Effects of water and methanol on the molecular organization of 1-butyl-3-methylimidazolium tetrafluoroborate as functions of pressure and concentration

Abstract

The structural organization in mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)])/water or methanol was studied by infrared spectroscopy. No drastic change in the concentration dependence of the alkyl C-H band frequency was observed at high concentration of the ionic liquid. This behavior indicates a clustering of the ionic liquid in alkyl regions. Nevertheless, the presence of methanol significantly perturbs the ionic liquid-ionic liquid associations in the imidazolium region. On the basis of the responses to change in pressure and concentration, two different types of O-H species, i.e., free O-H and bonded O-H, were observed in the O-H stretching region. For [bmim][BF(4)]/water mixtures, the compression leads to loss of the free O-H band intensity. It is likely that free O-H is switched to bonded O-H as high pressures are applied. For [bmim][BF(4)]/methanol mixtures, the free O-H is still stable under high pressures.

High Pressure Phase Behavior of Two Imidazolium-Based Ionic Liquids, [bmim][BF4] and [bmim][PF6]

“…The green nature of RTILs as solvent is difficult to evaporate, which prevents the pollution on environment. In another point of view, however, exactly because of the merit in RTILs, distillation through evaporation, which is an important approach to recycle and purity common organic solvents, cannot be applied to RTILs (Chang et al, 2008b;Su et al, 2010). Moreover, RTILs are very hazardous to the environment if they are released.…”

“…Generally, RTILs are classified into several groups depending on the cationic series, imidazolium, pyridinium, and alphatic quaternary ammonium series. Most of studies so far concern with the results at atmospheric pressure, but recently an increasing number of works using high pressure is reported (Chang et al, 2007(Chang et al, , 2008a(Chang et al, , 2008b(Chang et al, , 2008cSu et al, 2009Su et al, , 2010Umebayashi et al, 2009aUmebayashi et al, , 2009b. A merit of the use of high pressure as a varialbe is summarized as follows.…”

Probing Intermolecular Interactions in Ionic Liquid–Water Mixtures by Near‐Infrared Spectroscopy

“…[11] As we know, hydrogen bonding is best observed in IR or Raman spectra as vibrational spectroscopy is a very powerful tool to explore the structural and dynamic properties of the mixtures of ILs and water. Unfortunately, these studies are very limited, [22][23][24][25][26][27][28] in particular for research devote to the interaction of ILs-water in the water-rich region. This may be due to lack of a suitable technique that has non-invasive and in situ capabilities without any pretreatment of samples.…”

Vibrational Spectroscopy for Studying Hydrogen Bonding in Imidazolium Ionic Liquids and their Mixtures with Cosolvents

“…Moreover, this group was able to show that the vibrational modes of single water molecules dissolved in ILs are a viable probe for their polarity. Chang et al [34,35] analysed the structural organization in aqueous solutions of 1-butyl-3-methylimidazolium halides under high pressure. Their study elucidates that the imidazolium C--H groups seem to be more favourable sites for hydrogen bond formation compared with the C--H groups of the alkyl chains.…”