Solutions in Solvents Other than Water

Water is the only solvent in which the composition of sugars has been systematically explored. Stevens1674 has determined the composition of several aldoses in pyridine-d5 by -n.m.r, spectroscopy at 300 MHz. There are scattered data on solutions in organic solvents (mainly pyridine, dimethyl sulfoxide, and N,N-dimethylformamide), but only rarely have four (or more) components of such solutions been quantitatively determined. The data that have been encountered are collected in Table VII undoubtedly, there are others that have been missed. 

Kuhn and Grassner168 were the first to realize that the solution composition of sugars may vary considerably with a change of solvent. They stated that D-fructose in N,N-dimethylformamide exists in furanose forms to the extent of 80%. (This value is probably too high compare with Table VII.) 

The only systematic study published on the influence of solvents on the solution equilibria of sugars is contained in two articles by Perlin.51-57 This work showed that, in other solvents, the a / -pyranose ratio is higher than in water (if the a-anomeric hydroxyl group is axial), and that there is a greater proportion of the furanose forms. The increase in the a-pyranoses is caused by the increased anomeric effect the possible reason for the increase in the furanose forms has been discussed in Section III, 1. The anomeric effect becomes particularly important in nonpolar solvents for example, in a chloroform solution of evernitrose 

Mackie and Perlin87 found that, when OH-2 is axial, there is a great increase in the proportion of the a-pyranose form in dimethyl sulfoxide, but there is little when it is equatorial (see Table VII). Typical of that small increase is the gradual change in the proportion of the a-pyranose form of lactose on addition of ethanol to the aqueous solution170 in water, 37% in 50% ethanol, 40% and in 80% ethanol, 42.5%, 

When compared with those in other Tables, the data in Table VII show that Perlin s conclusions are generally valid. 2,3-Anhydro-D-mannose and 2-C-(hydroxymethyl)-D-ribose (hamamelose) are exceptions there is actually somewhat less furanose in their solutions in dimethyl sulfoxide and pyridine, respectively, than in water but these can hardly be regarded as typical sugars. 

Idose is an exception to the rule that the proportion of the pyranoses is lower in organic solvents than in water. In 1 1 dimethyl sulfoxide-acetone, the / -pyranose content is much higher (Table VII) than in water,66 for reasons as yet unknown. 

It is still not clear why the furanose content is generally higher in organic solvents than in water. The effect on solvation of the water structure [p. 24] has been proposed as an explanation it seems to explain the interesting fact3 that addition of even a small proportion ( 10%) of dimethyl sulfoxide to an 

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The same regularities hold for solutions in solvents other than water except that there is a different proportionality factor ... 

In solutions, the distances between the centers of ions and of the nearest atoms of the surrounding solvent molecules can also be measured by x-ray and neutron diffraction, but with a somewhat larger uncertainty, 2pm. In aqueous solutions, if the water molecule is assigned a constant radius r = 138 pm (one half of the experimental collision diameter), then the distances t((I -0 )/pm = 138-fr,/pm have been established by Marcus within the experimental uncertainty, with the same ionic radii as in the crystals [45, 46], These radii, as selected in Ref 6 and annotated there, are listed in Table 2.8. The distances between the centers of ions in solutions in solvents other than water and of the nearest atoms of the solvents have also been determined in some cases reported by Ohtaki and Radnai [50] and confirm the portability of the Tj values among solvents, provided the mean solvent coordination number is near that in water. 

Since production of OH (agJ and reaction with H+(ag) go hand in hand when we are dealing with aqueous solutions, a base can be described either as a substance that produces OH (aq) or as a substance that can react with H+fag). In solvents other than water, the latter description is more generally useful. Therefore, we postulate a substance has the properties of a base if it can combine with hydrogen ions. 

Table II shows the average end-to-end distance over 20 ps for mannitol and sorbitol in vacuuo and in solution of an argon-like (L-J) solvent and SPC/E water. The average lengths all indicate sickle shapes, except for mannitol in water which is fully extended. This points to a specific solute-solvent interaction between mannitol and water, not just an unspecific solvent effect that is not present in solvent other than water. The model non-aqueous solvent is very artificial, but it should represent the main features of the class of non-polar, spherically symmetric solvents.

These ideas were rather limiting since they only applied to aqueous solutions. There were situations where acid-base reactions were taking place in solvents other than water, or even in no solvent at all. This problem was addressed in 1923 by the Danish chemist Johannes Bronsted (1879-1947) and the English chemist Thomas Lowry (1874-1936) when they independentiy proposed a more general definition of acids and bases, and the study of acids and bases took a great step forward. This theory became known as the Bronsted-Lowry theory of acids and bases. 

Potentials in Non-Aqueous Solutions.—Many measurements of varying accuracy have been made of voltaic cells containing solutions in non-aqueous media in the earlier work efforts were made to correlate the results with the potentials of similar electrodes containing aqueous solutions. Any attempt to combine two electrodes each of which contains a different solvent is doomed to failure because of the large and uncertain potentials which exist at the boundary between the two liquids. It has been realized in recent years that the only satisfactory method of dealing with the situation is to consider each solvent as an entirely independent medium, and not to try to relate the results directly to those obtained in aqueous solutions. Since the various equations derived in this and the previous chapter are independent of the nature of the solvent, they may be applied to voltaic cells containing solutions in substances other than water. 

