BOOKS
A LOOK AT IONIC LIQUIDS Introducing a FIELD OF CHEMISTRY that is constantly evolving REVIEWED BY ROBIN D. ROGERS
IF EVER THERE WAS a case of a reporter
becoming part of the story, it would have to be Michael Freemantle’s pivotal role in the growth of the field now known as ionic liquids. Ionic liquids are quite literally defined as salts that melt below 100 °C, an admittedly arbitrary definition. The macroscopic property of being a liquid combined with properties inherent in many salts fueled an expansion of research interest into the use of ionic liquids as solvents, with green chemistry often a purported goal. For most researchers engaged in the study of ionic liquids today, it is the range and tunability of the physical, chemical, and biological property sets possible in salts that are liquid at or near ambient temperatures that have led to an explosion of interest in a wide range of diverse applications—lunar mirrors, paint compatibilizers, heat pump fluids, cellulose solvents, propellants, and pharmaceuticals. Freemantle’s early reports in Chemical & Engineering News continue to be highly cited as pivotal in bringing new people into the field, as a result of both the timing of the stories and the style of writing. His new book, “An Introduction to Ionic Liquids,” provides a good overview and introduction, starting in the mid-1990s, through the eyes of a trained reporter. I remember my first meeting with Freemantle in Greece in 2000 when he was a guest at the NATO Advanced Research Workshop “Green Industrial Applications of Ionic Liquids” that Ken Seddon, director of the Queen’s University Ionic Liquid Laboratories in Belfast, Northern Ireland;
“Green Credentials of Ionic Liquids,” “Electrochemistry,” “Catalysis,” “Inorganic Chemistry,” “General Organic Reactions,” “Named Organic Reactions,” “Biotechnology,” “Analysis,” and “Applications.” The first two chapters might actually be some of the more contentious. Two areas where there has been much debate in the field are, first, definitions, nomenclature, and abbreviations, and, second, the history of the field. The introduction, for example, suggests that ionic liquids consist exclusively or almost exclusively of ions; however, the entire field of “protic ionic liquids” including the purported “first ionic liquid” (see below) might not fit such a definition. Similarly, the classes of cations and anions are now quite dated given the dozens of new cation and anion classes that have been reported recently.
Sergei Volkov of the V. I. Vernadsky Institute of General & Inorganic Chemistry of the National Academy of Sciences, Ukraine; and I had organized. Freemantle, camera in hand, was walking the beach during a break in the AN conference, and we INTRODUCTION chatted about many TO IONIC of the same contenLIQUIDS, tious topics still being by Michael discussed today. Are Freemantle, RSC Publishing, 2009, ionic liquids new? Are 281 pages, $82 they green/safe/toxic? THE HISTORY CHAPTER is disappointing hardback (ISBN: Who is using them, to me, and the author falls into the trap of 978-1-84755how much do they using modern terms and thinking to rein161-0) cost, and when will terpret older chemistry. Key dates in the they be commonplace history of the field are all selected in hindin industry? Throughout the next decade, sight, while in fact they had little to do with many of his stories continued to cover these key questions for the IONIC LIQUIDS Is it time for deployment? field and prompt research into answering the questions. Deployment? Publications/ Patents “An Introduction to Ionic Liq20,000 uids” is at times a personal view of the field and at others a discussion of commonly accepted history, 15,000 which perhaps can be misleading. Overall it is a high-level introduction that whets the appetite for 10,000 more information. At its best, it encourages a drive to develop a 5,000 deeper understanding of the field in order to find out why there has Innovation been so much excitement among 0 practitioners, as well as so much 00 05 10 15 20 1995 disappointment. SOURCE: Chemical Abstracts Service The book is quite ambitious, and its 281 pages and 14 chapters cover an incredible range of chemistry, the research understanding and strategies and each chapter could easily be a standdeveloped in the field from the mid-1990s alone book. This can be understood just onward. For example, as indicated above, by reviewing the titles of each chapter: the description of protic ionic liquids often “Introduction,” “History,” “Synthesis of does not fit into what some define as an ionIonic Liquids,” “Properties of Ionic Liqic liquid; this debate is ongoing. The birth uids,” “Ionic Liquids as Designer Solvents,” of ionic liquids being attributed to a 1914
If ever there was a case of a reporter becoming part of the story, it would have to be Michael Freemantle’s pivotal role in the growth of the field now known as ionic liquids. WWW.CEN-ONLINE.ORG
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Purity I Precision I Value paper where a protic salt was prepared is quite widely cited in the field, but the identification of a salt liquid at room temperature would seem to have little to do with the development of research strategies based on the notion that liquid salts could be used as solvents, materials, or even pharmaceuticals. However, to the author’s credit, this is exactly how many scientists and engineers in the field describe ionic liquid history. The remaining chapters are based more on science than perception and thus serve as a reasonably short introduction to some of the early work carried out in the field. Nonetheless, these chapters can only give a feel for where the field has been, and they certainly should not be expected to be complete. A good example of the field of ionic liquids and the problems anyone will have trying to provide complete coverage can be found in chapter 14. The number of applications is growing, and knowledge is being developed in areas that simply do not fit into convenient categories, such as synthesis, electrochemistry, and so on. These are placed in vignettes in the last chapter and might serve as a fitting juxtaposition to chapters 1 and 2 where the definitions and history provided are focused on the much older view of what ionic liquids are and from where they arose.
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THE APPLICATIONS of ionic liquids are
growing into novel areas far afield from the green-solvent push in the mid-1990s. Many of these applications arose from a greater experimental and theoretical understanding of ionic liquids at an ionic level as complex materials and much less from the macroscopic observation that a salt could be a liquid at room temperature. Overall, this book is easy to read, and I would recommend it for those new to the field who want to get a flavor of what is developing in the area. I would caution that one should always verify for oneself what is considered “common knowledge” and remember that there is a tremendous amount of very good work that could not possibly fit into an overview of this type. Freemantle has brought us the introduction—the field must provide the sustaining chapters. ROBIN D. ROGERS is Robert Ramsay Chair of Chemistry and director of the Center for Green Manufacturing at the University of Alabama, Tuscaloosa, as well as editor-in-chief of Crystal Growth & Design.
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