Palladium sulfate

Acetic acid analogs can also be formed from a one-step C-H activation process using a palladium sulfate catalyst.15 A free radical process was ruled out for this formal eight-electron oxidation due to the high selectivities observed (90% based on methane converted) (Equation (7)). 

Palladium is attacked by concentrated nitric acid, particularly in the presence of nitrogen oxides. The reaction is slow in dilute nitric acid. Finely divided palladium metal reacts with warm nitric acid forming paUadium(ll) nitrate, Pd(NOs)2. Hydrochloric acid has no affect on the metal. Reaction with boiling sulfuric acid yields palladium sulfate, PdS04, and sulfur dioxide. 

Several gas detector tubes are used in conjunction with common colorimetric reactions to detect butadiene. The reactions include the reduction of chromate or dichromate to chromous ion and the reduction of ammonium molybdate and palladium sulfate to molybdemun blue (Saltzman Harman, 1989). 

Materials. Palladium acetate was prepared by oxidizing palladium black in acetic acid by 02 or by nitric acid (20). Material from nitric acid oxidation was crystallized five times or more before use, or more often, was purified by the following procedure. Finely powdered palladium acetate was made into a paste with sulfuric acid and digested at 140°-150°C for 30 min. Palladium (II) was thus converted into palladium sulfate, and crucial impurities were destroyed. Palladium sulfate was dissolved in water. After the sulfuric acid was neutralized, the addition of excess acetic acid precipitated purified palladium acetate. Oxi-dizable impurities were removed from acetic acid by repeated fractionation from CrOa and KMn04 solutions. Olefins were treated with alumina before use to remove peroxides. The reproducibility of the rate data was used as a test of the purity of reagents since the results were erratic when inadequate precautions had been taken. 

After calcination, palladium sulfate was deposited by impregnation to incipient wetness with an acidic solution of PdS04 2H20 (Alfa products) in water. An additional amount of sulfuric acid was added to the solution to aid the palladium sulfate dissolution. The amount of sulfuric acid in the solution was adjusted to obtain a S042YPd2+ ratio of 10 in the catalyst. Catalysts were dried and stored in air at 350 K. 

Fig. 1 shows the activity of a palladium sulfate-based 7-alumina-supported catalyst in the oxidation of 1-butene. Although deactivation of these catalysts is lower than for palladium chloride-based catalysts, Fig. 1 shows that the activity steadily decreases in time. Fig. 1 shows that the drop in activity can be (more or less arbitrary) divided into two stages. The first stage, from 0 to 2.5 h, is characterized by a rapid decrease in activity. After 2.5 h the activity only slowly decreases further in time. 

Fig. 4 shows the TPR profiles of the fresh and spent catalyst. Curve C shows the desorption of hydrocarbons during reduction of the spent catalyst, formed by reduction of carbonaceous deposits on the catalyst surface. The hydrogen consumption profiles of the catalyst (see Curve A and B) show the two peaks, characteristic of palladium sulfate-based catalysts, with a vanadium oxide reduction peak at approximately 400 K and a sulfate reduction peak at 600 K [11,13,16]. The peak position of the sulfate reduction peak is comparable for both catalysts. For the spent catalyst, however, an additional small hydrogen consumption is observed at 700 K, which coincides with the large peak in the FID signal,... 

For the palladium catalysts the formation of palladium sulfate/sulfite, which is stable up to temperature of around 650 °C, is known to inhibit the oxidation of CH4 [18]. This seemed not to be the case for the ignition of H2 and CO, which is very little, if at all, deactivated. However, for the CO there was a change in the behavior at higher conversions, instead of a very fast increase to total conversion there was a fast increase to above 90 % but then the conversion flattened out and became constant for several hundreds of degrees before reaching total conversion. Showing that in fact the activity of the catalysts was changed. 

On the basis of oxidation of ethylene, ripeness indicator targeted to ethylene was developed specifically for apples by the University of Arizona (USA) in 2005. (Riley, 2006). An indicator compound based on ammonium molybdates ((NH ) MoO ) as a visual dye (white) on palladium sulfate (PdSO )-catalyst indicator sticker can react with ethylene gas to produce molybdemrm oxide (MoOj) (dark blue), then the indicator is initially white and gradually changes to light blue and finally dark blue (Klein et al., 2006). Trade name of this sticker is namely RediRipe°. 

Lithium aluminum hydride Magnesium turnings Manganous carbonate Manganous chloride Mercuric chloride Mercury Methylamine Methylformamide Nitroethane Norpseudoephedrine Palladium sulfate Perchloric acid Phenylacetic acid Phenylacetone Phenylacetonitrile Phenylmagnesium bromide Phosphorus... 

Palladium black Palladium sulfate Perchloric acid Phosphorus pentachloride Platinum Platinum chloride Sodium acetate Sulfuric acid Thionyl chloride... 

Palladium sulfate is used by at least one manufacturer. It has a positive interference from H2S but H2S may be removed in a preconditioning layer at the front of the tube. If this is the case the manufacturer will state some finite level of H2S where interference initiates (for example, greater than 500 ppm H2S causes a positive error). Consult manufacturers instruction sheets for this information. Propylene and hydrocarbons of five or more carbon atoms will cause interfering discolorations making the palladium sulfate detection principle ineffective for liquefied petroleum gas (LPG). (Palladium chloride is used by at least one manufac-... 

