Measurement of Acid-Base Equilibrium Constants in Acetonitrile/18-Crown-6 Solutions

Article abstract of DOI:10.1021/ac00263a041

Absorbance data were collected at three wavelength for different mixtures of acetonitrile solutions of acetic acid and substituted phenolates in order to define ionic equilibria.Formation of hydrogen bonded adducts between acid and phenolate in concentration-dependent stoichiometry renders the data, even from very dilute solutions, too complex for an exact algebraic analysis.A quite accurate assessment of the acid-base equilibrium constants is possible, by using only the calculated concentrations of free acids and bases at each ratio of acid/base.Plotting such apparent equilibrium constants vs. the acid/base ratio permits an extrapolation to zero acid concentration in which limit the true value of the acid-base equilibrium constant can be obtained.A similar technique can lead to an estimation of formation constants for conjugate adducts in acetonitrile.