Tributylphosphine

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.

Tributylphosphine
Names
IUPAC name
Tributylphosphane
Preferred IUPAC name
Tributylphosphane
Other names
Tributylphosphine
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.012.410
EC Number
  • 213-651-2
UNII
Properties
C12H27P
Molar mass 202.322 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 (302 °F; 423 K) at 50 mmHg)
negligible
Solubility organic solvents such as heptane
Hazards
Main hazards Stench, Flammable, Corrosive
R-phrases (outdated) R11 R17 R20/21/22 R34 R38
NFPA 704 (fire diamond)
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
3
1
2
Flash point 117 °C (243 °F; 390 K)
168 °C (334 °F; 441 K)
Related compounds
Related Tertiary phosphine
 Trimethylphosphine
Triphenylphosphine
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Preparation

Tributylphosphine is prepared industrially by the hydrophosphination of phosphine with butene: the addition proceeds by a free radical mechanism, and so the Markovnikov rule is not followed.[1]

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 under an inert atmosphere.

The phosphine is also easily alkylated. For example, benzyl chloride gives the phosphonium salt:[2]

PBu3 + PhCH2Cl → [PhCH2PBu3]Cl

Tributylphosphine is 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)[3]

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.[4] 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").[2]

Although tributylphosphine is generally regarded as toxic, its biological effects can be manipulated by drug delivery strategies. For example, a photoactivatable version of tributylphosphine has been used to induce disulfide bond cleavage and reductive stress in living cells.[5]

Odor

The main laboratory inconvenience of tributylphosphine is its unpleasant smell.

Hazards

Tributylphosphine is moderately toxic, with an LD50 of 750 mg/kg (oral, rats).[2]

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References
  1. Trofimov, Boris A.; Arbuzova, Svetlana N.; Gusarova, Nina K. (1999). "Phosphine in the synthesis of organophosphorus compounds". Russian Chemical Reviews. 68. doi:10.1070/RC1999v068n03ABEH000464.
  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
  3. 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.
  4. 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.
  5. Tirla, A.; Rivera-Fuentes, P. (2016). "Development of a Photoactivatable Phosphine Probe for Induction of Intracellular Reductive Stress with Single‐Cell Precision". Angew. Chem. Int. Ed. 55 (47): 14709–14712. doi:10.1002/anie.201608779. hdl:20.500.11850/123593.
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