A mechanistic study of the electro-oxidation of bromide in acetonitrile and the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide at platinum electrodes

The oxidation of bromide has been investigated by linear sweep and cyclic voltammetry at platinum electrodes in the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, ([C(4)mim][NTf2]), and the conventional aprotic solvent. acetonitrile, (MeCN). Similar voltammetry was observed in both solvents, despite their viscosities differing by more than an order of magnitude. DigiSim(R) was employed to simulate the voltammetric response. The mechanism is believed to involve the direct oxidation of bromide to bromine in a heterogeneous step, followed by a homogenous reaction to form the tribromide anion: 2Br(-) --> Br-2 + 2e(-)

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.

Oxidation of N,N,N ',N '-tetraalkyl-para-phenylenediamines in a series of room temperature ionic liquids incorporating the bis(trifluoromethylsulfonyl)imide anion

The five room temperature ionic liquids: 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CnMIM][N(Tf)(2)], n = 2, 4, 8, 10) and n-hexyltriethylammonium bis(trifluoromethylsulfonyl)imide ([N-6222][N(Tf)(2)]) were investigated as solvents in which to study the electrochemical oxidation of N,N,N',N'-tetramethyl-para-phenylenediamine (TMPD) and N,N,N',N'-tetrabutyl-paraphenylenediamine (TBPD), using 20 mul micro-samples under vacuum conditions. The effect of dissolved atmospheric gases on the accessible electrochemical window was probed and determined to be less significant than seen previously for ionic liquids containing alternative anions. Chronoamperometric transients recorded at a microdisk electrode were analysed via a process of non-linear curve fitting to yield values for the diffusion coefficients of the electroactive species without requiring a knowledge of their initial concentration. Comparison of experimental and simulated cyclic voltammetry was then employed to corroborate these results and allow diffusion coefficients for the electrogenerated species to be estimated. The diffusion coefficients obtained for the neutral compounds in the five ionic liquids via this analysis were, in units of 10(-11) m(2) s(-1), 2.62, 1.87, 1.12, 1.13 and 0.70 for TMPD. and 1.23, 0.80, 0.40, 0.52 and 0.24 for TBPD (listed using the same order for the ionic liquids as stated above). The most significant consequence of changing the cationic component of the ionic liquid was found to be its effect on the solvent viscosity; the diffusion coefficient of each species was found to be approximately inversely proportional to viscosity across the series of ionic liquids, in accordance with Walden's rule. (C) 2003 Elsevier B.V. All rights reserved.

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.

Electrochemical Determination of Manganese Solubility in Mercury via Amalgamation and Stripping in the Room Temperature Ionic Liquid n-Hexyltriethylammonium Bis(trifluoromethanesulfonyl)imide, [N-6,N-2,N-2,N-2][NTf2]

The solubility of manganese in mercury was determined electrochemically via amalgamation and stripping in the room temperature ionic liquid n-hexyltriethylammonium bis(trifluoromethanesulfonyl)imide, [N-6,N-2,N-2,N-2][NTf2]. A hemispherical mercury electrode was made by electrodepositing mercury onto a planar platinum microelectrode. Cyclic voltammetry of Mn2+ in [N-6,N-2,N-2,N-2][NTf2] at the mercury microhemisphere electrode was investigated at temperatures of 298, 303 and 313 K. The solubility of Mn in Hg was determined on the basis of the charge under the reduction peak (Mn2+ --> Mn-0) and the corresponding reoxidation.

Temperature-Driven Mixing-Demixing Behavior of Binary Mixtures of the Ionic Liquid Choline Bis(trifluoromethylsulfonyl)imide and Water

The ionic liquid (2-hydroxyethylammonium)trimethylammonium) bis(trifluoromethylsulfonyl)imide (choline bistriflimide) was obtained as a supercooled liquid at room temperature (melting point = 30 degrees C). Crystals of choline bistriflimide suitable for structure determination were grown from the melt in situ on the X-ray diffractometer. The choline cation adopts a folded conformation, whereas the bistriflimide anion exhibits a transoid conformation. The choline cation and the bistriflimide anion are held together by hydrogen bonds between the hydroxyl proton and a sulfonyl oxygen atom. This hydrogen bonding is of importance for the temperature-dependent solubility proper-ties of the ionic liquid. Choline bistriflimide is not miscible with water at room temperature, but forms one phase with water at temperatures above 72 degrees C (equals upper critical solution temperature). H-1 NMR studies show that the hydrogen bonds between the choline cation and the bistriflimide anion are substantially weakened above this temperature. The thermophysical properties of water-choline bistriflimide binary mixtures were furthermore studied by a photopyroelectric technique and by adiabatic scanning calorimetry (ASC). By photothermal analysis, besides highly accurate values for the thermal conductivity and effusivity of choline bistriflimide at 30 degrees C, the detailed temperature dependence of both the thermal conductivity and effusivity of the upper and lower part of a critical water-choline bistriflimide mixture in the neighborhood of the mixing-demixing phase transition could be determined with high resolution and accuracy. Together with high resolution ASC data for the heat capacity, experimental values were obtained for the critical exponents alpha and beta, and for the critical amplitude ratio G(+)/G(-). These three values were found to be consistent with theoretical expectations for a three dimensional Ising-type of critical behavior of binary liquid mixtures.

