A majority of chemical reactions are carried out in solution. The use of a solvent as reaction medium makes it easy to control reaction conditions such as temperature, pressure, pH, rate of mass transfer, and concentration of reactant. Water is the most popular solvent. However, by using appropriate non-aqueous solvents, substances that are insoluble in water can be dissolved, substances that are unstable in water remain stable, and chemical reactions that are impossible in water become possible. The reaction environments are markedly wider in non-aqueous solvents than in water.
The widespread use of non-aqueous solvents, especially dipolar aprotic solvents, began in the 1950s in various fields of pure and applied chemistry and has contributed greatly to later advances in chemical sciences and technologies. From the very beginning, electrochemistry in non-aqueous solutions has played an important role in exploring new chemical possibilities as well as in providing the methods to evaluate static solvent effects on various chemical processes. Moreover, many new electrochemical technologies have been developed using non-aqueous solvents. Recently, electrochemistry in nonaqueous solutions has made enormous progress: the dynamic solvent effects on electrochemical processes have been greatly elucidated and solvent effects are now understood much better than before. On the other hand, however, it is also true that some useful solvents have properties that are problematic to human health and the environment. Today, efforts are being made, under the ramework of ‘green chemistry’, to find environ mentally benign media for chemical processes, including harmless non-aqueous solvents, immobilized solvents, ionic liquids, supercritical fluids, aqueous systems, and even solventless reaction systems. For electrochemical purposes, replacing hazardous solvents by harmless solvents, ionic liquids and supercritical fluids appears to be promising.
This book was written to provide readers with some knowledge of electrochemistry in non-aqueous solutions, from its fundamentals to the latest developments, including the current situation concerning hazardous solvents. The book is divided into two parts. Part I (Chapters 1 to 4) contains a discussion of solvent properties and then deals with solvent effects on chemical processes such as ion solvation, ion complexation, electrolyte dissociation, acid-base reactions and redox reactions. Such solvent effects are of fundamental importance in understanding chemistry in non-aqueous solutions; furthermore, their quantitative evaluations are often carried out by means of electrochemical techniques. Part II (Chapters 5 to 12) mainly deals with the use of electrochemical techniques in non-aqueous solutions. In Chapter 5, the fundamentals of various electrochemical techniques are outlined in preparation for the following chapters. In Chapters 6 to 9, the applications of potentiometry, conductimetry, polarography, voltammetry, and other new electrochemical techniques in non-aqueous solutions are discussed by focusing on the chemical information they provide. Chapters 10 and 11 examine methods of selecting and purifying the solvents and electrolytes of electrochemical importance. Finally, in Chapter 12, some practical applications of non-aqueous solvents in modern electrochemical technologies are discussed. These include their use in batteries, capacitors and display devices, and such processes as electrolytic refining, plating, synthesis and polymerization. The applicability of ionic liquids and supercritical fluids as environmentally benign media for electrochemical technology is also dealt with.
Most chemists are familiar with chemistry in aqueous solutions. However, the common sense in aqueous solutions is not always valid in non-aqueous solutions. This is also true for electrochemical measurements. Thus, in this book, special emphasis is placed on showing which aspects of chemistry in non-aqueous solutions are different from chemistry in aqueous solutions. Emphasis is also placed on showing the differences between electrochemical measurements in non-aqueous systems and those in aqueous systems. The importance of electrochemistry in non-aqueous solutions is now widely recognized by non-electrochemical scientists – for example, organic and inorganic chemists often use cyclic voltammetry in aprotic solvents in order to determine redox properties, electronic states, and reactivities of electroactive species, including unstable intermediates. This book will therefore also be of use to such non-electrochemical scientists. I obtained most of the information included in this book from the publications of many scientists in this field. I would like to express my sincere thanks to all of them. I also would like to thank my coworkers for their cooperation, the editorial and production staff of Wiley-VCH for their help and support, and my wife for her assistance and patience.