Ionic liquid

An ionic liquid is a liquid that contains essentially only ions. Some ionic liquids, such as ethylammonium nitrate, are in a dynamic equilibrium where at any time more than 99.99% of the liquid is made up of ionic rather than molecular species. In the broad sense, the term includes all molten salts, for instance, sodium chloride at temperatures higher than 800 °C. Today, however, the term "ionic liquid" is commonly used for salts whose melting point is relatively low (below 100 °C). In particular, the salts that are liquid at room temperature are called room-temperature ionic liquids, or RTILs. Image File history File links Ionicliquidmini. ... Image File history File links Ionicliquidmini. ... ion (disambiguation) An ion is an atom or group of atoms with a net electric charge. ... Ethylammonium nitrate (m. ... A magnified crystal of a salt (halite/sodium chloride) Salt covering the floor of Bad Water in Death Valley, CA, the lowest point in the US. A salt, in chemistry, is any ionic compound composed of cations (positively charged ions) and anions (negative ions) so that the product is neutral... This articles section called Other facts does not cite its references or sources. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ...

1-butyl-3-methylimidazolium salts or bmim

Image File history File links bmim structure File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links bmim structure File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

History

Whereas the date of discovery, as well as discoverer, of the "first" ionic liquid is disputed, one of the earlier known ionic liquids was [EtNH₃]⁺ [NO₃]^- (m.p. 12 °C), the synthesis of which was published in 1914.^[1] Much later, series of ionic liquids based on mixtures of 1,3-dialkylimidazolium or 1-alkylpyridinium halides and trihalogenoaluminates, initially developed for use as electrolytes, were to follow.^[2],^[3] An important property of the imidazolium halogenoaluminate salts was that they were tuneable – viscosity, melting point and the acidity of the melt could be adjusted by changing the alkyl substituents and the ratio of imidazolium or pyridinium halide to halogenoaluminate.^[4] An electrolyte is a substance containing free ions which behaves as an electrically conductive medium. ... The pitch drop experiment at the University of Queensland. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... Acidity is a controversial novelette written for the popular South Asian website Chowk. ... An alkyl is a univalent radical containing only carbon and hydrogen atoms arranged in a chain. ... Imidazole is a heterocyclic aromatic organic compound. ... Pyridinium cation Pyridinium refers to the cationic form of pyridine. ...

A major drawback was their moisture sensitivity and, though to a somewhat lesser extent, their acidity/basicity, the latter which can sometimes be used to an advantage. In 1992, Wilkes and Zawarotko reported the preparation of ionic liquids with alternative, 'neutral', weakly coordinating anions such as hexafluorophosphate ([PF₆]^-) and tetrafluoroborate ([BF₄])^-, allowing a much wider range of applications for ionic liquids.^[5] It was not until recently that a class of new, air- and moisture stable, neutral ionic liquids, was available that the field attracted significant interest from the wider scientific community. Anions that interact weakly with cations are optimistically termed non-coordinating anions, although a better term is weakly coordinating anion.[1] Non-coordinating anions are useful in studying the reactivity of electrophilic cations. ... Hexafluorophosphate is an anion with chemical formula of [PF6]-. It is a good leaving group. ... The structure of the tetrafluoroborate anion, BF4− Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with many stable and important species including tetrafluomethane, CF4, and the closely related anion perchlorate, ClO4−. It arises by the reaction of fluoride salts with the Lewis acid BF3. ...

More recently, people have been moving away from [PF₆]^- and [BF₄]^- since they are highly toxic, and towards new anions such as bistriflimide [(CF₃SO₂)₂N]^- or even away from halogenated compounds completely. Moves towards less toxic cations have also been growing, with compounds like ammonium salts (such as choline) being just as flexible a scaffold as imidazole. Bistriflimide, an anion with the chemical formula of [(CF3SO2)2N]-. Category: ... Imidazole is a heterocyclic aromatic organic compound. ...

