Dipartimento di Chimica Organica E. Paternò, Università degli Studi di Palermo, Viale delle Scienze-Parco d'Orleans II, 90128 Palermo, Italy.
J Org Chem. 2010 Jul 16;75(14):4828-34. doi: 10.1021/jo100914p.
The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solution led us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which was studied by means of spectrophotometric titration at 298 K. In order to evaluate the importance of electronic effect of the substituents present on the aromatic ring, both electron-withdrawing and -donor substituents were taken into account. Furthermore, to have a measure of the importance of the steric effect of the substituents both para- and ortho-substituted benzoic acids were analyzed. The probe reaction was studied in two ionic liquids differing for the ability of the cation to give hydrogen bond and pi-pi interactions, namely [bm(2)im][NTf(2)] and [bmpyrr][NTf(2)]. Data collected show that benzoic acids are less dissociated in ionic liquid than in water solution. Furthermore, the equilibrium constant values seem to be significantly affected by both the nature of ionic liquid cation and the structure of the acid. In particular, the ortho-steric effect seems to operate differently in water and in the aromatic ionic liquid, determining in this solvent medium a particular behavior for ortho-substituted benzoic acids.
需要衡量一些取代苯甲酸在离子液体溶液中的强度，这促使我们使用对硝基苯酚钠的质子化平衡作为探针反应，在 298 K 下通过分光光度滴定法进行研究。为了评估芳香环上取代基电子效应的重要性，我们考虑了吸电子和供电子取代基。此外，为了衡量取代基的空间效应的重要性，我们分析了对位和邻位取代苯甲酸。探针反应在两种离子液体中进行研究，这两种离子液体阳离子的氢键和π-π相互作用能力不同，分别为[bm(2)im][NTf(2)]和[bmpyrr][NTf(2)]。收集的数据表明，苯甲酸在离子液体中的解离程度低于在水溶液中的解离程度。此外，平衡常数值似乎受到离子液体阳离子的性质和酸的结构的显著影响。特别是，邻位空间效应在水中和芳香离子液体中的作用方式不同，在这种溶剂介质中，邻位取代苯甲酸表现出特殊的行为。
