Protactinium chlorides

In the fall of 1934, Dr. Grosse reduced this pure oxide by two methods and obtained from it the metal protactinium, which is even rarer than radium, but much more permanent in air. In die first method, he bombarded the oxide on a copper target, in a high vacuum, with a stream of electrons. After a few hours, he obtained a shiny, partly sintered, metallic mass, stable in air. In his second method, he converted the oxide to the iodide (or chloride or bromide) and cracked it in a high vacuum on an electrically heated tungsten filament, according to the reaction ... 

Niobium and tantalum(V) chlorides and tantalum(V) bro-midef yield the complexes MX6-CHSCN, and protactinium(V) bromide yields orange PaBr8 3CH8CN if the same procedure is used. 

Although protactinium(V) chloro complexes can also be prepared using methyl cyanide as the solvent (32) (cf. PaBrg" and Pale ), the use of thionyl chloride has several advantages. Thus, it means that one can start with protactinium(V) hydroxide and not the pentachloride, thionyl chloride itself affords protection against atmospheric moisture and dry-atmosphere boxes are not necessary for the preparations, and, in addition, protactinium(V) concentrations up to 0.5 M have been obtained by dissolving the hydroxide in thionyl chloride (75). Such solutions are quite stable in contrast to the hydrolytic condensation reactions which occur in concentrated hydrochloric acid at Pa(V) concentrations as low as 10 M. 

Protactinium monocarbide was prepared by carbothermic reduction of the pent-oxide and treated with iodine (400 C), bromine (350 C), and thionyl chloride (200°C) in evacuated sealed tubes to give the appropriate pentahalide. The tetraiodide was obtained by interaction of the monocarbide with either protactinum pentaiodide (600 °C) or mercury(ii) iodide (500 °C) in vacuo. 

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