Peter Licence

Vapourisation of ionic liquids

Eight common imidazolium based ionic liquids have been successfully evaporated in ultra-high vacuum, their vapours analysed by line of sight mass spectrometry and their heats (enthalpy) of vapourisation determined. They were found to evaporate as ion pairs, with heats of vapourisation which depend primarily on the coulombic interactions within the liquid phase and the gas phase ion pair. An electrostatic model is presented relating the heats of vapourisation to the molar volumes of the ionic liquids.

Sustainable technology: Green chemistry

Modern life depends on the petrochemical industry — most drugs, paints and plastics derive from oil. But current processes for making chemical products are not sustainable in terms of resources and environmental impact. Green chemistry aims to tackle this problem, and real progress is being made.

Chemical reactions in supercritical carbon dioxide: from laboratory to commercial plantThis work was presented at the Green Solvents for Catalysis Meeting held in Bruchsal, Germany, 13–16th October 2002.

The application of supercritical carbon dioxide in continuous, fixed bed reactors has allowed the successful development of a variety of industrially viable synthetic transformations. The world’s first, multi-reaction, supercritical flow reactor was commissioned in 2002 as a direct result of the successful collaboration between the Clean Technology Group at the University of Nottingham and the fine chemicals manufacturer, Thomas Swan & Co. Ltd. We highlight the development of this project from laboratory to plant scale, particularly in the context of the hydrogenation of isophorone. Phase data for the system; isophorone + H2 + CO2, are presented for the first time. Overall, we present a progress report about an on-going Green Chemistry initiative that has successfully forged strong links between Industry and Academia.

Synthesis of benzimidazoles in high-temperature water

The objective of this research was to conduct constructive organic chemistry in water and to achieve yields that were comparable to, or better than, those in conventional media. The synthesis of 2-phenylbenzimidazole from 1,2-phenylenediamine and benzoic acid was chosen as a benchmark reaction. The reaction parameters, such as temperature, density and reaction time, have been systematically studied to understand whether the solvent properties of high-temperature water can have a positive effect on the chemistry. The reaction was performed in a new design of batch-type autoclave and was also monitored in situ by UV-vis spectroscopy. By tuning the parameters, the yield has been optimised to around 90%. The optimised conditions were then applied to related benzimidazoles, some of which crystallised from solution in situ to yield single crystals that were sufficiently pure to be analysed directly by X-ray diffraction, without any further purification.

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.

Continuous catalytic reactions in supercritical fluids

Abstract Recent heightened awareness of the environmental impacts associated with a large proportion of established chemical processes has led to the application of considerable pressures on the chemical industry, both regulatory and consumer driven, to adopt a cleaner and greener approach to manufacture. The economies of scale and associated efficiencies of continuous processes have long been a contributing factor in the design and efficient running of many large-scale industrial plants. When successfully combined with a versatile and environmentally benign solvent system such as supercritical fluids (SCFs), continuous processing can be seen to be suitable for a wide variety of reactions (hydrogenation, hydroformylation, alkylation, etc.). which can be conducted efficiently in an environmentally sensitive way. This review article aims to show the reader how the marriage of these two technologies is helping chemistry to achieve this goal.

Pyrrolidinium-Based Ionic Liquids. 1-Butyl-1-methyl Pyrrolidinium Dicyanoamide: Thermochemical Measurement, Mass Spectrometry, and ab Initio Calculations

The standard molar enthalpy of formation of the ionic liquid 1-butyl-1-methylpyrrolidinium dicyanamide has been determined at 298 K by means of combustion calorimetry, while the enthalpy of vaporization and the mass spectrum of the vapor (ion pairs) have been determined by temperature-programmed desorption and line of sight mass spectrometry. Ab initio calculations for 1-butyl-1-methylpyrrolidinium dicyanamide have been performed using the G3MP2 and CBS-QB3 theory, and the results from homodesmic reactions are in excellent agreement with the experiments.

Supercritical fluids: A route to palladium-aerogel nanocomposites

Supercritical carbon dioxide (scCO2) is used to prepare novel silica aerogel composites containing nano-particles of palladium. The material produced has been found to exhibit a Pd loading of 8% by wt. The particles deposited fit within two discrete size ranges of <6 nm and 15–20 nm as analysed by XRD and TEM. We demonstrate that scCO2 may be successfully applied to prepare catalytic support materials based upon aerogels and that the catalyst is active in a continuous flow reactor leading to effective hydrogenation of cyclohexene.

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).