Hydrogenolysis platinum-catalyzed

Acid-catalyzed cracking and platinum-catalyzed hydrogenolysis proceed simultaneously over dual-function catalysts. The distribution of the scission products is determined by the relative strengths of the acidic and metal-type catalytic components. 

Other pure mechanisms of cracking are thermal cracking and hydrogenolysis over metals. Very detailed investigations on platinum catalyzed hydrogenolysis of various alkanes, e. g., the isomeric hexanes, have been published recently (6-8). 

The presence of an allylamine system in pseudoakuammigine, postulated in XLVIII, is confirmed by the platinum-catalyzed hydrogenolysis of pseudoakuammigine methiodide, which affords a dihydromethine base, C23H30N2O3, by fission of the C-21 to Nb bond the apo base methiodide similarly yields a dihydromethine. Both bases still contain the ethylidene group, and contain one additional C -methyl group. 

The synthesis of p-aminophenol was accomplished by the platinum catalyzed hydrogenation of nitrobenzene in aqueous sulfuric acid with concomitant acid catalyzed rearrangement of the intermediate phenylhydroxylamine (Scheme 19.2).3 The addition of quaternary ammonium salts or DMS0 -33 decreased the rate of phenylhydroxylamine hydrogenolysis to give more time for the rearrangement to take place. 

As previously mentioned, Davis (8) has shown that in model dehydrocyclization reactions with a dual function catalyst and an n-octane feedstock, isomerization of the hydrocarbon to 2-and 3-methylheptane is faster than the dehydrocyclization reaction. Although competitive isomerization of an alkane feedstock is commonly observed in model studies using monofunctional (Pt) catalysts, some of the alkanes produced can be rationalized as products of the hydrogenolysis of substituted cyclopentanes, which in turn can be formed on platinum surfaces via free radical-like mechanisms. However, the 2- and 3-methylheptane isomers (out of a total of 18 possible C8Hi8 isomers) observed with dual function catalysts are those expected from the rearrangement of n-octane via carbocation intermediates. Such acid-catalyzed isomerizations are widely acknowledged to occur via a protonated cyclopropane structure (25, 28), in this case one derived from the 2-octyl cation, which can then be the precursor... 

Dehydrocyclization, 30 35-43, 31 23 see also Cyclization acyclic alkanes, 30 3 7C-adsorbed olefins, 30 35-36, 38-39 of alkylaromatics, see specific compounds alkyl-substituted benzenes, 30 65 carbene-alkyl insertion mechanism, 30 37 carbon complexes, 32 179-182 catalytic, 26 384 C—C bond formation, 30 210 Q mechanism, 29 279-283 comparison of rates, 28 300-306 dehydrogenation, 30 35-36 of hexanes over platintim films, 23 43-46 hydrogenolysis and, 23 103 -hydrogenolysis mechanism, 25 150-158 iridium supported catalyst, 30 42 mechanisms, 30 38-39, 42-43 metal-catalyzed, 28 293-319 n-hexane, 29 284, 286 palladium, 30 36 pathways, 30 40 platinum, 30 40 rate, 30 36-37, 39... 

Naphthol has been reduced to 1-decalol using platinum,5 Raney nickel,6 and Raney copper.7 The reactions catalyzed by nickel and copper required elevated temperatures and pressure. The present procedure allows the preparation of substantial quantities of 1-decalol under much more convenient conditions and shorter reaction times. Previous methods5-7 require costly catalysts or high-pressure equipment and frequently result in a high degree of hydrogenolysis. The submitters have found that the present method is applicable to a wide variety of aromatic nuclei, some of which are listed in Table I. 

The palladium catalyzed hydrogenolysis of 5,5-dimethyl 1,3-cyclohexane-dione (59) in acidic medium gave good yields of the cyclohexanone, 60 (Eqn. 20.41). 5 In iiie absence of acid, a platinum catalyst gave a higher selectivity for the hydrogenolysis of one of the carbonyl groups of 1,3-cyclohexanedione than did palladium. ... 

The first examples of skeletal rearrangements on metals were reported by the Soviet school of catalysis. A major step in hydrocarbon chemistry was the finding that platinum, unlike palladium and nickel, selectively catalyzes the hydrogenolysis of cyclopentane hydrocarbons. At about 300°C, on the classical Zelinskii platinum-charcoal catalyst, cyclopentane yields -pentane as sole reaction product (3, 4), while palladized charcoal is completely inactive (J) and nickel-alumina produces all the possible acyclic hydrocarbons, from methane to pentane (5-7). 

On the other hand, the selective dehydrocyclization, which does not allow the formation of secondary-primary C-C bonds, must involve only two methylic carbon atoms in the 1 and 5 positions. Although the reverse reaction (selective hydrogenolysis of methylcyclopentane) could be observed on platinum catalysts of low dispersion at 220°C (86), the selective dehydrocyclization of methylpentanes on these catalysts is detectable only at higher temperatures (280°-300°C), where it competes with another process, ascribed to Mechanism C (33). Fortunately, it was found recently that iridium supported on AI2O3 or SiOj selectively catalyzes at 150°C the cyclic type interconversion of 2-methyl- and 3-methylpentanes (88). n-Hexane under the same conditions yields only cracked products (702) (Scheme 52). Similarly,... 

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