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24 novembre 2011 4 24 /11 /novembre /2011 02:56

Production and applications

The white allotrope can be produced using several different methods. In one process, calcium phosphate, which is derived from phosphate rock, is heated in an electric or fuel-fired furnace in the presence of carbon and silica. Sony VAIO VGN-CR13/B Battery

Elemental phosphorus is then liberated as a vapour and can be collected under phosphoric acid.

White phosphorus has an appreciable vapour pressure at ordinary temperatures. The vapour density indicates that the vapour is composed of P4 molecules up to about 800 °C. Above that temperature, dissociation into P2 molecules occurs.Sony VAIO VGN-CR13/L Battery

It ignites spontaneously in air at about 50 °C, and at much lower temperatures if finely divided. This combustion gives phosphorus (V) oxide:

P4 + 5 O2 ? P4O10

Because of this property, white phosphorus is used as a weapon.Sony VAIO VGN-CR13/P Battery

Non-existence of cubic-P8

Although white phosphorus converts to thermodynamically more stable red allotrope, the formation of the cubic P8 is not observed in the condensed phase. Derivatives of this hypothetical molecule have, however, been prepared from phosphaalkynes.Sony VAIO VGN-CR13/R Battery

Red phosphorus

Red phosphorus may be formed by heating white phosphorus to 250 °C (482 °F) or by exposing white phosphorus to sunlight. Red phosphorus exists as an amorphous network. Upon further heating, the amorphous red phosphorus crystallizes. Sony VAIO VGN-CR13/W Battery

Red phosphorus does not ignite in air at temperatures below 240 °C, whereas white phosphorus ignites at about 30 °C. Red phosphorus can be converted to white phosphorus upon heating to 260 °C, as can be seen when one strikes a match.

It is a controlled substance (precursor) in Russia and much of the rest of the former Soviet Union, due to its use in illicit amphetamine production.Sony VAIO VGN-CR131E/L Battery

Hittorf's violet phosphorus

Monoclinic phosphorus, or violet phosphorus, is also known as Hittorf's Metallic Phosphorus.In 1865, Hittorf heated red phosphorus in a sealed tube at 530 °C. The upper part of the tube was kept at 444 °C. Brilliant opaque monoclinic, or rhombohedral, crystals sublime.Sony VAIO VGN-CR13G Battery

Violet phosphorus can also be prepared by dissolving white phosphorus in molten lead in a sealed tube at 500 °C for 18 hours. Upon slow cooling, Hittorf's allotrope crystallises out. The crystals can be revealed by dissolving the lead in dilutenitric acid followed by boiling in concentrated hydrochloric acid.Sony VAIO VGN-CR13G/B Battery

In 1865 Johann Wilhelm Hittorfdiscovered that when phosphorus was recrystallized from molten lead, a red/purple form is obtained. This purple form is sometimes known as Hittorf's phosphorus. In addition, a fibrous form exists with similar phosphorus cages. Below is shown a chain of phosphorus atoms which exhibits both the purple and fibrous forms.Sony VAIO VGN-CR13G/L Battery

Reactions of violet phosphorus

It does not ignite in air until heated to 300 °C, and it is insoluble in all solvents. It is not attacked by alkali and only slowly reacts with halogens. It can be oxidised by nitric acid to phosphoric acid.Sony VAIO VGN-CR13G/P Battery

If it is heated in an atmosphere of inert gas, for example nitrogen or carbon dioxide, it sublimes and the vapour condenses as white phosphorus. If, however, it is heated in a vacuum and the vapour condensed rapidly, violet phosphorus is obtained. It would appear that violet phosphorus is a polymer of high relative molecular mass, which on heating breaks down into P2 molecules.Sony VAIO VGN-CR13G/R Battery

On cooling, these would normally dimerize to give P4 molecules (i.e. white phosphorus) but, in vacuo, they link up again to form the polymeric violet allotrope.

Black phosphorus

Black phosphorus is the thermodynamically stable form of phosphorus at room temperature and pressure. Sony VAIO VGN-CR13G/W Battery

It is obtained by heating white phosphorus under high pressures (12,000 atmospheres). In appearance, properties and structure it is very like graphite, being black and flaky, a conductor of electricity, and having puckered sheets of linked atoms.

Black phosphorus has an orthorhombic structure and is the least reactive allotrope: a result of its lattice of interlinked six-membered rings. Sony VAIO VGN-CR13T/L Battery

Each atom is bonded to three other atoms. A recent synthesis of black phosphorus using metal salts as catalysts has been reported.

