Gourt Home::Gourt :: Triphenylphosphine
| Triphenylphosphine | |
|---|---|
| General | |
| Systematic name | Triphenylphosphane |
| Molecular formula | C18H15P |
| Molar mass | 262.29 g/mol |
| Appearance | white solid |
| CAS number | |
| Properties | |
| Density and phase | 1.1 g/cm3, solid |
| Solubility in water | Insoluble |
| Melting point | 80 °C |
| Boiling point | 377 °C |
| Basicity (pKa) for PPh3H+ | 2.73 |
| Structure | |
| Molecular shape | Pyramidal |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| EU classification | not listed |
| NFPA 704 | |
| Flash point | 180 °C |
| RTECS number | SZ3500000 |
| Supplementary data page | |
| Structure and properties | n = 1.59; εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related tertiary phosphines | Trimethylphosphine Tris(3-sulfophenyl)phosphine Phosphine |
| Related compounds | Triphenylamine Triphenylarsine Triphenylphosphine oxide Triphenylphosphine sulfide Pd(PPh3)4 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Chemical infobox | |
Triphenylphosphine (in Europe: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 - 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 dissolves in non-polar organic solvents such as benzene and diethyl ether]], but not in water.
Preparation, structure, handling
Although it is inexpensive, triphenylphosphine can be prepared in the laboratory by treatment of phosphorus trichloride with phenylmagnesium bromide or phenyllithium. The industrial synthesis involves the reaction between phosphorus trichloride, chlorobenzene, and sodium.D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. ISBN 0-444-89307-5. PPh3 is pyramidal with a chiral propeller-like arrangement of the three phenyl rings. The rigidity of PPh3 contributes to the ease with which its derivatives crystallize.
Principal reactions with chalcogens, halogens, and acids
Triphenylphosphine undergoes slow oxidation by air to give triphenylphosphine oxide, OPPh3:
- 2 PPh3 + O2 → 2 OPPh3
This impurity can be removed by recrystallisation of PPh3 from either hot ethanol or hot isopropanol.D. D. Perrin, W. L. F. Armarego, D. R. Perrin, Purification of Laboratory Chemicals, 2nd ed.; Pergamon: New York, 1980; p 455. This method capitalizes on the fact that OPPh3 is more polar and hence more soluble in hydroxylic solvents than PPh3. The easy oxygenation of PPh3 is exploited in its use to deoxygenate organic peroxides, which generally occurs with retention of configuration:
- PPh3 + RO2H → OPPh3 + ROH (R = alkyl)
Triphenylphosphine abstracts sulfur from polysulfide compounds, episulfides, and elemental sulfur. Simple organosulfur compounds such as thiols and thioethers are unreactive, however. The phosphorus-containing product is SPPh3. This reaction can be employed to assay the "labile" S0 content of a sample, say vulcanized rubber. Triphenylphosphine selenide, SePPh3, does not readily form upon treatment of PPh3 with either allotrope of Se. Salts of selenocyanate, SeCN-, are used as the Se0 source. TePPh3 is unknown and apparently unstable. Aryl azides react with PPh3 to give imido analogue of OPPh3 via the Staudinger reaction:
- PPh3 + PhN3 → PhNPPh3 + N2
- PPh3 + RN3 + H2O → OPPh3 + N2 + RNH2
Cl2 adds to PPh3 to give *Cl, which exists as the moisture-sensitive phosphonium salt,
PPh3 is a weak base, but does form stable salts with strong acids such as HBr.
Principal organic reactions
PPh3 is widely used in organic synthesis. The properties that guide its usage are its nucleophilicity and its reducing character.Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289 The nucleophilicity of PPh3 is indicated by its reactivity toward electrophilic alkenes, such as Michael-acceptors, and alkyl halides.
