Liquid Phase Isomerization of C6C8 Alkenes on Heteropolyoxometalates

The isomerization of 1-hexene, 1-heptene and 1-octene has been observed in the liquid phase between 303 and 343 K on the solid ammonium salts of 12-tungstophosphoric (H3PW12O40), 12-molybdophosphoric (H3PMo12O40) and 12-tungstosilicic (H4SiW12O40) acid and their parent acids. Double bond and cis— trans isomerizations of the olefins are strongly catalyzed by H3PW12O40, (NH4)3PW12O40 and H4SiW12O40 and weakly by H3PMo12O40, (NH4)4SiW12O40 and (NH4)3PMo12O40 at near ambient temperatures. No skeleton isomerization of any of the olefins was observed at temperatures up to 343 K. Variations of the product distributions with reaction time and the dependence of selectivity on the conversion are reported. The isomerization is tentatively attributed to the formation of carbocations and 1,2-hydride shifts.