|$), rate equation ($kt=ko+k_H+ [H_3O^+]+k_{OH}[OH^-]$) and product analysis. The half-life ($T\frac{1}{2}$) of hydrolytic degradation in neutral media at $45^{\circ}C$ was ca. 3 months.

• Applied Biological Chemistry
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• v.39 no.1
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• pp.70-76
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• 1996

A series of the herbicidal pyridylsulfonyl areas, none substitutent, 1-(4,6-dimethoxypyrimidine-2-yl)-3-(2-pyridylsulfonyl) urea, 3 and 3-trifluoromethyl substitutent, 1-(4,6-dimethoxypyrimidine-2-yl)-3-(3-trifluoromethyl-2-pyridylsulfonyl) urea, 5(Flazasulfuron) were synthesizied and the rate of hydrolysis of their has been studied in 25%(v/v) aqueous dioxane at $45^{\circ}C$. From the results of solvent effect($m{\ll}1,\;n{\ll}3\;&\;{\mid}m{\mid}{\ll}{\mid}{\ell}{\mid}$), thermodynamic parameter (${\Delta}S^{\neq}=0.54{\sim}\;-2.19\;e.u.\;&\;{\Delta}H^{\neq}=0.025\;Kcal.mol.^{-1}$), hydrolysis product analysis, $pK_a$ constant(3: 4.9 & 5: lit.4.6) and the rate equation, a marked difference in the kinetics of the reaction of 3 and 5(Flazasulfuron) was observed. It may be concluded that the hydrolysis of 5 proceeds through the $A-S_N2Ar$ reaction via conjugate acid$(5H^+)$ below pH 7.0, whereas, above pH 9.0, the hydrolysis proceeds through irreversibly $(E_1)_{anion}$ and reversibly $(E_1CB)_R$ mechanism via conjugate base(CB), respectively. But in case of 5, $A-S_N2Ar,\;(E_1)anion\;and\;(E_1CB)_R$ mechanism involved Smile rearrangement. The mate of rearrangement of 5 to a 3-trifluoromethyl-2-pyridylpyrimidinyl urea(PPU) in acid and 3-trifluoromethyl-2-pyridyl-4.6-dimethoxypyridinyl amine (PPA) in base was increased about 3.5 times by the introduction of trifluoromethyl group in the 3-position on the 2-pyridyl ring. From the basis of these findings, a possible mechanism for the hydrolysis of 5 was proposed and discussed.

• Economic and Environmental Geology
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• v.48 no.2
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• pp.131-145
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• 2015

Thermodynamic prediction of weathering products from primary aquifer minerals around underground disposal sites was investigated. The distribution of solubility quotients for kaolinite-smectite reactions showed the trend of reaching at equilibrium with Ca-, Mg-, and Na-smectite for deep groundwaters in granitic aquifers. The values of $10^{-14.56}$, $10^{-15.73}$, and $10^{-7.76}$ were proposed as equilibrium constants between kaolinite and Ca-, Mg-, and Na-smectite end members, respectively. On stability diagrams, most of deep groundwaters were located at equilibrium boundaries between stability fields of kaolinite and smectites or on stability fields of smectites and illite. Shallow groundwaters in basic rock aquifer were plotted at the same stability areas of deep granitic groundwaters on stability diagrams. The results indicated that the primiary mineralogical composition may be important to predict weathering products in deep aquifers.

• Journal of the Korean Chemical Society
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• v.44 no.2
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• pp.120-126
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• 2000

The rate constants for the hydrolysis of 2-phenyl-4H,5H-3-methyl-3-thiazolinium perchlorate(PTP) derivatives were detemined by the use of ultraviolet visible spectrophotometer in water. The rate equations which could be applied over a wide pH ranges were obtained. On the basis of rate equation, hydrolysis product analysis, general base catalysis, and substituent effect, a plausible mechanism of the hydrolysis is proposed: Below pH 4.0, the reaction is initiated by addition of water, while above pH 9.0, Michael type nucleophilic addition takes place. In the pH range of $4.5{\sim}8.0$, these two reactions appear to occur competitively.

• Journal of the Korean Chemical Society
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• v.42 no.5
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• pp.539-548
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• 1998

Multidentate N,O-containing ligands, such as N,N'-bis(2-hydroxybenzyl)-ethylenediamine(BHED), N,N'-bis(2-hydroxybenzyl)-propylenediamine(BHPD), N,N'-bis(2-hydroxybenzyl)-diethylenetriamine(BHDT), N,N'-bis(2-hydroxybenzyl)-triethylenetriamine(BHTT) and N,N'-bis(2-hydroxybenzyl)-tetraethylenepentaamine (BHTP) were synthesized by reduction of the imine group of Bis(salicylidene)-ethylendiamine(BSED), Bis (salicylidene)-propylenediamine(BSPD), Bis(salicylidene)-diethylentriamine(BSDT), Bis(salicylidene)-triethylenetetraamine(BSTT) and Bis(salicylidene)-tetraethylenepentaamine(BSTP). Proton dissociation constants of the ligands and stability constants of transition metal(Ⅱ) ion complexes with BHED, BHPD, BHDT, BHTT, and BHTP were determined by potentiometic titration. The sequence of stability constants $(logK_{ML})$ of complex increases as BHED Zn(Ⅱ) which follows the Irving-Williams series.

• Analytical Science and Technology
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• v.7 no.2
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• pp.173-179
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• 1994

The point of present study was focused on developing the method for the determination of dissociation constant by means of FIA conjunction with Diode Array Spectrphotometry or spectrophotometry along with small amount of Bromocresol Green(mg order) within short time. On the calculation with computer, the indicator with pK=7 has been shown the most sensitive reaction when little amount of base or acid has been added. The pKa of Bromothymol Blue and Bromocresol Green were measured as 7.31 and 4.82 respectively with spectrophotometry after activity correction by Kielland method (Reported value by Bishop, 7.30 and 4.79). The pKa of Bromocresol Green by FIA was obtained as 4.78 and was comparable with other values determined by other methods.

• Journal of the Korean Chemical Society
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• v.42 no.1
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• pp.36-41
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• 1998

In this study, the extraction of Co(Ⅱ) and Cu(Ⅱ) into chloroform solution of dithizone, distribution ratios, extractabilities and extraction rate constants of the metal complexes were compared in each case with which thiocyanate ion was or not used as the auxiliary ligand. The use of the thiocyanate ion increased threefold the distribution ratio for Co(Ⅱ) complex in a basic solution and twofold for Cu(Ⅱ) complex in a wide pH range. And the extractability was also augmented from about 90 to 99 for Co(Ⅱ) and from 95 to 99 for Cu(Ⅱ) in a given period. The extraction rate constants were $k_1\;:\;1.2{\times}10^5$, $k_2\;:\;1.34{\times}10^{17}\; mol^{-1}dm^3s^{-1}$ in case of Co(Ⅱ) and$k_1\;:\;1.1{\times}10^8$, $k_2\;:\;2.83{\times}10^{10}\; mol^{-1}dm^3s^{-1}$ in case of Cu(Ⅱ) on the extraction of dithizonate complexes into chloroform solution.