:Ionic liquid

The term "ionic liquid" in the general sense was used as early as 1943.{{cite journal |title=The Viscosity of Pure Liquids. II. Polymerised Ionic Melts |journal=Trans. Faraday Soc. |volume=39 |date=1943 |pages=59–67 |author=R. M. Barrer |doi=10.1039/tf9433900059}}

The discovery date of the "first" ionic liquid is disputed, along with the identity of its discoverer. Ethanolammonium nitrate (m.p. 52–55 °C) was reported in 1888 by S. Gabriel and J. Weiner.{{cite journal |title=Ueber einige Abkömmlinge des Propylamins |journal=Chemische Berichte |volume=21 |issue=2 |date=1888 |pages=2669–2679 |author=S. Gabriel |author2=J. Weiner |doi=10.1002/cber.18880210288 |url=https://zenodo.org/record/1425545 |access-date=2019-07-06 |url-status=live |archive-url=https://web.archive.org/web/20200207094812/https://zenodo.org/record/1425545 |archive-date=2020-02-07}} In 1911 Ray and Rakshit, during preparation of the nitrite salts of ethylamine, dimethylamine, and trimethylamine observed that the reaction between ethylamine hydrochloride and silver nitrate yielded an unstable ethylammonium nitrite ({{chem|C|2|H|5}}){{chem|NH|3|+}}·{{chem|NO|2|-}} , a heavy yellow liquid which on immersion in a mixture of salt and ice could not be solidified and was probably the first report of room-temperature ionic liquid.{{cite journal |last1=Rây |first1=Prafulla Chandra |last2=Rakshit |first2=Jitendra Nath |date=1911 |title=CLXVII.—Nitrites of the alkylammonium bases: ethylammonium nitrite, dimethylammonium nitrite, and trimethylammonium nitrite |journal=J. Chem. Soc., Trans. |language=en |volume=99 |pages=1470–1475 |issn=0368-1645 |doi=10.1039/CT9119901470}}{{cite journal |last=Tanner |first=Eden E. L. |date=July 2022 |title=Ionic liquids charge ahead |journal=Nature Chemistry |language=en |volume=14 |issue=7 |pages=842 |bibcode=2022NatCh..14..842T |issn=1755-4349 |pmid=35778557 |doi=10.1038/s41557-022-00975-4 |s2cid=250181516 |url=https://www.nature.com/articles/s41557-022-00975-4|url-access=subscription }} Later in 1914, Paul Walden reported one of the first stable room-temperature ionic liquids ethylammonium nitrate ({{chem|C|2|H|5}}){{chem|NH|3|+}}·{{chem|NO|3|-}} (m.p. 12 °C).Paul Walden (1914), Bull. Acad. Sci. St. Petersburg, pages 405-422. In the 1970s and 1980s, ionic liquids based on alkyl-substituted imidazolium and pyridinium cations, with halide or tetrahalogenoaluminate anions, were developed as potential electrolytes in batteries.{{cite journal |title=Electrochemical scrutiny of organometallic iron complexes and hexamethylbenzene in a room-temperature molten salt |author=H. L. Chum |author2=V. R. Koch |author3=L. L. Miller |author4=R. A. Osteryoung |journal=J. Am. Chem. Soc. |date=1975 |volume=97 |pages=3264–3265 |issue=11 |doi=10.1021/ja00844a081}}{{cite journal |title=Dialkylimidazolium chloroaluminate melts: a new class of room-temperature ionic liquids for electrochemistry, spectroscopy and synthesis |author=J. S. Wilkes |author2=J. A. Levisky |author3=R. A. Wilson |author4=C. L. Hussey |journal=Inorg. Chem. |date=1982 |volume=21 |pages=1263–1264 |issue=3 |doi=10.1021/ic00133a078}}

For the imidazolium halogenoaluminate salts, their physical properties—such as viscosity, melting point, and acidity—could be adjusted by changing the alkyl substituents and the imidazolium/pyridinium and halide/halogenoaluminate ratios.{{cite journal |title=Potentiometric investigation of dialuminium heptachloride formation in aluminum chloride-1-butylpyridinium chloride mixtures |author=R. J. Gale |author2=R. A. Osteryoung |journal=Inorganic Chemistry |date=1979 |volume=18 |pages=1603–1605 |issue=6 |doi=10.1021/ic50196a044}} Two major drawbacks for some applications were moisture sensitivity and acidity or basicity. In 1992, Wilkes and Zawarotko obtained ionic liquids with 'neutral' weakly coordinating anions such as hexafluorophosphate ({{chem|PF|6|-}}) and tetrafluoroborate ({{chem|BF|4|-}}), allowing a much wider range of applications.{{cite journal |author1=J. S. Wilkes |author2=M. J. Zaworotko |title=Air and water stable 1-ethyl-3-methylimidazolium based ionic liquids |journal=Chemical Communications |year=1992 |issue=13 |pages=965–967 |doi=10.1039/c39920000965}}