One of the forms of red/black phosphorus is a cubic solid.Sony VAIO VGN-CR13T/P Battery

Diphosphorus

The diphosphorus allotrope (P2) can be obtained normally only under extreme conditions (for example, from P4 at 1100 kelvin). Nevertheless, some advancements were obtained in generating the diatomic molecule in homogenous solution, under normal conditions with the use by some transition metal complexes (based on for example tungsten and niobium).Sony VAIO VGN-CR13T/R Battery

Diphosphorus is the gaseous form of phosphorus, and the thermodynamically stable form above 1200 °C and until 2000 °C. The dissociation of tetraphosphorus (P4) begins at lower temperature: the percentage of P2 at 800 °C is ? 1%. At temperatures about 2000 °C, the diphosphorus molecule begins to dissociate into atomic phosphorus.Sony VAIO VGN-CR13T/W Battery

Phosphorus nanorods

Phosphorus nanorods were synthesized as P?12 polymers in two modifications.

The red-brown phase differs from red phosphorus and is also stable in air for weeks. Electron microscope showed the red-brown form as having long, parallel nanorods with a diameter between 0.34 nm and 0.47 nm.Sony VAIO VGN-CR15/B Battery

Although phosphorus (P) has 24 isotopes from 24P to 47P, only one of these isotopes is stable 31P; as such, it is considered a monoisotopic element. The longest-lived radioactive isotopes are 33P with a half-life of 25.34 days and 32P with a half-life of 14.263 days. Sony VAIO VGN-CR150E/B Battery

All other have half-lives under 2.5 minutes, most under a second. The least stable is 25P with a half-life shorter than 30 nanoseconds—the half-life of 24P is unknown.

Standard atomic mass: 30.973762(2) u

Radioactive isotopes of phosphorus include: Sony VAIO VGN-CR190 Battery

  • 32P; a beta-emitter (1.71 MeV) with a half-life of 14.3 days which is used routinely in life-science laboratories, primarily to produce radiolabeled DNA and RNAprobe, e.g. for use in Northern blots or Southern blots. Because the high energy beta particles produced penetrate skin and corneas,Sony VAIO VGN-CR190E/L Battery
  • and because any 32P ingested, inhaled, or absorbed is readily incorporated into bone and nucleic acids, OSHA requires that a lab coat, disposable gloves, and safety glasses or goggles be worn when working with 32P, and that working directly over an open container be avoided in order to protect the eyes.Sony VAIO VGN-CR190E/P Battery
  • Monitoring personal, clothing, and surface contamination is also required. In addition, due to the high energy of the beta particles, shielding this radiation with the normally used dense materials (e.g. lead), gives rise to secondary emission of X-rays via a process known as Bremsstrahlung, meaning braking radiation.Sony VAIO VGN-CR190E/R Battery
  • Therefore shielding must be accomplished with low density materials, e.g. Plexiglas, Lucite, plastic, wood, or water.
  • 33P; a beta-emitter (0.25 MeV) with a half-life of 25.4 days. It is used in life-science laboratories in applications in which lower energy beta emissions are advantageous such as DNA sequencing. Phosphorus-33 can be used to label nucleotides. Sony VAIO VGN-CR190E/W Battery
  • It is less energetic than 32P, giving a better resolution. A disadvantage is its higher cost compared to 32P, as most of the bombarded 31P will have acquired only one neutron, while only some will have acquired two or more. Its maximum specific activity is 5118 Ci/mol.Sony VAIO VGN-CR19VN/B Battery

Phosphoric acid, also known as orthophosphoric acid or phosphoric(V) acid, is a mineral (inorganic) acid having thechemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way.Sony VAIO VGN-CR19XN/B Battery

The term phosphoric acid can also refer to a chemical orreagent consisting of phosphoric acids, usually orthophosphoric acid.

Orthophosphoric acid chemistry

Pure anhydrous phosphoric acid is a white solid that melts at 42.35 °C to form a colorless, viscous liquid.Sony VAIO VGN-CR20 Battery

Most people and even chemists refer to orthophosphoric acid as phosphoric acid, which is the IUPAC name for this compound. The prefix ortho is used to distinguish the acid from other phosphoric acids, called polyphosphoric acids two(ii). Orthophosphoric acid is a non-toxic, inorganic, rather weak triprotic acid, which, when pure, is a solid at room temperatureand pressure.Sony VAIO VGN-CR21/B Battery