Characteristics

Ionic liquids are electrically conductive and have extremely low vapor pressure. (Their noticable odours are likely due to impurities.) Their other properties are diverse. Many have low combustibility, exellent thermal stability, a wide liquid range, and favorable solvating properties for diverse compounds. Many classes of chemical reactions, such as Diels-Alder reactions and Friedel-Crafts reactions, can be performed using ionic liquids as solvents. Recent work has shown that ionic liquids can serve as solvents for biocatalysis ^[6]. The miscibility of ionic liquids with water or organic solvents varies with sidechain lengths on the cation and with choice of anion. They can be functionalized to act as acids, bases or ligands, and have been used as precusor salts in the preparation of stable carbenes. Because of their distinctive properties, ionic liquids are attracting increasing attention in many fields, including organic chemistry, electrochemistry, catalysis, physical chemistry, and engineering; see for instance magnetic ionic liquid. In chemistry and physics, Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. ... Solvation is the attraction and association of molecules of a solvent with molecules or ions of a solute. ... A chemical reaction occurs when vapours of hydrogen chloride in a beaker and ammonia in a test tube meet to form a cloud of a new substance, ammonium chloride A chemical reaction is a process that results in the interconversion of chemical substances [1]. The substance or substances initially involved... The Diels-Alder reaction The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. ... The Friedel-Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877. ... A substance is soluble in a fluid if it dissolves in the fluid. ... An anion is an ion with negative charge. ... An acid (often represented by the generic formula HA) is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a pH of less than 7. ... A base in chemistry is a chemical substance which has a free pair of electrons to bind a hydrogen ion commonly referred to as a proton (IUPAC definition). ... In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a... A persistent carbene (also known as a stable carbene) is a particular carbene demonstrating particular stability despite being a reactive intermediate. ... Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting of primarily carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, halogens as well... English chemists John Daniell (left) and Michael Faraday (right), both credited to be founders of electrochemistry as known today. ... In chemistry and biology, catalysis is the acceleration (increase in rate) or slowing down of a chemical reaction by means of a substance, called a catalyst, that is itself not consumed by the overall reaction. ... Physical Chemistry is the combined science of physics, chemistry, thermodynamics, and quantum mechanics which functions to provide molecular-level interpretations of observed macroscopic phenomena. ... Engineering is the design, analysis, and/or construction of works for practical purposes. ... A magnetic ionic liquid was identified by Satoshi Hayashi and Hiro-o Hamaguchi of the University of Tokyo in 2004 as an ionic liquid based on the imidazole 1-butyl-3-methylimidazolium chloride and ferric chloride. ...

Despite their extremely low vapor pressures, some ionic liquids can be distilled under vacuum conditions at temperatures near 300 C ^[7]. Some ionic liquids (such as 1-butyl-3-methylimidazolium nitrate) generate flammable gases on thermal decomposition. Thermal stability and melting point depend on the components of the liquid. Distillation is a means of separating liquids through differences in their boiling points. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ...

The solubility of different species in imidazolium ionic liquids depends mainly on polarity and hydrogen bonding ability. Simple aliphatic compounds are generally only sparingly soluble in ionic liquids, whereas olefins show somewhat greater solubility, and aldehydes can be completely miscible. This can be exploited in biphasic catalysis, such as hydrogenation and hydrocarbonylation processes, allowing for relatively easy separation of products and/or unreacted substrate(s). Gas solubility follows the same trend, with carbon dioxide gas showing exceptional solubility in many ionic liquids, carbon monoxide being less soluble in ionic liquids than in many popular organic solvents, and hydrogen being only slightly soluble (similar to the solubility in water) and probably varying relatively little between the more popular ionic liquids. (Different analytical techniques have yielded somewhat different absolute solubility values.) In chemistry, non-aromatic and non-cyclic (acyclic) organic compounds are called aliphatic. ... It has been suggested that this article or section be merged with Solution. ... A synonym for the more widely accepted term, alkene. ... Hydrogenation is a chemical reaction in which unsaturated bonds between carbon atoms are reduced by attachment of a hydrogen atom to each carbon. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Carbon monoxide, with the chemical formula CO, is a colourless, odourless and tasteless gas. ... This article is about the chemistry of hydrogen. ...

