Keith E. Johnson

Electrochemistry of 1-Butyl-3-methyl-1H-imidazolium Tetrafluoroborate Ionic Liquid

The electrochemistry of l-butyl-3-methyl-1H-imidazolium tetrafluoroborate (BmimBF 4 ) ionic liquid was investigated by cyclic voltammetry and Osteryoung square wave voltammetry. Impurity chloride was identified, its concentration was determined and a way to eliminate it was demonstrated. Constant current electrolysis of BmimBF 4 was performed and products were analyzed by 1 H, 13 C, and 19 F-NMR and gas chromatography-mass spectrometry. BF 3 and fluorocarbons are produced at the anode while Bmim + undergoes dimerization and dealkylation reactions at the cathode after reduction to a carbene.

Brønsted acidity and the medium: fundamentals with a focus on ionic liquids.

Fundamental aspects of Brønsted acidity in ionic liquid systems, in relation to those of simple protic molecules in the gas phase, pure protic molecules in the condensed phase and solutions of protic molecules in molecular systems, are presented. The variety of acidities possible, beyond those observed in aqueous systems, is emphasised and discussed in terms of differences of solvent levelling, ionisation, dissociation, homo-/hetero-conjugate ion speciation and the stabilisation of proton-transfer products from solvent to solvent. It is argued that data regarding aqueous systems do not necessarily explain acid/base behaviour in other liquids satisfactorily. Methods of measuring acidity are reviewed, particularly by spectrophotometry and electrochemistry and recommendations proffered for estimating speciation and acidity of ionic liquids of various complexities.

Composition and electronic spectra of some dimethyl sulfoxide complexes of transition metal ions

Abstract The dimethyl sulfoxide complexes of Cr(III), Mn(II) Mn(III), Fe(III), Co(II), Ni(II) and Cu(II) were obtained as their perchlorates and characterized by thorough chemical analysis and measurements of electronic spectra. The complexes are liable to incorporate extra dimethyl sulfoxide and perchloric acid beyond the composition M(DMSO)6(ClO4)n. Dimethyl sulfoxide is comparable to urea regarding its spectrochemical and nephelauxetic strength

The origin of the conductivity maximum in molten salts. I. Bismuth chloride

A new theory is presented to explain the conductivity maxima of molten salts (versus temperature and pressure). In the new theory, conductivity is due to ions hopping from counterion to counterion, and its temperature dependence can be explained with an ordinary Arrhenius equation in which the frequency prefactor A (for hopping opportunities) and activation energy E(a) (for hopping) are density dependent. The conductivity maximum is due to competing effects: as density decreases, the frequency of opportunities for hopping increases, but the probability that an opportunity is successfully hopped decreases due to rising E(a) caused by the increased hopping distance. The theory is successfully applied to molten bismuth (III) chloride, and supported by density-functional based molecular dynamics simulations which not only reproduce the conductivity maximum, but disprove the long-standing conjecture that this liquid features an equilibrium between BiCl(3) molecules, and BiCl(2)(+) and BiCl(4)(-) ions that shifts to the left with increasing temperature.

The origin of the conductivity maximum in molten salts. II. SnCl2 and HgBr2

The phenomenon of electrical conductivity maxima of molten salts versus temperature during orthobaric (closed-vessel) conditions is further examined via ab initio simulations. Previously, in a study of molten BiCl3, a new theory was offered in which the conductivity falloff at high temperatures is due not to traditional ion association, but to a rise in the activation energy for atomic ions hopping from counterion to counterion. Here this theory is further tested on two more inorganic melts which exhibit conductivity maxima: another high-conducting melt (SnCl2, σmax = 2.81 Ω(-1) cm(-1)) and a low-conducting one (HgBr2, σmax = 4.06 × 10(-4) Ω(-1) cm(-1)). First, ab initio molecular dynamics simulations were performed and again appear successful in reproducing the maxima for both these liquids. Second, analysis of the simulated liquid structure (radial distributions, species concentrations) was performed. In the HgBr2 case, a very molecular liquid like water, a clear Grotthuss chain of bromide transfers was observed in simulation when seeding the system with a HgBr(+) cation and HgBr3 (-) anion. The first conclusion is that the hopping mechanism offered for molten BiCl3 is simply the Grotthuss mechanism for conduction, applicable not just to H(+) ions, but also to halide ions in post-transition-metal halide melts. Second, it is conjectured that the conductivity maximum is due to rising activation energy in network-covalent (halide-bridging) melts (BiCl3, SnCl2, PbCl2), but possibly a falling Arrhenius prefactor (collision frequency) for molecular melts (HgBr2).

