Kinetics of Double-Bond Isomerizations Among 1-Octene and cis and trans Linear Internal Octenes on Dry Amberlyst15 Catalyst: Adsorbed Alcohol Becomes an Active Site

The double-bond isomerization of 1-octene to an equilibrium distribution of all seven linear octene isomers on a dry Amberlyst15 catalyst was followed at 90°C using gas chromatography to resolve five of the seven isomers. The simplest kinetic models that fit observed data over several hours indicated that carbenium ions are likely intermediates in these isomerizations. The C2 octyl carbenium ion appeared to be more stable than the C3 and C4 octyl carbenium ions, leading to a lower equilibrium trans to cis ratio in 2-octene than in 3-octenes and 4-octenes. At equilibrium, [2-octyl carbenium ion] / [3-octyl carbenium ion] = 1.6. The octene adsorption coefficient for double-bond isomerization on this catalyst was 0.4–0.5, indicating a rather weak adsorption. However, the concurrent dimerization of octene to branched hexadecene isomers required an adsorption coefficient of ~40, indicating octene adsorbs onto two different types of sites on this catalyst. The primary alcohol 2-ethyl-1-hexanol was added to reaction mixtures to suppress octene dimerization, and the active isomerization site in this work was a molecule of 2-ethyl-1-hexanol adsorbed onto a supported sulfonic acid group of the initial resin. This new site was less active than the original acid site.