• Bulletin of the Korean Chemical Society
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• 제25권9호
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• pp.1346-1350
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• 2004

Pseudo-first order rate constants $(k_{obs})$ are reported for the following solvolyses in approximately isodielectric mixtures: 3- and 4-methoxybenzyl chloride, bromo- and chlorodiphenylmethane, and 4-chloro-, 4,4'-dichloro and 4-methyl-chlorodiphenylmethane in 0-80% v/v nitromethane-methanol mixtures; and bromo- and chlorodiphenylmethane and 4-methyl-chlorodiphenylmethane in various acetonitrile-methanol mixtures (in the range 0-50% v/v) at$25^{\circ}C.$ These data, and literature data for t-butyl halides (Cl, Br, and I), and for p-methoxybenzoyl chloride, show rate maxima in solvent compositions of ca. 30% aprotic cosolvent, explained by a stoichiometric solvent effect on electrophilic solvation. Linear relationships are observed between $(k_{obs})/[MeOH]^2$ and [AP]/[MeOH], where [AP] refers to the molar concentration of aprotic cosolvent. The results are consistent with competing third order contributions to $k_{obs}$, $k_{MM}[MeOH]^2$ with hydrogen-bonded methanol as electrophile, and $k_{MAP}[MeOH][AP]$ with hydrogen-bonding disrupted by the aprotic solvent.

• 공업화학
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• 제32권5호
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• pp.532-540
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• 2021

4-도데카노일옥시벤젠술폰산나트륨(sodium dodecanoyl-4-oxybenzenesulfonate; DOBS) 염은 저온에서도 효과적인 표백력과 살균력을 나타내는 물질이다. 본 연구에서는 물(W)-극성 비양자성 용매 계를 사용하는 알칼리 조건하에서 dodecanoyl chloride와 sodium 4-hydroxybenzene sulfonate로부터 DOBS의 온화하고 효율적인 합성방법을 조사하였다. 먼저 물만을 용매로 사용하고 온도 또는 시간을 변화시키며 반응한 결과, 수율은 30 ℃와 1 h 이상의 반응 조건에서 대부분 약 5% 정도로 낮게 나타났다. 효율적인 용매 계를 발견하기 위하여 극성 비양자성 용매의 종류를 변화시키며 물과 혼합하여 제조한 다양한 용매계에서 수율에 미치는 영향을 평가하였다. 수율은 아세톤(acetone; AC)과 물을 혼합한 용매 계에서 가장 우수하였으며, 온화한 반응조건(30 ℃, 1 h 및 상압)의 반응에서 약 82%의 높은 값을 나타냈다. 제조한 DOBS는 높은 표백력 및 살균력을 보여 표백활성화제로서 활용이 가능함을 확인하였다.

• Carbon letters
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• 제23권
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• pp.55-62
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• 2017

We report on the dispersion state of partially reduced graphene oxide (PRGO) in organic solvents, namely methyl ethyl ketone, ethyl acetate, methylene chloride, toluene, and xylene, by controlling the carbon to oxygen (C/O) atomic ratio of the PRGOs. A two-phase solvent exchange method is also proposed to transfer PRGO from water to an aprotic solvent, such as methyl ethyl ketone. We achieve relatively good dispersion in aprotic and non-polar solvents by controlling the C/O atomic ratio of the PRGOs and applying the two-phase solvent exchange method. There is an increase in the glass transition temperatures with the dispersion of PRGOs into amorphous polymers, in particular a $4.4^{\circ}C$ increase for poly(methyl methacrylate) and $3.0^{\circ}C$ increase for polycarbonate. Good dispersion of PRGO in a nonpolar polymer, such as linear low density polyethylene, is also obtained.

• Archives of Pharmacal Research
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• 제18권6호
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• pp.454-457
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• 1995

To improve the yield of genuine aglycones from glycosides, the conditions of alkaline hydrolysis were investigated, and a modified method was established. The modified method empolyed pyridine as an aprotic solvent. To complete the hydrolysis and obtain 20(S)-protopanaxadiol (1) and 20(S)-protopanaxatriol(2), which are the genuine aglycones of ginsenosides, total ginsenosides were refluxed with sodium methoxide in pyridine. Addition of methanol, a protic polar solvent to the reaction miuxture, led partial hydrolysis yielding a mixture of the genuine prosapogenols. Of the prosapogenols compound 3 and 6 characteristically possessed D-glucopyranosyl moiety attached at the sterically hindered C-20 hydroxyl group. 3 and 6 were not obtaijned by other hydrolysisw methods except by the soil bacterial hydrolysis.

