Alasdair W. Taylor

Measuring and predicting Delta(vap)H298 values of ionic liquids.

We report the enthalpies of vaporisation (measured using temperature programmed desorption by mass spectrometry) of twelve ionic liquids (ILs), covering four imidazolium, [C(m)C(n)Im]+, five pyrrolidinium, [C(n)C(m)Pyrr]+, two pyridinium, [C(n)Py]+, and a dication, [C3(C1Im)2]2+ based IL. These cations were paired with a range of anions: [BF4]-, [FeCl4]-, [N(CN)2]-, [PF3(C2F5)3]- ([FAP]-), [(CF3SO2)2N]- ([Tf2N]-) and [SCN]-. Using these results, plus those for a further eight imidazolium based ILs published earlier (which include the anions [CF3SO3]- ([TfO]-), [PF6]- and [EtSO4]-), we show that the enthalpies of vaporisation can be decomposed into three components. The first component is the Coulombic interaction between the ions, DeltaU(Cou,R), which is a function of the IL molar volume, V(m), and a parameter R(r) which quantifies the relative change in anion-cation distance on evaporation from the liquid phase to the ion pair in the gas phase. The second and third components are the van der Waals contributions from the anion, DeltaH(vdw,A), and the cation, DeltaH(vdw,C). We derive a universal value for R(r), and individual values of DeltaH(vdw,A) and DeltaH(vdw,C) for each of the anions and cations considered in this study. Given the molar volume, it is possible to estimate the enthalpies of vaporisation of ILs composed of any combination of the ions considered here; values for fourteen ILs which have not yet been studied experimentally are given.

Effect of Viscosity on Steady-State Voltammetry and Scanning Electrochemical Microscopy in Room Temperature Ionic Liquids

The electrochemical properties of a series of room temperature ionic liquids (RTILs) were studied using voltammetric methods and scanning electrochemical microscopy (SECM). The RTILs consisted of 1-alkyl-3-methylimidazolium cations, [C(n)C(1)Im](+), and either bis[(trifluoromethyl)sulfonyl]imide anions, [Tf(2)N](-), or hexafluorophosphate anions, [PF(6)](-). The effect of RTIL viscosity on mass transfer dynamics within each RTIL was studied electrochemically using ferrocene as a redox probe. In the case of the [C(n)C(1)Im][Tf(2)N] RTILs, the viscosity was altered by changing the alkyl chain length. [C(4)C(1)Im][PF(6)] was used for comparison as its viscosity is significantly higher than that of the [C(n)C(1)Im][Tf(2)N] RTILs. The RTIL viscosity affected the ability to record steady-state voltammograms at ultramicroelectrodes (UMEs). For example, it was possible to record steady-state voltammograms at scan rates up to 10 mV s(-1) in [C(2)C(1)Im][Tf(2)N] using 1.5 mum radius disk UMEs, but non-steady-state behavior was observed at 50 mV s(-1). However, at 12.5 microm radius UMEs, steady-state voltammetry was only observed at 1 mV s(-1) in [C(2)C(1)Im][Tf(2)N]. The RTIL viscosity also affected the ability to record SECM feedback approach curves that agreed with conventional SECM theory. In the most viscous [C(n)C(1)Im][Tf(2)N] RTILs, feedback approach curves agreed with conventional theory only when very slow tip approach speeds were used (0.1 microm s(-1)). These observations were interpreted using the Peclet number, which describes the relative contributions of convective and diffusive mass transfer to the tip surface. By recording feedback approach curves in each RTIL at a range of tip approach speeds, we describe the experimental conditions that must be met to perform SECM in imidazolium-based RTILs. The rate of heterogeneous electron transfer across the RTIL/electrode interface was also studied using SECM and the standard heterogeneous electron transfer rate constant, k(0), for ferrocene oxidation recorded in each RTIL was higher than that determined previously using voltammetric methods.

Spectroelectrochemistry at ultrahigh vacuum: in situ monitoring of electrochemically generated species by X-ray photoelectron spectroscopy

The electrochemical reduction of Fe(III) to Fe(II) in the ionic liquid (IL) mixture of 1-ethyl-3-methylimidazolium ethylsulfate, [C(2)C(1)Im][EtOSO(3)], and 1-butyl-3-methylimidazolium tetrachloroferrate (III), [C(4)C(1)Im][Fe(III)Cl(4)], was monitored in situ by X-ray photoelectron spectroscopy (XPS).

Heterogeneous electron transfer kinetics at the ionic liquid/metal interface studied using cyclic voltammetry and scanning electrochemical microscopy.

