| Abstract
| - The protonation equilibria of N-phenylbenzohydroxamic, benzohydroxamic, salicylhydroxamic, andN-p-tolylcinnamohydroxamic acids have been studied at 25 °C in concentrated sulfuric, hydrochloric,and perchloric acid media; the UV−vis spectral measurements were analyzed using the Hammettequation and the Bunnett−Olsen and excess acidity methods. The medium effects observed in theUV spectral curves were corrected with the Cox−Yates and vector analysis methods. The HA acidityfunction based on benzamides provided the best results. The range of variation of the solvationcoefficient m* is similar to that of amides, this indicating similar solvation requirements for amidesand hydroxamic acids. For the same substrate, the observed variations of pKBH+ with the mineralacid used was justified by formation of solvent-separated ion pairs; for the same mineral acid, theobserved changes in pKBH+ can be explained by the solvation of BH+. The change of the pKBH+values was in reasonably good agreement with the sequence of the catalytic efficiency of the mineralacids used, HCl > H2SO4> HClO4.
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