Precipitation of Pd metal

Dlphenyl-2-benzoylethane (2),2 A mixture of benzylideneacetophenone 1 (2.08 g. to mmol) and paladkim acetate (2.0 g, 10 mmol) in benzene (150 ml) end AcOH (40 mL) was teOuxed under Mining unto the precipitation of Pd metal ceased. The insoluble Pd was fltered ell and the Orate after wasting wlh water was concentrated in vacuum. The residue,... 

Black precipitate of bismuth metal Violet coloration with stannous salts the following interfere strong reducing agents (hydrogen sulfide, dithionites, sulfites, and selenites) also, U, V, Te, Hg, Bi, Au, Pd, Se, Sb... 

From mixtures of platinum metals, Ru and Os can be separated by distillation as volatile tetroxides, and a double precipitation of Pd, Rh, and Ir hydroxides (with Fe used as collector) at pH 8 enables them to be separated from platinum. 

In contrast to the usual Wacker-conditions, optimum rates and catalyst stability in the Pd/batophenanthroline-catalyzed olefin oxidations was observed in the presence of NaOAc (pH = 11.5). Under such conditions, the catalyst-containing aqueous phase could be recycled with about 2-3 % loss of activity in each cycle. In the absence of NaOAc precipitation of Pd-black was observed after the second and third cycles. Nevertheless, kinetic data refer to the role of a hidroxo-bridged dimer (Scheme 8.1) rather than the so-called giant palladium clusters which could easily aggregate to metallic palladium. 

The Wacker oxidation was discovered by Smidt and co-workers at Consortium fiir Electrochemie (a subsidiary of Wacker Chemie and Farbwerken Bayer). It is actually a combination of known reactions and thus not a catalytic reaction in the strictest sense (Scheme 1). The first and most basic reaction, the oxidation of ethene in aqueous solution was first discovered by Phillips in 9AP The precipitation of palladium metal from a palladium(II) chloride solution was used as a test for olefins. However, it was the discovery by Smidt and co-workers that the Pd(0) formed could be regenerated by cupric chloride that made the reaction a commercial success. The final step, the oxidation of CuCl to CuCl2 is one of the fastest reactions in inorganic chemistry, The three reactions add up to the simple air oxidation of ethene to ethanal. At one point over two billion pounds a year of ethanal was produced by the Wacker process. Presently, the Monsanto acetic acid process has largely replaced the Wacker procednre.t" ... 

Most other metal ions give precipitates with salicylaldoxime only in neutral or weakly alkaline solutions. Palladium and gold salts in acetic acid solutions also give precipitates of Pd(C7He02N2) 2 and metallic gold, respectively. 

Ru to Pt. The reaction of gaseous HN3 with Pd or Pt surfaces produces highly explosive layers of azides at ambient temperature [71]. The catalytic decomposition of HN3 in He on the surface of the heavier metals of the platinum group at 320 to 360 K quantitatively yields N2 and NH4N3 [63]. The precipitation of Pd from aqueous HNO3 as Pd(N3)2 is complete, when at least twice the molar quantity of HN3 is used [72]. 

---