Double bond migration of 1-butene without protonated intermediate on D-ZSM-5

A novel reaction of the double bond migration (DBM) of 1-butene was found on Brønsted 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 H/D isotope exchange reaction of the OD groups of zeolites forming 1:1 complex with 1-butene was absent during DBM. This indicates that the protonation from BAS to the adsorbate is not essential to the conversion of the 1-butene to the hydrogen-bonded cis- and trans-2-butenes on the BAS of ZSM-5. If the widely-accepted carbocation or alkoxy intermediate is assumed, the acidic OD groups should be converted to OH groups upon the DBM of 1-butene to 2-butene. The H/D isotope exchange reaction of OD groups due to the proton transfer occurred at higher temperature than the DBM. By comparison with other zeolites, this new type of reaction was found to be catalyzed by strong BAS, which takes place more rapidly than the proton transfer from BAS.