Nonideal Behavior of Alkylammonium Salts in Organic Solvents at Elevated Temperatures

Osmometric vapor-pressure-lowering measurements on toluene, butylbenzene, chlorobenzene, and chloronaphthalene solutions of several secondary, tertiary, and quaternary long-chain (at least five carbon atoms per chain) alkylammonium chlorides, bromides, thiocyanates, nitrates, and perrhenates in the temperature range between 50-130 degrees C show an appreciable amount of molecular association. The extent (number of aggregated units) and/or the degree (size of aggregated units) of aggregation decreases with the number of carbon atoms per chain, the polarity of the solvent, and the temperature, but increases with the size of the anions and the solute concentration. The data were treated quantitatively in terms of activity coefficients via the Gibbs-Duhem relation and also in terms of specific oligomer formation. The latter treatment shows the salts to form a dimer and one (exceptionally two) higher oligomer, for which the association constants have been calculated.