Trimetaphosphimic Acid, [NH(POOH)]₃

Trimetaphosphimic Acid, [NH(POOH)]₃, was obtained by the action of water on a sodium acetate ethereal solution of P₃N₃Cl₆ (q.v.,). The acid was soluble in water, and was obtained as a colloidal substance on evaporation. It gave a series of salts. The trisodium salt, Na₃H₃P₃N₃O₆.4H₂O, crystallised in rhombic prisms below 80° C., whilst above 80° C. a monohydrate was formed. The trisilver salt was precipitated in plates when silver nitrate was added to a nitric acid solution of the sodium salt. A hexasilver salt, Ag₆P₃N₃O₆, was thrown down as a white precipitate when an excess of ammoniacal silver nitrate was added to a solution of the trisodium trimetaphos- phimate. On heating or long standing in solution, especially in the presence of strong acids, the metaphosphimates are hydrolysed into ammonium salts and phosphoric acid. Several cyclic structures are possible for the acids; the metaphosphimic ring contains the radicals —NH—PO(OH)—, the nitrilophosphoric ring the radicals —N=P—(OH)₂—. On the former hypothesis, di- and tri-meta-phosphimic acids are:—

and , respectively.