What are the types of ionic liquids



Ionic liquids (engl. Ionic liquids) are liquids that only contain ions. They are therefore liquid salts without the salt being dissolved in a solvent such as water. For a long time, hot molten salts (with table salt above 800 ° C) were the only known examples of such liquids.

Nowadays one speaks of ionic liquids in connection with salts, which are already liquid at temperatures below 100 ° C.

Examples of cations used are alkylated imidazolium, pyridinium, ammonium or phosphonium ions. A wide variety of ions are used as anions, from simple halide to more complex inorganic ions such as tetrafluoroborates to large organic ions such as trifluoromethanesulfonimide (cf. bmim).

The size of the ions involved hinders the formation of a strong crystal lattice. Even a small amount of thermal energy is therefore sufficient to overcome the lattice energy and break up the solid crystal structure.

history

In 1914, ethylammonium nitrate appeared[1] with a melting point of 12 ° C as the first ionic liquid in the literature, but the potential of this class of substances has not yet been given special attention. In the following years he was mainly concerned with electrochemical publications[2][3] with the properties of the novel substance. Not until 1983, with the synthesis of chloroaluminate melts[4] As a non-aqueous and polar solvent for transition metal complexes, the broad field of application of ionic liquids was recognized. The first publications about its use as catalysts[5] and as a solvent[6] for organic reactions there were the late eighties.

The synthesis of hydrolysis-stable ionic liquids (English "room temperature Ionic Liquids", RTILs) succeeded in 1992 by the working group around Wilkes[7] and drove the development forward quickly. Current publications and numerous patents deal with synthesis[8][9][10] new liquids, with their application as solvents and catalysts[11][12][13], with the systematic study of their chemical and physical properties[14][15][16], with toxicological studies[17][18][19] and their application in the field of analytical separation processes[20][21][22][23][24].

properties

Ionic liquids are characterized by a number of interesting properties: They are thermally stable, non-flammable, have an extremely low, barely measurable vapor pressure and have very good dissolving properties for numerous substances. In addition, due to their purely ionic structure, they also have interesting electrochemical properties, such as electrical conductivity, which is often accompanied by a high electrochemical stability (i.e. against oxidations and reductions). By varying the side chains of the cation and selecting suitable anions, the solubility in water or organic solvents, for example, can be largely freely determined. The same applies to the melting point and the viscosity. They can also be set as acids, bases or ligands by means of appropriate functional groups.

use

In principle, the molecular diversity of ionic liquids enables them to be used in a variety of technical fields of application:

  • as an electrolyte in fuel cells, capacitors, batteries, metal finishing, dye solar cells. With the help of the ionic liquids it is even possible to electrodeposit alkali metals.
  • as a release agent and / or additive: lubricants & hydraulic fluids, antistatic additives.
  • as an electro-elastic material, e.g. in actuators
  • Heat transport / heat storage: thermal fluids, PCM media.
  • as special analytics: matrix materials for GC-Headspace & MALDI-TOF-MS, solvents for Karl Fischer titration, media for protein crystallization, electrophoresis.

Cellulose finishing

With an occurrence of around 700 billion tons, cellulose is the largest natural organic chemical on earth in terms of quantity and is therefore of great importance as a renewable raw material. Even of the 40 billion tons reproduced annually by nature, only about 0.2 billion tons are used as raw material for further processing. An extended use of cellulose as a renewable raw material has so far been prevented by the lack of a suitable solvent for chemical processes. Robin Rogers and colleagues from the University of Alabama have found out, however, that through the use of ionic liquids it is now possible for the first time to provide real solutions of cellulose in technically usable concentrations [25]. The new technology therefore opens up great potential for processing cellulose.

For example, in the production of cellulose fibers from so-called chemical pulp, various auxiliary chemicals, especially carbon disulfide (CS2), currently have to be used in large quantities and then disposed of. In addition, due to the nature of the process, considerable amounts of wastewater must be disposed of. These processes can be significantly simplified by using ionic liquids, as they are used as solvents and are almost completely recycled. The "Institute for Textile Chemistry and Chemical Fibers" (ITCF) in Denkendorf and BASF are jointly investigating the properties of fibers that are spun in a pilot plant from cellulose dissolved with the help of ionic liquids. [26]

Environmental balance

The long-term environmental effects of ionic liquids are still being investigated. It is currently known that ionic liquids with longer alkyl side chains in particular tend to be toxic. Even if there is no risk of inhalation poisoning due to the non-volatility of the compounds, wastewater can be problematic. Due to the large number of possible combinations, however, one expects to achieve the desired physico-chemical properties with the lowest possible toxicity in the medium term.

