The isomerization of 3,3-dimethylbut-1-ene, 3-methylcyclopent-1-ene, and methylenecyclopentane over γ-alumina

Abstract Skeletal isomerization of 3,3-dimethylbut-1-ene (33DMB1) and double-bond migration of 3-methylcyclopent-1-ene (3MCP = ) and methylenecyclopentane (MCP) have been studied over γ-alumina. The activity for the isomerization of all three alkenes increases with increasing catalyst activation temperature. Addition of fluoride to the catalyst greatly increases its activity. Treatment of the γ-Al 2 O 3 catalysts with H 2 S results in some enhancement of activity for 33DMB1 and MCP isomerization but reduces activity for 3MCP = isomerization by ~90%. The importance of initial water content of the alumina on subsequent activity is discussed. It is concluded that skeletal isomerization of 33DMB1 and double-bond migration in MCP occur via carbonium ion intermediates on Bronsted acid centers whereas double-bond migration in 3MCP = occurs predominantly via π-allylic intermediates on Lewis acid sites.