Mechanism of sulphomethylation of β-naphthol : Kinetics of the formation of sodium 2-hydroxy-1-naphthylmethanesulphonate from bis-(2-hydroxy-1-naphthlyl)methane

Abstract

Sulphomethylation of β-naphthol, i.e. the reaction of bis-(2-hydroxy-1-naphthyl)methane (BHNM; I) with sodium sulphite to form 2-hydroxy-1-naphthylmethanesulphonate (SNMS; II), has been studied kinetically by iodometry of sodium sulphite. The rate law, ν = k [BHNM], together with the relation k vs. [OH −] suggests a S N1 mechanism via the dianion of BHNM (V) and quinone-methide (VIII). This shows that quinonemethide (VIII) and not BHNM is an intermediate in the sulphomethylation of β-naphthol. The behaviour of BHNM in aqueous alkali is discussed in terms of the alkalimetric titration and UV spectra.