Properties of White Phosphorus

White phosphorus is soft and waxy and readily soluble in many organic solvents such as carbon disulphide and benzene. Solubilities (25°C) per 100 g solvent are 1.27 g in CCI4, 1.39 g in Et20, 3.7 g in CgHg, 0.30 g in acetone and 1000 g in CS2. Its molecular weight in solvents corresponds to P4, as it is in the liquid and vapour states. At 20°C, the cubic crystalline form has a density of 1.83 g/cc, Moh s hardness = 0.5, with mp = 44.1°C, bp = 280°C and vapour pressure of 0.173 mm. 

When heated at 230-300°C in the absence of air, white P is converted to the red allotropic form (see below). White P also transforms to red nnder the action of light or x-ray radiation. 

It has long been recognised that white phosphorus will glow in the dark and this Inminescence is attribnted to a slow oxidation of the P4 vaponr emitted. This oxidation results in the formation of unstable HPO and PO2 species and the emission of visible light (Chapter 13.4). In a closed vessel, luminescence continues until all the available oxygen is nsed up [21,22]. 

The element will combine vigorously with halogens, with sulphur and many metals. It is a reducing agent and with concentrated alkalies, phosphine and hydrogen are produced (4.13,4.14). Phosphine is produced in reactions (4.15) and (4.16) [23], and under the appropriate conditions, white P can be reduced to P4H2, P4H and various other hydrides (Section 4.4), 

White phosphorus will precipitate copper and lead from aqueous solutions of their salts. Lumps of white phosphorus, if placed in copper sulphate solution, will rapidly become coated with black copper phosphide, which is in turn reduced to metallic copper. Sulphur chloride is reduced to sulphur (4.17), and thionyl chloride and potassium iodate are also reduced (4.18,4.19). 

---

Information regarding the physical and chemical properties of white phosphorus and white phosphorus smoke is located in Table 3-2. 

TABLE 3-2. Physical and Chemical Properties of White Phosphorus... 

FIGURE 155. The mystical title page of Johann Heinrich Cohausen s 1717 treatise on phosphorus. Hermes and the flying dragon are sources of fire and light—properties of white phosphorus. 

Between about 1780 and 1850 a variety of fire-making devices were invented. The pyrophoric properties of white phosphorus were utilised in the earliest form of matches, which consisted of strips of paper tipped with the element and sealed in glass tubes. When broken, the paper would catch fire. The first striking matches ( friction lights ) were invented by J. Walker of England in 1826, but these did not contain phosphorus. Shortly afterwards a great improvement was achieved by C. Sauria of France who incorporated white P in the formulation. 

The remaining four elements form molecular solids. The atoms of white phosphorus, sulfur, and chlorine are strongly bonded into small molecules (formulas, P4, S8, and Cl2, respectively) but only weak attractions exist between the molecules. The properties are all appropriate to this description. Of course there is no simple trend in the properties since the molecular units are so different. 

The use of white phosphorus (P4) is an exception to the rule of using the most stable form, since red phosphorus is more stable (but its properties are less reproducible). 

White phosphorus has a white waxy appearance that turns slightly yellow with age and impurities. There are two allotropic forms of white phosphorus. The alpha (a) form has a cubic crystal structure, and the beta (P) form has a hexagonal crystalline structure. White phosphorus is extremely reactive and will spontaneously burst into flame when exposed to air at a temperature of about 35°C. It must be kept under water. But this property of spontaneous combustion has made it useful for military applications. 

These experts collectively have knowledge of white phosphorus s physical and chemical properties, toxicokinetics, key health end points, mechanisms of action, human and animal exposure, and quantification of risk to humans. All reviewers were selected in conformity with the conditions for peer review specified in Section 104(I)(13) of the Comprehensive Environmental Response, Compensation, and Liability Act, as amended. 

Because it is a mixture, the physical properties of red phosphorus are variable. Thus, the density ranges from 2.10 to 2.34, depending on the completeness of the transformation from the white to the violet allotrope. The vapor formed when red phosphorus is heated is identical with that formed by white phosphorus in either case, condensation of these vapors produces white phosphorus. The red modification is much less active chemically than the white variety and is insoluble in those solvents which dissolve white phosphorus. 

