In terms of the mechanism of action, we studied how additives modify the kinetic constants of the reaction cycle. According to our hypothesis, reactions involving Oacylurea as a reagent will be significantly modified. In the case of pyridine, anhydride formation (k2) and O-acylurea hydrolysis (k3) were one order of magnitude faster compared to the without or other additives (Table , Figure ). All additives favor anhydride hydrolysis (k4), while pyridine accelerated hydrolysis most, 12-fold faster than without pyridine, thereby shortening the anhydride half-life from 9 minutes to 46 seconds. Moreover, the decreased half-life also decreased the maximum anhydride formed to 2.5 mM (Table , Figure ). Although all additives reduced the half-life of the anhydride, 1,2,4-triazole showed the least catalytic activity and did not significantly decrease the maximum anhydride concentration (Table , Figure ). These differences in catalytic activity can be explained by their nucleophilicities in water at pH 6. Even though DMAP has a greater nucleophilicity than pyridine, its nucleophilicity is decreased because it is protonated at pH 6. DMAP has a higher pKa (9.7) 39 in water than 1,2,4triazole (pKa = 2.4) and pyridine (pKa = 5.23) . Therefore, at pH 6, 1,2,4-triazole and pyridine are not pronated, but 1,2,4-triazole showed the least catalytical ability, because azoles are less nucleophilic than pyridines. 42 As we established that pyridine is the most successful additive, we tested the effect of its concentration by fueling 100 mM C3 with 50 mM EDC with various amounts of pyridine on the selectivity. With increasing pyridine concentration from 0 to 35 mM, the reaction cycle became faster with accelerated rate constants of all reactions. Especially, EDC consumption was faster (Table , Figure ), and anhydride was present for as short as 50 minutes (Figure ). Between a pyridine concentration of 0 and 35 mM, the maximum anhydride decreased from 6.5 mM to 1.6 mM (Figure ) due to the accelerated hydrolysis. However, it remained roughly constant above 10 mM pyridine. Similarly, the amount of EDC used to form the unwanted N-acylurea significantly decreased from 39 % to 1 % but only marginally decreased beyond 10 mM pyridine (Figure and S4). Therefore, pyridine concentrations greater than 10 mM result in similar values in the consumption of EDC to produce both anhydride and N-acylurea (Figure , Table ). These optimized conditions greatly improve over the original conditions-the catalyst can now undergo over 450 activation-deactivation cycles before its concentration falls below 1%.