A clean process for the production of oxygenated limonene derivatives starting from orange oil

The production of several oxygenated derivatives of limonene was carried out by using orange oil and molecular oxygen as the sole initial reactants under solvent-free conditions. Palladium-copper supported on carbon and hydrotalcite-like compounds displayed good catalytic properties to accelerate autoxidation reactions of limonene yielding a mixture of the different oxygenated derivatives, mainly 1,2- and 8,9-epoxylimonene, 1,2,8,9-diepoxylimonene, carveol and carvone. Palladium supported on copper-magnesium-aluminium hydrotalcite displayed the best properties due to its higher catalytic activity and lifetime. The pelletized form of these catalysts can be easily recovered and reused. A reactor design combining recirculation and oxygen bubbling through a catalytic bed of the pelletized catalyst produced the highest reaction rate. Vacuum distillation of the final product mixture allowed easy separation of the 1,2/8,9-limonene epoxides. The other required compounds, mainly carveol and carvone, were not completely separated and remained together with the other oxygenated products, such as the di-epoxylimonene isomers. (c) 2007 Society of Chemical Industry.