Acidity functions: an update

Abstract

. 61, 2225 (1983).The subject of acidity functions is reviewed, with emphasis on rnodcrn developrncnts. H o and othcr scales determined in acid media, using the Hammett cancellation assumption (zero'th order approximation) are discussed bricfly. The extension to strongly basic systems is also documcnted. Literature references to acidity function scalcs in aqueous acid, aqueous acidlorganic solvcnt, and aqueous base media are tabulated, togcther with those in aqueous baselorganic solvent mixtures at both variable and fixed base concentration. Over 400 acidity functions are referenced, including several electrochemical scales. Various approaches to developing universal functions from the data are discussed. Proton activity scales, based on the Yates-McClelland method of pKBH+ determination, and on electrochemical HoF scales, are prominent among these. Carpentier's method is mentioned, and the first-order approximation, assumed linearity among log activity coefficient ratios, is used to introduce the Bunnett-Olsen and excess acidity (X-function) methods. A brief critical discussion of which method to use is provided. Future developments anticipate the second-order approximation, with a quadratic dependence of log ionization ratios upon X-functions. The review cites 337 individual references. [Traduit par le journal]

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