Mechanism of isomerization of hydrocarbons on metals. Part 10.—Isomerization and dehydrocyclization of 2-methyl[2-13C]hexane on a 10 % Pt–Al2O3 catalyst

Abstract

The contact reactions of 2-methyl[2-¹³C]hexane and 2-methyl[6-¹³C]hexane have been investigated at 270 and 360°C, respectively, over a 10% Pt–Al₂O₃ catalyst. The isomerizations of 2-methylhexane and 2,3-dimethylpentane, at 270°C, are very similar: the orders as a function of hydrogen are positive (0.2–1.75) and all the products are obtained by a one-step process according to either a bond-shift or a cyclic mechanism (the latter being predominant). The positive order, together with the absence of scrambling, is consistent with Frennet's model, assuming hydrocarbon adsorption on several contiguous metal sites.

At 360°C, aromatization also takes place. 2-Methyl[6-¹³C]hexane yields hardly any methyllabelled toluene, showing that 1–6 and not 1–5 ring closure is the major mechanism of this reaction.