DETERMINATION OF BINDING CONSTANTS AND STOICHIOMETRIES OF SHORT-RANGE, HYDROGEN-BONDING SOLVATION BY USE OF A PROTON-TRANSFER INDICATOR REACTION

摘要

A recent method for determination of stoichiometries and binding constants for short-range, hydrogen bonding solvation is reviewed and new results are presented. The method exploits the sensitivity of a proton-transfer equilibrium, K-PT, to changes in solvent composition. Solvation numbers and binding constants for primary and secondary stages of solvation of an aminophenol proton-transfer adduct and the free phenol and amine are determined as adjustable parameters when model isotherms are fitted to K-PT versus [S] data, where [S] is the concentration of a hydrogen-bonding minor component of a mixed solvent, Results for most of the twenty-three aprotic solvents investigated are modeled by bifurcation-type hydrogen bonding of two or more electron pairs to a single polar hydrogen. Results for the seven protic solvents studied, including new data for ethanol, 2-choloroethanol, and 2,2-dichloroethanol, are modeled by two, or possibly three, successive stages of solvation, assumed to involve hydrogen-bonded chains. Preliminary results indicate that solvation by water is amenable to this analysis. (C) 1997 Elsevier Science B.V. [References: 28]