Electrochemical properties of 1-butyl-3-methylimidazolium bromide melt containing water impurities

The effect of a water impurity (1.8–10 wt %) on the conductivity of the ionic liquid-H₂O binary system was studied in a wide temperature range. It was shown that the interaction between components is characteristic of this system, and the molar ratio of components 1: 1 is boundary between the structures of solution and melt. The basic kinetic features of electrochemical reduction of water of the BMImBr-H₂O binary system were determined by voltammetry with linear potential sweep. The transfer coefficient for the cathodic process (α = 0.46) and H₂O molecule diffusivities were determined depending on the water content ( $ D_{H_2 O} The effect of a water impurity (1.8–10 wt %) on the conductivity of the ionic liquid-H₂O binary system was studied in a wide temperature range. It was shown that the interaction between components is characteristic of this system, and the molar ratio of components 1: 1 is boundary between the structures of solution and melt. The basic kinetic features of electrochemical reduction of water of the BMImBr-H₂O binary system were determined by voltammetry with linear potential sweep. The transfer coefficient for the cathodic process (α = 0.46) and H₂O molecule diffusivities were determined depending on the water content ( = (0.2–1.3) × 10⁻¹⁰ cm²s⁻¹). Original Russian Text ? E.P. Grishina, A.M. Pimenova, L.M. Ramenskaya, O.V. Kraeva, 2008, published in Elektrokhimiya, 2008, Vol. 44, No. 11, pp. 1352–1358.     

The physicochemical properties of the low-temperature ionic liquid silver bromide-1-butyl-3-methylimidazolium bromide

The physicochemical properties of the low-temperature ionic liquid based on 1-butyl-3-methylimidazolium bromide (BMImBr) and silver bromide were studied. Differential scanning calorimetry, Fourier transform IR spectroscopy, densimetry, viscometry, and conductometry measurements were performed to determine the dependences of the parameters under study on the concentration of AgBr. It was shown that the temperature and concentration behavior of the physicochemical properties of BMImBr-AgBr melts characterized the interaction between the system components with the formation of complex particles.     

Physicochemical properties of 1-butyl-3-methylimidazolium acetate

Characteristic IR and UV absorption bands, as well as oxidation half-wave potential on a platinum disc electrode in the cyclic mode were determined for the low-temperature hydrophilic ionic liquid 1-butyl-3-methylimidazolium acetate. Temperature dependences of the refractive index, density, and ansolute viscosity were determined in the temperature range 298–328 K. The activation energy of viscous flow was calculated.     

Anodic oxidation of silver in 1-butyl-3-methylimidazolium bromide ionic liquid

Electrochemical oxidation of silver in the 1-butyl-3-methylimidazolium bromide ([BMIm]Br) ionic liquid is studied by cyclic voltammetry, chronopotentiometry, chronoammetry, and gravimetry. Two electrode processes irreversibly proceed on the silver electrode in the potential range studied: the formation of compound [BMIm]⁺[AgBr₂]^?, which is soluble in [BMIm]Br, and difficultly soluble AgBr.     

Bromination of alkylbenzenes in 1-butyl-3-methylimidazolium bromide and its dibromide complex

Alkylbenzenes were subjected to bromination with molecular bromine using 1-butyl-3-methylimidazolium bromide as solvent. A complex of 1-butyl-3-methylimidazolium bromide with bromine was synthesized. It ensured bromination of alkylbenzenes with no bromine and solvent. The results of bromination in binary solvents and ionic liquids, 1-butyl-3-methylimidazolium bromide and tribromide were compared. The bromination of ethylbenzene with 1-butyl-3-methylimidazolium tribromide was accompanied by formation of a considerable amount of α-bromoethylbenzene, which is not typical of electrophilic aromatic substitution process.     

