Bicyclic imidazolium-based ionic liquids: synthesis and characterization

We previously reported the use of imidazole as starting compound for preparing a bicyclic imidazolium ionic liquid, [b-3C-im][NTf₂], with an overall 29% isolated yield in four synthetic steps. This new room temperature ionic liquid was shown to be far more chemically stable than commonly used [bmim][PF₆], [bdmim][PF₆], and [bdmim][NTf₂]. Because of this intriguing chemical stability, it prompted us to develop a more generalized and high yielding synthesis so that molecular diversity of bicyclic ionic liquids may be explored. In this work, we amended the previous synthetic route by employing 4-chlorobutyronitrile or 5-chlorovaleronitrile as starting materials and successfully developed a five-step synthesis of a series of novel bicyclic imidazolium-based ionic liquids in 40-53% overall isolated yields. We investigated intrinsic reactivity of all bicyclic ionic liquids prepared and found that, under strongly basic conditions, among all tested ionic liquids the 5,5-membered [R-3C-im][NTf₂] ionic liquids were most stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf₂] ionic liquid was 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. Under identical condition, the commonly used [bmim][NTf₂] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases, only [bmim][PF₆] was deuterium exchanged (50% within 1 h) and all other ionic liquids gave no detectable exchanges even after 25 days at ambient temperature. Moreover, both [bmim][NTf₂] and [bdmim][NTf₂] ionic liquids were readily methylated at C-2 position with methyl iodide under basic condition at room temperature. Under the same condition, [R-3C-im][NTf₂] and [R-4C-im][NTf₂] ionic liquids were completely stable and chemically inert. We envisioned that [R-3C-im][NTf₂] should be well suited as solvents for organic synthesis.     

Dissociation quotients of succinic acid in aqueous sodium chloride media to 225°C

The first and second molal dissociation quotients of succinic acid were measured potentiometrically with a hydrogen-electrode, concentration cell. These measurements were carried out from 0 to 225°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The dissociation quotients from this and two other studies were combined and treated with empirical equations to yield the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: log K_1a=–4.210±0.003; H _1a ⁰ =2.9±0.2 kJ-mol^–1; S _1a ⁰ =–71±1 J-mol^–1-K^–1; and C _p1a ⁰ =–98±3 J-mol^–1-K^–1; and for the second acid dissociation equilibrium at 25°C: log K_2a=–5.638±0.001; H _2a ⁰ = –0.5±0.1 kJ-mol^–1; S _2a ⁰ =–109.7±0.4 J-mol^–1-K^–1; and C _p2a ⁰ = –215±8 J-mol^–1-K^–1.     

Derivation of the transport equation for electrons moving through random impurities

A single (nonrelativistic, spinless) electron subject to a constant external electric field interacts with impurities located on an infinitely extended lattice by a potential of random strength. The random strength is given by a field of Gaussian random variables. We show the existence of the averaged dynamics and prove that in the weak coupling limit, 0, ₂ t= fixed, one obtains the usual transport equation for the velocity distribution.Work supported by a Max Kade Foundation fellowship.On leave of absence of the Fachbereich Physik der Universität München.     

离子液体相转移催化环己醇氧化制备环己酮

以不同种类的离子液体作为相转移催化剂,用双氧水作为氧化剂,Na2WO4·2H2O为催化剂,在适当的反应条件下,能有效进行相转移催化环己醇氧化制备环己酮.实验结果表明,采用酸性离子液体[C16mim]HSO4和[C14mim]HSO4相转移催化合成环己酮,可提高环己酮的产率,具有反应条件温和、操作简便、需用时间短、相转移催化剂可以循环使用等优点.在反应温度为90℃,反应时间为50min条件下,环己醇的转化率高达100%,选择性99%以上.     

Analysis of selected ionic liquid cations by ion exchange chromatography and reversed-phase high performance liquid chromatography

The chromatographic behavior of 8 ionic liquids - 7 homologues of 1-alkyl-3-methylimidazolium and 4-methyl-N-butylpyridinium - has been investigated with a strong cation exchange adsorbent. In particular, the dependence of the retention properties of these solutes on mobile phase composition, pH, and buffer concentration was evaluated with the aim of optimizing and improving the selectivity and retention of solute separation. While using the SCX stationary phase, several interactions occurred with varying strengths, depending on the mobile phase composition. Cation exchange, nonspecific hydrophobic interactions, and adsorption chromatography behavior were observed. Reversed phase chromatography occurred at low concentrations of acetonitrile, electrostatic and adsorption interactions at higher organic modifier concentrations. Elevated buffer concentrations lowered the retention factors without affecting the selectivity of ionic liquids. Obtained results were further compared to the chromatographic behaviour of ionic liquids in the reversed phase system. All analyzed ionic liquids follow reversed-phase behavior while being separated. Much lower selectivity in the range of highly hydrophilic compounds is obtained. This suggests preferred use of ion chromatography for separation and analysis of compounds below 4 carbon atoms in the alkyl side chain.     

