Dipolarity versus Polarizability and Acidity versus Basicity of Ionic Liquids as a Function of Their Molecular Structures

Abstract

The four empirical solvent polarity parameters according to the Catalán scale--solvent acidity (SA), solvent basicity (SB), solvent polarizability (SP), and solvent dipolarity (SdP)--of 64 ionic liquids (ILs) were determined by the solvatochromic method. The SA parameter was determined solely by using [Fe(II)(1,10-phenanthroline)2(CN)2] (Fe), the SB parameter by using the pair of structurally comparable dyes 3-(4-amino-3-methylphenyl)-7-phenylbenzo[1,2-b:4,5-b']difuran-2,6-dione (ABF) and 3-(4-N,N-dimethylaminophenyl)-7-phenylbenzo[1,2-b:4,5-b']-difuran-2,6-dione (DMe-ABF), and the SP and SdP parameters by using the homomorphic pair of 4-tert-butyl-2-(dicyanomethylene)-5-[4-(diethylamino)benzylidene]-Δ(3)-thiazoline (Th) and 2-[4-(N,N-dimethylamino)benzylidene]malononitrile (BMN). The separation of SP and SdP for a set of 64 various ILs was performed for the first time. Correlation analyses of SP with physicochemical data related to ionization potentials of anions of ILs as well as with theoretical data show the correctness of the applied method. The found correlations of the Catalán parameters with each other and with the alkyl-chain length of 1-alkyl-3-methylimidazolium-type ILs gives new information about interactions within ILs. An analytical comparison of the determined Catalán parameters with the established Kamlet-Taft parameters and the Gutmann acceptor and donor numbers is also presented.

Hydrogen-bond acidity of ionic liquids: an extended scale

“…13,23,32,38,50 Furthermore, for the cyclic-based ILs with the same number of carbon atoms in the alkyl chains, the predicted α values follow the expected trend: 1-alkyl-3-methylimidazolium > 1,3-dialkylimidazolium ~ 1-alkylpyridinium > 1-alkyl-1-methylpyrrolidinium > 1-alkyl-1-methylpiperidinium. For the non-cyclic cations, ammonium-based ILs are more acidic than the phosphonium-based fluids.…”

“…In addition, the prediction results concerning the influence of the alkyl side chain length on the hydrogen-bond donor strength of the IL cation are consistent with the experimental data, as well as with data published by other authors. 13,23,32,38,50 The variety of cations used, along with the high variability of α values (between 0.235 and 0.820), guarantees the widespread application of eqn (10), and further validates the a priori cation-anion interaction energy descriptors for the prediction of the hydrogen-bond donor ability of ILs.…”

“…S1 in the ESI, † the α values of 1-methyl-3-alkylimidazoliumbased ILs obtained in this work are in close agreement with those reported by Fredlake and co-workers 40 and Mellein and co-workers, 38 and are lower than those reported by Spange and co-workers. 13,23,34 However, and in general, a closer inspection of Fig. S1 in the ESI † clearly evidences high discrepancies on the reported α values between various researchers, this being an indication on the need for developing a generalized and coherent polarity scale.…”

“…13,15,17,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][47][48][49][50][51] It should be highlighted that the hydrogen-bond acceptor strength of an IL is dominated by its anion while the hydrogen-bond donor ability is essentially controlled by the cation and only slightly depends upon the anion of the IL. 18,19 Thus, and since we were focused on developing an extended series for the hydrogen-bond acidity of ILs, ILs comprising a fixed anion ([NTf 2 ] − ) and a wide range of cations (imidazolium-, pyridinium-, piperidinium-, pyrrolidinium-, ammonium-, sulfonium-, and phosphonium-based) were selected.…”

Physicochemical Properties of Proteomic Ionic Liquids Matrices for MALDI-MS

“…The values depend on the solvent properties and their interactions [21]. It has been reported that polarizability of RTILs reduce viscosity and increase ionic diffusion [19,[22][23][24].…”