Introduction
Applications of White Phosphorus
White phosphorus is the linchpin synthetic intermediate for the production of virtually all phosphorus-containing non-ferti-lizer chemicals. However, it is produced by the energy-intensive thermal process, and is a toxic and pyrophoric substance. We are targeting methods to produce phosphorus-containing chemicals that bypass P4 as an intermediate, in search of more environmentally friendly, less energy intensive processes for the manufacture of phosphorus-containing chemicals.
Phosphoric Acid as a Precursor to Chemicals Traditionally Derived from White Phosphorus
Michael B. Geeson and Christopher C. Cummins
Preparation of Phosphorus-Containing Compounds
Including P−C, P−F and P−H bonds
One-pot synthesis of primary phosphines
tetrabenzylphosphonium chloride
via: P(SiCl3)H
PH2Cl
[TBA]3[P3O9].2H2OHSiCl3, 110 ℃, 96 h
thenH2O or basic alumina
64%
Conditions: (i): benzyl chloride, MeCN, 70 ℃, 24 h. (ii): methyllithium (3.0 M, THF, 7 equiv). (iii): XeF2 (8 equiv.), DCM, thawing,then Li[BArF20]. (iv): H2O (15 equiv.), DCM, −78 ℃.
Hypothesis: trichlorosilane can protonate phosphide intermediate
− SiCl4
not observed
monoalkylation
Synthesis and Characterization of the Bis(Trichlorosilyl)Phosphide Anion
Sum of single bond covalent radii: 2.27 Å P−Si bond length: 2.143(2) Å
X-ray crystallography
The bis(trichlorosilyl)phosphide anion is prepared by heating the TBA salt of trimetaphosphate and trichlorosilane to 110 ℃ in a steel reactor. It can be recrystallized from DCM/pentane to give a free-flowing white powder.
High temperature and pressure synthesis Determination of byproducts and mass balance
Solid-state structure of [Si(P3O9)2]2−,
determined by X-ray diffraction
Volatile gas from reaction hydrogenates and olefin
cat. [(COD)Ir(py)(PCy3)][PF6]
DCM, 0 °C
HO i-Pr HO i-Pr
Selective Alkylation to give Primary Phosphines
With this work, we have shown it is possible to prepare phosphorus-containing fine chemicals without passing through P4, a toxic and pyrophoric intermediate. Our ongoing studies on this fascinating small anion show promise for further reaction development, especially for P−C bond formation. Finally, reductions in trichlorosilane hold promise for preparing previously known small anions, allowing their utility in chemical synthesis to be demonstrated.
fosinoprilPO
HOH
Lit.6 steps2.2 H2O2
OO
N
OOO
P
CO2H
PH2Ph PhPh Cy
90%
MeCN, 2h, 23 ℃
Application to Sulfur Chemistry: An Alternative to Lawesson's Reagent
Phosphorus Industry Overview
Phosphate
rock
Ca5(PO4)3F
White
phosphorus
P4Phosphoric
acid
H3PO4
Fertilizer
[NH4][H2PO4]Specialist
chemicals
Thermal
Process
Wet
Process
carbon
SiO2
1500 ℃H2SO4
5%95%
-172
.10
-171
.70
-171
.33
-170 -172 -174(ppm)
31P NMR spectroscopy
1JP−Si = 151 Hz
Synthesis from phosphoric acid
Na3P3O9 [TBA]3[P3O9].2H2Oion-exchange
3 H3PO4 + 3 NaCl Na3P3O9 + 3 HCldehydration
− 3 H2O
[TBA]3[P3O9].2H2O [TBA][P(SiCl3)2]HSiCl3
110 ℃, 72 h
70%, 10 g
1/3 [TBA]3[P3O9] [TBA][P(SiCl3)2] + 4 H2 + 4 O(SiCl3)2110 ℃, 72 h
8 HSiCl3
Characterization by 29Si NMR
Industrial synthesis of primary phosphines
hydrophosphinationRPH3 +
radical mechanism
H2P(CH2CH2R)
HP(CH2CH2R)2
P(CH2CH2R)3(neat)
Phosphoric acid used in place of trimetaphosphate
4-phenylbutylphosphine is a precursor to fosinopril
Trichlorosilyl-substituted anions have seen a flurry of activity in recent years, now known for the elements C, Si, Ge, N, P, and S. The sulfur species, [TBA][Cl3SiS], was targeted with the current methodology in order to replace the originally rep-orted synthesis which employed H2S, toxic, flammable, and pungent gas.
