Nuclear magnetic resonance studies of iminium salts. Part 11. Anionic participation of iminium salts in Phosgenation reactions

Iminium salts act as catalysts in the reaction of phosgene and phenols or thiols to yield chloroformates, which are important synthetic intermediates. This effect is explained in terms of the nucleophilicity of the chloride anion of the salts on the basis of an n.m.r. identification of various intermediates. The mechanism of nucleophilic assistance of iminium salts towards the substrate can be understood as an increase of the nucleophilicity of phenol or thiol by proton abstraction from the OH or SH group by the chloride anion.