Diethyl ether dielectric constant

Bonhote and co-workers [10] reported that ILs containing triflate, perfluorocar-boxylate, and bistrifylimide anions were miscible with liquids of medium to high dielectric constant (e), including short-chain alcohols, ketones, dichloromethane, and THF, while being immiscible with low dielectric constant materials such as alkanes, dioxane, toluene, and diethyl ether. It was noted that ethyl acetate (e = 6.04) is miscible with the less-polar bistrifylimide and triflate ILs, and only partially miscible with more polar ILs containing carboxylate anions. Brennecke [15] has described miscibility measurements for a series of organic solvents with ILs with complementary results based on bulk properties. 

The marked changes in the carbonyl IR bands accompanying the solvent variation from tetrahydrofuran to MeCN coincide with the pronounced differences in colour of the solutions. For example, the charge-transfer salt Q+ Co(CO)F is coloured intensely violet in tetrahydrofuran but imperceptibly orange in MeCN at the same concentration. The quantitative effects of such a solvatochromism are indicated by (a) the shifts in the absorption maxima and (b) the diminution in the absorbances at ACT. The concomitant bathochromic shift and hyperchromic increase in the charge-transfer bands follow the sizeable decrease in solvent polarity from acetonitrile to tetrahydrofuran as evaluated by the dielectric constants D = 37.5 and 7.6, respectively (Reichardt, 1988). The same but even more pronounced trend is apparent in passing from butyronitrile, dichloromethane to diethyl ether with D = 26, 9.1 and 4.3, respectively. The marked variation in ACT with solvent polarity parallels the behaviour of the carbonyl IR bands vide supra), and the solvatochromism is thus readily ascribed to the same displacement of the CIP equilibrium (13) and its associated charge-transfer band. As such, the reversible equilibrium between CIP and SSIP is described by (14), where the dissociation constant Kcip applies to a... 

Organic solvents. Addition of organic solvents decreases the solubility of proteins by reducing the dielectric constant of the medium. For the precipitation of enzymes, methanol, ethanol or propanol are mostly used, but acetone and diethyl ether can also be employed. The principal disadvantage of organic solvents is their tendency to cause stmctural damage of enzyme molecule. 

Fig. 9.4.23 Dispersibility of colloidal systems of a kind of metals in various organic liquids. er. Relative dielectric constant of liquids A, electron affinity disp, dispersion (O) floe, flocculation ( ) upon stirring, the suspension becomes turbid then particles slowly sediment) coag, coagulation ( immediately after stirring of the suspension, particles aggregate again to sediment). ( ) Boundary between disp and floe ( ) boundary between Hoc and coag. Broken lines divide each region, (a) Hexane, (b) benzene, (c) diethyl ether, (d) ethyl acetate, (e) letrahydrofuran. (0 dichloroethane. (g) benzyl alcohol, (h) 2-butanol, (i) butanol, (j) acetone, (k) ethanol. (From Ref, 23.)...

DNs range from zero (solvents like hexane, tetrachloromethane), through modest donors (acetonitrile 14.1, acetone 17), to good donors like water (18), to superb donors like DMSO (29.8) and, best of all, HMPA (38.8) (see table 3.7). The DN enables us to rationalize why a solvent such as nitromethane, (6r= 35.8) is considered to be fairly nonpolar, although it has a higher dielectric constant than diethyl ether (Sr = 4.2) and tetrahydrofuran (Sr = 7.6) which are often thought to be more polar solvents than their dielectric constants would indicate. The DN of nitromethane is only 2.7, compared with that of 19.2 for diethyl ether and 20 for tetrahydrofuran. These ether solvents are much better electron-pair donors than nitromethane. 

Drijvers and Goethals 52) have reported that excess sulphide functions (monomer and polymer) and diethyl ether have no detectable effect on the dissociation of two sulphonium tetrafluoroborate salts in methylene chloride and nitrobenzene, when present in similar proportions to those in corresponding polymerisation reactions. In contrast to this, however, Jones and Plesch 51) have shown that the dissociation constant of triethyloxonium hexafluorophos-phate in methylene chloride at 0°C increases by a factor of - 2 when small quantities of tetrahydrofuran are added. The latter molecule has a lower dielectric constant than methylene chloride and might therefore be expected to reduce dissociation. These workers have interpreted their results in terms of specific solvation of the cation by ether molecules, with subsequent reduction in the effective charge density of the positive ion and hence in the coulombic force favouring ion pairing, e.g. 

