Ionic liquids are a fascinating class of novel solvents, which are attracting attention as possible 'green' alternative to volatile molecular organic solvents to be applied in catalytic and organic reactions and electrochemical and separation processes. Over 200 room temperature ionic liquids are known but for most of them physico-chemical data are incomplete or lacking. Furthermore, despite the incredible number of potential ionic liquids (evaluated as > 10(14)), generally only a few imidazolium-based salts are used in synthesis. Moreover, most of the data reported to date were focused on the effect that these new solvents have on chemical reaction products; only a few reports evidence the effect on reaction mechanisms or rate or equilibrium constants. In this review, the physico-chemical properties of the most used ionic liquids, that are relevant to synthesis, are discussed and a decided emphasis is placed on those properties that most clearly illuminate the ability of ionic liquids to affect the mechanistic aspects of some organic reactions. Copyright (c) 2004 John Wiley & Sons, Ltd
Electrospray ionization mass spectrometry applied to ionic liquids allowed the study of loosely bonded supramolecules, originating from these organic salts. Based on the observation that ionic liquids formed cationic [C(q+1)X(q)](+) and anionic [C(q)X(q+1)](-) supramolecular aggregates, we have investigated mixed networks, formed by different cations coordinated to a selected anion or by different anions bonded to a given cation, i.e., [C1...X...C2](+) and [X1...C...X2](-), with the aim to build a scale of the cation-anion interaction strength. The qualitative order of intrinsic bond strength to Br- was found to be the following: [emim](+) > [bmim](+) > [mor1,2](+) > [hmim]+ > [omim](+) > [mor1,4](+) > [bupy](+) > [bpyrr](+) > [picol](+) > [bm(2)im](+) > [TBA](+). Similarly, the interaction energies to 1-butyl-3-methylimidazolium (bmim) species envisaged two classes of anions: species tightly coordinated to the cationic moiety that include CF3COO(-), Br(-), N(CN)2(-), and BF4(-) and anions loosely interacting with the alkylimidazolium species such as OTf(-), PF6(-), and Tf2N(-).
The kinetics of water vapour sorption by several anhydrous hydrophobic and hydrophilic ionic liquids (ILs) were gravimetrically determined at 25 degrees C and two levels of humidity, namely 43 and 81%. A simple equation was used to fit the data. The kinetic parameters obtained from the different ILs were compared and the differences were related to the IL structures. Results showed that even hydrophobic ILs absorb water at an unexpected speed
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