Cross-Dehydrocycloaddition of 1,3-Butadien with Isoprene over MgO and ZrO2

Article abstract of DOI:10.1246/bcsj.64.1332

A mixture comprising of equal amounts of 1,3-butadiene (BD) and isoprene(IPN) was allowed to react over MgO and ZrO2 at 473 K in order to examine the relation between the product distribution and the reaction mechanisms.Over ZrO2 the most abundant product was 4-ethyltoluene, which was produced by a base-catalyzed Diels-Alder reaction between BD and IPN, followed by double-bond migration and dehydrogenation.In the Diels-Alder reaction, IPN acts as a diene and BD acts as a dienophile.Over MgO, o-xylene was primarily produced by anionic mechanisms.Among the products formed from BD and IPN, 4-ethyltoluene was produced most, though the production of 3-ethyltoluene was considerable.The active sites on ZrO2 were strongly poisoned by both CO2 and NH3.The active sites on MgO were completely poisoned by CO2, and were modified by NH3 in such a way that the reaction mechanisms changed from the anionic mechanisms to those involving Diels-Alder reaction.