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 basic kinetic studies, the identities of many of the cyclic and acyclic intermediates, 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. Substitution to give 1,2,4-benzenetriol is observed as is oxidative cleavage of the C1-C2 bond to give the diacid. The major products of all of the triols are those of oxidative cleavages, occurring mainly between ortho hydroxy-substituted carbons to give diacids but also between one hydroxy and one unsubstituted carbon to give acidaldehydes. Many smaller intermediates in the degradations are identified, and pathways are proposed for the larger compounds.