Palladium cyanides

The effects of tin/palladium ratio, temperatnre, pressnre, and recycling were studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140°C by measurement of in situ variable temperature XRD. ESCA studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present. 

VI. Palladium Cyanide Addition with Hydride Elimination... 

The reaction of olefins with palladium cyanide appears analogous to the others mentioned earlier. Propylene and palladium cyanide at 150 °C produce mainly methacrylonitrile along with lesser amounts of crotono-nitrile and isobutyronitrile 17). 

The reduced product probably arises from the reaction of the intermediate palladium cyanide adduct with hydrogen cyanide. 

Palladium Cyanide, Pd(CN)2, was known to Berzelius,3 who obtained it by decomposition of a palladium salt with mercuric cyanide. It also results when palladium oxide is boiled with a solution of mercuric cyanide. These reactions afford a useful method of separating palladium from its congeners. When heated in air cyanogen is evolved and spongy palladium left. 

Palladium cyanide is very stable insoluble in acids, it dissolves in potassium cyanide, yielding ... 

During the following 15 years, only small advances were achieved in increasing catalyst efficiencies. Independently, Fenton [9a] at Union Oil and Nozaki [9b] at Shell Development Company (USA) discovered several related palladium chlorides, palladium cyanides, and zero-valent palladium complexes as catalysts. Sen and co-workers [10] reported that cationic bis(triphenyl-phosphine)-palladium tetrafluoroborate complexes in aprotic solvents such as dichloromethane, produced ethylene/carbon monoxide copolymers under very mild conditions. The reaction rates were, however, very low, as were the molecular weights. 

In the early 1980s, workers at Shell could demonstrate melt processability of polyketone produeed by palladium cyanide catalysts, after extensive extraction of catalyst residues from the polymers and blending these with other polymers such as styrene/acrylonitrile copolymer. From these studies, it was suggested that thermoplastic properties were possible in principle, and that the polyketone backbone was not inherently unstable in the melt as previously concluded. However, catalyst extraction did not offer a viable production option from a technical and economic viewpoint. 

Crude platinum from South America was also a source of rhodium. It is, however, not known whether it was the same sample in which Wollaston had discovered palladium. Having dissolved a certain amount of crude platinum in aqua regia and neutralized the excess of the acid with alkali, Wollaston first added an ammonium salt to precipitate platinum as ammonium chloroplatinate. Mercury cyanide was added to the remaining solution (here the experience in separating palladium proved useful) and palladium cyanide precipitated. Then Wollaston removed the excess of mercury cyanide from the solution and evaporated it to dryness a beautiful dark-red precipitate was formed which, in the scientist s opinion, was double chloride of sodium and of the new metal. 

History. William Hyde Wollaston discovered rhodium in 1804 in crude platinum ore from South America soon after his discovery of another element, palladium. He dissolved the ore in aqua regia, neutralized the acid with sodium hydroxide (NaOH), and precipitated the platinum by treatment with salmiac (i.e., ammonium chloride, NH Cl) as ammonium hexa-chloroplatinate (NH PtClJ. Palladium was then removed as palladium cyanide by treatment with mercuric cyanide. The remaining material was a red material containing rhodium chloride salts from which rhodium metal was obtained by reduction with hydrogen gas. 

Except iron-palladium cyanide and nickel-nitroprusside, all complex cyanides are coloured. Therefore the colour of the solid settled after completion of the injection will indicate whether a reasonable distribution over the support has been achieved. Precipitation of cyanide... 

Wollaston worked on his assignment in accordance with the mutual agreement He dissolved natural platinum in aqua regia, removed the black residue by filtering and examined the filtrate. The excess of aqua regia was evaporated. When he added mercury cyanide, drop by drop, a yellow precipitate was formed. On calcination a metal was obtained that was not platinum. He named the new element palladium after the asteroid Pallas, discovered in 1802. The discovery year for palladium was 1803. Today we know that it was the almost insoluble palladium cyanide Pd(CN)j that Wollaston precipitated with mercury cyanide. 

Wollaston continued his investigation of the aqua regia solution of platinum in 1803. He then discovered an additional metal in the following way. An aqua regia solution was partially neutralized with sodium hydroxide. Platinum was precipitated with ammonium chloride in the usual way and palladium with mercury cyanide. The common precipitates of chloroplatinate and palladium cyanide were removed by filtering. Hydrochloric add was added to the filtrate and the solution was evaporated to dryness. Wollaston tried to dissolve the residue in alcohol but a beautiful dark-red powder remained undissolved. It proved to be a double chloride of sodium and a new element Wollaston called the new metal rhodium because of the rose colors of its salts. The metal itself was prepared by hydrogen reduction and washing away the sodium chloride with water. 

Palladium cyanide, produced by spot reactions on filter paper impregnated with mercuric cyanide (compare Test 2), is washed free of acid with water and then spotted with an alcohol solution of methyl yellow. The indicator changes to red Idn. Limit 0.4 y Pd). ... 

The dimerization of ethylene into n-butenes by means of tetrachlo-robis(ethylene)palladium in nonhydroxylic media (benzene or dioxane) has been attempted [246]. Other palladium salts (fluoride, bromide, iodide, nitrate) tested in the dimerization of olefins do not form complexes of the type (C2H4),Pd2X4. Palladium cyanide dimerizes ethylene twice as slowly as PdCL, probably on account of deactivation of the catalyst by a polyethylene deposit formed along with the dimer. 

