Photocatalytic oxygenation

Fig. 17.4 Photocatalytic oxygen (O) and Fe(II) ( ) production by photocatalytic reaction. Ti02 powder (JCR-TIO-5, 13 mg) suspended in an aqueous solution (5.0 ml) of 5.6 mM Fe(III) chloride was irradiated using a 500 W high pressure Hg lamp. Light of wavelength shorter than 340 nm was removed using a cut-off glass filter. Before photoirradiation started, the solution was bubbled with argon.

Although the absolute amount of the photocurrents is governed by various factors such as the oxidation potentials of olefins and the extent of adsorption of olefins on the electrode, the above findings show that the reactive olefins in the photocatalytic oxygenation exhibit photocurrents and the olefins which do not exhibit photocurrents are unreactive in the photocatalytic oxygenation. On the other hand, the olefins which exhibit photocurrents are not always reactive. For example, stilbene shows a higher photocurrent than DPE, but is not so reactive as DPE. The electron transfer to the excited semiconductor takes place more efficiently from stilbene than from DPE due to the lower oxidation potential of the former, but in the subsequent free radical reactions, stilbene is less reactive than DPE (33). 

Therefore, it can be concluded that for the photocatalytic oxygenation to occur, the electron transfer from the olefin to the positive hole has to take place, but the overall reactivity of the olefins is governed by the efficiency of free radical processes as exemplified in Table II. 

Though the investigation of photocatalytic oxygenations performed of the laboratory scale are often motivated by attempts to understand and mimic the catalytic cycle of cytochrome P450 (a natural catalyst of monooxygenation reactions), the results obtained [159, 253, 266] could be applied to industrial processes as well. 

An interesting but under explored method for the formation of 1,2-dioxetanes employing the photocatalytic oxygenation of olefins with dioxygen via selective radical coupling using 9-mesityl-10-methylacridinium ion as an electron-transfer photocatalysis has also appeared (Equation 6) <2004JA15999>. 

Scheme 13.3 Photocatalytic oxygenation of anthracene with Oz using Acr+-Mes [61].

Scheme 13.5 Photocatalytic oxygenation of tetraphenylethylene (TPE) with 02 using Acr+-Mes [63],...

Ohkubo, K., Nanjo, T. and Fukuzumi, S. (2005) Efficient photocatalytic oxygenation of aromatic alkene to... 

Kotani, H., Ohkubo, K. and Fukuzumi, S. (2004) Photocatalytic oxygenation of anthracenes and olefins with dioxygen via selective radical coupling using 9-mesityl-10-mefhylacridinium ion as an effective electron-transfer photocatalyst. Journal of the American Chemical Society, 126 (49), 15999-16006. 

Ohmori, T., H. Takahashi, H. Mametsuka and E. Suzuki (2000). Photocatalytic oxygen evolution on 0 -I,e2O films using Fe3+ ion as a sacrificial oxidizing agent. Physical Chemistry Chemical... 

Photocatalytic Oxygenation of Hydrocarbons on T OJ ron-Porphyrin Hybrid Catalysts. 

For natural waters and hydrometeors, reaction (5.81) is the key formation process of hydrated electrons. However, little is known about the rate of formation of superoxides in natural aqueous solution. It is clear that different photosensitizers (and mixtures of them) provide a large variety of photocatalytic oxygen activation. The formation of hydrated electrons can explain many processes such as autoxidation and corrosion. This looks at first confusing because Q q works as a reducing species but the key oxidizing species in solution is the OH radical (a strong electron acceptor similar to the atmospheric gas phase), which is produced in a chain of electron transfer processes ... 

Table 213. Photocatalytic oxygenation of ethylbenzene by decatungstate both in homogeneous and heterogeneous conditions with (RfN)4Wio032 Hyflon membrane.

Photocatalytic CO2 reduction by a ternary Zn-Cu-Ga LDH has been combined with WO3 photocatalytic oxygen generation [45]. The two processes have been coupled electrically, allowing the transfer of electrons from water oxidation to Zn-Cu-Ga LDH photocatalytic CO2 reduction, while protons diffuse through a polymer electrolyte (Scheme 1.16). The overall process taking place separately in two compartments forms methanol and water from CO2 and O2. 

Del Pilar-Albaladejo J, Dutta PK (2014) Topotactic transformation of zeolite supported cobalt (II) hydroxide to oxide and comparison of photocatalytic oxygen evoluti[Pg.148]

Fukuzumi S, Kishi T, Kotani H, Lee Y-M, Nam W (2011) Highly efficient photocatalytic oxygenation reactions using water as an oxygen source. Nat Chem 3(1) 38-41... 

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