Direct photooxidation and xanthene-sensitized oxidation of naphthols: quantum yields and mechanism

Oelgemöeller, Michael, Mattay, Jochen, and Görner, Helmut (2011) Direct photooxidation and xanthene-sensitized oxidation of naphthols: quantum yields and mechanism. Journal of Physical Chemistry: Part A, 115 (3). 6. pp. 280-285.

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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 (O(2)(-)), 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 O(2)(-), the latter of which is formed by scavenging of the xanthene radical anion by oxygen, does also contribute.

Item ID: 16784
Item Type: Article (Research - C1)
ISSN: 1520-5215
Date Deposited: 15 Jun 2011 07:04
FoR Codes: 03 CHEMICAL SCIENCES > 0305 Organic Chemistry > 030505 Physical Organic Chemistry @ 50%
03 CHEMICAL SCIENCES > 0306 Physical Chemistry (incl Structural) > 030606 Structural Chemistry and Spectroscopy @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 100%
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