Thermal transformation of monoterpenes within thionin‐supported zeolite Na‐Y. Acid‐catalyzed or electron transfer‐induced?

Several monoterpenes (monocyclic, bicyclic or acyclic) isomerize and finally transform to p‐cymene in the dark upon loading within thionin‐supported zeolite Na‐Y. The same reactions occur in Na‐Y dried under the same conditions as thionin/Na‐Y. It is postulated that the thermal treatment of Na‐Y generates ‘electron holes’ (probably acidic sites). The transformation of monoterpenes occurs more likely via an electron transfer‐induced reaction subordinated to the occurrence of the acidic sites. The radical cation of the more thermodynamically stable monoterpene, α‐terpinene, eventually dehydrogenates to p‐cymene. For comparison, the same reactions were performed within methyl viologen‐supported Na‐Y.