Properties of Red Phosphorus

Many varieties of the so-called red phosphorus (P , n 4), both amorphous and crystalline, are now known. All are polymeric with colours desaibed as brown-red, yellowish-red, pale-red, bright-red, dark-red, pnrple-red, violet and so forth. While some of these variations can be associated with differences of crystalline form, other factors inflnencing colour include degree of crystallinity, degree of polymerisation, presence of impurities, and particle size effects. Many of these factors have been unrecognised when precise measurements of physical properties have been reported, and variations in published data will be found. Black phosphorus, the high-pressure form, is also highly polymeric, but has (historically) been considered as a form separate from the white or red varieties (see Chapter 4.1). 

Generally, varieties of red P are less reactive, they have much higher molecular weight and are considerably less soluble than the white forms of the element. Some typical parameters of the common red forms are as follows  

Melting point 580°C under pressure Boiling point Sublimes 400°C at NTP Solubility Insoluble in water and all ordinary solvents Density 2.15-2.35 g/cm  

Transition points (solid) -184.5, -223.6, -242.7°C Heat of fusion 0.270 kcal/mol Heat of vaporisation 3.493 kcal/mol Heat of formation (at 25°C) 2.29 kcal Interatomic distance P-H = 1.421 A Interbond angle H/P/H = 93.5° 

Note There exists an anthracene-based orange dyestuff, Crysaniline , which has also been known in some quarters as phosphine . The word phosphene has been used to describe an impression of light on the retina, when it is caused by stimulation other than rays of light. 

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Properties of Red Phosphorus.—Rod amorphous phosphorus, in the state of powder, is lustreless, and destitute of crystalline structcre. Its color varies from a scarlet to... 

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. 

From a comparison of the properties of red allotropic jfijosphorus and the ordinary variety, it will be seen that the invention of SHK8TTER is a great boon to those engaged in manufactories where phosphorus is largely used, and particularly to producers of instantaneous lighta or lncifer matches, inasmuch as the red phosphorus is perfectly free from those pernicious... 

U. J. J. Leverrier exposed to air a soln. of phosphorus in ether or in phosphorus trichloride, washed the product in warm water, and dried it in vacuo over sulphuric acid. The analysis corresponded with phosphorus tetritoxide, P40. B. Reinitzer and H. Goldschmidt obtained a similar product by the action of phosphorus oxychloride on zinc, magnesium, or aluminium at 100°, or on yellow phosphorus at 250°. They added that the substance obtained with yellow phosphorus has the composition of phosphorus tetritoxide, but not its properties. Its properties approximate closely to those of red phosphorus. 

Elemental phosphorus exists in several allotropic forms (Van Wazer 1982). The best known and most important commercially is the a-white phosphorus whose properties are given in Table 3-2. Commercial white phosphorus is 99.9% pure, with a slight yellow color caused by traces of red phosphorus impurities. Hence, white phosphorus also is known as yellow phosphorus. When a-white phosphorus is cooled below -79.6°C, P-white phosphorus forms. Other important solid allotropes of phosphorus are red and black phosphorus (Van Wazer 1982). 

Red Phosphorus.—The chief chemical properties of red or amorphous phosphorus were determined by the discoverer and other early investigators. As compared with white phosphorus, both red and scarlet phosphorus are relatively inert, except in respect to certain reactions which depend largely on the extent of surface exposed to aqueous reagents. 

The chemical properties partly resemble those of white, partly those of red, phosphorus. It does not glow in the air, but does so in ozone. It is rapidly attacked by alkalies, giving hypophosphite and phosphine which is not spontaneously inflammable. It is coloured intensely black by ammonia. It dissolves in aqueous alcoholic potash giving red solutions from which acids precipitate a mixture of phosphorus and solid hydride. It dissolves in phosphorus tribromide to the extent of about 0-5 gram in 100 grams of the solvent at about 200° C. It is said to be non-poisonous its physiological properties probably resemble those of red phosphorus (q.v.). 

The explanation of the properties of red and black phosphorus lies in their structure. These substances are high polymers, consisting of giant molecules extending throughout the crystal. In order for such... 

High amounts of ATH can be added to the polyol stream where PU casting systems need flame retardancy. To pass the UL94 V-0 test about 300 phr are required. The addition of red phosphorus and ATH is much more effective and does not affect the insulating properties of the resins. A typical formulation would have 100 phr of ATH and 20 phr of red phosphorus. 

Also of interest are salts of melamine (see Chapter 24). In the nylons these can be used with bright colours (unlike red phosphorus) and do not adversely affect electrical properties. They do, however, decompose at about 320°C. Similar materials are very important in giving flame-retardant properties to polyurethane foams. 

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 ... 

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). 

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. 

Nano-modified aluminum trihydrate show a good synergistic characteristics for improving the flame retardant properties of HIPS, when combined with red phosphorus (23). 

T. Thomson 15 thought that he had obtained what he called a carburet of phosphorus— or carbon phosphide—when impure calcium phosphide is decomposed by water, and the lime removed by hydrochloric acid the residual carbon phosphide was collected on a filter and quickly washed. It was said to be a brownish-yellow, soft, tasteless, inodorous, infusible powder, which suffers no alteration in dry air below 100°, but takes fire at a red-heat when the phosphorus bums to phosphoric acid while the carbon is not changed. It attacks moisture from the air, forming a hydrocarbon, and carbon dioxide. The properties of the alleged phosphide correspond with those of a mixture of carbon and phosphoric acid with perhaps a small proportion of phosphorus. J. J. Berzelius said that a similar... 

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