Palladium sponge

Palladium-reihe, /. palladium series, -salz, n. palladium salt, -schwamm, m. palladium sponge. -Schwarz, n. palladium black, -was-serstoff, m. palladium hydride. 

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

Palladium dichloride is prepared by dissolving palladium metal in aqua regia or hydrochloric acid in the presence of chlorine. Alternatively, it may be prepared by heating palladium sponge with chlorine gas at 500°C... 

Palladium oxide is prepared by heating palladium sponge in oxygen at 350°C. The oxide is obtained as a black powder. The oxide also may be prepared specially for catalytic use by heating a mixture of palladium chloride and potassium nitrate at 600°C and then leaching out water-soluble residue. A hydrated form of the oxide, which is acid soluble can be prepared by precipitation from solution, for example, by hydrolysis of palladium nitrate. The brown hydrated oxide converts to black anhydrous oxide on heating. Its solu-bdity in acids decreases with lowering of water content. 

The palladium complex was purchased from Strem Chemical Company and was used as received. Alternatively, material prepared from palladium sponge and nitrosonium tetraf1uoroborate in acetonitrile worked equally well. 

Palladium-catalyzed aryl-aryl coupling, 66, 70 PALLADIUM-CATALYZED COUPLING OF ARYL HALIDES, 66, 67 Palladium sponge, 66, 54... 

Palladium occurs in the form of foil and wire which in appearance greatly resemble platinum also in the form of palladium-sponge, a gray spongy mass, and as palladium black. The compact metal is soluble in nitrohydrochloric acid. Palladium sponge is soluble also in hydrochloric acid in the presence of air. 

The hydrogen can be nearly completely removed by absorption with palladium-sponge, and the nitrogen remains. 

Physical Varieties of Palladium.—Palladium may be prepared in several different physical states, namely, as the ordinary compact metal, as colloidal metal, as palladium sponge, and finally as palladium black. Of these, the last named is not pure palladium, but an indefinite mixture in a state of very fine division. Each of these varieties has its own peculiar physical characteristics. 

At very low temperatures, such as those of liquid air, palladium sponge has an extremely large capacity for hydrogen, and palladium sponge at — 190° C. has therefore been recommended as a convenient substance for removing the last traces of hydrogen from other gases.5... 

Graham also found palladium sponge to exhibit a selective absorption for alcohol in preference to water, a power not manifested either by platinum sponge or by spongy iron. For example, palladium sponge was left in contact with a mixture of alcohol and water in a sealed tube for two days. At the expiration of this time the supernatant liquid was removed and found to contain less alcohol, whilst the portion retained by the palladium contained more alcohol in proportion than the original mixture. 

Ammonium Brom-palladite, (NH4)2PcLBr4, may be prepared1 in a similar manner to the preceding salt. Its crystals are olive brown in colour, anhydrous, and very stable in air. They readily dissolve in water. Upon ignition a residue of palladium sponge is obtained. 

When palladium is heated to dull redness in oxygen palladous oxide is formed. But it is difficult to oxidise the metal completely by this method owing to the sintering of the metal, which renders oxidation slow. Palladium sponge is most suitable for the purpose, and should be heated in pure oxygen at temperatures rising slowlv from 700° C. to 840° C.7... 

Leidie and Quennessen3 prepared the dioxide by treatment of palladium sponge with sodium peroxide, but unfortunately were unable to isolate it. 

From binary alkali hydrides and platinum (palladium) sponge at 573 623 K under 0.8 bar (Pd compounds 70bar) hydrogen colorless powders, sensitive to air and moisture ordered structures (Figure 8) by npd on deuterides P4/mbm, Z = 2 isostmctural to RbsPdFs planar [PtELi] (or... 

Catalytic activation of hydrogen condensed either in the palladium sponge or in the foil was disclosed in the same paper [15]. At the ambient temperature, persalt of iron became protosalt and chlorine-water was transformed into hydrochloric acid. 

Besides the compact membrane catalysts described in Section II, there are two types of composite membrane catalyst porous and nonporous. Composite catalyst consists of at least two layers. The first bilayered catalyst was prepared by N. Zelinsky [112], who covered zinc granules with a porous layer of palladium sponge. The sponge became saturated with the hydrogen evolved during hydrochloric acid reaction with zinc and at room temperature actively converted hydrocarbon iodates into corresponding hydrocarbons. 

In a strong hydrogen current in the presence of palladium sponge or palladium on barium sulfate at 25- lOO C, the quaternary salts 257 were converted to compounds Adams platinum oxide and... 

Dehydrogenation of the tetrahydropyrido[2,l-/i]quinazolinone 203 over palladium sponge at 275°C afforded the pyrido[2,l-6]quinazolinone 286. ° Dehydrogenation of compounds 332 (R = R = H, = 0, 1) with the mercuric acetate-EDTA complex yielded compounds 99 ( = 0,1) in high yields. ... 

Derivation Reaction of palladium nitrate or palladium sponge with glacial acetic acid. 

The behavior of carbon monoxide-hydrogen mixtures in the presence of metals of the platinum group lias been made the subject of special study by a number of investigators. Orloff82 was the first to observe that under certain conditions in the presence of a nickel-palladium catalyst, a reaction took place which resulted in the formation of ethylene. This is in contradiction to the observations of Breteau,88 who stated that in the presence of palladium sponge, carbon monoxide and hydrogen react in the cold to form methane and that at 400° C. this transformation becomes fairly rapid. Recently it has seemed desirable that the experiments of Orloff... 

PALLADIUM BLACK or PALLADIUM SPONGE (7440-05-3, platinum metal) Powdered form is highly reactive catalyst, and may cause fire and explosions on contact with many substances including oxidizers, acetone, strong acids, finely divided aluminum, dioxygen difluoride, ethyl... 

Cavallito (66) reports that neither it nor 3-benzoxypyridine was hydrogenated in the presence of Willstatter s palladium sponge catalyst (67). Under low pressure conditions in ether or dioxane Raney nickel and platinum oxide were ineffective. However, other examples show that reduction takes place readily under a variety of conditions. Biel used Raney nickel at 125° and 50 atm (68), excellent yield of 6-propyl-3-hydroxypiperidine resulted from reduction of the pyridine in acetic acid with platinum oxide (69). Ruthenium in the conversion of 3-hydroxypyridine in aqueous solution gave very high yield of the corre-... 

Effects of Halogens- A study of the partial catalytic oxidation of CH4 over palladium sponge catalysts by Cullis et al. yielded some information quite relevant to its use for complete oxidation in air pollution control. They found that (1) the presence of higher alkanes or of partial oxidation products of methane, HCHO and CH3OH, retard the overall oxidation of the CH4 (2) the wide variety of halomethanes studied retarded the oxidation of CH4 to different extents and (3) some chloromethanes increased the production of HCHO with high selectivity. They attributed the latter to the modification of the elecuonic properties of the catalyst surface by the chloromethane to inhibit the further oxidation of the HCHO. 

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