Basic (cationic) dyes. Basic dyes are water-soluble and produce colored cations in solution. They are mostly amino and substituted amino compounds soluble in acid and made insoluble by the solution being made basic. They become attached to the fibers by formation of salt linkages (ionic bonds) with anionic groups in the fiber. They are used to dye paper, polyacrylonitrile, modified nylons, and modified polyesters. In solvents other than water, they form writing and printing inks. The principal chemical classes are triaryl methane or xanthenes. Basic brown 1 is an example of a cationic dye that is readily protonated under the pH 2 to 5 conditions of dyeing [5]. 

Acid-base reactions in solvents other than water are of both theoretical and practical significance, and their fundamental chemistry is becoming increasingly understood. It should be realized at the outset that solvents play an active rather than a passive role in acid-base reactions and that water as a solvent, though of unique importance, is highly atypical. The important considerations are general dielectric-constant efiects, acidic behavior and basic behavior of solvents, and specific interactions of solvent with solute. 

The Pfeiffer Effect in Nonaqueous Solvents. Alcohols. Because inner complexes are usually not soluble in water, and because the Pfeiffer effect has not yet been demonstrated to occur with an inner complex, the effect was studied in solvents other than water. One obvious choice is the lower alcohols because these solvents will dissolve most inner complexes and are suitable for polarimetric studies. However, Landis (11) has reported that the Pfeiffer effect does not take place in methanol with tris(l,10-phenanthroline)zinc(II) ion and d-a-bromocamphor-7r-sulfonate (BCS) as the optically active environment. He reports that the final solutions were cloudy therefore, their optical rotatory properties would be difficult to study, and the question was still open. 

The concepts and equations of acid-base dissociation have referred chiefly to aqueous solutions. Recently, interest in the behavior of acids and bases in solvents other than water has increased considerably. The classical definition of an acid and a base, which is satisfactory for water solutions, is too limited for other solvents. Because of the great importance of the general question of the acid-base equilibrium, the clear and fruitful views of Bronsted are exhaustively considered in a special (fourth) chapter. ... 

Fig. 6, in which the equivalent conductance of sodium iodide in ethyl alcohol at 25° is plotted as ordinates against the logarithms of the dilution, represents the behavior of many salts in solvents other than water. It will be seen that although the equivalent conductance is apparently approaching a maximum, the latter is much farther removed from the experimentally determined points than is the case with water solutions at corresponding dilutions. 

In recent years, several works have appeared on the alkali degradation of PET in solvents other than water. Thus, Collins and Zeronian56 have reported that treatment of PET with methanolic sodium hydroxide causes a faster degradation than when using aqueous sodium hydroxide. In the same way, Oku et al.51 converted PET quantitatively by reaction at 150°C with sodium hydroxide dissolved in anhydrous ethylene glycol. Disodium terephthalate was obtained as the major product, being precipitated from the ethylene glycol solution. Terephthalic acid was easily recovered by dissolution in water of the sodium salt followed by acidification with HC1. H-NMR measurements of the... 

In order to get MM4 to reproduce the structures and energies of the aldohexapy-ranoses in an adequate way then, it was found that in addition to the usual force field required for alkanes and alcohols, one had to explicitly include three additional different effects the anomeric effect, the gauche effect, and the delta-two effect. While all of these effects are known experimentally to occur in sugars, they were measured and studied only in aqueous solutions. The sngars are generally insoluble in solvents other than water, and they tend to decompose on heating. This leaves solvation as a problem still to be addressed. 

The Arrhenius theory was the first scientific theory of acidity acids provided hydrogen ions, H (aq), in an aqueous solution (as the only cations) and bases provided hydroxide ions, OH"(aq) in aqueous solution (as the only anions). One of the problems with the Arrhenius theory is that it is rather restrictive since many reactions are carried out in solvents other than water or in the gas phase in the absence of solvent. These non-aqueous solvents include liquid ammonia and liquid sulfur dioxide. 

Although continuum solvation models do appear to reproduce the structural and spectroscopic properties of many molecules in solution, parameterization remains an issue in studies involving solvents other than water. In addition, the extension of these approaches to study proteins embedded in anisotropic environments, such as cell membranes, is clearly a difficult undertaking96. As a result, several theoretical studies have been undertaken to develop semi-empirical methods that can calculate the electronic properties of very large systems, such as proteins28,97 98. The principal problem in describing systems comprised of many basis functions is the method for solving the semi-empirical SCF equations ... 

When the substance is dissolved in a solvent other than water, the formula (or name) of the solvent is given, and, if known, the number of moles of it per mole of solute. When the concentration is not given, the solution is understood to be dilute. ... 

Although the entire discussion of electrochemistry thus far has been in terms of aqueous solutions, the same principles apply equaly well to nonaqueous solvents. As a result of differences in solvation energies, electrode potentials may vary considerably from those found in aqueous solution. In addition the oxidation and reduction potentials characteristic of the solvent vary with the chemical behavior of the solvent. as a result of these two effects, it is often possible to carry out reactions in a nonaqueous solvent that would be impossible in water. For example, both sodium and beryllium are too reactive to be electroplated from aqueous solution, but beryllium can be electroplated from liquid ammonia and sodium from solutions in pyridine. 0 Unfortunately, the thermodynamic data necessary to construct complete tables of standard potential values are lacking for most solvents other than water. Jolly 1 has compiled such a table for liquid ammonia. The hydrogen electrode is used as the reference point to establish the scale as in water ... 

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