Room temperature ionic liquids

Room temperature ionic liquids consist of bulky and asymmetric organic cations such as 1-alkyl-3-methylimidazolium, 1-alkylpyridinium, N-methyl-N-alkylpyrrolidinium and ammonium ions. A wide range of anions is employed, from simple halides, which generally inflect high melting points, to inorganic anions such as tetrafluoroborate and hexafluorophosphate and to large organic anions like bis-trifluorsulfonimide, triflate or tosylate. There are also many interesting examples of uses of ionic liquids with simple non-halogenated organic anions such as formate, alkylsulfate, alkylphosphate or glycolate. As an example, the melting point of 1-butyl-3-methylimidazolium tetrafluoroborate or [bmim][BF₄] with an imidazole skeleton is about -80 °C, and it is a colorless liquid with high viscosity at room temperature. An ion is an atom or group of atoms with a net electric charge. ... A ball-and-stick model of the ammonium cation Fumes from hydrochloric acid and ammonia forming a white cloud of ammonium chloride Ammonium is also an old name for the Siwa Oasis in western Egypt. ... An anion is an ion with negative charge. ... A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. ... The structure of the tetrafluoroborate anion, BF4− Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with many stable and important species including tetrafluomethane, CF4, and the closely related anion perchlorate, ClO4−. It arises by the reaction of fluoride salts with the Lewis acid BF3. ... Hexafluorophosphate is an anion with chemical formula of [PF6]-. It is a good leaving group. ... Triflate, more formally known as trifluoromethanesulfonate, has the structure CF3SO3-. It is an extremely stable polyatomic ion, being the conjugate base of triflic acid (CF3SO3H), one of the strongest acids known and a super acid. ... The tosylate group with a generic R group attached (where R can be anything, typically a carbon). ... Formate or methanoate is the ion is HCOO- (formic acid minus one hydrogen ion). ... Glycolic acid (or hydroxyacetic acid) is the smallest α-hydroxy acid (AHA). ... The structure of the tetrafluoroborate anion, BF4− Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with many stable and important species including tetrafluomethane, CF4, and the closely related anion perchlorate, ClO4−. It arises by the reaction of fluoride salts with the Lewis acid BF3. ... Imidazole is a heterocyclic aromatic organic compound. ... The pitch drop experiment at the University of Queensland. ...

It has been pointed out that in many synthetic processes using transition metal catalyst, metal nanoparticles play an important role as the actual catalyst or as a catalyst reservoir. It also been shown that ionic liquids (ILs) are an appealing medium for the formation and stabilization of catalytically active transition metal nanoparticles. More importantly, ILs can be made that incorporate co-ordinating groups,^[8], for example, with nitrile groups on either the cation or anion (CN-IL). In various C-C coupling reactions catalyzed by palladium catalyst, it has been found the palladium nanoparticles are better stabilized in CN-IL compared to non-functionalized ionic liquids; thus enhanced catalytic activity and recyclability are realized. ^[9] A nitrile is any organic compound which has a -C≡N functional group. ... A cation is an ion with positive charge. ... An anion is an ion with negative charge. ...

Food science

The application range of ionic liquid also extends to food science. [bmim]Cl for instance is able to completely dissolve freeze dried banana pulp and the solution with an additional 15% DMSO lends itself to Carbon-13 NMR analysis. In this way the entire banana compositional makeup of starch, sucrose, glucose, and fructose can be monitored as a function of banana ripening.^{[citation needed]} Freeze drying (also known as Lyophilization) is a dehydration process typically used to preserve a perishable material, or to make the material more convenient for transport. ... This article or section does not cite its references or sources. ... Dimethyl sulfoxide (DMSO) is the chemical compound (CH3)2SO. This colorless liquid is an important dipolar aprotic solvent. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz, 18. ... Starch (CAS# 9005-25-8) is a complex carbohydrate which is insoluble in water; it is used by plants as a way to store excess glucose. ... Sucrose (common name: table sugar, also called saccharose) is a disaccharide (glucose + fructose) with the molecular formula C12H22O11. ... Glucose (Glc), a monosaccharide (or simple sugar), is the most important carbohydrate in biology. ... Fructose (or levulose) is a simple sugar (monosaccharide) found in many foods and is one of the three most important blood sugars along with glucose and galactose. ...

