Inter- und intramolekulare Umlagerung der Sulfogruppe in 2-Naphtol-1-sulfonsäure

The isomerisation of 2-naphthol-1-sulfonic acid (potassium salt) into 2-naphthol-6-sulfonic acid has been studied using labelled sulfuric acid (H₂³⁵SO₄). In 40 to 50% aqueous sulfric acid the reaction takes place exclusively by an intermolecular mechanism (protio-desulfonation and resulfonation). In glacial acetic acid, in the presence of an excess of sulfuric acid, the rearrangement is partly intramolecular. With an equimolar amount of sulfuric acid the rearrangement is completely intramolecular. This reaction is first order with respect to 2-naphthol-1-sulfonic acid and zeroth order with respect to excess of sulfuric acid. A mechanism for the reaction is proposed.