The tertiary phosphines are characterized by their readiness to pass into derivatives containing pentavalent phosphorus, and consequently they form addition compounds with sulphur, carbon bisulphide, chlorine, bromine, the halogen acids and the alkyl halides with great readiness.
The oxychloride, bromides, and other compounds were subsequently discovered; here we need only notice Moissan's preparation of the trifluoride and Thorpe's discovery of the pentafluoride, a compound of especial note, for it volatilizes unchanged, giving a vapour of normal density and so demonstrating the stability of a pentavalent phosphorus compound (the pentachloride and pentabromide dissociate into a molecule of the halogen element and phosphorus trichoride).
It does not dissociate on heating as do the pentachloride and pentabromide, thus indicating the existence of pentavalent phosphorus in a gaseous compound; dissociation, however, into the trifluoride and free fluorine may be brought about by induction sparks of 150 to 200 mm.
For these reasons, one must assume the existence of pentavalent nitrogen in the diazonium salts, in order to account for their basic properties.
These involve pentavalent nitrogen.