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RISS 인기검색어
- 검색키워드
- 주제어 : alcohol-water mixtures (검색결과 2 건)
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알코올-물 혼합용매계에서 4-치환된 벤질 유도체의 반응성-선택성에 대한 반응속도 모델
For solvolyses of various benzyl substrates in ethanol-water (EW) and methanol-water (MW) mixtures, product selectivities (S) are reported for chlorides at 75 ˚C defined as follows using molar concentrations: S = ([ether product]/[alcohol product]) x ([water]/[alcohol solvent]). The results support earlier evidence that solvolyses of 4-nitrobenzyl substrates are S_(N)2 processes, which are not susceptible to mechanistic changes over the whole range of solvents from water to alcohol. S values at 25 and/or 45 ˚C in EW and MW, and additional kinetic data including kinetic solvent isotope effects (KSIE) are reported for solvolyses of 4-nitrobenzyl mesylate and tosylate. A kinetic model, explaining both rates and product, is proposed; a general medium effect due to solvent polarity is combined in one parameter with solvent effects on the nucleophilicity of the water and alcohol molecules acting as nucleophiles in S_(N)2 reactions. According to this model, as alcohol is added to water the rate of reaction decreases due to a decrease in solvent polarity, but the nucleophilicity of water increases relative to alcohol. The availability of experimental rate and product data over the whole range of solvent compositions from alcohol to water, reveals limitations of alternative approaches using activities.
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Determination of water content in alcohol mixture solvents using the 1H NMR chemical shift change
화학 공정 산업에서 유기용매에 함유된 수분 함량을 측정하는 것은 매우 중요한 과정이다. 칼 피셔 적정법과 가스 크로마토그래피 등을 활용하는 기존의 분석 방법은 측정을 수행하는 데 수분이 없는 조건, 상당한 시간을 필요로 한다. 이를 개선하기 위한 방법으로 수소 핵자기공명분광법의 화학적 이동 차이에 기반한 알코올 용매 내 수분 함량 분석법이 개발되었다. 본 연구에서는 수소 핵자기공명분광법의 화학적 이동 변화를 활용하여 각각 메탄올과 t-부탄올, 메탄올과 에탄올 혼합물의 수분 함량을 측정했다. 이를 통해 알코올 비율에 따라 수분 함량과 알코올 분자의 화학적 이동이 상관 관계를 보임을 확인하였다. 또한, 화학적 이동 변화를 이용하여 알코올 혼합 용매와 물 사이의 수소 결합의 경향성을 확인하였다. Determination of the water content in organic solvents is important in the chemical process industry. However, the widely used analytical methods such as Karl Fisher titration and gas chromatography require a significant amount of time or moisture-free conditions. Therefore, a simple method that relies on chemical shift difference between water and alcohol peaks in 1H NMR spectroscopy was developed for the determination of water content in alcohol solvents. This study observed the chemical shift changes in 1H NMR spectroscopy depending on water contents to test the feasibility of the method in alcohol-mixture solvents such as methanol-ethanol and methanol-t-butanol. The correlations between chemical shift change and water content with different alcohol ratios have been founded through the experimental results for alcohol mixtures. In addition, the chemical shift changes have shown the characteristic behaviors of hydrogen bonding between alcohol mixtures and water.
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