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.