The rates of the acid-catalysed hydrolysis of diethyl 2-pyridyl phosph
ate and of the base-promoted hydrolysis of N-methyl-8-(dimethylphospho
ryloxy)quinolinium ion have been determined in the presence of differe
nt cations as buffer components. For both substrates the rate depends
on the nature of the cations, indicating the participation of a substr
ate-cation complex in the reaction.