DOUBLE-BOND MIGRATION OF 1-BUTENE WITHOUT PROTONATED INTERMEDIATE ON D-ZSM-5

A novel reaction of the double bond migration (DBM) of l-butene was fo und on Bronsted acid sites (BAS) of H(D)-ZSM-5 below 230 K, which does not involve either carbocation or alkoxy intermediate. The activation energy was obtained as 49 +/- 4 kJ mol(-1) on D-ZSM-5. The KID isotop e exchange reaction of the OD groups of zeolites forming 1:1 complex w ith I-butene was absent during DBM. [GRAPHICS] This indicates that the protonation from BAS to the adsorbate is not essential to the convers ion of the l-butene to the hydrogen-bonded cis- and trans-2-butenes on the BAS of ZSM-5. If the widely-accepted carbocation or alkoxy interm ediate is assumed, the acidic OD groups should be converted to OH grou ps upon the DBM of I-butene to 2-butene. The H/D isotope exchange reac tion of OD groups due to the proton transfer occurred at higher temper ature than the DBM. By comparison with other zeolites, this new type o f reaction was found to be catalyzed by strong BAS, which takes place more rapidly than the proton transfer from BAS. (C) 1998 Elsevier Scie nce B.V. All rights reserved.