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Chemical compound From Wikipedia, the free encyclopedia
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.
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Preferred IUPAC name
Methylidenetri(phenyl)phosphane | |
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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 prepared from methyltriphenylphosphonium bromide by its deprotonation using a strong base like butyllithium:[1]
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:
The phosphorus-containing product is triphenylphosphine oxide.
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:
Methylenetriphenylphosphorane has become a standard tool for synthetic organic chemists.[6]
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