Methylenetriphenylphosphorane
From Wikipedia, the free encyclopedia
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| Names | |
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| Preferred IUPAC name
Methylidenetri(phenyl)phosphane | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
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| UNII | |
CompTox Dashboard (EPA) |
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| 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).
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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.
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
