With a little water it forms arsenic oxychloride, AsOCl, and with excess of water it is completely decomposed into hydrochloric acid and white arsenic. It combines directly with ammonia to form a solid compound variously given as AsCl3.3NH3 or 2AsCl3.7NH3, or AsCl3.4NH3 Arsenic trifluoride, AsF3, is prepared by distilling white arsenic with fluorspar and sulphuric acid, or by heating arsenic tribromide with ammonium fluoride; it is a colourless liquid of specific gravity 2.73, boiling at 63° C; it fumes in air, and in contact with the skin produces painful wounds.
Halogen Compounds.-Phosphorus trifluoride, PF 3, discovered by Davy, may be obtained mixed with the pentafluoride; by direct combination of its elements; from the tribromide and arsenic trifluoride (Maclvor); from the tribromide and zinc fluoride, and from dried copper phosphide and lead fluoride (H.
Soc., 1877, 25, p. 122), may be obtained by burning the trifluoride in fluorine, from the pentachloride and arsenic trifluoride and from the trifluoride and bromine, the first formed fluorobromide, PF 3 Br 21 decomposing into the pentabromide and pentafluoride: 5PF 3 Br 2 =3PF 5 +2PBr 5.
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.
Phosphorus trifluorodichloride, PF3C12, prepared from chlorine and the trifluoride, is a pungentsmelling gas, which at 250° gives the pentachloride and fluoride.