Solvents Of Low Dielectric Constant Research Articles

The chemistry of ethylene oxide. III. Reaction of ethylene oxide in amine solution.

A kinetic study has been made of the reaction of ethylene oxide in pyridine solution in the presence of strong acids. The rate has been found to be dependent upon the concentration of acid and of oxide over a wide range of concentrations at 25°C. The specific rate constant, however, varies markedly with the nature of the acid anion and appears to decrease with increasing basic strength of the anion. The absence of large salt effects seems to indicate that the anion effect is of a physical rather than chemical nature and the results are therefore tentatively attributed to the nature of solutions of electrolytes in solvents of low dielectric constant.

Dielectric Behavior of Solutions of Electrolytes in Solvents of Low Dielectric Constant I. A Calorimetric Method for Measuring Losses

The experimental equipment and method used to determine calorimetrically the energy absorption in a radiofrequency field by several electrolytes in solvents of low dielectric constant is described. The dipole conductivity and the loss factor for these systems are then calculated from the experimental data.

Dielectric Behavior of Solutions of Electrolytes in Solvents of Low Dielectric Constant. II. Dielectric Absorption

The dielectric losses in solutions of salts in several low dielectric constant solvents are studied as a function of frequency and concentration, using the calorimetric method. The results are interpreted according to the Debye theory, and critical frequencies, molecular radii, and dipole moments are evaluated wherever feasible. Solutions of tri-isoamylammonium picrate in benzene and diphenylmethane behave as a monodisperse system having a single well-defined polar structure relatively independent of concentration. Corresponding solutions of tetra-n-butylammonium thiocyanate, in contrast, show a marked departure from theoretical behavior for a monodisperse system, having a broad distribution of relaxation times and a high degree of association strongly dependent on concentration. Di-n-butyldioctadecylammonium thiocyanate shows monodisperse behavior at low concentrations, with more physically and electrically different polar bodies appearing as the concentration is increased. These results are in good agreement with polarization, conductance, and cryoscopic measurements for these systems.

The dielectric capacity of electrolytes in mixed solvents: ion association in solutions of magnesium sulphate

The remarkable achievements of Debye and Hückel, Onsager, and their colleagues in explaining and rationalizing the experimental data upon the behaviour of strong electrolytes in dilute solution have naturally led to much intensive research directed towards the extension of their theories to ranges of greater ionic concentration. From this work the theory of ion association, sponsored by Niels Bjerrum, has emerged with marked success. Assuming that the forces between oppositely charged ions obey the simple Coulomb law, Bjerrum has calculated the probability of such ions being within a distance, q 0 , at which the thermal energy per degree of freedom is but one-quarter of the electrostatic energy holding the ions together. Oppositely charged ions at less than this distance from one another are termed short-range pairs. The true degree of association (1— α *) of an electrolyte, as distinguished from the classical conception of undissociated molecules, is a measure of the number of short-range pairs, and Bjerrum has shown that the law of mass action may be applied to this association to develop a relation which reproduces the activities of electrolytes in more concentrated solution with remarkable fidelity. Onsager (1927) has calculated some approximate values of the true degree of association by consideration of the discrepancies between experimental conductivity data for aqueous solutions and the figures derived from his equation. Similar, and more extensive and more accurate measurements have been made by Davies (1927). In solvents of lower dielectric constant, the increased inter-ionic forces lead to still wider discrepancies, and many workers have shown that electrolytes which are almost completely non-associated in water are appreciably associated in solvents of reduced dielectric capacity. Martin (1928) has shown that the alkali metal halides are incompletely dissociated in benzonitrile and that the association obeys a generalized law of mass action. Fuoss and Kraus (1933 a ) have observed the same effects with the alkali metal nitrates dissolved in ammonia and other solvents of low dielectric constant. The mass-action constants derived from their results are in complete agreement with those predicted by the Bjerrum ion-association theory and, using measurements of the conductivity of tetra iso - amylammonium nitrate in dioxan-water mixtures, the same workers (1933 b ) have succeeded in extending the theory to include higher forms of association. Swift (1938) has confirmed the views of Fuoss and Kraus for ions of small radii by an investigation of the conductivities of solutions of the alkali metal halides in dimethylamine.

Studies in the substituted quaternary azonium compounds

1. The molecular weights of phenyldimethylazonium, phenylmethylethylazonium, phenylmethylbenzylazonium and phenylpropylbenzylazonium iodides are lower in ethyl alcohol than in water; in the case of phenyldiethylazonium iodide this relation is reversed. The degree of association is, therefore, lower in ethyl alcohol, a solvent of low dielectric constant, than in water, a solvent which has a very high value. It is, therefore, clear that the Nernst-Thomson rule is not followed in these four cases.

The Properties of Electrolytes as Related to Their Constitution

By taking into account specific as well as distributed interaction between ions due to Coulomb forces, a general theory of electrolytes results which accounts for the properties of electrolytic solutions in all solvents whatever the value of their dielectric constant. The influence of specific interaction is the greater, the lower the dielectric constant of the solvent medium. Due to specific interaction, ions associate to ion‐pairs and to more complex neutral aggregates as well as to triple ions and more complex charged aggregates. The results of experiment are quantitatively accounted for at lower concentrations and qualitatively at higher concentrations. Specific ionic interaction effects depend upon the size, shape, and charge distribution of the ions. In solvents of low dielectric constant, the constitutional factors come to light. The conductance, freezing point and molecular polarization of electrolytes in solution are considered.