Organophosphorus compounds are

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

s containing

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

. They are used primarily in

pest control Pest control is the regulation or management of a species defined as a pest; any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the damage done and will range ...

as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective

insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed t ...

s, although some are extremely toxic to humans, including

sarin Sarin (NATO designation GB G-series, "B"">Nerve_agent#G-series.html" ;"title="hort for Nerve agent#G-series">G-series, "B" is an extremely toxic synthetic organophosphorus compound.VX nerve agents. Organophosphorus chemistry is the corresponding science of the properties and reactivity of organophosphorus compounds. Phosphorus, like

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

, is in group 15 of the periodic table, and thus phosphorus compounds and nitrogen compounds have many similar properties. 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 A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as '' side ...

, but need not have a direct phosphorus-carbon (P-C) bond. Thus a large proportion of pesticides (e.g.,

malathion Malathion is an organophosphate insecticide which acts as an acetylcholinesterase inhibitor. In the USSR, it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion. Pesticide use Malathion is a pe ...

), are often included in this class of compounds. Phosphorus can adopt a variety of

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

s, 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 In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central io ...

σ and their valency λ. In this system, a phosphine is a σ³λ³ compound.

Organophosphorus(V) compounds, main categories

Phosphate esters and amides

Phosphate ester In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered ...

s have the general structure P(=O)(OR)₃ feature P(V). Such species are of technological importance as

flame retardant The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...

agents, and

plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticiz ...

s. Lacking a P−C bond, these compounds are in the technical sense not organophosphorus compounds but esters of phosphoric acid. 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 Cyclophosphamide (CP), also known as cytophosphane among other names, is a medication used as chemotherapy and to suppress the immune system. As chemotherapy it is used to treat lymphoma, multiple myeloma, leukemia, ovarian cancer, breast cancer ...

. Also derivatives containing the thiophosphoryl group (P=S) include the pesticide

. The organophosphates prepared on the largest scale are the zinc dithiophosphates, as additives for motor oil. Several million kilograms of this

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. M ...

are produced annually by the reaction of phosphorus pentasulfide with alcohols. : In the environment, these compounds break down via

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysi ...

to eventually afford

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

and the organic alcohol or amine from which they are derived.

Phosphonic and phosphinic acids and their esters

Phosphonates are esters of phosphonic acid and have the general formula RP(=O)(OR')₂. Phosphonates have many technical applications, a well-known member being glyphosate, better known as Roundup. With the formula (HO)₂P(O)CH₂NHCH₂CO₂H, this derivative of

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...

is one of the most widely used herbicides.

Bisphosphonate Bisphosphonates are a class of drugs that prevent the loss of bone density, used to treat osteoporosis and similar diseases. They are the most commonly prescribed drugs used to treat osteoporosis. They are called bisphosphonates because they ...

s are a class of drugs to treat

osteoporosis Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to bone fragility, and consequent increase in fracture risk. It is the most common reason for a broken bone a ...

. The nerve gas agent

sarin Sarin (NATO designation GB G-series, "B"">Nerve_agent#G-series.html" ;"title="hort for Nerve agent#G-series">G-series, "B" is an extremely toxic synthetic organophosphorus compound.glufosinate Glufosinate (also known as phosphinothricin and often sold as an ammonium salt) is a naturally occurring broad-spectrum herbicide produced by several species of ''Streptomyces'' soil bacteria. Glufosinate is a non-selective, contact herbicide, ...

. Similar to glyphosate mentioned above, it has the structure CH₃P(O)(OH)CH₂CH₂CH(NH₂)CO₂H. : 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 Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one ...

. In the Horner–Wadsworth–Emmons reaction and the Seyferth–Gilbert homologation, phosphonates are used in reactions with

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containi ...

compounds. The

Kabachnik–Fields reaction In organophosphorus chemistry, the Kabachnik–Fields reaction is a three-component organic reaction forming α-aminomethylphosphonates from an amine, a carbonyl compound, and a dialkyl phosphonate, (RO)2P(O)H (that are also called dialkylphosphit ...

is a method for the preparation of aminophosphonates. These compounds contain a very inert bond between phosphorus and carbon. Consequently, they hydrolyze to give phosphonic and phosphinic acid derivatives, but not phosphate.

