Physical Chemistry Division, National Chemical Laboratory, Pune 411 008, India.
Phys Chem Chem Phys. 2012 Feb 28;14(8):2754-61. doi: 10.1039/c2cp23256a. Epub 2012 Jan 23.
Polarity studies in two classes of imidazolium-based protic ionic liquids (PILs) possessing HSO(4), HCOO, CH(3)COO and CH(3)CH(2)COO anions were carried out using a solvatochromic method from 298.15 to 353.15 K. For 1-methylimidazolium class of PILs, E(T)(30) was found to be independent over the entire range of temperature, while E(T)(30) was noted to decrease with a rise in temperature in the case of 1-butylimidazolium class of PILs containing CH(3)COO and CH(3)CH(2)COO anions. The E(T)(30) value decreases in both the classes upon varying the anions (HSO(4), HCOO, CH(3)COO and CH(3)CH(2)COO). The E(T)(30) value is controlled by hydrogen bond acceptor basicity, β, and dipolarity/polarizability, π*. The E(T)(30) value for PILs varies inversely to the strength of the coulombic interaction between ions in PILs. Strong interactions between ions lead to lower E(T)(30) values. Unlike the poor thermal effect on E(T)(30), the Kamlet-Taft parameters i.e. α, β and π* have pronounced thermal effect in the imidazolium-based PILs. Variation in the Kamlet-Taft parameters is controlled by the stabilization of ions and the degree of proton transfer from Brønsted acid to Brønsted base.
两类分别含 HSO(4)、HCOO、CH(3)COO 和 CH(3)CH(2)COO 阴离子的咪唑基质子离子液体 (PILs) 的极性研究，是在 298.15 至 353.15 K 温度范围内，通过溶致变色法进行的。对于 1-甲基咪唑基 PILs，E(T)(30)在整个温度范围内是独立的，而对于含 CH(3)COO和 CH(3)CH(2)COO阴离子的 1-丁基咪唑基 PILs，E(T)(30)随温度升高而降低。改变阴离子(HSO(4)、HCOO、CH(3)COO和 CH(3)CH(2)COO)时，两类 PILs 的 E(T)(30)值均降低。E(T)(30)值受氢键给体碱性 β 和偶极矩/极化率 π控制。PILs 的 E(T)(30)值与 PILs 中离子间库仑相互作用的强度成反比。离子间的强相互作用导致较低的 E(T)(30)值。与 E(T)(30)受温度影响较小不同，Kamlet-Taft 参数（即 α、β 和 π）在咪唑基 PILs 中受温度影响显著。Kamlet-Taft 参数的变化受离子稳定化和质子从布朗斯特酸向布朗斯特碱转移程度的控制。
