Quantitative analysis of solvent effects in highly aqueous media. Application of the SWAG procedures and a critical appraisal of the additivity principle

Article abstract of DOI:10.1021/ja00159a047

This paper describes a study on medium effects of 25 monohydric and polyhydric alcohols on the neutral hydrolysis of 1-benzoyl-3-phenyl-1,2,4-triazole in highly aqueous media. Dependences of pseudo-first-order rate constants on molality of added alcohol are quantitatively analyzed in terms of pairwise Gibbs energy interaction parameters for initial state and transition state. Additivity of pairwise group interaction parameters (SWAG procedure) is applied, and the validity of additivity is critically examined. Excellent additivity is observed in series of monohydric alcohols and vicinal diols. In series of polyhydric alcohols, group contributions to the observed rate effects, as expressed in pairwise group interaction parameters, are, however, strongly dependent on the position of hydroxyl groups in the alcohol. This (apparent) nonadditivity behavior is discussed in terms of the hydration characteristics of the cosolvents. The importance of hydration shell overlap in determining medium effects is supported by kinetic data in ternary 1-propanol-urea-water mixtures.