ILs are typically colorless viscous liquids. They are often moderate to poor conductors of electricity, and rarely self-ionize.{{citation needed|date=February 2024}} They do, however, have a very large electrochemical window, enabling electrochemical refinement of otherwise intractable ores.{{Ullmann|doi=10.1002/14356007.l14_l01|title=Ionic liquids|pp=550-551}}

They exhibit low vapor pressure, which can be as low as 10⁻¹⁰ Pa.{{cite journal |title=Thermodynamic Properties of 1-Butyl-3-methylimidazolium Hexafluorophosphate in the Ideal Gas State |author=Yauheni U. Paulechka |author2=Gennady J. Kabo |author3=Andrey V. Blokhin |author4=Oleg A. Vydrov |author5=Joseph W. Magee |author6=Michael Frenkel |name-list-style=amp |journal=Journal of Chemical & Engineering Data |date=2002 |volume=48 |pages=457–62 |issue=3 |doi=10.1021/je025591i}} Many have low combustibility and are thermally stable.

The solubility properties of ILs are diverse. Saturated aliphatic compounds are generally only sparingly soluble in ionic liquids, whereas alkenes show somewhat greater solubility, and aldehydes often completely miscible. Solubility differences 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 good solubility in many ionic liquids. Carbon monoxide is less soluble in ionic liquids than in many popular organic solvents, and hydrogen is only slightly soluble (similar to the solubility in water) and may vary relatively little between the more common ionic liquids.

Many classes of chemical reactions, The miscibility of ionic liquids with water or organic solvents varies with side chain lengths on the cation and with choice of anion. They can be functionalized to act as acids, bases, or ligands, and are precursors salts in the preparation of stable carbenes. Because of their distinctive properties, ionic liquids have been investigated for many applications.

File:Commonly used cations.png

Some ionic liquids can be distilled under vacuum conditions at temperatures near 300 °C.{{cite journal |title=The distillation and volatility of ionic liquids |author=Martyn J. Earle |author2=José M.S.S. Esperança |author3=Manuela A. Gilea |author4=José N. Canongia Lopes |author5=Luís P.N. Rebelo |author6=Joseph W. Magee |author7=Kenneth R. Seddon |author8=Jason A. Widegren |name-list-style=amp |journal=Nature |date=2006 |volume=439 |pages=831–4 |issue=7078 |bibcode=2006Natur.439..831E |pmid=16482154 |doi=10.1038/nature04451 |s2cid=4357175}} The vapor is not made up of separated ions,{{cite journal |title=Volatile times for ionic liquids |author=Peter Wasserscheid |journal=Nature |date=2006 |volume=439 |page=797 |issue=7078 |bibcode=2006Natur.439..797W |pmid=16482141 |doi=10.1038/439797a |doi-access=free}} but consists of ion pairs.{{cite journal |title=Vapourisation of ionic liquids |author=James P. Armstrong |author2=Christopher Hurst |author3=Robert G. Jones |author4=Peter Licence |author5=Kevin R. J. Lovelock |author6=Christopher J. Satterley |author7=Ignacio J. Villar-Garcia |name-list-style=amp |journal=Physical Chemistry Chemical Physics |date=2007 |volume=9 |pages=982–90 |issue=8 |bibcode=2007PCCP....9..982A |pmid=17301888 |doi=10.1039/b615137j}}

ILs have a wide liquid range. Some ILs do not freeze down to very low temperatures (even −150 °C), The glass transition temperature was detected below −100 °C in the case of N-methyl-N-alkylpyrrolidinium cations fluorosulfonyl-trifluoromethanesulfonylimide (FTFSI).{{cite journal |last=Reiter |first=Jakub |title=Fluorosulfonyl-(trifluoromethanesulfonyl)imide ionic liquids with enhanced asymmetry |journal=Physical Chemistry Chemical Physics |date=2 Sep 2012 |volume=15 |issue=7 |pages=2565–2571 |bibcode=2013PCCP...15.2565R |pmid=23302957 |doi=10.1039/c2cp43066e}} Low-temperature ionic liquids (below 130 K) have been proposed as the fluid base for an extremely large diameter spinning liquid-mirror telescope to be based on the Moon.{{cite journal |author=E. F. Borra |author2=O. Seddiki |author3=R. Angel |author4=D. Eisenstein |author5=P. Hickson |author6=K. R. Seddon |author7=S. P. Worden |name-list-style=amp |title=Deposition of metal films on an ionic liquid as a basis for a lunar telescope |date=2007 |journal=Nature |volume=447 |issue=7147 |pages=979–981 |bibcode=2007Natur.447..979B |pmid=17581579 |doi=10.1038/nature05909 |s2cid=1977373}}

Water is a common impurity in ionic liquids, as it can be absorbed from the atmosphere and influences the transport properties of RTILs, even at relatively low concentrations.

File:P1010480-1s.JPG

Classically, ILs consist of salts of unsymmetrical, flexible organic cations with symmetrical weakly coordinating anions. Both cationic and anionic components have been widely varied.

