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

The heterogeneously catalyzed alkoxylation of limonene and alpha-pinene with C-1-C-5 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 (C-1-C-5 alcohols) are compared in relation to their activity for the heterogeneously catalyzed alkoxylation of limonene and alpha-pinene.