Stability of bicyclic guanidine superbases and their salts in water

Abstract

Bicyclic guanidines are widely used in organic chemistry as strong basic reagents and catalysts. They are also utilized in CO₂ chemistry, ring opening polymerization reactions and in cellulose dissolution or processing as ionic liquids. Despite their wide applicability, they are usually sensitive to water, especially under alkaline conditions. The salts of guanidines usually exhibit slower degradation rates but are still somewhat prone to hydrolysis. We studied the hydrolysis rates of a series of different bicyclic guanidines and their carboxylate salts under different aqueous conditions. It appears that bicyclic guanidines and their salts are in principle stable in water but undergo hydrolysis in the presence of hydroxide ions (OH⁻). Therefore, it is feasible to design bicyclic guanidine bases that are highly tolerant to water, but can still simultaneously possess different desirable chemical characteristics, like hydrophobicity to allow compatibility under varying conditions.