Direct Photooxidation and Xanthene-Sensitized Oxidation of Naphthols: Quantum Yields and Mechanism
- 17 December 2010
- journal article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry A
- Vol. 115 (3), 280-285
- https://doi.org/10.1021/jp108832x
Abstract
The photoinduced oxidation of 1-naphthol to 1,4-naphthoquinone and of 5-hydroxy-1-naphthol to 5-hydroxy-1,4-naphthoquinone was studied by steady-state and time-resolved techniques. The direct photooxidation of naphthols in methanol or water takes place by reaction of the naphoxyl radical (•ONaph) with the superoxide ion radical (O2•−), the latter of which results from the reaction of the solvated electron with oxygen after photoionization. The sensitized oxidation takes place by energy transfer from the xanthene triplet state to oxygen. From the two oxygen atoms, which are consumed, one is incorporated into the naphthol molecule giving naphthoquinone and the second gives rise to water. The effects of eosin, erythrosin, and rose bengal in aqueous solution, pH, and the oxygen and naphthol concentrations were studied. The quantum yield of the photosensitized transformation was determined, which increases with the naphthol concentration and is largest at pH > 10. The quantum yield of oxygen uptake is similar. The pathway involving singlet molecular oxygen is suggested to operate for the three sensitizers. The alternative pathway via electron transfer from the naphthol to the xanthene triplet state and subsequent reaction of •ONaph with O2•−, the latter of which is formed by scavenging of the xanthene radical anion by oxygen, does also contribute.Keywords
This publication has 65 references indexed in Scilit:
- Syntheses and Photophysical Behavior of Porphyrin Isomer Sn(IV) ComplexesInorganic Chemistry, 2009
- Visible-light-mediated photodegradation of 17β-estradiol: Kinetics, mechanism and photoproductsJournal of Photochemistry and Photobiology A: Chemistry, 2009
- Comparative study of the UV and UV/VUV-induced photolysis of phenol in aqueous solutionJournal of Photochemistry and Photobiology A: Chemistry, 2007
- Photoreactions in clay media: singlet oxygen oxidation of electron-rich substrates mediated by clay-bound dyesJournal of Photochemistry and Photobiology A: Chemistry, 2002
- Mechanism of oxidation of phenol and 2,6-dimethylphenol in the presence of Cr(phen)33+ excited state: the role of O2Journal of Photochemistry and Photobiology A: Chemistry, 2001
- Monosubstituted naphthalenes as quenchers and generators of singlet molecular oxygenJournal of Photochemistry and Photobiology A: Chemistry, 1999
- Solvent effects on rates of photochemical reactions of rose bengal triplet state studied by nanosecond laser photolysisJournal of Photochemistry and Photobiology A: Chemistry, 1999
- Polymeric photosensitizers 2. Photosensitized oxidation of phenol in aqueous solutionJournal of Photochemistry and Photobiology A: Chemistry, 1998
- Sensitized photooxidation of 2,3- and 2,7-dihydroxynaphthalenes in alkaline waterJournal of Photochemistry and Photobiology A: Chemistry, 1998
- Photo-oxidation of phenol and monochlorophenols in oxygen-saturated aqueous solutions by different photosensitizersJournal of Photochemistry and Photobiology A: Chemistry, 1997