KINETIC-STUDIES ON ANTHRALIN PHOTOOXIDATION

Abstract— The photooxidation of the antipsoriatic drug anthralin (1,8‐dihydroxy‐9‐anthrone) has been studied by several kinetic techniques, including direct observation of 1O2 (1Δg) luminescence at 1.27 μm. The rate of deactivation of 1O2 increases at higher pH, demonstrating that the trihydroxy‐anthracene anion is the reactive species. Direct determination of the rate constant of 1O2 deactivation (kR+kQ) in deuterated buffer systems by luminescence quenching gave a value of 3.0 times 108M−1−1 for the anion; the neutral anthrone is unreactive. The rate constant for the neutral anthrone in benzene‐d6 is 2.8 times 104 M−1 s−1 Competition experiments with tetramethylethylene in acetonitrile gave a rate constant for reaction alone (kR) of 2.1 times 108 M−1 s−1 for the anion. Copyright © 1990, Wiley Blackwell. All rights reserved