occur through formation of ruthenium(II1) species and free radicals.
The major change in industrial chemical processes towards homogeneous catalysis and the reasons for this were surveyed by Dr. D. Forster of the Monsanto Company, St. Louis, Missouri, in the last of the four main lectures. The catalysis of methanol carbonylation by a rhodium in place of a cobalt complex has the advantages of operation at lower temperatures and pressures with a higher selectivity and the use of a very much lower metal concentration in the catalyst. The water gas shift reaction and the fundamental chemistry involved in its catalvsis by rhodium complexes in acidic media were also reviewed, as was the catalysis of olefin hydrocarboxylation by rhodium and iridium complexes.
Cluster Compounds of the Platinum Metals
The session on cluster compounds of the platinum metals was opened by Dr. G. Longoni of the lrniversity of Milan who described the synthesis and characterisation of high nuclearity carbonyl clusters of platinum and rhodium and suggested that these clusters may till the gap between co-ordination and solid state chemistry. Professor J. Shapley of the Ihiversity of Illinois then discussed the syn- thesis of a range of cluster compounds where a metal-hydride bond was used to couple two metal centres in inter- and intramolecular reac- tions. The synthesis of heterometallic cluster compounds containing rhodium was the subject of the lecture by Professor F. G. A. Stone of Bristol lhiversity who showed that tungsten carbvne complexes and compounds with metal-metal double bonds can react with simple co-ordination compounds to give a variety of cluster complexes.
in the world, were outlined by Mr. Howard Hush who emphasised that the concentration of these metals in the ore amounts to only 3 parts per million and that therefore some ten tons of rock have to be mined and brought to the surface to yield one ounce of platinum.
The separation and refining of the six platinum group metals to the high degree of purity essential in many of their applications involves a complicated series of selective pre- cipitation operations from solutions containing these metals. Even in favourable conditions repeated dissolution and reprecipitation are required, and in order to improve on this proce- dure separation techniques have been developed based upon solvent extraction. A ioint paper by I h . M. J. Cleare and Mr. R. A. Grant of the Johnson Matthey Research Centre and Mr. P. Charlesworth of Matthey Rustenburg Refiners outlined the new method and related its mechanism to the complex chemistry of the platinum metals. The advantages of this approach include a reduction in processing time, a lower lock-up of valuable metals, a higher yield at lower cost and the possibilities of automation.
The industrial relevance of the chemistry of the platinum metals was discussed by Dr. D. T. ‘Thompson, also of the Johnson Matthey Research Centre at Sonning Common. Dealing briefly with the extensive use of palladium in liquid phase hydrogenation, with platinum on carbon in phosphoric acid electrolytes in fuel cells, the oxidation of ammonia to nitric acid over rhodium-platinum gauze catalysts and the hydrocracking and reforming of hydrocarbons over supported platinum metal catalysts, he turned to the relatively new subject of industrial homogeneous catalysis, first used for
a major process in the version of ethylene to
early 1960s for the acetaldehyde. Since
As a source of background information on the platinum metals, their extraction, refining and applications, a further series of papers was
rhodium catalysts hydroformylation
have been introduced for the of olefins and the carbonyla-
presented. Operations at Rustenburg Platinum Mines, the largest source of the platinum metals
mercial development transformations were
of a number of organic emphasised, such as the
Platinum Metals Rev., 1981, 25, (4)