Tetraalkylammonium salts solvation

Association trends also reflect for the most part increasing solvation with decreasing size (Table 4). Tetraalkylammonium salts become less associated as the size of the alkyl group becomes larger, an expected trend for these relative-... 

LiCl, NaN03, and tetraalkylammonium salts can be used as supporting electrolytes. For the electrolytic generation of solvated electrons mainly LiCl has been employed [343,344]. A reversible reference electrode in EDA is the Zn(Hg)/Zn" electrode [345], but the Hg pool [246] or the aqueous calomel electrode, fitted with a suitable salt bridge, is also applicable. 

Many salts are soluble in DMSO, so the choice of supporting electrolyte is less restricted than in most other nonaqueous solvents. In general, perchlorates, even KCIO4, nitrates, and halides, are soluble, whereas fluorides, cyanides, sulfates, and carbonates are not thus not only NaC104, LiCl, NaNO, and tetraalkylammonium salts can be used but also such salts as NH4PF6 and NH4SCN. The ability of DMSO to solvate ions is also of importance in the indirect electrolytic hydrodimerization of, for example, acrylonitrile using Na(Hg) [388]. 

The perfluoroisopropylsilver complex 12 is heterolytically labile, existing in solution in dynamic equilibrium with solvated Ag+ and the anionic bis(perfluoroisopropyl)silver anion, which can be isolated in the form of the tetraalkylammonium salt 13 (equation 10)24. 

The above treatment has led to a deeper understanding of the solvent effect. Whereas alkali metal salts and tetraalkylammonium salts displayed analogous behaviour on the basis of thermodynamic data calculated from the temperature dependence of the constant X for ion-pair formation, the non-Coulombic part of the Gibbs energy reflected different behaviours of these two kinds of cation. Whereas in solutions of alkali metal salts the alkali metal ions coordinate solvent molecules, and hence ion-pair formation is accompanied by displacement of solvent molecules from the solvate sphere, the interactions of the tetraalkylammonium salts, as they do not coordinate solvent, can be ascribed primarily to dispersion... 

A recent study reports the solvation dynamics of coumarin 153 and 6-propionyl-2-dimethylaminon-aphthalene (PRODAN) in [emim][BF4] and [bmim] [BF4]. The fluorescence decay profiles showed biphasic solvation dynamics as was observed for molten tetraalkylammonium salts.- The results were interpreted as indicating a short-lived component resulting from the motion of the anion, followed by a longer-lived component resulting from the motion of both the anion and the cation. In the same papers, estimates of the value of (30) were made for these solvents based on comparisons of the values for each probe molecule in conventional solvents. The values obtained (48.9 from coumarin 153 and 47.1 kcal mol" from PRODAN for [bmim][BF4]) were somewhat lower than those measured directly using Reichardt s dye.- ... 

In certain electrolytic media the concentration of salts is so high that the medium could be regarded as consisting of a solvated salt. This is thus the case in the strong solutions (10 M) of many salts in ammonia in which the vapor pressure of ammonia at ambient temperature is less than 1 atm. It also applies to the strong solutions of tetraalkylammonium /7-tolue-nesulfonates in water, used sometimes in organic electrochemistry. 

Ethanol has also received considerable attention as a solvent over a long period of time. Data on this solvent, however, are rather few compared to methanol and very few systematic studies exist. Several solubility studies have been made since the publication of Seidell and Linke. Thomas has reported solubilities for the alkali metal iodides at 20 and 25°C, and observed a decrease in solubility with an increase in ionic radius of the cation. Deno and Berkheimer have reported the solubilities of several tetraalkylammonium perchlorates. In every case the solid phase was the pure salt. Solubilities for several rare earth compounds have been reported.Since all of these salts form solvates in the solid phase, the results cannot be used in thermodynamic calculations without the corresponding thermodynamic values for the solid phases. Solubilities of silver chloride, caesium chloride, silver benzoate, silver salicylate and caesium nitrate have been measured in ethanol, using radioactive tracer techniques. Burgaud has measured the solubility of LiCl from 10.2 to 57.6°C and observed that there is a transition from the four-solvated solid phase to the non-solvated phase at 20.4°C. 

It was shown by Strauss et ai [St 77] that in frozen methanol the O—H vibration bands become narrower, and in frozen methanol solutions of alkali metal salts the solute causes the appearance of fine structure in the spectrum. Appropriate assignment of the distinct bands has contributed to the understanding of the solvation processes. With a series of detailed examinations employing this method, Symons et al [St 76, St 77, Sy 75a, Sy 75b, Sy 75c] investigated the structures of alcoholic solutions of alkali metal and tetraalkylammonium halides. 

Corresponding tetraalkylammonium (TAA) salts (R N Y " or Q Y ) provided that the cations contain more than 16 carbon atoms, have much better solubility patterns. Indeed salts R N Y are well soluble in hydrocarbons, even when Y are such inorganic anions as F , Cl or CN. Thus Q Y " could be very efficient sources of anionic reagents, not only assuring homogeneity in nonpolar solvents but also high activity of anions. The reason for the latter behaviour is that anions in nonpolar solvents are weakly solvated and that cation-anion interactions, in the case of tetraalkylammonium cations. 

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