Deuterium Exchange Reactions with Substituted Aromatics. II. The Monohalogenated Benzenes and Naphthalenes

Abstract

The platinum-catalysed exchange between heavy water and the monohalogenated benzenes and naphthalenes has been studied at 130-180 °C. Rate of exchange is found to decrease with increasing size of halogen substituent. Naphthalene derivatives exchange more slowly than the corresponding members of the benzene series. Rate of exchange increases with increasing ionization potential. From this correlation it is postulated that chemisorption of aromatic molecules on active platinum occurs through π-complex formation. In the benzene series, exchange in the ortho-position is slower than in the meta- or para-positions which react at approximately the same speed. ortho-Exchange increases with increasing size of halogen substituent. This deuteration technique is applicable to tritium labelling especially for aromatics since radiochemical by-product formation is minimized.