What is triethylphosphine compound?

Triethylphosphine is an organophosphorus compound with molecular formula, C6H15P or P(CH2CH3)3 or Et3P. The preferred IUPAC name is triethylphosphane.

Triethylphosphine is a colorless, unpleasant-smelling liquid or low melting solid. The molar mass of triethylphosphine is 118.16 g/mol.

The boiling point of triethylphosphine is 400-401 K. It is used as a neutral ligand in co-ordination chemistry.

Structure and bonding of triethylphosphine

 Triethylphosphine is a derivative of phosphine. The central phosphorus atom is sp3 hybridized and contain one lone pair of electron. Hence it has a pyramidal structure.

Since phosphorus atom in tercovalent triethylphosphine compound has a lone pair of electrons, it behaves as a good nucleophile in many reactions. It is because of this lone pair act as a good reducing agent.

Preparation of triethylphosphine

Triethylphosphine is prepared most conveniently by the reaction of excess of Grignard reagent on phosphorus trichloride or triphenylphosphite.

3CH3CH2MgBr + PCl3  → (CH3CH2)3P + 3MgBrCl

3CH3CH2MgBr + P(OC6H5)3  → P(CH3CH2)3 + 3C6H5-OMgCl

Reactions of triethylphosphine

Triethylphosphine is a highly basic organophosphorus compound and hence it reacts with strong acids to give salts. For example, with strong halogen acids, preferably with HI it gives salts with formula, [HPEt3]I.

Since triethylphosphine is a reducing agent, it is easily combine with atmospheric oxygen, often undergoing spontaneous combustion and forms triethylphosphine oxide.

 It also oxidized to triethylphosphine oxide by ozone. On the other hand, controlled oxidation is readily carried out with nitric acid. Triethylphosphine is also reacts with a variety of oxygen-containing compounds.

2Et3P + O2  → 2Et3P=O | Et3P +O3  → Et3P=O + O2

Et3P + HNO3  → Et3P=O

Uses of triethylphosphine

Triethylphosphine is a neutral ligand. The phosphorus atom has a lone pair of electrons through which it can form co-ordinate bond with transition metal atom resulting in the formation of complex compounds.

For this reason, triethylphosphine is mainly used in co-ordination chemistry. For example, with silver iodide it forms an air stable solid complex with molecular formula, AgI(PEt3).

Toxic effect of triethylphosphine

PEt3 is toxic. It converts to a low toxicity phosphine oxide upon treatment with sodium hypochlorite or hydrogen peroxide.

Why do triethylphosphine weaker base than triethylamine?

It has been experimentally observed that triethylphosphine is a weaker base than triethylamine. The possible explanation is that salvation effect is less important in triethylphosphine than in corresponding amine.

Because of the larger size of the phosphorus atom than nitrogen atom, the charge density is more diffused in triethylphosphine than in triethylamine.

 

Why do Et3P stronger nucleophile than Et3N?

 

Triethylphosphine is a stronger nucleophile than triethylamine; this is illustrated by the fact that aminophosphine combine with alkyl halide to give phosphonium salts not ammonium salts.

This greater nucleophilicity of triethylphosphine can be explained on the basis of size of phosphorus and nitrogen atom.

Phosphorus atom has larger size than nitrogen atom and hence the lone of electrons on phosphorus atom has a greater polarizability than that of nitrogen.

However according to Henderson, the greater nucleophilicity, that is, greater rate of reaction, is accounted for by the entropy of activation term in the two reactions.

When phosphonium halides are treated with moist silver oxide, the phosphonium hydroxide is produced.

(C2H5)4P⁺I^– + AgOH → (C2H5)4P⁺OH^– + AgI.

The quaternary phosphonium hydroxides (Et4P⁺OH^–) are strongly basic, comparably in strength with the quaternary ammonium hydroxides and sodium hydroxide.

When heated they form the trialkylphosphine oxide (Et3P=O) and a hydrocarbon. (C2H5)4P⁺OH^–  → (C2H5)3P  +  CH3CH3

 

 

 

• What is triethylphosphine compound?
• Structure and bonding of triethylphosphine
• Preparation of triethylphosphine
• Reactions of triethylphosphine
• Uses of triethylphosphine compound
• Why do Et3P stronger nucleophile than Et3N?
• Why do Et3P weaker base than Et3N?

 

Triethylphosphine-structure, bonding, preparation, reactions and uses, Et3P stronger nucleophile than Et3N, Et3P weaker base than Et3N