Ethanol dielectric constant

The reaction of 9-cyanofluorenyl anion (9-CFA, prepared from 9-cyanofluorene and sodium ethoxide) with alkyl and benzyl halides in ethanol is shown to be an Sn2 reaction from a kinetic study (Bowden and Cook, 1968). Qualitative application of the Hughes-Ingold theory of solvent effects predicts that, for an SN2 reaction of this charge type, an increase in the dielectric constant of the medium will cause a small rate decrease. That should be the case if the reaction is studied in ethanol (dielectric constant, D, 24 2) and DMSO (D, 48-9) is added. The data for the 9-CFA alkylation are in accord with this prediction, as seen in Table 10. 

Ethyl acetate (dielectric constant = 6.02 at 20 C, Dipole Moment = 1.88 D) and ethanol (dielectric constant = 23.8 at 20°C, Dipole Moment = 1.68 D) are aprotic and nonpolar solvents. The l- -octylth-ymine in these solvents forms hydrogen-bonded pairs, and then form double layers by the stacking interaction of thymine bases. Finally, the double layers aggregate by van der Waals interaction to form... 

Referring to Eq. V-69, calculate the value of C for a 150-A film of ethanol of dielectric constant 26. Optional Repeat the calculation in the SI system. 

The ultraviolet spectra of the pyridinecarboxylic acids (334) were initially interpreted assuming that the proportion of the zwitterion structure 335 was not appreciable,and the early pK work was inconclusive. However, Jaffe s calculations based on the Hammett equation indicated that about 95% of nicotinic and isonicotinic acids existed in the zwitterion form, and ultraviolet spectral data showed that the actual percentages of picolinic, nicotinic, and isonieotinie acids existing in the zwitterion form in aqueous solution are 94, 91, and 96%, respectively.This was later confirmed by Stephenson and Sponer, who further demonstrated that the proportion of the zwitterion form decreases in solvents of low dielectric constant, becoming very low in ethanol. Dipole moment data indicate that isonicotinic acid exists as such in dioxane, and 6-hydroxypyridine-3-carboxyiic acid has been shown to exist in form 336 u.sing pK data. ... 

The importance of the solvent, in many cases an excess of the quatemizing reagent, in the formation of heterocyclic salts was recognized early. The function of dielectric constants and other more detailed influences on quatemization are dealt with in Section VI, but a consideration of the subject from a preparative standpoint is presented here. Methanol and ethanol are used frequently as solvents, and acetone,chloroform, acetonitrile, nitrobenzene, and dimethyl-formamide have been used successfully. The last two solvents were among those considered by Coleman and Fuoss in their search for a suitable solvent for kinetic experiments both solvents gave rise to side reactions when used for the reaction of pyridine with i-butyl bromide. Their observation with nitrobenzene is unexpected, and no other workers have reported difficulties. However, tetramethylene sulfone, 2,4-dimethylsulfolane, ethylene and propylene carbonates, and salicylaldehyde were satisfactory, giving relatively rapid reactions and clean products. Ethylene dichloride, used quite frequently for Friedel-Crafts reactions, would be expected to be a useful solvent but has only recently been used for quatemization reactions. ... 

The problem of the isolation of quaternary salts, even when fornied, is,-in some cases, an acute one. Water or ethanol is friBquently held very tenaciously and this possibility may be the reason that so many workers still use non-hydrie solvents, such as benzene, despite the fact that reactions in such solvents are usually slow clearly the best solvents are the non-hydric ones of high dielectric constant. 

In order to go further into the experimental check we constructed Arrhenius plots of the fluorescence quantum yield of BMPC in a few solvents (methanol, ethanol, propanol, hexanol and methylene chloride), all of which showed good linearity. The activation energies and A/kp ratios, calculated from the slopes and intercepts of those plots, are collected in Table 1. The smooth increase of both parameters in the alcohol series is mainly associated with the increase of solvent viscosity. On the other hand, decrease of the solvent dielectric constant from 32.7 (methanol) to 8.9 (dichloromethane) causes a small but significant increase of the activation energy also, this increase is probably somewhat compensated by the decrease of the viscous-flow... 

On the assumption that = 2, the theoretical values of the ion solvation energy were shown to agree well with the experimental values for univalent cations and anions in various solvents (e.g., 1,1- and 1,2-dichloroethane, tetrahydrofuran, 1,2-dimethoxyethane, ammonia, acetone, acetonitrile, nitromethane, 1-propanol, ethanol, methanol, and water). Abraham et al. [16,17] proposed an extended model in which the local solvent layer was further divided into two layers of different dielectric constants. The nonlocal electrostatic theory [9,11,12] was also presented, in which the permittivity of a medium was assumed to change continuously with the electric field around an ion. Combined with the above-mentioned Uhlig formula, it was successfully employed to elucidate the ion transfer energy at the nitrobenzene-water and 1,2-dichloroethane-water interfaces. 

