Nucleophilicity in ionic liquids. 3. Anion effects on halide nucleophilicity in a series of 1-butyl-3-methylimidazolium ionic liquids.
Nucleophilicity in ionic liquids. 3. Anion effects on halide nucleophilicity in a series of 1-butyl-3-methylimidazolium ionic liquids.
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DOI：
10.1021/jo049636p
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发表时间：
2004-08
期刊：
影响因子：
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通讯作者：
N. Lancaster;T. Welton
中科院分区：
文献类型：
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作者：
N. Lancaster;T. Welton
我们继续研究离子液体中卤化物的亲核性，重点研究当阳离子为 [bmim](+) 时改变阴离子 ([BF(4)](-)、[PF(6)](-)、[SbF(6)](-)、[OTf](-) 和 [N(Tf)(2)](-)) 的影响（其中 bmim = 1-丁基-3-甲基咪唑鎓)。发现所有卤化物的亲核性在所有离子液体中均低于在二氯甲烷中。改变阴离子会影响卤化物亲核性的顺序，例如，在[bmim][BF(4)]中，亲核性顺序为Cl(-)>Br(-)>I(-)，而在[bmim][N(Tf)(2)]中，亲核性顺序为Cl(-)<Br(-)<I(-)。还发现每种离子液体中每种卤化物的亲核性不同，[bmim][BF(4)]中氯化物的亲核性几乎是[bmim][SbF(6)]中的四倍。类似地，溴化物在[bmim][BF(4)]中的亲核性是[bmim][PF(6)]中的四倍多。测量了每种离子液体中氯化物反应的活化参数 DeltaG++、DeltaH++ 和 DeltaS++，以及 [bmim][BF(4)] 和 [bmim][PF(6)] 中溴化物反应。这些数据还相互比较，并与二氯甲烷中的类似反应进行比较（其中这些参数已针对自由离子和离子对进行了估计）。这些研究表明，由于离子液体内的溶剂-溶质相互作用，离子液体中的反应具有高活化自由能垒。对这些相互作用进行了描述和讨论。
We have continued the study of halide nucleophilicity in ionic liquids, concentrating on the effect of changing the anion ([BF(4)](-), [PF(6)](-), [SbF(6)](-), [OTf](-), and [N(Tf)(2)](-)) when the cation is [bmim](+) (where bmim = 1-butyl-3-methylimidazolium). It was found that the nucleophilicities of all the halides were lower in all of the ionic liquids than in dichloromethane. Changing the anion affected the order of halide nucleophilicity, e.g., in [bmim][BF(4)] the order of nucleophilicity was Cl(-)>Br(-)>I(-) while in [bmim][N(Tf)(2)] the order was Cl(-)<Br(-)<I(-). It was also found that the nucleophilicity of each halide was different in each ionic liquid, with chloride being almost four times as nucleophilic in [bmim][BF(4)] as in [bmim][SbF(6)]. Similarly bromide was more than four times as nucleophilic in [bmim][BF(4)] as in [bmim][PF(6)]. The activation parameters DeltaG++, DeltaH++, and DeltaS++ have been measured for the reaction of chloride in each of the ionic liquids, plus the reaction of bromide in [bmim][BF(4)] and [bmim][PF(6)]. These data were also compared to each other as well as to a similar reaction in dichloromethane (where these parameters have been estimated for both the free ion and the ion-pair). These studies show that the reaction in the ionic liquids has a high activation free energy barrier, due to the solvent-solute interactions within the ionic liquids. These interactions are described and discussed.