Safety

Due to their non-volatility, effectively eliminating a major pathway for environmental release and contamination, ionic liquids have been considered as having a low impact on the environment and human health, and thus recognized as solvents for green chemistry. However, this is distinct from toxicity, and it remains to be seen how 'environmentally-friendly' ILs will be regarded once widely used by industry. Research into IL aquatic toxicity has shown them to be as toxic or more so than many current solvents already in use ^[10]. A new review paper on this aspect has just appeared ^[11]. Available research also shows that mortality isn't necessarily the most important metric for measuring their impacts in aquatic environments, as sub-lethal concentrations have been shown to change organisms' life histories in meaningful ways. According to these researchers balancing between zero VOC emissions, and avoiding spills into waterways (via waste ponds/streams, etc.) should become a top priority. However, with the enormous diversity of substituents available to make useful ILs, it should be possible to design them with useful physical properties and less toxic chemical properties. Green Chemistry is the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. ... Volatile organic compounds (VOCs) are organic chemical compounds that have high enough vapour pressures under normal conditions to significantly vaporize and enter the atmosphere. ...

Despite their low vapor pressure many ionic liquids have also found to be combustible and therefore require careful handling ^[12]. Brief exposure (5 to 7 seconds) to a flame torch will ignite these IL's and some of them are even completely consumed by combustion. In chemistry and physics, Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. ... Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ...

See also

• 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆) for an often encountered ionic liquid.
• Aza-Baylis-Hillman reaction for the use of a chiral ionic liquid in asymmetric synthesis.

1-Butyl-3-methylimidazolium hexafluorophosphate, also known as BMIM-PF6, is a viscous, colourless, hydrophobic ionic liquid. ... The Aza-Baylis-Hillman reaction or aza-BH reaction in organic chemistry is a variation of the Baylis-Hillman reaction and describes the reaction of an electron deficient alkene usually an α,β-unsaturated carbonyl compound with an imine in the presence of a nucleophile. ... The two optical isomers of bromochlorofluoromethane Chiral synthesis (also called asymmetric synthesis) is organic synthesis which preserves or introduces a desired chirality. ...

External links

Major academic groups

• QUILL, Belfast, UK
• Prof. Robin Rogers, University of Alabama, Tuscaloosa, USA
• Prof. Tom Welton, Imperial College, London, UK
• Prof. Peter Wasserscheid, Universität Erlangen-Nürnberg, Erlangen, Germany
• Prof. Joan Brennecke, University of Notre Dame, Indiana, USA
• Prof. Doug MacFarlane, Monash University, Melbourne, Australia
• Prof. Frank Endres, Clausthal-Zellerfeld, Germany
• Prof. Hiroyuki Ohno, Tokyo University of Agriculture and Technology, Japan
• Prof. Sundaram Balasubramanian, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
• Prof. Juliusz Pernak, Poznan, Poland
• Prof. Paul J. Dyson, Ecole Polytechnique Fédéral de Lausanne, Lausanne, Switzerland
• Dr. Fei Zhaofu, Ecole Polytechnique Fédéral de Lausanne, Lausanne, Switzerland
• Prof. Yuan Kou, PKU Green Chemistry Center, Peking University, Beijing, P. R. China
• Prof. Uma Ramachandran, National Institute of Pharmaceutical Education and Research (NIPER), Punjab, India

Other

• Special Issue on Ionic Liquds in the Int. J. Mol. Sci.
• Ionic Liquids @ organic-chemistry.org
• Toxicity article on rcs.org
• IUPAC Ionic Liquids Database
• Ionic Liquids in the Dortmund Data Bank

References

• Air and water stable ionic liquids in physical chemistry F. Endres, S. Zein El Abedin, Phys. Chem. Chem. Phys., 8 (2006) 2101. DOI:10.1039/b600519p
• S. Fujita, H. Kanamaru, H. Senboku and M. Arai. Preparation of Cyclic Urethanes from Amino Alcohols and Carbon Dioxide Using Ionic Liquid Catalysts with Alkali Metal Promoters. Int. J. Mol. Sci. 2006, 7, 438-450