Room-temperature ionic liquids (RTILs) are dominated by salts derived from 1-methylimidazole, i.e., 1-alkyl-3-methylimidazolium. Examples include 1-ethyl-3-methyl- (EMIM), 1-butyl-3-methyl- (BMIM), 1-octyl-3 methyl (OMIM), 1-decyl-3-methyl-(DMIM), 1-dodecyl-3-methyl- (dodecylMIM). Other imidazolium cations are 1-butyl-2,3-dimethylimidazolium (BMMIM or DBMIM) and 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium (DAMI). Other N-heterocyclic cations are derived from pyridine: 4-methyl-N-butyl-pyridinium (MBPy) and N-octylpyridinium (C8Py). Conventional quaternary ammonium cations also form ILs, e.g. tetraethylammonium (TEA) and tetrabutylammonium (TBA).

Typical anions in ionic liquids include the following: tetrafluoroborate (BF₄), hexafluorophosphate (PF₆), bis-trifluoromethanesulfonimide (NTf₂), trifluoromethanesulfonate (OTf), dicyanamide (N(CN)₂), hydrogensulfate ({{chem2|HSO4-}}), and ethyl sulfate (EtOSO₃). Magnetic ionic liquids can be synthesized by incorporating paramagnetic anions, illustrated by 1-butyl-3-methylimidazolium tetrachloroferrate.

Protic ionic liquids are formed via a proton transfer from an acid to a base.{{cite journal |last1=Greaves |first1=Tamar L. |last2=Drummond |first2=Calum J. |date=2008-01-01 |title=Protic Ionic Liquids: Properties and Applications |journal=Chemical Reviews |volume=108 |issue=1 |pages=206–237 |issn=0009-2665 |pmid=18095716 |doi=10.1021/cr068040u |url=https://doi.org/10.1021/cr068040u|url-access=subscription }} In contrast to other ionic liquids, which generally are formed through a sequence of synthesis steps, protic ionic liquids can be created more easily by simply mixing the acid and base.

Phosphonium cations (R₄P⁺) are less common but offer some advantageous properties.{{cite journal |author=K. J. Fraser |author2=D. R. MacFarlane |journal=Aust. J. Chem. |date=2009 |volume=62 |issue=4 |pages=309–321 |title=Phosphonium-Based Ionic Liquids: An Overview |doi=10.1071/ch08558}}{{cite journal |author=Jiangshui Luo |author2=Olaf Conrad |author3=Ivo F. J. Vankelecom |name-list-style=amp |journal=Journal of Materials Chemistry |date=2012 |volume=22 |issue=38 |pages=20574–20579 |title=Physicochemical properties of phosphonium-based and ammonium-based protic ionic liquids |doi=10.1039/C2JM34359B |url=https://lirias.kuleuven.be/bitstream/123456789/369396/2/JMC_+Physicochemical+properties+of+phosphonium-based+and+ammonium-based+protic+ionic+liquids.pdf |access-date=2018-05-16 |url-status=live |archive-url=https://web.archive.org/web/20170922102430/https://lirias.kuleuven.be/bitstream/123456789/369396/2/JMC_+Physicochemical+properties+of+phosphonium-based+and+ammonium-based+protic+ionic+liquids.pdf |archive-date=2017-09-22}}{{cite journal |last=Tripathi |first=Alok Kumar |date=2021 |title=Ionic liquid–based solid electrolytes (ionogels) for application in rechargeable lithium battery |journal=Materials Today Energy |language=en |volume=20 |pages=100643 |doi=10.1016/j.mtener.2021.100643 |s2cid=233581904}} Some examples of phosphonium cations are trihexyl(tetradecyl)phosphonium (P_6,6,6,14) and tributyl(tetradecyl)phosphonium (P_4,4,4,14).

Polymerized ionic liquids, poly(ionic liquid)s or polymeric ionic liquids, all abbreviated as PIL is the polymeric form of ionic liquids.{{cite journal |author=A. Eftekhari |author2=O. Seddiki |title=Synthesis and Properties of Polymerized Ionic Liquids |date=2017 |journal=European Polymer Journal |volume=90 |pages=245–272 |doi=10.1016/j.eurpolymj.2017.03.033}} They have half of the ionicity of ionic liquids since one ion is fixed as the polymer moiety to form a polymeric chain. PILs have a similar range of applications, comparable with those of ionic liquids but the polymer architecture provides a better chance for controlling the ionic conductivity. They have extended the applications of ionic liquids for designing smart materials or solid electrolytes.Ionic Liquid Devices, Editor: Ali Eftekhari, Royal Society of Chemistry, Cambridge 2018, https://pubs.rsc.org/en/content/ebook/978-1-78801-183-9 {{Webarchive|url=https://web.archive.org/web/20190330105026/https://pubs.rsc.org/en/content/ebook/978-1-78801-183-9 |date=2019-03-30}}Polymerized Ionic Liquids, Editor: Ali Eftekhari, Royal Society of Chemistry, Cambridge 2018, https://pubs.rsc.org/en/content/ebook/978-1-78801-053-5 {{Webarchive|url=https://web.archive.org/web/20190330104657/https://pubs.rsc.org/en/content/ebook/978-1-78801-053-5 |date=2019-03-30}}