改性离子液体中异丁烷与丁烯的烷基化反应

向由无水三氯化铝和盐酸三乙基胺合成的离子液体中溶入不同过渡金属（铜、铁、锌等）离子，考察它们对离子液体催化异丁烷与丁烯烷基化反应性能的影响。结果表明：过渡金属离子的加入能不同程度地影响离子液体的催化性能。溶入Cu2+和Cu+后，离子液体的催化性能有显著的改善，当Cu2+的摩尔加入量为三氯化铝的5%时，烷基化油收率达到丁烯体积的178%，对C8的选择性为75%，烷基化油辛烷值（RON）为92.2，并且离子液体可以重复使用。     

The partial hydrogenation of benzene to cyclohexene by nanoscale ruthenium catalysts in imidazolium ionic liquids

The controlled decomposition of an Ru(0) organometallic precursor dispersed in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF(6)), tetrafluoroborate (BMI.BF(4)) or trifluoromethane sulfonate (BMI.CF(3)SO(3)) ionic liquids with H(2) represents a simple and efficient method for the generation of Ru(0) nanoparticles. TEM analysis of these nanoparticles shows the formation of superstructures with diameters of approximately 57 nm that contain dispersed Ru(0) nanoparticles with diameters of 2.6+/-0.4 nm. These nanoparticles dispersed in the ionic liquids are efficient multiphase catalysts for the hydrogenation of alkenes and benzene under mild reaction conditions (4 atm, 75 degrees C). The ternary diagram (benzene/cyclohexene/BMI.PF(6)) indicated a maximum of 1 % cyclohexene concentration in BMI.PF(6), which is attained with 4 % benzene in the ionic phase. This solubility difference in the ionic liquid can be used for the extraction of cyclohexene during benzene hydrogenation by Ru catalysts suspended in BMI.PF(6). Selectivities of up to 39 % in cyclohexene can be attained at very low benzene conversion. Although the maximum yield of 2 % in cyclohexene is too low for technical applications, it represents a rare example of partial hydrogenation of benzene by soluble transition-metal nanoparticles.     

含离子液体［bmim］Cl的反应介质中马肝醇脱氢酶的催化特性

 研究了马肝醇脱氢酶(HLADH)在含离子液体1-丁基-3-甲基咪唑氯酸盐(［bmim］Cl)的反应介质中的催化特性. 以乙醇为底物时,该酶在［bmim］Cl含量≤0.15 g/ml的体系中的活力高于在不含离子液体的体系中的活力; 离子液体浓度过高(＞0.15 g/ml)对酶活性有明显的抑制作用. 反应温度和pH对含离子液体的反应介质中酶活力的影响规律与不含离子液体时的规律相似. 与不含离子液体的反应介质相比, HLADH在含0.05 g/ml ［bmim］Cl的体系中催化乙醇氧化的活化能下降,酶反应的Vmax和Km均升高. 反应体系中低浓度(≤0.1 g/ml)的离子液体能提高酶的热稳定性,但高浓度(＞0.1 g/ml)的离子液体可降低酶的热稳定性. 紫外二阶导数光谱显示,在含不同浓度离子液体的反应介质中酶分子构象的变化有较大的差异.     

离子液体中的生物催化反应

本文综述了近年来离子液体中生物催化反应的研究进展。离子液体作为新的绿色溶剂,用于生物催化反应具有以下特点:在离子液体中酶有良好的稳定性、选择性和反应活性。离子液体可溶解极性大的反应物, 产物易分离,酶和离子液体可重复使用。对离子液体中的生物催化进行了展望。     

Cyclic Voltammograms of Ferrocene on Multi‐Walled Carbon Nanotubes (MWCNTs)‐Modified Edge Plane Pyrolytic Graphite (EPPG) Electrode in Room Temperature Ionic Liquids (RTILs) of 1‐Ethyl‐3‐Methylimidazolium Tetrafluoroborate (EMIBF4)

In this work, the electrochemical behavior of ferrocene (Fc) was investigated by cyclic voltammetry (CV) in room temperature ionic liquids (RTILs) of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIBF₄) on glass carbon (GC), edge plane pyrolytic graphite (EPPG) and multi‐walled carbon nanotube (MWCNTs)‐modified EPPG electrodes, respectively. The results demonstrated that on GC electrode, pairs of well‐defined reversible peaks were observed, while for the electrode of EPPG, the peak potential separation (ΔE_p) is obviously larger than the theoretical value of 59 mV, hinting that the electrode of EPPG is distinguished from the commonly used electrode, consistent with the previous proposition that EPPG has many “defects”. To obtain an improved electrochemical response, multi‐walled carbon nanotubes (MWCNTs) were modified on the electrode of EPPG; the increased peak current and promoted peak potential separation not only proved the existence of “defects” in MWCNTs, but also supported that “creating active points” on an electrode is the main contribution of MWCNTs. Initiating the electrochemical research of Fc on the MWCNTs‐modified EPPG electrode in RTILs and verifying the presence of “defects” on both EPPG and MWCNTs using cyclic voltammograms (CVs) of Fc obtained in RTILs of EMIBF₄, is the main contribution of this preliminary work.