Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 21, Issue 7, Pages 2855-2861Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201404810
Keywords
electron transfer; organocatalysis; oxidation; photochemistry; redox chemistry
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Funding
- Ministry of Education, Culture, Sports, Science and Technology (MEXT) [26620154, 26288037]
- ALCA project from JST, Japan
- Grants-in-Aid for Scientific Research [26288037, 26620154] Funding Source: KAKEN
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Photoinduced hydroxylation of neat deaerated benzene to phenol occurred under visible-light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), which acts as a super photooxidant in the presence of water. Photocatalytic solvent-free hydroxylation of benzene derivatives with electron-withdrawing substituents such as benzonitrile, nitrobenzene, and trifluoromethylbenzene used as neat solvents has been achieved for the first time by using DDQ as a super photooxidant to yield the corresponding phenol derivatives and 2,3-dichloro-5,6-dicyanohydroquinone (DDQH(2)) in the presence of water under deaerated conditions. In the presence of dioxygen and tert-butyl nitrite, the photocatalytic hydroxylation of neat benzene occurred with DDQ as a photocatalyst to produce phenol. The photocatalytic reactions are initiated by oxidation of benzene derivatives with the singlet and triplet excited states of DDQ to form the corresponding radical cations, which associate with benzene derivatives to produce the dimer radical cations, which were detected by the femto-and nanosecond laser flash photolysis measurements to clarify the photocatalytic reaction mechanisms. Radical cations of benzene derivatives react with water to yield the OH-adduct radicals. On the other hand, DDQ(center dot-) produced by the photoinduced electron transfer from benzene derivatives reacts with the OH-adduct radicals to yield the corresponding phenol derivatives and DDQH(2). DDQ is recovered by the reaction of DDQH(2) with tert-butyl nitrite when DDQ acts as a photocatalyst for the hydroxylation of benzene derivatives by dioxygen.
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