AN EXAMPLE OF THE VALORIZATION OF TERPENES - THE SELECTIVE ISOMERIZATION OF 3-CARENE TO 2-CARENE IN THE PRESENCE OF SILICA-SUPPORTED NICKEL-CATALYSTS MODIFIED BY TETRABUTYL TIN

The cyclic olefin, 3-carene, undergoes an isomerization of the carbon- carbon double bond to produce 2-carene, a precursor in the synthesis o f(-)-menthol. This isomerization is observed over silica supported nic kel, but the selectivity is reduced by side reactions producing trimet hylheptenes by hydrogenative ring opening of the cyclopropyl ring. Sel ectivity for C=C bond isomerization is dramatically increased by surfa ce modification of the nickel metal catalyst by reaction with tetra-n- butyl tin, The most selective of these silica supported nickel/tin cat alysts produces 2-carene with 91% selectivity at 48% conversion.