Triphenylphosphine oxide
Overview
 
Triphenylphosphine oxide (often abbreviated TPPO) is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula OP(C6H5)3. Often chemists abbreviate the formula by writing Ph3PO or PPh3O (Ph = C6H5). This white crystalline compound is a common side product in reactions involving triphenylphosphine
Triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

. It is a popular reagent to induce the crystallizing
Crystallization
Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid...

 of chemical compounds.
Ph3PO is tetrahedral molecule related to POCl3.
Discussions
Encyclopedia
Triphenylphosphine oxide (often abbreviated TPPO) is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula OP(C6H5)3. Often chemists abbreviate the formula by writing Ph3PO or PPh3O (Ph = C6H5). This white crystalline compound is a common side product in reactions involving triphenylphosphine
Triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

. It is a popular reagent to induce the crystallizing
Crystallization
Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid...

 of chemical compounds.

Structure and properties

Ph3PO is tetrahedral molecule related to POCl3. The oxygen center is relatively basic. The rigidity of the backbone and the basicity of the oxygen center make this species a popular agent to crystallize otherwise difficult to crystallize molecules. This trick is applicable to molecules that have acidic hydrogen atoms, e.g. phenol
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...

s.

As a by-product of organic synthesis

Ph3PO is a by-product of many useful reactions in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

 including the Wittig
Wittig reaction
The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide to give an alkene and triphenylphosphine oxide....

, Staudinger
Staudinger reaction
The Staudinger reaction or Staudinger reduction is a chemical reaction in which the combination of an azide with a phosphine or phosphite produces an iminophosphorane intermediate. Combined with the hydrolysis of the aza-ylide to produce a phosphine oxide and an amine, this reaction is a mild...

, and Mitsunobu reaction
Mitsunobu reaction
The Mitsunobu reaction is an organic reaction that converts an alcohol into a variety of functional groups, such as an ester, using triphenylphosphine and an azodicarboxylate such as diethyl azodicarboxylate or diisopropyl azodicarboxylate . The alcohol undergoes an inversion of stereochemistry...

s. It is also formed when PPh3Cl2 is employed to convert alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s into alkyl chlorides.
Ph3PCl2 + ROH → Ph3PO + HCl + RCl


Triphenylphosphine can be regenerated from the oxide by treatment with trichlorosilane
Trichlorosilane
Trichlorosilane is a chemical compound containing silicon, hydrogen, and chlorine. At high temperatures, it decomposes to produce silicon, and therefore purified trichlorosilane is the principal source of ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce...

.
Ph3PO + SiHCl3 → PPh3 + 1/n (OSiCl2)n + HCl


Triphenylphosphine oxide can be difficult to remove from reaction mixtures by means of chromatography. It is poorly soluble in hexane and cold diethyl ether. Trituration or chromatography of crude products with these solvents often leads to a good separation of triphenylphosphine oxide.

Coordination chemistry

Ph3PO is an excellent ligand for "hard" metal centers. A typical complex is the tetrahedral species NiCl2(OPPh3)2.

Ph3PO is a common impurity in PPh3. The oxidation of PPh3 by oxygen, including air, is catalyzed by many metal ions:
2 PPh3 + O2 → 2 Ph3PO




Other reading

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