Alkoxylation of limonene and alpha-pinene over beta zeolite as heterogeneous catalyst Original Research Article

The heterogeneously catalyzed alkoxylation of limonene and alpha-pinene with C1–C5 alcohols to 1-methyl-4-[alpha-alkoxy-isopropyl]-1-cyclohexene in the presence of beta zeolite in liquid phase has been studied in both a discontinuous batch reactor and a continuous flow-type apparatus with a fixed bed reactor. In both reactor types, methanol and limonene as feedstock react to 1-methyl-4-[alpha-methoxy-isopropyl]-1-cyclohexene with a yield of about 85%. Thus, the beta zeolite seems to be more active and selective for methoxylation of limonene than other catalysts described in the literature for this reaction type. For the methoxylation of alpha-pinene, however, the highest yield of the corresponding alpha-terpinyl methyl ether is only up to 50% in both reactor types, as several bicyclic and double addition products are formed in parallel. The selectivity for all addition products together can reach values of about 85%. The other zeolites and solid acids applied for the methoxylation of alpha-pinene reveal considerably lower conversion and selectivity. We discuss the dependencies of conversion, selectivity and product distribution on temperature, WHSV, TOS, pressure and the starting material ratio. The possibility for a regeneration of beta zeolite with air or oxygen is shown as well. Different linear and branched alcohols (C1–C5 alcohols) are compared in relation to their activity for the heterogeneously catalyzed alkoxylation of limonene and alpha-pinene.