Previously reported synthetic procedures for synthesizing carmofur at room temperature required 159 stirring under nitrogen for 20 hours with yields that are often under 35%, and other procedures 160 that synthesize carmofur at 90°C are challenging to reproduce . To probe the thermal 161 reaction kinetics and the temperature dependence of isocyanate reaction rates, we plotted the 162 concentration of product formation over time with various temperatures. Table , Entries 19 and 25-29 summarizes the results of the temperatures screened. Although we initially conducted all of our kinetics in 60°C, it was later found that the optimal temperature range for synthesizing carmofur in pyridine is 40-50°C. While higher temperatures initially gave faster conversion to carmofur, we observed lower overall endpoint yields presumably due to thermal decomposition pathways that result in 5-FU being re-formed (Fig. ).