Reaction of elemental chalcogens with imidazolium acetates to yield imidazole-2-chalcogenones: direct evidence for ionic liquids as proto-carbenes

Mechanistic analysis of the reaction between elemental sulfur or selenium and 1,3-dialkylimidazolium acetate ionic liquids, in the absence of an external base or solvent, affords evidence for the equilibrium presence of carbene species in these ionic liquids. It demonstrates the potential to control, through anion selection, the concentration of carbene in stable ionic liquids.     

Ionic Liquids as Novel Reaction Media for the Synthesis of Copoly(ester-amide)s Containing 9,10-Anthraquinone Moiety

The use of ionic liquids as novel solvents for the synthesis of aromatic copoly(ester-amide)s, containing a 9,10-anthraquinone moiety in the main chain, from the polycondensation reaction of terephthaloyl chloride and various ratios of p-phenylenediamine and 1,4-dihydroxyanthraquinone is reported. 1,3-Dialkylimidazolium-based ionic liquids are suitable reaction media for the synthesis of copoly(ester-amide)s. These copolymers exhibit color characteristics and thermal stability. The presence of the amide groups in the backbone of these polymers enhances their thermal stabilities. Inherent viscosities of the polymers obtained in 1,3-dialkylimidazolium bromide range from 0.28 to 0.42 dL/g.     

Hydrogen bonds in imidazolium ionic liquids

It is critically important to understand the structural properties of ionic liquids. In this work, the structures of cations, anions, and cation-anion ion-pairs of 1,3-dialkylimidazolium based ionic liquids were optimized systematically at the B3LYP/6-31+G level of DFT theory, and their most stable geometries were obtained. It was found that there exist only one-hydrogen-bonded ion-pairs in single-atomic anion ionic liquids such as [emim]Cl and [emim]Br, while one- and two-hydrogen-bonded ion-pairs in multiple atomic anion ionic liquids such as [emim]BF(4) and [emim]PF(6) exist. Further studies showed that the cations and anions connect each other to form a hydrogen-bonded network in 1,3-dialkylimidazolium halides, which has been proven by experimental measurement. Furthermore, the correlation of melting points and the interaction energies was discussed for both the single atomic anion and multiple atomic anion ionic liquids.     

新型对称烷基咪唑离子液体介质中酶催化合成l-乙酸薄荷酯

设计合成三种新型对称烷基咪唑六氟磷酸盐离子液体——1,3-二正丁基咪唑六氟磷酸盐([DnBIM][PF6]), 1,3-二异丁基咪唑六氟磷酸盐([DiBIM][PF6])和1,3-二仲丁基咪唑六氟磷酸盐([DsBIM][PF6]). 以脂肪酶pseudomonas cepacia催化l-薄荷醇和乙酸酐的酯化过程为模型反应, 分别考察不同介质中酶的活性、反应性和稳定性, 结果表明作为反应介质三种新型离子液体均优于经典离子液体1-正丁基-3-甲基咪唑六氟磷酸盐和有机溶剂正己烷. 在三种新的离子液体中, [DiBIM][PF6]具有最好的亲生物性而被选择作为模型反应介质. 此外, 影响l-薄荷醇转化率的各种因素(包括反应温度、底物投料比、离子液体用量和含水量)及酶的重复利用性也被详细研究. 在最佳反应条件下, l-薄荷醇转化率达到97.4%, 酶促反应速度、平衡转化率和半衰期分别是正己烷中的12.7, 4.6和15.1倍. 脂肪酶重复使用10次后催化活性没有明显减少. 由于三种新型离子液体互为同分异构体, 以上事实还表明除憎水性和亲核性以外离子液体的空间构型也是影响酶行为的一个重要因素.     

The effect of the anion on the physical properties of trihalide-based N,N-dialkylimidazolium ionic liquids

Low viscosity, high density trihalide-based 1-n-butyl-3-methylimidazolium ionic liquids have been prepared and characterised. Key physical properties (density, conductivity, melting point, refractive index, surface tension and diffusion coefficient) of the ionic liquids have been determined and are compared with those of other 1,3-dialkylimidazolium molten salts. The relationship between anion identity and the physical properties of the ionic liquids under investigation is discussed.     

