The effect of water content on room-temperature ionic liquids (RTILs) was studied by Karl Fischer titration and cyclic voltammetry in the following ionic liquids: tris(P-hexyl)tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P14,6,6,6][NTf2], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [C4mpyrr][NTf2], 1-hexyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate [C6mim][FAP], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4mim][NTf2], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4dmim][NTf2], N-hexyltriethylammonium bis(trifluoromethylsolfonyl)imide [N6,2,2,2][NTf2], 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6], 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim][NTf2], 1-butyl-3-methylimidazolium tetrafluoroborate [C4mim][BF4], 1-hexyl-3-methylimidazolium iodide [C4mim][I], 1-butyl-3-methylimidazolium trifluoromethylsulfonate [C4mim][OTf], and 1-hexyl-3-methylimidazolium chloride [C6mim][Cl]. In addition, electrochemically relevant properties such as viscosity, conductivity, density, and melting point of RTILs are summarized from previous literature and are discussed. Karl Fisher titrations were carried out to determine the water content of RTILs for vacuum-dried, atmospheric, and wet samples. The anion in particular was found to affect the level of water uptake. The hydrophobicity of the anions adhered to the following trend: [FAP]− > [NTf2]− > [PF6]− > [BF4]− > halides. Cyclic voltammetry shows that an increase in water content significantly narrows the electrochemical window of each ionic liquid. The electrochemical window decreases in the following order: vacuum-dried > atmospheric > wet at 298 K > 318 K > 338 K. The anodic and cathodic potentials vs ferrocene internal reference are also listed under vacuum-dried and atmospheric conditions. The data obtained may aid the selection of a RTIL for use as a solvent in electrochemical applications.

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 -.

The electrochemical reduction of oxygen is reported in four room temperature ionic liquids (RTILs) based on quaternary alkyl -onium cations and heavily fluorinated anions in which the central atom is either nitrogen or phosphorus. Data were collected using cyclic voltammetry and potential step chronoamperometry at gold, platinum, and glassy carbon disk electrodes of micrometer dimension under water-free conditions at a controlled temperature. Analysis via fitting to appropriate theoretical equations was then carried out to obtain kinetic and thermodynamic information pertaining to the electrochemical processes observed. In the quaternary ammonium electrolytes, reduction of oxygen was found to occur reversibly to give stable superoxide, in an analogous manner to that seen in conventional aprotic solvents such as dimethyl sufoxide and acetonitrile. The most significant difference is in the relative rate of diffusion; the diffusion coefficients of oxygen in the RTILs are an order of magnitude lower than in common organic solvents, and for superoxide these values are reduced by a further factor of 10. In the quaternary phosphonium ionic liquids, however, more complex voltammetry is observed, akin to that expected for the reduction of oxygen in acidified organic media. This is shown to be consistent with the occurrence of a proton abstraction reaction between the electrogenerated superoxide and quaternary alkyl phosphonium cations following the initial electron transfer.