Nonaqueous solvent systems

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... 

S. Payne, Chap. 8 in T. C. Waddington (ed.), Nonaqueous Solvent Systems, pp. 301-25, Academic Press, London, 1965. 

Most small organic molecules are soluble in mixed organic-aqueous solvents and can be easily analyzed using RPLC. However, there are some polar compounds which are not soluble in typical RPLC solvent systems or are unstable in an aqueous mobile phase system. These compounds can be analyzed on an RPLC column with a nonaqueous solvent system. This technique is called "nonaqueous reversed phase chromatography" (NARP).20-21 The NARP technique is primarily used for the separation of lipophilic compounds having low to medium polarity and a molecular weight larger than... 

There are numerous examples of cations of the interhalogens, and a great deal is known about the behavior of such species. The species that have been more fully studied involve only one type of halogen such as I3+, Br3+, and Cl3+. In general, the production of these species requires rather stringent conditions that may include nonaqueous solvent systems. For example, a reaction that takes place in anhydrous sulfuric acid can be used to produce I3 +. ... 

For lithium electrolytes, the only variable in salt structure is the anion. In a given nonaqueous solvent system, the dissociation of a lithium salt would be... 

Photoreduction of cobalt(III) complexes in nonaqueous solvent systems has been little studied because of the limited solubility of cobalt(III) complexes and their tendency to photooxidize the solvent. Irradiation with 365-mjj. light of cis- or trans-Co(en)2C 2 + and Co(en)2Cl(DMSO)2+ in dimethylsulfoxide (DMSO) leads rapidly to production of a green tetrahedral cobalt(II) product apparently with concurrent solvent oxidation.53,71 Irradiation with 365-mjx light of the molecular Co(acac)3 in benzene rapidly gives a red precipitate which may be the cobalt(II) acetylacetonate.53... 

We have to expect such selectivity changes and it would be very interesting to measure them. Unfortunately, the solvent polymeric membranes mentioned can usually not be contacted with nonaqueous solvent systems because of the expected increased solubility of the membrane components involved. 

Although many nonaqueous solvent systems have been studied, the discussion here will be limited to a few representative solvents ammonia, a basic solvent sulfuric acid, an acidic solvent and bromine trifluoride. an aprotic solvent. In addition a short discussion of the chemistry taking place in solutions of molten salts is included. 

The chemistry of molten salts as nonaqueous solvent systems is one that has developed extensively from the 1960s till the present, and only a brief survey can be given here. The most obvious difference when compared with the chemistry of aqueous solutions are the strongly bonded and stable nature of the solvent, a concomitant resistance to destruction of the solvent by vigorous reactions, and higher concentrations of vanous species, particularly coordinating anions, than can be obtained in saturated solutions in water. 

T,C. Waddington, Nonaqueous Solvent Systems, Academic Press, London, 1965. 

When HPLC is used as part of the analysis, the mobile phase is typically a mixture of methanol and methyl-tert-butyl ether (i.e., 50 50, v/v), although other HPLC solvents for LC/MS using APCI (e.g., water, tetrahydrofuran) can be used. It is important to note that if combustible nonaqueous solvent systems are used, water or a halogenated solvent such as methylene chloride or chloroform should be added to the mobile phase postcolumn to suppress ignition in the ion source. In addition, the APCI source must be vented outside the laboratory and should not allow air into the ionization chamber. A scan range of m/z 300 to 1000 will include the known carotenoids and their most common esters. 

Fig. 10.19. Spectroscopic celt for HF solutions. All internal parts- are Kel-F, Teflon, or, in the case of window material, sapphire ov silver chloride. A commercial Teflon valve may be substituted for the custom Kcl-F valve shown here, (Reproduced from II. II. Hyman and I. J, Kate Nonaqueous Solvent Systems, f. C. Wuddington h d., p. 47 (l%5) by permission of Academic Press Inc.)... 

Silicone oil was also recently employed by the group of Peng as an alternative nonaqueous solvent system for suspention polymerisation [22]. Silicone oil has the advantage of being cheap, inert and rather viscous, which enhances the stability of the monomer droplets in suspension. In this case, composite MIP beads were prepared including magnetic nanoparticles. FesCL nanoparticles (average diameter... 

