Bicyclanes III. The acid‐catalysed isomerization of perhydronaphthalene and perhydroindane

Abstract

KONINKLIJKE/SHELL-LABORATORIUM, AMSTERDAMThe formation of the bicyclo[3.3.0]octane ring system by isomerization of perhydronaphthalene and perhydroindane has been studied. Experiments were performed in the liquid phase under the influence of aluminium halides and in the gas phase at 300-500" in the presence of a silica-alumina catalyst. In both types of reaction a great number of compounds were formed.From the liquid-phase reaction product of perhydronaphthalene a hydrocarbon carrying two methyl groups per molecule could be separated by prep arative GLC; its structure could not be determined.In the liquid as well as in the gas-phase experiments with perhydroindane the five isomeric methyl-cis-bicyclo[3.3.O]octanes were formed besides a large number of unidentified degradation products.Experiments with the individual isomers revealed that under the conditions of the gas-phase reactions their stabilities differ considerably; l-methyl-cisbicyclo[3.3.0]octane is the most stable, the endo-2-methyl derivative the least stable isomer. IntroductionIn continuation of our investigation into the chemistry of bicyclanes 1. z, we wished to pay attention to hydrocarbons containing the bicyclo[3.3.0]-octane ring system. Unfortunately, the conventional syntheses of these compounds are usually complicated and, therefore, not suitable for the preparation of adequate amounts. More attractive routes for the formation of some of the methyl derivatives would seem to be the acid-catalysed isomerizations of perhydronaphthalene and perhydroindane, which reactions have occasionally been mentioned in the literature. Apart from the possible preparative value of these reactions a careful study might contribute to our understanding of hydrocarbon isomerizations proceeding by way of carbonium ions.