Triphenylphosphine - Ph₃P

What is Triphenylphosphine?

Triphenylphosphine with IUPAC name: triphenylphosphane is a common organophosphorus compound with the formula P(C₆H₅)₃ that is frequently abbreviated as PPh₃ or Ph₃P. It is widely used in organic and organometallic compound synthesis because it is an effective reducing agent as well as a neutral ligand. At room temperature, PPh₃ crystals are relatively air-stable and colourless. Non-polar organic solvents such as benzene and diethyl ether dissolve it.

Table of Contents

• Preparation of Triphenylphosphine – Ph₃P
• Properties of Triphenylphosphine – Ph₃P
• Reactions of Triphenylphosphine – Ph₃P
• Uses of Triphenylphosphine – Ph₃P
• Frequently Asked Questions – FAQs

Preparation of Triphenylphosphine – Ph₃P

In the laboratory, triphenylphosphine can be synthesised by reacting phosphorus trichloride with phenylmagnesium bromide or phenyl lithium.

PCl₃ + 3C₆H₅MgBr → P(C₆H₅)₃ + 3MgClBr

PCl₃ + 3C₆H₅Li → P(C₆H₅)₃ + 3LiCl

The reaction between phosphorus trichloride, chlorobenzene, and sodium is used in industrial synthesis.

PCl₃ + 3PhCl + 6Na → PPh₃ + 6 NaCl

Structure of Triphenylphosphine – Ph₃P

The Triphenylphosphine molecule has 36 bonds in total. There are 21 non-H bonds, 18 multiple bonds, 3 rotatable bonds, 18 aromatic bonds, 3 six-membered rings, and 1 phosphane (s).

Triphenylphosphine crystallises in both triclinic and monoclinic forms. In both cases, the molecule has a pyramidal structure with three phenyl groups arranged in a propeller-like pattern.

Triphenylphosphine’s central phosphorus atom is sp³ hybridized. The phosphorus atom is directly connected to three phenyl groups via a P – C sigma bond, and one sp³ hybridised orbital contains a single pair of electrons.

Properties of Triphenylphosphine – Ph₃P

It is a white crystalline solid with a density of 1.1 g/cm³. At room temperature, triphenylphosphine is colourless and relatively air-stable. It has a lower polarity. The dipole moment is about 1.42D. It is soluble in nonpolar organic solvents like benzene and diethyl ether.

Triphenylphosphine has a melting point of 350K and a boiling point of 650K.

Toxic Nature: Triphenylphosphine is a poisonous substance found in nature. When it comes into contact with our skin, respiratory system, or eyes, it can cause irritation.

Reactions of Triphenylphosphine – Ph₃P

Triphenylphosphine reactions include:

Oxidation

Triphenylphosphine is slowly oxidised by air to produce triphenylphosphine oxide.

2PPh₃ + O₂ → 2OPPh₃

Sulfur is extracted from polysulfide compounds, episulphides, and elemental sulphur by triphenylphosphine.

Chlorination

Cl₂ reacts with PPh₃ to form triphenylphosphine dichloride ([PPh₃Cl]Cl), which exists as the moisture-sensitive phosphonium halide. In organic synthesis, this reagent is used to convert alcohols to alkyl chlorides.

2Ph₃PCl₂ + NH₂OH·HCl + Ph₃P → {[Ph₃P]2N}Cl + 4HCl + Ph₃PO

Protonation

PPh₃ is an ineffective base. With strong acids such as HBr, it forms isolable triphenylphosphonium salts:

P(C₆H₅)₃ + HBr → [HP(C₆H₅)₃]+Br^–

Uses of Triphenylphosphine – Ph₃P

• Triphenylphosphine is used in the synthesis of Chlorambucil, which has been shown to be cytotoxic in breast and pancreatic cancers.
• It is also used to make -Tocopherol analogues for monitoring antioxidant status.
• Triphenylphosphine is used in a variety of applications, including sensitizers, heat stabilisers, light stabilisers, antioxidants, flame retardants, antistatic agents, rubber antiozonants, and analytical reagents.
• Triphenylphosphine is used in the synthesis of vitamin D2, vitamin A, clindamycin, and other drugs.
• The Wittig reaction, which converts aldehydes and ketones to alkenes, was Ph₃P’s first significant use in organic synthesis.
• Triphenylphosphine is also used as a transition metal-ligand in olefin polymerizations and in the Suzuki, Mitsunobu, and Appel reactions.
• In homogeneous catalysis, triphenylphosphine is a standard ligand.