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Acid dissociation constants in water have been determined for proton loss from a series of N-aryl-N′-cyanoguanidines 1. Treatment of the same compounds with a strong base, butyllithium, followed by excess methyl iodide leads to successive N-methylation to yield mono-, di- and tri-methylated N-aryl-N′-cyanoguanidines. The mechanism of the methylation is discussed.

A series of N-aryl-N′-cyanoguanidines has been prepared and studied in [2H6]Me2SO by 1H and 15N NMR spectroscopy. The 15N NMR coupling patterns for natural abundance and 15N-enriched guanidines show unequivocally a structure with the CN conjugated with the cyano group. The invariance of δH for the nitrogen bound protons with guanidine concentration, the temperature variation, the lack of water-induced change in δH, the linear free energy relationship (LFER) analysis and coupling patterns, all show that no prototropic tautomerisation is occurring on the NMR timescale. The findings are considered in terms of possible dissociative and non-dissociative mechanisms.