室温离子液体中乙酸钠和氯苄催化合成乙酸苄酯

在多种1,3-二烷基咪唑和烷基吡啶室温离子液体中考察了较温和条件下乙酸 钠和氯化苄作用合成乙酸苄酯反应。在反应温度下（60 ℃）,熔融的三水合乙酸 钠与离子液体相混溶,氯苄同乙酸钠作用得到乙苄酯,它与四氟硼酸1-乙基-3-甲 基咪唑离子液体不溶而分层。反应结束后产物乙酸苄酯可直接倾析得到,乙酸苄酯 产率达到90%,纯度超过99%。此离子液体催化体系简化了产物分离,离子液体可以 重复使用。     

Ionic liquids as novel and recyclable reaction media for N-alkylation of amino-9,10-anthraquinones by trialkyl phosphites

Ionic liquids such as 1,3-dialkylimidazolium bromides make excellent catalysts and solvents for N-alkylation of amino-9,10-anthraquinones in the presence of trialkyl phosphites. For triethyl phosphite, [bpim][Br] gave better results. The ionic liquids are successfully regenerated and reused.     

烷基磺酸阴离子无卤素离子液体的物理化学性质研究(英文)

通过一步法合成了基于1,3-二烷基咪唑阳离子和甲烷磺酸或对甲苯磺酸阴离子的无卤素离子液体,并对它们的物理化学性质如聚集行为、表面性质、热性质、密度、黏度、折光率和电化学性质等进行了详细研究.结果表明在甲烷磺酸阴离子基离子液体中观察到离子液体中普遍存在的离子簇行为;同等条件下[BEim]MS的荧光光谱强度较[BEim]TS弱;[C12Mim]MS展现出液晶行为;[TS]-基离子液体有着较高的折光率,大于1.51.     

Exploration of 4,5-dimethyl-1H-imidazole N-oxide derivatives in the synthesis of new achiral and chiral ionic liquids

New 1-alkoxy-3-alkyl-4,5-dimethylimidazolium bromides were synthesized by alkylation of the corresponding 1-alkylimidazole 3-oxides, which were conveniently prepared via condensation of α-(hydroxyimino)ketones, primary aliphatic amines, and formaldehyde. By using enantiomerically pure chiral amines, optically active imidazolium salts were obtained. Treatment with sodium tetrafluoroborate in acetone yielded the corresponding imidazolium tetrafluoroborates. All these compounds, with only one exception, were obtained as oils, which are considered as potential ionic liquids and ‘chiral ionic liquids’. The reduction of the chiral or non-chiral 1-alkylimidazole 3-oxides with Raney-Ni, followed by alkylation with alkyl bromides and subsequent ion exchange to tetrafluoroborates, gave the corresponding 1,3-dialkylimidazolium salts, most of them showing properties of ionic liquids. The alkylation of 1-butyl-4,5-dimethylimidazole 3-oxide and the corresponding imidazole, respectively, with 1,3-dibromopropane led to the first bis-imidazolium dibromides and bis-tetrafluoroborates.     

室温离子液体浸取分离牛磺酸与硫酸钠固体混合物

在多种1,3-二烷基咪唑室温离子液体中考察了牛磺酸的溶解性能,并利用对牛磺酸溶解度较大的氯化1-甲基-3-丁基咪唑离子液体([C₄MIm]Cl)为浸取剂,在较温和条件下实现了硫酸钠和牛磺酸固体混合物的分离.浸取得到的溶有牛磺酸的离子液体经乙醇离析后可高产率地得到牛磺酸(＞98.5%),纯度超过99.5%.此方法简化了牛磺酸/硫酸钠固体混合物的分离,离子液体可以重复使用多次.     