Many applications have been considered, but few have been commercialized.{{cite book |title=Commercial Applications of Ionic Liquids |editor=Shiflett, Mark B. |publisher=Springer International |year=2020 |isbn=978-3-030-35245-5}}{{cite journal |title=Applications of ionic liquids in the chemical industry |journal=Chem. Soc. Rev. |volume=37 |pages=123–150 |year=2008 |last1=Plechkova |first1=Natalia V. |last2=Seddon |first2=Kenneth R. |issue=1 |pmid=18197338 |doi=10.1039/b006677j}} ILs are used in the production of gasoline by catalyzing alkylation.{{cite journal |title=Review of Isobutane Alkylation Technology Using Ionic Liquid-Based Catalysts—Where Do We Stand? |year=2020 |last1=Kore |first1=Rajkumar |last2=Scurto |first2=Aaron M. |last3=Shiflett |first3=Mark B. |journal=Industrial & Engineering Chemistry Research |volume=59 |issue=36 |pages=15811–15838 |doi=10.1021/acs.iecr.0c03418 |s2cid=225512999}}{{cite web |title=Ionic liquid alkylation technology receives award |date=January 2, 2018 |website=Oil and Gas Engineering |url=https://www.oilandgaseng.com/articles/ionic-liquid-alkylation-technology-receives-award/ |access-date=June 10, 2021 |url-status=live |archive-url=https://web.archive.org/web/20220125080438/https://www.oilandgaseng.com/articles/ionic-liquid-alkylation-technology-receives-award/ |archive-date=January 25, 2022}}

File:2,4-Me2pentaneRoute.png (gasoline component) as practiced by Chevron.]]

An IL based on tetraalkylphosphonium iodide is a solvent for tributyltin iodide, which functions as a catalyst to rearrange the monoepoxide of butadiene. This process was commercialized as a route to 2,5-dihydrofuran, but later discontinued.{{Ullmann|doi=10.1002/14356007.l14_l01|title=Ionic Liquids|year=2007|last1=Meindersma|first1=G. Wytze|last2=Maase|first2=Matthias|last3=De Haan|first3=André B.|isbn=978-3527306732}}

ILs improve the catalytic performance of palladium nanoparticles.{{cite journal |author=Zhao, D. |author2=Fei, Z. |author3=Geldbach, T. J. |author4=Scopelliti, R. |author5=Dyson, P. J. |journal=J. Am. Chem. Soc. |date=2004 |volume=126 |pages=15876–82 |title=Nitrile-Functionalized Pyridinium Ionic Liquids: Synthesis, Characterization, and Their Application in Carbon-Carbon Coupling Reactions |issue=48 |pmid=15571412 |doi=10.1021/ja0463482}} Furthermore, ionic liquids can be used as pre-catalysts for chemical transformations. In this regard dialkylimidazoliums such as [EMIM]Ac have been used in the combination with a base to generate N-heterocyclic carbenes (NHCs). These imidazolium based NHCs are known to catalyse a number transformations such as the benzoin condensation and the OTHO reaction.{{cite journal |journal=Chemistry: A European Journal |volume=20 |issue=43 |date=2014 |pages=13889–13893 |title=Ionic Liquids as Precatalysts in the Highly Stereoselective Conjugate Addition of α,β‐Unsaturated Aldehydes to Chalcones |author=L.Ta |author2=A. Axelsson |author3=J. Bilj |author4=M. Haukka |author5=H. Sundén |pmid=25201607 |doi=10.1002/chem.201404288 |url=http://publications.lib.chalmers.se/records/fulltext/204508/local_204508.pdf |access-date=2021-03-16 |url-status=live |archive-url=https://web.archive.org/web/20210930043317/https://publications.lib.chalmers.se/records/fulltext/204508/local_204508.pdf |archive-date=2021-09-30}}

Recognizing that approximately 50% of commercial pharmaceuticals are salts, ionic liquid forms of a number of pharmaceuticals have been investigated. Combining a pharmaceutically active cation with a pharmaceutically active anion leads to a Dual Active ionic liquid in which the actions of two drugs are combined.{{cite journal |title=Crystalline vs. Ionic Liquid Salt Forms of Active Pharmaceutical Ingredients: A Position Paper |author=J. Stoimenovski |author2=D. R. MacFarlane |author3=K. Bica |author4=R. D. Rogers |journal=Pharmaceutical Research |date=2010 |volume=27 |issue=4 |pages=521–526 |pmid=20143257 |doi=10.1007/s11095-009-0030-0 |s2cid=207224631}}{{cite journal |title=BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity |author=Frank Postleb |author2=Danuta Stefanik |author3=Harald Seifert |author4=Ralf Giernoth |name-list-style=amp |journal=Zeitschrift für Naturforschung B |date=2013 |volume=68b |issue=10 |pages=1123–1128 |doi=10.5560/ZNB.2013-3150 |doi-access=free}}

