Methylenetriphenylphosphorane

Methylenetriphenylphosphorane
Names
IUPAC name
Methylene(triphenyl)phosphorane
Identifiers
3487-44-3
3D model (Jmol) Interactive image
ChemSpider 121606
PubChem 137960
Properties
C19H17P
Appearance yellow solid
Density 1.19 g/cm3
decompose
Solubility THF
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references


Methylenetriphenylphosphorane is an organophosphorus compound with the formula Ph3PCH2. It is the parent member of the phosphorus ylides, popularly known as Wittig reagents. It is a highly polar, highly basic species.

Preparation and use

Methylenetriphenylphosphorane is prepared from triphenylphosphine and methyl bromide followed by deprotonation of the resulting phosphonium salt using a strong base like butyllithium:[1]

Ph3PCH3Br + BuLi → Ph3PCH2 + LiBr + BuH

The compound is generally not isolated, instead it is used in situ.

Methylenetriphenylphosphorane is used to replace oxygen centres in aldehydes and ketones with a methylene group:

R2CO + Ph3PCH2 → R2C=CH2 + Ph3PO

The phosphorus-containing product is triphenylphosphine oxide.

Structure

Crystallographic characterization of the colourless ylide reveals that the phosphorus is approximately tetrahedral. The PCH2 centre is planar and the P=CH2 distance is 1.661 Å, which is much shorter than the P-Ph distances (1.823 Å).[2] The compound is usually described as a combination of two resonance structures:

Ph3P+CH2 Ph3P=CH2

References

  1. Georg Wittig U. Schoellkopf (1973). "Methylenecyclohexane". Org. Synth.; Coll. Vol., 5, p. 751
  2. Bart, J. C. J. "Structure of the non-stabilized phosphonium ylid methylenetriphenylphosphorane". Journal of the Chemical Society B: Physical Organic J. Chem. Soc. B. 1969: 350–365. doi:10.1039/J29690000350.
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