N-substituted heterocyclic cations. Part IX. The preparation and chloride-ion catalysed unimolecular acidolysis of 2-[chloromercury(II)]-1,3-dimethylbenzimidazolium ions in aqueous solution

The 5-nitro-, 5-chloro-, 5-methyl-, and unsubstituted-1,3-dimethylbenzimidazolium ions react with mercury(II) chloride in mildly alkaline solution to give the corresponding 2-[chloromercury(II)]-derivatives. The latter are stable for long periods in aqueous perchloric acid at 65°, but readily undergo acidolysis in the presence of chloride ion, through unimolecular heterolysis of the corresponding dichloro- and trichloro-mercury(II) derivatives. The effect of substituents on the rate of the one-chloride-ion catalysis is small, and on the rate of the two-chloride-ion-catalysed acidolysis is even smaller.