The chemical structure of orthophosphoric acid is shown above in the data table. Orthophosphoric acid is a verypolar molecule; therefore it is highly soluble in water. The oxidation state of phosphorus (P) in ortho- and other phosphoric acids is +5; the oxidation state of all the oxygen atoms (O) is ?2 and all the hydrogen atoms (H) is +1. Sony VAIO VGN-CR21E/L Battery

Triprotic means that an orthophosphoric acid molecule can dissociate up to three times, giving up an H+ each time, which typically combines with awater molecule, H2O, as shown in these reactions:

H3PO4(s) + H2O(l) H3O+(aq) + H2PO4?(aq)Ka1= 7.25×10?3

H2PO4?(aq)+ H2O(l) H3O+(aq) + HPO42?(aq)Ka2= 6.31×10?8

HPO42?(aq)+ H2O(l) H3O+(aq) +  PO43?(aq)Ka3= 3.98×10?13

The anion after the first dissociation, H2PO4?, is the dihydrogen phosphate anion. Sony VAIO VGN-CR21E/P Battery

The anion after the second dissociation, HPO42?, is the hydrogen phosphate anion. The anion after the third dissociation, PO43?, is the phosphate or orthophosphateanion. For each of the dissociation reactions shown above, there is a separate acid dissociation constant, called Ka1, Ka2, and Ka3 given at 25 °C.Sony VAIO VGN-CR21E/W Battery

Associated with these three dissociation constants are corresponding pKa1=2.12 , pKa2=7.21 , and pKa3=12.67 values at 25 °C. Even though all three hydrogen (H) atoms are equivalent on an orthophosphoric acid molecule, the successive Ka values differ since it is energetically less favorable to lose another H+ if one (or more) has already been lost and the molecule/ion is more negatively-charged.Sony VAIO VGN-CR21S/L Battery

Because the triprotic dissociation of orthophosphoric acid, the fact that its conjugate bases (the phosphates mentioned above) cover a wide pH range, and, because phosphoric acid/phosphate solutions are, in general, non-toxic, mixtures of these types of phosphates are often used as buffering agents or to make buffer solutions, where the desired pH depends on the proportions of the phosphates in the mixtures.Sony VAIO VGN-CR21S/P Battery

Similarly, the non-toxic, anion salts of triprotic organic citric acid are also often used to make buffers. Phosphates are found pervasively in biology, especially in the compounds derived from phosphorylated sugars, such as DNA, RNA, and adenosine triphosphate (ATP). There is a separate article on phosphate as an anion or its salts.Sony VAIO VGN-CR21S/W Battery

Upon heating orthophosphoric acid, condensation of the phosphoric units can be induced by driving off the water formed from condensation. When one molecule of water has been removed for each two molecules of phosphoric acid, the result ispyrophosphoric acid (H4P2O7). Sony VAIO VGN-CR21Z/N Battery

When an average of one molecule of water per phosphoric unit has been driven off, the resulting substance is a glassy solid having an empirical formula of HPO3 and is called metaphosphoric acid. Metaphosphoric acid is a singly anhydrous version of orthophosphoic acid and is sometimes used as a water- or moisture-absorbing reagent.Sony VAIO VGN-CR21Z/R Battery

Furtherdehydrating is very difficult, and can be accomplished only by means of an extremely strong desiccant (and not by heating alone). It produces phosphoric anhydride, which has an empirical formula P2O5, although an actual molecule has a chemical formula of P4O10. Phosphoric anhydride is a solid, which is very strongly moisture-absorbing and is used as a desiccant.Sony VAIO VGN-CR220E/R Battery

Composition and pH of a phosphoric acid aqueous solution

For a given total acid concentration [A] = [H3PO4] + [H2PO4?] + [HPO42?] + [PO43?] ([A] is the total number of moles of pure H3PO4which have been used to prepare 1 liter of solution), the composition of an aqueous solution of phosphoric acid can be calculated using the equilibrium equations associated with the three reactions described above together with the [H+][OH?] = 10?14 relation and the electrical neutrality equation. Sony VAIO VGN-CR23/B Battery

Possible concentrations of polyphosphoric molecules and ions is neglected. The system may be reduced to a fifth degree equation for [H+] which can be solved numerically, yielding:

For large acid concentrations, the solution is mainly composed of H3PO4. For [A] = 10?2, the pH is close to pKa1, giving an equimolar mixture of H3PO4 and H2PO4?.Sony VAIO VGN-CR23/L Battery

For [A] below 10?3, the solution is mainly composed of H2PO4? with [HPO42?] becoming non negligible for very dilute solutions. [PO43?] is always negligible. Note that the above analysis does not take into account ion activity coefficients; as such, the pH and molarity of a real phosphoric acid solution may deviate substantially from the above values.Sony VAIO VGN-CR23/N Battery