Electrochemical and spectroscopic studies of Solochrome Violet RS

Abstract A new peak for the reduction of Solochrome Violet RS (SVRS) was found by using differential pulse polarography at temperatures below 10°C. To elucidate the electrode reaction mechanism for the reduction of SVRS, UV-visible spectroscopy and other electrochemical techniques have also been used. Although the disproportionation of the hydrazo intermediate, intramolecular hydrogen bonding, protonation or deprotonation, and aggregation could make the SVRS system very complicated, the most likely explanation for the appearance of the low temperature peak is the azo/hydrazone tautomeric equilibrium. The important role of the adsorption of SVRS on the mercury electrode has also been emphasized.

Cyclic voltammetry of Li2S, FeS and FeS2 in LiCl−KCl eutectic melt

Abstract Cyclic voltammetric studies of lithium sulfide, iron sulfide and iron disulfide in molten LiCl−KCl indicate several stages in the redox chemistry of sulfur and iron. The reactions postulated for sulfide ion are 2 S 2 − → − 2 e S 2 2 − → − e S 2 − → − e S 2 and 2 S 2 − → − e S 2 3 − → − e S 2 2 − The electrode reactions for the iron sulfides include the simple Fe S 2 → e Fe S 2 − , Fe S 2 → − e F e 2 + + S 2 − 2 FeS → − e Fe S 2 − + F e 2 + and F e 2 + → − e F e 3 + as well as the reduction of J and X phases formed by complex chemical reactions. Thermodynamic calculations of electrode potentials were useful in the assignment of voltammetric peaks to given processes.

Determination of barium at ng ml−1 levels by flame emission spectrometry after ion-exchange separation from 1000-fold amounts of calcium

Abstract Atomic spectrometric techniques for the determination of ng ml −1 levels of barium in the presence of calcium are examined. Flame atomic absorption spectrometry appears to be free of interferences, but is subject to error from instrumental variations or high noise levels. Flame atomic emission spectrometry has an easily accessible detection limit of 5 ng ml −1 , but is subject to serious interference by calcium. This is solved by an efficient ion-exchange separation of barium from 1000-fold amounts of calcium in an all-plastic apparatus.

Protons: Affinity and Reduction in Ionic Liquids

Proton affinities dictate that protic salts are dissociated into molecules in the gas phase. In the liquid phase, protons are associated with charge neutral base molecules or homoconjugate/heteroconjugate anions. For example, liquids prepared from a base and a hydrogen halide contain the protonated base and either the halide or the halohydrogenate(I) anion; thus 2 classes of proton may be available for reduction. It happens that the anionic protic species are more readily reduced. This situation extends to complex hydrogen halides and anhydrous carboxylic acids. NMR data provide evidence of proton transfer and spectrophotometry can give a measure of acidity. Protic species alone may or may not ionize, depending on the proton affinity of the species itself. The formation of salts from a base and a protic species is discussed in terms of the pair of dissociation constants for dimethylsulphoxide, acetonitrile, water, and the gas phase, with limitations imposed by solvent leveling noted.

Electrochemical and 1H NMR studies of proton behavior of ImCl and LiCl solution in acetonitrile

The role of the proton in extending the electrochemical window and promoting the stripping efficiency of alkali metals has been studied in acetonitrile solution. The platinum hydride surface generated in the hydrogen evolution was considered responsible for the potential shift of 1-ethyl-3-methyl-1H-imidazolium (Im+) reduction in the absence of lithium. In lithium chloride solution, the lithium layer deposited on the electrode may be the main cause for the stretch of the solvent electrochemical window because of the high overpotential of Im+ reduction on that surface. The proton may affect the properties of the passive layer on newly deposited alkali metal surfaces and then improve the performance of the alkali metal anodes. Keywords: 1-ethyl-3-methyl-1H-imidazolium chloride, protons, acetonitrile, lithium reduction.