Organic compound with at least one covalent carbon–phosphorus bond
Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are
chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.[2]
Phosphorus, like nitrogen, is in group 15 of the periodic table, and thus phosphorus compounds and nitrogen compounds have many similar properties.[3][4][5] 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 phosphorus-carbon (P-C) bond.[citation needed] Thus a large proportion of pesticides (e.g., malathion), are often included in this class of compounds.
alcoholysis of phosphorus oxychloride. A variety of mixed amido-alkoxo derivatives are known, one medically significant example being the anti-cancer drug cyclophosphamide. Also derivatives containing the thiophosphoryl group (P=S) include the pesticide malathion. The organophosphates prepared on the largest scale are the zinc dithiophosphates, as additives for motor oil. Several million kilograms of this coordination complex are produced annually by the reaction of phosphorus pentasulfide with alcohols.[6]
In the environment, these compounds break down via hydrolysis to eventually afford phosphate and the organic alcohol or amine from which they are derived.
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 is one of the most widely used herbicides. Bisphosphonates are 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.
Illustrative examples of phosphonates and phosphinates in the order shown: Sarin (phosphonate), Glyphosate (phosphonate), fosfomycin (phosphonate), zoledronic acid (phosphonate), and Glufosinate (phosphinate). In aqueous solution, phosphonic acids ionize to give the corresponding organophosphonates.
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.
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 [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. Approximately 2M kg are produced annually of the chloride and the related sulfate.[6] 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
arylation
of organophosphines:
PR3 + R'X → [PR3R'+]X−
The methylation of triphenylphosphine is the first step in the preparation of the Wittig reagent.
Wittig reagent
Ph3PCH2, and pentaphenylphosphorane, a rare pentaorganophophorus compound.
, 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.
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
The parent compound of the phosphines is PH3, called phosphine in the US and British Commonwealth, but phosphane elsewhere.[8] Replacement of one or more hydrogen centers by an organic substituents (alkyl, aryl), gives PH3−xRx, an organophosphine, generally referred to as phosphines.
From the commercial perspective, the most important phosphine is
Their nucleophilicity is evidenced by their reactions with
Staudinger reduction for the conversion of organic azides to amines and in the Mitsunobu reaction 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.[10]
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, [P(NHC)]2, where NHC is an
compounds of phosphorus(I)
and (II) are generated by reduction of the related organophosphorus(III) chlorides:
