Photosensitized Oxidation of Alkenes Adsorbed on Pentasil Zeolites

Abstract

Photosensitized oxidation of trans,, trans-stilbene (TS), and 2,3-dihydro-γ-pyran (DHP) included in the internal framework of Na-ZSM-5 zeolites was investigated. The zeolite samples having adsorbed the alkenes were suspended in isooctane or pentaerythritol trimethyl ether (PTE), and the sensitizers, 9,10-dicyanoanthracene (DCA) and hypocrellin A (HA), were dissolved in the solution. The molecular sizes of both of the sensitizers and the solvents are greater compared with the channels of the zeolites. The isolation of the alkenes within the zeolites from the sensitizers in surrounding solution prevents them from undergoing electron transfer. On the other hand, singlet oxygen was produced in the solution and diffused into the internal framework of the zeolites to react with the alkenes. Thus, only singlet oxygen oxidation products were obtained and no product derived from superoxide radical anion was detected. By addition of water after the alkene adsorption, the photosensitized oxidation product distributions can be dramatically varied depending upon the aluminum content of the zeolite framework and the molecular dimensions of the substrates. Possible interpretations of these effects are discussed in terms of the locations of the reactants.

Photodebromination of dibromobutane: Possibility and evidence

“…Unfortunately, due to the incompatibility of the instrumental response (> 5 ns) with the lifetime of Py * (s < 4 ns), the results were not fruitful. Nevertheless, a 2 h photolysis with DEA (10 mM) and Py-Coð5-NH 2 -phenÞ 2þ 3 (1 mM) could degrade 2,3-DBB (1 mM in DMSO) to some extent, evidenced by the appearance of the characteristic absorption peak of alkene near 1630 cm À1 in the solutions photolyzed (Fig. 5).…”

“…Inspired by the unique electron transfer processes in photosynthesis [1], many synthetic analogues have been designed, in which novel molecules capable of performing light-induced charge separation were synthesized and showed promise in many prospects, including solar energy conversion [2], heterogeneous catalysis [3], optical chemical analysis [4], photovoltaics [5] and reexposurable photographics [6]. Impressive as they are, there has been less research aimed at the photodegradation of organic pollutants, like organic dibromides.…”

Photoisomerization and Photooxygenation of 1,4-Diaryl-1,3-dienes in a Confined Space

“…40 DPBs believed to be included as cisoid conformers within the narrow channels of ZSM-5 zeolites reacted with singlet oxygen more efficiently than in solution. 31 The current study is devoted to understanding the singlet excited-state behavior of DPB and DTB included within a well-defined organic capsule made up of two molecules of OA. The goals of the current undertaking included finding answers to the following questions: (a) Are there any preferences between the isomers (trans,trans; cis,trans; and cis,cis; see Figure 1 for structures) for the OA Figure 1) included within OA capsule was investigated and compared with that in hexane solvent.…”

Selective Formation of Allylic HydroperoxidesviaSinglet OxygeneneReaction

“…151 triggered interest to examine the dye-sensitized photooxygenation of organic compounds within the confined environment of the faujasite Y cavities. The study of singlet oxygen reactions with alkenes using alternative supramolecular systems as microreactors 152 , such as pentasil zeolites 153 , nafion membranes 154 and surfactant vesicles 155 , has attracted considerable attention recently, but will not be examined in the present chapter.…”