Absorption of Water by Room-Temperature Ionic Liquids: Effect of Anions on Concentration and State of Water

Abstract

Near-infrared (NIR) spectrometry was successfully used for the non-invasive and in situ determination of concentrations and structure of water absorbed by room-temperature ionic liquids (RTILs). It was found that RTILs based on 1-butyl-3-methylimidazolium, namely, [BuMIm]+ [BF4]-, [BuMIm]+ [bis((trifluoromethyl)sulfonyl)amide, or Tf2N]- and [BuMIm]+ [PF6]-, are hydroscopic and can quickly absorb water when they are exposed to air. Absorbed water interacts with the anions of the RTILs, and these interactions lead to changes in the structure of water. Among the RTILs studied, [BF4]- provides the strongest interactions and [PF6]- the weakest. In 24 hours, [Bu-MIm]+ [BF4]- can absorb up to 0.320 M of water, whereas [Bu-MIm]+ [PF6]- can only absorb 8.3 x 10(-2) M of water. It seems that higher amounts of water can be absorbed when the anion of the RTIL can strongly interact and hence stabilize absorbed water molecules by forming hydrogen bonds with them or inducing hydrogen bonds among water molecules. More importantly, the NIR technique can be sensitively used for the noninvasive, in situ determination of absorbed water in RTILs, without any pretreatment, and at limits of detection as low as 3.20 x 10(-3) M.

Raman Spectroscopy and Ab-Initio Model Calculations on Ionic Liquids

“…This was successfully demonstrated by use of near-infrared (NIR) spectrometry for determination of water absorbed in 1-butyl-3-methylimidazolium liquids. Among these [C 4 6 ] À ) anions interacted with water in decreasing order, and the interaction leads to changes in the structure and behavior of the water [74]. [77].…”

TTA solvation kinetics in the ionic liquid BumimTf2N

“…Second, in cyclohexane, the rather low viscosity (as compared to BumimTf 2 N) most probably favors de-correlation of the H 2 O---TTA pairs formed through k 1 readily after the keto-hydrate has dissociated, so that although viscosity is low, the overall equilibrium needs time to be reached in cyclohexane. Finally, it has been repeatedly mentioned by various authors that water may exist as clusters or nanodomains in ILs [10,17,22]. In such a case, the effective (i.e.…”

“…For all the solutions of this work, the water amount was adjusted by a rigorous degassing procedure, according to a previously published protocol [9], followed by addition of the required amount of ultra pure water, which was dissolved in the IL. The water amount in the BumimTf 2 N solutions of this work was measured taking advantage of the work of Tran and co-workers [10], extending the TTA, purchased from ACROS Organics (99.5%), was contacted with deionized water in slight excess for about one week in the dark and at room temperature. The solid obtained, after drying, was recrystallized from diethylether, and the white powder, characteristic of the hydrated keto form of TTA [11], was stored at 8 °C in the dark.…”

Study On The Structures And Interactions Binary System Composed By The Ionic Liquids [Bmim][Ala] and Water /Methanol Using The Vibrational Spectra

“…Among the various spectroscopic methods, infrared spectroscopy and Raman spectroscopy play important roles in investigations on the structural properties and interactions of ionic liquids [40][41][42][43]. Exploration of hydrogen-bonding systems in which solvation, considered as a series of equilibria, can be quantified offers an interesting opportunity to explore solvent effects in recognition at a molecular level by combining experiments and theoretical calculation.…”