ILs can extract specific compounds from plants for pharmaceutical, nutritional and cosmetic applications, such as the antimalarial drug artemisinin from the plant Artemisia annua.{{cite journal |journal=Journal of Natural Products |volume=69 |issue=11 |date=2006 |pages=1653–1664 |title=Comparative assessment of technologies for extraction of artemisinin |author=A. Lapkin |author2=P. K. Plucinski |author3=M. Cutler |pmid=17125242 |doi=10.1021/np060375j}}

The dissolution of cellulose by ILs has attracted interest.{{cite journal |title=Dissolution of Cellose with Ionic Liquids |author=Richard P. Swatloski |author2=Scott K. Spear |author3=John D. Holbrey |author4=Robin D. Rogers |name-list-style=amp |journal=Journal of the American Chemical Society |date=2002 |volume=124/18 |pages=4974–4975 |issue=18 |citeseerx=10.1.1.466.7265 |pmid=11982358 |doi=10.1021/ja025790m |s2cid=2648188}} A patent application from 1930 showed that 1-alkylpyridinium chlorides dissolve cellulose.Charles Graenacher, Manufacture and Application of New Cellulose Solutions and Cellulose Derivatives Produced therefrom, US 1934/1943176. Following in the footsteps of the lyocell process, which uses hydrated N-methylmorpholine N-oxide as a solvent for pulp and paper. The "valorization" of cellulose, i.e. its conversion to more valuable chemicals, has been achieved by the use of ionic liquids. Representative products are glucose esters, sorbitol, and alkylgycosides.{{cite journal |last=Ignatyev |first=Igor |author2=Charlie Van Doorslaer |author3=Pascal G.N. Mertens |author4=Koen Binnemans |author5=Dirk. E. de Vos |journal=Holzforschung |date=2011 |volume=66 |issue=4 |pages=417–425 |title=Synthesis of glucose esters from cellulose in ionic liquids |doi=10.1515/hf.2011.161 |s2cid=101737591 |url=https://lirias.kuleuven.be/handle/123456789/321763 |access-date=2021-05-13 |url-status=live |archive-url=https://web.archive.org/web/20170830193820/https://lirias.kuleuven.be/handle/123456789/321763 |archive-date=2017-08-30|url-access=subscription }} IL 1-butyl-3-methylimidazolium chloride dissolves freeze-dried banana pulp and with an additional 15% dimethyl sulfoxide, lends itself to carbon-13 NMR analysis. In this way the entire complex of starch, sucrose, glucose, and fructose can be monitored as a function of banana ripening.{{cite journal |author=Fort D.A, Swatloski R.P., Moyna P., Rogers R.D., Moyna G. |year=2006 |title=Use of ionic liquids in the study of fruit ripening by high-resolution 13C NMR spectroscopy: 'green' solvents meet green bananas |journal=Chem. Commun. |volume=2006 |issue=7 |pages=714–716 |pmid=16465316 |doi=10.1039/B515177P}}{{cite journal |title=Energy-efficient extraction of fuel and chemical feedstocks from algae |journal=Green Chemistry |volume=14 |issue=2 |date=2012 |pages=419–427 |author=R. E. Teixeira |doi=10.1039/C2GC16225C}}

Beyond cellulose, ILs have also shown potential in the dissolution, extraction, purification, processing and modification of other biopolymers such as chitin/chitosan, starch, alginate, collagen, gelatin, keratin, and fibroin.{{cite journal |last1=Mahmood |first1=Hamayoun |last2=Moniruzzaman |first2=Muhammad |date=2019 |title=Recent Advances of Using Ionic Liquids for Biopolymer Extraction and Processing |journal=Biotechnology Journal |language=en |volume=14 |issue=12 |pages=1900072 |issn=1860-7314 |pmid=31677240 |doi=10.1002/biot.201900072 |s2cid=207833124 |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/biot.201900072 |access-date=2021-01-17 |url-status=live |archive-url=https://web.archive.org/web/20210122014716/https://onlinelibrary.wiley.com/doi/abs/10.1002/biot.201900072 |archive-date=2021-01-22|url-access=subscription }}{{cite journal |last1=Chen |first1=Jin |last2=Xie |first2=Fengwei |last3=Li |first3=Xiaoxi |last4=Chen |first4=Ling |date=2018-09-17 |title=Ionic liquids for the preparation of biopolymer materials for drug/gene delivery: a review |journal=Green Chemistry |language=en |volume=20 |issue=18 |pages=4169–4200 |issn=1463-9270 |doi=10.1039/C8GC01120F |s2cid=106290272 |url=https://pubs.rsc.org/en/content/articlelanding/2018/gc/c8gc01120f |access-date=2021-01-17 |url-status=live |archive-url=https://web.archive.org/web/20210122053159/https://pubs.rsc.org/en/content/articlelanding/2018/gc/c8gc01120f |archive-date=2021-01-22}} For example, ILs allow for the preparation of biopolymer materials in different forms (e.g. sponges, films, microparticles, nanoparticles, and aerogels) and better biopolymer chemical reactions, leading to biopolymer-based drug/gene-delivery carriers. Moreover, ILs enable the synthesis of chemically modified starches with high efficiency and degrees of substitution (DS) and the development of various starch-based materials such as thermoplastic starch, composite films, solid polymer electrolytes, nanoparticles and drug carriers.{{cite journal |last1=Ren |first1=Fei |last2=Wang |first2=Jinwei |last3=Xie |first3=Fengwei |last4=Zan |first4=Ke |last5=Wang |first5=Shuo |last6=Wang |first6=Shujun |date=2020-04-06 |title=Applications of ionic liquids in starch chemistry: a review |journal=Green Chemistry |language=en |volume=22 |issue=7 |pages=2162–2183 |issn=1463-9270 |doi=10.1039/C9GC03738A |s2cid=213702088 |url=https://pubs.rsc.org/en/content/articlelanding/2020/gc/c9gc03738a |access-date=2021-01-17 |url-status=live |archive-url=https://web.archive.org/web/20210124091435/https://pubs.rsc.org/en/content/articlelanding/2020/gc/c9gc03738a |archive-date=2021-01-24}}

