Ionic liquid

Ionic liquids (English Ionic Liquids, and Room Temperature Ionic Liquids ( RTIL ) ) are organic salts whose ions by charge delocalization and steric effects hinder the formation of a stable crystal lattice. Therefore, even small thermal energy sufficient to overcome the power grid and to break up the solid crystal structure. It thus are salts that are liquid at temperatures below 100 ° C without the salt is dissolved in a solvent such as water.

Examples of cations used, which can be alkylated, in particular: imidazolium, pyridinium, pyrrolidinium, guanidinium, uronium, thiouronium, piperidinium, morpholinium, ammonium and phosphonium. As anions, halides and complex ions, such as tetrafluoroborate, trifluoroacetate, triflates, tosylates hexafluorophosphates phosphinates and come into question. And organic ions such as imides and amides, can be anions.

By varying the substituent of a given cation and the anion, by varying the physico- chemical properties of an ionic liquid can be varied within wide limits and optimized technical requirements go. In addition to the melting point can thus affect the solubility of, for example, homogeneous catalysts, products or reactants in the ionic liquid.

History

1914 described Paul Walden with ethylammonium nitrate, which has a melting point of 12 ° C, the first ionic liquid in the literature. The potential of this class of compounds gave no special attention to the science. In the following years were occupied mainly electrochemical publications with the properties of the new substance. Until 1983, with the synthesis of chloroaluminate melts as non-aqueous and polar solvents for transition metal complexes, one recognized the broad field of application of ionic liquids. The first publications on their use as catalysts and as a solvent for organic reactions, it was in the late 1980s.

The synthesis of hydrolysis-stable ionic liquids succeeded in 1992 by the group of Wilkes and drove the development progressing rapidly. Recent publications and numerous patents dealing with the synthesis of new liquids. The work is concerned with the continued use as solvents and catalysts, with the systematic study of their chemical and physical properties, toxicological studies and their application in the field of analytical separation processes.

Properties

Ionic liquids are characterized by a number of interesting properties. They are thermally relatively stable, difficult to ignite and have a very low, hardly measurable vapor pressure and have for many substances of very good solution properties. They also have interesting electrochemical properties, such as electrical conductivity, which is often accompanied by a high electrochemical stability against oxidation and reduction, due to their purely ionic structure. Can be described by the Poisson - Boltzmann equation, the electrostatic interactions between the ions.

By varying the side chains of the cation and the selection of suitable anion, for example, the solubility in water or organic solvents can be determined largely free. The same applies to the melting point and viscosity. With the appropriate functional groups can be synthesized as acids, bases or ligands.

Use

The molecular diversity of ionic liquids in principle allows its use in a variety of technical applications:

Chemical Engineering
Chemical Reaction Engineering
For the synthesis of nanoparticles and nanomaterials, in which case can act ionic liquids as template
Biochemical Engineering
Ionic compressor, an isothermal operating displacement compressor
As solvents for organic and inorganic syntheses, as well as for the synthesis of polymer
As an electrolyte in fuel cells, capacitors, batteries, metal finishing, dye solar cells. Using the ionic liquids, it is even possible to electrodeposit alkali metals.
As a release agent and / or additive: lubricants and hydraulic fluids, anti-static additives.
As an electro- elastic material, such as actuators
Heat transport / heat storage: thermal fluids, PCM media.
As Spezialanalytika: matrix materials for GC Headspace and MALDI -TOF -MS, the solvent for the Karl Fischer method, media for protein crystallization, electrophoresis.
Ionic liquids on single-crystal surfaces in ultrahigh vacuum are in basic research as model systems for electrode | electrolyte interfaces used

Electrolyte in dye solar cells

By means of dye solar cells can utilize a wide range of the light spectrum compared to crystalline silicon solar cells, which also allows use in low light or lower light intensity. The ionic liquids can be used as a novel electrolyte material. The benefit here is in their conductivity, which provides the required Ladungstranport. In combination with the properties of a low melting point and a very low vapor pressure, an application opens at temperatures from -20 to 80 ° C. They also have a high electrochemical stability. An application aims at using these cells eg as a charger for mobile phones in regions without a universal power supply.

Cellulose finishing

Cellulose with an incidence of about 700 billion tons of the most abundant natural organic chemical on earth and as a renewable resource of great importance. Of the annual simulated by the 40 billion tons nature only about 0.2 billion tons are used as raw material for further processing. An expanded use of cellulose as a feedstock has to, that it lacks a suitable solvent. Robin Rogers and colleagues from the University of Alabama have found that it is possible by the use of ionic liquids provide solutions of cellulose in technically useful concentrations. They must in the production of, for example, synthetic cellulosic fibers (e.g., viscose rayon) of so-called dissolving pulp currently different auxiliary chemicals, especially carbon disulfide are ( CS2), used in large quantities, and then recycled or disposed of. In addition, due to the process significant amounts must be worked from wastewater. These processes can possibly be simplified by the use of ionic liquids, since they could be used as a solvent and almost completely recycled. The Institute for Textile Chemistry and Chemical Fibers ( ITCF ) in Denkendorf and BASF jointly examine the properties of fibers are spun in a pilot plant with the help of ionic liquids dissolved cellulose.

The good solubility of cellulose in ionic liquids opens various possibilities for producing materials based on renewable resources. In a one-step synthesis can be coupled in the presence of cellulose in the solvent Kupfer-II-chlorid/Chrom-II-chlorid-Katalysatoren 1-ethyl- 3- methylimidazolium chloride are reacted at 80-120 ° C to 5-hydroxymethylfurfural (HMF ), which as a a potential building block for plastics on the basis of biomass is considered.

Pharmaceuticals

A variety of commercially available pharmaceuticals are present as salts. As pharmaceutically active ionic liquids are already known. It combines a pharmaceutically active cation with an equally active anion. The objective is a pharmaceutically active salt to obtain the properties of an ionic liquid. The pharmaceutical effect of the new ionic liquid has ideally to a synergetic effect.

Environmental Accounting

The long-term environmental effects of ionic liquids are still under investigation. Is currently known that especially ionic liquids with longer alkyl side chains tend to be toxic. Although there is no danger of poisoning due to the non-volatility of the compounds by inhalation, waste water can be problematic. Due to the large number of possible combinations but one expects the medium to achieve the desired physico-chemical properties at the lowest possible toxicity.

Lattice energy Alkylation Guanidine Homogeneous catalysis Poisson–Boltzmann equation Ionic liquid piston compressor Non-coordinating anion Digital Object Identifier Tetrahedron Letters Journal of Chemical & Engineering Data Analyst Pharmaceutical Research (journal)

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