Boron phosphide, BP

Boron phosphide, BP, is prepared by heating boron phospho-iodide to 450°-500° in a current of hydrogen. The iodine can also be removed from the phospho-iodide by heating with mercury or silver. Another method of preparation consists in heating the compound BBr₃.PH₃ to 300°, when hydrogen bromide is eliminated.

Boron phosphide is a light, amorphous, maroon-coloured powder, insoluble in the usual inorganic and organic solvents. It burns in chlorine in the cold and in bromine when warmed; at 200° it burns brilliantly in oxygen, and it also reacts with heated sulphur. It is not affected by iodine, nitrogen, phosphorus, or arsenic even at a red heat. It is attacked by numerous metals at a red heat, and is easily oxidised by concentrated nitric acid or fused alkali nitrates.

When heated in hydrogen at 1000°, a brown boron subphosphide, B₅P₃, is produced which is much less reactive than the phosphide.