Halophosphinic acids

Preparation and Properties of Organophosphines. AUphatic phosphines can be gases, volatile Hquids, or oils. Aromatic phosphines frequentiy are crystalline, although many are oils. Some physical properties are Hsted in Table 14. The most characteristic chemical properties of phosphines include their susceptabiUty to oxidation and their nucleophilicity. The most common derivatives of the phosphines include halophosphines, phosphine oxides, metal complexes of phosphines, and phosphonium salts. Phosphines are also raw materials in the preparation of derivatives, ie, derivatives of the isomers phosphinic acid, HP(OH)2, and phosphonous acid, H2P(=0)0H. 

In general, if the desired carbon—phosphoms skeleton is available in an oxidi2ed form, reduction with lithium aluminum hydride is a powerful technique for the production of primary and secondary phosphines. The method is appHcable to halophosphines, phosphonic and phosphinic acids as well as thein esters, and acid chlorides. Tertiary and secondary phosphine oxides can be reduced to the phosphines. 

See Phosphorus tribromide Sulfur acids Phosphorus trichloride Sulfur acids See Other IODINE COMPOUNDS, HALOPHOSPHINES, NON-METAL HALIDES... 

Protonation of phosphinic acid, phosphites, or halophosphines by FSOjH or FSOjH-SbFj in SOj at low T yields phosphonium ions, as observed in H and P NMR spectra, e.g. ... 

Organosilanes and HSiClj reduce selectively halophosphines, phosphonous acids and phosphonic acids and estersUnlike ionic metal hydrides, organosilanes do not attack C—P bonds. The organosilane reductions usually can be performed without solvents. In addition, they occur with retention of configuration at the phosphorus. 

Methods for the preparation and properties of tervalent phosphorus acid derivatives with one or two P—C bonds were reviewed in detail by Sasse in Houben-Weyl, Vol. 12/1 (published 1963) and by Regitz in Houben- Weyl, Vol. El (published 1982) Another valuable review on this subject is Vol. 4 in Kosolapoff and Maier s Organophosphorus Compounds (published 1972), which contains lists on all known compounds up to ca 1970. These should always be consulted for information of the preparation of compounds known before the above publication times. Yearly reviews on the preparation and chemistry of halophosphines and tervalent phosphorus acid derivatives are published in Specialist Periodical Reports, Organophosphorus Chemistry (from Yo. 1,1970) ... 

Tervalent phosphorus acid derivatives are normally liquids or low-melting solids which can be purified by distillation, or sometimes by recrystallization from a non-polar solvent. Most are oxidized in contact with the atmosphere, and many are easily hydrolyzed, so they must be kept under an inert atmosphere (N2 or Ar) during all manipulations. Flasks should be predried and solvents dried and deoxygenated before use. Tervalent phosphorus acid derivatives are, with few exceptions, thermally stable and can be kept indefinitely in ampoules under an inert gas (many halophosphines dissolve stopcock grease and should not be kept in stoppered flasks for prolonged periods). Inert solvents are hydrocarbons, ethers and, for most compounds, dichloromethane, ethyl acetate and tertiary amines. Aminophosphines react vigorously with tetrachloromethane and slowly with trichloromethane, and most tervalent phosphorus acid derivatives are oxidized by dimethyl sulphoxide and react with alcohols. 

Trifluoromethylphosphonous acid is obtained by hydrolysis of the halophosphine, but its sodium salt is sodium trifluoromethyl phosphinate. 

Phosphonium salts are produced by acidification of an appropriate ylid (6.422) or by adding halophosphines or alkyl halides to ylids (6.377, 6.378). Phosphonium cations are obtained by reacting phosphorus pentachloride with phosphorus pentaphenyl (6.477) or with lithio biphenyl (480). Oxiranes react with phosphines to produce betaines which, in the presence of acids, give hydroxy-alkyl phosphonium salts (3.114). 

Halophosphines are reduced by HSiClj (9.205). Similarly phosphonic and phosphonous acids and esters are reduced by Pli2SiH2, but no Si-P bonds are formed (9.206-9.208). 

The hydrogen atoms of the two CH groups are acidic, in contrast to those of the BH groups, which are hydridic. Therefore, selective functionalization of the carbon atoms is possible by electrophilic substitution or deprotonation with strong bases followed by subsequent reaction with electrophiles. However, the steric bulk of the clusters requires appropriate reactivity of the electrophile to obtain the desired product in acceptable yields. Phosphorus-containing compounds such as halophosphines are suitable for this type of functionalization of carboranes. In 1963, the first reaction with phosphines was described and until today it has ranained the method of choice for phosphorus functionalization of carboranes. 

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