Tantalum bromides Preparation

Preparation of Niobium(V) and Tantalum(V) Halides. The niobium(V) and tantalum (V) chloride and bromide were prepared in a system of sealed, evacuated bulbs by reacting the pure metal with gaseous halogen. For the chlorides the metal was maintained at 300° to 350° under a chlorine pressure of approximately 70 mm. of Hg the chlorine pressure was maintained By keeping the liquid chlorine immersed in a dry ice-acetone bath. For the bromides the metal was maintained at a temperature of 400° to 450° under a bromine pressure of approximately 250 mm. of Hg, maintained by leaving the liquid bromine at room temperature. 

The action of carbon tetrachloride or a mixture of chlorine with a hydrocarbon or carbon monoxide on the oxide.—H. N. Warren 9 obtained aluminium chloride by heating the oxide to redness with a mixture of petroleum vapour and hydrogen chloride or chlorine, naphthalene chloride or carbon tetrachloride was also used. The bromide was prepared in a similar manner. E. Demarpay used the vapour of carbon tetrachloride, the chlorides of chromium, titanium, niobium, tantalum, zirconium, cobalt, nickel, tungsten, and molybdenum H. Quantin, a mixture of carbon monoxide and chlorine and W. Heap and E. Newbery, carbonyl chloride. 

Tantalum(V) bromide may be prepared by bromination of tantalum carbide or of mixtures of tantalum (V) oxide and carbon. It is most conveniently prepared by reaction between the elements,1 either at atmospheric pressure, using an inert carrier gas, or in vacuo. The reaction of bromine vapor with tantalum powder in a nitrogen atmosphere forms the basis of the procedure outlined below. 

The a-rhombohedral form of boron (a-boron) was first reported by L. V. McCarty, J. S. Kasper, F. H. Horn, B. F. Decker, and A. E. Newkirk.1 Of the many allotropic forms of boron, it has the simplest structure.2 It may be prepared by the pyrolysis of boron(III) iodide on a tantalum filament at 800-1000°C., but the product is usually contaminated by other allotropic varieties of boron.1,4 Recently, Hagenmuller and Naslain showed that boron(III) bromide may be reduced by... 

This apparatus has been successfully used in the preparation of niobium(V) bromide, tantalum(V) bromide, tungsten(YI) chloride, and molybdenum(V) chloride. ... 

Fig. 311. Preparation of tantalum (IV) bromide, a) boat containing TaBrs f) cold trap h) grooved stopcock for fine flow regulation s) induction coil ...

Fig. 312. Preparation of niobium (V) and tantalum (V) bromides, a) receiver /)cold finger rn) boat containing the metal o)tubular electric furnace r)reactor tube s) saturation tube.

More care has to be taken for the preparation of binary chlorides and bromides, RCI3 and RBr3. The anhydrous salts are moisture-sensitive and they are obtained as (hepta- or hexa-) hydrates upon crystallization from hydrochloric or hydrobromic acid solutions. Simple dehydration of the hydrates in an HCl or HBr gas flow, respectively, appears to be possible (Seifert et al. 1985) but the less skfllliil chemist produces halide products more or less contaminated with oxyhahde, ROX. Sublimation of the raw product in an all-tantalum apparatus at higher temperatures (650 C to 950 C) and low pressures (10 bar) produces pure trihalides (with the exception of the rare-earth elements europium and 3dterbium where mixed-valent (+2/+3) or even dihalides are obtained under these conditions). 

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