Carbodiimide-driven anhydride formation from carboxylic acids is useful in a variety of non-equilibrium systems. While there are multiple strategies to control deactivation (anhydride hydrolysis) rates, control over activation (anhydride formation) rates is limited. We show that pyridine derivatives reversibly form adducts with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide methiodide in water. These adducts are unreactive with carboxylic acids and thus reduce the anhydride formation rate while prolonging carbodiimide lifetime. This reaction network expansion provides control over the non-equilibrium chemistry of the system by analogy with biology. This control is achieved in part with more-nucleophilic pyridines, which give higher adduct concentrations and longer anhydride lifetimes.The best results are obtained with 4-methoxypyridine, which more than doubles the time to the anhydride’s maximum concentration and lengthens its lifetime by roughly 20%, compared to EDC controls. This strategy can be used to control the formation of transient polymer network hydrogels, increasing the time to reach peak modulus by 230% and the lifetime by 45%.
Author(s): William S. Salvia, Georgia Mantel, Nirob K. Saha, Chamoni W. H. Rajawasam
Advisor(s): Dominik Konkolewicz, C. Scott Hartley, Department of Chemistry and Biochemistry
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