methyl-ptoluenesulfonate), DIC = N,N-diisopropylcarbodiimide). After 24 hours, we measured the amount of catalyst that had disappeared by analytical HPLC. We assume here that the formation of the N-acylurea is the only pathway by which the precursor is irreversibly converted. Put differently, the concentration N-acylurea is equal to the concentration precursor lost. CMC formed the largest amount of unwanted N-acylurea (53%, as expressed in the amount of fuel used to make N-acylurea), and EDC ranked second with a value of 33% (Figure ). DIC showed the least formation of N-acylurea (17%). Because of DIC's poor water solubility, we focused the rest of this study on EDC.