Photoreactions of organic compounds adsorbed on zeolites.

摘要

As this new area of Photochemistry in Zeolites has been investigated, the catalytic activity of these materials has been found. The internal spaces of zeolites can have effects on organic photochemical reactions. {dollar}gamma{dollar}-Irradiation of zeolites enhances the low temperature catalytic activity of alkylaromatic compounds through their Bronsted acid sites. The irradiated solids have long-lived excited states with lifetimes as long as years at room temperature. The reactions on the zeolites occur in the channels or cavities of those solids. The mechanism of these reactions involves the dealkylation of benzenium ion to a chemisorbed carbonium ion followed by transalkylation or isomerization. The intermolecular transalkylation reactions are prevented because their transition states would be too large to be accommodated in the cavities of zeolites. The reactivity is a function of the number of acid sites in the zeolite and increases as the degree of substitution of the alkyl group increases. The channel size of the zeolites controls the ratio of the product isomers. It was found that {dollar}gamma{dollar}-irradiated H-mordenite treated with methylene chloride methylated iso-propylbenzene. When iso-propylbenzene containing iso-propylbenzenehydroperoxide was the reactant the yields of non-oxygenated products were enhanced while oxygenated products were also formed.; The photolysis at 300 nm of trans-stilbene adsorbed on zeolites has also been studied. Isomerization to cis-stilbene, cycloaddition to dihydrophenanthrene followed by oxidation to phenanthrene, and dimerization, all occur. The cis-trans photoisomerization reaction of trans-stilbene on the zeolite is not favorable, because the sizes of the zeolite cavities and channels make the smaller trans-stilbene more stable than cis-stilbene. However, zeolites can catalyze the cycloaddition of cis-stilbene to dihydrophenanthrene which is subsequently oxidized to phenanthrene.