Organophosphorus chemistry

Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.

In a descriptive but only intermittently used nomenclature, phosphorus compounds are identified by their coordination number σ and their valency λ.

A variety of mixed amido-alkoxo derivatives are known, one medically significant example being the anti-cancer drug cyclophosphamide.

Several million kilograms of this coordination complex are produced annually by the reaction of phosphorus pentasulfide with alcohols.

[6] Phosphoryl thioates are thermodynamically much stabler than thiophosphates, which can rearrange at high temperature or with a catalytic alkylant to the former:[7]: 73–76 In the environment, all these phosphorus(V) compounds break down via hydrolysis to eventually afford phosphate and the organic alcohol or amine from which they are derived.

In general, they are less basic than the corresponding phosphine oxides, which can adduce to thiophosphoryl halides:[7]: 73 Some phosphorus sulfides can undergo a reverse Arbuzov rearrangement to a dialkylthiophosphinate ester.

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.

The latter are produced by reaction of a phosphorus trichloride with a poor metal-alkyl complex, e.g. organomercury, organolead, or a mixed lithium-organoaluminum compound.

[9] Replacement of one or more hydrogen centers by an organic substituents (alkyl, aryl), gives PH3−xRx, an organophosphine, generally referred to as phosphines.

[citation needed] From the commercial perspective, the most important phosphine is triphenylphosphine, several million kilograms being produced annually.

Phosphines are reducing agents, as illustrated in the Staudinger reduction for the conversion of organic azides to amines and in the Mitsunobu reaction for converting alcohols into esters.

[11] A few halophosphines are known, although phosphorus' strong nucleophilicity predisposes them to decomposition, and dimethylphosphinyl fluoride spontaneously disproportionates to dimethylphosphine trifluoride and tetramethylbiphosphine.

[13] Alternatively alkylation of phosphorus trichloride gives a halophosphonium cation, which metals reduce to halophosphines.

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

Compounds where phosphorus exists in a formal oxidation state of less than III are uncommon, but examples are known for each class.

These phosphorus(I) species are rare but are stable provided that the organic substituents are large enough to prevent catenation.