------------------------------------------- Preparation of Palladium(II)Chloride, PdCl2 ------------------------------------------- From Brauer's: Palladium (II) Chloride The anhydrous salt is prepared by heating loose palladium sponge (contained in a porcelain boat set in a glass tube) to a dull red heat in a stream of Cl2. According to Krustinsons, the decomposition pressure of PdCl2 reaches 1 atm. at 738°C. By dissolving finely divided Pd in conc. HCl through which Cl2 is bubbled, one obtains a solution in which both H2PdCl4 and H2PdCl6 can be detected. Concentrating the solution also yields a residue of PdCl2. PdCl2 Solution for the Detection of CO Winkler gives the following method for preparing this solution. Pure Pd (0.2 g.) is dissolved with gentle heating in about 10 ml. of aqua regia. The solution Is evaporated to dryness in a 50-ml. porcelain dish placed on a steam bath. The residue is dissolved in 10 ml. of 20% hydrochloric acid and the solution is again evaporated to dryness; this last procedure is repeated three times. The resulting residue, which is now completely nitrate-free, is mixed with 2 g. of KBr and dissolved (gentle heating) in 10 ml. of 1 N HCl. After dilution to about 150 ml. with water, a few particles of pumice and 1 ml. of alcohol are added to the solution. which is then boiled for about 10 minutes in an Erlenmeyer flask in order to reduce any Pd (M) not decomposed during the drying to Pd (H) and to drive off the excess alcohol. After cooling. 2.5 g. of CH3COONa . 3 H2O is dissolved In the liquid. The solution Is filtered through a small wad of cotton wool and diluted to 200 ml. with the water used for washing the cotton wool. The clear, reddish- brown liquid, which contains 0.1% palladium. is stable when stored in a flask provided with a ground-glass stopper. To be on the safe side, It Is best to filter the solution before use; It should be stored In the dark. REFERENCES: J. Krustinsons. Z. Elektrochem. 44, 537 (1938); L. Winkler. Z. Anal. Chem.100, 321 (1935); 97, 18 (1934); also describes analytical methods for detecting CO with PdCI2 solutions. Explicit directions for the preparation of palladium catalysts using PdCI2 are given by R. Mozingo in Organic Syntheses, collective vol. III, p. 685 (Wiley, New York, 1955). - - - - - J. J. Berzelius prepared palladium dichloride or palladous chloride, by evaporating to dryness a solution. of palladium in aqua regia, and dehydrating the residue by a gentle heat. L. R. von Fellenberg obtained the chloride, as a rose-red sublimate, and a garnet-red mass, by heating palladium sulphide in a current of chlorine; and E. H. Keiser and M. B. Breed obtained it as a sublimate by heating spongy palladium to dull redness in chlorine; the anhydrous chloride can be distilled at a low red-heat in a current of chlorine when it yields a sublimate of deliquescent, dark red, acicular crystals. N. W. Fischer obtained a solution. of the chloride by exposing palladium to hydrochloric acid and air; the process of dissolution is then a slow one. If chlorine is passed into hydrochloric acid in contact with palladium, the metal dissolves quickly to form the dichloride; and if nitric acid is added to the hydrochloric acid, some palladous nitrate is formed. By evaporating the hydrochloric acid solution over quicklime, the chloride is obtained in reddish-brown, prismatic crystals, which, if free from nitric acid, remain dry. L. N. Vauquelin found that when palladium is dissolved in aqua regia, and the nitric acid removed by repeated evaporation with hydrochloric acid, there remains a brownish-yellow, crystalline mass, which, according to the analyses of R. J. Kane, is the dihydrate, PdCI2-2H2O. The dichloride obtained by dehydrating the dihydrate is a browniish-black mass; the sublimed salt appears as rose-red, or dark red, acicular crystals; the unsublimed salt is a garnet-red crystalline mass. The dihydrate forms reddish-brown, prismatic crystals. V. M. Goldschmidt said that the crystals are probably rhombohedral. L. Pauling discussed the structure. E. H. Keiser and M. B. Breed gave 2.5 for the sp. gr; and G. Beck, 4.00 for the sp. gr. at 18 degrees and 44 for the mol. vol. J. J. Berzelius observed that the anhydrous salt fuses without decomposition when gently heated in a glass vessel; when fused in a platinum vesed, it acquires a bluish-green colour by taking up platinum chloride. When.strongly heated, chlorine and palladium are formed. F. Puche found that the dissociation begins at 600 degrees, and attains one atmosphere of pressure at 920 degrees. References: J. J. Berzelius, Pogg. Ann., 13, 454 (1828); Schweigger's Jour, 7, 66 (1813); L. R. von Fellenberg, Pogg. Ann., 50, 61 (1840); E. H. Keiser and M. B. Breed, Chem. News, 69, 197, 211 (1894), N. W. Fischer, Schweigger's Jour., 51,197 (1827), Pogg. Ann. 9, 256 (1827); 10, 607 (1827); L. N. Vauquelin, Ann. Chim. Phys., (1), 88, 167 (1813), R. J. Kane, Phil. Trans., 132,275 (1842); V. M. Goldschmidt, Skrift. Norske Akad. Oslo, 5 (1925); L. Pauling, Proc. Nat. Acad. 15, 709 ( (1929); Puche, Compt. Rend. 200, 1206 (1935) Interestinly, the aqua regia method appears to be the very first method, and from the above, it can be seen that oxidation methods not using chlorine gas or nitric acid proceed very slowly, though IMHO if violent agitation under pressure such as in a SRV were employed, quicker results should be attained. As far as electrochemical methods, these abstracts were found, lending some credence to the science behind Uncle Fester's method: Electrochemical solution of palladium in hydrochloric acid. A. I. Vol'fson, A. I. Ryazanov, and G. D. Chigrinova. Zhur. Vsesoyuz. Khim. Obshchestva im. D. I. Mendeleeva 5 , 712(1960).