Silane reagents (R3SiH) seems to be most common for this transformation, but I am not sure if this is "simple" or even convenient (might be OK for Ph3P=O, but could be incompatible with other functional groups present in the molecule).

Hi,

 One of these should do it. (pictures don't show unfortunately)

Bill

Phosphine oxide reductions

 Reduction of phosphine oxides to the corresponding phosphine derivatives in Mg/Me3SiCl/DMI system

Manabu Kuroboshi a, ⇑, Toshihito Kita a, Asuka Aono a, Toshimasa Katagiri a, Seiya Kikuchi a,

Syoko Yamane a, Hiromu Kawakubo b, Hideo Tanaka a

Tetrahedron Letters 56 (2015) 918–920

Unraveling the Catalytic Cycle of Tertiary Phosphine Oxides Reduction with Hydrosiloxane and Ti(OiPr)4 through EPR and 29Si NMR Spectroscopy

Christelle Petit ; Evelyne Poli; Alain Favre-Réguillon; et al

ACS Catal., 2013, 3 (7), pp 1431–1438

 2.3.REDUCTION OF TPO  ON 100 G SCALE

In a jacketed glass reactor of 1L equiped with mechanical stiring, dropping funnel, temperature and Raman optical probes was added 100 g (0.36 mole) of  triphenylphosphine oxide (TPO), 700 mL of cyclohexane, 10 g of Na2SO4  and 50.77 g (0.38 mole) of tetramethyldisiloxane (TMDS). The reaction mixture was stirred and heat to 60°C. Then, 10.21 g  (0.035 mole) of Ti(OiPr)4  was added and then the heterogenous  mixture  is stirred  for  14  h  at  60 °C.   Aliquots  were  taken  for 31P NMR  analysis.  The reaction mixture was then cooled, filtrated over porous glass and the solid was washed with 3 x 50 mL of   pentane.   The   resulting   white   solid   was   recristallized   from   acetone   yielding   94.4g   of triphenylphosphine (quantitative yield). Unreacted TMDS in the filtrate must be destroyed by carefull addition  of  a  3  M  alcoholic  solution  of  KOH  at  room   temperature  with  rigourous  stirring.  TMDS decomposes on contact with bases, forming hydrogen. m.p. 80°C (Litt. 82:83°C).

General and Selective Copper-Catalyzed Reduction of Tertiary and Secondary Phosphine Oxides: Convenient Synthesis of Phosphines

Yuehui Li , Shoubhik Das , Shaolin Zhou , Kathrin Junge , and Matthias Beller *

J. Am. Chem. Soc., 2012, 134 (23), pp 9727–9732

R = aryl, alkyl

General procedure for hydrosilylation −phosphination reaction: A 10-mL dried Schlenk tube containing a stirring bar was charged with Cu(OTf) 2 (13.5 mg, 0.0375 mmol) and the corresponding secondary phosphine oxide (0.25 mmol). Under Ar flow dry toluene (2 mL) and TMDS [tetramethyldisiloxane] (90 μL, 0.5 mmol) were added, and the mixture was stirred at 100 ° C for 10 h. Then, the reaction mixture was cooled to room temperature and N,N′-dimethylethylenediamine (5.2 μ L, 0.05 mmol), Cs2CO3 (164 mg, 0.5 mmol), and the respective halide compound (0.25 mmol) were added under Ar flow. The suspension was allowed to heat to 110 °C and stirred overnight. Then, the reaction mixture was cooled to 0 °C and 3 N methanolic KOH was added slowly. After the mixture was stirred vigorously for 5 h at room  temperature, water (3 mL) was added and the mixture was extracted with ethyl acetate which was washed by 1 N HCl solution (aq., 5 mL) and saturated NaHCO3 solution (aq., 5 mL). Then, the organic phase was dried by Na2SO4 and concentrated under vacuum. The residue was purified by silica gel column chromatography

Also: By Li, Yuehui; Lu, Liang-Qiu; Das, Shoubhik; Pisiewicz, Sabine; Junge, Kathrin; Beller, Matthias

From Journal of the American Chemical Society (2012), 134(44), 18325-18329.

