Oxidative Dehydrogenation of Butane and Cyclohexane

There are fewer studies of oxidative dehydrogenation of butane, and even fewer for cyclohexane than ethane or propane. The performance of the better catalysts in these two reactions are summarized in Table VII and Fig. 5. Because of the larger number of secondary carbon atoms in these molecules, they are more reactive with gaseous oxygen than the smaller alkanes. In ex- 

Calculated Conversions and Product Distributions in the Postcatalytic Void Volume for Various Assumed Species Desorbed from V-Mg Oxide during Propane Oxidation at 570°C (from Ref. 32) 

Summary Data of Oxidative Deydrogenation of Butane and Cyclohexane 

In addition to the corresponding alkenes, dehydrogenation of butane and cyclohexane could result in butadiene and benzene, which are very stable conjugated unsaturated hydrocarbons. Therefore, it should be possible to attain high yields of butadiene or benzene. Indeed, the data in Table VII show that these products represent substantial fractions of the dehydrogenation products in most cases. 

The first step of the activation of butane and cyclohexane has been assumed to be the cleavage of a secondary C—H bond, with minor contributions from primary C — H bonds in the case of butane. This picture is supported only by indirect evidence. When the relative rates of reaction of various alkanes were compared on a V-Mg oxide and Mg2V207 catalyst (Table VIII), it was found that alkanes with only primary carbons (ethane) reacted most slowly. Those with secondary carbons (propane, butane, and cyclohexane) reacted faster, with the rate being faster for those with more secondary carbon atoms. Finally, the alkane with one tertiary carbon (2-methylpropane) reacted faster than the ones with either a single or no secondary carbon (26). From these data, it was estimated that the relative rates of reaction of a primary, secondary, and tertiary C—H bond in alkanes on the V-Mg oxide catalyst were 1, 6, and 32, respectively (26). 

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