Exchange of alkanes with deuterium over γ-alumina. A Brønsted linear free energy relationship

Abstract

The exchange behaviour of a series of alkanes, including cycloalkanes, with deuterium over γ-alumina has been investigated. Different types of hydrogen atoms within the same molecule are found to exchange at different rates and in some cases a quantitative estimate of the relative activities has been made. These results and a comparison of reaction rates of different molecules indicate that the reaction intermediates are carbanionic in character. A linear relation between hydrogen exchange activity and hydrocarbon acidity has been obtained and is shown to be an example of the Brønsted catalysis law.

All the exchange reactions took place in a stepwise manner and, for the cycloalkanes, exchange could be followed at lower temperatures without complication from isomerization and addition.