Phosphine oxides, imides, and chalcogenides

Phosphine oxides (designation σ⁴λ⁵) have the general structure R₃P=O with formal oxidation state V. Phosphine oxides form

hydrogen bond In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...

s and some are therefore soluble in water. The P=O bond is very polar with a dipole moment of 4.51 D for triphenylphosphine oxide. Compounds related to phosphine oxides include phosphine imides (R₃PNR') and related chalcogenides (R₃PE, where E = S, Se, Te). These compounds are some of the most thermally stable organophosphorus compounds.

Phosphonium salts and phosphoranes

Compounds with the formula R₄⁺⁻ comprise the phosphonium salts. These species are tetrahedral phosphorus(V) compounds. From the commercial perspective, the most important member is tetrakis(hydroxymethyl)phosphonium chloride, (CH₂OH)₄l, which is used as a fire retardant in

textile Textile is an Hyponymy and hypernymy, umbrella term that includes various Fiber, fiber-based materials, including fibers, yarns, Staple (textiles)#Filament fiber, filaments, Thread (yarn), threads, different #Fabric, fabric types, etc. At f ...

s. Approximately 2M kg are produced annually of the chloride and the related sulfate. They are generated by the reaction of phosphine with

formaldehyde Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...

in the presence of the mineral acid: :PH₃ + HX + 4 CH₂O → (CH₂OH)₄⁺⁻ A variety of phosphonium salts can be prepared by

alkylation Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effectin ...

and arylation of organophosphines: :PR₃ + R'X → R₃R'⁺⁻ The methylation of triphenylphosphine is the first step in the preparation of the Wittig reagent. : The parent phosphorane (σ⁵λ⁵) 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. Phosphorus

ylide An ylide or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms ...

s 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.

Organophosphorus(III) compounds, main categories

Phosphites, phosphonites, and phosphinites

Phosphites, sometimes called phosphite esters, have the general structure P(OR)₃ with oxidation state +3. Such species arise from the alcoholysis of phosphorus trichloride: :PCl₃ + 3 ROH → P(OR)₃ + 3 HCl The reaction is general, thus a vast number of such species are known. Phosphites are employed in the Perkow reaction and the Michaelis–Arbuzov reaction. They also serve as ligands in organometallic chemistry. Intermediate between phosphites and phosphines are phosphonites (P(OR)₂R') and phosphinite (P(OR)R'₂). Such species arise via alcoholysis reactions of the corresponding phosphinous and phosphonous chlorides ((PClR'₂) and PCl₂R', respectively).

Phosphines

The parent compound of the phosphines is PH₃, called

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

in the US and British Commonwealth, but phosphane elsewhere. Replacement of one or more hydrogen centers by an organic substituents (alkyl, aryl), gives PH_3−xR_x, an organophosphine, generally referred to as phosphines. From the commercial perspective, the most important phosphine is

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...

, several million kilograms being produced annually. It is prepared from the reaction of

chlorobenzene Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses Historical The major use of chlorob ...

, PCl₃, and sodium. Phosphines of a more specialized nature are usually prepared by other routes. Phosphorus halides undergo nucleophilic displacement by organometallic reagents such as

Grignard reagent A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide . ...

s. Organophosphines are nucleophiles and

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...

s. Two major applications are as reagents in the Wittig reaction and as supporting

phosphine ligand A metal-phosphine complex is a In coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. ...

s in

homogeneous catalysis In chemistry, homogeneous catalysis is catalysis by a soluble catalyst in a solution. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysi ...

