Reactions of phenylium ions with gaseous hydrocarbons. 1. methane,ethane, and propane

The reaction of free tritiated phenylium ion, generated from nuclear decay of [l,4-T₂]-benzene in the presence of simple gaseous hydrocarbons RH (R = CH₃, C₂H₅, C₃H₇; partial pressure: 10-100 torr), yields predominantly the corresponding tritiated C₆H₅R products. The effects of gaseous nucleophilic acceptors (NuH = NH₃, CH₃OH) on the reaction with CH₄, were also investigated. Phenylium ion confirms its exceedingly high reactivity even toward pure σ- -type substrates, as well as its considerable site selectivity, demonstrated by the distinct preference for the C-H bonds of the substrate. The stability features of the ionic intermediates from addition of phenylium ion with RH have been evaluated, as well as their fragmentation and isomerization mechanisms. The behaviour of phenylium ion toward simple aliphatic hydrocarbons in the gas phase (10-100 torr) is discussed and compared with previous mechanistic hypotheses from ICR mass spectrometric studies, carried out at much lower pressures (10^-5 torr).