Cellulose is the most abundant biorenewable material, with a long and well-established technological base. 1 Derivitized products have many important applications in the fiber, paper, membrane, polymer, and paints industries.Cellulose consists of polydisperse linear glucose polymer chains ( Figure 1) which form hydrogen-bonded supramolecular structures; 2 cellulose is insoluble in water and most common organic liquids. The growing willingness to develop new cellulosic materials results from the fact that cellulose is a renewable resource, although many of the technologies currently used in cellulose processing are decidedly nongreen. 3 For example, viscose rayon is prepared from cellulose xanthate (production over 3,000,000 tons per year) utilizing carbon disulfide as both reagent and solvent. Most recently, processes using more environmentally acceptable nonderivitizing solvents (N-methylmorpholine-N-oxide (NMNO) and phosphoric acid) have been commercialized. Solvents are needed for dissolution that enable homogeneous phase reactions without prior derivitization. 4 Graenacher 5 first suggested in 1934 that molten N-ethylpyridinium chloride, in the presence of nitrogen-containing bases, could be used to dissolve cellulose; however, this seems to have been treated as a novelty of little practical value since the molten salt system was, at the time, somewhat esoteric and has a relatively high melting point (118°C). We were interested in examining whether other solvents that would now be described as ionic liquids (ILs) 6 would dissolve cellulose and, especially, whether the availability of a wide and varied range of ILs, coupled with the current understanding of their solvent properties, 7 would allow flexibility and control in the processing methodology, with increased solution efficiency and reduction or elimination of undesirable solvents.Ionic liquids, containing 1-butyl-3-methylimidazolium cations ([C 4 mim] + ) were screened with a range of anions, from small, hydrogen-bond acceptors (Cl -) to large, noncoordinating anions ([PF 6 ] -) also including Br -, SCN -, and [BF 4 ] -. In addition, variations in cation alkyl-substituent from butyl through octyl were investigated for the chloride salts. Dissolution experiments were carried out using cellulose-dissolving pulps (from cellulose acetate, lyocell, and rayon production lines), fibrous cellulose (Aldrich), and Whatman cellulose filter papers. The cellulose samples were added to the ionic liquids without pretreatment, in glass vials, and heated without agitation on a heating plate or in a domestic microwave oven. Table 1 summarizes the results obtained using high MW dissolving pulp (DP ≈ 1000). Stirring cellulose in the ILs under ambient conditions did not lead to dissolution, although the cellulose fibers were wetted by the ILs. However, on heating to 100-110°C , cellulose slowly dissolved in the Cl --, Br --, and SCN --containing ILs to yield increasingly viscous solutions.Dissolution rates could be significantly improved by heating in a microwave oven. ...

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Hydrophilic ionic liquids can be salted-out and concentrated from aqueous solution upon addition of kosmotropic salts forming aqueous biphasic systems as illustrated by the phase behavior of mixtures of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and K3PO4.

A series of novel hexafluorophosphate salts, based on N,N¾-dialkylimidazolium and substituted N-alkylpyridinium cations, display liquid crystalline behaviour at temperatures above their melting point. The temperature range over which liquid crystalline behaviour is observed increases markedly with increasing alkyl chain length. Alkyl substitution at the 3- and 4-positions on the pyridinium ring results in a decrease in the melting point compared with the equivalent unsubstituted salt, but also leads to a large decrease in the tendency towards liquid crystalline behaviour (or mesogenicity). The salts prepared are fully characterised using a wide variety of techniques, including NMR and IR spectroscopy, DSC, and single crystal X-ray diffraction in the case of 1-dodecyl-3-methylimidazolium hexafluorophosphate. The effect of preparing mixtures containing different proportions of two cations is also reported

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The model room temperature ionic liquid, 1,3-dimethylimidazolium chloride, has been studied by neutron diffraction for the first time. The diffraction data are used to derive a structural model of this liquid using Empirical Potential Structure Refinement. The model obtained indicates that significant charge ordering is present in the liquid salt and that the local order in this liquid closely resembles that found in the solid state. As in the crystal structure, hydrogen-bonding interactions between the ring hydrogens and the chloride dominate the structure. The model is compared with the data reported previously for both simple alkyl substituted imidazolium halides and binary mixtures with AlCl3.

A series of long-chain 1-alkyl-3-methylimidazolium salts ([C n -mim]X, n ) 12-18) containing the anions, chloride, bromide, trifluoromethanesulfonate (OTf), and bis(trifluoromethanesulfonyl)imide (TFI), have been synthesized and characterized. The salts have amphiphilic characteristics, and the thermotropic phase behavior of these salts and the analogous tetrafluoroborate salt has been investigated by variable temperature small-angle X-ray scattering, polarizing optical microscopy, and differential scanning calorimetry. The salts form lamellar, sheetlike arrays in the crystalline phase and an enantiomeric smectic liquid crystalline phase at higher temperatures, except for the salts containing the bis(trifluoromethanesulfonyl)imide anion which melt directly to form isotropic liquids. The nature of the anion influences the size of the interlayer spacing in both the crystal and in the mesophase. The interlayer spacing in the mesophase is largest for the anions with the greatest ability to form a three-dimensional hydrogen-bonding lattice, following the order [TFI] -< [OTf] -< [BF 4 ] -< Br -< Cl -.

New low-cost ionic liquids containing methyl-and ethyl-sulfate anions can be easily and efficiently prepared under ambient conditions by the reaction of 1-alkylimidazoles with dimethyl sulfate and diethyl sulfate. The preparation and characterization of a series of 1,3-dialkylimidazolium alkyl sulfate and 1,2,3-trialkylimidazolium alkyl sulfate salts are reported. 1,3-Dialkylimidazolium salts containing at least one non-methyl N-alkyl substituent are liquids at, or below room, temperature. Three salts were crystalline at room temperature, the single crystal X-ray structure of 1,3-dimethylimidazolium methyl sulfate was determined and shows the formation of discrete ribbons comprising of two anion-cation hydrogen-bonded chains linked via intra-chain hydrogen-bonding, but little, or no inter-ribbon hydrogen-bonding. The salts are stable, water soluble, inherently 'chloride-free', display an electrochemical window of greater than 4 V, and can be used as alternatives to the corresponding halide salts in metathesis reactions to prepare other ionic liquids including 1-butyl-3-methylimidazolium hexafluorophosphate.