Aromatic hydrocarbons palladium catalysts

Alicyclic hydrocarbons, Six-membered rings (Continued) aromatic rings Palladium catalysts, 230 Raney nickel, 265 Cyclohexanes by other routes /-Butyllithium, 58 Menthol, 172 Potassium /-butoxide, 252 Zinc bromide, 349... 

Aromatic Aldehydes. Carbon monoxide reacts with aromatic hydrocarbons or aryl haHdes to yield aromatic aldehydes (see Aldehydes). The reaction of equation 24 proceeds with yields of 89% when carried out at 273 K and 0.4 MPa (4 atm) using a boron trifluoride—hydrogen fluoride catalyst (72), whereas conversion of aryl haHdes to aldehydes in 84% yield by reaction with CO + H2 requires conditions of 423 K and 7 MPa (70 atm) with a homogeneous palladium catalyst (73) and also produces HCl. 

The reaction of arylbromides with amines affords mostly the corresponding aromatic hydrocarbon by using palladium catalysts, but the expected substituted anilines are formed in good yields by using a nickel (II) catalyst. 

The palladium(O) complex undergoes first an oxydative addition of the aryl halide. Then a substitution reaction of the halide anion by the amine occurs at the metal. The resulting amino-complex would lose the imine with simultaneous formation of an hydropalladium. A reductive elimination from this 18-electrons complex would give the aromatic hydrocarbon and regenerate at the same time the initial catalyst. 

If, instead of a palladium catalyst, a nickel catalyst, such as the bipyridylnickel(II) bromide, is used for the arylation of amines (Fig. 7), the reduction of the aryl halide into the corresponding aromatic hydrocarbon is still present for the primary or secondary benzylamines but, the arylation into substituted anilines is the main reaction even most often the only one, for the other types of amines. 

More recently Hartog and Zwietering (103) used a bromometric technique to measure the small concentrations of olefins formed in the hydrogenation of aromatic hydrocarbons on several catalysts in the liquid phase. The maximum concentration of olefin is a function of both the catalyst and the substrate for example, at 25° o-xylene yields 0.04, 1.4, and 3.4 mole % of 1,2-dimethylcyclohexene on Raney nickel, 5% rhodium on carbon, and 5% ruthenium on carbon, respectively, and benzene yields 0.2 mole % of cyclohexene on ruthenium black. Although the cyclohexene derivatives could not be detected by this method in reactions catalyzed by platinum or palladium, a sensitive gas chromatographic technique permitted Siegel et al. (104) to observe 1,4-dimethyl-cyclohexene (0.002 mole %) from p-xylene and the same concentrations of 1,3- and 2,4-dimethylcyclohexene from wi-xylene in reductions catalyzed by reduced platinum oxide. 

Aromatic hydrocarbons, such as benzene add to alkenes using a ruthenium catalyst a catalytic mixture of AuCVAgSbFs, or a rhodium catalyst, and ruthenium complexes catalyze the addition of heteroaromatic compounds, such as pyridine, to alkynes. Such alkylation reactions are clearly reminiscent of the Friedel-Crafts reaction (11-11). Palladium catalysts can also be used to for the addition of aromatic compounds to alkynes, and rhodium catalysts for addition to alkenes (with microwave irradiation). " Note that vinyhdene cyclopropanes react with furans and a palladium catalyst to give aUylically substituted furans. ... 

Compound A has the formula CsH. It reacts rapidly with KMn04 to give CO2 am a carboxylic acid, B (C7H 02), but reacts with only 1 molar equivalent of H2 on cat alytic hydrogenation over a palladium catalyst. On hydrogenation under conditions that reduce aromatic rings, 4 equivalents of H2 are taken up, and hydrocarbon C (CeHis) is produced. What are the structures of A, B, and C Write the reactiomj... 

Eisen and Ivanov [54] converted hydrocarbons of various types in a stream of hydrogen on a 0.5% palladium on silica gel catalyst. For carrying out reaction chromatographic analysis of hydrocarbon mixtures, optimum temperatures for the hydrogenation of aromatic hydrocarbons are 315—325°C. Simultaneously at the specified temperatures hydrogenation of olefins, diolefins, cyclopentenes, etc., occurs. Conversions of the hydrocarbons are presented in Table 4.1. 

Eisen and Ivanov [60] elaborated a pulse, micro-catalytic gas chromatographic method of selective hydrogenation of alkenes and cyclohexenes at 90°C on 5% palladium on silica gel as the catalyst. Under these conditions aromatic hydrocarbons are not hydrogenated, and cyclopentenes are hydrogenated to an insignificant extent. 

Skeletal rearrangements of saturated hydrocarbons on CePd3 were studied by Le Normand et al. (1984). Hydrogenolysis of methylcyclopentane, isomerization of 2-methyl-pentane and aromatization of 3-methylhexane were performed at 350 or 360°C. The results were compared with those of classical Pd/Al203, Pd/Si02 or Pd/Ce02 catalysts. The activity of CePd3 itself was very low and palladium atoms seemed to play a minor role. For example, the initial reaction of methylcyclopentane was the selective formation of isopentane, which is not observed on classical palladium catalysts. Air treatment at... 

Abstract The transition-metal-catalyzed cydotrimerization of alkynes has been used extensively in synthesis during the past 25 years. However, until recently there have been no procedures for the cydotrimerization of arynes. This chapter shows that this transformation can be efficiently achieved with palladium catalysts, and that it opens new avenues in the synthesis of polycyclic aromatic hydrocarbons. 

Palladium catalysts have been used for cycloaddition of dimethylacetylene di-carboxylate (DMAD) to polycyclic arynes 3, 77 and 79 (Schemes 34-36). All these reactions exhibit the same reactivity pattern as is observed in the [2+2+2] cycloaddition of benzyne to DMAD (see Sect. 3.1) Pd2(dba)3 leads selectively to the cocycloaddition of one molecule of aryne and two molecules of DMAD, while Pd(PPh3)4 induces the reaction of two molecules of aryne with one molecule of DMAD. Both reactions afford the corresponding polycyclic aromatic hydrocarbons in good yields and with high chemoselectivity, constituting a novel and versatile method for the synthesis of functionalized PAHs under mild reaction conditions [70-72] (Scheme 34). 

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