The structure of [Co(H-tptz)Cl-3] center dot H2O (tptz=2,4,6-tri(2-pyridyl)-1,3,5-triazine) prepared by crystallization from the ionic liquid, N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide

The structure of tris-chloro[2,6-bis(2'-pyridyl)-4-(2'-pyridinium)-1,3,5-triazine]cobalt(II) monohydrate, [Co(C18H13N6)Cl-3]center dot H2O (C2/c (No. 15), a = 7.783(11), b = 22.42(3), c = 11.001(15) angstrom, beta = 90.05(2)degrees), crystallized from the open air reaction of CoCl2 and 2,4,6-tri(2-pyridyl)-1,3,5-triazine in the ionic liquid, N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide is reported. The structure consists of six coordinate cobalt in an octahedral geometry bonded to the tridentate tptz ligand and three chlorines. The non-coordinating pyridyl group in the tptz ligand is protonated (with the protonated nitrogen crystallographically disordered over two possible sites), providing overall charge neutrality for the complex.

Crystal structures of imidazolium bis(trifluoromethanesulfonyl)imide 'ionic liquid' salts: the first organic salt with a cis-TFSI anion conformation

Crystal structures of two examples of an important class of ionic liquids, 1,3-dimethylimidazolium and 1,2,3-triethylimidazolium bis(trifluoromethanesulfonyl)imide have been characterized by single crystal X-ray diffraction. The anion in the 1,3-dimethylimidazolium example (mp 22 degreesC), adopts an unusual cis-geometry constrained by bifurcated cation-anion C-H...O hydrogen-bonds from the imidazolium cation to the anion resulting in the formation of fluorous layers within the solid-state structure. In contrast, in the 1,2,3-triethylimidazolium salt (mp 57 degreesC), the ions are discretely packed with only weak C-H...O contacts between the ions close to the van der Waals separation distances, and with the anion adopting the twisted conformation observed for all other examples from the limited set of organic bis( trifluoromethanesulfonyl) imide crystal structures. The structures are discussed in terms of the favorable physical properties that bis(trifluoromethanesulfonyl) imide anions impart in ionic liquids.

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.

Volumetric properties and enthalpies of solution of alcohols CkH2k+1OH (k = 1, 2, 6) in 1-methyl-3-alkylimidazolium bis(trifluoromethylsulfonyl)imide {[C1CnIm][NTf2] n = 2, 4, 6, 8, 10} ionic liquids

We present a study on the effect of the alkyl chain length of the imidazolium ring in 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, [C1CnIm][NTf2] (n = 2 to 10), on the mixing properties of (ionic liquid + alcohol) mixtures (enthalpy and volume). We have measured small excess molar volumes with highly asymmetric curves as a function of mole fraction composition (S-shape) with more negative values in the alcohol-rich regions. The excess molar volumes increase with the increase of the alkyl-chain length of the imidazolium cation of the ionic liquid. The values of the partial molar excess enthalpy and the enthalpy of mixing are positive and, for the case of methanol, do not vary monotonously with the length of the alkyl side-chain of the cation on the ionic liquid – increasing from n = 2 to 6 and then decreasing from n = 8. This non-monotonous variation is explained by a more favourable interaction of methanol with the cation head group of the ionic liquid for alkyl chains longer than eight carbon atoms. It is also observed that the mixing is less favourable for the smaller alcohols, the enthalpy of mixing decreasing to less positive values as the alkyl chain of the alcohol increases. Based on the data from this work and on the knowledge of the vapour pressure of {[C1CnIm][NTf2] + alcohol} binary mixtures at T = 298 K reported in the literature, the excess Gibbs free energy, excess enthalpy and excess entropy could be then calculated and it was observed that these mixtures behave like the ones constituted by a non-associating and a non-polar component, with its solution behaviour being determined by the enthalpy.

Influence of the cation on the solubility of CO2 and H 2 in ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion

Experimental values for the solubility of carbon dioxide and hydrogen in three room temperature ionic liquids based on the same anion- (bistrifluoromethylsulfonyl)imide [Ntf2]-and three different cations-1-butyl-3-methylimidazolium, [C4mim], 1-ethyl-3- methylimidazolium, [C2mim] and trimethyl-butylammonium, [N 4111]-are reported between 283 and 343 K and close to atmospheric pressure. Carbon dioxide, with a mole-fraction solubility of the order of 10-2, is two orders of magnitude more soluble than hydrogen. The solubility of CO2 is very similar in the three ionic liquids although slightly lower in the presence of the [C2mim] cation. In the case of H2, noticeable differences were observed with larger mole fraction solubilities in the presence of [N4111] followed by [C 4mim]. All of the mole-fraction solubilities decrease with increasing temperature. From the variation of Henry's law constants with temperature, the thermodynamic functions of solvation were calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law constants from appropriate smoothing equations, is always better than ±1%. © Springer Science+Business Media, LLC 2007.

Electrical conductivity and glass formation in nitrile-functionalized pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids: chain length and odd–even effects of the alkyl spacer between the pyrrolidinium ring and the nitrile group

The electrical conductivity of a series of pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids, functionalized with a nitrile (cyano) group at the end of an alkyl chain attached to the cation, was studied in the temperature range between 173 K and 393 K. The glass formation of the ionic liquids is influenced by the length of the alkyl spacer separating the nitrile function from the pyrrolidinium ring. The electrical conductivity and the viscosity do not show a monotonic dependence on the alkyl spacer length, but rather an odd-even effect. An explanation for this behavior is given, including the potential energy landscape picture for the glass transition.