Photocatalytic degradation of 4-chlorophenol. 2. The 4-chlorocatechol pathway

The TiO2-mediated photocatalytic degradation of 4-chlorocatechol is studied as a branch of the degradation of 4-chlorophenol. In addition to some basi c kinetic studies, the identities of many of the cyclic and acyclic interme diates, verified in most cases with authentic samples, are reported. From 4 -chlorocatechol, the major product is hydroxylation to form 5-chloro-1,2,4- benzenetriol. A small amount of 4-chloropyrogallol is also produced. Substi tution to give 1,2,4-benzenetriol is observed as is oxidative cleavage of t he C1-C2 bond to give the diacid. The major products of all of the triols a re those of oxidative cleavages, occurring mainly between ortho hydroxy-sub stituted carbons to give diacids but also between one hydroxy and one unsub stituted carbon to give acid-aldehydes. Many smaller intermediates in the d egradations are identified, and pathways are proposed for the larger compou nds.