The IL 1-butyl-3-methylimidazolium chloride has been investigated for the recovery of uranium and other metals from spent nuclear fuel and other sources.Ch. Jagadeeswara Rao, K.A. Venkatesan, K. Nagarajan, T.G. Srinivasan and P. R. Vasudeva Rao, Electrodeposition of metallic uranium at near ambient conditions from room-temperature ionic liquid, Journal of Nuclear Materials, 408 (2011) 25–29.

ILs are potential heat transfer and storage media in solar thermal energy systems. Concentrating solar thermal facilities such as parabolic troughs and solar power towers focus the sun's energy onto a receiver, which can generate temperatures of around {{convert|600|C}}. This heat can then generate electricity in a steam or other cycle. For buffering during cloudy periods or to enable generation overnight, energy can be stored by heating an intermediate fluid. Although nitrate salts have been the medium of choice since the early 1980s, they freeze at {{convert|220|C}} and thus require heating to prevent solidification. Ionic liquids such as [C₄mim][{{chem|BF|4}}] have more favorable liquid-phase temperature ranges (−75 to 459 °C) and could therefore be excellent liquid thermal storage media and heat transfer fluids.{{cite journal |journal=International Solar Energy Conference |date=2001 |pages=445–451 |title=Novel ionic liquid thermal storage for solar thermal electric power systems |author=Banqui Wu |author2=Ramana G. Reddy |author3=Robin D. Rogers |name-list-style=amp}}

ILs can aid the recycling of synthetic goods, plastics, and metals. They offer the specificity required to separate similar compounds from each other, such as separating polymers in plastic waste streams. This has been achieved using lower temperature extraction processes than current approaches[http://www.bioniqs.com/applications_plastics.php] {{webarchive|url=https://web.archive.org/web/20090312011018/http://www.bioniqs.com/applications_plastics.php|date=March 12, 2009}} and could help avoid incinerating plastics or dumping them in landfill.

ILs can replace water as the electrolyte in metal-air batteries. ILs are attractive because of their low vapor pressure. Furthermore, ILs have an electrochemical window of up to six volts{{cite journal |title=Ionic-liquid materials for the electrochemical challenges of the future |author=Michel Armand |author2=Frank Endres |author3=Douglas R. MacFarlane |author4=Hiroyuki Ohno |author5=Bruno Scrosati |name-list-style=amp |journal=Nature Materials |date=2009 |volume=8 |pages=621–629 |issue=8 |bibcode=2009NatMa...8..621A |pmid=19629083 |doi=10.1038/nmat2448}} (versus 1.23 for water) supporting more energy-dense metals. Energy densities from 900 to 1600 watt-hours per kilogram appear possible.{{cite journal |journal=Technology Review |title=Betting on a Metal-Air Battery Breakthrough |date=November 5, 2009 |url=http://www.technologyreview.com/energy/23877/ |access-date=November 7, 2009 |url-status=live |archive-url=https://web.archive.org/web/20091106101323/http://www.technologyreview.com/energy/23877/ |archive-date=November 6, 2009}}

ILs can act as dispersing agents in paints to enhance finish, appearance, and drying properties.Examples are the TEGO brand dispersers by Evonik, used in their Pliolite brand paints. ILs are used for dispersing nanomaterials at IOLITEC.

