• 대한화학회지
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• 제65권1호
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• pp.9-14
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• 2021

이 연구에서는 1기압 298 K 기체 상태에서 페난트렌에 두 개의 OH 라디칼이 연쇄적으로 작용하여 페난트렌이 분해되는 반응 과정을 B3LYP/6-31G(d,p) 기저함수를 사용하여 DFT 계산을 수행하였다. 계산 결과 두 개의 OH 라디칼이 연쇄적으로 페난트렌에 작용하는 경우에도 phenanthren-9-ol 생성 반응이 phenanthren-1-ol 생성 반응보다 유리할 것으로 예측된다. 한편 OH 첨가와 H 추출 과정에 대한 우선성은 상온에서 OH 첨가 과정이 유리할 것으로 예측되었다.

• Korean Chemical Engineering Research
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• 제53권1호
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• pp.83-90
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• 2015

본 연구에서는 multi-walled carbon nanotube (MWCNT) 표면에 자유 라디칼 중합 가능한 methacrylate기를 다량으로 도입하기 위한 연구를 수행하였다. 먼저, MWCNT 표면에 카르복실기(-COOH)를 도입하기 위하여 황산과 질산의 혼산으로 초음파로 처리하면서 2시간 산화시켜 MWCNT-COOH를 합성하였다. 합성된 MWCNT-COOH를 염화티오닐(thionyl chloride)와 반응시켜 MWCNT-COCl을 합성하고, triethylenetetramine (TETA)와 반응시켜 MWCNT-$NH_2$를 합성하였다. 합성된 MWCNT-$NH_2$와 3-(acryloyloxy)-2-hydroxypropyl methacrylate (AHM)의 투입 몰 비를 변화시키면서 Michael 부가 반응으로 MWCNT 표면에 methacrylate기가 도입된 MWCNT-AHM을 합성하였다. MWCNT의 표면 개질정도는 fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA)와 원소분석(elemental analysis, EA) 분석을 통해 개질 반응의 진행 정도와 최적 개질 조건을 확인하였다. 그 결과 MWCNT-$NH_2$에 접목되어 있는 TETA에 대하여 AHM의 반응 몰 비를 1:10로 하고 8시간 반응시켰을 때 methacrylate기가 가장 많이 도입되는 조건임을 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제23권9호
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• pp.1263-1307
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• 2002

Pseudo-first-order rate constants (kobs) have been determined for the nucleophilic substitution reactions of p-nitrophenyl diphenyl phosphinate (PNPDPP) with substituted phenoxides (XC6H4O - ) and butane-2,3-dione monoximate (Ox- ) in 0.1 M borate buffer (pH = 10.0) at 25.0 ${\pm}0.1^{\circ}C$. The kobs value increases sharply upon addition of cethyltrimethylammonium bromide (CTAB) to the reaction medium up to near 7 ${\times}$ 10-4 M CTAB and then decreases smoothly upon further addition of CTAB. The rate enhancement upon the addition of CTAB is most significant for the reaction with -O2CC6H4O- and least significant for the one with C6H5O- , indicating that the reactivity of these aryloxides in the presence of CTAB cannot be determined by the basicity alone. The strength of the interaction of these anionic aryloxides with the positively charged micellar aggregates has been suggested to be an important factor to determine the reactivity in the presence of CTAB. The kobs value for the reaction with Ox- increases also upon the addition of CTAB. However, the increase in the kobs value is much more significant for the reaction with Ox- than for the one with ClC6H4O- , indicating that Ox- is less strongly solvated than ClC6H4O- in H2O. The ${\alpha}-effect$ shown by Ox- in H2O has been attributed to the ground-state solvation difference between Ox- and ClC6H4O- .

