Tributylphosphine

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Tributylphosphine
IUPAC name

Tributylphosphane

Other names

Tributylphosphine

Identifiers
CAS number 998-40-3 YesY

 EC number 213-651-2
Jmol-3D images Image 1
Properties
Molecular formula C12H27P
Molar mass 202.32 g mol−1
Appearance Colorless oily liquid
Density 0.82 g/ml
Melting point −60 °C; −76 °F; 213 K
Boiling point 240 °C; 464 °F; 513 K ((150 °C @ 50 mmHg))
Solubility in water negligible
Solubility organic solvents such as heptane
Dipole moment ?
Hazards
R-phrases R11 R17 R20/21/22 R34 R38
Main hazards Stench, Flammable, Corrosive
NFPA 704
3
1
2
Flash point 117 °C; 243 °F; 390 K
Autoignition temperature 168 °C; 334 °F; 441 K
Related compounds
Related Tertiary phosphine Trimethylphosphine
Triphenylphosphine
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Tributylphosphine is the organophosphorus compound with the formula P(C
4H
9)
3. Abbreviated or PBu
3, it is a tertiary phosphine. It is an oily liquid at room temperature, with a nauseating odor. It reacts slowly with atmospheric oxygen, and rapidly with other oxidizing agents, to give the corresponding phosphine oxide. It is usually handled using air-free techniques.

Preparation

Tributylphosphine is prepared industrially by the addition of phosphine to butene: the addition proceeds by a free radical mechanism, and so the Markovnikov rule is not followed.

PH
3 + 3CH
2=CHCH
2CH
3 → P(CH
2CH
2CH
2CH
3)
3

Tributylphosphine can be prepared in the laboratory by reaction of the appropriate Grignard reagent with phosphorus trichloride although, as it is commercially available at reasonable prices, it is rare to have to perform the small-scale preparation.

3 BuMgCl + PCl
3 → PBu
3 + 3 MgCl
2

Reactions

Tributylphosphine reacts with oxygen to give the phosphine oxide:

2 PBu3 + O2 → 2 OPBu3

Because this reaction is so fast, the compound is usually handled using syringe techniques.

The phosphine is also easily alkylated. For example, benzyl chloride gives the phosphonium salt:[1]

PBu3 + PhCH2Cl → [PhCH2PBu3]Cl

Tributylphosphine most commonly encountered as a ligand in transition metal complexes. Tributylphosphine is also a common ligand for the preparation of complexes of transition metals in low oxidation states. It is cheaper and less air-sensitive than trimethylphosphine and other trialkylphosphines. Although its complexes are generally highly soluble, they are often more difficult to crystallize compared to complexes of more rigid phosphines. Furthermore, the 1H NMR properties are less easily interpreted and can mask signals for other ligands. Compared to other tertiary phosphines, it is compact (cone angle: 136°) and basic (χ-parameter: 5.25 cm–1)[2]

Use

Tributylphosphine finds some industrial use as a catalyst modifier in the cobalt-catalyzed hydroformylation of alkenes, where it greatly increases the ratio of straight-chain aldehydes to branched-chain aldehydes in the product mixture.[3] However, tricyclohexylphosphine is even more effective for this purpose (although more expensive) and, in any case, rhodium catalysts are usually preferred to cobalt catalysts for the hydroformylation of alkenes.

It is the precursor to the pesticide 2,4-dichlorobenzyltributylphosphoniumchloride ("Phosfleur").[1]

Odor

The main laboratory inconvenience of tributylphosphine is its strongly unpleasant smell. Manipulations must be carried out in an efficient fume hood, and glassware which has come into contact with the compound must be decontaminated before leaving the hood. The manipulation of large quantities requires specific precautions to prevent the release of the vapour into the environment.

Hazards

Tributylphosphine is moderately toxic, with an LD50 of 750 mg/kg (oral, rats).[1]

References

  1. ↑ 1.0 1.1 1.2 Jürgen Svara, Norbert Weferling and Thomas Hofmann "Phosphorus Compounds, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_545.pub2
  2. ↑ Rahman, M. M.; Liu, H. Y.; Prock, A.; & Giering, W. P. (1987). "Steric and Electronic Factors influencing Transition-Metal–Phosphorus(III) Bonding". Organometallics 6 (3): 650–58. doi:10.1021/om00146a037. 
  3. ↑ Bell, P.; Rupilus, W.; & Asinger, F. (1968). "Zur Frage der Isomerenbildung bei der Hydroformylierung Höhermolekularer Olefine mit Komplexen Kobalt- und Rhodiumkatalysatoren". Tetrahedron Lett. 9 (29): 3261–66. doi:10.1016/S0040-4039(00)89542-8. 

External links

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