Elucidation of the electrochemical oxidation pathway of ammonia in dimethylformamide and the room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

The direct electrochemical oxidation of ammonia has been examined in both the organic solvent dimethylformamide (DMF) and the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][N(Tf)(2)]. The corresponding voltammetric responses have been shown to be similar in each solvent with a broad oxidative wave occurring upon the introduction of ammonia to the solution and the appearance of a new reductive wave following the oxidation. The oxidative reaction process has been examined and a suitable reaction pathway has been deduced, corresponding to the formation of ammonium cations after oxidation of the ammonia. A linear response of limiting current against vol% ammonia was observed in both DMF and [EMIM][N(Tf)(2)], suggesting potential application for analytical methods.

Kinetic analysis of the reaction between electrogenerated superoxide and carbon dioxide in the room temperature ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and hexyltriethylammonium bis(trifluoromethylsulfonyl)imide

The reduction of oxygen in the presence of carbon dioxide has been investigated by cyclic voltammetry at a gold microdisk electrode in the two room-temperature ionic liquids 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ([EMIM][N(Tf)(2)]) and hexyltriethylammonium bis(trifluoromethylsulfonyl)imide ([N-6222] [N(Tf)(2)]). With increasing levels of CO2, cyclic voltammetry shows an increase in the reductive wave and diminishing of the oxidative wave, indicating that the generated superoxide readily reacts with carbon dioxide. The kinetics of this reaction are investigated in both ionic liquids. The reaction was found to proceed via a DISP1 type mechanism in [EMIM][N(Tf)(2)] with an overall second-order rate constant of 1.4 +/- 0.4 x 10(3) M-1 s(-1). An ECE or DISP1 mechanism was determined to be the most likely pathway for the reaction in [N-6222][N(Tf)(2)], with an overall second-order rate constant of 1.72 +/- 0.45 x 10(3) m(-1) s(-1).

Determination of ammonia based on the electro-oxidation of hydroquinone in dimethylformamide or in the room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

The results detail a novel methodology for the electrochemical determination of ammonia based on its interaction with hydroquinone in DMF. It has been shown that ammonia reversibly removes protons from the hydroquinone molecules, thus facilitating the oxidative process with the emergence of a new wave at less positive potentials. The analytical utility of the proposed methodology has been examined with a linear range from 10 to 95 ppm and corresponding limit-of-detection of 4.2 ppm achievable. Finally, the response of hydroquinone in the presence of ammonia has been examined in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide, [EMIM][N(Tf)(2)]. Analogous voltammetric waveshapes to that observed in DMF were obtained, thereby confirming the viability of the method in either DMF or [EMIM][N(Tf)(2)] as solvent. (C) 2003 Elsevier B.V. All rights reserved.

Voltammetry of oxygen in the room-temperature ionic liquids 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide and hexyltriethylammonium bis((trifluoromethyl)sulfonyl)imide: One-electron reduction to form superoxide. Steady-state and transient behavior in the same cyclic voltammogram resulting from widely different diffusion coefficients of oxygen and superoxide

The electrochemical reduction of oxygen in two different room-temperature ionic liquids, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide ([EMIM][N(Tf)(2)]) and hexyltriethylammonium bis((trifluoromethyl)sulfonyl)imide ([N-6222][N(Tf)(2)]) was investigated by cyclic voltammetry at a gold microdisk electrode. Chronoamperometric measurements were made to determine the diffusion coefficient, D, and concentration, c, of the electroactive oxygen dissolved in the ionic liquid by fitting experimental transients to the Aoki model. [Aoki, K.; et al. J. Electroanal. Chem. 1981, 122, 19]. A theory and simulation designed for cyclic voltammetry at microdisk electrodes was then employed to determine the diffusion coefficient of the electrogenerated superoxide species, O-2(.-), as well as compute theoretical voltammograms to confirm the values of D and c for neutral oxygen obtained from the transients. As expected, the diffusion coefficient of the superoxide species was found to be smaller than that of the oxygen in both ionic liquids. The diffusion coefficients of O-2 and O-2(.-) in [N-6222][N(Tf)(2)], however, differ by more than a factor of 30 (D-O2 = 1.48 x 10(-10) m(2) s(-1), DO2.- = 4.66 x 10(-12) m(2) s(-1)), whereas they fall within the same order of magnitude in [EMIM][N(Tf)(2)] (D-O2 = 7.3 x 10(-10) m(2) s(-1), DO2.- = 2.7 x 10(-10) m(2) s(-1)). This difference in [N-6222][N(Tf)(2)] causes pronounced asymmetry in the concentration distributions of oxygen and superoxide, resulting in significant differences in the heights of the forward and back peaks in the cyclic voltammograms for the reduction of oxygen. This observation is most likely a result of the higher viscosity of [N-6222][N(Tf)(2)] in comparison to [EMIM][N(Tf)(2)], due to the structural differences in cationic component.