For most potentiometric measurements either the saturated calomel reference electrode or the silver/silver chloride reference electrode are used. These electrodes can be made compact, are easily produced, and provide reference potentials that do not vary more than a few millivolts. The discussion in Chapter 5 outlines their characteristics, preparation, and temperature coefficients. The silver/silver chloride electrode also finds application in nonaqueous titrations, although some solvents cause the silver chloride film to become soluble. Some have utilized reference electrodes in nonaqueous solvents that are based on zinc or silver couples. From our own experience, aqueous reference electrodes are as convenient for nonaqueous systems as are any of the prototypes that have been developed to date. When there is a need to rigorously exclude water, double-salt bridges (aqueous/nonaqueous) are a convenient solution. This is true even though they involve a liquid junction between the aqueous electrolyte system and the nonaqueous solvent system of the sample solution. The use of conventional reference electrodes does cause some difficulties if the electrolyte of the reference electrode is insoluble in the sample solution. Hence the use of a calomel electrode saturated with potassium chloride in conjunction with a sample solution that contains perchlorate ion can cause erratic measurements due to the precipitation of potassium perchlorate at the junction. Such difficulties normally can be eliminated by using a double junction that inserts another inert electrolyte solution between the reference electrode and the sample solution (e.g., a sodium chloride solution). 

Although solvents such as dimethylformamide have been tried, the use of anhydrous benzene and anhydrous hydrogen cyanide appears to remain as the most general nonaqueous solvent system and several new Reissert compounds have been prepared by this method. " With the use of anhydrous hydrogen cyanide this method suffers from an obvious disadvantage. 

Yun, K-S., Joo, S., Kim, H-J., Kwak, J., Yoon, E. (2004). Silicon micromachined infrared thin-layer cell for in situ spectroelectrochemical analysis of aqueous and nonaqueous solvent system. Electroanalysis 17 959-64. 

Mixed nonaqueous solvent systems are also of great interest and potential versatility as protein solvents, as they are for simple electrolytes (Evers and Kay, 1960). Their systematic use should enormously extend the range of nonaqueous solvent systems and properties. This is already suggested by several studies (cf. Doty et al, 1956 Yang and Doty, 1957). Many solvents not capable of dissolving a given protein may do so in mixtures with a small amount of a nonaqueous good solvent for the particular solute. In another connection, the addition of less than 1 % of one nonaqueous solvent to a solution of a macromolecule in another nonaqueous solvent can profoundly alter the physical chemical properties of the solution (Eirich et al., 1951 Doty et al., 1956). 

Some interesting conductance studies of protein-nonaqueous solvent systems have been carried out. Greenberg and Larson (1935), for example, found that gelatin, casein, and edestin dissolved in glacial formic acid (D = 56.5 at 16°C) showed marked increases of conductivity over that of the solvent, whereas no conductivity increment was observed with the same proteins dissolved in glacial lactic or acetic (D = 6.15 at 20°C) acids. This is in accord with the conclusions reached in Section IV,B,1, that in solvents of low dielectric constant, ion-pairing (in these cases, of the protein cations to lactate and acetate counterions) is essentially complete. Con-... 

Tarr, B.D. Yalkowsky, S.H. A new parenteral vehicle for the administration of some poorly water soluble anti-cancer drugs. J. Parenteral Sci. Technol. 1987, 41, 31-33. Rajagopalan, N. Dicken, C.M. Ravin, L.J. Stemson, L.A. A study of the solubility of amphotericin B in nonaqueous solvent systems. J. Parenteral Sci. Technol. 1988, 42, 97-102. 

Efforts to decontaminate electronics and sensitive equipment are exploring the use of nonaqueous solvent systems such as supercritical carbon dioxide. Nanoparticles of certain metal oxides are being studied as candidates for future dry decontamination systems. Other work is under way to identify decontamination materials that would be safe and approved for use on aircraft surfaces. 

Domon, B. Hostettmann, M. Hostettmann, K., Droplet counter-current chromatography with nonaqueous solvent systems. /. Chromatography 1982,246,133. 

For most solutes, the effective hydrogen-bond basicity is constant over all the solvent systems however, in the case of some specific solutes, including anilines and pyridines, the effective solute hydrogen-bond basicity varies with the solvent system. Therefore, the descriptor P is preferably used for partition between water and rather nonaqueous solvent systems, while an alternative P° can be used for partition between water and aqueous solvent systems [Abraham and Rafols, 1995]. 

Recent research has demonstrated that enzymes can function in various low-water environments (1-4), and that the properties of enzymes can be favorably modified by nonaqueous solvents (5-7). Increased substrate solubility, reversal of hydrolytic reactions, and improved thermostability are among the practical advantages afforded by nonaqueous solvents. However, the role of water in enzymatic reactions at low water concentrations is not generally understood, and there is some uncertainty regarding how much the conformation of a protein changes as solvent water is removed (8.9). Nonaqueous solvent systems therefore represent important media in which to examine enzyme structure and function at the molecular level. Such studies will prove valuable for the application of enzymes in low-... 

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