Hydrolysis of Limonene Epoxide over Hierarchical Zeolites

Selective synthesis of limonene 1,2-diol from limonene epoxide was performed over hierarchical zeolites synthesized by a top-down strategy. Acid treatment of commercial zeolite (CBV-500) induced formation of mesopores, increased Si/Al ratio and stronger Brönsted acid sites with a low penalty on microporosity and crystallinity. The highest selectivity (78%) was obtained over USYAl0.1 zeolite that presented the highest content of Brönsted acid sites among the tested materials. Furthermore, residual water of the solvent promoted the synthesis of limonene 1,2-diol. Solvent-free conditions favored isomerization rather than hydrolysis of limonene epoxide. USYAl0.1 can be used up to 5 times for limonene epoxide isomerization. The addition of water to the reaction together with zeolite structure increases selectivity to the desired limonene-1,2-diol from limonene epoxide (up to 93%). Limonene 1,2-diol synthesis is thermodynamically feasible and it is favored with several non-polar solvents. Furthermore, DFT calculations suggested that limonene epoxide is adsorbed onto trans -configuration and that the trans- diaxal diol is formed by an attack of water in anti -position with respect to the location of the epoxide. Graphical Abstract