Quaternization
PPh3 combines with most alkyl halides to give phosphonium salts. The facility of the reaction follows the usual pattern whereby alkyl iodides and benzylic and allylic halides are particularly efficient reactants: These salts, which are readily isolated as crystalline solids, react with strong bases to form ylides:- CH3PPh3+ + base → * + baseH+
Mitsunobu reaction
In this reaction, a mixture of PPh3 and diisopropyl azodicarboxylate (“DIAD”, or its diethyl analogue, DEAD) converts an alcohol and a carboxylic acid to an ester. The DIAD is reduced as it serves as the hydrogen acceptor, and the PPh3 is oxidized to OPPh3.Appel reaction
PPh3 is oxidized again to OPPh3 in this application, which covert alcohols to alkyl halides using CX4 (X = Cl, Br):- PPh3 + CBr4 + RCH2OH → OPPh3 + RCH2Br + HBr + HCBr3
Principal transition metal derivatives
Triphenylphosphine binds well to most transition metals, especially those in the middle and late transition metals of groups 7-10.C. Elschenbroich, A. Salzer ”Organometallics : A Concise Introduction” (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3527281657 In terms of steric bulk, PPh3 has a cone angle of 145°, which is intermediate between those of P(C6H11)3 (170°) and P(CH3)3 (115°). The blossoming of homogeneous catalysis is attributable to Wilkinson's popularization of PPh3; a prominent outcome of his research being the then revolutionary hydroformylation catalyst RhH(PPh3)3(CO)2.
It is telling that the corresponding triphenylamine shows little tendency to bind to metals. The difference reflects the greater steric crowding around the nitrogen atom, which is smaller and favors a more tetrahedral geometry. Far more similar to PPh3, triphenylarsine, AsPh3, forms complexes analogously.
An important technique for the characterization of metal-PPh3 compounds is 31P NMR spectroscopy. Substantial shifts occur upon complexation and 31P-31P spin-spin coupling can often give insight into the stereochemistry of complexes containing multiple phosphine ligands.
Illustrative PPh3 complexes:
- tetrakis(triphenylphosphine)palladium(0) is widely used to catalyse C-C coupling reactions in organic synthesis, see Heck reaction.
- Wilkinson's catalyst, RhCl(PPh3)3 is a square planar Rh(I) complex of historical significance used to catalyze the hydrogenation of alkenes.
- Vaska's complex, trans-IrCl(CO)(PPh3)2, is also historically significant; it was used to establish the scope of oxidative addition reactions. This early work provided the insights that led to the flowering of the area of homogeneous catalysis.
- NiCl2(PPh3)2 is an four coordinate Ni(II) complex that exists as an equilibrium mixture of paramagnetic tetrahedral and diamagnetic square planar geometries. In contrast PdCl2(PPh3)2 is square planar.
Organophosphorus chemistry
Triphenylphosphine is commonly employed as a precursor to other organophosphines. Lithium in THF and Na or K in NH3 react with PPh3 to give Ph2PM (M = Li, Na, K). One complication is that these reactions generate equal amounts of phenyllithium (or sodium, potassium analogs thereof) C6H5M, but these species can be selectively converted to benzene by careful use of acid. Treatment of the resulting alkali metal diphenylphosphide with an alkylating agent RX gives PRPh2. This method can be used to prepare such ligands as PMePh2, methyldiphenylphosphine. The corresponding reaction with dihaloalkanes gives bis(diphenylphosphino)alkanes. For example, ethylene dibromide and Ph2PM react to give Ph2PCH2CH2PPh2, known as 1,2-Bis(diphenylphosphino)ethane or dppe. Weak acids such ammonium chloride, converts Ph2PM (M = Li, Na, K) into Ph2PH, known as diphenylphosphine.
Sulfonation of PPh3 gives tris(3-sulfophenyl)phosphine, P(C6H4-3-SO3-)3. This anionic phosphine is usually isolated as the trisodium salt and is known as TPPTS. In contrast to PPh3, TPPTS is a water soluble as are its metal derivatives. Rhodium complexes of TPPTS are used in certain industrial hydroformylation reactions because the water-soluble catalyst is readily separated from the organic products.
Polymeric analogues of PPh3 are known whereby polystyrene is modified with PPh2 groups at the para position. Such polymers can be employed in many of the applications used for PPh3 with the advantage that the polymer, being insoluble, can be separated from products by simple filtration of reaction slurries. Such polymers are prepared via treatment of 4-lithiophenyl-substituted polystyrene with PPh2Cl.
Safety
PPh3 should be handled in a well ventillated area, preferrably a fume hood.
References
External links
Tertiary phosphines | Aromatic compounds | Reagents for organic synthesis
Triphenylphosphan | Trifenilfosfina | Triphénylphosphine | Trifenilfosfina | トリフェニルホスフィン
"Triphenylphosphine"
