Methylenetriphenylphosphorane is an

organophosphorus compound Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbo ...

with the formula Ph₃PCH₂. It is the parent member of the phosphorus

ylide An ylide () or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both ...

s, popularly known as

Wittig reagent In organic chemistry, Wittig reagents are organophosphorus compounds of the formula R3P=CHR', where R is usually phenyl. They are used to convert ketones and aldehydes to alkenes: : Preparation Because they typically hydrolyze and oxidize readily, ...

s. It is a highly polar, highly basic species.

Preparation and use

Methylenetriphenylphosphorane is prepared from

methyltriphenylphosphonium bromide Methyltriphenylphosphonium bromide is the organophosphorus compound with the formula C6H5)3PCH3r. It is the bromide salt of a phosphonium cation. It is a white salt that is soluble in polar organic solvents. Synthesis and reactions Methyltrip ...

by its deprotonation using a strong base like

butyllithium Butyllithium may refer to one of 5 isomeric organolithium reagents of which 3 are commonly used in chemical synthesis: * ''n''-Butyllithium, abbreviated BuLi or nBuLi * ''sec''-Butyllithium, abbreviated ''sec''-BuLi or sBuLi, has 2 stereoisomers, ...

: :Ph₃PCH₃Br + BuLi → Ph₃PCH₂ + LiBr + BuH The phosphorane is generally not isolated, instead it is used in situ. The estimated pK_a of this

carbon acid In organic chemistry, a carbanion is an anion with a lone pair attached to a tervalent carbon atom. This gives the carbon atom a negative charge. Formally, a carbanion is the conjugate base of a carbon acid: : where B stands for the base. The ca ...

is near 15.

Potassium tert-butoxide Potassium ''tert''-butoxide (or potassium ''t''-butoxide) is a chemical compound with the formula CH3)3COKsub>''n'' (abbr. KOtBu). This colourless solid is a strong base (pKa of conjugate acid is 17 in H2O), which is useful in organic syn ...

has been used in place of

butyl lithium Butyllithium may refer to one of 5 isomeric organolithium reagents of which 3 are commonly used in chemical synthesis: * ''n''-Butyllithium, abbreviated BuLi or nBuLi * ''sec''-Butyllithium, abbreviated ''sec''-BuLi or sBuLi, has 2 stereoisomers, ...

Sodium amide Sodium amide, commonly called sodamide (systematic name sodium azanide), is the inorganic compound with the formula . It is a salt composed of the sodium cation and the azanide anion. This solid, which is dangerously reactive toward water, is whit ...

has also been used a base. Methylenetriphenylphosphorane is used to replace oxygen centres in

aldehydes In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

and

ketones In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

with a methylene group, i.e., a

methylenation In organic chemistry, methylenation is a chemical reaction that inserts a methylene () group into a chemical compound: :\ce \longrightarrow \ce\ce In a related sense, it also describes a process in which a divalent group of a starting material ...

: :R₂CO + Ph₃PCH₂ → R₂C=CH₂ + Ph₃PO The phosphorus-containing product is

triphenylphosphine oxide Triphenylphosphine oxide (often abbreviated TPPO) is the organophosphorus compound with the formula , also written as or (Ph = ). It is one of the more common phosphine oxides. This colourless crystalline compound is a common but potentially u ...

Structure

Crystallographic characterization of the colourless ylide reveals that the phosphorus atom is approximately tetrahedral. The PCH₂ centre is planar and the ''P=C''H₂ distance is 1.661 Å, which is much shorter than the P-Ph distances (1.823 Å). The compound is usually described as a combination of two

resonance structure In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...

s: :Ph₃P⁺CH₂⁻ ↔ Ph₃P=CH₂

Uses

Methylenetriphenylphosphorane has become a standard tool for synthetic organic chemists.{{Cite journal, author1=B. E. Maryanoff , author2=A. B. Reitz , name-list-style=amp , title = The Wittig olefination reaction and modifications involving phosphoryl-stabilized carbanions. Stereochemistry, mechanism, and selected synthetic aspects , year = 1989 , journal = Chem. Rev. , volume = 89 , issue = 4 , pages = 863–927 , doi = 10.1021/cr00094a007

Related reagents

(Chloromethylene)triphenylphosphorane (Chloromethylene)triphenylphosphorane is the organophosphorus compound with the formula Ph3P=CHCl (Ph = phenyl). It is a white solid but is usually generated and used in situ as a reagent in organic synthesis. It is structurally and chemically ...

Methoxymethylenetriphenylphosphine Methoxymethylenetriphenylphosphorane is a Wittig reagent used for the homologization of aldehydes, and ketones to extended aldehydes, an organic reaction first reported in 1958. The reagent is generally prepared and used in situ. It has blood-red ...

Carbomethoxymethylenetriphenylphosphorane Carbomethoxymethylenetriphenylphosphorane is a Chemical substance, chemical compound used in Organic compound, organic syntheses. It contains a phosphorus atom bound to three phenyl groups, and doubly bound to the alpha position of methyl acetate. ...

References

Organophosphorus compounds Quaternary phosphonium compounds Phosphorus(V) compounds Phenyl compounds Bases (chemistry)