Chemical reagent

Pure 75–85% aqueous solutions (the most common) are clear, colourless, odourless, non-volatile, rather viscous, syrupy liquids, but still pourable. Phosphoric acid is very commonly used as an aqueous solution of 85% phosphoric acid or H3PO4.Sony VAIO VGN-CR23/P Battery

Because it is a concentrated acid, an 85% solution can be corrosive, although nontoxic when diluted. Because of the high percentage of phosphoric acid in this reagent, at least some of the orthophosphoric acid is condensed into polyphosphoric acids in a temperature-dependent equilibrium, but, for the sake of labeling and simplicity, Sony VAIO VGN-CR23/R Battery

the 85% represents H3PO4 as if it were all orthophosphoric acid. Other percentages are possible too, even above 100%, where the phosphoric acids and water would be in an unspecified equilibrium, but the overall elemental mole content would be considered specified. Sony VAIO VGN-CR23/W Battery

When aqueous solutions of phosphoric acid and/or phosphate are dilute, they are in or will reach an equilibrium after a while where practically all the phosphoric/phosphate units are in the ortho- form.

Preparation of hydrogen halides

Phosphoric acid reacts with halides to form the corresponding hydrogen halide gas (steamy fumes are observed on warming the reaction mixture). This is a common practice for the laboratory preparation of hydrogen halides.Sony VAIO VGN-CR240E/B Battery

Rust removal

Phosphoric acid may be used as a "rust converter", by direct application to rusted iron, steel tools, or surfaces. The phosphoric acid converts reddish-browniron(III) oxide, Fe2O3 (rust) to black ferric phosphate, FePO4.Sony VAIO VGN-CR240N/B Battery

"Rust converter" is sometimes a greenish liquid suitable for dipping (in the same sort of acid bath as is used for pickling metal), but it is more often formulated as a gel, commonly called naval jelly. It is sometimes sold under other names, such as "rust remover" or "rust killer". As a thick gel, it may be applied to sloping, vertical, or even overhead surfaces.Sony VAIO VGN-CR25G/N Battery

After treatment, the black ferric-phosphate coating can be scrubbed off, leaving a fresh metal surface. Multiple applications of phosphoric acid may be required to remove all rust. The black phosphate coating can also be left in place, where it will provide moderate further corrosion resistance (such protection is also provided by the superficially similar Parkerizing and blued electrochemical conversion coating processes).Sony VAIO VGN-CR290EAL Battery

Processed food use

Food-grade phosphoric acid (additive E338) is used to acidify foods and beverages such as various colas, but not without controversy regarding its health effects. It provides a tangy or sour taste and, being a mass-produced chemical, is available cheaply and in large quantities.Sony VAIO VGN-CR290EAN Battery

The low cost and bulk availability is unlike more expensive seasonings that give comparable flavors, such as citric acid which is obtainable from lemons and limes. However, most citric acid in the food industry is not extracted from citrus fruit, but fermented by Aspergillus niger mold from scrap molasses, waste starch hydrolysates and phosphoric acid.Sony VAIO VGN-CR290EAP Battery

Biological effects on bone calcium and kidney health

Phosphoric acid, used in many soft drinks (primarily cola), has been linked to lower bone density in epidemiological studies. For example, a study[2] using dual-energy X-ray absorptiometry rather than a questionnaire about breakage, provides reasonable evidence to support the theory that drinking cola results in lower bone density. Sony VAIO VGN-CR290EAR Battery

This study was published in the American Journal of Clinical Nutrition. A total of 1672 women and 1148 men were studied between 1996 and 2001. Dietary information was collected using a food frequency questionnaire that had specific questions about the number of servings of cola and other carbonated beverages and that also made a differentiation between regular, Sony VAIO VGN-CR290EAW Battery

caffeine-free, and diet drinks. The paper cites significant statistical evidence to show that women who consume cola daily have lower bone density. Total phosphorus intake was not significantly higher in daily cola consumers than in nonconsumers; however, the calcium-to-phosphorus ratios were lower.Sony VAIO VGN-CR29XN/B Battery

On the other hand, another study suggests that insufficient intake of phosphorus leads to lower bone density. The study does not examine the effect of phosphoric acid, which binds with magnesium and calcium in the digestive tract to form salts that are not absorbed, but rather studies general phosphorus intake.Sony VAIO VGN-CR305E/RC Battery

