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Palladium Chloride Catalyst in Olefin Oxidations

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Palladium Chloride Catalyst in Olefin Oxidations Palladium Chloride Catalyst in Olefin Oxidations NEW PRODUCTION PROCESSES FOR ACETONE AND METHYL ETHYL KETONE The use of noble metal salts or compounds being re-oxidised. This is accomplished by in homogeneous catalysis is relatively new, and an instantaneous reaction with cupric chloride the oxidation of ethylene to acetaldehyde which is present in considerable excess. using palladium chloride as catalyst is among During the re-oxidation of the palladium the first industrial scale processes in this the cupric chloride is reduced to cuprous field (I, 2). chloride; this is in turn oxidised back to Since this process was first reported it has cupric chloride by oxygen or air. Under the become known as the Wacker Process and conditions of operation the rate of oxidation has found wide acceptance. Studies have of the cuprous chloride is of the same order been intensified by its originators, the as the rate of reduction of cupric chloride. Consortium fur Elektrochemische Industrie The individual reactions represented by GmbH, Munich, and by others to extend its equations I, 2, 3 and 4 are thus summarised scope for the production of other industrially by equation 5: important compounds by analogous tech- I. R-CH=CH, !-PdCl, I-H,O -+ niques. R-CO - CH, +I'd +zEICl In a paper presented at the Sixth World Petroleum Congress in Frankfurt in June 2. Pd+2CuCL---tPdClz +2CuCI this year Dr Jiirgen Smidt, Director of the 3. R -CH =CH, -1-ZCUClz-kH,O -+ Consortium, and Dr Hans Krekeler, of R-CO -CH, i2C~Cl+-2HCl Farbwerke Hoechst AG, Frankfurt, described 4. ~CUC~+&O,+~HC~-->ZCUCI,+H,O the production on a pilot plant scale of PdCl,; CuCI, acetone and methyl-ethyl-ketone from propy- 5. R - CH = CHz-1- 4 0 2 + lene and butylene streams using palladium R -CO-CH, chloride as catalyst (3). As in the oxidation (R= -CH, or -C,H,) of ethylene to acetaldehyde, the oxidation of the olefin is believed to proceed via the Comparison of the rates of absorption formation of a PdC1,-olefin x-complex, (equal to the respective rates of reaction) of followed by hydrolysis of the latter : the lower olefins in aqueous solutions of palladium chloride/cupric chloride at 70°C R-CH=CH, -t [PdCl& -+ and atmospheric pressure shows marked [PdCl,R ~ CH CHJ + C1- differences between ethylene, propylene and and the isomers of butylene. The absorption rate [PdClaR ~~ CH =CH,]-+HzO -+ of propylene is about one-third, and the R-CO -CH, -1 Pd IzH++3Cl- rate for butylene-r about one-quarter, of During the reaction the palladium chloride that of ethylene. The differences in rates of is reduced to metallic palladium, and in absorption of the butylene isomers are order to carry out the process continuously considerable-the absorption rate of a com- the palladium must be kept in solution by mercial mixture of 60 per cent butylene-I, Platinum Metals Rev., 1963, 7, (4),132-133 132 34 per cent butylene-2 and 6 per cent butane Among the advantages of the direct is one-seventh to one-eighth of that of oxidation of olefins using palladium chloride ethylene; the absorption rate of a 95 per cent as a homogeneous liquid phase catalyst is mixture of butylene-2 with butane is less that mixtures of olefins and saturated than one-fourteenth that of ethylene. hydrocarbons may be used as feedstocks without prior separation and that the products Commercial Process are obtained in high purity. Only one main Operation of the oxidation process on a product is obtained, and its output is not commercial scale is generally carried out dependent on the manufacture or sale of a using mixtures obtained from cracking second product. The life of the palladium processes and containing about go per cent chloride/cupric chloride catalyst solution is olefin with corresponding paraffins. The virtually unlimited, as homogeneous catalysts latter do not take part in the reaction and are not prone to deactivation by poisoning as act only as inert diluents. Olefin reaction are supported heterogeneous catalysts. and oxidation of the catalyst solution are H. C. usually carried out in separate stages, the removal of the acetone or methyl-ethyl-ketone and their subsequent purification being References achieved by steam-stripping and distillation operations. Over 95 per cent conversion of I J. Smidt et al., Angewandte Chernie, 1959, 71, 176 the olefins to the ketones is obtained, and 2 J. Smidt, W. Hafner, R. Jira, R. Sieber, J. final yields of purified acetone and methyl- Sedheier and A. Sabel, ibid., 1962, 74, 93 ethyl-ketone exceed 92 per cent and 85 per 3 J. Smidt and H. Krekeler, Paper 40, Section IV, 6th World Petroleum Congress, Frankfurt, cent respectively. June 1963 New Homogeneous Catalysts for Hydrogenation PLATINUM-TIN CHLORIDE COMPLEXES None of the noble metal complexes stannous chloride and chloroplatinic acid in previously found active for homogeneous which the platinum is in the f2 oxidation hydrogenations has efficiently catalysed the state were characterised as their triphenyl- hydrogenation of ethylene and acetylene, but methylphosphonium salts. it has recently been reported by workers at In a second communication, from Professor du Pont in a letter to the American Chemical Wilkinson and his co-workers in the Inorganic Society (I) that the complex compound Chemistry Research Laboratories of Imperial formed by interacting chloroplatinic acid College (2), the preparation of analogous with stannous chloride dihydrate in methanol Rh(I), Ru(I1) and Ir(I1) complex anions in the absence of air will catalyse these having the formulae [RhCl(SnCl,)]~;, reactions at room temperature and atmos- [RUC~~(S~C~,),]~-and [IrClp(SnC1,)2]2- 1s pheric pressure. Acetylene yields a mixture also described; these were isolated as their of about 25 per cent ethylene and 75 per cent tetra-alkylammonium salts. ethane. G. C. B. The role of the stannous chloride is to accelerate the rate at which the unsaturated References hydrocarbon becomes co-ordinated to the I R. D. Cramer, E. L. Jenner, R. V. Lindsey and platinum, and also to stabilise the platinum V. G. Stolberg,J. Am. Chem. SOC.,1963, 85, compound against reduction by hydrogen. (111, 1691 The mechanism of the catalysis is not dis- 2 A. G. Davies, G. Wilkinson and J. F. Young, cussed, but complex anions derivated from ibid., 1692 Platinum Metals Rev., 1963, 7 , (41,133-133 133 .
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