. Their nucleophilicity is evidenced by their reactions with alkyl halides to give phosphonium salts. Phosphines are nucleophilic catalysts in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

, e.g. the Rauhut–Currier reaction and Baylis-Hillman reaction. Phosphines are

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth met ...

s, as illustrated in the

Staudinger reduction The Staudinger reaction is a chemical reaction of an organic azide with a phosphine or phosphite produces an iminophosphorane. The reaction was discovered by and named after Hermann Staudinger. The reaction follows this stoichiometry: :R3P + R ...

for the conversion of organic azides to amines and in the

Mitsunobu reaction The Mitsunobu reaction is an organic reaction that converts an alcohol into a variety of functional groups, such as an ester, using triphenylphosphine and an azodicarboxylate such as diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylat ...

for converting alcohols into esters. In these processes, the phosphine is oxidized to phosphorus(V). Phosphines have also been found to reduce activated carbonyl groups, for instance the reduction of an α-keto ester to an α-hydroxy ester.

Phosphaalkenes and phosphaalkynes

Compounds with carbon phosphorus(III) multiple bonds are called

phosphaalkene Phosphaalkenes (IUPAC name: alkylidenephosphanes) are organophosphorus compounds with double bonds between carbon and phosphorus(III) with the formula R2C=PR. In the compound phosphorine one carbon atom in benzene is replaced by phosphorus. The ...

s (R₂C=PR) and phosphaalkynes (RC≡P). They are similar in structure, but not in reactivity, to imines (R₂C=NR) and

nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix '' cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including me ...

s (RC≡N), respectively. In the compound

phosphorine Phosphorine (IUPAC name: phosphinine) is a heavier element analog of pyridine, containing a phosphorus atom instead of an aza- moiety. It is also called phosphabenzene and belongs to the phosphaalkene class. It is a colorless liquid that is ...

, one carbon atom in benzene is replaced by phosphorus. Species of this type are relatively rare but for that reason are of interest to researchers. A general method for the synthesis of phosphaalkenes is by 1,2-elimination of suitable precursors, initiated thermally or by base such as

DBU The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a po ...

, DABCO, or

triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...

: :

Thermolysis Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ...

of Me₂PH generates CH₂=PMe, an unstable species in the condensed phase.

Organophosphorus(0), (I), and (II) compounds

Compounds where phosphorus exists in a formal oxidation state of less than III are uncommon, but examples are known for each class. Organophosphorus(0) species are debatably illustrated by the carbene adducts, (NHC)sub>2, where NHC is an

N-heterocyclic carbene A persistent carbene (also known as stable carbene) is a type of carbene demonstrating particular stability. The best-known examples and by far largest subgroup are the ''N''-heterocyclic carbenes (NHC) (sometimes called Arduengo carbenes), for ex ...

. With the formulae (RP)_n and (R₂P)₂, respectively, compounds of phosphorus(I) and (II) are generated by reduction of the related organophosphorus(III) chlorides: :5 PhPCl₂ + 5 Mg → (PhP)₅ + 5 MgCl₂ :2 Ph₂PCl + Mg → Ph₂P-PPh₂ + MgCl₂

Diphosphene Diphosphene is a compound having the formula (PH)2. It exists as two geometric isomer Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, ...

s, with the formula R₂P₂, formally contain phosphorus-phosphorus double bonds. These phosphorus(I) species are rare but are stable provided that the organic substituents are large enough to prevent

catenation In chemistry, catenation is the bonding of atoms of the same element into a series, called a ''chain''. A chain or a ring shape may be ''open'' if its ends are not bonded to each other (an open-chain compound), or ''closed'' if they are bonded ...

. Many

mixed-valence Inner sphere electron transfer (IS ET) or bonded electron transfer is a redox chemical reaction that proceeds via a covalent linkage—a strong electronic interaction—between the oxidant and the reductant reactants. In inner sphere electron tran ...

compounds are known, e.g. the cage P₇(CH₃)₃.

References

External links

* organophosphorus chemistry
users.ox.ac.uk

* NMR predictor for organophosphorus compound chemical shifts from Alan Brisdon's Research Grou
Link
{{Authority control Functional groups