Singlet oxygen photochemical generation

Using a single-channel chip micro reactor, singlet oxygen is generated by photochemical means in presence of catalytic amounts of Rose Bengal [21]. By [4 -i- 2] cycloaddition of this oxygen species to a-terpinene, the product ascaridole is obtained. 

Schmidt R (2006) Photosensitized generation of singlet oxygen. Photochem Photobiol 82 1161-1177... 

SCAIANO, J.C., R.W. Redmond, B. Mehta, and J.T. Arnason Efficiency of the Photoprocesses Leading to Singlet Oxygen ( Ag) Generation by a-Terthienyl Optical Absorption, Optoacoustic Calorimetry and Infrared Luminescence Studies. Photochem. Photobiol. 54, 655 (1990). 

Milller-Breitkreutz, K., Mohr, H., Briviba, K., and Sies, H., Inactivation of viruses by chemically and photochemically generated singlet oxygen,/. Photochem. Photohiol B Biol, 30, 63,1995. 

Photochemical irradiation of dimethyl and diethyl sulphoxides yields the corresponding sulphone in the presence of air and a photosensitizer such as methylene blue in yields up to 99% . Sulphoxides are also oxidized when they act as traps for persulphoxides, the intermediate formed on reaction of a sulphide with photochemically generated singlet oxygen - , equation (9). Isotope studies have shown that such reactions proceed through a linear sulphurane intermediate . Persulphones also react with sulphoxides in a similar manner , equation (10). 

Delmelle, M. (1978). Generation of singlet oxygen by the retina. Photochem. Pathobiol. 27, 731-734. 

Nevertheless, in the sensor study of heterogeneous reactions of singlet oxygen, it is better to employ selective sources that do not generate other active particles and produce though low, but stable concentrations of 02( ). These sources can be photochemical and chemical... 

Bicyclopropylidene (1) readily reacted with photochemically generated singlet oxygen at 30-35°C to give spiro[2.3lhexan-4-one (203) and 7-oxadi-spiro [2.0.2.1]heptane (202) [104,1411. Bicyclopropylidene epoxide 202 can also be prepared by epoxidation of 1 with m-chloroperbenzoic acid in the presence of Na2C03 [141] or with KHSOs/acetone [74]. Bicyclopropylidene (1) was found to quench the fluorescence of 9,10-dicyanoanthracene [81]. 

A photooxidative reaction in which molecular oxygen is incorporated into the reaction products(s). Three mechanisms appear to be common for such processes (a) reaction of triplet O2 with free radicals that have been generated photochemically (b) reaction of photochemically produced singlet oxygen with a molecular species and (c) the production of superoxide anion which then acts as the reactive species. See also Photooxidation... 

Evidence for adiabatic photolytic cycloreversions at room temperature has been obtained more frequently in recent years [121,122], The adiabatic generation of singlet oxygen by photochemical cycloreversion of the anthracene and 9,10-dimethylanthracene endoperoxides 105 and 106 proceeds with wavelength-dependent quantum yields of 0.22 and 0.35, respectively, and involves the second excited singlet state of the endoperoxides [123]. Photodissociation of the 1,4-endoperoxide from l,4-dimethyl-9,10-diphenylanthracene was found to yield both fragments, i.e., molecular oxygen and l,4-dimethyl-9,10-diphenylanthracene, in their electronically excited state [124]. 

As illustrated in Scheme 3.26, the role of the Pd(II) porphyrin complex is the photochemically sensitized generation of singlet oxygen Oj), which forms the allylic hydroperoxide 14. Subsequent Fe3+ porphyrin-catalyzed hydrogen abstraction from 14 yields the peroxy radical 16, while the catalytic Fe3+ species is recycled by homolytic 0—0 bond cleavage of 14 to give the alkoxy radical 17. Both radicals 16 and 17 are involved in the dark reaction where the remaining cyclohexene is consumed. 

Photochemically generated singlet oxygen adds selectively to C(20)-C(22) pseu-dodiosgenin diacetate (82) to give via (83) diosone (85), an important intermediate... 

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