Zinc Group Phosphides

Zinc phosphides have been made chiefly by reactions (1) and (2). Molten zinc unites readily with phosphorus. A compound Zn₃P₂ was prepared by the action of phosphorus vapour on zinc dust; the zinc oxide present was reduced and also gave phosphide. The phosphide was a grey, well-crystallised substance which did not mix with molten zinc. It was sublimable in hydrogen over 1000° C. and when heated in the air oxidised to zinc phosphate. It was not attacked by water, but acids gave phosphine and zinc salts. The hydrophosphide, obtained by the action of phosphine on zinc ethide in ether cooled with ice and salt, is much less stable. It is a white powder which is at once decomposed by cold water giving phosphine and zinc hydroxide.

Cadmium phosphides have been obtained by direct union, as well as by the action of phosphine on ammoniacal cadmium sulphate.

Mercury forms several phosphides, i.e. Hg₃P, Hg₃P₂, Hg₃P₄, which have been described as resulting from the action of phosphine in aqueous solution on mercurous or mercuric salts. These products were easily oxidised by air, halogens and aqua regia.

Boron is hardly affected by phosphorus even at high temperatures, but there are indications of a reaction when BPO₄ is heated with sodium. A phosphoiodide BPI₂ or BPI is made by heating BI₃ with phosphorus, or by bringing the same substances together in CS₂ solution. When the phosphoiodide was heated to 500° C. in hydrogen, BP was left as a maroon-coloured powder, which was not affected by water or mineral acids up to 400° C., but was hydrolysed by boiling alkalies or by superheated steam, giving borates or boric acid respectively and phosphine.11 It was violently oxidised by nitric acid and burned in oxygen. When heated at 200° C. in a current of ammonia the phosphorus was displaced by nitrogen and the very stable boron nitride, BN, was formed.