The mechanism of double-bond isomerization of olefins on solid acids

1-Hexene Double Bond Isomerization Reaction Over SO 4 = Promoted NiO, Al2O3 and ZrO2 Acid Catalysts

“…trans)-3-hexene formation [13,15,17,18]; or if all hexene isomers appear at the same time, the isomerization follows, instead, a p-allylic intermediate formation [19,20]. A higher acidic strength facilitates hydrogen transfer but also favors paraffin and aromatic formation.…”

“…With acid catalysts, DBI reaction of a-olefins may proceed as a consecutive-parallel reaction starting with a proton addition from the substrate to the terminal doublebond with the formation of carbenium ion followed by proton elimination [13,15,17,18], or with the formation of a p-allylic intermediate when all isomers appear at the start of the reaction [19,20].…”

Using kinetics to study intermediates in acid catalyzed reactions on solids

“…In the event, it is not; the actual isomer mixture is catalyst specific. This seems to rule out an effect due to the electronic nature of the precursor carbocation [68,71]. Rather, it indicates some kind of configurational constraint at the location of the active site [72].…”

“…On acid catalysts, initial eis/trans ratios were observed to be above the equilibrium value for Si/A1 [67] Si/Mg [68] and other solid catlysts [691. Questions such as ~Is the cis/trans ratio the same for various molecules on the same catalyst?"…”

“…Figure 1 shows the selectivity plot for cis-and trans-2-hexene formation from 1-hexene on HY zeolite catalyst at 200°C [3]. There is no doubt that both isomers are primary products of the 1-2 double bond shift [68,70]. The initial selectivities measured from the slopes are 0.4!5 for cis ~-ud 0.500 for trans.…”