This study explores the isomerization of limonene-1,2-epoxide (LE) from kinetic and mechanistic viewpoints, using a dendritic ZSM-5 zeolite (d-ZSM-5) as a highly selective catalyst for the formation of dihydrocarvone (DHC) in the form of diastereoisomers (cis + trans). Ethyl acetate, a green solvent, was used at mild reaction temperatures (50–––70 °C). DHC, which can also be extracted from caraway oil, is widely used as an intermediate for epoxylactone production and as a constituent in flavors and perfumes. Kinetic modeling of LE isomerization was performed using a reaction network with eight parallel reactions and the corresponding rate equations, derived from the assumption of the rate-limiting surface reactions. The large standard errors in the statistical results of some kinetic parameters of the initial data fitting suggested that three of those reactions can be neglected to describe the kinetic model more accurately. This refinement resulted in standard errors in the kinetic parameters lower than ca. 11 %, confirming the statistical reliability of the modified kinetic model. Activation energies of 41.1 and 162 kJ/mol were estimated for the formation of cis-DHC and trans-DHC, respectively. Density Functional Theory (DFT) calculations revealed the preferred pathway for both cis and trans-LE conversion to DHC and carveol. The rate-determining step, carbocation formation (ΔEact = 234 kJ/mol), precedes near-instantaneous dihydrocarvone formation under the studied conditions.

Acknowledgements Luis A. Gallego-Villada is grateful to Universidad de Antioquia for their support during his research internship through the project 2022-53000 as part of the “Convocatoria Programática 2021-2022: Ingeniería y Tecnología” program, as well as the “Beca Doctoral Universidad de Antioquia” scholarship. D.P.S., M.A-D., and J.C. are gratefully acknowledged to the European Research Council Horizon 2020 research and innovation program TODENZE project (ERC101021502). Julián E. Sánchez-Velandia is grateful to Universidad Jaume I for the postdoctoral position during 2022-2023 (programa Propi UJI) and the project (PID2020-11962RBC33),MCIN/AEI/10.13039/501100011033/European Union NextGeneration EU/PRTP.