Variation in the chemistry of the TiO2-mediated degradation of hydroxy- and methoxybenzenes: electron transfer and HOads center dot initiated chemistry

The early degradation product distributions from TiO2-mediated photocatalyt ic degradations of a series of multiply hydroxylated benzenes and their met hoxylated analogs is reported. The methoxylated compounds show a distinct t rend away from ring-opening reactions that are attributed to electron trans fer chemistry towards hydroxylations and demethylations that are attributed to hydroxyl-type chemistry. The initial rates of the reactions suggest tha t this is not simply due to the availability of the extra carbon sites. It is instead hypothesized that the compounds with hydroxyl groups are bound t o the TiO2 in such a way as to facilitate electron transfer and its subsequ ent chemistry. Addition of isopropyl alcohol to the degradations slows the degradations of the methoxylated compounds more than it does the hydroxylat ed compounds and particularly inhibits the demethylation and hydroxylation reactions. It is suggested that the question of whether an organic substrat e must be bound to the photocatalyst at the time of excitation may be depen dent on the type of chemistry being observed. (C) 2001 Elsevier Science B.V . All rights reserved.