Ionic associations of amine hydrochlorides dissolved in amines. Conductance measurements and consequences on solvated electron-ammonium ion reactivity

Abstract

Conductance measurements performed on solutions of ammonium chloride, RNH/sub 3//sup +/Cl/sup -/, in amino solvents, RNH/sub 2/, give information about ionic associations in these media. Previous results obtained by a pulse radiolysis technique concerning recombination rate constants between solvated electrons e/sub s//sup -/ and RNH/sub 3//sup +/ cations are discussed in terms of these associations. Three typical cases have been studied. In the first one (hydrazine, N/sub 2/H/sub 4/), ionic association is negligible so that the absolute rate constant for the recombination e/sub s/- + RNH/sub 3//sup +/ can be deduced from the experimental rate constants by the sole ionic strength effect (K/sub II//sup 0/ = (6 +- 1) x 10/sup 7/ M/sup -1/s/sup -1/). In the second case (propylamine, n-PrNH/sub 2/), pairing is so important that only the rate constant related to the pair can be obtained (k = (6.0 +- 0.6) x 10/sup 8/ M/sup -1/ s/sup -1/). In the third case (ethylenediamine, EDA), conductance data show the presence of isolated ions, pairs, triple ions, and even quadrupoles, in the concentration range 10/sup -4/-1 M. The limiting molar conductance of the ammonium chloride, EDAH/sup +/Cl/sup -/, is found to be ..lambda../sup 0/ = 74.6 +- 0.1 cm/sup 2/more » ..cap omega../sup -1/ mol/sup -1/ at 25/sup 0/C. Equilibrium constants are deduced for the pairing (k/sub p/ = (6.35 +- 0.10) x 10/sup 3/ M/sup -1/) and for the triple ion association (K/sub T/ approx. 9 M/sup -1/). This knowledge enables us to obtain the value of the rate constant of the solvated electron with the isolated cation EDAH/sup +/, i.e., NH/sub 2/C/sub 2/H/sub 4/NH/sub 3//sup +/: k/sub II//sup 0/ = (2.0 +- 0.2) x 10/sup 10/ M/sup -1/ s/sup -1/.« less