Palladium substitutions

In addition to the presence of these elements in ores, they are also available from recycled feeds, such as catalyst wastes, and as an intermediate bulk palladium platinum product from some refineries. The processes that have been devised to separate these elements rely on two general routes selective extraction with different reagents or coextraction of the elements followed by selective stripping. To understand these alternatives, it is necessary to consider the basic solution chemistry of these elements. The two common oxidation states and stereochemistries are square planar palladium(II) and octahedral platinum(IV). Of these, palladium(II) has the faster substitution kinetics, with platinum(IV) virtually inert. However even for palladium, substitution is much slower than for the base metals so long as contact times are required to achieve extraction equilibrium. 

Guilhaume, N Peter, SD Primet, M. Palladium-substituted lanthanmn cuprates application to automotive exhaust pmification. Appl. Catal, B Environmental, 1996, Volume 10, Issue 4,325-344. 

R.W. Sidwell, H. Zhu, R.J. Kee, D.T. Wickham, C. Schell, and G. S. Jackson. Catalytic Combustion of Premixed Methane-Air on a Palladium-Substituted Hexalumi-nate Stagnation Surface. Proc. Combust. Inst., 29,2002. 

An alloy contains atoms of more than one element and has the properties of a metal. In a solution alloy the components are randomly dispersed. In a heterogeneous alloy the components are not evenly di rsed and can be distinguished at a macroscopic level In an intermetallic compound the components have interacted to form a compound substance, as in CU3AS 12.39 Statement (b) is false. 12.41 (a) True (b) false (c) false 12.43 (a) Nickel or palladium, substitutional alloy (b) copper, substitutional alloy (c) silver, substitutional alloy 12.45 (a) True (b) false (c) false (d) false... 

Sidwell RW, Zhu H, Kee RJ, Wickham DT, Schell C, Jackson GS Catalytic combustion of premixed methane/air on a palladium-substituted hexaluminate stagnation surface, Proc Combust Inst 29 1013—1020, 2002. 

Kogan, V., Aizenshtat, Z., Popovitz-Biro, R., et al. (2002). Carbon-Carbon and Carbon-Nitrogen Coupling Reactions Catalyzed by Palladium Nanoparticles Derived from a Palladium Substituted Keggin-Type Polyoxometalate, Org. Lett., 4, pp. 3529-3532. 

In a lOOmL round-bottomed flask fitted with a magnetic stirrer is placed a mixture of palladium (II) chloride (89mg, O.Smmol), p-benzoquinone (5.94g, 55mmol) and 7 1 dimethylformamide/water (20mL). To the solution, t-decene [substitute safrole for this compound) (7.0g, 50mmc4) is added in 10 min and the mixture is stirred at room temperature for 7h. The solution is poured into cold 3 normal hydrochloric acid (lOOmL) and extracted with 5 portions of ether. The extracts are combined and washed with three portions of 10% aqueous sodium hydroxide solution and a portion of brine, and then dried After removal of the solvent, the residue is distilled to give 2-decanone [P2P] yield 6.1g (78%). 

Allylic acetoxy groups can be substituted by amines in the presence of Pd(0) catalysts. At substituted cyclohexene derivatives the diastereoselectivity depends largely on the structure of the palladium catalyst. Polymer-bound palladium often leads to amination at the same face as the aoetoxy leaving group with regioselective attack at the sterically less hindered site of the intermediate ri -allyl complex (B.M. Trost, 1978). 

Pd(II) compounds coordinate to alkenes to form rr-complexes. Roughly, a decrease in the electron density of alkenes by coordination to electrophilic Pd(II) permits attack by various nucleophiles on the coordinated alkenes. In contrast, electrophilic attack is commonly observed with uncomplexed alkenes. The attack of nucleophiles with concomitant formation of a carbon-palladium r-bond 1 is called the palladation of alkenes. This reaction is similar to the mercuration reaction. However, unlike the mercuration products, which are stable and isolable, the product 1 of the palladation is usually unstable and undergoes rapid decomposition. The palladation reaction is followed by two reactions. The elimination of H—Pd—Cl from 1 to form vinyl compounds 2 is one reaction path, resulting in nucleophilic substitution of the olefinic proton. When the displacement of the Pd in 1 with another nucleophile takes place, the nucleophilic addition of alkenes occurs to give 3. Depending on the reactants and conditions, either nucleophilic substitution of alkenes or nucleophilic addition to alkenes takes place. 

