Ionic Liquids as Green Solvents - Essay Example

Ionic Liquids as Green Solvents Ionic liquids are a group of organic salts that exist as liquids at temperatures lower than 100˚C. They have low vapor pressures and are chemically and thermally stable. They have attracted a lot of attention recently as they emit no volatile organic compounds (VOC’s) and have been labeled as green solvents. They are used as catalysts, electrolytes and solvents in a number of industries. This paper will try to enumerate the importance of ionic liquids and their applications in pharmaceutical and other industries. In comparison to molecular liquids that cannot be fabricated from scratch these ionic liquids can be designed (Earl & Seddon 2000) to suit the requirements for a particular reaction. The anions and cations can be varied to get the required end product. Ionic liquids have large anions and cations of low symmetry to reduce the lattice energy and reduce the melting point of the salts. Anions contribute towards the functions and chemistry of ILs and cations contribute towards the variable physical properties and stability of ILs (Bӧhme 2006). Ionic salts can be simple salts i.e. made up of one type of anion and cation or binary ionic liquids which are a mixture of two salts with varying melting points depending on their composition. Image: Wikipedia. Some cations used in ionic liquids Applications of ionic liquids Ionic liquids are used to substitute traditional solvents like volatile organic compounds (VOC’s) for their variable properties, low energy inputs and reusability. They are also used to extract various compounds such as metal ions, biomolecules and organosulfurs by using two phase extraction. The most commonly studied systems contain ammonium, phosphonium, sulfonium, pyridinium, imidazolium and pyrrolidinium cations. Common anions include hexafluorophosphate [PF]6-, tetrafluoroborate [BF]4-, bis(trifyl)imide [NTf]2 and chloride, Cl-. Advantages of ionic liquids over other solvents Melting point, viscosity, density and the affinity towards water can be made to differ based on the structure of ions. Miscibility of salt in water can be varied and this is an important property to consider when the end product has to be separated or extracted from the solvent. Reactions in ionic liquids can occur at relatively low temperatures than other catalytic reactions that may need temperatures of 300˚C or above. Their low volatility permits their use in vacuum or low- pressure environment (HaiBo et al 2007). Ionic liquids help in minimizing and eliminating waste, improves chemical syntheses and extractions or separations (Holbrey, Turner & Rogers 2003). The reaction solvents are reusable and do not diminish in content which is a major advantage over traditional solvents that are sometimes volatile like the VOC’s. However, the most important feature of these ionic liquids that has led to the great amount of interest in them is the ease with which these can be manipulated to suit the needs of a particular reaction. Most of the properties that are attributed to reaction solvents can be redesigned to reduce or eliminate the losses in solvents and the reaction path can be modified to optimize reactions. This can be useful in recovering and reusing the solvents and making them less harmful to the environment. Ionic liquids present a vast scope for chemists to come up with newer and more efficient reaction solvents. Scientists are hopeful that this will allow them to explore unchartered areas of chemical reactivity as well. The immense potential of ionic liquids to be designed as biodegradable (Holbrey, Turner & Rogers 2003) or be made to break down into products that are easily assimilated in nature. Ionic liquids find wide use as they have low cost of production, low toxicity, high solute capacity, moderate cohesion with solutes. They are also chemically inert and can be designed to be non- flammable and highly selective. A lot is yet to be known about these wondrous compounds as scientists continue their pursuit in finding ionic liquids that are best suited to every type of reactions. Applications of IL in industries The wide range of applications of ionic liquids includes their use as solvents in various industries. 1. In chemical industries ionic liquids have been used to scavenge acids from other chemical processes. This was first carried out by BASF when 1- alkylimidazole was used to remove acid from an existing reaction and the ionic liquid formed was easily separated from the reaction mixture. They now manufacture tailor-made IL for customers under the name of BASIONIC (Ionic liquids, BASF). Electrodeposition, electroplating and electropolishing are other uses of ILs in chemical industries (Schubert 2005). 