{{Main|Ionic liquids in carbon capture}}

ILs and amines have been investigated for capturing carbon dioxide {{chem|CO|2}} and purifying natural gas.{{cite web |title=C&E News |url=http://pubs.acs.org/subscribe/journals/cen/87/i28/toc/toc_i28.html |access-date=2009-08-01 |url-status=live |archive-url=https://web.archive.org/web/20160109084317/http://pubs.acs.org/subscribe/journals/cen/87/i28/toc/toc_i28.html |archive-date=2016-01-09}}{{cite journal |author1=Barghi S.H. |author2=Adibi M. |author3=Rashtchian D. |year=2010 |title=An experimental study on permeability, diffusivity, and selectivity of CO2 and CH4 through [bmim][PF6] ionic liquid supported on an alumina membrane: Investigation of temperature fluctuations effects |journal=Journal of Membrane Science |volume=362 |issue=1–2 |pages=346–352 |doi=10.1016/j.memsci.2010.06.047}}{{cite journal |author1=Mota-Martinez M. T. |author2=Althuluth M. |author3=Berrouk A. |author4=Kroon M.C. |author5=Peters Cor J. |year=2014 |title=High pressure phase equilibria of binary mixtures of light hydrocarbons in the ionic liquid 1-hexyl-3-methylimidazolium tetracyanoborate |journal=Fluid Phase Equilibria |volume=362 |pages=96–101 |doi=10.1016/j.fluid.2013.09.015}}

Some ionic liquids have been shown to reduce friction and wear in basic tribological testing,{{cite journal |last1=Bermúdez |first1=María-Dolores |last2=Jiménez |first2=Ana-Eva |last3=Sanes |first3=José |last4=Carrión |first4=Francisco-José |date=2009-08-04 |title=Ionic Liquids as Advanced Lubricant Fluids |journal=Molecules |language=en |volume=14 |issue=8 |pages=2888–2908 |pmid=19701132 |doi=10.3390/molecules14082888 |doi-access=free |pmc=6255031}}{{cite journal |last=Minami |first=Ichiro |date=2009-06-24 |title=Ionic Liquids in Tribology |journal=Molecules |language=en |volume=14 |issue=6 |pages=2286–2305 |pmid=19553900 |doi=10.3390/molecules14062286 |doi-access=free |pmc=6254448}}{{cite journal |last1=Somers |first1=Anthony E. |last2=Howlett |first2=Patrick C. |last3=MacFarlane |first3=Douglas R. |last4=Forsyth |first4=Maria |date=2013-01-21 |title=A Review of Ionic Liquid Lubricants |journal=Lubricants |language=en |volume=1 |issue=1 |pages=3–21 |doi=10.3390/lubricants1010003 |doi-access=free |url=http://dro.deakin.edu.au/eserv/DU:30062736/somers-areviewofionic-2013.pdf |access-date=2019-08-16 |url-status=live |archive-url=https://web.archive.org/web/20181104022458/http://dro.deakin.edu.au/eserv/DU:30062736/somers-areviewofionic-2013.pdf |archive-date=2018-11-04}}{{cite journal |last1=Zhou |first1=Feng |last2=Liang |first2=Yongmin |last3=Liu |first3=Weimin |date=2009-08-19 |title=Ionic liquid lubricants: designed chemistry for engineering applications |journal=Chemical Society Reviews |language=en |volume=38 |issue=9 |pages=2590–9 |issn=1460-4744 |pmid=19690739 |doi=10.1039/b817899m}} and their polar nature makes them candidate lubricants for tribotronic applications. While the comparatively high cost of ionic liquids currently prevents their use as neat lubricants, adding ionic liquids in concentrations as low as 0.5 wt% may significantly alter the lubricating performance of conventional base oils. Thus, the current focus of research is on using ionic liquids as additives to lubricating oils, often with the motivation to replace widely used, ecologically harmful lubricant additives. However, the claimed ecological advantage of ionic liquids has been questioned repeatedly and is yet to be demonstrated from a life-cycle perspective.{{cite journal |last1=Petkovic |first1=Marija |last2=Seddon |first2=Kenneth R. |last3=Rebelo |first3=Luís Paulo N. |last4=Pereira |first4=Cristina Silva |date=2011-02-22 |title=Ionic liquids: a pathway to environmental acceptability |journal=Chem. Soc. Rev. |language=en |volume=40 |issue=3 |pages=1383–1403 |issn=1460-4744 |pmid=21116514 |doi=10.1039/c004968a}}

Ionic liquids' low volatility effectively eliminates a major pathway for environmental release and contamination.

Ionic liquids' aquatic toxicity is as severe as or more so than many current solvents.{{cite journal |title=Acute toxicity of ionic liquids to the zebrafish (Danio rerio) |author=C Pretti |author2=C Chiappe |author3=D Pieraccini |author4=M Gregori |author5=F Abramo |author6=G Monni |author7=L Intorre |name-list-style=amp |journal=Green Chem. |date=2006 |volume=8 |pages=238–240 |issue=3 |doi=10.1039/b511554j}}{{cite journal |author=D. Zhao |author2=Y. Liao |author3=Z. Zhang |name-list-style=amp |title=Toxicity of Ionic Liquids |date=2007 |journal=CLEAN - Soil, Air, Water |volume=35 |issue=1 |pages=42–48 |doi=10.1002/clen.200600015}}{{cite journal |author=J Ranke |author2=S Stolte |author3=R Störmann |author4=J Arning |author5=B Jastorff |name-list-style=amp |title=Design of sustainable chemical products – the example of ionic liquids |date=2007 |journal=Chem. Rev. |volume=107 |issue=6 |pages=2183–2206 |pmid=17564479 |doi=10.1021/cr050942s}}