The salting-out effect and phase separation in aqueous solutions of tri-sodium citrate and 1-butyl-3-methylimidazolium bromide

The aim of this work is to obtain further evidence about the salting-out effect produced by the addition of tri-sodium citrate to aqueous solutions of water miscible ionic liquid 1-butyl-3-methylimidazolium bromide ([C₄mim][Br]) by evaluating the effect of tri-sodium citrate on the thermodynamic properties of aqueous solutions of this ionic liquid. Experimental measurements of density and sound velocity at different temperatures ranging from (288.15 to 308.15) K, the refractive index at 308.15 K and the liquid–liquid phase diagram at different temperatures ranging from (288.15 to 338.15) K for aqueous solutions containing 1-butyl-3-methylimidazolium bromide ([C₄mim][Br]) and tri-sodium citrate (Na₃Cit) are taken. The apparent molar volume of transfer of [C₄mim][Br] from water to aqueous solutions of Na₃Cit have positive values and it increases by increasing salt molality. Although at high IL molality, the apparent molar isentropic compressibility shows similar behaviour with that of the apparent molar volume. However at low concentrations of IL, the apparent molar isentropic compressibility of transfer of [C₄mim][Br] from water to aqueous solutions of Na₃Cit have negative values. The effects of temperature and the addition of Na₃Cit and [C₄mim][Br] on the liquid–liquid phase diagram of the investigated system have been studied. It was found that an increase in temperature caused the expansion of the one-phase region. The presence of Na₃Cit triggers a salting-out effect, leading to significant upward shifts of the liquid–liquid de-mixing temperatures of the system. The effect of temperature on the phase-forming ability in the system investigated has been studied based on a salting-out coefficient obtained from fitting the binodal values to a Setschenow-type equation for each temperature. Based on cloud point values, the energetics of the clouding process have been estimated and it was found that both of entropy and enthalpy are the driving forces for biphasic formation.     

The influence of water on the physicochemical characteristics of 1-butyl-3-methylimidazolium bromide ionic liquid

A modified synthesis of 1-butyl-3-methylimidazolium bromide (BMImBr) was suggested and performed, and some physicochemical properties of the product containing 0.64–13.6 wt % water were determined. Water increased the electrical conductivity and decreased the viscosity and melting point of the substance but weakly influenced its density. Water in amounts of 5–8 wt % (45–50 mol %) caused structural changes. The BMImBr · 0.5H₂O crystal hydrate was found to be stable thermodynamically.     

Electrochemical oxidation of tantalum and niobium in 1-butyl-3-methylimidazolium bromide melt containing water admixtures

The niobium and tantalum anodic oxidation is studied using electrochemical methods in a ionic liquid, 1-butyl-3-methylimidazolium bromide (BMImBr), containing water admixtures. It is found that resistive oxide layers are formed on the metal surface in the polarization process and their growth follows the complicated parabolic or inverse logarithmic laws. It is shown that under the given conditions, the chemical stability of oxide layers on niobium is considerably lower than that on tantalum.     

The changes of crystalline structure of cellulose during dissolution in 1-butyl-3-methylimidazolium chloride

The morphology and crystalline structure changes of cellulose during dissolution in 1-butyl-3-methylimidazolium chloride [(BMIM)Cl] were investigated by optical microscopy and synchrotron radiation wide-angle X-ray diffraction (WAXD). Neither swelling nor dissolution of cellulose was observed under the melting point of [BMIM]Cl. While the temperature was elevated to 70 °C, the swelling phenomenon of cellulose happened with the interplanar spacing of ( _boxclose_boxclose_boxclose0 1\bar{1}0 ) and (020) planes increased slightly. With the temperature further going up to 80 °C, cellulose was dissolved gradually with the crystallinity (W _c,x) and crystalline index (CrI) of cellulose decreased rapidly, which indicated the crystalline structure of cellulose was destroyed completely and transformed into amorphous structure.     

Thermodynamic properties of 1-alkyl-3-methylimidazolium bromide ionic liquids

Heat capacities and enthalpies of phase transitions for a series of 1-alkyl-3-methylimidazolium bromide ionic liquids have been measured by adiabatic calorimetry. Thermodynamic properties of the compounds were calculated in the temperature range of (5 to 370) K. Water was found to have an additive contribution to the heat capacities of [C₄mim]Br in the liquid state above T_fus and in the solid state below 160 K at w(H₂O) ⩽ 5 · 10⁻³.     

