Organophosphorus Compound

any one of numerous organic compounds containing phosphorus that form a broad class. A distinction is made between organophosphorus compounds in which the phosphorus is directly bonded to carbon in the molecules and organophosphorus compounds in which the phosphorus is bonded to the organic part of the molecules by a heteroatom—oxygen, nitrogen, or sulfur (this is mainly the case for esters and other acid derivatives of phosphorus). The latter are widely distributed in nature, primarily as esters of phosphoric, pyrophosphoric, and triphosphoric acids; these include nucleic acids, many important coenzymes, adenosine triphosphate—the energy carrier in living organisms—and a number of vitamins. Organophosphorus compounds containing a phosphorus-carbon bond, for example, β-aminoethylphosphonic acid (ciliatin), were discovered in nature in the 1960’s.

Classification. No single classification of organophosphorus compounds exists. Organophosphorus compounds are classified according to various characteristics. For example, according to the number of P—C bonds, they are classified as alkylphospines (RPH₂), dialkylphospines (R₂PH), and trialkylphospines (R₃P) and their derivatives (henceforth R will denote an organic radical).

On the basis of the valence state of phosphorus, researchers distinguish the derivatives of trivalent and pentavalent phosphorus. Also known are compounds of bicoordinated, tetracoordinated, pentacoordinated, and hexacoordinated phosphorus: in compounds such as tetracoordinated phosphorus, the phosphorus atom carries a positive charge, whereas the charge is negative in the hexacoordinated phosphorus.

Organophosporus compounds can also be classified according to the nature of the phosphorus function as phosphines, phos-phine oxides (R₃PO), phosphine sulfides (R₃PS), phosphine imines (R₃PNR′), methylene phosphines (R₃P ═ CR′R″), and phosphonium compounds (R₄P ⁺ X^–). Also included are acids containing oxygen, such as phosphonous acid (RPO₂H₂), phosphinous acid (R₂POH), phosphonic acid (RPO₃H₂), and phosphinic acid (R₂PO₂H) and their various sulfur and nitrogen analogs and derivatives, as well as various organic derivatives (esters, amides, anhydrides) of hypophosphorous acid (H₃PO₂), phosphorous acid (H₃PO₃), phosphoric acid (H₃PO₄) and other acids. In addition, there are known organophosphorus compounds with a P—P bond, for example diphosphines, triphos-phines, and tetraphosphines and the corresponding cyclophos-phines and their derivatives.

Preparation. Methods of C—P bond formation are very important in the synthesis of organophosphorus compounds. These include (1) the Arbuzov reaction: (RO)₃P + R′X → R′PO(OR)₂+ RX; (2) the Michaelis-Becker reaction: (RO)₂PONa + R′X → R′PO(OR)₂ + NaX; (3) synthesis with organometallic compounds, for example, PCl₃ + 3RMgX → R₃P + 3MgXCl; (4) phosphorylation according to a Friedel-Crafts type of reaction:

(5) the addition of phosphorus pentachloride to olefins: C₆H₅CH ═ CH₂ + 2PCl₅ → C₆H₅CHCl—CH₂PCl₄ · PCl₅; (6) the alkylation of elemental phosphorus, for example,

(7) the diene synthesis reaction:

and (8) the addition of organophosphorus compounds containing the P—H bond to olefins, carbonyl compounds, and Schiff bases, for example, (RO)₂PHO + NH₃ + CH₂O → NH₂CH₂PO(OR)₂.

Esters and other acid derivatives of phosphorus are usually obtained by the action of chloranhydrides of these acids on alcohols, often in the presence of bases that bind the released HCl. For example, RPOCl₂ + 2R′OH + 2(C₂H₅)₃N → RPO(OR′)₂ + 2(C₂H₅)₃N · HCl.

Compounds that contain the P ═ N bond are prepared by the action of azides on trivalent phosphorus compounds: R₃P + C₆H₅N₃→ R₃P ═ NC₆H₅ + N₂ or by the phosphase reactions: RSO₂N₂ + PCl₅ → RSO₂N ═ PCl₃ + 2HCl. Methylenephosphines are synthesized most often by the action of bases on phosphonium salts:

[⁺ R₃PCH₂R′]Cl^– + NaOR′ → R₃P ═ CHR′ + NaCl + R′OH

Uses. Organophosphorus compounds are used in technology, agriculture, medicine, and scientific research. The manufacture of organophosphorus pesticides has reached large-scale proportions. Although highly effective, such pesticides are toxic for humans and animals, and their application necessitates precautionary measures. One advantage they do possess is that they do not accumulate in the environment.

In medicine, organophosphorus compounds are used mainly in opthalmology. Biologically important phosphates, such as adenosine triphospate, cocarboxylase, and a number of vitamins, are also valuable.

As complex-forming agents, organophosphorus compounds are used in ore concentration and in the production of uranium and other metals. Many organophosphorus compounds are used as additives in lubricants to increase their working properties, in components of plastic and fibers to make them noncombustible (antipyrenes), in solvents, and in hydraulic fluids. Advancements have also been made in the field of organophosphorus complex-ones, which are used for the separation of metals, as well as for other purposes.

Organophosphorus compounds have acquired considerable value in organic synthesis. For example, methylenephosphines are used in the synthesis of olefins from carbonyl compounds (Wittig reaction), and pyrophosphorous acid esters, in peptide synthesis. Various biologically important phosphates are used in biochemical, molecular-biological, and physiological research, and oxides of trialkylphosphines serve as catalysts in carbodi-imide synthesis. Phosphorus-containing polymers, prepared from phosphorus-containing monomers or by the phosphorylation of high-molecular compounds, such as cellulose, polyethylene, and rubber, are also widely used in the preparation of noncombustible materials and ion-exchange resins. Organophosphorus compounds also include such war gases as Sarin, Soman, Tabun, and phosphoryl thiocholines.