title: Solvent-Free Photooxidation of Alkanes by Dioxygen with 2,3-Dichloro-5,6-dicyano-p-benzoquinone via Photoinduced Electron Transfer.
abstract: Photooxidation of alkanes by dioxygen occurred under visible light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) which acts as a super photooxidant. Solvent-free hydroxylation of cyclohexane and alkanes is initiated by electron transfer from alkanes to the singlet and triplet excited states of DDQ to afford the corresponding radical cations and DDQ(⋅-) , as revealed by femtosecond laser-induced transient absorption measurements. Alkane radical cations readily deprotonate to produce alkyl radicals, which react with dioxygen to afford alkylperoxyl radicals. Alkylperoxyl radicals abstract hydrogen atoms from alkanes to yield alkyl hydroperoxides, accompanied by regeneration of alkyl radicals to constitute the radical chain reactions, so called autoxidation. The radical chain is terminated in the bimolecular reactions of alkylperoxyl radicals to yield the corresponding alcohols and ketones. DDQ(⋅-) , produced by the photoinduced electron transfer from alkanes to the excited state of DDQ, disproportionates with protons to yield DDQH2 .
authors.affiliation: Division of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka, 565-0871, Japan. ookubo@chem.eng.osaka-u.ac.jp.|Department of Material and Life Science, Graduate School of Engineering, Osaka University and SENTAN Japan Science and Technology Agency (JST), Suita, Osaka, 565-0871, Japan. ookubo@chem.eng.osaka-u.ac.jp.|Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 120-750, Korea. ookubo@chem.eng.osaka-u.ac.jp.
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University and SENTAN Japan Science and Technology Agency (JST), Suita, Osaka, 565-0871, Japan.
authors.forename: Kensaku
authors.initials: K
authors.lastname: Hirose
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 120-750, Korea. fukuzumi@chem.eng.osaka-u.ac.jp.|Faculty of Science and Technology, Meijo University, SENTAN Japan Science and Technology Agency (JST), Nagoya, Aichi, 468-8502, Japan. fukuzumi@chem.eng.osaka-u.ac.jp.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
keywords: electron transfer; oxygenation; photoredox catalysis; quinone; radical