Experimental and theoretical studies on solvation in aqueous solutions of ionic liquids carrying different side chains: the n-butyl-group versus the methoxyethyl group

Abstract

We used solvatochromic compounds to probe solvation in mixtures of water, W, and four ionic liquids (ILs), 1-R-3-methylimidazoliumX, where R ¼ n-butyl or methoxyethyl and X ¼ acetate and chloride; these are denoted as (C 4 MeImAc), (C 3 OMeImAc), (C 4 MeImCl), and (C 3 OMeImCl). Our aim was to investigate the effects on solvation when an ether linkage is substituted for a -CH 2group in the IL side chain. We used the solvatochromic probes 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (WB) and 5nitroindoline, 1-methyl-5-nitroindoline to determine the solvent polarity, E T (WB), and Lewis basicity, SB, respectively. From UV-Vis spectral data, we calculated E T (WB) as a function of the water mole fraction (c W ) at different temperatures; from 15 to 60 C for WB in IL-acetate-W; 25 C for SB and WB in ILchloride-W. For all IL-W mixtures, the dependence of E T (WB) on c W is non-linear and, surprisingly, shows negligible dependence on the nature of the side chain. Values of the SB of IL-W were higher for C 4 MeImX-W than for C 3 OMeImX. A rationale for these results is the deactivation of the ether oxygen due to the formation of intramolecular hydrogen bonds with the hydrogens of the imidazolium ring. Our hypothesis is confirmed by quantum chemistry and molecular dynamics calculations (energy of the conformers and radial distribution functions), density, and 1 H NMR data (chemical shifts, line widths). We attributed the non-linear dependence of the solvatochromic parameters on c W to preferential solvation of the dyes. We treated E T (WB) data with a model that includes the formation of the complex solvent IL-W. Equilibrium constants for solvent exchange in the solvation layer of WB were calculated; their values showed that IL-W is the most efficient solvent species present.

Cellulose in Ionic Liquids and Alkaline Solutions: Advances in the Mechanisms of Biopolymer Dissolution and Regeneration

“…This is done by performing cycles of "heating/cooling of the material" in the simulation box, followed by comparing certain MD-calculated properties, e.g., solution density or potential energy with those obtained in the first, or equilibration phase. Good agreement between these sets of parameters (before and after annealing) indicates reliable results [75,83].…”

“…To probe this hypothesis (deactivation of the H-bonding between the ether linkage and C2-H), ILs with C2-CH3 instead of C2-H were studied, namely, 1-butyl-2,3-dimethylimidazolium acetate (Figure 8c) and 1-(2-methoxyethyl)-2,3-dimethylimidazolium acetate (Figure 8d). Although this The lower efficiency of PrOMeImAcO was attributed to simultaneous "deactivation" of the ether oxygen (Lewis base) and C 2 -H (Lewis acid) of the imidazolium ring due to intramolecular hydrogen bonding, as shown in Figure 9, based on MD calculations [75]. The lower efficiency of PrOMeImAcO was attributed to simultaneous "deactivation" of the ether oxygen (Lewis base) and C2-H (Lewis acid) of the imidazolium ring due to intramolecular hydrogen bonding, as shown in Figure 9, based on MD calculations [75].…”

“…Although this The lower efficiency of PrOMeImAcO was attributed to simultaneous "deactivation" of the ether oxygen (Lewis base) and C 2 -H (Lewis acid) of the imidazolium ring due to intramolecular hydrogen bonding, as shown in Figure 9, based on MD calculations [75]. The lower efficiency of PrOMeImAcO was attributed to simultaneous "deactivation" of the ether oxygen (Lewis base) and C2-H (Lewis acid) of the imidazolium ring due to intramolecular hydrogen bonding, as shown in Figure 9, based on MD calculations [75]. To probe this hypothesis (deactivation of the H-bonding between the ether linkage and C2-H), ILs with C2-CH3 instead of C2-H were studied, namely, 1-butyl-2,3-dimethylimidazolium acetate (Figure 8c) and 1-(2-methoxyethyl)-2,3-dimethylimidazolium acetate (Figure 8d).…”

“…The colors used to denote the atoms are red, cyan, white, and navy blue for oxygen, carbon, hydrogen, and nitrogen, respectively. The distances between the atoms are (in nm) O···H-C 2 = 0.239 (A); O···H-C 2 = 0.468 ((B); open structure); O···H-C 5 -= 0.243 (C), reproduced from[75], with permission from RSC, 2017.…”

Binary mixtures of ionic liquids-DMSO as solvents for the dissolution and derivatization of cellulose: Effects of alkyl and alkoxy side chains

“…In a recent publication on solvation by aqueous solutions of C4MeImAc and C3OMeImAc, we attributed the dependence of solvatochromic parameters on the nature of the side-chain of C3OMeIm + to the formation of intramolecular hydrogen bonding between the ether oxygen with C2-H and C4-H of the imidazolium ring; the former is stronger, see Figure (de Jesus, Pires, Mustafa, Riaz, & El Seoud, 2017). This cycling behavior of C3OMeIm + -indicated by theoretical calculations-was corroborated with 1 H NMR spectroscopy (de Jesus, Pires, Mustafa, et al, 2017). Note that C4MeImAc is not subject to this side-chain/imidazolium ring hydrogen bonding.…”