SN2 fluorination reactions in ionic liquids: a mechanistic study towards solvent engineering |
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Authors: | Oh Young-Ho Jang Hyeong Bin Im Suk Song Myoung Jong Kim So-Yeon Park Sung-Woo Chi Dae Yoon Song Choong Eui Lee Sungyul |
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Institution: | Department of Applied Chemistry, Kyunghee University, Yongin, Gyeoggi 446-701, Korea. |
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Abstract: | In the catalysis of S(N)2 fluorination reactions, the ionic liquid anion plays a key role as a Lewis base by binding to the counterion Cs(+) and thereby reducing the retarding Coulombic influence of Cs(+) on the nucleophile F(-). The reaction rates also depend critically on the structures of ionic liquid cation, for example, n-butyl imidazolium gives no S(N)2 products, whereas n-butylmethyl imidazolium works well. The origin of the observed phenomenal synergetic effects by the ionic liquid mim-(t)OH]OMs], in which t-butanol is bonded covalently to the cation mim], is that the t-butanol moiety binds to the leaving group of the substrate, moderating the retarding interactions between the acidic hydrogen and F(-). This work is a significant step toward designing and engineering solvents for promoting specific chemical reactions. |
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