Preface

The field of Room Temperature Ionic Liquids (RTILs) is an increasingly mature area. <sup>1</sup> At present, the main synthetic approaches and key components are fairly defined, though with some continuing exploration and expansion. Thus, quaternary ammonium, imidazolium, and pyridinium salts with a variety of anions, many of them highly fluorinated dominate the field. The cations are generally accessed via quaternization of the parent amines, imida‐ zoles, and pyridines, which sometimes leads directly to the RTIL (for so-called "halide-free" RTILs). More often, the final RTIL is accessed via anion metathesis of the starting halidecontaining salt. The challenges associated with RTIL purity from this approach are welldocumented. 2

Because of the wide and diverse range of RTILs that can be accessed via this simple ap‐ proach, they do merit the term "designer solvents" as their physical properties can be wide‐ ly tuned with respect to viscosity, electrochemical stability, density, solubility/miscibility, and thermal stability, to name just a few. The challenges of synthesizing, characterizing, and demonstrating purity continues to push the development of general and reliable computa‐ tional methods for the prediction of new RTILs for particular applications. 3

Another inescapable issue is the cost and potential toxicity of RTILs. Although toxicity to the user is not as much of an issue, since the negligible volatility of the majority of these materi‐ als means that exposure is largely limited to direct contact or ingestion, there is still concern regarding their disposal and recycling. 4 Further, the cost of the most popular RTILs, such as BMIM BF4 and BMIM NTf2, still considerably exceeds that of conventional solvents and ef‐ fectively precludes their use in all but the most high value of applications. To specifically address this issue, a newer variant on the RTIL theme has emerged – deep eutectic solvents (DES). 5 Although related, they fundamentally differ in that they are simply combinations of two compounds (often two solids) that result in a mixture with a dramatically lowered melt‐ ing point. An example is the very common DES comprised of choline chloride and urea in a 1:2 molar ratio. While choline chloride has a melting point in excess of 300 C and urea has a melting point of 12\_ C, this DES exhibits a melting point of 12 C. Additional advantages include the low toxicity and relative abundance (and thus low cost) of both components. As a result, this DES exhibits a cost that is comparable to that of conventional organic solvents such as DMF and acetonitrile. This new area is discussed specifically in one chapter in this book in the context of applications in Organic Synthesis, although many other applications can and have been explored.

In addition to DES, this book features chapters that cover a wide range of RTIL concepts and applications. One section of chapters focusses on one of the earlier areas of explosive explo‐ ration – their use as recyclable solvents in synthesis – including a chapter on Green Pericy‐

clic Reactions Assisted by Ionic Liquids and one on Palladium-coupling reactions in Ionic Liquids. A more recent variant on this synthesis theme is found in the chapter on Applica‐ tions of Ionic Liquids in the Synthesis of Inorganic Nanomaterials.

Related to conventional synthesis, RTILs have found very fruitful applications in the area of enzymatic synthesis as they are often able to stabilize and even enhance the activity of vari‐ ous enzymes in a largely non-aqueous environment. Developments in this area are found in the chapters Engineering of Enzymatics Reactions using Ionic Liquids and Solvent Depend‐ ence of Enzymatic Enantioselectivity.

As mentioned above, the ability to predict and rationally design RTILs with specific proper‐ ties continues to be of great importance, and this topic is addressed in several chapters, in‐ cluding: Structural and Physical Aspects of Ionic Liquid Aggregates in Solution, Thermal Behavior of Pure Ionic Liquids, Solubility of Solids, Liquids and Gases in Ionic Liquids. Ex‐ traction issues are more specifically addressed in several additional chapters, including Ion‐ ic Liquids as Amphiphile Self-assembly Media, Ionic Liquids as Surfactants: Applications as Demulsifiers, and Extraction Based on Dispersive Assisted by Ionic Liquids.

Many of these extraction and solubilization properties find their greatest application in one specific area – biomass isolation and transformation. It is therefore not surprising to find several chapters that address different aspects of this highly important area: Imidazoliumbased Ionic Liquids as Solvents for Analysis of Lipophilic Extractive from Biomass, Dissolu‐ tion and Hydrolysis of Lignocellulosic Biomass Using Tailored Ionic Liquids, Pyridiniumbased Ionic Liquids: Applications for Cellulose Processing, Utilization of Ionic Liquids in Wood and Wood-related Applications: a review, and Ionic Liquids as Green Solvents for Ring-opening Graft Polymerization of Caprolactones onto Hemicelluloses.

A great diversity of other applications continue to arise and are reflected in the chapters of the two remaining sections. First are electrochemical applications (Electochemical Prepara‐ tion of Titanium and its Alloys and High-performance Supercapacitors Based on Ionic Liq‐ uids), followed by a range of other interesting uses: Spectroscopic Study on Lubrication and Tribo-corrosion Mechanisms of Ionic Liquids Applied to Improve the Dispersion of Solids in Elastomers, Ionic Liquids in Vulcanization of Elastomers, Ionic Liquids Facilitated Develop‐ ment of Absorption Refrigeration, and New Classes of Ionic Liquids for Dye-sensitized Solar Cells.

