Palladium catalysts dioxide

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

The hydrogenation of pyrazolylacetylenes shows no peculiarities. Ethynylpyra-zoles are hydrogenated in high yields to the corresponding ethane derivatives on Raney nickel catalyst, platinum dioxide, or palladium catalyst at room temperature in alcohol solution. 

Burch, R. and Urbano, F.J. (1995) Methane combustion over palladium catalysts The effect of carbon dioxide and water on the activity, Appl. Catal. A 123, 173. 

Keywords Asymmetric Hydrogenation m Carbon Dioxide m Carbonylation m Dimethylformamide Enantioselectivity m Formic Acid m Homogeneous Hydrogenation n Palladium Catalysts Radical Reactions m Ruthenium Catalysts m Supercritical Fluids m Solvent Replacement... 

Catalytic hydrogenation in supercritical carbou dioxide has been studied. The effects of temperature, pressure, and CO2 concentration on the rate of reaction are important. Hydrogenation rates of the two double bonds of an unsaturated ketone on a commercial alumina-supported palladium catalyst were measured in a continuous gra-dient-less internal-recycle reactor at different temperatures, pressures, and C02-to-feed ratios. The accurate control of the organic, carbon dioxide, and hydrogen feed flow rates and of the temperature and pressure inside the reactor provided reproducible values of the product stream compositions, which were measured on-line after separation of the gaseous components (Bertucco et al., 1997). 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

The reaction achieved considerable attention over the years, and various alterations have been reported. Behr also reported the combination of carbon dioxide, butadiene and ethylene oxide to give the hydroxyester of the acids depicted in Scheme 19. A nickel-catalyzed analogous system using triphenylphosphine or triisopropylphosphite takes a different route as cyclopentanecarboxylic acids are reported as the main product [126]. A palladium catalyst immobilized on a phosphine-decorated polystyrene polymer [127] or on silica also proved to be active [128]. 

Carnahan et al. obtained good yields of alcohols and glycols by hydrogenation of lower mono- and dicarboxylic acids over ruthenium dioxide or Ru-C at 135-225°C and 34-69 MPa H2 (eqs. 10.1 and 10.2).8 In general, the optimum temperature was about 150°C. The chief side reaction was hydrogenolysis of the alcohols, as exemplified in the formation of ethanol from oxalic acid and of butanol and propanol from succinic acid (see eq. 10.2). Platinum and palladium catalysts were ineffective under similar or even more severe conditions. 

According to Freifelder, in most instances ruthenium catalyst is superior to nickel catalyst for the hydrogenation of furans to tetrahydrofurans the hydrogenation can be carried out at 70-100°C and 7 MPa H2.185 He refers to an example in which 2-furfu-rylamine was hydrogenated without solvent over ruthenium dioxide at 100°C and 8 MPa H2 in 10 min, compared to the temperatures of < 150°C and a reaction time of 30 h at 7 MPa H2 that were required for hydrogenation with Raney Ni. Hydrogenation of P-(2-furyl)alkylamines and an A-ethyl-2-furylalkylamine to the corresponding tetrahydro compounds was performed satisfactorily over palladium catalyst in ethanol in the presence of hydrochloric acid at room temperature and 0.62 MPa H2 (eq. 12.102)197 and over 5% Rh-C in neutral solvent at room temperature and 0.15 MPa... 

Thiophene 1,1-dioxide with a shielded sulfur atom was hydrogenated without difficulty to the tetrahydro derivative, sulfolane, over palladium catalyst in acetic acid at room temperature and atmospheric hydrogen pressure (eq. 12.121).249... 

Forms sensitive explosive mixtures with bromine chlorine iodine heptafluoride (heat- or spark-sensitive) chlorine dioxide dichlorine oxide iodine heptafluoride (heat-or spark-sensitive) dinitrogen oxide dinitrogen tetraoxide oxygen (gas) 1,1,1-trisazidomethylethane palladium catalyst. Mixtures with liquid nitrogen react with heat to form an explosive product. 

The kinetics and mechanism of methane combustion have been the subject of many investigations, e.g.. Refs. 43-47, because of the importance of natural gas as a potential fuel for catalytic combustors. Under conditions expected in catalytic combustors, i.e., excess oxygen, a first order in methane is generally observed [48], whercas a variety of orders has been observed for other hydrocarbons [13]. The actual mechanism appears to be quite complex and depends on the fuel used. For instance, inhibiting effects are observed for the products carbon dioxide and water in methane combustion over supported palladium catalysts [49,50]. The inhibition of methane adsorption and the formation of a surface palladium hydroxide were proposed to explain the observation. 

Allene carboxylic acids have been cyclized to butenolides with copper(II) chloride. Allene esters were converted to butenolides by treatment with acetic acid and LiBr. Cyclic carbonates can be prepared from allene alcohols using carbon dioxide and a palladium catalyst, and the reaction was accompanied by ary-lation when iodobenzene was added. Diene carboxylic acids have been cyclized using acetic acid and a palladium catalyst to form lactones that have an allylic acetate elsewhere in the molecule. With ketenes, carboxylic acids give anhydrides and acetic anhydride is prepared industrially in this manner [CH2=C=0 + MeC02H (MeC=0)20]. 

When applied to triple bonds, hydrocarboxylation gives a,p-unsaturated acids under very mild conditions. Triple bonds give unsaturated acids and saturated dicar-boxylic acids when treated with carbon dioxide and an electrically reduced nickel complex catalyst. Alkynes also react with NaHFe(CO)4, followed by CuCl2 2 H2O, to give alkenyl acid derivatives. A related reaction with CO and palladium catalysts in the presence of SnCE also leads to conjugated acid derivatives. Terminal alkynes react with CO2 and Ni(cod)2, and subsequent treatment with DBU (p. 1132) gives the a,p-unsaturated carboxylic acid. ... 

DEHYDROGENATION Anthraquinone. Chloranil. 2,3-Dichloro-5,6-dicyano-l,4-benzoquinone. Diethyl azodicarboxylate. Manganese dioxide. Palladium catalysts. Potassium hydride. Palladium-on-carbon. N,N,N, N -Tetraincthylethylcnc diamine. Trifluoroacetic acid. 

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