Palladium chloride metal salts

Palladium catalysts are useful alternatives to Adams platinum oxide catalyst described in Section 111,150. The nearest equivalent to the latter is palladium chloride upon carbon and it can be stored indefinitely the palladium salt is reduced to the metal as required ... 

Substitution at the Carbon—Chlorine Bond. Vinyl chloride is generally considered inert to nucleophilic replacement compared to other alkyl halides. However, the chlorine atom can be exchanged under nucleophilic conditions in the presence of palladium [7440-05-3] Pd, and certain other metal chlorides and salts. Vinyl alcoholates, esters, and ethers can be readily produced from these reactions. 

Catalysts for dielectric surfaces are more complex than the simple salts used on metals. The original catalysts were separate solutions of acidic staimous chloride [7772-99-8J, used to wet the surface and deposit an adherent reducing agent, and acidic palladium chloride [7647-10-17, which was reduced to metallic palladium by the tin. This two-step catalyst system is now essentially obsolete. One-step catalysts consist of a stabilized, pre-reacted solution of the palladium and staimous chlorides. The one-step catalyst is more stable, more active, and more economical than the two-step catalyst (21,23). A separate acceleration or activation solution removes loose palladium and excess tin before the catalyzed part is placed in the electroless bath, prolonging bath life and stability. 

Palladium catalysts have been prepared by fusion of palladium chloride in sodium nitrate to give palladium oxide by reduction of palladium salts by alkaline formaldehyde or sodium formate, by hydrazine and by the reduction of palladium salts with hydrogen.The metal has been prepared in the form of palladium black, and in colloidal form in water containing a protective material, as well as upon supports. The supports commonly used are asbestos, barium carbonate, ... 

Monosubstituted and 1,2-disubstituted olefins can be oxidized to aldehydes and ketones by palladium chloride and similar salts of noble metals.367 1,1-Disubstituted olefins generally give poor results. The reaction is used industrially to prepare acetaldehyde from ethylene... 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

The preparation of organopalladium compounds by exchange reactions of palladium salts and organo-lead, -tin, or -mercury compounds is apparently not the only way that they can be obtained but it does seem to be the most useful way. Convincing evidence is now available to show that direct metalation of aromatic compounds with palladium salts (palladation) can occur. Since the initial report of Cope and Siekman 32> that palladium chloride reacted readily with azobenzene to form an isolable chelated, sigma-bonded arylpalladium compound, several additional chelated arylpalladium compounds have been prepared. 

At this point the surface is hydrophilic but still not capable of promoting deposition either of copper or nickel in order to create sites at which these metals will form it is necessary to activate the surface by depositing nuclei of palladium. Originally this was done in two steps, immersion of the components in a solution containing stannous chloride and then transferring them to one based on palladium chloride—from which the metal was deposited. Now however these are combined in a single immersion in a colloidal solution of palladium chloride containing also tin salts in both stannous and stannic states. A typical solution of this type would comprise ... 

In some preliminary studies on the eflFect of the metallic anion a series of reactions was run in which chloride in both the palladium and copper salts was replaced by other anions. When acetate was used, results similar to the chloride systems were obtained although product distribution was somewhat different see also Table 1). Both bromide and iodide were found to inhibit the reaction, and no products were isolated. For the oxyanions, nitrate, sulfate, and acetylacetonate, vinyla-tion products of these oxyanions in addition to the acetate vinylation products were found. Because of the increased complexity of these systems, they were not investigated further. All chloride-containing systems investigated—PdCl2, Na2PdCl4, (NH3)2PdCl2, and 7r-allylpalladium chloride—had similar reactivities and vinylation-product distributions. 

This process was discovered at the end of 1956 when, in the laboratory of the Consortium, ethylene together with oxygen and a trace of hydrogen was passed over a palladium-on-carbon catalyst and the formation of acetaldehyde was observed. Then, it was found that addition of oxidizing metal salts such as cupric and ferric chlorides increases the yield of acetaldehyde. 

Olefin oxidation with an aqueous palladium chloride solution according to eqs. (2)-(4) occurs stoichiometrically. A catalytic reaction is only possible if the metallic palladium can be reoxidized immediately. With gaseous oxygen, conditions to oxidize even finely divided palladium black are not optimal. However, metal salts such as cupric and ferric chlorides, chromates, heteropoly acids of phosphoric acid with molybdic and vanadic acids, or other oxidants - e. g., ben-zoquinone is used in kinetic investigations [10] - are suitable for reoxidation of the palladium metal. This fact explains the increase of the yield of acetaldehyde in the first experiments of the Consortium carried out in the presence of cupric and ferric chlorides, as mentioned above. 

The selectivity of palladium and gold for alkene oxidation to aldehydes 28,29,170) was attributed initially to adsorption strength. However, electrooxidation in the presence of palladium ions indicates possible homogeneous alkene insertion, similar to the Wacker process 304). Homogeneous reaction is also involved in redox oxidations of hydrocarbons. In this case, the nature of the metal ions is expected to control selectivity. Indeed, toluene yields 20% benzaldehyde in electrolytes containing Ce salts, while oxidation proceeds to benzoic acid with Cr redox catalysts 311). In addition, the concentration of redox catalysts appears to affect yields in nonelectrochemical oxidation of ethylene large amounts of palladium chloride promote butene formation at the expense of acetaldehyde 312). Finally, the role of the electrolyte and solvent should not be ignored. For instance, electrooxidation of ethylene on carbon, in aqueous solution of acetic acid yields acetaldehyde 313) in the... 

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