The electrochemical behavior of a redox-active, ferrocene-modified ionic liquid (1-ferrocenylmethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) in acetonitrile and in an ionic liquid electrolyte (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) is reported. Reversible electrochemical behavior was observed in each electrolyte with responses typical of those for unmodified ferrocene observed in each medium. In the ionic liquid electrolyte, the diffusion coefficient of the redox-active ionic liquid increased by a factor of 5 upon increasing the temperature from 27 to 90 degrees C. The kinetics of electron transfer across the ionic liquid/electrode interface were studied using cyclic voltammetry, and the standard heterogeneous electron transfer rate constant, k (0) was determined to be 4.25 x 10 (-3) cm s (-1). Scanning electrochemical microscopy was then also used to probe the heterogeneous kinetics at the interface between the ionic liquid and the solid electrode and conventional kinetic SECM theory was used to determine k (0). The k (0) value obtained using SECM was higher than that determined using cyclic voltammetry. These results indicate that SECM is a very useful technique for studying electron transfer dynamics in ionic liquids.

An ultra high vacuum-spectroelectrochemical study of the dissolution of copper in the ionic liquid (N-methylacetate)-4-picolinium bis(trifluoromethylsulfonyl)imide

Ultra high vacuum-spectroelectrochemistry was used to investigate the electrochemically generated Cu species in the ionic liquid (N-methylacetate)-4-picolinium bis(trisfluoromethylsulfonyl)imide, [MAP][Tf(2)N]. The diffusion of Cu(+) across the surface of the ionic liquid was monitored in situ by X-ray photoelectron spectroscopy (XPS). A numerical procedure was developed to simulate the surface process from which, the apparent diffusion coefficient of Cu(+) across the surface is estimated to be 3.5 x 10(-5) cm(2) s(-1). Bulk diffusion process of Cu(+) in [MAP][Tf(2)N] was investigated ex situ for comparison with the surface process.

X‐Ray Photoelectron Spectroscopy of Ferrocenyl‐ and Ferrocenium‐Based Ionic Liquids

X-ray photoelectron spectroscopy (XPS) is used to study a series of five 1-(ferrocenylmethyl)-3-methylimidazolium- and 1-(ferroceniummethyl)-3-methylimidazolium-based salts. All samples emit good photoelectron fluxes with sharp, well-resolved photoelectron peaks. Due to the low volatility of imidazolium-salts at ambient temperature, no modification of the XP spectrometer was required. Two of the salts exhibit supercooling behaviour, allowing XPS to be recorded at room temperature on liquid samples without the need for charge neutralisation. The photoelectron peaks can be assigned to the component atoms of the salts, based on previous studies on ferrocene, ferrocenium-compounds and ionic liquids. Oxidation of the ferrocenyl moiety to ferrocenium shiftsthe Fe 2p and cyclopentadienyl C 1s photoelectron peaks to higher binding energy but does not affect the imidazolium and anion peaks. Under charge-neutralisation conditions, in which the sample is flooded with low-energy electrons, the ferrocenium moiety of the salt 1-(ferroceniummethyl)-3-methylimidazolium di(hexafluorophosphate) is partially reduced.

Acidity and basicity of halometallate-based ionic liquids from X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been used to investigate a series of 1-octyl-3-methylimidazolium halometallate ionic liquids of the general formula (1 − χ)[C8C1Im]Cl–χMCly (where χ is the mole fraction of metal halide and y = 2 or 3). The ionic liquids emitted good photoelectron fluxes allowing the measurement of high quality spectra with good peak resolution. Interrogation of the XPS data has allowed the prediction of trends in solvent parameters for these ionic liquids, including hydrogen bond basicity and Lewis acidity. Clear changes to the shape and energy of metal originated photoelectron peaks, as a function of mole fraction of metal halide, aids the identification of complex polynuclear anions within the ionic liquids.

Borane-substituted imidazol-2-ylidenes: syntheses in vacuo.

The serendipitous discovery of an efficient reactive distillation is reported. Two borane-substituted imidazol-2-ylidenes have been prepared in high yield from precursor tetrafluoroborate derived room temperature ionic liquids by reactive distillation at T > 500 K and p < 1 × 10(-4) mbar.

Rapid and clean synthesis of phthalimide derivatives in high-temperature, high-pressure H2O/EtOH mixtures

A variety of phthalimide derivatives have been synthesised effectively in high-temperature, high-pressure H2O/EtOH mixtures (HTHP-H2O/EtOH) as the solvent. This clean method is based on the condensation of o-phthalic acid and amines and affords phthalimide compounds as pure crystals in most cases, because of the dehydrating effect and change in solvation properties of H2O/EtOH at high pressures and temperatures. After conducting a series of model reactions, it was found that a mixture, 1/1 v/v H2O/EtOH, was appropriate for obtaining good yields combined with high purity of the phthalimides. Moderate to excellent yields were obtained depending on the nature of the amine. Aromatic amines generally afforded higher yields than aliphatic ones except for 3-hydroxypropylamine, where a yield up to 95% was obtained.