Synthesis of trans-stilbene through the hydrogenation of diphenylacetylene

Trans-stilbene (trans-ST) was produced through the hydrogenation of diphenylacetylene (DPA). Pd-based intermetallic compounds (IMCs) supported on silica were applied to the selective hydrogenation of DPA into cis- and trans-ST. Pd3Bi/SiO2 showed the highest selectivity to stilbenes without accelerating the deep hydrogenation into diphenylethane (DPE), after DPA was completely converted. Proton-type zeolites were examined for the isomerization of cis-ST, the main product in the hydrogenation of DPA, into trans-ST. H-USY zeolite partially exchanged with Na+ ions gave the highest activity owing to the appropriate acid strength and enough space inside the pores for cis-ST to enter. The mixture of Pd3Bi/SiO2 and H-USY gave trans-ST yield of 74 mol% through the one-pot reaction of DPA. The isomerization rate was significantly retarded by coexisting DPA and DPE molecules.