On the one hand, this can be attributed to the fact that the reactions for compounds 5a-c were not conducted in pure aqueous medium, but instead in a DMF-water mixture (comparison of hydrolysis halflives of 5a). On the other hand, the acyl phosphates 2, 5b and 5c have sterically more demanding residues, which disfavors nucleophilic attack of the catalyst. Nevertheless, hydrolysis takes place in all cases, indicating that these fuels can be put to use in chemically-driven steady states.