The evolution of the products from the catalytic hydrogenation (Rh/Al203) of the five isomeric diene derivatives of 1,3-di-tert-butylbenzene ( 9) is compared with the formation of the observable cyclohexene intermediates and the saturated products from arene 9 to determine which diene (or dienes), upon adsorption on the catalyst, best represents the structure of the intermediate(s) formed in the rate-determining surface reaction of the arene. Although the comparison indicates that little or no diene is desorbed during the hydrogenation of the arene, the observed competitive reactivity of the dienes, their interconversions, and the products of hydrogen addition indicate that the preferred reaction path for the hydrogenation of the arene proceeds via the addition of the first hydrogen atom to a tert-butyl-substituted carbon atom. Relative to cyclohexene, the rates of conversion of 1,5-di-tert-butyl-1,3-cyclohexadiene (13), 1,3-di-tert-butyl-1,4-cyclohexadiene (11), arene 9, and cyclohexene at 30 °C and 0.88 atm of H2 are 3.8:2.7:2.6 X 10"2:1.00. Under these conditions the turnover number of cyclohexene is 0.40 mol s-1 (mol of surface Rh)"1.In exploring the mechanism of the rhodium-catalyzed evidence of the structure and reactivity of the intermehydrogenation of aromatic hydrocarbons we have sought diates that may effect the rate and, particularly, the
Supplementary Material Available: Electron micrographs showing the PS-Pd, PS-b-Pd, and PS-anthracene-Pd catalysts (Figure 1), a tabular comparison of the yields and reaction times for decarbonylation of aldehydes by and 1% Pd/C (Table III), and a tabular summary of the effect of functional groups on polystyrene on hydrogenation of 1-octene by palladium/polystyrene catalysts (Table V) (3 pages). Ordering information is given on any current masthead page.
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