Photoinduced electron-transfer reactions in two room-temperature ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium hexafluorophosphate

Photoinduced electron transfer in two room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF(6)) and 1-octyl-3-methylimidazolium hexafluorophosphate (OMIM-PF(6)), has been investigated using steady-state fluorescence quenching of 9,10-dicyanoanthracene with a series of single electron donors. From these fluorescence quenching rates, reorganization energy (lambda) values and k(diff) values can be derived from a Rehm-Weller analysis. In many cases, these fluorescence quenching reactions occur at rates larger than what would be expected based on the Smoluchowski equation. In addition, lambda values of 10.1 kcal/mol and 16.3 kcal/mol for BMIM-PF(6) and OMIM-PF(6), respectively, have been determined.     

Electrochemical behavior of copper in 1-butyl-3-methylimidazolium bromide-copper(II) bromide binary ionic liquid

The methods of potentiometry, voltammetry, and gravimetry are used to study the electrochemical behavior of copper in the BMImBr-CuBr₂ ionic liquid (0?C30.5 mol % CuBr₂). It is shown that electrochemical reduction of copper(II) occurs irreversibly, in two one-electron stages (transfer coefficient ?? of the cathodic process are 0.58 and 0.46, accordingly, for the first and second stages). Diffusion coefficients of copper-containing ions D _Cu(II) at 60°C are 1.3 × 10^?7 and 1.6 × 10^?7 cm² s^?1 in melts with the CuBr₂ concentration of 0.1 and 1.5 mol kg^?1 of BMImBr, accordingly. High (up to 98%) deposition efficiency and high-quality copper deposit can be obtained in the potential range of ?2.0 to ?1.8 V (vs. a platinum quasireference electrode). It is found that the copper corrosion rate grows at an increase in the CuBr₂ concentration in the binary melt and is comparable with that in aqueous solutions of H₂SO₄-CuSO₄.     

The kinetics of thermal decomposition of 1-butyl-3-methylimidazolium hexafluorophosphate

It is demonstrated that 1-butyl-3-methylimidazolium hexafluorophosphate decomposes in a vacuum in the temperature interval of T=(410 to 505) K according to zero-order kinetics with the activation energy EA=68.0+/-2.8 kJ.mol-1.     

Electroconductivity of low-temperature ionic liquid 1-butyl-3-methylimidazolium bromide-silver bromide. Effects of AgBr concentration and temperature

The effects of temperature and component ratio to electroconductivity of ionic liquid BMImBr — (1.5 to 1.88 mol %) Ag Br were studied. At 10 mol % AgBr concentration, the properties of ionic liquid were stabilized and the values of specific electroconductivity χ, viscosity-corrected specific electroconductivity χη, and equation coefficients of the temperature curve of χ changed insignificantly. The diffusion coefficient of silver complex ion was calculated: D _{Ag + p} = 1.07 × 10⁻⁷ cm²s⁻¹.     

The nature of associates of 1,4-dinitrobenzene dianion with 1-butyl-3-methylimidazolium and 1-butyl-2,3-dimethylimidazolium cations

Association of 1,4-dinitrobenzene (1,4-DNB) dianion (DA) with 1-butyl-3-methylimidazolium (bmim⁺) and 1-butyl-2,3-dimethylimidazolium (bdmim⁺) cations, whose salts are widely used as ionic liquids, was studied by cyclic voltammetry. In 0.1 M solution of Bu₄NClO₄ in DMF, associates with the number of coordinated cations up to four in the case of bmim⁺ and two in the case of bdmim⁺ are formed. The partial stability constant values for the associates of bmim⁺ are 40, 20, 5, and 3.2 L mol⁻¹, of bdmim⁺ − 24 and 1.9 L mol⁻¹. The higher number of coordinated bmim+ cations is attributed to the formation of, along with ion pairs, hydrogen bonds between 1,4-DNB DA and bmim⁺ due to the labile hydrogen atom at position 2 of the imidazole ring, in contrast to bdmim⁺, which is involved only into the ion-pair interactions.     