A clinical study by Heaney and Rafferty using calcium-balance methods found no impact of carbonated soft drinks containing phosphoric acid on calcium excretion. The study compared the impact of water, milk, and various soft drinks (two with caffeine and two without; Sony VAIO VGN-CR31S/D Battery

two with phosphoric acid and two with citric acid) on the calcium balance of 20- to 40-year-old women who customarily consumed ~3 or more cups (680 mL) of a carbonated soft drink per day. They found that, relative to water, only milk and the two caffeine-containing soft drinks increased urinary calcium, Sony VAIO VGN-CR323/W Battery

and that the calcium loss associated with the caffeinated soft drink consumption was about equal to that previously found for caffeine alone. Phosphoric acid without caffeine had no impact on urine calcium, nor did it augment the urinary calcium loss related to caffeine. Sony VAIO VGN-CR33 Battery

Because studies have shown that the effect of caffeine is compensated for by reduced calcium losses later in the day, Heaney and Rafferty concluded that the net effect of carbonated beverages—including those with caffeine and phosphoric acid—is negligible, and that the skeletal effects of carbonated soft drink consumption are likely due primarily to milk displacement.Sony VAIO VGN-CR382 Battery

Other chemicals such as caffeine (also a significant component of popular common cola drinks) were also suspected as possible contributors to low bone density, due to the known effect of caffeine on calciuria. One other study, involving 30 women over the course of a week, suggests that phosphoric acid in colas has no such effect, and postulates that caffeine has only a temporary effect, which is later reversed. Sony VAIO VGN-CR490EBL Battery

The authors of this study conclude that the skeletal effects of carbonated beverage consumption are likely due primarily to milk displacement (another possible confounding factor may be an association between high soft drink consumption and sedentary lifestyle).Sony VAIO VGN-CR490EBN Battery

Cola consumption has also been associated with chronic kidney disease and kidney stones through medical research. The preliminary results suggest that cola consumption may increase the risk of chronic kidney disease.Sony VAIO VGN-CR490EBP Battery

Medical use

Phosphoric acid is used in dentistry and orthodontics as an etching solution, to clean and roughen the surfaces of teeth where dental appliances or fillings will be placed. Phosphoric acid is also an ingredient in over-the-counter anti-nausea medications that also contain high levels of sugar (glucose and fructose). Sony VAIO VGN-CR490EBR Battery

This acid is also used in many teeth whiteners to eliminate plaque that may be on the teeth before application.

Preparation

Phosphoric acid can be prepared by three routes – the thermal process, the wet process and the dry kiln process.Sony VAIO VGN-CR490EBT Battery

Thermal phosphoric acid

This very pure phosphoric acid is obtained by burning elemental phosphorus to produce phosphorus pentoxide and dissolving the product in dilute phosphoric acid. This produces a very pure phosphoric acid, since most impurities present in the rock have been removed when extracting phosphorus from the rock in a furnace. Sony VAIO VGN-CR490EBW Battery

The end result is food-grade, thermal phosphoric acid; however, for critical applications, additional processing to remove arsenic compounds may be needed.

Elemental phosphorus is produced by an electric furnace. At a high temperature, a mixture of phosphate ore, silica and carbonaceous material (coke, coal etc...) produces calcium silicate, phosphorus gas and carbon monoxide. Sony VAIO VGN-CR50B/W Battery

The P and CO off-gases from this reaction are cooled under water to isolate solid phosphorus. Alternatively, the P and CO off-gases can be burned with air to produce phosphorus pentoxide and carbon dioxide.

Wet phosphoric acid

Wet process phosphoric acid is prepared by adding sulfuric acid to tricalcium phosphate rock, typically found in nature as apatite.

The reaction is: Sony VAIO VGN-CR51B/W Battery

Ca5(PO4)3X + 5 H2SO4 + 10 H2O ? 3 H3PO4 + 5 CaSO4·2H2O + HX
where X may include OH, F, Cl, and Br

The initial phosphoric acid solution may contain 23–33% P2O5, but can be concentrated by the evaporation of water to produce commercial- or merchant-gradephosphoric acid, which contains about 54% P2O5. Sony VAIO VGN-CR520E/J Battery

Further evaporation of water yields superphosphoric acid with a P2O5 concentration above 70%.

