KARL-FISCHER MECHANISM AND BUNSEN REACTION

(Mechnism of the Karl Fischer and Bunsen reaction). The isolation of the addition compounds of sulphur trioxide and methanol or cyclohexylamine shows that sulphur trioxide is an intermediate in the reaction between sulphite and iodide in water as the solvent. A sulphur trioxide addition compound is also found with the Karl Fischer reaction in pyridine. It is demonstrated that the pyridine-sulphur trioxide adduct is formed by sulphur trioxide and pyridine in a secondary reaction. Using methanol as the solvent, sulphur trioxide as an intermediate does not tell whether the reaction occurs via hydrogen sulphite or methyl sulphite; it can be formed in both cases. Known results from the literature hint at hydrogen sulphite as the intermediate, which means that the Karl Fischer and Bunsen reaction both have the same mechanism.