AbstractThe distribution equilibria of hydrochloric, nitric, perchloric, sulphuric and phosphoric acids between aqueous solutions and a solution of tricaprylmethyl‐ammonium chloride in organic solvent have been investigated. The organic phases have been studied by infra‐red and nuclear magnetic resonance spectroscopy. As a result, it is found that at low aqueous acidity the extraction of these acids is governed by the ion exchange reaction, forming the mono‐quaternary ammonium salts of monobasic acids and the mono‐, di‐ (and tri‐) quaternary ammonium salts of di‐ (and tri‐) basic acids, and at higher acidity by the formation of the adducts to quaternary ammonium salts with a