A cautionary note on thermal runaway reactions in mixtures of 1-alkyl-3-methylimidazolium ionic liquids and <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide

N-Methylmorpholine-N-oxide (NMMO) cannot be completely separated by extraction from mixtures with common 1,3-dialkylimidazolium ionic liquids (ILs) due to strong ionic interactions between the two components. At elevated temperatures, above approx. 90 °C, especially under dry conditions and in the presence of acid, alkylating or acylating agents, remaining NMMO in ILs tends to undergo autocatalytic degradation. This is a highly exothermic, unstoppable process that results in explosions, flames, and complete charring of the reaction mixtures. Thus, caution must be exercised when drying or heating ILs that were in previous contact with NMMO, and the absence of amine oxide must be confirmed to avoid potential danger.     

Identification of 1,3-dialkylimidazolium salt supramolecular aggregates in solution

The nature of the interactions between 1,3-dialkylimidazolium cations and noncoordinating anions such as tetrafluoroborate, hexafluorophosphate, and tetraphenylborate has been studied in the solid state by X-ray diffraction analysis and in solution by (1)H NMR spectroscopy, conductivity, and microcalorimetry. In the solid state, these compounds show an extended network of hydrogen-bonded cations and anions in which one cation is surrounded by at least three anions and one anion is surrounded by at least three imidazolium cations. In the pure form, imidazolium salts are better described as polymeric supramolecules of the type {[(DAI)(3)(X)](2+)[(DAI)(X)(3)](2-)}(n) (where DAI is the dialkylimidazolium cation and X is the anion) formed through hydrogen bonds of the imidazolium cation with the anion. In solution, this supramolecular structural organization is maintained to a great extent, at least in solvents of low dielectric constant, indicating that mixtures of imidazolium ionic liquids with other molecules can be considered as nanostructured materials. This model is very useful for the rationalization of the majority of the unusual behavior of the ionic liquids.     

Ultrasonic chemical oxidative degradations of 1,3-dialkylimidazolium ionic liquids and their mechanistic elucidations

A highly efficient process for oxidative degradation of 1,3-dialkylimidazolium ionic liquids in hydrogen peroxide/acetic acid aqueous medium assisted by ultrasonic chemical irradiation is, for the first time, described. It is shown that more than 93% of the 1,3-dialkylimidazolium cation with the corresponding Cl-, Br-, BF4- and PF6- counter-anions at a concentration of 2.5 mM can be degraded at 50 degrees C within 12 h while at 72 h the conversions approach 99%. A tentative mechanism for the degradation of these ILs is for the first time proposed through a detailed kinetic analysis of several characteristic transients and/or immediate products, which are identified during the ILs degradation using GC-MS. The results clearly indicate that three hydrogen atoms in the imidazolium ring are the first sites preferably oxidized, followed by cleavage of the alkyl groups attached to the N atoms from the ring. The nature of the alkyl chain length on the imidazolium ring and the type of counter anion do not seem to affect the degradation process. Further, selective fragmentations of C-N bonds of the imidazolium or derived ring lead to ring opening, forming degraded intermediates. It is also shown that acetoxyacetic acid and biurea are the final kinetically stable degraded products from the ILs under the degradation conditions.     

Ionic liquids as efficient phase-transfer catalysts for the solid base-promoted monoalkylation of diethyl malonate

Ionic liquids （ILs） based on 1,3-dialkylimidazolium and tetraalkylammonium cations were employed as a series of efficient, environmentally benign phase-transfer catalysts （PTCs） for the base-promoted monoalkylation of diethyl malonate. The influence of various heterogeneous bases on yields was studied. Good yields and high selectivity were obtained. Solvent-free, mild reaction condition, short reaction time, and easy purification were the merits of this method. The catalytic system （IL-hase） could also be recycled after the extraction of products with ether.     