Effect of acetonitrile on the solubility of carbon dioxide in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide

The effect of the addition of acetonitrile on the solubility of carbon dioxide in an ionic liquid, the 1-ethyl-3- methylimidazolium bis(trifluoromethanesulfonyl)amide, [C(2)mim][NTf2], was studied experimentally at pressures close to atmospheric and as a function of temperature between 290 and 335 K. It was observed that the solubility of carbon dioxide decreases linearly with the mole fraction of acetonitrile from a value of 2.6 x 10(-2) in the pure ionic liquid at 303 K to a mole fraction of 1.3 x 10(-2) in the mixture [C(2)mim][NTf2] + CH3CN with x(CH3CN) = 0.77 at the same temperature. The gas solubility decreases with temperature, and the thermodynamic properties of solvation could be calculated. The vapor pressures of the [ C2mim][ NTf2] + CH3CN mixtures were measured in the same temperature range, and strong negative deviations from Raoult's law were obtained: up to 36% for a mixture with x(CH3CN) = 0.46 at 334 K. Negative excess molar volumes of approximately -1 cm(3) mol(-1) at equimolar composition could also be calculated from density measurements of the pure components and of the mixtures. These observations are confirmed by neutron diffraction studies and are compatible with the existence of strong ion-dipole interactions in the mixed liquid solvent.

Comment on the preparation of the ionic liquid 1-ethyl-3-methylimidazolium ethanoate: a unique monomeric, homoleptic pentacoordinate lead ethanoate complex

Atomic absorption spectroscopy of the ionic liquid 1-ethyl-3-methylimidazolium ethanoate ([emim](2)[O2CMe]), prepared according to International Patent WO 96/18459, showed it to contain large amounts of lead impurity: (ca. 0.5 M): [emim](2)[Pb(O2CMe)(4)] was isolated and shown crystallographically to contain the first known example of a monomeric, homoleptic pentacoordinate lead(ii) carboxylate complex, with a stereochemically active lone-pair.

Tris(1-ethyl-3-methylimidazolium) hexabromidoeuropate(III)

The crystal structure of the title compound, (C6H11N2)(3-)[EuBr6], consists of 1-ethyl-3-methylimidazolium cations and centrosymmetric octahedral hexabromidoeuropate anions. The [EuBr6](3-) anions are located at the corners and face-centres of the monoclinic unit cell. Characteristic hydrogen-bonding interactions can be observed between the bromide anions and the acidic H atoms of the imidazolium cations.

Green synthesis of ZnO nanoparticles in a room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Nanoparticles of ZnO with the wurtzite structure have been successfully synthesized via a microwave through the decomposition of zinc acetate dihydrate in an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, as a solvent. Fundamental characterizations including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were conducted for the ZnO nanostructures.

Kinetic model for the hydrolysis of lignocellulosic biomass in the ionic liquid, 1-ethyl-3-methyl-imidazolium chloride†

The kinetics of the acid-catalysed hydrolysis of cellobiose in the ionic liquid 1-ethyl-3-methylimidazolium chloride, [C(2)mim]Cl, was studied as a model for general lignocellulosic biomass hydrolysis in ionic liquid systems. The results show that the rate of the two competing reactions, polysaccharide hydrolysis and sugar decomposition, vary with acid strength, and that for acids with an aqueous pK(a) below approximately zero, the hydrolysis reaction is significantly faster than the degradation of glucose, thus allowing hydrolysis to be performed with a high selectivity in glucose. In tests with soluble cellulose, hemicellulose (xylan), and lignocellulosic biomass (Miscanthus grass), comparable hydrolysis rates were observed with bond scission occurring randomly along the biopolymer chains, in contrast to end-group hydrolysis observed with aqueous acids.

