The system's behavior upon refueling was studied by monitoring the concentration of NaphPO4 and NaphAcPO4 during sequential additions of either acetic anhydride or EDC (Figure and). Whereas the acetic anhydride driven reaction cycle reached its NaphAcPO4 peak concentration within a few seconds, the EDC driven system required several minutes. As can also be seen from Table (entry 12), the activation yield in the case of EDC was slightly lower compared to acetic anhydride. This can be attributed to a slower forward reaction, which is likely due to the additional elemental step of acid activation that makes hydrolysis (more) competitive. The hydrolysis kinetics are almost superimposable in both cases, indicating the exceptional robustness of this reaction cycle. Specifically, we found that the organophosphate NaphPO4 was fully regenerated, and no signs of pyrophosphate -as a kinetically inert side product resulting from activation of phosphorus rather than carbon -were detected by HPLC or 31 P-NMR spectroscopy (Figure and S6). Regarding the issue of waste buildup, both the direct and indirect activation strategies, have advantages and disadvantages. On the one hand, the use of acetic anhydride is essentially free of side products, yet leads to a decrease in pH due to the release of acetic acid as a waste product. This buildup of acetic acid could potentially cause issues when performing a large number of cycles, unless it is neutralized with a base or by the presence of highly concentrated buffer systems. On the other hand, addition of EDC hydrochloride, does not alter the pH of the system significantly, but leads to N-acylurea byproducts and to 1-ethyl-3-(3-dimethylaminopropyl)urea (EDU) as a terminal waste product (acetic acid is recycled in this activation mode).