Reaction control photochemical reactions with zeolite

Shape selectivity and orbital confinement effects are direct results of the physical dimensions of the available space in microscopic vessels and are independent of the chemical composition of nano-vessels. However, the chemical composition in many cases cannot be ignored because in contrast to traditional solution chemistry where reactions occur primarily in a dynamic solvent cage, the majority of reactions in nano-vessels occur in close proximity to a rigid surface of the container (vessel) and can be influenced by the chemical and physical properties of the vessel walls. Consequently, we begin this review with a brief examination of both the shape (structure) and chemical compositions of a unique set of nano-vessels, the zeolites, and then we will move on to examine how the outcome of photochemical reactions can be influenced and controlled in these nanospace environments. 

These natural minerals are alkali aluminum silicates and have been used as molecular sieves and cation exchangers. Recently they have been used to control some organic photochemical reactions, du Pont chemists1 have prepared lithiated zeolites by treatment of sodium aluminum silicates such as zeolite 13X with LiNO,. These silicates, designated Li-X and Li-Y, can effect rearrangement of a-alkyl-deoxybenzoins top-alkylbenzophenones in nearly quantitative yield. Thus photolysis... 

Oxidation of Aliphatic Compounds. - A general review of the use of supra-molecular systems as microreactors for photochemical reactions contains a section dealing with the photosensitized oxidation of alkenes included in zeolites, nation membranes and vesicles. Particular consideration is given to the possibility of controlling the form and environment of the sensitizer and substrate so that the reaction selectively follows an energy-transfer or an ET pathway. The same authors have also provided a more substantial review on the same theme. Recent developments in relation to the stereochemistry and mechanism of the ene photooxygenation of alkenes by O2 have also been reviewed. ... 

Alternative approaches that have been explored for control of photochemical reactions include irradiation in liquid crystals [7], micelles [8], inclusion complexes [9], and zeolites [10]. In addition, photochemistry of monolayers [11] and on surfaces [12] (e.g., alumina, silica, clays, and semiconductors) has received considerable attention. Each of these methods has potential for regiocontrol and/or stereocontrol of certain photochemical processes. However, reactions between different groups (e.g., intermolecular photocycloadditions) are difficult to modulate with most of these approaches. 

Vitamin D Analogues - A patent covering the photochemical conversion of the diene (112) into the triene (113) within what is called a microreactor has been published. The microreactor system is a zeolite with the appropriate size of the cavity to provide stereochemical control of the reaction. The use of the 2,7-dimethyl-3,6-diazacyclohepta-1,6-diene tetrafluoroborate/biphenyl filter solution has allowed the double wavelength irradiation (290-300 nm and X. > 330 nm) of procalcitriol as a route to la,25-dihydroxycholecalciferol. A study of the control that can be exercised upon the reaction by changes in temperature was carried out. The results of a study of the influence of intensity on the picosecond laser irradiation of provitamin D have been published. Other research has been aimed at the examination of the photochemical behaviour of previtamin 03. ... 

Other Fission Processes. - The photochemically induced fission reactions of a series of naphthylmethyl alkanoates have been described. Some factors that control the ease of bond cleavage within the esters were identified. Irradiation of (200) in a NaY zeolite using 308 nm light results in C-O bond fission and the formation of an acetyl radical. Irradiation of perfluoroacetyl fluoride at 254 nm in the gas phase brings about fission of CO-F bond with the formation of fluorine atoms and perfluoroacetyl radicals. ... 

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

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