Electrolytes for dye-sensitized solar cells based on interhalogen ionic salts and liquids

In this paper, we report on the preparation of interhalogen ionic liquids of the general formula [K+]XY2-, where K+=1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, or N-alkylpyridinium; XY2-=IBr2- or I2Br-. These compounds were characterized in solution and the solid state by NMR, IR, Raman, and mass spectroscopy. The crystal structure of the compound [Me2BuIm]IBr2 (7) shows that the IBr2- anion has a linear Br-I-Br structure. Indications of an equilibrium between different forms of XY2- anions in solution are observed. Interhalogen ionic salts and liquids were used as electrolyte components for encapsulated monolithic dye-sensitized solar cells. Overall light-to-electricity conversion efficiencies up to 6.4%, 5.0%, and 2.4% at 1000 W/m2 were achieved by using electrolytes based on interhalogen ionic salts and gamma-butyrolactone, glutaronitrile, or native ionic liquids as solvents, respectively. Moreover, in terms of stability, the cell performance lost 9-14% of the initial performance after 1000 h illumination at 350 W/m2.     

Free-radical polymerization of C-vinyltetrazoles: Effect of the nature of ionic solvents

High-molecular-mass polymers (M _w up to 2.2 × 10⁶) have been synthesized by the free-radical polymerization of 5-vinyl-and 2-methyl-5-vinyltetrazoles in ionic liquids with 1,3-dialkylimidazolium and tetraalkylphosphonium cations. Effects of the structure of monomers, the nature of ionic solvents, and the conditions of polymerization on the yield and molecular mass of poly(C-vinyltetrazoles) are studied. The structure and thermal characteristics of the polymers are examined. It has been shown that the incorporation of the methyl substituent at the second position of the 5-vinyltetrazoel heterocycle in ionic media gives rise to higher molecular mass polymers and improves their solubility.     

A group contribution method for estimation of glass-transition temperature of 1,3-dialkylimidazolium ionic liquids

Glass-transition temperature (T _g) of ionic liquids (ILs) plays a key role in assessment of their potential for electrolyte application purposes. In this communication, a new group contribution model is presented for the prediction of the T _g of 1,3-dialkylimidazolium, a class of ILs, which has great potentialities to serve as electrolyte. To develop this model, the contribution of ILs’ anions and cations is separately considered. This simple model shows a low average relative deviation of 1.94 % for a data set including 109 experimental glass-transition temperature.     

Ionic Liquids as Novel Reaction Media for the Synthesis of Condensation Polymers

The use of ionic liquids as novel solvents for the synthesis of condensation polymers was investigated. A series of ionic liquids including new ones was synthesized and purified. 1,3‐Dialkylimidazolium‐based ionic liquids seem to be suitable reaction and activating media for the synthesis of high‐molecular‐weight aromatic polyimides and polyamides. Inherent viscosities of the polymers obtained in 1,3‐dialkylimidazolium bromides range from 0.52 to 1.35 dL/g.     

Synthesis of arylboronates by the palladium catalysed cross-coupling reaction in ionic liquids

The palladium catalysed cross-coupling reaction of aryl iodides and bromides with pinacolborane in 1,3-dialkylimidazolium tetrafluoroborates and hexafluorophosphates producing arylboronates is described.     

Fluorous imidazolium room-temperature ionic liquids based on HFPO trimer

Imidazole substituted with a polyfluoropolyether chain based on HFPO trimer combined with various polyfluoroalkyl triflates produced novel highly fluorous ionic liquids. Their metathesis with four different anions generated a final set of 20 fluorous ionic liquids of waxy or viscous liquid character, which are all soluble in perfluorinated solvents. Two model reactions using selected ionic liquid, the opening of a THF ring with benzoyl chloride under Friedel-Crafts conditions and substitution of benzyl chloride with sodium azide, led to decomposition of the ionic liquid. However, Diels-Alder reaction of 2,3-dimethylbuta-1,3-diene with dimethyl acetylenedicarboxylate in a fluorous ionic liquid resulted in a reasonable enhancing of the reaction rate with smooth recycle of the fluorous solvent. The fluorophilicity of these fluorous ionic liquids ranges from more than 10 for water, toluene or dichloromethane to less than 0.2 for acetonitrile or methanol.