Pulse radiolysis study of chlorpromazine and promazine free radicals in aqueous solution

Abstract

·OH radicals may react with chlorpromazine in four different ways, viz.(i) electron transfer to produce the cation radical, (ii) addition to the sulphur atom followed by acid-catalysed OH^– elimination to yield the cation radical, (iii) addition to the aromatic rings to produce cyclohexadienyl type radicals, and (iv) abstraction of hydrogen atoms from the —CH₂— which is in the α position to the ring nitrogen. Electron transfer and addition to the sulphur atom each account for 40% of the ·OH radicals. Similar considerations apply to promazine.

The hydrated electron may attach itself to either the sulphur atom in promazine or its aromatic system with equal probability. Addition to the sulphur atom probably leads to immediate cleavage of the carbon–sulphur bond whereas addition to the aromatic system probably produces an anion radical. The lifetime of this anion radical is sufficiently long to enable electron transfer between itself and another promazine molecule to occur to produce the promazine cation radical.

With chlorpromazine, the hydrated electron probably reacts solely with the aromatic system to eliminate chloride ions by the end of the reaction. The promazine radical which is produced simultaneously may add on to another chlorpromazine molecule to produce a cyclohexadienyl type radical.