Tuesday, February 19, 2008

The Chemistry of Phosphorus and its Compounds

1. Discovery and Naming of Phosphorus

The word phosphorus is derived from the ancient Greek words phos, meaning 'light', and phorus, meaning 'bringing'.

Uncertainty still surrounds the date on which phosphorus was first made. We can be fairly sure the place was Hamburg in Germany, and that the year was probably 1669, but the month and day are not recorded, though it must have been night-time. The alchemist who made the discovery stumbled upon a material the like of which had never been seen. Unwittingly he unleashed upon an unsuspecting world one of the most dangerous materials ever to have been made. On that dark night our lone alchemist was having no luck with his latest experiments to find the philosopher's stone. Like many before him he had been investigating the golden stream, urine, and he was heating the residues from this which he had boiled down to a dry solid. He stoked his small furnace with more charcoal and pumped the bellows until his retort glowed red hot. Suddenly something strange began to happen. Glowing fumes filled the vessel and from the end of the retort dripped a shining liquid that burst into flames. Its pungent, garlic-like smell filled his chamber. When he caught the liquid in a glass vessel and stoppered it he saw that it solidified but continued to gleam with an eerie pale-green light and waves of flame seemed to lick its surface. Fascinated, he watched it more closely, expecting this curious cold fire to go out, but it continued to shine undiminished hour after hour. Here was magic indeed. Here was phosphorus.

Source: The 13th Element The Sordid Tale of Murder, Fire, and Phosphorus (John Emsley) Page 4(WSU Library QD181.P1.E447 2000)

Bones, guano, excrement, and fish have been used as fertilizer since antiquity. The major element in these substances responsible for the increase in crop yield was not discovered until 1669. This discovery has been credited to Hennig Brandt, an impoverished German merchant who sought to become rich by converting base metal to gold. According to the account by G. W. von Leibniz1, Brandt made the discovery while carrying out alchemical experiments with urine. The substance he obtained glowed in the dark and burst into flame when exposed to air; it was subsequently named phosphorus, a term derived from “light I bear.”

Source: Comprehensive Inorganic Chemistry Vol 2 (J.C. Bailar) Page 389 (WSU Library QD 151.2.C64 V2)

2. Occurrence and Extraction of Phosphorus

Though more than 200 phosphate minerals are known, only those of the apatite type, for example, fluoroapatite [3Ca3(PO4)2Ca(F, CI)2], are commercial sources.

Source: Advanced Inorganic Chemistry (F. A. Cotton) Page 384 (WSU Library QD.151.2.C68.1999)

Phosphorus is made from naturally occurring calcium phosphates, of which huge deposits exist. The principal minerals are fluoroapatite, and its hydroxy equivalent, Hydroxyapatite. If the phosphate is treated with sulfuric acid, calcium sulfate is precipitated and soluble phosphates are formed. Conversion of phosphate to phosphorus depends on two useful facts, first, that silica being a relatively nonvolatile acid will displace volatile acids such as P 4O10 from their salts, and second, that carbon will reduce such oxides to phosphorus and CO.

Source: Simple Inorganic Substances (Sanderson) Page 74-75 (WSU Library QD 151.2.S26.1989)

For a century after its discovery, the only source of phosphorus was urine. As the demand for phosphorus and phosphates increased, guano and bones became the main source. In fact, the need for bones in England was so great in the early 1800s that battlefields of Europe were turned to as the source of supply. Bone ash from South America was also a source of phosphate. Bone contains ca. 23% mineral matter, of which calcium phosphate' calculated as Ca3(PO4)2 makes up 87%, and calcium carbonate 12%. Most of the bones were converted to phosphate fertilizers by treatment with sulfuric acid. Phosphatic minerals are quite abundant on the Earth. Phosphorus is the 11 th element in order of abundance in crustal rocks of the Earth and it occurs there to the extent of about 1120 ppm.

Source: Encyclopedia of Inorganic Chemistry (R. B. King) Page 3144 (QD 148.E53.1994 V.6)

3. General Properties of Phosphorus

Phosphorus has only one stable isotope, 31p; its atomic mass, which has been measured with extreme accuracy, is 30.973762. Sixteen radioactive isotopes are known, of which 32P is by far most important; it is made on the multikilogram scale by the neutron irradiation of 32S(n,p) or 31P(n,γ) in a nuclear reactor and is a pure β emitter of half life 14.28 days.

