Zeolites selective photo-oxidation

A new concept of selective photo-oxidation in zeolite cages has been recently proposed [47], The hydrocarbon radical cation-Oz charge-transfer pair is generated inside the cavities of alkali zeolites, in which the large electrostatic field stabilizes the highly polar charge transfer states of hydrocarbon-Oz collisi-onal pair and allows to control the pathways of further transformation. 

Shimizu K,Akahane H,KodamaT and Kitayama Y (2004), Selective photo-oxidation of benzene over transition metal-exchanged BEA zeolite , Appl Catal A Gen, 269,75-80. 

These intrazeolite singlet oxygen ene reactions have synthetic potential because the cis effect observed in solution is suppressed in the zeolite [13]. Consequently, allylic hydroperoxides which are inaccessible by other routes may be available via this new technology. For example, photo-oxidations of aryl-substituted alkenes, 7, in sensitizer-doped NaY react to generate the allylic hydroperoxides as the major or exclusive product [17]. In contrast, in solution, the hydroperoxides are formed in only 5-20% yields, with 2-1-2 and 4-1-2 adducts dominating the reaction mixtures. In the case of 2-methyl-5-phenyl-2-hexene, 8, the regio-selectivity for 8b and 8c improved from 47% to 94% and the diastereoselectivity from 10% to 44% as the reaction is moved from solution into the zeolite [18] ... 

Since all of the CdS clusters reside in the sodalite cages of the zeolite Y framework, the larger supercages of the structure are still available for absorption of substrate molecules - in this case olefins for photo- oxidation via electron transfer. Colloidal CdS in free solution has been used for such oxidations previously(19) and in a competitive oxidation of styrene and 1,1-diphenylethylene we find that unconfined bulk CdS will effect oxidation in a ratio of 1 2 for these two olefins (irradiation at 365nm). In the zeolite confined system we find however that the ratio becomes 1 1 ie a slight shift in selectivity toward the smaller substrate as may be expected on the basis of size/diffusion effects. From the viewpoint of the enzyme mimic, we have here a system... 

The photodegradation of hexabromocyclododecane in aqueous solution has been obtained by Fe -oxalate and Fe -citrate complexes, in the presence of H2O2 and simulated sunlight. " Fe-g-C3N4 (Fe-CN) and titanium silicate zeolite (TS-1) hybrid materials have been produced from dicyandiamide, metal chloride as precursors and TS-1 as a support. The material has been applied as heterogeneous catalyst for the photo-catalytic selective oxidation of benzene to phenol, in the presence of H2O2 as benign oxidant under ambient conditions. Noticeably, the hybrid... 

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