Phenylmagnesium bromide

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Phenylmagnesium bromide
Phenylmagnesium bromide, OR2 = ether or THF
PhMgBr THF adduct
IUPAC name bromido(phenyl)magnesium
Other names PMB
Identifiers
CAS number [100-58-3]
SMILES Br[Mg]c1ccccc1
Properties
Molecular formula C6H5MgBr
Molar mass 181.31 g/mol
Appearance Colorless crystals
Density 1.14
Solubility in water Reacts violently
Basicity (pKb) strong base
Hazards
MSDS External MSDS
Main hazards flammable
R-phrases R12 R14 R15 R20 R22 R35 R41
S-phrases S16 S26 S30 S33 S36
S37 S39 S42 S45
Flash point  ?°C
Related compounds
Related compounds Phenyllithium
Magnesium bromide
Methylmagnesium chloride
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Phenylmagnesium bromide, with the simplified formula C6H5MgBr, is a a magnesium-containing organometallic compound. It is so commonly used that it is commercially available as a solution in diethyl ether or tetrahydrofuran (THF). Phenylmagnesium bromide is a Grignard reagent. It is often used as a synthetic equivalent for the phenyl "Ph−" synthon.

Contents

[edit] Preparation

Phenylmagnesium bromide is commercially available as solutions of diethyl ether or THF. It may be prepared in the laboratory by treating bromobenzene with magnesium metal, usually in the form of ribbon. A small amount of iodine may be used to activate the magnesium to initiate the reaction.[1]

Polar solvents, such as ether or THF, are required to solvate (complex) the magnesium(II) center. The solvent must be aprotic solvents since alcohols and water react with phenylmagnesium bromide to give benzene. Carbonyl-containing solvents such as acetone and ethyl acetate are incompatible with the reagent.

[edit] Structure

Although phenylmagnesium bromide is routinely represented as C6H5MgBr, the molecule is more complex. The compound invariably forms an adduct with two OR2 ligands from the ether or THF solvent. Thus, the Mg is tetrahedral and obeys the octet rule. The Mg-O distances are 2.01 and 2.06 Å whereas the Mg-C and Mg-Br distances are 2.2 and 2.44 Å, respectively.[2]

[edit] Chemistry

Phenylmagnesium bromide is a strong nucleophile as well as a strong base. It can abstract even mildly acidic protons, thus the substrate must be protected where necessary. It often adds to carbonyls, such as ketones, aldehydes.[1][3] With carbon dioxide, it reacts to give, after an acidic workup, benzoic acid.

[edit] References

  1. ^ a b Donald L. Robertson (2007-01-03). Grignard Synthesis: Synthesis of Benzoic Acid and of Triphenylmethanol. MiraCosta College. Retrieved on 2008-01-25.
  2. ^ Stucky, G. D.; Rundle, R. E. (1963). "The Structure of Phenylmagnesium Bromide Diethyletherate and the Nature of Grignard Reagents". J. Am. Chem. Soc. 85: 1002. doi:10.1021/ja00890a039. 
  3. ^ W. E. Bachmann and H. P. Hetzner. "Triphenylcarbinol". Org. Synth.; Coll. Vol. 3: 839.