Formic acid behaves differently. The expected octadienyl formate is not formed. The reaction of butadiene carried out in formic acid and triethylamine affords 1,7-octadiene (41) as the major product and 1,6-octadiene as a minor product[41-43], Formic acid is a hydride source. It is known that the Pd hydride formed from palladium formate attacks the substituted side of tt-allylpalladium to form the terminal alkene[44] (see Section 2.8). The reductive dimerization of isoprene in formic acid in the presence of Et3N using tri(i)-tolyl)phosphine at room temperature afforded a mixture of dimers in 87% yield, which contained 71% of the head-to-tail dimers 42a and 42b. The mixture was treated with concentrated HCl to give an easily separable chloro derivative 43. By this means, a- and d-citronellol (44 and 45) were pre-pared[45]. 

The development of methods for aromatic substitution based on catalysis by transition metals, especially palladium, has led to several new methods for indole synthesis. One is based on an intramolecular Heck reaction in which an... 

Indoles with carbocyclic halogen or triflate substituents are potential starting materials for vinylation, arylation and acylation via palladium-catalysed pro-cesses[l]. Indolylstannanes. indolylzinc halides and indolylboronic acids are also potential reactants. The principal type of substitution which is excluded from such coupling reactions is alkylation, since saturated alkyl groups tend to give elimination products in Pd-catalysed processes. 

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. 

Isotope Effects on Superconductivity. Substitution of hydrogen by deuterium affects the superconducting transition temperature of palladium hydride [26929-60-2] PdH2 (54,55), palladium silver hydride, Pd Ag H D ( 6), and vanadium—2itconium—hydride, N(57). 

Palladium and Palladium Alloys. Palladium is used in telephone equipment and in electronics appHcations as a substitute for gold in specific areas. Palladium is plated from ammoniacal and acid baths available along with chelated variations as proprietary processes. One typical alkaline bath uses 8 g/L diammine-dinitropalladium, 100 g/L ammonium nitrate, and 10 g/L sodium nitrite. The pH is adjusted to 9—10 using ammonium hydroxide, and the bath is operated at 100 A/m at 50° C. If ammonium sulfamate, 100 g/L, is used in some baths to replace the nitrate and sodium nitrite salts, the bath is mn at lower temperature, 25—35°C, and a pH of 7.5—8.5. A palladium—nickel alloy, 75% Pd, is plated from a bath having 6 g/L palladium from the same salt, 3 g/L nickel from nickel sulfamate concentrate, and 90 g/L ammonium hydroxide. The bath is operated at 20—40°C with 50-100 A/m/... 

There are reports of an increasing number of palladium-assisted reactions, in some of which the palladium has a catalytic function. Thus furan and thiophene undergo facile palladium-assisted alkenylation giving 2-substituted products. Benzo[6 Jfuran and TV- acetyl-indole yield cyclization products, dibenzofurans and carbazoles respectively, in addition to alkenylated products (8UOC851). The arylation of pyrroles can be effected by treatment with palladium acetate and an arene (Scheme 86) (81CC254). 

The palladium-promoted conversion of 1,3-dienes to pyrroles proceeds via 4-acetoxy-2-alkenylpalladium complexes (Scheme 50g) (81CC59), and a similar pathway may be involved in the palladium mediated reaction of but-2-ene-l,4-diol with primary amines to give A-substituted pyrroles (74CC931). 

An equal weight of precipitated barium carbonate (93 g.) may be substituted for the barium hydro.xide and sulfuric acid to give a palladium on barium carbonate catalyst. The amount of hydrochloric acid should then be reduced to 8.2 ml. 

Hydrogenation of 19-hydroxy-3a- and 3j5-substituted-A -steroids over platinum or rhodium yields increased amounts of 5j9-products as compared to the corresponding 19-desoxy series (hydroxyl group effect). In contrast, the A -19-carboxaldehyde (27) gives only the 5a-product when hydrogenated over either palladium or platinum. ... 

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. ... 

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