ZEOLITES AS CATALYSTS IN ORGANIC-REACTIONS - CONDENSATION OF ALDEHYDES WITH BENZENE-DERIVATIVES

Reactions of four aldehydes with five aromatic compounds have been carried out on a series of USY zeolites with unit cell size in the 24.56 to 24.25-t1 range. Conversion decreased in the order formaldehyde > benzaldehyde > acetaldehyde > propionaldehyde and also in the series anisole > toluene > benzene > chlorobenzene. For aliphatic aldehydes a mixture of ortho-ortho', ortho-para', and para-para' diarylmethanes was obtained. USY zeolites show a higherpara-directing selectivity than AICl3. Benzaldehyde reacted with benzene derivatives to afford mixtures of diaryland triarylmethanes. Formation of ditolyl- and dianisylmethanes in the corresponding reactions indicated that bulky triarylmethanes, once formed inside the crystalline framework, have strong diffusional limitations to get out of the zeolite cavities and can undergo subsequent protolytic cleavage. A decrease in the activity of the zeolite to catalyze hydride transfer reactions lead to a decrease on the diphenylmethane yield. Finally, diphenylmethane appears as a primary product indicating that a series of consecutive reactions such as the formation of diarylcarbinols followed by protonation, water elimination, and hydride abstraction are taking place inside the pores of the zeolite before the real primary product comes out from the zeolite. © 1991.