Digestion of the phosphate ore using sulfuric acid yields the insoluble calcium sulfate (gypsum), which is filtered and removed as phosphogypsum. Wet-process acid can be further purified by removing fluorine to produce animal-grade phosphoric acid, or by solvent extraction and arsenic removal to produce food-grade phosphoric acid.Sony VAIO VGN-CR52B/W Battery

Other applications

  • Phosphoric acid is used as an external standard for phosphorus-31 Nuclear magnetic resonance (NMR).
  • Phosphoric acid is used for high-performance liquid chromatography.
  • Phosphoric acid is used as a chemical oxidizing agent for activated carbon production, as used in the Wentworth Process.Sony VAIO VGN-CR590EBL Battery
  • Phosphoric acid is used as the electrolyte in phosphoric acid fuel cells.
  • Phosphoric acid is used with distilled water (2–3 drops per gallon) as an electrolyte in oxyhydrogen (HHO) generators.
  • Phosphoric acid is used as an electrolyte in copper electropolishing for burr removal and circuit board planarization.Sony VAIO VGN-CR590EBN Battery
  • Phosphoric acid is used as a flux by hobbyists (such as model railroaders) as an aid to soldering.
  • In compound semiconductor processing, phosphoric acid is a common wet etching agent: for example, in combination with hydrogen peroxide and water it is used to etch InGaAs selective to InP.Sony VAIO VGN-CR590EBP Battery
  • Hot phosphoric acid is used in microfabrication to etch silicon nitride (Si3N4). It is highly selective in etching Si3N4 instead of SiO2, silicon dioxide.
  • Phosphoric acid is used as a cleaner by construction trades to remove mineral deposits, cementitious smears, and hard water stains.Sony VAIO VGN-CR590EBR Battery
  • Phosphoric acid is also used as a chelant in some household cleaners aimed at similar cleaning tasks.
  • Phosphoric acid is also used in hydroponics pH solutions to lower the pH of nutrient solutions. While other types of acids can be used, phosphorus is a nutrient used by plants, especially during flowering, making phosphoric acid particularly desirable.
  • Phosphoric acid is used as a pH adjuster in cosmetics and skin-care products.Sony VAIO VGN-CR590EBT Battery
  • Phosphoric acid can be used as a dispersing agent in detergents and leather treatment.
  • Phosphoric acid can be used as an additive to stabilize acidic aqueous solutions within a wanted and specified pH range
  • Phosphoric acid is the ingredient that provides acidity to Coca-Cola and Pepsi sodas.Sony VAIO VGN-CR590EBW Battery

Organophosphorus compounds are degradable organic compounds containing carbon–phosphorus bonds (thus excluding from phosphate and phosphite esters, which lack such kind of bonding), used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Sony VAIO VGN-CR60B/L Battery

Organophosphorus chemistry is the corresponding science of the properties and reactivity of organophosphorus compounds. Phosphorus shares group 5 in the periodic table with nitrogen and phosphorus compounds and nitrogen compounds are somewhat related.Sony VAIO VGN-CR60B/P Battery

The definition of organophosphorus compounds is variable, which can lead to confusion. In industrial and environmental chemistry, an organophosphorus compound need contain only an organic substituent, but need not have a direct P-C bond. Thus most pesticides, e.g., malathion, are often included in this class of compounds.Sony VAIO VGN-CR60B/R Battery

Phosphorus can adopt a variety of oxidation states, and it is general to classify organophosphorus compounds based on their being derivatives of phosphorus(V) vs phosphorus(III), which are the predominant classes of compounds. In a descriptive but only intermittently used nomenclature, phosphorus compounds are identified by their coordination number ? and their valency ?. In this system, a phosphine is a ?3?3 compound.Sony VAIO VGN-CR61B/L Battery

Phosphate esters have the general structure P(=O)(OR)3 feature P(V). Such species are of technological importance as flame retardant agents, and plasticizers. Lacking a P?C bond, these compounds are in the technical sense not organophosphorus compounds but esters of phosphoric acid. Sony VAIO VGN-CR61B/N Battery

Many derivatives are found in nature, such as phosphatidylcholine. Phosphate ester are synthesized by alcoholysis of phosphorus oxychloride. A variety of mixed amido-alkoxo derivatives are known, one medically significant example being the anti-cancer drug cyclophosphamide. Sony VAIO VGN-CR61B/P Battery

Also derivatives containing the thiophosphoryl group (P=S) include the pesticidemalathion. The organophosphates prepared on the largest scale are the zinc dithiophosphates, as additives for motor oil. Several million kilograms of thiscoordination complex are produced annually by the reaction of phosphorus pentasulfide with alcohols.Sony VAIO VGN-CR61B/R Battery

Phosphonates are esters of phosphonic acid and have the general formula RP(=O)(OR')2. Phosphonates have many technical applications, a well-known member beingGlyphosate, better known as Roundup. With the formula (HO)2P(O)CH2NHCH2CO2H, this derivative of glycine is one of the most widely used herbicides. Sony VAIO VGN-CR62B/L Battery

Bisphosphonatesare a class of drugs to treat osteoporosis. The nerve gas agent Sarin, containing both C–P and F–P bonds, is a phosphonate.

