Di-, Tri-imido- and -amido-thiophosphates

A great variety of Di-, Tri-imido- and -amido-thiophosphates, chiefly in the form of their ammonium salts, was obtained by the action of ammonia, usually in the liquid form, on phosphorus pentasulphide. Some of the ammonia could be driven off by heating under reduced pressure, leaving the acid salts.

Gaseous ammonia at ordinary temperatures reacted with phosphorus pentasulphide giving a hexammoniate, P₂S₅.6NH₃, and perhaps a heptammoniate, P₂S₅.7NH₃. The former may rearrange itself so as to give tetrammonium diimidopentathiodiphosphate:—



The addition of another molecule of ammonia, either by means of liquid ammonia or by saturating with the gas, yields a substance having the empirical composition of the heptammoniate, which, however, may consist of equal mols of (a) diammonium nitrilodithiophosphate, N≡P(SNH₄)₂, and (b) triammonium imidotrithiophosphate, HN=P(SNH₄)₃. On treatment with liquid ammonia the nitrilo- compound dissolved and could be obtained by evaporating the solvent, while the imido-compound, being sparingly soluble, crystallised. The nitrilo-compound lost one or more molecules of ammonia when heated in a vacuum. When treated with KOH or NaOH it gave hydrated dipotassium or disodium compounds as oils, the latter of which could be made to crystallise. Characteristic insoluble salts were those of lead (yellow) and of barium (white). The imido-compound, HN=P(SNH₄)₃, was a white crystalline substance which deliquesced in moist air and gradually lost ammonia. It was insoluble in all ordinary solvents. It was hydrolysed slowly by water and smelt of H₂S. It lost one molecule of NH₃ when warmed to 50° C. in a vacuum. By heating at gradually increasing temperatures from 90° to 180° C. in an atmosphere of H₂S it was transformed into the free acid.