翻訳と辞書 Words near each other ・ Shi (kana) ・ Shi (personator) ・ Shi (poetry) ・ Shi (surname) ・ Shi Bao ・ Shi Bao (Water Margin) ・ Shi Chaoyi ・ Shi Chonggui ・ Shi Dakai ・ Shi Dan ・ Shi De Yang ・ Shi Deru ・ Shi Dongpeng ・ Shi Dongshan ・ Shi En ・ Shi epoxidation ・ Shi Er Sheng Xiao Cheng Shi Ying Xiong ・ Shi Family Grand Courtyard ・ Shi Fangjing ・ Shi Feng ・ Shi Guangnan ・ Shi Guangsheng ・ Shi Guihong ・ Shi Hairong ・ Shi Haoran ・ Shi Hengxia ・ Shi Hong ・ Shi Hongjun ・ Shi Hu ・ Shi Hu (artist) Dictionary Lists mini英和辞書 mini和英辞書 Webster 1913 Latin-English FOLDOC Wikipedia English ウィキペディア

翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Shi epoxidation ： ウィキペディア英語版 Shi epoxidation The Shi epoxidation is a chemical reaction described as the asymmetric epoxidation of alkenes with oxone (potassium peroxymonosulfate) and a fructose-derived catalyst (1). This reaction is thought to proceed via a dioxirane intermediate, generated from the catalyst ketone by oxone (potassium peroxymonosulfate). The addition of the sulfate group by the oxone facilitates the formation of the dioxirane by acting as a good leaving group during ring closure. It is notable for its use of a non-metal catalyst. The reaction was first discovered by Yian Shi, of Colorado State University in 1996. == Brief Historical Background == Many attempts at the synthesis of an efficient non-metal catalyst were made before one was discovered. The problem with previous catalysts was the rapid decomposition/oxidation of the dioxirane intermediate and lack of electrophilicity of the reactive ketone. Aromatic ketones were proposed, and many subsequent variations of oxoammoniumsalts were used, but were ineffective in promoting epoxidation because of the oxidative instability of the amide groups and high flexibility of the seven-membered rings. Enantioselectivity of these early catalysts were also lowered because of large distances between the asymmetric subunits and reaction centers, yielding less than 10 percent in enantiomeric excess. The catalyst discovered by Yian Shi's group in 1996 was derived from D-fructose, and has a stereogenic center close to the reacting center (ketone)- the rigid six-membered ring structure of the catalyst and adjacent quaternary ring group minimizes epimerization of this stereocenter. Oxidation by the active dioxirane catalyst takes place from the si-face, due to steric hindrance of the opposing re-face. This catalyst functions efficiently as an asymmetric catalyst for unfunctionalized trans-olefins. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shi epoxidation」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.