Formation of Ethylcyclopentadiene and the Reaction Mechanism in Vapor-Phase Reaction of Cyclopentadiene with Ethylene over Silicon Carbide

Abstract

apor-phase reaction of cyclopentadiene with ethylene over silicon carbide has been investi-gated at atmospheric pressure in relation with the reaction mechanism. The reaction was always accompanied with a formation of carbonaceous deposit over silicon carbide, and at 300 400-C, only 2-norbornene was formed whereas selective formation of an equimolar mixture of 1- and 2-ethylcyclopentadiene was observed above 500-C. When 0.10 atm of cyclopentadieneand 0.40 atm of ethylene were feeded at a contact time of 93. 3 g-SiC*r/g-mol at 570°, the yield and the selectivity of ethylcyclopentadiene were 5.4% and 48.3%, respectively. These results suggest that ethylcyclopentadiene was produced by the isomerization of 2-norbornene or by the hydrogen transfer of biradical compound, which were formed by the addition of ethylene to cyclopentadiene. On the other hand, exchange of deuterium atoms for hydrogen atoms of cyclopentadiene molecule was observed in the reaction of cyclopentadiene with deuterium gas over the carbonaceaus deposit at 570-C.The carbonaceous material was thus found to partici-pate in the hydrogen transfer. The rate constants for addition of various unsaturated hydro-carbons to cyclopentadiene were kinetically determined, and the order of the constant was ethylene<acetylene<butadiene. On the basis of this result, mechanism of the addition of these unsaturated hydrocarbOns to cyclopentadiene was discussed.