Acid-catalysed hydrolysis of substituted acetanilides

Abstract

The rate of hydrolysis of N-acetylsulphanilic acid has been measured over a wide range of acidities and temperatures in H₂SO₄. In H₂SO₄(<75% w/w) the data fit well the Bunnett and Bunnett–Olsen criteria of an A-2 mechanism. In more concentrated acid Arrhenius parameters indicate a change to an A-1 mechanism and the rate increases with increasing acidity. Seven other substituted acetanilides exhibit this behaviour in H₂SO₄, and 2,4,6-tribromoacetanilide does so also in HClO₄. Evaluation of W and ϕ values confirm the existence of an A-1 mechanism.