1,3-Butadiene, hydrogenation over platinum

It is not intended that the literature concerning the hydrogenation of alkenylalkynes and dialkynes shall be reviewed in detail. However, the hydrogenation of molecules as unsaturated as these provides further examples of the operation of the thermodynamic factor which are of interest. The palladium-, platinum-, and nickel-catalyzed hydrogenations of vinylacetylene (H2C=CH—C=CH) provides 1,3-butadiene as the major initial product butenes and butane are also produced (57). The product distributions are constant in liquid phase reactions until the parent hydrocarbon has been removed, showing that vinylacetylene is more strongly adsorbed than 1,3-butadiene and the butenes. The relative yields of butenes and butane resemble those obtained in 1,3-butadiene hydrogenation over these metals (see Section III, F, 6). 

Examples include hydrogenation of propanal over nickel, dehydrogenation of ethanol over copper-cobalt, dehydrogenation of methylcyclohexane to toluene over platinum, hydroformylation of olefins catalyzed by cobalt hydrocarbonyls on solid polymers, hydrogen-ion catalyzed hydration of olefins on ion exchangers, dehydrogenation of 1-butene to butadiene over chromia-alumina, and various hypothetical reactions. 

Third, n-allyl complexes are formed by palladium and cobalt analogous complexes of nickel and platinum are less stable, while ruthenium, rhodium, and iridium are not yet known to form them. In catalytic reactions the deuteration of cyclic paraffins over palladium has provided definite evidence for the existence of rr-bonded multiply unsaturated intermediates, while 7r-allylic species probably participate in the hydrogenation of 1,3-butadiene over palladium and cobalt, and of 1,2-cyclo-decadiene and 1,2-cyclononadiene over palladium. Here negative evidence is valuable platinum, for example does not form 7T-allylic complexes readily and the hydrogenation of 1,3-butadiene using platinum does not require the postulate that 7r-allylic intermediates are involved. Since both fields here are fairly well studied it is unlikely that this use of negative evidence will lead to contradiction in the light of future work. 

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