Deuterium Exchange Reactions with Substituted Aromatics. III. Heterocyclics and Polycyclic Hydrocarbons

Abstract

Platinum-catalysed deuterium exchange reactions between heavy-water and polycyclic aromatics and heterocyclics have been investigated. The results confirm a charge-transfer-no-bond adsorption mechanism for catalytic chemisorption. Degree of catalyst poisoning increases with decreasing ionization potential for aromatic molecules of similar complexity, e.g., anthracene and phenanthrene. As the number of nodal planes in the bonding orbitals of the more complex polycyclic aromatics increases, a decrease is observed in catalyst poisoning. Exchange of pyridine is slower than benzene and this is attributed to an additional interaction of the pyridine molecule with the catalyst through its lone-pair of electrons. The reactivity of n-octane supports extension of the authors' π-complex chemisorption theory to molecules possessing only σ-electrons. Anisole, cyclohexane, nitrobenzene, cyclohexene, and phenyl cyanide exchange in an anomalous manner.