Degradation pathway of pralidoxime chloride in concentrated acidic solution

The degradation products of pralidoxime chloride (1) (X- = Cl-) in concentrated aqueous solutions (less than or equal to 50% w/v) were identified using one or more methods: HPLC, polarography, voltammetry, MS and/or NMR. The products found were the 2-cyano-, 2-carboxamido- and 2-carboxy-1-methyl-pyridinium chlorides, 1-methyl pyridinium chloride, cyanide ion, ammonia and carbon dioxide. 1-Methyl-2-pyridone was indirectly identified by the presence of cyanide ion. The degradation rate increased with increasing pH values between pH 1 and 3.2 and with increasing concentrations between 1 and 50% w/v pralidoxime chloride. The results suggest that 1 (X- = Cl-) is dehydrated by a hydroxyl-ion catalyzed reaction ot the nitrile 2 which is hydrolyzed to either the pyridone 6 and cyanide ion or to 2-carboxamido-1-methyl-pyridinium chloride 3. The amide is hydrolyzed to give the 2-carboxy derivative 4 which finally is decarboxylated to give 1-methylpyridinium chloride 5.