Nonaqueous solvents solvent classification

In nonaqueous solvents, the classification of strong and weak acids, and the pH scales are dramatically different ... 

Work under this classification (76AHCS1, p. 31) continues to be sparse. Heat-of-solution data provide a useful method for estimating A// for tautomeric processes in nonaqueous solvents, as was illustrated in the case of 2-pyridone 15a/2-hydroxypyridine 15b equilibrium (76TL2685). Heats of dehydration of 4-hydroxypyrazolines into pyrazoles and 5-hydroxyisoxazolines... 

Fig. 8. Classification of ESR spectra (—296 K) of solutions of alkali metals in a variety of nonaqueous solvents rM is the electron-cation encounter lifetime, and A is the metal hyperfine coupling constant, in hertz THF = tetrahydrofuran, EA = ethylamine, DG = diglyme, MA = methylamine (—220 K), 1,2PDA = 1,2-propanediamine, EDA = ethylenediamine, AM = ammonia (—240 K).

Unfortunately, a single classification scheme suited to all areas of nonaqueous solvent study has not yet been devised the criteria that are useful in one area often are not appropriate for another.38... 

TABLE 7.5 A Solvent Classification Scheme for Nonaqueous Solvents... 

Nonaqueous Solvents. Many organic compounds are not soluble in water, and the investigator who desires to study their electrochemistry must resort to organic solvents. The solvents most often used are the so-called dipolar aptotic solvents that belong to Class 5a in the classification scheme of Table 7.5. These are solvents with moderately large dielectric constants and low proton availability. This aptotic character tends to simplify the electrochemical reactions often the primary product is a stable radical cation or anion that is produced by removal or addition of an electron. 

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. 

The diversity of solvents makes classification very complex and many different ways of classifying solvents have been used. Broadly, solvents may be classified as aqueous, nonaqueous molecular, nonaqueous ionic, and atomic. The ways in which solvents are classified according to their chemical constitution and then according to their physical properties are briefly discussed below. 

A classification of solubilization isotherms for small polar molecules into nonaqueous solvents by surfactants, based on the strength of interaction between solubilizate and surfactant, has been proposed by Kon-no and Kitahara (Kon-no, 1972a). When the moles of material solubilized per mole of surfactant are plotted against the relative vapor pressure, p/p°, of the system at constant temperature (where p is the vapor pressure of the water in the system and p" is the vapor pressure of pure water), isotherms are obtained whose shapes reflect the strength of the solubilizate-surfactant interaction. Systems having strong surfactant-solubilizate interaction are concave to the plp° axis, whereas those showing weak interaction are convex to that axis. Systems with very weak solubilizate-surfactant interaction show almost linear isotherms. 

While most of the solvents of interest here are aprotic, in the sense defined in the introduction, they may be further classified with regard to their solvent type. Kolthoff [4] has categorized these solvents in a useful way. Only the classifications useful for nonaqueous studies have been included below. That is, the protic solvents (amphiprotic solvents in Kohltoff s terminology) are not included in this chapter. The classes and definitions are as follows ... 

Normal-phase sorbents such as silica and Florisil are used to isolate low to moderate polarity species from nonaqueous solutions. Examples of applications include lipid classification, plant pigment separations, and separations of fat-soluble vitamins from lipid extracts, as well as the clean-up of organic solvent concentrates obtained from a previous SPE method or liquid-liquid extraction. Alumina is used to remove polar species from nonaqueous solutions. Examples include vitamins in feeds and food and antibiotics and other additives from feed. Normal-phase chromatography has been used for a number of years, and most applications for normal-phase column chromatography may be easily transferred over to normal-phase SPE. 

More recently, classification according to the paint or lacquer system has come to be preferred. Here, a distinction is made between solvent paints or lacquers (that is, those with organic solvents), low-solvent systems, water-soluble binders, aqueous dispersions, nonaqueous dispersions, and powder coatings. 

The presentation of the data in this section is according to solvent which are arranged in alphabetical order by nonaqueous component. Within this classification the electrolytes are arranged alphabetically by name. Information on the temperature range, concentration range, vapor pressure data, differential vapor pressures and solvent activities are included wherever possible. 

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