PHOSPHONIC SALTS AND OXIDES Phosphonium Salts.—The chloride, large transparent cubes can be obtained by direct combination of phosphine and hydrogen chloride at —30° C but decomposes on rise of tempera ture. The bromide may be prepared similarly or by heating phos phorus with hydrobromic acid at 110° in sealed tubes; it is unstable in air and is decomposed by water. The iodide is readily obtained by mixing phosphorus and iodine in carbon disulphide in a retort, distilling off the solvent, adding the requisite quantity of water and subliming the iodide : Caustic alkali or more water decomposes it to phosphine and iodide or hydriodic acid.
Just as amines (q.v.) are derivatives of ammonia, so phosphine gives rise to primary, secondary and tertiary phosphines, and organic phosphonium bases correspond to phosphonium salts. The primary and secondary phosphines, and are formed when alkyl iodides are heated with phosphonium iodide and zinc oxide to 150° C, the reaction mixture is treated with water, whereby the primary phosphine is obtained, and the secondary phosphine is liberated from its hydriodide by caustic soda. The tertiary phosphines and quaternary phosphonium salts are formed by the same reaction at higher temperatures ( 18o° C) and without the use of zinc oxide. The primary and secondary phosphines are colourless liquids (except methylphosphine which boils at —14° C) of unpleasant odour; they react neutral but form salts with acids, and are often spontaneously inflammable; nitric acid oxi dizes them to mono- and di-alkylphosphinic acids, respectively, and The tertiary phosphines tend to give derivatives of quinquevalent phosphorus, and therefore readily form addition compounds and are oxidized to phosphine oxides, The quaternary phosphonium salts resemble the corresponding nitrogen compounds, being stable towards aqueous alkalis but converted by digestion with moist silver oxide to the very strongly alkaline phosphonium hydroxide ; on heating, they decompose to the phosphine oxide and a hydrocarbon : The alkylphosphinic acids are colourless crystalline compounds, readily soluble in water or alcohol, and dibasic, whereas the di alkylphosphinic acids are monobasic.
Oxides.—Three oxides are well defined, viz., P204, P4010; others (e.g., and have been described and also disputed. Phosphorus oxide, is a product of the limited combustion of phosphorus in air; if the element is burned in a hard glass tube and a rapid current of air is passed over it, the oxide may be condensed in a metal condenser and removed later by warming it. It sublimes in feathery crystals and melts at 22° to a colour less mobile liquid of sp.gr. 1.936 and boiling point 173°. Vapour density determinations indicate the formula above about 300° in a sealed tube it decomposes to phosphorus and the tetr oxide. It is slowly oxidized by air and rapidly by oxygen (with inflammation at to phosphoric oxide; with cold water it slowly gives phosphorus acid, but with hot water it reacts violently, forming phosphorus, phosphine, phosphoric acid, and other products; hot alkalis decompose it similarly, but cold dilute alkalis form phosphites. Chlorine or bromine converts it chiefly to or whereas iodine forms the di-iodide, and hydrogen chloride and phosphorus pentachloride react with it as follows: It combines violently with sulphur to give which sublimes as highly lustrous plates (m.p. 102° ; b.p. 295°) and which is readily decomposed by water to sulphuretted hydrogen and phos phoric acid. Ammonia reacts to give the diamide P(OH) (NH2)2 and its ammonium salt. Phosphorus oxide has a peculiar garlic like odour and is very poisonous; the odour and toxicity of phos phorus vapour are probably due to this oxide. Phosphorus tetroxide, or better since its molecular complexity is not certain, is obtained (see col. I) as lustrous, deliquescent crystals ; it is not the anhydride of hypophosphoric acid (see below), for water decomposes it to phosphorus and phosphoric acids. Phosphoric oxide, phosphoric anhydride (loosely termed "pentoxide"), is P4010 even at very high temperatures; it is ob tained by the burning of phosphorus in excess of air or oxygen, as a soft flocculent powder which sublimes to transparent mono clinic crystals. It reacts violently with water and can be reduced to the element by heating with carbon.