• 한국염색가공학회지
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• 제24권1호
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• pp.39-44
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• 2012

To improve flame retardation of poly(ethylene terephthalate) (PET) against burning, resorcinol bis(diphenyl phosphate) (RDP), phosphorous containing flame retardant, was incorporated into PET backbone by radical reaction pathway. Radical endcapping of PET with RDP was confirmed by spectroscopic and thermal analysis. From 400 MHz $^{31}P$ solid state FT-NMR spectrum of PET with RDP (PET-RDP), phosphorus spectra peak in RDP was found at ca. -10 ppm. Furthermore, P-C bond stretching vibration peaks were found ca. $530cm^{-1}$ in FT-IR spectrums of PET-RDP. These results indicated that RDP can be chemically bound at the ends of PET by radical addition method. Thermal characteristics of pure PET (pPET) and PET-RDP were measured and evaluated by TGA thermal analysis. There was not significant changes in thermal characteristics of PET-RDP compared to that of pPET.

• Bulletin of the Korean Chemical Society
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• 제19권7호
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• pp.776-779
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• 1998

Second-order rate constants have been measured spectrophotometrically for the addition reaction of a series of alicyclic amines to 3-butyn-2-one to yield their respective enamines at 25.0 'C. The reactivity of the amines increases with increasing the basicity of the amines. However, the Bronsted-type plot obtained exhibits a downward curvature as the basicity of the amines increases, i.e. βnuc decreases from 0.3 for low basic amines (pKa < 9) and to 0.1 for highly basic amines (pKa > 9). Such a curvature in the Bronsted-type plot is clearly indicative of a change in the reaction mechanism or transition state structure. From the corresponding reactions run in D2O, the magnitude of kinetic isotope effect (KIE) has been calculated to be about 0.8 for highly basic amines and 1.21 for weakly basic amines. The difference in the magnitude of KIE also supports a change in the reaction mechanism or transition state structure upon changing the basicity of the amines. Furthermore, the small KIE clearly suggests that H+ transfer is not involved in the rate-determining step, i.e. the addition reaction is considered to proceed via a stepwise mechanism in which the attack of the amines to the acetylene is the rate-determining step. The curvature in the Bronsted-type plot has been attributed to a change in the degree of bond formation between the amine and the acetylene.

• 생명과학회지
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• 제5권4호
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• pp.155-161
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• 1995

The effects of substrate concentration, enzyme concentration, reaction temperature, and water content were investigated in intramolecular esterification. This study used cyclohexane as organic solvent, power lipase as enzyme, and benzyl alcohol and octanoic acid as substrate. The initial reaction rate was found to be proportional to enzyme concentration; followed Michaelis-Menten equation for octanoic acid; and was inhibited by benzyl alcohol . The observed initial reaction rate first increased, then decreased with increasing reaction temperature, giving rise to the maximum rate at 20$\circ$. The drop in the reaction rate at higher temperature was to partition equilibrium change of substrate between organic solvent and hydration layer of enzyme molecule in addition to the deactivation by enzyme denaturation. Water layer surrounding enzyme molecule seemed to activate in organic solvent and the realistic reaction was done in the water layer. In the enzymatic reaction in organic solvent, the initial reaction rate was influenced by partition quilibrium of substrate, so the optimum condition of substrate concentration, enzyme concentration, reaction temperature, and water content would give a good design tool.

• Bulletin of the Korean Chemical Society
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• 제18권4호
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• pp.374-379
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• 1997

The rate constants for the nucleophilic addition of thiophenol derivatives (p-OCH3, H, p-CH3, m-CH3, p-Br and p-NO2) to 4'-[N-(9-acridinyl)]-1'-(N-methanesulfonyl)-3'-methoxyquinonediimide (AMQD) were determined by ultraviolet spectrophotometer in water at 5 ℃, and rate equations which can be applied over a wide pH range were obtained. On the basis of pH-rate profile, Bronsted plot, adduct analysis, general base catalysis and substituent effect, a plausible mechanism of this addition reaction was proposed: Below pH 2.5, the reaction proceeded by the addition of thiophenol molecule to 6'-position of quinonoid after protonation at the acridinyl nitrogen. Above pH 6.2, the addition of sulfide anion to 6'-position of quinonoid was rate controlling. However, in the range of pH 3.0-6.0, these two reactions occured competively.

