Main and side reactions in the Karl Fischer solution

The new investigations show that in Karl Fischer (KF) solutions various equilibria compete depending on the reaction conditions. In alcoholic media mainly alkyl sulphite is oxidised. The oxidation of hydrogen sulphite has only a small influence, which increases with rising water concentrations and proceeds via SO3 as intermediate product. The oxidation of the SO2 by aerial oxygen takes place as a side reaction in the KF reagents. In here alkyl sulphate and sulphate are formed in almost equal concentration, indicating, that hydrogen sulphite is oxidised