Dehydrocyclization Reaction of n-Heptenes over a Chromium Oxide Catalyst Supported on Alumina

Abstract

The dehydrocyclization reaction of n-heptenes over a chromium oxide catalyst supported on alumina has been studied in the temperature range of 400-450C in a flow reactor to elucidate the mechanism of the dehydrocyclization. A small amount of n-heptadienes, which was yet much more than that of toluene was detected in the reaction at lower conversion of n-heptenes. Migration of the double bond in n-heptenes proceeded so rapidly in comparison with dehydrocyclizationreaction, that the equilibrium compostion of n-heptenes was attained before several per cent of n-heptenes were converted to toluene. No difference was observedin the initial rate of formation of toluene either from 1-heptene or 3-heptene. Results of the pulse reaction showed that the rate of fermation of toluene decreased in the order: methylcyclohexenes n-heptadiene n-heptenes n-heptane. The mechanism by way of n-heptadienes is preferred to the Twigg-type mechanism consisting of direct cyclization of n-heptenes.