Photooxidation of Phenol, Cresols, and Dihydroxybenzenes^1,2

Evaluation of conceptual models of natural organic matter (humus) from a consideration of the chemical and biochemical processes of humification

“…Richard and Grabner (1999) state that hydroquinone is particularly relevant environmentally because it absorbs radiation in the ultraviolet portion of the solar spectrum, and it has long-lived triplet states that are efficiently populated. Joschek and Miller (1966) found that irradiation of hydroquinone both in the presence and absence of oxygen in water produced similar products. Oxidation and hydroxylation products were formed along with a C-C dimer, 2,2',6,6'-tetrahydroxybiphenyl.…”

“…Much less is known about the structures of thearubigins. Haslam (1998) has pointed out that the benzotropolone ring arises from oxidative condensation of the otho-dihydroxy- Joschek and Miller (1966) (Scheme I) and Richard and Grabner (1999) (Scheme II).…”

“…Proposed mechanisms for photolysis of hydroquinone according to Joschek and Miller (1966) (Scheme I) and Richard and Grabner (1999) (Scheme II). ...... 18 Figure 11.…”

Kinetic studies of hydroxyquinone formation from water soluble benzoquinones

“…The concentrations of the stock solutions in our experiments were typically 1×10 -3 mol dm -3 . 1,4-Benzoquinones are photosensitive compounds in solution, 7,8,[31][32][33][34][35][36][37] therefore fresh solutions were prepared for all experiments in brown glass volumetric flask.…”

“…The effect of substituents on the hydroxyquinone formation and the quinone reduction is not well understood. 7 The direct formation of hydroxyquinone in the photochemical process is unlikely because the triplet excited states of benzoquinones are strong oxidizing agents. 8,9 Thus, it is more likely that this triplet quinone oxidizes another quinone molecule to hydroxyquinone.…”