I hope that you enjoy reading these chapters as much as I have and that they inspire you to explore newer and even more exciting possibilities of involving RTILs in your research. The future remains exciting.

> **Scott T. Handy** Professor of Chemistry Middle Tennessee State University USA

#### **References:**

clic Reactions Assisted by Ionic Liquids and one on Palladium-coupling reactions in Ionic Liquids. A more recent variant on this synthesis theme is found in the chapter on Applica‐

Related to conventional synthesis, RTILs have found very fruitful applications in the area of enzymatic synthesis as they are often able to stabilize and even enhance the activity of vari‐ ous enzymes in a largely non-aqueous environment. Developments in this area are found in the chapters Engineering of Enzymatics Reactions using Ionic Liquids and Solvent Depend‐

As mentioned above, the ability to predict and rationally design RTILs with specific proper‐ ties continues to be of great importance, and this topic is addressed in several chapters, in‐ cluding: Structural and Physical Aspects of Ionic Liquid Aggregates in Solution, Thermal Behavior of Pure Ionic Liquids, Solubility of Solids, Liquids and Gases in Ionic Liquids. Ex‐ traction issues are more specifically addressed in several additional chapters, including Ion‐ ic Liquids as Amphiphile Self-assembly Media, Ionic Liquids as Surfactants: Applications as

Many of these extraction and solubilization properties find their greatest application in one specific area – biomass isolation and transformation. It is therefore not surprising to find several chapters that address different aspects of this highly important area: Imidazoliumbased Ionic Liquids as Solvents for Analysis of Lipophilic Extractive from Biomass, Dissolu‐ tion and Hydrolysis of Lignocellulosic Biomass Using Tailored Ionic Liquids, Pyridiniumbased Ionic Liquids: Applications for Cellulose Processing, Utilization of Ionic Liquids in Wood and Wood-related Applications: a review, and Ionic Liquids as Green Solvents for

A great diversity of other applications continue to arise and are reflected in the chapters of the two remaining sections. First are electrochemical applications (Electochemical Prepara‐ tion of Titanium and its Alloys and High-performance Supercapacitors Based on Ionic Liq‐ uids), followed by a range of other interesting uses: Spectroscopic Study on Lubrication and Tribo-corrosion Mechanisms of Ionic Liquids Applied to Improve the Dispersion of Solids in Elastomers, Ionic Liquids in Vulcanization of Elastomers, Ionic Liquids Facilitated Develop‐ ment of Absorption Refrigeration, and New Classes of Ionic Liquids for Dye-sensitized Solar

I hope that you enjoy reading these chapters as much as I have and that they inspire you to explore newer and even more exciting possibilities of involving RTILs in your research. The

**Scott T. Handy**

USA

Professor of Chemistry

Middle Tennessee State University

Demulsifiers, and Extraction Based on Dispersive Assisted by Ionic Liquids.

Ring-opening Graft Polymerization of Caprolactones onto Hemicelluloses.

tions of Ionic Liquids in the Synthesis of Inorganic Nanomaterials.

ence of Enzymatic Enantioselectivity.

Cells.

X Preface

future remains exciting.

1. Freemantle, M. An Introduction to Ionic Liquids. Royal Chemical Society, 2009.

2. For recent papers discussing this issue and the synthesis of halide-free RTILs, see: Vander Hoogerstraete, T.; Jamar, S.; Wellens, S.; Binnemans, K. "Determination of Halide Impurities in Ionic Liquids by Total Reflection X-ray Fluorescence Spectrometry." Anal. Chem. 2014, 86, 3931-3938. And Graesvik, J.; Eliasson, B.; MIkkola, J-P. "Halogen-free ionic liquids and their utilization as cellulose solvents." J. Mol. Struct. 2012, 156-163.

3. Rooney, D.; Johan, J.; Ramesh, G. "Thermophysical properties of ionic liquids." Topics in Curr. Chem. 2010, 290, 185-212. Zhang, S.; Lu, X.; Zhou, Q.; Li, X.; Zhang, X.; Li, S. Ionic Liq‐ uids: Physicochemical Properties, Elsevier, 2009.

4. Rubio, A.M.; Tomas-Alonso, F.; Fernandez, J.H.; Perez delos Rios, A.; Fernandez, F.J.H. "green aspects of ionic liquids." In Ionic Liquids in Separation Technology, 2014, 82-93.

5. Russ, C., Koenig, B. Low melting mixtures in organic synthesis – an alternative to ionic liquids? Green Chem. 2012, 14, 2969-2982. Fransisco, M., van den Bruinhorst, A., Kroon, M.C. Low-transition-temperature mixtures (LTTMs): A new generation of designer solvents. Angew. Chem. Int. Ed. 2013, 52, 3074-3085. Zhang, Q., Vigier, K.D., Jerome, F. Deep eutectic solvents: syntheses, properties, and applications. Chem. Soc. Rev. 2012, 41, 7104-7146.

**Section 1**
