The kinetics of H/D exchange in cyclopentane

摘要

The exchange of hydrogen for deuterium (H/D exchange)in cyclopentane (cp) is a promising test reaction for studying support effects in heterogeneously metal-catalyzed reactions,such as differences in stability and activity in,e.g., benzene or tetralin hydrogenation reactions.In order to employ this test reaction,a full understanding of the H/D exchange mechanism is essential.Howevery,chear insight in the observed kinetics and selectivities is alcking in tghe literature.In this paper,a kinetic model that adequately describes the observed activtiy and orders in CP and D_2 is developed.It is shown that the selectivity is eetermined in a series of reactions after the rate-determining steP.To understand the observed selectivities a monte Carlo model is developed which accurately simulates the observed exchange patterns adn reveals the relative contributions of four competitive intermediates.One intermediate (a pi-bonded eta-cyclopentene)can rotate in a nonactivated mechanism via an allylic intermediate.The model reveals the number of rotations each intermediate experiences and can be as high as~20,even if only 5 Datoms are observed in the product.This number of rotations is a better measure of the H/D exchange than teh conventional "multiplicity." The H/D exchange of CP together with these insights can be applied to investigate in detail the influence of the support on the catalytic properties of supported metal particles.