ChemInform Abstract: FORMATION OF THE TRITYL CATION IN PULSE IRRADIATED SOLUTIONS OF TRIPHENYLMETHYL CHLORIDE IN CYCLOHEXANE. EVIDENCE FOR AN INTERMEDIATE RADICAL CATION

Abstract

The absorption spectrum observed on nanosecond pulse irradiation of triphenylmethyl chloride, ϕ3 CCl, solutions in cyclohexane results from the formation of three intermediates: the triphenyl-methyl radical (absorption maximum 340 nm), the trityl cation (absorption maximum between 400 and 450 nm) and a second positive ion species (absorption maximum 360 nm). The free radical, formed by electron attachment to ϕ3 CCl with a rate constant of 3.7 × 1012 dm3 mol–1 s–1, undergoes a reversible reaction with O2 for which the forward and backward rate constants are 1.2 × 109 dm3 mol–1 s–1 and 1.0 × 107 s–1, respectively at 20°C. In a 10–3 mol dm–3 solution the trityl cation grows in over several hundred ns while over the same timescale the absorption at 360 nm decays. The rate constant for reaction of the cyclohexane radical cation with ϕ3 CCl is 2.5 × 1011 dm3 mol–1 s–1. The initial product of this reaction, which is considered to be responsible for the 360 nm absorption, is thought to be the radical cation ϕ3 CCl+, which is converted to the trityl cation by further reaction with ϕ3 CCl with a rate constant of 5 ± 2 × 109 dm3 mol–1 s–1. The trityl cation transfers its charge to TMPD with a rate constant of 8.7 × 109 dm3 mol–1 s–1.