Arylation of dialkyl ethers by gaseous phenylium ions. Formation and behaviour of dialkylphenyloxonium ions in the gas phase

Abstract

Tritiated phenylium ions, obtained in the gas phase from the spontaneous decay of 1,4-ditritiobenzene, have been allowed to react with dialkyl ethers (MeOPrⁿ, MeOPrⁱ, and PrⁱOPrⁿ) in the pressure range 20–400 Torr and in the presence of a thermal radical scavenger (O₂, 4 Torr). The effects of a gaseous base (NH₃, 4 Torr) on the reaction carried out at the highest pressure were also investigated. Singlet phenylium ion confirms its distinct affinity toward the n-centre of the substrate (ca. 80% for MeOPr), although significant insertion into the alkyl groups of PrⁱOPrⁿ is observed as well. The stability and reactivity features of the formed dialkylphenyloxonium ions, under the experimental conditions chosen, have been studied as well as their fragmentation and isomerization mechanisms. The behaviour of dialkylphenyloxonium ions in the gas state (20–400 Torr) is consistent with previous mechanistic hypotheses from mass spectrometric studies, carried out at much lower pressures (below 1 Torr).