Also: Reduction of phosphine oxides to phosphines with the InBr3/TMDS system

By Pehlivan, Leyla; Metay, Estelle; Delbrayelle, Dominique; Mignani, Gerard; Lemaire, Marc

From Tetrahedron (2012), 68(15), 3151-3155

The simplest way I think is to use the mixture of 3 equiv of poly(methylhydrosiloxane), (PMHS), and 1 equiv of Ti(OiPr)4 in toluene under inert gas at 80-90 °C for ca. 1 h.  The mixture should be intensively black all the time. Then, you stir it still under inert gas with 10 eq of 15% KOH at 80-90°C until the phases are clear, cool down, separate phases and wash the organics with water. The organic layer contains pure PPh3. If you can follow the process with 31P-NMR, this is of big advantage. Alternatively, you can stir the mixture after the reduction  with 20 eq of ca. 15% HF in a plastic bottle at RT for 2-3 h, then wash the toluene layer with NaHCO3. It is even more convenient work-up.

A simpler way would be Try one of the several reducing reactions e.g. with the easily available borane.

Dr. Mirza Arshad Ali Beg

You may convert the Phosphine oxide to phosphine dichloride and react the dichloride with the easily available substituted borane.

Dr. Mirza Arshad Ali Beg

If you are talking about gram amounts: cost wise it best to throw the phoshine oxide away. The silane reduction works, but generates more waste (and costs) that the original amount of  Ph3P=O. The triflate and Cs salts should not be necessary for the reduction of a triphenylphosphine oxide (neither for a secondary one)

If you are in the kg or ton range you should look into the BASF patents going via the triphenyldichlorophoshorane and reduction with metals (Al).

Kind regards

Peter

I am not sure it is worth the effort, most of the chemicals described above are not cheap, and you will have quite a lot of waste, energy and time invested in the process. On a lab scale, we just buy the PhP3.

LiAlH4-reduction of phosphine oxides is classical method.

@Boyan Iliev  - I agree but sitations is not straightforward in the case of labeled compounds

I agree with Andrei, LiAlH4 is most convenient for the reduction of aryl phosphine oxides on the laboratory scale. However, unless your phosphine is unusual (ie not simply triphenyl phosphine) in terms of other subtituents on the aryl ring or isotopically labeled in some way, LiAlH4 costs more or less the same as reagent grade triphenyl phosphine and so the economic viability of reduction is questionable.

See: Gilheany et al. Org. Biomol. Chem., 2012, 10, 3531

Reaction with oxalyl chloride generates a salt, treatment with LiAlH4 gives the phosphine. Treatment with NaBH4 generates the phosphine borane.

Several workable approaches are already mentioned above. To my opinion beside LiAlH4, the use of Cl3SiH (in the presence or absence of a tertiary amine) is the cheapest and easiest way to get the phosphine. From the list of possible reagents above I miss Si2Cl6, Ph2SiH2, Ph3SiH or iBu2AlH.

See some references for these below:

Engel, R. In Handbook of Organophosphorus Chemistry; Engel, R. Ed.; Marcel Dekker: New York, 1992; pp. 193-240.

Gilheany, D. G.; Mitchell, C. M. In The Chemistry of Organophosphorus Compounds; Hartley, F. R. Ed.; Wiley-Interscience: Chicester, 1990; pp. 152-190.

Edmundson, R. S. In The Chemistry of Organophosphorous Compounds; Hartley, F. R. Ed.; Wiley-Interscience: Chicester, 1992; pp. 288-407.

Naumann, K. et al., J. Am. Chem. Soc. 1969, 91, 7012-7023.

Naumann, K. et al. J. Am. Chem. Soc. 1969, 91, 2788-2789. 

DeBruin, et al. J. Am. Chem. Soc. 1969, 91, 7027-7030.

Horner, L.; Balzer, W. D. Tetrahedron Lett. 1965, 6, 1157-1162. 

Imamoto, T. In Handbook of Organophosphorus Chemistry; Engel, R. Ed.; Marcel Dekker: New York, 1992; pp. 1-54.  

Marsi, K. L. J. Org. Chem. 1974, 39, 265-267.  

C. A. Busacca et al., J. Org. Chem., 2008, 73 (4) 1524-1531.                                                                                                                        

One of my product is generating triphenylphosphine oxide 300 kg/ day. Can we decompose this in to phenol and recover it ???

I would like to make reference to my old answer above. Convert the oxide to the Ph3PCl2 and reduce with a metal. Details you will find in the old BASF patents

Most of the chemicals described above are expensive. Just check this patent US3780111A, Converted the oxide to the Ph3PCl2 using phosphrous oxychloride and reduce with a electrolytic iron dust.

Good concept, the given procedure seems workable.

Short hint: the reactant is PCl5 and the P(O)Cl3 is formed during the reaction