Phenylmagnesium bromide

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Phenylmagnesium bromide
Phenylmagnesium bromide.svg
Names
IUPAC name
Bromido(phenyl)magnesium
Other names
PMB, (bromomagnesio)benzene [ citation needed ]
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.002.607 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 202-867-2
PubChem CID
  • InChI=1S/C6H5.BrH.Mg/c1-2-4-6-5-3-1;;/h1-5H;1H;/q;;+1/p-1 X mark.svgN
    Key: ANRQGKOBLBYXFM-UHFFFAOYSA-M X mark.svgN
  • InChI=1/C6H5.BrH.Mg/c1-2-4-6-5-3-1;;/h1-5H;1H;/q;;+1/p-1/rC6H5BrMg/c7-8-6-4-2-1-3-5-6/h1-5H
    Key: ANRQGKOBLBYXFM-ZAQPMBKGAV
  • Br[Mg]c1ccccc1
Properties
C6H5MgBr
Molar mass 181.315 g·mol−1
AppearanceColorless crystals
Density 1.14 g cm−3
Reacts with water
Solubility 3.0M in diethyl ether, 1.0M in THF, 2.9M in 2-MeTHF
Acidity (pKa)45 (conjugate acid)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Causes severe skin burns and serious eye damage, very flammable, volatile
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-acid.svg
Danger
H225, H314
P210, P233, P240, P241, P242, P243, P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P370+P378, P403+P235, P405, P501
Flash point −45 °C (−49 °F; 228 K)
Safety data sheet (SDS) External MSDS
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Phenylmagnesium bromide, with the simplified formula C 6 H 5 Mg Br , is a magnesium-containing organometallic compound. It forms colorless crystals. 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

Preparation

Phenylmagnesium bromide is prepared by reaction of bromobenzene with magnesium metal. Preparation of phenylmagnesium bromide.jpg
Phenylmagnesium bromide is prepared by reaction of bromobenzene with magnesium metal.

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

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

Structure

Structure of ether adducts of phenylmagnesium bromide where OR2 an ether. PhMrBrL2.png
Structure of ether adducts of phenylmagnesium bromide where OR2 an ether.

Although phenylmagnesium bromide is routinely represented as C6H5MgBr, the compound's structure is more complicated. Like most Grignard reagents, phenylmagnesium bromide is invariably observed as an adduct with various Lewis bases. Examples include the diethyl ether and tetrahydrofuran complexes C6H5MgBr[O(C2H5)2]2 and C6H5MgBr(OC4H8)2, respectively. [2] [3] Thus, the Mg in those adducts is tetrahedral and obeys the octet rule. The Mg–O distances are 201 and 206 pm, and the Mg–C and Mg–Br distances are 220 pm and 244 pm, respectively in the diethyl ether complex. In their reactions of these complexes, these ether ligands dissociate. [2]

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] [4] With carbon dioxide, it reacts to give benzoic acid after an acidic workup. If three equivalents are reacted with phosphorus trichloride, triphenylphosphine can be made.

References

  1. 1 2 Robertson, D. L. (2007-01-03). "Grignard Synthesis: Synthesis of Benzoic Acid and of Triphenylmethanol". MiraCosta College . Retrieved 2008-01-25.
  2. 1 2 Stucky, G.; Rundle, R. E. (1964). "The Constitution of the Grignard Reagent, Phenylmagnesium Bromide Dietherate". Journal of the American Chemical Society. 86 (22): 4825–4830. Bibcode:1964JAChS..86.4825S. doi:10.1021/ja01076a020.
  3. ↑ Schröder, Friedrich Anton (1969). "Zur Kenntnis der Grignard-Verbindung C6H5MGBR(C4H8O)21,2 sowie über die Koordinationsverbindung MGBR2(C4H8O)4". Chemische Berichte. 102 (6): 2035–2043. doi:10.1002/cber.19691020628.
  4. ↑ Bachmann, W. E.; Hetzner, H. P. (1955). "Triphenylcarbinol". Organic Syntheses ; Collected Volumes, vol. 3, p. 839.
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