Source: Encyclopedia of Inorganic Chemistry (R. B. King) Page 3149 (QD 148.E53.1994 V.6)

Phosphorus is solid at room temperature. White phosphorus is soft, waxy and reactive. It reacts with moist air and gives out light (chemiluminescence). It ignites spontaneously in air at about 35 °C, and is stored under water to prevent this. It is highly toxic. It exists as tetrahedral P 4 molecules, and the tetrahedral structure remains in the liquid and gaseous states. Above 800 °C P 4 molecules in the gas begin to dissociate into P2 molecules, If white phosphorus is heated to about 250 °C, or a lower temperature in the presence of sunlight, then red phosphorus is formed. This is a polymeric solid, which is much less reactive than white phosphorus. It is stable in air and does not ignite unless it is heated to 400 °C. It is insoluble in organic solvents. Heating white phosphorus under high pressure results in a highly polymerized form of P called black phosphorus. This is thermodynamically the most stable allotrope. It is inert and has a layer

Source: Concise Inorganic Chemistry (J. D. Lee) Pages 475-476 (WSU Library QD 453.2.L44.1996)

4. Uses of Phosphorus

Phosphorus compounds have numerous applications particularly in: Animal foodstuffs Detergents Electrical materials Fertilizers Flame retardants Food additives Glass technology Matches Medicines Metal treatment Nerve gases Oil additives Pesticides Plastics Refractories Smoke generators Surfactants and Water treatment.

[Note the authors did not use commas in this list]

Source: Encyclopedia of Inorganic Chemistry (R. B. King) Page 3150 (QD 148.E53.1994 V.6)

5. Phosphorescence

Of all the possible transition metal coordination compounds, only those with d2, d3, d5, d6, and d8 configurations have been reported to phosphoresce (aside from those cases in which emission is localized on a ligand)… [so Phosphorus doesn’t phosphoresce it emits light as it reacts with O2]

The glow from phosphorus was the attraction of its discovery around 1669, but the mechanism for that glow was not fully described until 1974. It was known from early times that the glow would persist for a time in a stoppered jar but then cease. Robert Boyle in the 1680s ascribed it to "debilitation" of the air; in fact it is oxygen being consumed. By the 18th century it was known that in pure oxygen phosphorus does not glow at all, there is only a range of partial pressure where it does. In 1974 the glow was explained by R. J. van Zee and A. U. Khan. A reaction with oxygen takes place at the surface of the solid (or liquid) phosphorus, forming the short-lived molecules HPO and P2O2 that both emit visible light. The reaction is slow and only very little of the intermediates is required to produce the luminescence, hence the extended time the glow continues in a stoppered jar.

Source: Concepts of Inorganic Photochemistry (Adamson & Fleischauer) Page 41-43 (WSU Library QD 708.2.QA3)

6. Allotropes of Phosphorus

White Phosphorus: The most common form of phosphorus is white phosphorus, a solid obtained by the condensation of phosphorus vapor under water. Impurities such as arsenic and hydrocarbons are usually present.

Red Phosphorus: Commercial red phosphorus is prepared by heating white phosphorus at about 400° for several hours. Iodine, sulfur or sodium may be used as a catalyst.

Black Phosphorus: There are four forms of black phosphorus reported in the literature.

Liquid Phosphorus: The same liquid is obtained no matter whether white, red or black phosphorus is melted or the vapor is condensed.

Source: Comprehensive Inorganic Chemistry Vol 2 (J.C. Bailar) Pages 395-399 (WSU Library QD 151.2.C64 V2)

There are several structural forms (allotropes) of elemental phosphorus: white, red, Hittorf's and black being the best known. White phosphorus (also called yellow phosphorus) consists of clusters of four phosphorus atoms in a pyramidal array (P4) and this is the form made by the reduction of phosphate with carbon. When white phosphorus is heated under pressure at around 300°C for several days it changes to red phosphorus, which consists mainly of P4 tetrahedral linking together to create a random network. In 1865 a German chemist called Johann Hittorf (1824-1914) dissolved phosphorus in molten lead and allowed it to cool, whereupon purple crystals of a new form of phosphorus were formed, and this consists of clusters of eight and nine phosphorus atoms linked to form a kind of tube of phosphorus atoms. In 1916 an American chemist, Percy Bridgman (1882-1961), heated white phosphorus at 200°C under a pressure of 12,000 atmospheres and obtained black shiny crystals rather like graphite. This was black phosphorus, the most stable kind of phosphorus of all. The phosphorus atoms had arranged themselves into parallel layers, and like graphite this form, which it resembles, too was a semi-conductor of electricity. Other forms of black phosphorus, with different crystal shapes, can be made, depend- ing on the pressure and the length of time it is heated. Altogether about a dozen forms of phosphorus have been prepared ranging from crystal clear through all shades of orange, red, purple, brown and grey to deepest black.

Source: The 13th Element The Sordid Tale of Murder, Fire, and Phosphorus (John Emsley) Page 305 (WSU Library QD181.P1.E447 2000)

Phosphorus can reduce elemental iodine to hydroiodic acid, which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamine. For this reason, two allotropes of elemental phosphorus—red phosphorus and white phosphorus—were designated by the United States Drug Enforcement Administration as List I precursor chemicals under 21 CFR 1310.02 effective November 17, 2001.