Solvents which are poor donors are commonly used in glycoside synthesis, for instance dichlorometh-ane, cyclohexane or petroleum ether. These solvents favor SN2-type reactions. Solvents which are better donors, for instance ethers (diethyl ether, THF, etc.), acetonitrile, pyridine, nitromethane etc., each result in a typical change in the reaction course due to their different participation in the stabilization of the reaction intermediates. With ethers, acetonitrile and pyridine participation leads to onium-type intermediates (Scheme 5 8 and 9), which eventually provide, via fast equilibration, mainly the -anomer (8), due to their higher thermodynamic stability, based on the inverse anomeric effect .Thus a-product formation is often favored in these solvents (see Section 1.2.3.2.5). Solvents with even higher dielectric constants commonly result in lower diastereocontrol in glycoside synthesis. 

The solute-solvent complex model proposed above is further supported by results obtained from mixed-solvent experiments. In diethyl ether, Sq4 exists primarily as free squaraine (Fig. 3a). The addition of a complexing solvent should drive the equilibrium for complexation. As a result, both and Xp should shift to the red and the intensity of the p-emission should increase. To eliminate any complication due to the increase in dielectric constant of the mixed solvent during experimentation, the mixed-solvent experiment was first performed in a ternary system consisting of ether (e = 4.43), chloroform (e = 4.7), and n-hexane (e = 1.9). The addition of n-hexane in the mixture is to keep the dielectric constant constant as the concentration of chloroform increases. The absorption and fluorescence spectral results are summarized in Figs. 4a and 4b, respectively. The data showed that nd Xp shift to the red and the intensity of the P-emission increases as [CHCI3] increases at [CHCl3]<1.12 M. Simultaneously, an isosbestic point at -625 nm and isoemissive point -662 nm are observed in the absorption and fluorescence spectra, respectively. The observation of an isosbestic point in the absorption spectra and an isoemissive point in the emission spectra provide positive evidence that (1) Sq4 forms a complex with chloroform in the ethereal solutions,... 

A number of attempts were made to correlate the solvent effects with different solvent parameters, such as the dielectric constant Ej. [46], Z [47], 6 [48], Py [49], n [50], and so forth. The relationships between and these solvent parameters are quite scattered except n. The plot of of Sq4 as a function of solvent parameter n is given in Fig. 10. Along with the red-shift on a systematic and gradual change in the composition of the multiple emission band is observed (see insets in Fig. 10). Sq4 exhibits primarily a-emission in diethyl ether. As the solvent polarity increases, the intensity of the P-emission increases. The p-emission eventually dominates the fluorescence. Because the P-emission is the emission from the solute-solvent complex, the overall spectral results suggest that the solvent effect on may be due to the shift in equilibrium for the complex formation as n increases. For solvents with 7t ranging from 0.273 to 0.567, both a- and P-emission bands are discernible simultaneously. Assuming that the spectral bandwidths of these two bands are similar and that they are not sensitive to solvent. Law [30] has deconvoluted the contribution of the a- and P-bands in the multiple emissions. The relative intensity of these two bands can then be used to estimate the relative concentrations of the free squaraine and the complex. From the ratio of the a- and P-emissions and the molar concentration of the solvent, the equilibrium constants (K in these solvents are calculated. A plot of versus n is depicted in Fig. 11, and a linear plot is obtained. The result simply indicates that the equilibrium constant for solute-solvent complexation increases as n increases. 

Buergi and Baiker studied the influence of different solvents for the conformations of Cnd in the enantioselective hydrogenation of ketopanto-lactone. They claimed three conformations of Cnd at RT closed (1) , closed (2) and open (3) . The latter structure is the most stable in polar solvents and increases with solvent polarity, as suggested by experiments on the enantioselective hydrogenation to pantolactone with a maximal ee of 78% in toluene solution, which is the solvent with the lowest dielectric constant. The increase in dielectric constant in the series of cyclohexane, hexane, diethyl ether and THF, decreases ee up to 50% and in EtOH and water even to 15%, in accordance with a decrease in the population of the open (3) conformation of Cnd. 

The above formalism assumed that only the monomeric form of HOAc exists in the ether phase. Carboxylic acids are known to dimerize in organie solvents that have a low dielectric constant. Let us assume we have aeetie acid forming a dimer in the organic phase. This tendency may be more prominent if HOAc is dissolved in a nonpolar solvent like hexane as eom-pared to a moderately polar solvent like diethyl ether. The formation of a dimer can be depicted by ... 

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