Reaction of white phosphorus with sodium hydroxide or sodium eth-oxide in ethanol generates a dark red solution of an uncharacterized metastable phosphorus compound (9) which possesses nucleophilic properties (10). The red product decomposes slowly even at 0 to hydrogen, phosphine, and sodium hypophosphite (9). But addition of methyl iodide to the freshly prepared solution is reported to give methylphos-phine, methylphosphonic acid, dimethylphosphinic acid, and trimethyl-phosphine oxide (10). Analogous products were reported from reaction with isoamyl iodide, where isoamylphosphonic acid was obtained in 59% yield based on the iodide. 

The first volume of Topics in Current Chemistry (volume 220), dedicated to New Aspects in Phosphorus Chemistry was very attractive for a large number of readers. This success encouraged us to continue our efforts in presenting all the facets of modern phosphorus chemistry. What makes phosphorus so attractive that chemists have a natural tendency to use it Virtudly every chemist can take profit of the properties of such an element. Applications in different fields have already been realized or are under current investigation. A few of these applications and properties covering some aspects of catalysis, organometallic chemistry, polymer chemistry, biophosphates or carbonylphosphonate chemistry, use of white phosphorus etc... have been presented in the first volume. 

The elements of Period 3. Properties progress left to right) from solids (Na, Mg, Al, SI, P, S] to gases (Cl, Ar] and from the most metallic (Na) to the most nonmetalllc (Ar). The sticks of white phosphorus are In a heaker of water because they would ignite and hum In air (O2). 

The commonest form of phosphorus, and the one which is usually formed by condensation from the gaseous or liquid states, is the waxy, cubic, white form o -P4 (d 1.8232 gcm at 20°C). This, paradoxically, is also the most volatile and reactive solid form and thermodynamically the least stable. It is the slow phosphorescent oxidation of the vapour above these crystals that gives white phosphorus its most characteristic property. Indeed, the emission of yellow-green light from the oxidation of P4 is one of the earliest recorded examples of chemiluminescence, though the details of the reaction... 

The element phosphorus forms a variety of allotropic forms in the solid state. In the chemistry stockroom, you are likely to find red phosphorus and possibly white phosphorus (Figure B). As you can see, white phosphorus has the molecular formula P4, whereas red phosphorus might be represented as Px, where x is a very large number. The difference in properties between the two allotropes reflects the difference in their bonding patterns, molecular versus network covalent ... 

By far the most important redox reaction relative to chemical stability is the reaction between an oxidizable material and oxygen from air. The particle size and any droplets have a large effect on the combustion properties. Some substances react so rapidly in air that ignition occurs spontaneously. These so called pyrophoric compounds (white phosphorus, alkali metals, metal hydrides, some metal catalysts, and fully alkylated metals and nonmetals) must be stored in the absence of air. 

Black phosphorus is formed when white phosphorus is heated under very high pressure (12 000 atmospheres). Black phosphorus has a well-established corrugated sheet structure with each phos phorus atom bonded to three neighbours. The bonding lorces between layers are weak and give rise to flaky crystals which conduct electricity, properties similar to those of graphite. It is less reactive than either white or red phosphorus. 

The allotropes of phosphorus may be identified from their physical properties. White phosphorus can be identified from its chemiluminescence (a pale... 

Arsenic exhibits allotropy, which is characteristic of non-metals the usual, more stable, metallic form resembles the typical metals in appearance and in being a fairly good conductor of electricity. Under atmospheric pressure it begins to volatilise at about 450° C. and passes into a vapour containing complex molecules, As4, which at higher temperatures dissociate to As2 this complexity is not unusual in non-metals. The yellow allotrope, which is stable at low temperatures, resembles white phosphorus in being soluble in carbon disulphide—a property which emphasises the non-metallic character of this variety. The reactivity of the allotropes, as in the case of phosphorus, differs considerably. 

---