• Journal of the Korean Wood Science and Technology
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• 제40권2호
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• pp.110-122
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• 2012

This study investigated the effects of layered clay on the thermal curing behavior and tensile properties of resole phenol-formaldehyde (PF) resin/clay/cellulose nanocomposites. The thermal curing behavior of the nanocomposite was characterized using conventional differential scanning calorimetry (DSC) and temperature modulated (TMDSC). The addition of clay was found to accelerate resin curing, as measured by peak temperature ($T_p$) and heat of reaction (${\Delta}H$) of the nanocomposite’ curing reaction increasing clay addition decreased $T_p$ with a minimum at 3~5% clay. However, the reversing heat flow and heat capacity showed that the clay addition up to 3% delayed the vitrification process of the resole PF resin in the nanocomposite, indicating an inhibition effect of the clay on curing in the later stages of the reaction. Three different methods were employed to determineactivation energies for the curing reaction of the nanocomposite. Both the Ozawa and Kissinger methods showed the lowest activation energy (E) at 3% clay content. Using the isoconversional method, the activation energy ($E_{\alpha}$) as a function of the degree of conversion was measured and showed that as the degree of cure increased, the $E_{\alpha}$ showed a gradual decrease, and gave the lowest value at 3% nanoclay. The addition of clay improved the tensile strengths of the nanocomposites, although a slight decrease in the elongation at break was observed as the clay content increased. These results demonstrated that the addition of clay to resole PF resins accelerate the curing behavior of the nanocomposites with an optimum level of 3% clay based on the balance between the cure kinetics and tensile properties.

• 대한화학회지
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• 제33권1호
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• pp.127-134
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• 1989

${\beta},\;{\beta}$-diethoxycarbonylstryene 유도체(H, p-OCH$_3$, 3,4,5-(OCH$_3)_3$), 3,4,5-methylenedioxy)에 대한 3-mercaptopropionic acid의 친핵성 첨가반응 속도상수를 자외선 분광법으로 측정하여 넓은 pH 범위에서 적용될수 있는 속도식을 구하였다. pH에 따르는 속도상수의 변화, 일반염기촉매작용등을 바탕으로 이 첨가반응 메카니즘을 제안하였다. 즉 pH 6.0 이하에서는 중성인 3-mercaptopropionic acid 분자의 첨가로 이 반응이 시작되며 pH 6.0∼8.0영역에서는 이 중성분자와 황화음이온의 첨가가 경쟁적으로 일어나며, pH 8.0이상에서는 황화음이온에 의해서만 첨가반응이 진행된다.

• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.593-600
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• 2019

The combustion characteristics of methane/hydrogen pre-mixed flame have been investigated with swirl stabilized flame in a laboratory-scale pre-mixed combustor with constant heat load of 5.81 kW. Hydrogen/methane fuel and air were mixed in a pre-mixer and introduced to the combustor through a burner nozzle with different degrees of swirl angle. The effects of hydrogen addition and swirl intensity on the combustion characteristics of pre-mixed methane flames were examined using particle image velocimetry (PIV), micro-thermocouples, various optical interference filters and gas analyzers to provide information about flow velocity, temperature distributions, and species concentrations of the reaction field. The results show that higher swirl intensity creates more recirculation flow, which reduces the temperature of the reaction zone and, consequently, reduces the thermal NO production. The distributions of flame radicals (OH, CH, C₂) are dependent more on the swirl intensity than the percentage of hydrogen added to methane fuel. The NO concentration at the upper part of the reaction zone is increased with an increase in hydrogen content in the fuel mixture because higher combustibility of hydrogen assists to promote faster chemical reaction, enabling more expansion of the gases at the upper part of the reaction zone, which reduces the recirculation flow. The CO concentration in the reaction zone is reduced with an increase in hydrogen content because the amount of C content is relatively decreased.