• Bulletin of the Korean Chemical Society
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• 제4권1호
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• pp.55-57
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• 1983

• 대한화학회지
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• 제31권3호
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• pp.250-257
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• 1987

DMSO와 $H_2O$용매 중에서 결합구조가 밝혀진 동공의 크기를 달리한 토륨(IV) 착물들의 전기전도도를 측정하여 해리현상과 전해질의 행동을 알아 보고 DMSO용매중에서 polarography와 cyclic voltammography적 거동을 조사하여 합성착물의 산화환원반응 메카니즘, 가역성을 알아 보고 환원과정에 관여하는 전자수 및 착물의 확산계수를 계산하였다. 그 결과 반양성자성 용매에서 모든 착물들은 1:1전해질로, 물에서는 1:4전해질로 각각 행동하고, DMSO용매중에서 각 착물의 환원반응은 1전자 1단계의 환원반응으로 가역적이며 확산계수는 착물종에 따라 $5.831{\times}10^{-6}{\sim}6.900{\times}10^{-6}$이었다. 그리고 모든 착물의 물분자는 -1.8V(대조전극, SCE)이상에서 분해를 일으켜 수소기체를 발생한다.

• 대한화학회지
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• 제27권1호
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• pp.1-8
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• 1983

단일양성자성용매(메탄올, 에탄올, 1-프로판올)와 단일반양성자성용매(아세톤, 아세토니트릴, 아세토페논, 니트로벤젠) 및 이성분혼합용매계(메탄올-아세톤, 메탄올-아세토니트릴, 메탄올-벤젠)에서 염화나프탈렌술포닐과 피리딘의 친핵성치환반응에 미치는 용매효과를 전기전도도법으로 연구하였다. 단일양성자성용매의 반응속도상수는 유전상수가 큰 쪽에서 크게 관측되었고 반양성자성 용매의 반응속도상수는 유전상수가 큰 쪽에서 작게 나타났다. 아세토니트릴은 유전상수가 큰 반양성자성용매인데도 다른 반양성자성용매들보다 속도상수가 크게 관측되었다. 본 친핵성치환반응에서 용매효과는 ${\pi}^{\ast}$가 중요하고 염소이온의 이탈효과보다 수소결합형성이 전이상태를 안정화시키는데 기여함을 알 수 있었다.

• Elastomers and Composites
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• 제55권3호
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• pp.205-214
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• 2020

A series of wholly aromatic polyhyroxyamide (PHA) copolymers were prepared by direct polycondensation reaction of isophthalic acid and diacids containing bulky units with 3,3'-dihydroxybenzidine. The inherent viscosities of the PHAs measured at 35℃ in DMAc solution were in the range of 0.31-0.56 dL/g. The solubility study revealed that the PHAs were readily soluble in aprotic solvents such as, dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP) at room temperature and in less polar solvent such as pyridine. However, the polybenzoxazole (PBO) copoymers were quite insoluble in all organic solvents except partially soluble in concentrated sulfuric acid and partially soluble in NMP containing LiCl. The PBO copolymers showed maximum weight loss temperature in the range of 593-632℃ and high char yields in the range of 65.0-71.2% at 900℃ in a nitrogen atmosphere.

• Bulletin of the Korean Chemical Society
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• 제15권5호
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• pp.329-330
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• 1994

• Bulletin of the Korean Chemical Society
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• 제31권5호
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• pp.1199-1203
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for Michael-type reactions of 1-(X-substituted phenyl)-2-propyn-1-ones (2a-f) with a series of alicyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The $k_N$ value increases as the incoming amine becomes more basic and the substituent X changes form an electron-donating group (EDG) to an electron-withdrawing group (EWG). The Br${\o}$nsted-type plots are linear with ${\beta}_{nuc}$ = 0.48 - 0.51. The Hammett plots for the reactions of 2a-f exhibit poor correlations but the corresponding Yukawa-Tsuno plots result in much better linear correlations with ${\rho}$ = 1.57 and r = 0.46 for the reactions with piperidine while ${\rho}$ = 1.72 and r = 0.39 for those with morpholine. The amines employed in this study are less reactive in MeCN than in water for reactions with substrates possessing an EDG, although they are ca. 8 pKa units more basic in the aprotic solvent. This indicates that the transition state (TS) is significantly more destabilized than the ground state (GS) in the aprotic solvent. It has been concluded that the reactions proceed through a stepwise mechanism with a partially charged TS, since such TS would be destabilized in the aprotic solvent due to the electronic repulsion between the negative-dipole end of MeCN and the negative charge of the TS. The fact that primary deuterium kinetic effect is absent supports a stepwise mechanism in which proton transfer occurs after the rate-determining step.