Methylenetriphenylphosphorane

Methylenetriphenylphosphorane
Names
Preferred IUPAC name
Methylidenetri(phenyl)phosphane
Identifiers
CAS Number
  • 3487-44-3 checkY
3D model (JSmol)
  • Interactive image
ChemSpider
  • 121606
PubChem CID
  • 137960
UNII
  • 8GN8K95F62 checkY
CompTox Dashboard (EPA)
  • DTXSID20188410 Edit this at Wikidata
InChI
  • InChI=1S/C19H17P/c1-20(17-11-5-2-6-12-17,18-13-7-3-8-14-18)19-15-9-4-10-16-19/h2-16H,1H2
    Key: XYDYWTJEGDZLTH-UHFFFAOYSA-N
  • InChI=1/C19H17P/c1-20(17-11-5-2-6-12-17,18-13-7-3-8-14-18)19-15-9-4-10-16-19/h2-16H,1H2
    Key: XYDYWTJEGDZLTH-UHFFFAOYAU
  • C=P(C1=CC=CC=C1)(C2=CC=CC=C2)C3=CC=CC=C3
Properties
Chemical formula
 C19H17P
Appearance yellow solid
Density 1.19 g/cm3
Solubility in water
 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
Chemical compound

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 methyltriphenylphosphonium bromide by its deprotonation using a strong base like butyllithium:[1]

Ph3PCH3Br + BuLi → Ph3PCH2 + LiBr + BuH

The phosphorane is generally not isolated, instead it is used in situ. The estimated pKa of this carbon acid is near 15.[2] Potassium tert-butoxide has been used in place of butyl lithium.[3] Sodium amide has also been used a base.[4]

Methylenetriphenylphosphorane is used to replace oxygen centres in aldehydes and ketones with a methylene group, i.e., a methylenation:

R2CO + Ph3PCH2 → R2C=CH2 + Ph3PO

The phosphorus-containing product is triphenylphosphine oxide.

Structure

Crystallographic characterization of the colourless ylide reveals that the phosphorus atom 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).[5] The compound is usually described as a combination of two resonance structures:

Ph3P+CH2− ↔ Ph3P=CH2

Uses

Two examples of the Wittig reaction using methylenetriphenylphosphorane
Two examples of the Wittig reaction using methylenetriphenylphosphorane

Methylenetriphenylphosphorane has become a standard tool for synthetic organic chemists.[6]

Related reagents

References

  1. ^ Wittig, Georg; Schoellkopf, U. (1960). "Methylenecyclohexane". Organic Syntheses. 40: 66. doi:10.15227/orgsyn.040.0066.
  2. ^ Ling-Chung, Sim; Sales, Keith D.; Utley, James H. P. (1990). "Measurement of pKa Values for Phosphonium Salts via the Kinetics of Proton Transfer to an Electrogenerated Base". Journal of the Chemical Society, Chemical Communications (9): 662. doi:10.1039/C39900000662.
  3. ^ Fitjer, L.; Quabeck, U. Synthetic Communications 1985, 15(10), 855–864.
  4. ^ F. A. Bottino, G. Di Pasquale, A. Pollicino, A. Recca and D. T. Clark (1990). "Synthesis of 2-(2-hydroxyphenyl)-2H-benzotriazole monomers and studies of the surface photostabilization of the related copolymers". Macromolecules. 23 (10): 2662–2666. Bibcode:1990MaMol..23.2662B. doi:10.1021/ma00212a011.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ Bart, J. C. J. (1969). "Structure of the non-stabilized phosphonium ylid methylenetriphenylphosphorane". Journal of the Chemical Society B. 1969: 350–365. doi:10.1039/J29690000350.
  6. ^ B. E. Maryanoff & A. B. Reitz (1989). "The Wittig olefination reaction and modifications involving phosphoryl-stabilized carbanions. Stereochemistry, mechanism, and selected synthetic aspects". Chem. Rev. 89 (4): 863–927. doi:10.1021/cr00094a007.