see also

References

  1. Paul Walden, Bull. Acad. Sci. St. Petersburg 1914, 405-422
  2. Hurley, F; U.S. Patent 2,446,331, 1948.
  3. Hurley, F; Wier Jr, T.P .; Electrochem. Soc., 1951, 98, 207.
  4. Scheffler, Towner B .; Hussey, Charles L .; Seddon, Kenneth R .; Kear, Christopher M.; Armitage, Phillip D; Inorganic Chemistry (1983), 22 (15), 2099-100.
  5. Boon, J. A .; Levisky, J. A .; Pflug, J. L .; Wilkes, J. S .; J. Org. Chemistry, 1986, 51, 480-483.
  6. Fry, S. E .; Pienta, J. N .; J. Am. Chem. Society, 1985, 107, 6399-6400.
  7. Wilkes, J. S .; Zaworotko, M. J .; J. Chem. Soc. Chem. Commun., 1992, 965-967.
  8. Ogihara, W .; Yoshizawa, M .; Ohno, H .; Chemistry Letters, 2004, 33, 8.
  9. Dai, L .; Yu, S .; Shan, Y .; He, M .; Eur. J. Inorg. Chem. 2004, 237_241
  10. Kalb, R.; Wesner, W.; Hermann, R .; Kochan, M .; Schelch, M .; Staber, W.; Patent, 2005; WO2005021484
  11. Green, L .; Hemeon, I; Singer, R.D., Tetrahedron Lett., 2000, 41, 1343
  12. Judeh, Z. M. A .; Ching, C. B .; Bu, J .; McCluskey, A .; Tetrahedron Letters, 2002, 43, 5089-5091
  13. Seddon, K. R .; Robertson, A. Jramani, A .; Earle, M. J .; 2003, WO03020683
  14. Tokuda, H .; Hayamizu, K .; Ishii, K .; Susan, Abu Bin Hasan; Watanabe, M .; J. Phys. Chem. B .; 2004, 108, 16593-16600
  15. Tokuda, H .; Hayamizu, K .; Ishii, K .; Susan, Abu Bin Hasan; Watanabe, M .; J. Phys. Chem. B .; 2005, B-H
  16. Fredlake, C. P .; Crosthwaite, J. M .; Hert, D. G .; Aki, S .; Brennecke, J. F .; J. Chem. Eng. Data 2004, 49, 954-964
  17. Jastorff, B .; Störmann, R .; Ranke, J .; Mölter, K .; Stock, F .; Oberheitmann, B .; Hoffmann, W .; Hoffmann, J .; Nüchter, M .; Ondruschka, B .; Filser, J .; Green Chemistry, 2003, 5, 136-142
  18. Swatloski, R. P .; Holbrey, J. D .; Rogers, R. D .; Green Chemistry, 2003, 5, 361-363
  19. Swatloski, R. P .; Holbrey, J. D .; Rogers, R. D .; Memon, S. B .; Caldwell, G. A .; Caldwell, K. A .; Chem. Commun., 2004, 668-669
  20. Bösmann, A .; Datsevich, L .; Jess, A .; Lauter, A .; Schmitz, C .; Wasserscheid, P .; Chem. Commun., 2001, 2494-2495
  21. Zhang, S; Zhang, C .; Green Chemistry, 2002, 4, 376-379
  22. Pletnev, I. V .; Formanovskii, A. A; Smirnova, S. V .; Torocheshnikova, I. I.; Khachatryan, K. S .; Shvedene, N. V .; Nemilova, M. Yu .; Journal of Analytical Chemistry, 2003, 58, 7, 632-633
  23. Zhang, S .; Zhang, Q .; Zhang, C .; Ind. Eng. Chem. Res. 2004, 43, 614-622
  24. Baker, G. A .; Baker, S. N .; Pandey, S .; Bright, F. V .; Analyst, 2005, 130, 800-808
  25. Richard P. Swatloski, Scott K. Spear, John D. Holbrey, and Robin D. Rogers: Dissolution of Cellose with Ionic Liquids. In: Journal of the American Chemical Society. 124/18, 2002, pp. 4974-4975. doi: 10.1021 / ja025790m
  26. Frank Hermanutz, Frank Gähr, Klemens Massonne, Eric Uerdingen, oral presentation at the 45th Chemiefasertagung, Dornbirn, Austria, September 20th - 22nd, 2006

Category: Fabric group