Scandium trifluoride

The ore thortveitite is crushed and powdered. It is mixed with a large excess of ammonium hydrogen fluoride and heated at about 400°C for several hours in a platinum container under a stream of dry air. Silica is converted to volatile silicon tetrafluoride and swept out with dry air. Scandium oxide is converted to scandium trifluoride, SCF3 ... 

High-purity scandium oxide (i.e., 99.0 to 99.99 wt.% Sc) is an initial raw material used to produce a metallic scandium. After fluorination of the oxide, pure scandium is then prepared by calciothermic reduction of scandium trifluoride (ScFj) with pure calcium metal. The metallic scandium obtained undergoes subsequent refining by vacuum distillation, which ensures a purity of metal at the level 99.99 to 99.999 wt.% Sc. Tentative annual demand for ultrapure metallic scandium for different fields of application is estimated for the near future at 800 to 1000 kg per year. Total annual world production in 2000 of scandium, excluding China, was about 30 kg. Union Carbide and Johnson Matthey, as well as the research company Boulder, are the main manufacturers of scandium products from thortveitite, wastes of uranium, and tungsten production. 

The preparations of rare-earth trihalides can be found in various books (2-8) and in Taylor s review (2 ). This review, however, did not include the preparation of scandium and yttrium trihalides, and only covered the preparation of the trifluorides very briefly. We have reviewed the preparation of all the trihalides (including scandium and yttrium) from Taylor s review up to June 1979 and have also included some methods and references missed by Taylor. Although we have mentioned all the methods available for the preparation of the trihalides, emphasis has been placed on the methods used since Taylor s review, and these have been referenced fully, whereas for the other methods, Taylor s review is recommended as a source of references. 

All four trihalides of scandium are known. The trifluoride is very slightly soluble in H2Q. and is precipitated front scandium nitrate, Sc(NC>3)3,... 

A comparison of the volumes per formula unit for the trifluorides is more complicated than for the difluorides because of the changes in structure type. If these changes are ignored, then some correlation with electronic configuration is possible. For the first transition series the volume decreases from scandium to chromium, increases from chromium to iron, and decreases to cobalt. This is as expected for the characteristic ligand-field stabilization effects (49), comparable with those for the difluorides. In the second series, there is a decrease from... 

Scandium is a soft and silvery metal it is electropositive, tarnishing rapidly in air and reacting with water. It is generally obtained by chemical reduction, for example the reaction of the trifluoride with calcium. It has only one natural isotope, Sc. 

Higher coordination numbers of 8 -F 1 are adopted in the LT-YF3 type by the trifluorides of the larger ions TP+, bP+ and the smaller rare-earth ions Sm to Ln. The tysonite or LaF3 type with CN 9 + 3 is found for the trifluorides of the larger 4f and the 5f elements (see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry). 

Trimethylsilyl azide can be employed as an azide source for a diastereoselective substitution of hydroxy or acetoxy groups in a-position to the diene system in the presence of scandium(lll) triflate or boron trifluoride etherate. A 1,5-nucleo-... 

Intriguingly, boron trifluoride, the Lewis acid of choice for the cobalt alkyne cyclopropane, did not give any of the cycloaddition product on reaction with an aldehyde. Instead optimization studies showed that a catalytic quantity of scandium triflate induced the reaction. Also, there are marked differences in the reactivity and stereocontrol achieved. In this case, electron-rich aldehydes give better yields and for the first time with a cobalt alkyne, good stereocontrol. Again, no reaction was seen at all without the activating cobalt group. 

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