Mechanistic Studies on the Photooxidation of Chlorpromazine in Water and Ethanol

It has been established that chlorpromazine undergoes photooxidation via its cation radical, yielding chlorpromazine 5-sulfoxide as an ultimate photoproduct. Molecular oxygen has been found indispensable not only for the formation of chlorpromazine cation radical but also for the formation of the sulfoxide from the radical. Oxygen atom in the sulfoxide originates from the atmospheric oxygen and not from water, which was ascertained by both tracer experiment and kinetic analysis. It was concluded that phenazathionium ion is not involved in the reaction. The possibility of singlet oxygen participation in the photooxidation was also ruled out. An intermediate, which is formed from the cation radical, was found as a precursor of the sulfoxide and was tentatively assigned as a peroxyl type radical.