The physicochemical characteristics of the 1-butyl-3-methylimidazolium bromide-polyethylene glycol-water system

Mixtures of 1-butyl-3-methylimidazolium bromide (BMImBr) with polyethylene glycol (PEG) (molecular weights 1500 and 40000) containing 4–74 wt % BMImBr were studied. Thermogravimetric and differential scanning calorimetry measurements showed that the compatibility of BMImBr and PEG improved as the molecular weight of the polymer decreased. At a BMImBr: PEG₁₅₀₀ weight ratio of 1: 3, a phase-stable composite formed. The results of conductometric measurements were used to determine the diffusion coefficients D _± and conductivity f of BMImBr in mixtures. BMImBr behaved as a strong electrolyte in the mixtures under consideration. Cyclic voltammetry with a platinum electrode was used to show that, as distinct from the BMImBr-H₂O system, water in the BMImBr-PEG₁₅₀₀-H₂O system did not exhibit electrochemical activity within the “electrochemical window” of BMImBr.     

Effects of crosslinking ratio and aging time on properties of physical and chemical cellulose gels via 1-butyl-3-methylimidazolium chloride solvent

Papers used in the field of electro-responsive applications are known as Electroactive-papers (EAPaps), consisting primarily of a cellulose. 1-Butyl-3-methylimidazolium chloride is an interesting ionic liquid that acts as an effective cellulose solvent for EAPaps due to its high solubility without chain derivatization, less chain degradation, and stability in electro-responsive applications. In our work, physical and chemical cellulose gels were fabricated and studied for the effects of various crosslinking ratios (CR) and aging time (t_ag), with glutaraldehyde acting as the crosslinking agent. The crosslinking reaction conversion could be increased by increasing the CR and t_ag; the reaction products were ketone linkages and by-product water molecules. A difference in optical properties could be observed and related to the differing amounts of ketone linkages, as confirmed by FTIR-ATR quantitative analysis. UV–visible spectra showed that the prepared samples had a maximum wavelength λ_max nm, a characteristic of ketone linkages. By-product water molecules exhibited plasticizing effects, as observed by the decrease in the storage moduli (G′) at 1 day aging time. The outward migration of by-product water molecules caused a slight increase in G′ at 15 days aging time due to a closer packing. The by-product water molecules induced the H⁺-hopping and more disordered domains resulting in an ease in ion migration. Our paper-gels showed potential characteristics towards electro-responsive applications: less preparation time (<14 h) and stable gel properties.     

Lipase-catalysed polyester synthesis in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid

1-Butyl-3-methylimidazolium hexafluorophosphate ionic liquid was employed as a reaction medium for lipase-catalysed aliphatic polyester synthesis. Lipase PS-C exhibited excellent catalysis in polycondensation of diethyl octane-1,8-dicarboxylate and 1,4-butanediol at room temperature and at 60°C. A relatively high molecular weight polymer was obtained at 60°C.     

Friedel-Crafts sulfonylation in 1-butyl-3-methylimidazolium chloroaluminate ionic liquids.

1-Butyl-3-methylimidazolium chloroaluminate ionic liquids have been employed as an unconventional reaction media and as Lewis acid catalyst for Friedel-Crafts sulfonylation reaction of benzene and substituted benzenes with 4-methyl benzenesulfonyl chloride. The substrates exhibited enhanced reactivity, furnishing almost quantitative yields of diaryl sulfones, under ambient conditions. Studies concerning the effect of Lewis acidity of the ionic liquid on the initial extent of conversion of this reaction has been carried out. (27)Al NMR spectroscopy has been exploited as a tool to investigate the mechanistic details of the reaction. (27)Al NMR spectral studies show the predominance of [Al(2)Cl(7)](-) species in [bmim]Cl-AlCl(3), N = 0.67, acidic ionic liquid in the presence of 4-methyl benzenesulfonyl chloride, and after the reaction with the aromatic hydrocarbon, [AlCl(4)](-) species predominates. This change in speciation of aluminum can be attributed to the interaction of the Lewis acidic species [Al(2)Cl(7)](-) of the ionic liquid with the formed HCl during the sulfonylation reaction, which is evidenced by the control experiment. Preliminary investigations on Friedel-Crafts acylation further substantiate the argument.