Source: Environmental Phosphorus Handbook (Spencer, Beeton) Page 289 (WSU Library QD 181.P1.E68.2005)

7. Phosphate Cycle

The movement of phosphorus through the life cycles of the land and the sea and these consist of the uptake of phosphate by plants which may be eaten or simply die. Phosphate is leached from the land by weathering and carried by rivers to the sea; the leaching is a slow process but is helped by life on the land. The second movement is the precipitation of the phosphate in the sea as calcium phosphates which are deposited mostly on continental shelves. And the third movement which brings the wheel full circle is the geological uplifting of these marine deposits so that once again they are back on land and exposed to weathering.

Source: The Chemistry of Phosphorus (Emsley & Hall) Page 2 (WSU Library QD 181.P1.E45)

It is believed that in some ecosystems phosphorus is a limiting basic nutrient. Thus when detergents containing large amounts of phosphate builders became popular in the 1950s, and large amounts of treated sewage containing phosphates began to be released into rivers and lakes, there were severe problems of eutrophication because of an upsurge in growth of algae and other primitive plants. Because of the possibility of phosphates being implicated, [as the source of eutrophication] however, most detergent manufacturers have reduced the proportion of phosphate builders in detergents.

Source: Introduction to Phosphorus Chemistry (Goldwhite) Page 32 (WSU Library QD 181.P1.G67)

8. New Research in Phosphorus Chemistry

In [previous] volumes several experts reported on the recent progress of phosphorus chemistry in many fields. This chemistry is so rich, so diversified, that a new volume appeared to be necessary in order to cover some other aspects of such a topic and to point out the key role played by this element. Indeed contributions of this issue can be classified into three different groups: i) new developments of "old themes" with different approaches and ideas ii) state of the art for two topics of general interest and iii) emerging fields of research

Source: Topics in Current Chemistry New Aspects in Phosphorous Chemistry V (Springer Press) Page I (WSU Library QD 1.F58.V.250.2005)

A remarkable parallel chemistry has built up around the fact that, in low coordination numbers, phosphorus strongly resembles carbon. In many ways, low-coordinate phosphorus behaves more like its diagonal relative than its vertical neighbor, nitrogen. This has led to phosphorus being called "the carbon copy" and the establishment of a burgeoning field of chemistry at the interface between organic and inorganic chemistry

Source: Topics in Current Chemistry New Aspects in Phosphorous Chemistry V (Springer Press) Page 108 (WSU Library QD 1.F58.V.250.2005)

The last decades have seen the development of many important applications of organophosphorus compounds. There is no doubt that in the field of organic synthesis the Wittig synthesis of alkenes from ylides and carbonyl compounds and its phosphonate version, the so-called PO-olefination, play the most important role.

These reactions allowed for the synthesis of a large range of new phosphonate structures which have found application in the synthesis of complex natural products or drugs. In contrast to a-phosphonate carbanions, the corresponding, equally important a-phosphonate radicals have received much less attention.

Source: Topics in Current Chemistry New Aspects in Phosphorous Chemistry IV (Springer Press) Page 149 (WSU Library QD 1.F58.V.223.2003)

[very cool new research into bio-inorganic molecules.]

9. Phosphorus in Matches

Due to the high toxicity of white phosphorus, which exacted a fearful toll of lives among the early matchmakers, its use for matches was banned. This use had started in Finland in 1872, and was taxed out of existence in the United States in 1913. White phosphorus was replaced by the much less toxic red phosphorus. This changed to the development of the ‘safety match’. In such matches, the head contains approximately 50% potassium chlorate. A separate friction striking surface has as basic ingredients approximately 50% red phosphorus as the igniting agent.

Source: Encyclopedia of Inorganic Chemistry (R. B. King) Page 3150 (QD 148.E53.1994 V.6)

In addition to the safety match, there is also the "strike-anywhere" match. In this case, the two chemical components, the oxidizing agent (potassium chlorate) and the reducing agent (tetraphosphorus trisulfide, P4S3) are mixed in the match head. Any source of friction, such as the glass paper strip on the matchbox or a brick wall, can provide the activation energy necessary to start the reaction.

Source: Descriptive Inorganic Chemistry (Rayner-Canham) Page 325 (WSU Library QD151.5.R39.1999)

10. Phosphorus in Biological Systems

Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide that is most important for intracellular energy transfer. In this role, ATP transports chemical energy within cells for metabolism. It is produced as an energy source during the processes of photosynthesis and cellular respiration and consumed by many enzymes and a multitude of cellular processes including biosynthetic reactions, motility and cell division. In signal transduction pathways, ATP is used as a substrate by kinases that phosphorylate proteins and lipids, as well as by adenylate cyclase, which uses ATP to produce the second messenger molecule cyclic AMP.

Source: Physical Chemistry for the Biological Sciences (Hammes) Page (WSU Library QD271.M46 v.50 2007)

Hydroxyapatite is the principal ingredient of tooth enamel, and more susceptible to decay than the fluoroapatite. Treatment of teeth with fluoride attempts to replace the hydroxyl group with fluorine.

Source: Simple Inorganic Substances (Sanderson) Page 74-75 (WSU Library QD 151.2.S26.1989)

Friday, February 1, 2008