Stavroulakis M. “Electron transfer-induced dehydrogenation reactions within methyl viologen-supported zeolite Na-Y under non-irradiative conditions” Tetrahedron Lett

Abstract-Methyl viologen-supported zeolite Na-Y is a unique and very efficient medium for carrying out electron transferinduced reactions in the absence of an irradiation source (spontaneously). Several monoterpenes loaded within the supported zeolite are dehydrogenated to p-cymene. The reaction occurs even in the open air with formation of minor amounts of ascaridole depending on the substrate. It is proposed that the radical cations of the monoterpenes are formed by single electron transfer to Na-Y, with methyl viologen acting as a promoter. © 2001 Elsevier Science Ltd. All rights reserved. Radical ion pairs are orders of magnitude longer-lived within the pores and the channels of zeolites 1 than in solution, where rapid back electron transfer takes place. Therefore, the confined interior of zeolites should be an ideal medium to carry out electron transfer reactions of organic compounds. However, this aspect of intrazeolite chemistry, especially for zeolite Na-Y, has attracted little attention. We sought to test the efficiency of this system to carry out intrazeolite photoinduced electron transfer reactions. To our great surprise, MV 2+ -supported zeolite Na-Y is a unique and versatile system for performing electron transfer reactions in the absence of a light source (spontaneously). By adding a hexane solution of each of the monoterpenes 1-5 shown in In a representative example, 5 mg of limonene (3, 99% pure) dissolved in 5 mL of dry hexane was added to 0.5 g of MV 2+ /Na-Y. After 30 min of stirring under argon either in the dark, or under ambient light, 5 ml of moistened THF was added and the slurry was stirred for 2 h and then filtered. Analysis by GC or by GC/MS revealed that limonene was completely consumed; the products were 60% p-cymene 6, 15% terpinolene 4, 10% g-terpinene 2, 10% a-terpinene 1, and approximately 2-4% of alcohols with the molecular formula C 10 H 18 O