Abstract
The ionization of the oxonium ions of phenol, anisole, 4-chloro- and 4-methyl-phenol and 4-bromo-, 4-fluoro- and 4-methyl-anisole in concentrated aqueous sulfuric acid has been investigated using UV spectroscopy at 25°C. The sulfuric acid concentrations at half-ionization are within the range 75.2 to 81.8% H2SO4, corresponding with pKa's between -5.87 and -6.52 based on the H0a acidity function. The substituent effects on the ionization of PhO+ H2 and PhO+ HMe are small, the Hammet ρ values being 0.5 ± 0.1 and 0.9 ± 0.1, respectively.
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