John S. Wilkes

A short history of ionic liquids—from molten salts to neoteric solvents

Ionic liquids, defined here as salts with melting temperatures below 100 °C, evolved from traditional high temperature molten salts. Some materials we would now recognize as ionic liquids were observed as far back as the mid 19th century. The quest for useful molten salts with lower melting temperatures led to inorganic chloroaluminates, to organic chloroaluminates, then to the water and air stable salts now being developed for green chemistry applications.

Air and water stable 1-ethyl-3-methylimidazolium based ionic liquids

A series of novel air and water stable low melting salts based upon the 1-ethyl-3-methylimidazolium cation (EtMeim+) have been prepared and characterized; two salts, [EtMeim]BF4 and [EtMeim]MeCO2, are liquids under ambient conditions.

Complexation of Cp2MCl2 in a chloroaluminate molten salt: relevance to homogeneous Ziegler-Natta catalysis

Abstract Ethylene polymerization via Ziegler-Natta catalysis occurs in the ambient-temperature molten salt AlCl 3 ·MEIC (MEIC = 1-ethyl-3-methylimidazolium chloride) employing Cp 2 TiCl 2 as the catalyst and AlCl 3 - x R x (R = Me, Et) as a cocatalyst. Catalysis occurs only in melts with AlCl 3 :MEIC molar ratios > 1. Cp 2 ZrCl 2 and Cp 2 HfCl 2 with AlCl 3 - x R x cocatalysts are not catalytically active in acidic melts. 1 H NMR studies indicate formation of a strong 1:1 complex between Cp 2 TiCl 2 and AlCl 3 , while Zr and Hf form much weaker 1:1 complexes due to strong Zr-Cl and Hf-Cl bonding. This stronger M-Cl bonding for Zr and Hf is proposed to preclude the initiation reaction for ethylene polymerization in the molten salt.

Electrochemical Studies of Sodium Chloride as a Lewis Buffer for Room Temperature Chloroaluminate Molten Salts

The reaction of equal molar quantities of 1-methyl-3-ethylimidazolium chloride (MEICl) with AlCl 3 results in the formation of a conductive ambient-temperature ionic liquid that, when investigated voltammetrically, exhibits 4.4V of electroinactivity between the reduction of MEI + and the oxidation of AlCl 4 − . In this paper we investigate those equilibrium processes that control the chloroacidity in these ionic liquids

Surface tension measurements of highly conducting ionic liquids

The capillary rise method is used to measure the room temperature surface tension of several ionic liquids, selected mainly for their high electrical conductivity. They include salts based on the cations 1-ethyl-3-methylimidazolium (EMI+), 1-butyl-3-methylimidazolium (BMI+), and 1,3-dimethylimidazolium (DMI+), paired with anions such as GaCl4−, FeCl4−, C(CN)3−, N(CN)2−, SCN−, EtSO4−, BF4−, CF3SO3−, (CF3SO3)2N− (Tf2N−) and Au(CN)2−. The method consumes relatively little sample (<0.1 cm3) with measurement errors of 5%. Vacuum-dried samples are placed in the measurement cell under ambient (humid) air, but the meniscus is kept dry by a small flow of dry gas. Failure to dry the active interface leads to rapid contamination in the case of hydrophilic liquids, and to anomalously high surface tension. The highest surface tension measured (61 dyn cm−1) corresponds to DMI–N(CN)2.

Reversible Plating and Stripping of Sodium at Inert Electrodes in Room Temperature Chloroaluminate Molten Salts

Sodium has been suggested as a possible anode in high energy-density batteries using room temperature chloroaluminate molten salt electrolytes, but it cannot be used directly in typical melts because the reduction of Na + falls beyond the negative voltage limit. When a neutral melt of 1-methyl-3-ethylimidazolium chloride and aluminum chloride (MEIC/AlCl 3 ) is buffered with NaCl, and excess protons (1-methyl-3-ethylimidazolium chloride/HCl) are added, the negative voltage limit is extended to -2.4 V (vs. an Al/N=0.6 melt reference electrode) and the reversible plating and stripping of sodium is observed

Spectral identification of Al3Cl10− in 1-methyl-3-ethylimidazolium chloroaluminate molten salt

Abstract The IR specular reflection of molten 1-methyl-3-ethylimidazolium (MEI) Al 3 Cl 10 is reported. After elimination of vibrational bands due to MEI + , Al 2 Cl 7 − and Al 2 Cl 6 , the following bands were assigned to Al 3 Cl 10 − : 583, 540, 488, 424, 361, 293 and 174 cm −1 . MNDO-MOPAC calculations were carried out and the predicted frequencies and intensities agreed remarkably well with the experimental spectrum.

Low Temperature Chlorogallate Molten Salt Systems

Donnees sur les melanges de trichlorure de gallium et de chlorure de butyl-1 pyridinium ou de chlorure de methyl-1 ethyl-3 imidazolium, liquides a temperature ambiante

2,4,6-Trinitrotoluene thermal decomposition: kinetic parameters determined by the isothermal differential scanning calorimetry technique

Abstract The isothermal differential scanning calorimetry technique is used to determine kinetic parameters for the thermal decomposition of 2,4,6-trinitrotoluene (TNT). Values for the activation energy and pre-exponential factor are presented. An analysis of the thermochemical induction period data is presented which allows calculation of the activation energy of the induction reaction.

Manifestations of noncovalent interactions in the solid state. Dimeric and polymeric self-assembly in imidazolium salts via face-to-face cation—cation π-stacking

Abstract X-ray crystallographic investigation of the tertiary structure of simple 1-methylimidazolium (1-Meim) salts reveals that cation—cation face-to-face π—stacking with interplanar separations in the range typically seen for molecule—molecule and molecule—cation interactions are possible. Two salts are reported. 1-Meim-CF3SO3, 1, exists as a centrosymmetric dimer with an interplanar separation of only 3.16 A. The two imidazolium rings are slipped to the extent that the interaction can be regarded as a manifestation of C—H…C—H dipole interactions. 1-Meim-NO3 exists as a one-dimensional (1-D) polymer with interplanar separations of 3.65 A. The cations are not as severely slipped as for 1 and the interactions can be regarded as the result of cation—cation and anion—anion complementary electrostatics. Semi-empirical calculations are used to rationalize the π-π stacking in both 1 and 2. Crystal data: 1-Meim-CF3SO3, 1, triclinic, P1, a=6.416(3) A, b=7.617(4) A, c=9.569(4) A, α=85.36(4)°, β=86.08(3)°, γ=85.1...