Reductive amination of levulinic acid to different pyrrolidones on Ir/SiO2-SO3H: Elucidation of reaction mechanism

- Ir/SiO2-SO3H showed a high yield to pyrrolidone (88% at 24 h).
- Sulfonic groups on SiO2 improved the yield to pyrrolidones and avoided side reactions.
- Reductive amination occurs between LA and amine towards an intermediate amine that is then cycled.
- Theoretical and experimental findings are in a good agreement with the mechanism proposed.
- The substituents amines alter the contribution HOMO − LUMO and consequently modifying the yields obtained.

Levulinic acid (LA) transformation to different pyrrolidones via reductive amination was studied using an Ir/SiO2-SO3H catalyst in liquid phase. The effects of solvent, amine concentration, H2 partial pressure, catalyst mass, and reuse were studied. The spent catalysts were evaluated by DRIFTS to obtain evidence of the interaction of levulinic acid with aniline on the catalyst surface. The sulfonic groups on SiO2 improved the yield to pyrrolidones and avoided side reactions. A reaction mechanism is proposed where the reductive amination occurs between LA and amine towards an intermediate amine that is then cycled. The Gibbs free energy for the reaction mechanism was evaluated. Besides, the HOMO and LUMO of the amine reactants and intermediates using density functional theory (DFT) with the B3LYP-D3 method were theoretically determined to understand the rate-limiting and the cyclization steps.

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