One pathway to suppressing N-acylurea formation is to ensure the O-acylurea is as short-lived as possible. The Oacylurea lifetime can be decreased by increasing the precursor concentration or adding additives like pyridine. We first studied the effect of concentration precursor on forming N-acylurea by fueling the reaction cycle with 50 mM EDC with varying concentrations of C3 (50, 100, 200, and 300 mM). To follow the kinetics of the reaction cycle, we used a benzylamine quenching method developed by our group to measure the concentration of the product and EDC by converting the anhydride to a stable benzylamide and EDC to a guanidine, respectively. We also used a kinetic model to fit the experimental data of species involved in the reaction cycle every minute by solving a set of ordinary differential equations (see SI). The rate constants were determined by the model, and we could calculate the efficiency of the cycle, i.e., the percentage of fuel used to form the transient intermolecular anhydride. We found that, with increasing C3 concentration, the EDC was consumed faster (Table , Figure ), yielding a higher maximum anhydride concentration (3 mM to 14 mM) which was present for a shorter period (Figure ). Most importantly, the Nacylurea showed only a moderate decrease from 20 mM to 15 mM, respectively (Figure ). Since the anhydride is a transient product whose activation (formation) and deactivation (hydrolysis) occur simultaneously, the fraction of fuel successfully used to make the anhydride cannot be directly calculated by measuring the anhydride concentration. However, we used the kinetic model to calculate this fraction-by integrating the anhydride hydrolysis. Increasing C3 concentration from 50 mM to 300 mM increased the effective yield from 55% to 66%, while the N-acylurea yield decreased from 43% to 30% (Figure ). From these effective yields, we can define a term we call the selectivity (S), i.e., how much fuel is used for anhydride production relative to N-acylurea production. (Equation ). S scales from +100% to -100%, where -100% implies only N-acylurea is formed and +100% implies only anhydride is formed. We are aiming for an S of 100%. S is slightly different from simply comparing the yields, as S is independent of the O-acylurea hydrolyzed. Thus, it is not a measure of the cycle's efficiency but rather a description of the selectivity of anhydride over N-acylurea.