Nonaqueous solvent chemistry

In view of the difficulties that accompany the use of a nonaqueous solvent, one may certainly ask why such use is necessary. The answer includes several of the important principles of nonaqueous solvent chemistry that will be elaborated on in this chapter. First, solubilities are different. In some cases, classes of compounds are more soluble in some nonaqueous solvents than they are in water. Second, the strongest acid that can be used in an aqueous solution is H30+. As was illustrated in Chapter 9, any acid that is stronger than H30+ will react with water to produce H30+. In some other solvents, it is possible to routinely work with acids that are stronger than H30+. Third, the strongest base that can exist in aqueous solutions is OH-. Any stronger base will react with water to produce OH-. In some nonaqueous solvents, a base stronger than OH - can exist, so it is possible to carry out certain reactions in such a solvent that cannot be carried out in aqueous solutions. These differences permit synthetic procedures to be carried out in nonaqueous solvents that would be impossible when water is the solvent. As a result, chemistry in nonaqueous solvents is an important area of inorganic chemistry, and this chapter is devoted to the presentation of a brief overview of this area. 

Coordination compounds have been produced by a variety of techniques for at least two centuries. Zeise s salt, K[Pt(C2H4)Cl3], dates from the early 1800s, and Werner s classic syntheses of cobalt complexes were described over a century ago. Synthetic techniques used to prepare coordination compounds range from simply mixing the reactants to employing nonaqueous solvent chemistry. In this section, a brief overview of some types of general synthetic procedures will be presented. In Chapter 21, a survey of the organometallic chemistry of transition metals will be presented, and additional preparative methods for complexes of that type will be described there. 

When one considers the incredible number of chemical reactions that are possible, it becomes apparent why a scheme that systemizes a large number of reactions is so important and useful. Indeed, classification of reaction types is important in all areas of chemistry, and a great deal of inorganic chemistry can be systematized or classified by the broad types of compounds known as acids and bases. Many properties and reactions of substances are understandable, and predictions can often be made about their reactions in terms of acid-base theories. In this chapter, we will describe the most useful acid-base theories and show their applications to inorganic chemistry. However, water is not the only solvent that is important in inorganic chemistry, and a great deal of chemistry has been carried out in other solvents. In fact, the chemistry of nonaqueous solvents is currently a field of a substantial amount of research in inorganic chemistry, so some of the fundamental nonaqueous solvent chemistry will be described in this chapter. 

As a result, special techniques are often required in nonaqueous solvent chemistry. The physical properties of some of the commonly used nonaqueous solvents are shown in Table 5.4, and solubilities of inorganic compounds in some solvents have been described in Chapter 4. 

More information on optimization of reaction methods based on fundamental concepts of Brbnsted-Lowry adds and bases can be found in monographic sonrce. A chapter in another monograph addresses fundamentals of nonaqueous solvent chemistry. ... 

J. J. Lagowski, "The Chemistry of Nonaqueous Solvents," Inert Aprotic and Acidic Solvents, Vol. 3, Academic Press, Inc., New York, 1970 see also Chapt. 4. 

N2O4 has been extensively studied as a nonaqueous solvent system and it is uniquely useful for preparing anhydrous metal nitrates and nitrato complexes (p. 468). Much of the chemistry can be rationalized in terms of a selfionization equilibrium similar to that observed for... 

In the study of chemistry the results of observations on the transformations and properties of many materials are encountered. Schemes that provide structure to the information concerning this type of chemistry go a long way toward systematizing its study. One such approach is that of the chemistry of acids and bases. Closely related to the chemistry of acids and bases is the study of solvents other than water, the chemistry of nonaqueous solvents (see Chapter 10). In this chapter, several areas of acid-base chemistry and their application to reactions of inorganic substances will be described. 

The chemistry of the specific solvents discussed in this chapter illustrates the scope and utility of nonaqueous solvents. However, as a side note, several other nonaqueous solvents should at least be mentioned. For example, oxyhalides such as OSeCl2 and OPCl3 (described in the discussion of the coordination model earlier in this chapter) also have received a great deal of use as nonaqueous solvents. Another solvent that has been extensively investigated is sulfuric acid, which undergoes autoionization,... 

There is an extensive chemistry associated with the use of liquid ammonia as a nonaqueous solvent (see Chapter 10). Because it has a dielectric constant of 22 and a dipole moment of 1.46 D, ammonia dissolves many ionic and polar substances. However, reactions are frequently different than in water as a result of differences in solubility. For example, in water the following reaction takes place because of the insolubility of AgCl ... 

The properties of HF reflect the strong hydrogen bonding that persists even in the vapor state. As a result of its high polarity and dielectric constant, liquid HF dissolves many ionic compounds. Some of the chemistry of HF as a nonaqueous solvent has been presented in Chapter 10. Properties of the hydrogen halides are summarized in Table 15.9. 

Dolye, M., Lewittes, M. E., Roelofs, M. G. and Perusich, S. A. 2001. Ionic conductivity of nonaqueous solvent-swoUen ionomer membranes based on fluorosulfonate, fluorocarboxylate, and sulfonate fixed ion groups. Journal of Physical Chemistry B 105 9387-9394. 

Electrolytes are ubiquitous and indispensable in all electrochemical devices, and their basic function is independent of the much diversified chemistries and applications of these devices. In this sense, the role of electrolytes in electrolytic cells, capacitors, fuel cells, or batteries would remain the same to serve as the medium for the transfer of charges, which are in the form of ions, between a pair of electrodes. The vast majority of the electrolytes are electrolytic solution-types that consist of salts (also called electrolyte solutes ) dissolved in solvents, either water (aqueous) or organic molecules (nonaqueous), and are in a liquid state in the service-temperature range. [Although nonaqueous has been used overwhelmingly in the literature, aprotic would be a more precise term. Either anhydrous ammonia or ethanol qualifies as a nonaqueous solvent but is unstable with lithium because of the active protons. Nevertheless, this review will conform to the convention and use nonaqueous in place of aprotic .]... 

This chapter provides the groundwork of solution chemistry that is relevant to solvent extraction. Some of the concepts are rather elementary, but are necessary for the comprehension of the rather complicated relationships encountered when the solubilities of organic solutes or electrolytes in water or in nonaqueous solvents are considered. They are also relevant in the context of complex and adduct formation in aqueous solutions, dealt with in Chapter 3 and of the distribution of solutes of diverse kinds between aqueous and immiscible organic phases dealt with in Chapter 4. 

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