The electrochemical oxidation of catechol and dopamine on platinum in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]): Adsorption effects in ionic liquid voltammetry

The electrochemical oxidation of catechol and dopamine has been studied at a platinum micro-electrode (10 pm diameter) in two room temperature ionic liquids (RTILs): 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BE4]). For catechol in [C(2)mim][NTf2], an electrochemically quasi-reversible oxidation peak was observed at 1.1 V vs. Pt with a back peak at 0.4 V vs. Pt. This is assigned to the two-electron oxidation of catechol to doubly protonated o-benzoquinone. Double-step chronoamperometry gave a diffusion coefficient for the catechol and the oxidised species which is 3.8 x 10(-11) m(2) s(-1) for both. For catechol in [C(4)mim][BF4], a two-electron oxidation wave was observed at 1.0 V vs. Pt with no back peak. Another peak at less positive potential was also observed at 0.6 V vs. Pt in [C(4)mim][BF4] but not in [C(2)mim][NTf2] which is assigned to the adsorption of electrochemically formed neutral o-benzoquinone on the platinum electrode. The oxidised protonated o-benzoquinone is suggested to be deprotonated by the [BF4](-) anion, but not by the [NTf2](-) anion: hence adsorption of the neutral species at the platinum electrode, not the charged species. For dopamine in both RTILs, two chemically irreversible oxidation peaks were observed at 0.75 V and 1.1 V vs. Pt, and assigned to the oxidation of dopamine to the corresponding semi-quinone and the quinone. Potential-step chronoamperometry was carried out on the oxidation waves of dopamine in [C(2)mim][NTf2] and the diffusion coefficient of species in solution was calculated to be 6.85 x 10(-12) m(2) s(-1) and confirmed that the waves corresponded to one and two electron processes. A third wave was observed at 1.8 V vs. Pt which is attributed to the oxidation of the amine group to a radical cation with likely subsequent follow up chemistry. In [C(4)mim][BF4] a peak at less positive potential was observed for dopamine, similar to catechol which is assigned to the adsorption of the neutral quinone species on the platinum electrode formed by the reaction of the removal of protons from the oxidised dopamine with the [BF4](-) anion. (C) 2009 Elsevier B.V. All rights reserved.

Neutron diffraction, NMR and molecular dynamics study of glucose dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate

beta-D-glucose dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate in a 6 : 1 molar ratio (ionic liquid : glucose) has been studied by neutron scattering, NMR and molecular dynamics simulations. Good agreement was found between simulated neutron scattering profiles generated for isotopically substituted liquid systems and those experimentally determined as well as between simulated and experimental diffusion coefficients obtained by Pulsed Field Gradient NMR spectroscopy. The overriding glucose-ionic liquid interactions in the liquid are hydrogen-bonding between acetate oxygens and sugar hydroxyl groups. The ionic liquid cation was found to play only a minor role in the solvation of the sugar and does not participate in hydrogen-bonding with the sugar to any significant degree. NOESY experiments lend further evidence that there is no direct interaction between sugar hydroxyl groups and acidic hydrogens on the ionic liquid cation.

1-Ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide as solvent for the separation of aromatic and aliphatic hydrocarbons by liquid extraction - extension to C-7- and C-8-fractions

The ionic liquid 1-ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ([C(2)mim][NTf2]) was tested as solvent for the separation of aromatic and aliphatic hydrocarbons containing 7 or 8 carbon atoms (the C-7- and C-8-fractions). The liquid-liquid equilibria (LLE) of the ternary systems (heptane + toluene + [C(2)mim][NTf2]) and (octane + ethylbenzene + [C(2)mim][NTf2]), at 25 degrees C, were experimentally determined. The performance of the ionic liquid as the solvent in such systems was evaluated by means of the calculation of the solute distribution ratio and the selectivity. The results were compared to those previously reported for the extraction of benzene from its mixtures with hexane by using the same ionic liquid, therefore analysing the influence of the size of the hydrocarbons. It was found that the ionic liquid is also good for the extraction of C-7- and C-8- fraction aromatic compounds, just a greater amount of ionic liquid being needed to perform an equivalently efficient separation than for the C-6-fraction. It is also discussed how [C(2)mim][NTf2] performs comparably better than the conventional solvent sulfolane. The original 'Non-Random Two-Liquid' (NRTL) equation was used to adequately correlate the experimental LLE data.

Influence of water on the carbon dioxide absorption by 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide

The effect of the addition of water on the absorption of carbon dioxide by the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide was studied experimentally by measuring the low-pressure carbon dioxide solubility and the viscosity of the liquid solvent at temperatures from 303 to 323 K. Water is only partially miscible with the ionic liquid up to a mole fraction of 0.302 at 293 K, 0.321 at 303 K and 0.381 at 323 K. It was observed that the solubility of carbon dioxide decreases with the quantity of water from a mole fraction of 2.63 × 10-2 for the pure ionic liquid at 303.4 K to a value of 1.88 × 10-2, a reduction of 30% of the solubility, for a mole fraction of water of 0.28. The viscosity of the liquid solvent also decreases, up to 40% at 303 K, from 28.6 mPa s for the pure ionic liquid to 16.4 mPa s for a water mole fraction of 0.302.