Phosphinates feature two P–C bonds, with the general formula R2P(=O)(OR'). A commercially significant member is the herbicide Glufosinate. Similar to Glyphosate mentioned above, it has the structure CH3P(O)(OH)CH2CH2CH(NH2)CO2H.Sony VAIO VGN-CR62B/N Battery

The Michaelis–Arbuzov reaction is the main method for the synthesis of these compounds. For example, dimethylmethylphosphonate (see figure above) arises from the rearrangement of trimethylphosphite, which is catalyzed by methyl iodide. Sony VAIO VGN-CR62B/P Battery

In the Horner–Wadsworth–Emmons reaction and the Seyferth–Gilbert homologation, phosphonates are used in reactions with carbonyl compounds. The Kabachnik–Fields reaction is a method for the preparation of aminophosphonates. These compounds contain a very inert bond between phosphorus and carbon. Sony VAIO VGN-CR62B/R Battery

Consequently, they hydrolyze to give phosphonic and phosphinic acid derivatives, but not phosphate.

Phosphine oxides, imides, and chalcogenides

Phosphine oxides (designation ?3?3) have the general structure R3P=O with formal oxidation state V. Phosphine oxides form hydrogen bonds and some are therefore soluble in water. Sony VAIO VGN-CR70B/W Battery

The P=O bond is very polar with a dipole moment of 4.51 D for triphenylphosphine oxide.

Compounds related to phosphine oxides are the imides (R3PNR') and related chalcogenides (R3PE, where E = S, Se, Te). These compounds are some of the most thermally stable organophosphorus compounds, but few are useful in significant amounts.Sony VAIO VGN-CR71B/W Battery

Phosphonium salts and phosphoranes

Compounds with the formula [PR4+]X- comprise the phosphonium salts. These species are tetrahedral phosphorus(V) compounds. From the commercial perspective, the most important member is tetrakis(hydroxymethyl)phosphonium chloride, [P(CH2OH)4]Cl, which is used as a fire retardant in textiles.Sony VAIO VGN-CR72B/W Battery

Approximately 2M kg are produced annually of the chloride and the related sulfate.[4] They are generated by the reaction of phosphine with formaldehyde in the presence of the mineral acid:

PH3 + HX + 4 CH2O ? [P(CH2OH)4+]X-

A variety of phosphonium salts can be prepared by alkylation and arylation of organophosphines:Sony VAIO VGN-CR90HS Battery

PR3 + R'X ? [PR3R'+]X-

The methylation of triphenylphosphine is the first step in the preparation of the Wittig reagent.

The parent phosphorane (?5?5) is PH5, which is unknown. Related compounds containing both halide and organic substituents on phosphorus are fairly common. Those with five organic substituents are rare, although P(C6H5)5 is known, being derived from P(C6H5)4+ by reaction with phenyllithium.Sony VAIO VGN-CR90NS Battery

Phosphorus ylides are unsaturated phosphoranes, known as Wittig reagents, e.g. CH2P(C6H5)3. These compounds feature tetrahedral phosphorus(V) and are considered relatives of phosphine oxides. They also are derived from phosphonium salts, but by deprotonation not alkylation.Sony VAIO VGN-CR90S Battery

Comparison of phosphines and amines

The phosphorus atom in phosphines has a formal oxidation state ?3 (?3?3) and are the phosphorus analogues of amines. Like amines, phosphines have a trigonal pyramidal molecular geometry although often with smaller C-E-C angles (E = N, P), at least in the absence of steric effects.Sony VAIO VGN-CR92HS Battery

The C-P-C bond angle is 98.6° for trimethylphosphine increasing to 109.7° when the methyl groups are replaced by tert-butyl groups. When used as ligands, the steric bulk of tertiary phosphines is evaluated by their cone angle. The barrier to inversion is also much higher than in amines for a process like nitrogen inversion to occur, Sony VAIO VGN-CR92NS Battery

and therefore phosphines with three different substituents can be resolved into thermally stable optical isomers. Phosphines are often less basic than corresponding amines, for instance the phosphonium ion itself has a pKa of ?14 compared to 9.21 for the ammonium ion; trimethylphosphonium has a pKa of 8.65 compared to 9.76 for trimethylamine. Sony VAIO VGN-CR92S Battery

