Phosphorus Chloronitrides

It was shown by Liebig in 1832 that when PCl₅ was treated with dry ammonia and the product heated, a white stable sublimate was obtained. The empirical formula PNCl₂ was assigned to this substance by Laurent, while Gladstone and Holmes on account of its high vapour density represented it as (PNCl₂)₃.

Equal mols of PCl₅ and NH₄Cl may be heated to 150° C. in a sealed tube which is opened occasionally to permit the escape of hydrogen chloride formed according to the equation

nPCl₅ + nNH₄Cl = nPNCl₂ + 4nHCl

The product was extracted with petroleum ether and the insoluble part distilled up to nearly a red heat. The distillate, after washing with hot water, was redistilled under reduced pressure, and yielded the fractions described below. Alternatively, 120 to 130 grams of ammonium chloride may be added to 400 grams of phosphorus pentachloride dissolved in a litre of sym-tetrachloroethane, and the mixture boiled under a reflux condenser guarded by a calcium chloride drying tube until hydrogen chloride is no longer evolved. This requires about 20 hours. The ammonium chloride is filtered off and the solvent distilled away in a water-pump vacuum. The residue, about 220 grams of a pasty material, is freed from oil by suction and by washing with benzene at 0° C. This leaves about 100 grams of a crystalline powder which is recrystallised from benzene and fractionated at a low pressure. The fractions may be recrystallised from benzene.

When the powder is heated above 255° C. it changes to a colourless transparent solid, while at 350° C. there is produced a colourless elastic mass which resembles rubber in appearance and in its property of swelling when placed in benzene.

Melting- and boiling-points of the phosphorus chloronitrides or phosphonitrilic chlorides

Formula	(PNCl2)3	(PNCl2)4	(PNCl2)5	(PNCl2)6
Melting-point, ° C	114	123.5	41	91
Boiling-point (13 mm.), ° C	127	188	224	262
Boiling-point (760 mm.), ° C	256.5	328.5	Polymerises	Polymerises