A study of bipyridyl radical cations. Part II. The reaction of morphamquat {bis-N-[(2,6-dimethylmorpholin-4-yl)carbonylmethyl]-4,4′-bipyridylium} radical cation with oxygen in methanol
Abstract
The equilibrium, 2MQ+˙⇌(MQ+˙)2 between monomeric morphamquat radical cation, MQ+˙, and diamagnetic dimer molecules, (MQ+˙)2, has been examined by u.v. spectroscopy over the temperature range +81 to –88°, yielding ΔG°–13.4 kJ mol–1, ΔH°–55.3 kJ mol–1, and ΔS°–141 J K–1 mol–1, which confirm data from our e.s.r. study. The reaction of the morphamquat radical cation with oxygen has been followed by the stopped-flow technique over a range of temperature from +40 to –80°. At +40° the reaction is second-order in monomer and first-order in oxygen with a velocity constant of 1.6 × 10812 mol–2 s–1, whereas at –80° it is first-order in dimer and first-order in oxygen with a velocity constant of 84 l mol–1 s–1. The mechanism of these reactions is discussed.