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A phosphonium salt is a salt containing the phosphonium
Phosphonium

In chemistry, the phosphonium cation is a positively charged polyatomic ion with the chemical formula PH4+, resulting from protonation of phosphine....
 (PH4+) ion such as phosphonium iodide (PH4+I−). More commonly, phosphonium refer to an organic derivative such as tetraphenylphosphonium chloride
Tetraphenylphosphonium chloride

Tetraphenylphosphonium chloride is the chemical compound with the formula 4PCl, abbreviated Ph4PCl or PPh4Cl. Tetraphenylphosphonium and especially tetraphenylarsonium salts were formerly of interest in gravimetric analysis of perchlorate and related oxyanions....
, (C6H5)4P+ Cl- and tetramethylphosphonium iodide, [P(CH3)4]+I−.

Alkyltriphenylphosphonium salts are widely used for the preparation of Wittig reagents
Wittig reaction

The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl #Wittig reagents to give an alkene and triphenylphosphine oxide....
 for the Wittig reaction
Wittig reaction

The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl #Wittig reagents to give an alkene and triphenylphosphine oxide....
.






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A phosphonium salt is a salt containing the phosphonium
Phosphonium

In chemistry, the phosphonium cation is a positively charged polyatomic ion with the chemical formula PH4+, resulting from protonation of phosphine....
 (PH4+) ion such as phosphonium iodide (PH4+I−). More commonly, phosphonium refer to an organic derivative such as tetraphenylphosphonium chloride
Tetraphenylphosphonium chloride

Tetraphenylphosphonium chloride is the chemical compound with the formula 4PCl, abbreviated Ph4PCl or PPh4Cl. Tetraphenylphosphonium and especially tetraphenylarsonium salts were formerly of interest in gravimetric analysis of perchlorate and related oxyanions....
, (C6H5)4P+ Cl- and tetramethylphosphonium iodide, [P(CH3)4]+I−.

Alkyltriphenylphosphonium salts are widely used for the preparation of Wittig reagents
Wittig reaction

The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl #Wittig reagents to give an alkene and triphenylphosphine oxide....
 for the Wittig reaction
Wittig reaction

The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl #Wittig reagents to give an alkene and triphenylphosphine oxide....
. Such salts are readily made by the reaction of triphenylphosphine
Triphenylphosphine

Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PhosphorusPhenyl group or Ph3P....
 with an alkyl halide:

Phosphoniumsaltgeneral
Note that Ph stands for phenyl and X is a halide
Halide

A halide is a binary compound, of which one part is a halogen atom and the other part is an chemical element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound....
The reaction works well if the alkyl
Alkyl

An alkyl is a univalent Radical consisting of carbon and hydrogen atoms, arranged in a chain. The Alkyls form homologous series with the general formula CnH2n+1....
 group is methyl or an unhindered primary alkyl
Alkyl

An alkyl is a univalent Radical consisting of carbon and hydrogen atoms, arranged in a chain. The Alkyls form homologous series with the general formula CnH2n+1....
 group (as shown), but it is usually poor with secondary alkyl halides. Tertiary alkyl groups cannot form the ylide. The phosphonium salt is a stable compound which can often be purified by recrystallisation from ethanol
Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatility , flammable, colorless liquid....
.

To form the Wittig reagent (ylide
Ylide

An ylid or ylide is a electric charge molecule with a positive and a negative charge on adjacent atoms. They appear in organic chemistry as reagents or reactive intermediates....
), the phosphonium salt is suspended in a solvent such as diethyl ether
Diethyl ether

Diethyl ether, also known as ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor....
 or THF
Tetrahydrofuran

Tetrahydrofuran is a colorless, water-miscible organic liquid with low-viscosity at "room" temperature and pressure . It is a Heterocyclic compound compound with a chemical formula C4H8O, and is the fully Hydrogenation analog of the aromatic organic compound furan....
 and a strong base such as phenyllithium or n-butyllithium
N-Butyllithium

n-Butyllithium is the most prominent organolithium reagent. It enjoys wide use as a polymerisation initiator in the production of elastomers such as polybutadiene or Styrene-butadiene....
 is added.

One study demonstrates the use of benzyl alcohol
Benzyl alcohol

Benzyl alcohol is an organic compound with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn", thus benzyl alcohol is denoted as BnOH....
s as starting material for the synthesis of phosphonium acetates provided that the arene carries activating group
Activating group

In organic chemistry, a functional group is called an activating group if a benzene molecule to which it is attached more readily participates in electrophilic substitution reactions....
s:

Phosphoniumacetatesynthesis
:Note that Ac stands for acetyl
Acetyl

In organic chemistry, acetyl , is a functional group, the acyl of acetic acid, with chemical formula -CarbonOxygenCarbonHydrogen3. It is sometimes abbreviated as Ac ....
, the ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
 group is hydrolized
Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
 to a phenol
Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....


The phosphonium acetate
Acetate

An acetate, or ethanoate, is either a salt or ester of acetic acid.In chemistry, the abbreviation Ac refers to the acetyl group. The anion and the functional group may be written as -OAc and AcO-, or OAc respectively....
 group does not have an impact on the subsequent Wittig reaction.

Phosphonium halides

Phosphine
Phosphine

Phosphine is the common name for phosphorus trihydride , also known by the IUPAC name phosphane and, occasionally, phosphamine....
s (R3P) react with halogen
Halogen

|}The halogens or halogen elements are a chemical series of nonmetal chemical element from Periodic table group International Union of Pure and Applied Chemistry of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At....
s (X2) to phosphonium halides of the type R3PX2. The compound Ph3PBr2 (high melting solid) formed by reaction of triphenylphosphine
Triphenylphosphine

Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PhosphorusPhenyl group or Ph3P....
 and bromine
Bromine

Bromine , , meaning "stench " ), is a chemical element with the symbol Br and atomic number 35. A halogen element, bromine is a reddish-brown Volatility liquid at Standard conditions for temperature and pressure that is intermediate in reactivity between chlorine and iodine....
 is called bromotriphenylphosphonium bromide or dibromotriphenylphosphorane (now defined as a phosphorane
Phosphorane

A phosphorane is a functional group in chemistry with pentavalent phosphorus. It has the general structure PR5. The parent compound is the non-stable phosphoran PH5 or ?5-Phosphan according to IUPAC nomenclature....
) or simply triphenylphosphine dibromide. The dibromide and dichloride are commercially available as halogenation
Halogenation

Halogenation is a chemical reaction that incorporates a halogen atom into a molecule. More specific descriptions exist that specify the type of halogen: fluorination, chlorination, bromination, and iodination....
 reagents for instance in halogenation of alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
s and phenol
Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
s .

The compund triphenylphosphine dichloride
Triphenylphosphine dichloride

Triphenylphosphine dichloride, Ph3PCl2, is a Halogenation widely used in organic chemistry. Applications include the conversion of alcohols and ethers to alkyl chlorides, the cleavage of epoxides to vicinal dichlorides and the chlorination of carboxylic acids to acyl chlorides....
, Ph3PCl2, is reported has being an ionic compound
Ionic compound

In chemistry, an ionic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. Usually, the positively charged portion consists of metal cations and the negatively charged portion is an anion or polyatomic ion....
 (PPh3Cl)+Cl- in polar solutions and a molecular species with trigonal bipyramidal molecular geometry in apolar solution and in the solid state

See also

  • Organophosphorus chemistry