Keto–enol equilibria in mixed acetic sulphuric anhydrides

Abstract

Mixed acetic sulphuric anhydrides obtained from both equimolar SO₃–AcOH and SO₃–Ac₂O systems in liquid SO₂ are found at low temperature (⩽–20°) in equilibrium between the keto (CH₃·CO·OSO₃Y) and enol (CH₂:COH·OSO₃Y) forms (Y = SO₃^– or Ac). At room temperature a cleavage reaction is shown to occur through the intermediacy of keten, which reacts further to yield oligomers and sulpho-derivatives [reaction (i)]. CH₂:COH·OSO₃Y [graphic omitted] CH₂CO [graphic omitted] (i) This cleavage reaction appears specifically not to involve participation of acetylium ions, whereas previously these ions were normally considered as the principal precursor of keten intermediates.