The Basicity of 2,6-Dimethyl-4-pyrone

Abstract

Conductimetric and spectrophotometric measurements of the K_a of protonated 2,6-dimethyl-4-pyrone have been made. The conductimetrically determined value of pK_a = 0.17±0.03 was 0.2 pK units higher than the value of pK_a = -0.02±0.05 found spectrophotometrically . The spectrophotometric studies in concentrated sulfuric and hydrochloric acids revealed that, at low acid concentrations, the pyrone had an excess acidity slope parameter (m^‡) of -0.29. However, over a large acid concentration range, m^‡ was observed to vary in a way that caused moderate systematic errors in the excess acidity extrapolation procedure. For this reason the conductimetric value is considered more reliable.