Mechanism of photolytic formation of trityl ions from triphenylmethane on acidic solids

Abstract

The mechanism of the photo-generation of Ph₃C⁺ ions from Ph₃CH on the surfaces of acidic solids is deduced from observations on the chemisorption of Ph₃CH, Ph₃COH, and related compounds on anhydrous magnesium perchlorate and zirconium phosphate. Protonation of one of the phenyl groups of Ph₃CH is followed by light absorption and elimination of the tertiary proton from the carbonium ion in the excited state. The net result is an endothermic isomerization to diphenylmethylenecyclohexadiene which rapidly yields the Ph₃C⁺ ion by loss of a hydride ion, especially in the presence of O₂, at acidic sites.