2. ILs are used in processing cellulose to enrich it for use in other industries. It was Graenacher who discovered that molten N-ethylpyridinium chloride could be used to dissolve cellulose, in the presence of nitrogenous bases (Zhu et al 2006). This discovery has been a boon to society and will help to reduce our dependence on petroleum based non-renewable polymers and feed stock. 3. ILs are used in textile industries in which wool keratine or cellulose composite is used to produce fibers with anti-bacterial properties (Zhu et al 2006). 4. ILs find use as dispersal agents of paints and even nanomaterials. 5. They are useful in handling gas because of their low vapor pressure and high thermal stability. 6. Microreactors in combination with ILs are used to purify highly reactive organometallic compounds with lower operational risk. 7. ILs are used in batteries as substitutes to water as they increase the battery life because of low rate of evaporation. Commercial potential of ILs as green solvents ILs are effective substitutes to common organic solvents like benzene because of their low volatility. They are useful in extractions by applying phase transfer chemistry. They are used as re-usable catalysts for a number of reactions including biochemical reactions. They are also used as electrolytes in batteries and double layer supercapacitors (Rakita 2003). Their roles as heat transfer fluids in solar energy collectors are being established. Therefore, one finds that ionic liquids are now being used in many industries and will continue to be a viable means of green solvent. There is, therefore, certainly a bright future for ILs as green solvents barring the only disadvantage that they may be exploited for personal gains. They are after all, designable and can be used as flammable or toxic substance (Anderson 2008). Further studies have to be carried out to prepare a toxicology report on ionic liquids to be able to use them without inhibitions. However, the benefits far outweigh the possible undesirable properties of ionic liquids. The slightly higher initial cost of manufacture proves cheaper and more “green” in the longer run due to the wonderful properties of ionic liquids in terms of reusability, biodegradability and wide range of applications. References: Anderson, K 2008, Ionic Liquids: An Environmentally Friendly Alternative, Bi-Weekly Technology Communicator, [Online] Available http://www.techexchange.com/ thelibrary/ionic.html Bӧhme, C 22 November 2006, BASF Expose Dr Uerdingen, Journalists and Scientists in Dialogue, Ludwigshafen, [Online] Available http://www.basf.com/group/corporate/en/ function/conversions:/publish/content/innovations/events-presentations/raw-material-change/images/BASF_Expose_Dr_Uerdingen.pdf Earle, MJ & Seddon, KR 2000, Ionic liquids. Green solvents for the future, Pure Applied Chemistry, vol. 72, no.7, pp. 1391-1398. Green Chemistry Ionic Liquids- Useful Reaction Solvents 2010, Tokyo Chemical Industry Co. Ltd., Japan. Holbrey, JD, Turner, MB & Rogers, RD 2003, Selection of Ionic Liquids for Green Chemical Applications, Center for Green Manufacturing and Department of Chemistry, The University of Alabama, [Online] Available http://pubs.acs.org/doi/abs/10.1021/bk-2003-0856.ch001 Ionic Liquids- BASF- The Chemical Company- Corporate Website 2010, BASF, The Chemical Company Corporate Website, [Online] Available http://www.basf.com/group/corporate/en/innovations/research-verbund/research-projects/products/ionic-liquids Rakita, PE 2003, Challenges to the Commercial Production of Ionic Liquids, American Chemical Society, Washington, DC, [Online] Available http://pubs.acs.org/doi/abs/10.1021/bk-2003-0856.ch003 Schubert, T 2005,Electrodepositon and electroplating at IOLITEC, iIonic Liquids Today, issue 3-05, [Online] Available http://www.iolitec.de/download/newsletter/Ionic%20Liquids%20Today%2005-3.pdf Zhang, H, XiaoHai, Z, JinFeng,D, GaoYong, Z & CunXin, W 2007, A novel family of green ionic liquids with surface activities, iScience in China Press, [Online] Available http://www.springerlink.com/content/2376w51459n51466/ Zhao, H, Shuqian, X & Peishend, M 2005, Use of ionic liquids as "green" solvents for extractions, Journal of Chemical Technology and Biotechnology, vol. 80, pp. 1089-1096, [Online] Available http://www.ingentaconnect.com/content/jws/jctb/ 2005/00000080/00000010/art00002 Zhu, S Yuanxin, W, Chen, Q, Ziniu, Y, Wang, C, Yigang, D & Gang, W 2006, Dissolution of cellulose with ionic liquids and its application, Royal Society of Chemistry, [Online] Available http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm? doi=b601395c&JournalCode=GC Read More