-Powdered Palladium, placed on a graphite plate-type anode, was electrochemically. dissolved in a cell with a diaphragm. The current efficiency in I0 N HCI at 25-32 degrees with an anodic current density of 6.25 amp./sq. dm was 96% over 11.5 hrs. The resulting solution. contained 342 g. PdCl2./L Increasing the temperature of the electrolyte to 55-60 degrees lowered 71 to 95.2% over 14 hours., giving a solution. containing. 420 g. PdCl2/L. Increasing current density. to 12.5 amp./sq. dm., at 24-36 degrees, reduced the current efficency to 68.7%, giving a solution. containing. 491 g. PdCl2/L. in 12.75 hrs. The decrease in current efficnecy was ascribed to the passivation of the anode by solutionns. containing. 330-340 g. PdCl/L. A solution. contg.332 g. PdCl2/L. was obtained with current efficiency of 99.5% over 10 hrs.with 6 N HCI in the anolyte and IO N KCI in the catholyte at 25-32 degrees. Palladium was not deposited on the cathode in any of the experiments. Electrochemical method for preparation of salts. A. I. Ryazanov, G. D. Chigrinova, and A. I. Vol'fson. U.S.S.R. 138,922. Appl. July 28, 1939. PdCl2,TeCI4,and BiCI3 are obtained by anodic dissolution. of the respective metals in HCI in an electrolytic bath with 3 chambers. To intensify the process, the metals are used as powders and placed on graphite plate-type electrodes, provided with perforations for elimination of the salt solution. Electrochenucal solution of palladium in hydrochloric acid. A. 1. Vli'fson, A. I. Ryazanov, and G. D. Chigrinova. Zhur. Priklad. Khim 34, 173-6 (1961).-To develop, a commercial. electrochernical. process for the production of PdCl2 the anodic solution. of Palladium. powder and solid, in HCI was studied in a cell without a diaphragm. The powder was placed on a horizontal graphite anode. The solubility of Palladium in HCI at 20 degrees increased from 46.0 g./L. in 0..3 N HCI to 902.0 g./L. in 11 N HCL The anode potential was at the lowest electronegativity value in 6 N HCl Electrolysis of palladium anode in 6 and I0 N HCl (S - 542.0 and 810.0 g/L., with cathodic current.densities of 12.5-50 and anodic current.densities. of 6.25-25 amp./sq. dm. at 25 degrees produced solutions with concentration of 350 g/L. with a current efficiency of 90.2%.Increasing current density. from 7.5 to 12.5 and 25 amp./sq. .dm.. in I0 N HCI lowered current efficiency from 90.2 to 71.2 and 66.6% and p,from350 to250 and 47.2g./L. In 6 N HCl on electrolysis with current density of-6.25 amp./sq. dm., current efficiency of- 100%, and concentration 55.4 g/L.using the duration of electrolysis from 1 to 12.5 hours.in 10 N HCl with current density of 7.5 amp./sq. dm. lowered current efficiency from 100 to 90.2% and increased concentration from 20 to 350 g/L. Pallaium deposited on the Platinum cathode formed a slime which contaminated the electrolyte. Also, this abstract gives a thermochemical method of production. Chloridation of platinum metals with ammonium chloride. O. E. Zvyagintsev and L. D. Plaksina. Izvest. Sektora Platiny i Drugikh Blagorod. Metal. Inst. Obshchei i Neorg. Khim., Akad. Nauk S.S.S.R. No. 24, 121-8(1949).- Platinum and Palladium were chloridated with NH4Cl 1:2 at 250-400 degrees C.The reaction is more effective when metals are finely divided and in the presence of Fe and Cu but not Ni. Excess NH4Cl gave no advantage. Chloridation dropped sharply at temps. above 450 degrees. Palladium is chloridized more easily than Platinum. - - - - - While no practical work in the recycling of palladium has been attempted by any bees yet, long ago a couple of Dutch chemists from Amsterdam solved this type of problem in US Pat 3210152. It claims to be effective in recycling palladium chloride from spent organic reaction mixtures, which IMHO includes benzoquinone. As in some other inventions of interest to the Hive, this process requires completely anhydrous conditions. The Shell patent referenced above is titled "Regeneration of Metal-Containing Reaction Components and Process for the Production of Palladium Chloride", since this method requires no isolation of the reduced palladium, and directly produces palladium chloride, it would seem best for the purposes of those here. The solvent is glacial acetic acid and the required reagents are oxygen, hydrogen chloride and nitric oxide, the latter can be prepared by by dropping concentrated sulfuric acid onto sodium nitrite covered with two to three times it's weight in water [JACS 47, 2170 (1925)]. Impurities in the gas charge contribute most to catalyst degradation, another process for regeneration of wacker oxidation catalysts is in German Patent 1143499. This method is applicable to the reduced palladium recovered by filtration, or the reduced catalyst that tends to adhere to labware. Quite possibly, it may serve as an alternative method of preparing palladium chloride from palladium metal, it ends much the same as Bright Star's synthesis on Rhodium's page, using cuprous chloride and oxygen to form palladium chloride. Another reference of possible interest is Jap. Pat. 13,354 (1963), disclosing a simple method of separating cupric and palladium chloride.