ACID-BASE EQUILIBRIA OF HYDROCHLORIC AND HYDROBROMIC ACIDS IN ISOPROPYL AND TERT-BUTYL ALCOHOLS

Acid-base equilibria of hydrochloric and hydrobromic acids have been studied at 25 °C in isopropyl and tert-butyl alcohols and to a lesser extent in n-hexyl alcohol. Values of pKd(HCl) are 3.1, 5.5, and 4.2, and of pKd(HBr) 2.0, 5.0, and 4.1, respectively. Homoconjunction and protonation constants in t-BuOH of both acids, Kf(HX2-), Kf((HX)2X-), and Kf(H2X+) are 7, 8 × 101, and 8 for HCl and 2.0 × 101, 1.7 × 102, and 1.6 × 101 for HBr. Conductance and paH data provided conclusive evidence that with increasing concentration the dissociation 3HX ⇌ H2X+ + HX2- becomes more predominant. The behavior of HCl as a very weak base has been confirmed in acetonitrile as a solvent. From the above constants and from solubility products of several salts, transfer activity coefficients of various species with reference to methanol or acetonitrile as a solvent are reported. It is concluded that the above three alcohols are equally strong hydrogen bond acceptors as methanol and ethanol, but that isopropyl and tert-butyl alcohol are considerably weaker hydrogen bond donors than the normal alcohols. In this connection the methanolation (solvation) constant of the chloride ion in tert-butyl alcohol has been reported. © 1979 American Chemical Society.