Ultrasound can degrade solutions of imidazolium-based ionic liquids with hydrogen peroxide and acetic acid to relatively innocuous compounds.{{cite journal |title=Ultrasonic chemical oxidative degradations of 1,3-dialkylimidazolium ionic liquids and their mechanistic elucidations |author=Xuehui Li |author2=Jinggan Zhao |author3=Qianhe Li |author4=Lefu Wang |author5=Shik Chi Tsang |name-list-style=amp |journal=Dalton Trans. |date=2007 |issue=19 |pages=1875–1880 |pmid=17702165 |doi=10.1039/b618384k}}

Despite low vapor pressure many ionic liquids are combustible.{{cite journal |title=Combustible ionic liquids by design: is laboratory safety another ionic liquid myth? |display-authors=7 |author=Marcin Smiglak |author2=W. Mathew Reichert |author3=John D. Holbrey |author4=John S. Wilkes |author5=Luyi Sun |author6=Joseph S. Thrasher |author7=Kostyantyn Kirichenko |author8=Shailendra Singh |author9-link=Alan R. Katritzky |author9=Alan R. Katritzky |author10=Robin D. Rogers |name-list-style=amp |journal=Chemical Communications |date=2006 |volume=2006 |pages=2554–2556 |issue=24 |pmid=16779475 |doi=10.1039/b602086k}}{{cite web |title=Synthesis, Characterization and Combustion of Triazolium Based Salts |author1=Uwe Schaller |author2=Thomas Keicher |author3=Volker Weiser |author4=Horst Krause |author5=Stefan Schlechtriem |date=2010-07-10 |pages=1–23 |url=http://www.imemg.org/wp-content/uploads/IMEMTS%202010/presentations/synthesis_4_Schalller.pdf |access-date=2016-03-02 |url-status=live |archive-url=https://web.archive.org/web/20160307060022/http://www.imemg.org/wp-content/uploads/IMEMTS%202010/presentations/synthesis_4_Schalller.pdf |archive-date=2016-03-07}}

{{Blockquote|text=When Tawny crazy ants (Nylanderia fulva) combat fire ants (Solenopsis invicta), the latter spray them with a toxic, lipophilic, alkaloid-based venom. The Tawny crazy ant then exudes its own venom, formic acid, and self-grooms with it, an action which de-toxifies the fire ant venom. The mixed venoms chemically react with one another to form an ionic liquid, the first naturally occurring IL to be described.{{cite journal |year=2014 |title=On the Formation of a Protic Ionic Liquid in Nature |journal=Angewandte Chemie International Edition |volume=53 |issue=44 |pages=11762–11765 |last1=Chen |first1=Li |last2=Mullen |first2=Genevieve E. |last3=Le Roch |first3=Myriam |last4=Cassity |first4=Cody G. |last5=Gouault |first5=Nicolas |last6=Fadamiro |first6=Henry Y. |author6-link=Henry Fadamiro |last7=Barletta |first7=Robert E. |last8=O'Brien |first8=Richard A. |last9=Sykora |first9=Richard E. |last10=Stenson |first10=Alexandra C. |last11=West |first11=Kevin N. |last12=Horne |first12=Howard E. |last13=Hendrich |first13=Jeffrey M. |last14=Xiang |first14=Kang Rui |last15=Davis |first15=James H. |pmid=25045040 |doi=10.1002/anie.201404402}}}}

• 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆) for an often encountered ionic liquid
• Ionic liquids in carbon capture
• Ion gel
• Ioliomics, or studies of ions in liquids
• MDynaMix software for ionic liquids simulations
• Molten salt
• nanoFlowcell which uses ionic liquid in its car batteries
• Trioctylmethylammonium bis(trifluoromethylsulfonyl)imide

• {{cite journal |title=Structure and Nanostructure in Ionic Liquids |date=2015 |last1=Hayes |first1=Robert |last2=Warr |first2=Gregory G. |last3=Atkin |first3=Rob |journal=Chemical Reviews |volume=115 |issue=13 |pages=6357–6426 |pmid=26028184 |doi=10.1021/cr500411q |doi-access=free}}

{{reflist|colwidth=30em}}

• [http://www.il-eco.uft.uni-bremen.de/ Ionic Liquids Biological Effects Database] {{Webarchive|url=https://web.archive.org/web/20210421050407/http://il-eco.uft.uni-bremen.de/ |date=2021-04-21}}, free database on toxicology and ecotoxicology of ionic liquids
• [https://pubs.aip.org/aip/jcp/article-abstract/70/1/92/781705/Corresponding-states-for-ionic-fluids Corresponding states for ionic fluids]

{{Authority control}}

Category:Ions