Mercuric chloride is used by at least one manufacturer. It has a positive interference from H2S but does not have the hydrocarbon interference described above for palladium sulfate. This detection principle is preferred for LPG applications. H2S will produce a stain on mercuric chloride tubes even if mercaptans are not present. The approximate H2S sensitivity ratio is as follows One part per million H2S will produce a reading of 0.4 to 0.7 ppm mercaptans. Consult manufacturers for exact information if it does not appear in tube instruction sheets. 

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, Hcensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cyclohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NO in a buffered aqueous phosphoric acid... 

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 ... 

Hydrogenation. Hydrogenation is one of the oldest and most widely used appHcations for supported catalysts, and much has been written in this field (55—57). Metals useflil in hydrogenation include cobalt, copper, nickel, palladium, platinum, rhenium, rhodium, mthenium, and silver, and there are numerous catalysts available for various specific appHcations. Most hydrogenation catalysts rely on extremely fine dispersions of the active metal on activated carbon, alumina, siHca-alumina, 2eoHtes, kieselguhr, or inert salts, such as barium sulfate. 

The catalyst commonly used in this method is 5 wt % palladium supported on barium sulfate inhibited with quinoline—sulfur, thiourea, or thiophene to prevent reduction of the product aldehyde. A procedure is found in the Hterature (57). Suitable solvents are toluene, benzene, and xylene used under reflux conditions. Interestingly, it is now thought that Rosenmund s method (59) originally was successful because of the presence of sulfur compounds in the xylene used, since the need for an inhibitor to reduce catalyst activity was not described until three years later (60). 

This reaction is favored by moderate temperatures (100—150°C), low pressures, and acidic solvents. High activity catalysts such as 5—10 wt % palladium on activated carbon or barium sulfate, high activity Raney nickel, or copper chromite (nonpromoted or promoted with barium) can be used. Palladium catalysts are recommended for the reduction of aromatic aldehydes, such as that of benzaldehyde to toluene. 

By-Product Recovery. The anode slime contains gold, silver, platinum, palladium, selenium, and teUurium. The sulfur, selenium, and teUurium in the slimes combine with copper and sUver to give precipitates (30). Some arsenic, antimony, and bismuth can also enter the slime, depending on the concentrations in the electrolyte. Other elements that may precipitate in the electrolytic ceUs are lead and tin, which form lead sulfate and Sn(0H)2S04. 

Catalysts reduced with formaldehyde carry no adsorbed hydrogen and are less pyrophoric. Barium carbonate as a support may sometimes be advantageous in that the neutrality of the h3 drogenation mixture may be maintained. Barium sulfate or barium carbonate may be a better support than carbon, which may, in some instances, so strongly adsorb the derived product that recovery is difficult or incomplete. Palladium may be more completely and easily recovered from a spent catalyst where carbon rather than barium sulfate is the support. In general, the submitter prefers a catalyst prepared according to procedure C. 

Reduction of quinazoline oxides to quinazolines, catalytically (Raney nickel, palladium on charcoal) or with iron and ferrous sulfate in 85% alcohol can be extended to the preparation of benz-substituted quinazolines. ... 

As catalyst for the Rosenmund reaction palladium on a support, e.g. palladium on barium sulfate, is most often used. The palladium has to be made less active in order to avoid further reduction of the aldehyde to the corresponding alcohol. Such a poisoned catalyst is obtained for example by the addition of quinoline and sulfur. Recent reports state that the reactivity of the catalyst is determined by the morphology of the palladium surface." ... 

Many workers (5,6,7,87) have compared various metals for the selective hydrogenation of lower acetylenes to olefins, and it was always found that palladium was by far the most selective. This conclusion concurs with the usual synthetic experience, but under special circumstances other metals, such as platinum, may prove more useful (35,63). The catalyst support may also have an influence (21,65). Carbon, calcium carbonate, and barium sulfate are frequently used supports. Examples of some differences are noted later,... 

Support has been shown to influence selectivity and some workers have obtained higher yields of cis isomer over palladium-on-calcium carbonate or palladium-on-barium sulfate 21), whereas others find carbon satisfactory. In general, carbon support makes the more active catalyst and it is, therefore, more prone to become hydrogen poor. 

Choice of catalyst and solvent allowed considerable flexibility in hydrogenation of 8. With calcium carbonate in ethanol-pyridine, the sole product was the trans isomer 9, but with barium sulfate in pure pyridine the reaction came to a virtual halt after absorption of 2 equiv of hydrogen and traws-2-[6-cyanohex-2(Z)-enyl]-3-(methoxycarbonyl)cyclopentanone (7) was obtained in 90% yield together with 10% of the dihydro compound. When palladium-on-carbon was used in ethyl acetate, a 1 1 mixture of cis and trans 9 was obtained on exhaustive hydrogenation (S6). It is noteworthy that in preparation of 7 debenzylation took precedence over double-bond saturation. 

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