Halophosphines alkylation

Reduction of halophosphines [34-37] or alkyl phosphonates [38] using lithium aluminum hydride is commonly employed for the preparation of alkyl or aryl substituted primary phosphines (Eqs. 1-4) ... 

Organophosphorus compounds find wide use in the chemical industry as catalysts, intermediates, complexes, and end-use products. Arylphosphines and phosphine oxides are often produced by the reaction of a preformed Grignard reagent with a halophosphine or phosphine oxide. Yields are reduced by the production of unwanted side-reaction products such as biaryls. These unwanted products are reduced when the reaction is conducted under Barbier conditions. When alkyl and aryl halides are reacted with magnesium metal, a trihalophosphine or phosphine oxide, a metal halide or amine catalyst, in THE benzene mixtures, at reflux, good yields of phosphines or phosphine oxides are obtained [74]. For example, triphenylphosphine can be prepared in a 97.2% yield from the reaction of bromobenzene, trichlorophosphine, magnesium metal, aluminum chloride, and sodium chloride in THF-benzene at 70 80 C. 

Halophosphines are produced by reactions of phosphorus with alkyl chlorides, alkyl bromides, or aryl bromides in solution (12) and by reaction of red phosphorus in tlie presence of copper with alkyl halides in tlie vapor phase (13). Both methods require temperatures in excess of 2 )0°. The preparation of halopliosphines in solution is illustrated by the results of uncatalyzed white phosphorus reactions summarized in Table I (12). Alkyl dihalopliosphiues are the predominant products under these conditions, but appreciable yields of dialkylmonohalophos-phines are also obtained. The reaction temperature requirement de-... 

The lower alkyl halophosphines (6.138) are colourless liquids, heavier than water, which can be distilled without decomposition. They have a sharp disagreeable smell and can cause headaches and nausea. They are soluble in organic solvents and are very sensitive to moisture and air. Dimethylfluorophosphine, Me2PF, is particularly easily oxidised and is spontaneously inflammable in air. The halophosphines are generally very reactive, but their reactivity decreases with increasing molecular weight. 

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). 

Under conditions in which hydrogen chloride can be removed, successive chlorination of the alkyl group may occur with some halophosphines. 

At high temperatures (>ca. 250°C), phosphorus reacts with organic halides to produce aryl (alkyl) dihalophosphines and diaryl (dialkyl) halophosphines (Equation 10.70). 

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