However, triphenylphosphine (pKa 2.73) is more basic than triphenylamine (pKa ?5), mainly because the lone pair of the nitrogen in NPh3 is partially delocalized into the three phenyl rings. Whereas the lone pair on nitrogen is delocalized in pyrrole, the lone pair on phosphorus atom in the phosphorus equivalent of pyrrole (phosphole) is not. Sony VAIO VGN-CS118E/Q Battery

The reactivity of phosphines matches that of amines with regard to nucleophilicity in the formation of phosphonium salts with the general structure PR4+X?. This property is used in the Appel reaction for converting alcohols to alkyl halides. Phosphines are easily oxidized to the corresponding phosphine oxides, whereas amine oxides are less readily generated.Sony VAIO VGN-CS118E/R Battery

In part for this reason, phosphines are very rarely encountered in nature.

Synthetic routes

From the commercial perspective, the most important phosphine is triphenylphosphine, several million kilograms being produced annually. It is prepared from the reaction of chlorobenzene, PCl3, and sodium.Sony VAIO VGN-CS118E/W Battery

Phosphines of a more specialized nature are usually prepared by other routes. Phosphorus halides undergo Nucleophilic displacement by organometallic reagents such as Grignard reagents. Conversely, some syntheses entail nucleophilic displacement of phosphide anion equivalents ("R2P-") by aryl- and alkyl halides.Sony VAIO VGN-CS11S/P Battery

Primary (RPH2) and secondary phosphines (RRPH and R2PH) add to alkenes in presence of a strong base (e.g., KOH in DMSO).Markovnikov's rules apply. Similar reactions occur involving alkynes.[6] Base is not required for electron-deficient alkenes (e.g., derivatives of acrylonitrile) and alkynes.Sony VAIO VGN-CS11S/Q Battery

Under free-radical conditions the P-H bonds of primary and secondary phosphines add across alkenes. Such reactions proceed with anti-Markovnikov regiochemistry. AIBNor organic peroxides are used as initiators. Tertiary phosphine oxides and sulfides can be reduced with chlorosilanes and other reagents.Sony VAIO VGN-CS11S/W Battery

Reactions

The main reaction types of phosphines are as nucleophiles and bases. Their nucleophilicity is evidence by their reactions with alkyl halides to phosphonium salts. Phosphines are nucleophilic catalysts in the dimerization of enones in various reactions in organic synthesis, e.g. the Rauhut–Currier reaction.Sony VAIO VGN-CS11Z/R Battery

Phosphines are reducing agents, as illustrated in the Staudinger reduction converting azides to amines and in the Mitsunobu reaction for converting alcohols into esters. In these processes, the phosphine is oxidized to the phosphine oxide.Sony VAIO VGN-CS120J/P Battery

Phosphines have also been found to reduce activated carbonyl groups for instance the reduction of an ?-keto ester to an ?-hydroxy ester in scheme 2.In the proposed reaction mechanism, the first proton is on loan from the methyl group in trimethylphosphine (triphenylphosphine does not react).Sony VAIO VGN-CS120J/Q Battery,Sony VAIO VGN-CS120J/R Battery,Sony VAIO VGN-CS190JTB Battery,Sony VAIO VGN-CS190JTP Battery,Sony VAIO VGN-CS190JTQ Battery,Sony VAIO VGN-CS190JTR Battery

[A] (mol/L) pH [H3PO4]/[A] (%) [H2PO4?]/[A] (%) [HPO42?]/[A] (%) [PO43?]/[A] (%)
1 1.08 91.7 8.29 6.20×10?6 1.60×10?17
10?1 1.62 76.1 23.9 6.20×10?5 5.55×10?16
10?2 2.25 43.1 56.9 6.20×10?4 2.33×10?14
10?3 3.05 10.6 89.3 6.20×10?3 1.48×10?12
10?4 4.01 1.30 98.6 6.19×10?2 1.34×10?10
10?5 5.00 0.133 99.3 0.612 1.30×10?8
10?6 5.97 1.34×10?2 94.5 5.50 1.11×10?6
10?7 6.74 1.80×10?3 74.5 25.5 3.02×10?5
10?10 7.00 8.24×10?4 61.7 38.3 8.18×10?5
NaCl(s) + H3PO4(l) ? NaH2PO4(s) + HCl(g)
NaBr(s) + H3PO4(l) ? NaH2PO4(s) + HBr(g)
NaI(s) + H3PO4(l) ? NaH2PO4(s) + HI(g)

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