Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s containing

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

. They are used primarily in

pest control Pest control is the regulation or management of a species defined as a pest (organism), pest; such as any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the da ...

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

insecticide Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, i ...

s, although some are extremely toxic to humans, including

sarin Sarin (NATO designation GB nerve_agent#G-series.html" ;"title="hort for nerve agent#G-series">G-series, "B" is an extremely toxic organophosphorus compound.VX nerve agents. Phosphorus, like

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

, is in

group 15 , - ! colspan=2 style="text-align:left;" , ↓ Period , - ! 2 , , - ! 3 , , - ! 4 , , - ! 5 , , - ! 6 , , - ! 7 , , - , colspan="2", ---- ''Legend'' A pnictogen ( or ; from "to choke" and -gen, "generator") is any ...

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 In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...

, 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. The compound's name is presumably ...

), 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 Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

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 ion ...

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

Organophosphorus(V) compounds, main categories

Phosphate esters and amides

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

flame retardant Flame retardants are 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 combustion, ignition source and pr ...

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. Plasticizer ...

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 Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup. They are a major component of biological membranes and can easily be obtained from a variety of readily available sources, such as egg yolk or soyb ...

. Phosphate ester are synthesized by

alcoholysis In chemistry, solvolysis is a type of nucleophilic substitution (S1/S2) or elimination where the nucleophile is a solvent molecule. Characteristic of S1 reactions, solvolysis of a chiral reactant affords the racemate. Sometimes however, the ster ...

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 dithiophosphate Zinc dialkyldithiophosphates (often referred to as ZDDP) are a family of coordination compounds developed in the 1940s that feature zinc bound to the anion of a dialkyldithiophosphoric salt (e.g., ammonium diethyl dithiophosphate). These uncharge ...

s, as additives for motor oil. Several million kilograms of this

coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

are produced annually by the reaction of phosphorus pentasulfide with alcohols. Phosphoryl thioates are thermodynamically much stabler than thiophosphates, which can rearrange at high temperature or with a catalytic alkylant to the former: :SP(OR)₃ → OP(OR)₂SR In the environment, all these phosphorus(V) 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 reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

to eventually afford

phosphate Phosphates are the naturally occurring form of the element phosphorus. 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 orthop ...

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

Phosphonic and phosphinic acids and their esters

Phosphonate In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing Functional group, groups, where R is an organic group (alkyl, aryl). If R is hydrogen then the compound is a Phosphite_ester#Chemistry_of_HP(O)(OR ...

s 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 Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by EPSP inhibitor, inhibiting the plant enzyme 5-en ...

, 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. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

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 to treat osteoporosis. Evidence shows that they reduce the risk of fracture in ...

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 more porous bone, and consequent increase in Bone fracture, fracture risk. It is the most common reason f ...

. The nerve gas agent

sarin Sarin (NATO designation GB nerve_agent#G-series.html" ;"title="hort for nerve agent#G-series">G-series, "B" is an extremely toxic organophosphorus compound.glufosinate. 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 h ...

. 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 with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...

compounds. The Kabachnik–Fields reaction 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 +5. Phosphine oxides form

hydrogen bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

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

chalcogenide : 220px, Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment. A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elemen ...

s (R₃PE, where E = S, Se, Te). These compounds are some of the most thermally stable organophosphorus compounds. In general, they are less basic than the corresponding phosphine oxides, which can adduce to thiophosphoryl halides: :R₃PO + X₃PS → R₃P⁺–O–P⁺X₂–S⁻ + X⁻ Some phosphorus sulfides can undergo a reverse Arbuzov rearrangement to a dialkylthiophosphinate ester.

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, and different types of #Fabric, fabric. ...

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 an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

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 a chemical reaction that entails transfer of an alkyl group. 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 effecting al ...

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 Phenyllithium is an organometallic agent with the empirical formula . It is most commonly used as a metalating agent in organic syntheses and a substitute for Grignard reagents for introducing phenyl groups in organic syntheses. Crystalline phenyl ...

. 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 ...

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 ester file:Phosphite.svg, The general structure of a phosphite ester showing the lone pairs on the P In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be conside ...

s, 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 The Perkow reaction is an organic reaction in which a trialkyl phosphite ester reacts with a haloketone to form a dialkyl vinyl group, vinyl phosphate and an alkyl halide. In the related Michaelis–Arbuzov reaction the same reactants are known ...

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 phosphonous and phosphinous chlorides ((PCl₂R') and (PClR'₂) , respectively). The latter are produced by reaction of a

phosphorus trichloride Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic ...

with a poor metal-alkyl complex, e.g. organomercury, organolead, or a mixed

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

- organoaluminum compound.

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

chlorobenzene Chlorobenzene (abbreviated PhCl) is an aryl chloride and the simplest of the chlorobenzenes, consisting of a benzene ring substituted with one chlorine atom. Its chemical formula is C6H5Cl. This colorless, flammable liquid is a common solvent a ...

, PCl₃, and sodium. Phosphines of a more specialized nature are usually prepared by other routes. Phosphorus halides undergo

nucleophilic displacement In chemistry, a nucleophilic substitution (SN) is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). ...

by organometallic reagents such as

Grignard reagent Grignard reagents or Grignard compounds are chemical compounds 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 bromi ...

s. Organophosphines are nucleophiles and

ligand In coordination chemistry, a ligand is an ion or molecule with a 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 el ...

s. Two major applications are as reagents in the

Wittig reaction The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Most o ...

and as supporting phosphine ligands in

homogeneous catalysis In chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst in a solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in d ...

. Their nucleophilicity is evidenced by their reactions with

alkyl halide The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents of hydrogen atom. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalka ...

s to give phosphonium salts. Phosphines are nucleophilic catalysts in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

, 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 common reducing agents include hydrogen, carbon ...

s, as illustrated in the Staudinger reduction 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 azodicarboxy ...

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. A few halophosphines are known, although phosphorus' strong nucleophilicity predisposes them to decomposition, and dimethylphosphinyl fluoride spontaneously disproportionates to dimethylphosphine trifluoride and tetramethylbiphosphine. One common synthesis adds halogens to tetramethylbiphosphine disulfide. Alternatively alkylation of

gives a halophosphonium cation, which metals reduce to halophosphines.

Phosphaalkenes and phosphaalkynes

Compounds with carbon phosphorus(III) multiple bonds are called phosphaalkenes (R₂C=PR) and phosphaalkynes (RC≡P). They are similar in structure, but not in reactivity, to

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...

s (R₂C=NR) and

nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The name of the compound is composed of a base, which includes the carbon of the , suffixed with "nitrile", so for example is called " propionitrile" (or pr ...

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

phosphorine Phosphorine (IUPAC name: phosphinine) is a heavier Chemical element, 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 li ...

, 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, DABCO, or

triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. Like triethanolamine and the tetraethylammonium ion, it is often abbreviated TEA. It is a colourless volatile liquid with a strong fishy odor remini ...

: : Thermolysis 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 an organic molecule whose natural resonance structure has a carbon atom with octet rule, incomplete octet (a carbene), but does not exhibit the tremendous instability typically associated with ...

. 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 Diphosphenes, 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 chemical bond, bonding of atoms of the same Chemical element, element into a series, called a ''chain''. A chain or a Ring (chemistry), ring may be ''open'' if its ends are not bonded to each other (an open-chain c ...

. Bulky substituents also stabilize phosphorus radicals. Many mixed-valence compounds are known, e.g. the cage P₇(CH₃)₃.

References

External links

* Organophosphorus chemistry a
users.ox.ac.uk
* Organophosphorus chemistry a

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