Hydrogenation of Alkylcyclobutanes and Related Molecules

Note except for R at 623 K, curves for fresh and run-in catalysts are similar, although rates for the latter are of course much slower. 

A constant and recurrent theme in the study of metal-catalysed hydrocarbon transformations has been the complicating role of carbonaceous deposits, which are recognised as forms of the reactants that are dehydrogenated and form multiple bonds to the surface to an extent depending critically on temperature and hydrogen pressure. Analysis of the behaviour of alkanes and alicyclics has led to the conclusion that such species are inimical to the reactions of the latter, but are that the former may still be reactive in their presence and may even require their participation. This of course is not a new idea, but it still needs quantitative evaluation. 

The phenomenon of bistability was shown in the hydrogenation of n-propylcyclobutane, but curiously only with run-in Rh/Si02 catalyst.  

TABLE 11.7. Product Yields (%) from the Hydrogenation of Z- and -Dimethylcyclobutane on Various Metal Fihns ° 

The hydrogenation of methylenecyclobutane over Pt/pumice at 373 K gave about 90% of methylcyclobutane but above 473 K linear alkenes (especially E-2-pentene) were formed at 573 K, these appeared to arise through 1-methylcyclo-1-butene. No other studies of this reaction have been reported. 

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