Room Temperature Hydrolysis of Benzamidines and Benzamidiniums in Weakly Basic Water

Benzamidinium compounds have found widespread use in both medicinal and supramolecular chemistry. In this work, we show that benzamidiniums hydrolyze at room temperature in aqueous base to give the corresponding primary amide. This reaction has a half-life of 300 days for unsubstituted benzamidinium at pH 9, but is relatively rapid at higher pH's (e.g., t_1/2 = 6 days at pH 11 and 15 h at pH 13). Quantum chemistry combined with first-principles kinetic modeling can reproduce these trends and explain them in terms of the dominant pathway being initiated by attack of HO^- on benzamidine. Incorporation of the amidinium motif into a hydrogen bonded framework offers a substantial protective effect against hydrolysis.