Solvation of ions. Part VI. Activity coefficients of anions in methanol relative to dimethylformamide

Abstract

An attempt has been made to estimate semiquantitatively the contribution of hydrogen bonding to the free energy of solvation of anions in methanol. Hydrogen-bonding activity coefficients for some anions in methanol at 25°, relative to a standard state of 1M-solute in dimethylformamide at 25°, have been calculated from rate data, from equilibrium constants, and from the e.m.f. of electrodes, in methanol and in dimethylformamide. Hydrogen-bonding activity coefficients for bromide and iodide ion (ca.× 10^–5 and 4 × 10^–3, respectively) were obtained from all three sets of data. The association constants for tribromide-ion formation and for tri-iodide formation in dimethylformamide at 25° are 2 × 10⁶ and 6·5 × 10⁶, respectively. A method for calculating differences in the standard electrode potentials of anions in protic and in dipolar aprotic solvents is suggested.