On the protonation and deuteration of thioanisole and some of its methoxy-substituted derivatives†

Abstract

The protonation of thioanisols by strong acids, such as trifluoroacetic acid or trifluoromethane sulfonic acid was investigated by ¹H NMR spectroscopy, including experiments with deuterated acids. Contrary to reported literature and to general expectations, protonation of thioanisole does not occur exclusively at the methylmercapto group but also to a lower extent at the aromatic ring. In cases of methoxy-substituted thioanisols protonation can take place at both heteroatomic groups and at the aromatic ring. The sites of protonation depend on the substituent pattern as unambiguously indicated by deuteration.