Oxygenation and chlorination of aromatic hydrocarbons with hydrochloric acid photosensitized by 9-mesityl-10-methylacridinium under visible light irradiation

Kei Ohkubo, Kentaro Mizushima, Shunichi Fukuzumi

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37 Scopus citations

Abstract

Efficient photocatalytic oxygenation of toluene occurs under visible light irradiation of 9-mesityl-10-methylacridinium (Acr+-Mes) in oxygen-saturated acetonitrile containing toluene and aqueous hydrochloric acid with a xenon lamp for 15 h. The oxygenated products, benzoic acid (70 %) and benzaldehyde (30 %), were formed after the photoirradiation. The photocatalytic reaction is initiated by intramolecular photoinduced electron transfer from the mesitylene moiety to the singlet excited state of the Acr+ moiety of Acr+-Mes, which affords the electron-transfer state, Acr -Mes•+. The Mes•+ moiety can oxidize chloride ion (Cl-) by electron transfer to produce chlorine radical (Cl), whereas the Acr moiety can reduce O2 to O 2 •-. The Cl radical produced abstracts a hydrogen from toluene to afford benzyl radical in competition with the bimolecular radical coupling of Cl . The benzyl radical reacts with O2 rapidly to afford the peroxyl radical, leading to the oxygenated product, benzaldehyde. Benzaldehyde is readily further photooxygenated to yield benzoic acid with Acr-Mes•+. In the case of an aromatic compound with electron-donating substituents, 1,3,5-trimethoxybenzene, photocatalytic chlorination occurred efficiently under the same photoirradiation conditions to yield a monochloro-substituted compound, 2,4,6-trimethoxychlorobenzene.

Original languageEnglish
Pages (from-to)205-220
Number of pages16
JournalResearch on Chemical Intermediates
Volume39
Issue number1
DOIs
StatePublished - Jan 2013

Bibliographical note

Funding Information:
Acknowledgments This work was supported by a Grant-in-Aid (Nos. 20108010 and 23750014), a Global COE program from the Ministry of Education, Culture, Sports, Science and Technology, Japan and KOSEF/MEST through WCU project (R31-2008-000-10010-0), Korea.

Keywords

  • Chlorination
  • Electron transfer
  • Oxygenation
  • Photocatalysis
  • Radical cation

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