Original synthesis:
H2S, SiCl4[TEA][SH]
−78 ℃ [TEA][Cl3SiS]
Sum of single bond covalent radii: 2.19 Å
S−Si bond length: 1.9756(14) Å
Preparation of thiocarbonyl compounds using [TBA][Cl3SiS]
thioketone thioamide
Trichlorosilane is the key to selectivityLonger reaction times for H3PO4 compared to [P3O9]
3−
In the case of [P3O9]3−, a soluble silicophosphate forms
This species can be independently prepared and characterized: [TBA][P(SiCl3)2] + RClHSiCl3
RP
SiCl3
R
dialkylation
toluene
110 ℃96 h R
PSiCl3
H
+ HSiCl3
−[SiCl3]−R
PSiCl3
+ RCl
−Cl−
110 ℃96 h
Conclusions and Acknowledgments
(1) Schipper, W. Phosphorus: Too Big to Fail. Eur. J. Inorg. Chem. 2014, 2014 (10), 1567–1571.(2) Pham Minh, D.; Ramaroson, J.; Nzihou, A.; Sharrock, P. One-Step Synthesis of Sodium Tri-metaphosphate (Na3P3O9) from Sodium Chloride and Orthophosphoric Acid. Ind. Eng. Chem. Res. 2012, 51 (10), 3851–3854.(3) Benkeser, R. A.; Voley, K. M.; Grutzner, J. B.; Smith, W. E. Evidence for the Existence of the Trichlorosilyl Anion. J. Am. Chem. Soc. 1970, 92 (3), 697–698.(4) Anderson, N. G. et. al. Generation and Fate of Regioisomeric Side-Chain Impurities in the Preparation of Fosinopril Sodium. Org. Process Res. Dev. 1997, 1 (4), 315–319.(5) Geeson, M. B.; Cummins, C. C. Phosphoric Acid as a Precursor to Chemicals Traditionally Synthesized from White Phosphorus. Science 2018, 359 (6382), 1383–1385.
The Cummins GroupReferences
X-ray crystallography
Ph Ph
O
Ph Ph
S5 [TBA][Cl3SiS]
CHCl3110 ℃, 96 h 62%
thiol
Br SH1.1 [TBA][Cl3SiS]
DCM40 ℃, 18 h then H2O
62%
Me2N H
O
Me2N H
S
chlorobenzene110 ℃, 6 h
3 [TBA][Cl3SiS]
95%
Li[PF6]PH3
tris(trimethylsilyl)phosphine
lithium hexafluorophosphate
phosphine
(i) (ii)
(iii)(iv)
61%
>65% 70%
P(TMS)3
PhH2CCH2Ph
CH2Ph
ClCH2Ph
P
[TBA]Cl, H3PO4
HSiCl3, 110 ℃, 6 d
thenH2O or basic alumina 41%, 1.3 g
n-octylchloride PH2
Synthesis from bisulfate and trichlorosilane
43%, 3.0 g
Natural Resonance Theory
Sum = 89.2%
ClCl
ClCl
Cl
ClCl
Cl
Cl
39.6% 27.6% 22.0%
S
Si
S
Si
S
Si
HSiCl3, MeCN[TBA][HSO4]
23 ℃, 12 h [TBA][Cl3SiS]
*not all direct transformations
PCl3
PR3
InP
Li[PF6]P4S10
RPO3H2
indium phosphide
phosphonates
phosphorus sulfides
phosphorus trichloride
phosphines
lithium hexafluorophosphate organosulfur compounds,
lubricants
pharmaceuticals, herbicides, chelating agents
electronics
ligands, chemical reagents
battery electrolytes
all-purpose precursor
Science 2018, 359 (6382), 1383–1385.
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