EVIDENCE FOR BRANCHING OF LONG-CHAIN N-ALKANES VIA PROTONATED CYCLOALKANES LARGER THAN CYCLOPROPANE

The formation of monobranched isomers from n-alkanes over bifunctional faujasite-type catalysts is explained by proposing the occurrence of alkylcarbenium ions as reaction intermediates and by using the general rules of alkylcarbenium ion chemistry. Methyl branching of n-alkanes occurs mainly via substituted corner-protonated cyclopropane intermediates. Protonated cycloalkanes with larger rings must be invoked in order to explain the primary nature of isomers with side chains larger than methyl groups and to rationalize the observed methyl-, ethyl-, propyl-, and butyl-branching selectivities. © 1990.