Carbenium ions generated upon adsorption of 4-methoxystyrenes onto acid zeolites.: A kinetic study

Adsorption of vinylanisole and trans-(4-methoxyphenyl)-1-propene into HY, HB and HZSM-5 allows us to detect the corresponding substituted 1,3-bis(4-methoxyphenyl)-1-propylium (2), 1-(4-methoxyphenyl)-6-methoxy-1-indanylium (5) and 1,3-bis(4-methoxyphenyl)-2-propen-1-ylium (8) cations as reactive intermediates. The kinetics can be followed by conventional spectrophotometers. Cation 2 appears as the shorter lived species, decaying in hours for the HY sample and within days when embedded in HZSM-5 zeolite. Cyclic indanyl cation 5 shows a lifetime much longer than 2. A growth of 8 concomitantly with the decay of 2 has been also observed. This has been taken as a proof of a hydride transfer from neutral 1,3-bis(4-methoxyphenyl)-1-propenes (the corresponding acyclic dimers observed as products) as donors to cations 2 as accepters leading to 8. (C) 1998 Elsevier Science Ltd. All rights reserved.