Magnesium reaction with alkyl halides

Scheme 7.5. A series of reactions utilized to convert an alkyl halide (1-chlorobutane) to the corresponding alkyltin hydride. The alkyl halide, after reaction with magnesium to produce a Grignard reagent can be hydrolyzed to produce the alkane. The trialkyltin hyride can be used to convert other alkyl halides to their respective alkanes.

Grignard Synthesis.— The most important method for synthesizing aromatic alcohols is by the Grignard reaction, with magnesium alkyl or aryl halides (p. 77). The one given as an example of a tertiary aromatic alcohol may be prepared by the action of magnesium phenyl bromide, CeHs—Mg—Br, upon acetone. 

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. 

An efficient method for the reduction of alkyl and aryl halides is by reaction with magnesium and isopropanol. 1-Bromonaphthalene is reduced at the boiling point of isopropanol (82°). With a less reactive halide, for example chlorobenzene, a... 

Alternatively these compounds may be obtained from dialkylamino phosphine halides by reaction with alkyl magnesium halides ((7.168) and (7.169)), aluminium alkyls ((7.170) and (7.171)) or organolithium derivatives ((7.172) and (7.173)). Phenylphosphinous chloride can be condensed with a sodium amide derivative (7.174) or a trimethylsilyl derivative (7.175) to give a phosphinous amide. 

Grignard reagents, R-MgX or Ar-MgX, are typically prepared by the reaction of an alkyl halide, R-X, or an aryl halide, Ar-X, with magnesium metal in an anhydrous ethereal solvent (Eq. 19.3) the organometallic reagent dissolves as it is formed. You may note that carbon is transformed from an electrophilic center in the starting material R-X or Ar-X into a nucleophilic center in the product R-MgX or Ar-MgX in this process. 

The reaction is carried out by first reacting the alkyl or aryl halide with magnesium shavings in an ether suspension and then treating with silicon tetrachloride (prepared by passing chlorine over heated silicon). With methyl chloride the following sequence of reactions occur ... 

Grignard reaction is the use of alkyl magnesium halides to form a host of products by reaction with a variety of chemicals... 

Grignard reagent (Section 14.4) An organomagnesium compound of the type RMgX formed by the reaction of magnesium with an alkyl or aryl halide. 

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