In a related process, 1,4-dichlorobutene was produced by direct vapor-phase chlorination of butadiene at 160—250°C. The 1,4-dichlorobutenes reacted with aqueous sodium cyanide in the presence of copper catalysts to produce the isomeric 1,4-dicyanobutenes yields were as high as 95% (58). The by-product NaCl could be recovered for reconversion to Na and CI2 via electrolysis. Adiponitrile was produced by the hydrogenation of the dicyanobutenes over a palladium catalyst in either the vapor phase or the Hquid phase (59,60). The yield in either case was 95% or better. This process is no longer practiced by DuPont in favor of the more economically attractive process described below. 

Dehalogenation of monochlorotoluenes can be readily effected with hydrogen and noble metal catalysts (34). Conversion of -chlorotoluene to Ncyanotoluene is accompHshed by reaction with tetraethyl ammonium cyanide and zero-valent Group (VIII) metal complexes, such as those of nickel or palladium (35). The reaction proceeds by initial oxidative addition of the aryl haHde to the zerovalent metal complex, followed by attack of cyanide ion on the metal and reductive elimination of the aryl cyanide. Methylstyrene is prepared from -chlorotoluene by a vinylation reaction using ethylene as the reagent and a catalyst derived from zinc, a triarylphosphine, and a nickel salt (36). 

The mechanism of action of the cyanation reaction is considered to progress as follows an oxidative addition reaction occurs between the aryl halide and a palladium(O) species to form an arylpalladium halide complex which then undergoes a ligand exchange reaction with CuCN thus transforming to an arylpalladium cyanide. Reductive elimination of the arylpalladium cyanide then gives the aryl cyanide. 

Trimethylsiloxyphenyl isocyanide enters the cyclization reaction with [MCl2(NCPh)2] (M = Pt, Pd) to yield the homoleptic tetracarbenes 77 (M=Pt, Pd) (97JOM(541)51). Complex 77 (M = Pd) enters an interesting reaction with ammonia to yield the species 78 where two of this benzoxazol-2-ylidene ligands are deprotonated and become C-coordinated benzoxazole moieties, while the other two remain intact. Palladium(II) iodide in these conditions behaves differently yielding the di-Mo-cyanide complex, which in the presence of tetra- -butyl ammonium fluoride gives the dicarbene 79. 

C and weighed. The precipitate is almost insoluble in hot water, but dissolves readily in ammonia and cyanide solutions. Gold is reduced to the metal by the reagent, and platinum (if present in appreciable quantity) is partially precipitated either as a greenish complex compound or as the metal, upon boiling the solution. The precipitation of palladium is not complete in the presence of nitrates. 

Determination of silver as chloride Discussion. The theory of the process is given under Chloride (Section 11.57). Lead, copper(I), palladium)II), mercury)I), and thallium)I) ions interfere, as do cyanides and thiosulphates. If a mercury(I) [or copper(I) or thallium(I)] salt is present, it must be oxidised with concentrated nitric acid before the precipitation of silver this process also destroys cyanides and thiosulphates. If lead is present, the solution must be diluted so that it contains not more than 0.25 g of the substance in 200 mL, and the hydrochloric acid must be added very slowly. Compounds of bismuth and antimony that hydrolyse in the dilute acid medium used for the complete precipitation of silver must be absent. For possible errors in the weight of silver chloride due to the action of light, see Section 11.57. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

In the presence of aqueous acetic acid the 4//-azepi ne 9 yields the hydroxy derivative 10 a. Addition of methanol, in the presence of Sephadex LH20, and cyanide ion in the presence of palladium(II) acetate, are also successful and yield 4,5-dihydro-l //-azepines 10b and 10c, respectively.113... 

An approach to isobacteriochlorins1 ln-e makes use of Pd(II) or metal-free bilatrienes 1 as starting materials. Cyclization of the corresponding bilatriene derivatives is induced by base in the presence of palladium(II) or zinc(II) which exercise a template effect. Zinc can be readily removed from the cyclized macrotetracycles by acid whereas palladium forms very stable complexes which cannot be demetalated. Prior to the cyclization reaction, an enamine is formed by elimination of hydrogen cyanide from the 1-position. The nucleophilic enamine then attacks the electrophilic 19-position with loss of the leaving group present at the terminal pyrrole ring. 

To a solution of l. 47 g (0.03 mol) of sodium cyanide and 4.73 g (0.03 mol) of (-)-(.S)-x-methylbenzylamine hydrochloride in 5 mL of cold water is added 1 g (8.3 mmol) of free ( - )-(.S )-a-mcthylbcnzylaininc in 200 mL of CHjOH. 1.32 g (0.03 mol) of acetaldehyde is added at 0°C and the clear solution is kept at r.t. for five days. After evaporation of the solvent in vacuo, the residue is dissolved in 50 mL of 1 N HC1 and the solution is extracted twice with diethyl ether. After addition of 12 N HCl to adjust the acid concentration to approximately 5 N, the solution is retluxed for 6 h. The HCl is evaporated in vacuo and the residue is dried over sodium hydroxide. The crude. V-x-methylbenzylalaninc hydrochloride is dissolved in 200 mL of 50% ethanol and the pH is adjusted to 6.0 with NaHCOj. To this solution, 3.5 g of palladium hydroxide is added. After hydrogenolysis for 10 h, the catalyst is filtered off and washed with hot water. The filtrate is concentrated to 30%, and the pH is adjusted to 1 with dilute IIC1. The solution is evaporated to dryness and the alanine hydrochloride is extracted with three 20-inL portions of absolute ethanol. After cooling overnight at — 50°C, the precipitated salt is filtered. Pyridine is added to the alcoholic solution to precipitate crude alanine, which is dissolved in 2.5 mL of water. The pH is adjusted with pyridine to 5.5-6.0, and 10 mL of absolute ethanol arc added yield 0.45 g (17% over four steps) mp 290 C [a] 7 + 13.13 (0 = 2.32. 6 N IICi). 

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