Changing the solvent in which a reaction is carried out often exerts a profound effect on its rate and may, indeed, even result in a change in its mechanistic pathway. Thus for a halide that undergoes hydrolysis by the SN1 mode, increase in the polarity of the solvent (i.e. increase in e, the dielectric constant) and/or its ion-solvating ability is found to result in a very marked increase in reaction rate. Thus the rate of solvolysis of the tertiary halide, Me3CBr, is found to be 3 x 104 times faster in 50% aqueous ethanol than in ethanol alone. This occurs because, in the S,vl mode, charge is developed and concentrated in... 

Compounds with high dielectric constants such as water, ethanol and acetonitrile, tend to heat readily. Less polar substances like aromatic and aliphatic hydrocarbons or compounds with no net dipole moment (e. g. carbon dioxide, dioxane, and carbon tetrachloride) and highly ordered crystalline materials, are poorly absorbing. 

Table 1 Changes in hypothetical potential energies of attraction of oppositely charged spherical ions based on reductions in dielectric constant in passing from water to methanol and ethanol, and the computed changes in binding constant assuming the changes in potential energy are translated into free energies of binding3...

The recent introduction of non-aqueous media extends the applicability of CE. Different selectivity, enhanced efficiency, reduced analysis time, lower Joule heating, and better solubility or stability of some compounds in organic solvent than in water are the main reasons for the success of non-aqueous capillary electrophoresis (NACE). Several solvent properties must be considered in selecting the appropriate separation medium (see Chapter 2) dielectric constant, viscosity, dissociation constant, polarity, autoprotolysis constant, electrical conductivity, volatility, and solvation ability. Commonly used solvents in NACE separations include acetonitrile (ACN) short-chain alcohols such as methanol (MeOH), ethanol (EtOH), isopropanol (i-PrOH) amides [formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA)] and dimethylsulfoxide (DMSO). Since NACE—UV may present a lack of sensitivity due to the strong UV absorbance of some solvents at low wavelengths (e.g., formamides), the on-line coupling of NACE... 

One can easily adjust the values of the dielectric constants D(, and Dj to obtain the experimental values of W, as in Table 4.4. With a choice of = 19.6 and Dj. = 51.0 for water, and D. = 12.5 and Dj. = 31.8 for 50% water-ethanol, we obtain the experimental values of W. We now compute the total correlation function for the two-state model for succinic acid. Here the correlation cannot be computed as an average correlation of the two configurations (see Section 4.5). The total correlation of the equilibrated two-state model is... 

Using the model described above with dielectric constant Dj. = 34.2 and D(, = 12, and with Xq = 3.62 x 10, we can reproduce the experimental values of and kj for succinic acid. These are shown in Table 4.7. Note that the dielectric constant for the trans form is very close to the macroscopic dielectric constant of 50% mixture of water and ethanol (Hamed and Owen, 1958) (for which D = 49 at 25 °C the experimental values of pKi and pK2 reported in Table 4.6 are at 20 °C). As expected, the fitted dielectric constant for the cis configuration is far smaller than the macroscopic dielectric constant. Once we determined Dj and Xq, they were... 

FIGURE 3 2 Solvent extraction efficiencies (EF) as functions of dielectric constants (D), solubility parameters (6), and polarity parameters (P and E -). Solvents studied silicon tetrachloride, carbon disulfide, n pentane. Freon 113, cyclopentane, n-hexane, carbon tetradiloride, diethylether, cyclohexane, isooctane, benzene (reference, EF 100), toluene, trichloroethylene, diethylamine, chloroform, triethylamine, methylene, chloride, tetra-hydrofuran, l,4 dioxane, pyridine, 2 propanol, acetone, ethanol, methanol, dimethyl sulfoxide, and water. Reprinted with permission from Grosjean. ... 

Solvent effects have been investigated in isatin (193) hydrolysis. Results from ethanol-water and acetonitrile-water mixtures revealed that for alkaline hydrolysis log k was correlated with the reciprocal of the dielectric constant. A tetrahedral intermediate (194) is involved, which breaks down to yield the ring-opened amino acid (195). A comparison has been made of the lability of isatin (193) towards diethyl-amine and hydroxide ion, the latter showing the greater effect. ... 

---