Solutes in sulfuric acid. Part VIII. Protonation of phenol, 4-fluorophenol and the 2- and 4-sulfonates of anisole and phenol in concentrated aqueous sulfuric acid; determination of pKa values by means of 13C NMR

Autor: Ankie Koeberg-Telder, Hans Cerfontain, Hans J. A. Lambrechts
Rok vydání: 2010
Předmět:
Zdroj: Recueil des Travaux Chimiques des Pays-Bas. 102:293-298
ISSN: 0165-0513
DOI: 10.1002/recl.19831020603
Popis: The protonation of phenol (2), 4-fluorophenol (3), phenyl methanesulfonate, potassium phenyl sulfate and the potassium 2- and -4-sulfonates of both phenol and anisole in concentrated aqueous sulfuric acid at 30°C has been investigated using 13C NMR spectroscopy. The results show that phenol and 4-fluorophenol are protonated predominantly on the oxygen atom. This protonation is governed by the H0a acidity function. The pKa of the oxonium ions of 2 and 3 are -6.40 ± 0.05 and -6.41 ± 0.05, respectively. The protonation of phenyl methanesulfonate occurs at acid concentrations > 100%. Potassium phenyl sulfate in ≥20% H2SO4 hydrolyses very rapidly to give phenol. The 2- and 4-sulfonates of both phenol and anisole are protonated on both the -OR (R = H, Me) and the -SO3− groups; the sulfuric acid concentrations of half-protonation have been determined to be between 80.0 and 83.3% H2SO4, corresponding with pKa's of the conjugate acids between -6.34 and -6.66 based on the H0a scale.
Databáze: OpenAIRE
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