The reactions of S-alkylthioamidium iodides with some mercuric compounds have been studied. Mercuric carboxylates were found to react with S-alkylthioamidium iodides giving the corresponding acid anhydrides and amides in good yields along with alkylmercaptomercuric iodide. In addition, it was established that the reaction of mercuric cyanide with the iodides afforded α-dimethylaminomalononitriles by