Dichiarante Valentina, Betti Cecilia, Fagnoni Maurizio, Maia Angelamaria, Landini Dario, Albini Angelo
Department of Organic Chemistry, University of Pavia, Via Taramelli 10, 27100 Pavia, Italy.
Chemistry. 2007;13(6):1834-41. doi: 10.1002/chem.200601078.
The triplet N,N-dimethylaminophenyl cation, a highly reactive but chemospecific electrophile, has been used as a probe for characterizing the properties of reaction media for a series of imidazolium ILs. With the N-hexyl-N-methyl imidazolium derivatives (not with the N-butyl analogues), hydrogen transfer leading to the aniline was the main process. Trapping by iodide occurred with an inverse dependence on viscosity. Trapping by pi nucleophiles exhibited a more complex behavior. This was explained by the effect of both the bulk viscosity and the structure of the IL cation on both steps of the reaction, namely, initial electrophilic attack and ensuing cation elimination or nucleophile addition. However, with an excellent nucleophile, such as thiophene, or when the latter step was intramolecular, as with 4-pentenol, the difference was obliterated and trapping became uniform. Incorporation of the probe into the IL cation (through insertion into the C--H bond alpha to the imidazolium ring) was demonstrated, while no addition to the anion tested (including bis(trifluoromethanesulfonimide)) took place.
三联体N，N-二甲基氨基苯基阳离子是一种高活性但具有化学特异性的亲电试剂，已被用作表征一系列咪唑鎓离子液体反应介质性质的探针。对于N-己基-N-甲基咪唑鎓衍生物（而非N-丁基类似物），导致生成苯胺的氢转移是主要过程。碘离子的捕获与粘度呈反比。π亲核试剂的捕获表现出更复杂的行为。这是由于离子液体阳离子的体积粘度和结构对反应的两个步骤，即初始亲电攻击以及随后的阳离子消除或亲核试剂加成均产生了影响。然而，对于优异的亲核试剂，如噻吩，或者当后一步是分子内反应时，如4-戊烯醇的情况，这种差异就消失了，捕获变得一致。已证明探针会并入离子液体阳离子中（通过插入咪唑鎓环α位的C-H键），而未发生对所测试阴离子（包括双（三氟甲磺酰）亚胺）的加成反应。
