Fluorination of organodichlorophosphorus compounds with sodium hexafluorosilicate, Part 1 1a

Article abstract of DOI:10.1039/a800243f

Sodium hexafluorosilicate was used as a source of fluoride ion for nucleophilic fluorination of some selected organodichlorophosphorus compounds in the presence and absence of a multifunctional ethereal solvent, giving fluoro derivatives in low to moderat

Full text of DOI:10.1039/a800243f

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Fluorination of organodichlorophosphorus compounds with sodium
hexafluorosilicate, Part 11a
Omar Farooq
Research Laboratory, I&C Sector, Building 201-2W-17, 3M Central Research, St. Paul,
MN 55144-1000, USA
Sodium hexafluorosilicate was used as a source of
fluoride ion for nucleophilic fluorination of some selected
organodichlorophosphorus compounds in the presence
and absence of a multifunctional ethereal solvent, giving
fluoro derivatives in low to moderate yields.
δF Ϫ65.41 (d, JF–P 1104 Hz) with those of an authentic sample,10a
the compound was assigned as phenylphosphonic difluoride.
Phenylphosphonic chloride fluoride [δP 29.13 (JPF 1137 Hz)]
was formed in trace amounts (<1%). Redistillation gave phenyl-
phosphonic difluoride in 99% purity. When the same reaction
was repeated using 2 equiv. of sodium hexafluorosilicate in
presence of a multifunctional ether [tetraethylene glycol
dimethyl ether (tetraglyme)] for 15 min, only phenylphosphonic
difluoride was formed as a single product in 61% yield. No
monofluorinated product could be identified.
Halogen-exchange fluorination with metal fluorides is widely
used for fluorination of various types of organic compounds
including organosilicon and organophosphorus compounds.1b
The exchange is commonly carried out using sodium fluoride in
an aprotic polar solvent.2a Chlorine–fluorine exchange on such
chlorophosphines as phenyldichlorophosphine and bis[diethyl-
amino]chlorophosphines with sodium fluoride in tetramethyl-
ene sulfone (tetrahydrothiophene 1,1-dioxide) led to the corre-
sponding fluorides in 74% and 35% respectively.2a,b
R᎐POCl2 ϩ Na2SiF6 → R᎐POF2 ϩ R᎐POClF
R = Ph, PhO, EtO, C3H7, p-NO2PhO, CBr3CH2O
Scheme 1
In the fluorination with sodium fluoride, crown-ether sol-
vation affords advantages. Exclusive solvation of sodium ion by
the chelating crown ether enhances anion activation. The
unsolvated fluoride ion (‘naked fluoride’) is strongly nucleo-
philic. The procedure allowed the preparation of 2,5-dimethyl-
phenyldifluorophosphine in 87% and 2-methoxyphenyl- and
2-(N,N-dimethylamino)phenyl-difluorophosphines in 76% and
82% yield respectively.3a,b
Reaction of chlorophosphines with arsenic or antimony tri-
fluoride provides a simple route to fluorophosphoranes via an
oxidation–reduction mechanism. Thus, phenyltetrafluoro- and
diphenyltrifluoro-phosphoranes were prepared from phenyl-
chloro- and diphenylchloro-phosphines in 94% and 77% yield
respectively.4a Both (dimethylamino)- and (diethylamino)-
chlorofluorophosphines have been prepared in 6% and 3% yield
respectively from the corresponding dichloride using antimony
trifluoride.4b The procedure has been extended to prepare other
substituted difluoro- and monofluoro-phosphines in poor to
moderate yields.4c,d
Hexafluorosilicate anion as its sodium or ammonium salt has
been used to effect nucleophilic fluorination of organosilicon
compounds.5 We have previously reported the use of alkali
metal salts of perfluorinated complex anions as effective
fluorinating agents for nucleophilic fluorination of organo-
silicon compounds6–8 and organoboron compounds9 to obtain
the corresponding fluoro compounds in high yields. We now
report the use of sodium hexafluorosilicate as an effective
fluorinating agent for nucleophilic fluorination of some organo-
dichlorophosphorus compounds.
In the reaction of phenyl dichlorophosphate with sodium
hexafluorosilicate in 1:1 molar ratio for 15 min, analysis of the
distillate within a boiling point range of 80–95 ЊC/0.5 Torr
shows two products: phenyl difluorophosphate and phenyl
chlorofluorophosphate in the ratio 88:12. Redistillation of the
distillate gave phenyl difluorophosphate in 45% yield. The
NMR parameters of the product is shown in the Experimental
section.
Reaction of ethyl dichlorophosphate with sodium hexa-
fluorosilicate was carried out in 1:2 molar ratio for a few
minutes (0.1 h). The distillate within a boiling point range 85–
95 ЊC/760 Torr gave several products as identified in the 31P
NMR spectra. Ethyl difluorophosphate, difluorophosphoric
and monofluorophosphoric acids were formed in the ratio
90:7:3 to give a total conversion of 33% to the fluorinated
products. The reaction products are very sensitive to moisture.
Careful redistillation gave ethyl difluorophosphate in 18% yield.
Propylphosphonic dichloride was allowed to react, under the
similar conditions, with sodium hexafluorosilicate in 1:2 molar
ratio for 1 h to give the corresponding difluoride in 71% yield
and 98% purity.
In the reaction of p-nitrophenyl dichlorophosphate with
sodium hexafluorosilicate in 1:1 molar ratio for 0.5 h, the
corresponding difluoride, together with monofluoride, was
formed in 35% yield. Redistillation gave p-nitrophenyl di-
fluoride in 22% yield. In the reaction of 2,2,2-tribromoethyl
dichlorophosphate in 1:1 molar ratio for 0.5 h, the desired
difluorinated product is formed in relatively higher yield (75%).
The only by-product as identified in the 31P NMR spectra is the
monofluorophosphoric acid formed in a trace amount.
Reactions of various organochlorophosphorus compounds
with sodium hexafluorosilicate were carried out as a hetero-
genous mixture in the absence and presence of a high boiling
multifunctional ethereal solvent.
A mixture of phenyl-
Experimental
phosphonic dichloride and sodium hexafluorosilicate (Scheme
1) in a molar ratio 1:1 was heated to about 200 ЊC for 1.5 h in the
absence of solvent and then was subjected to distillation. The
distillate, collected within boiling point range 55–65 ЊC/0.5
Torr, was analyzed by 1H, 31P and 19F NMR spectroscopy. The
31P NMR spectrum gave a triplet (1:2:1) at δP 10.64 (t, JP–F
1103 Hz). By comparison of this and the 19F NMR spectrum at
Phenylphosphonic dichloride, phenyl dichlorophosphate, ethyl
dichlorophosphate, propylphosphonic dichloride, p-nitro-
phenyl dichlorophosphate, 2,2,2-tribromoethyl dichlorophos-
phate, sodium hexafluorosilicate were made available from
Aldrich as reagent grade chemicals. Tetraglyme, prior to use,
1
was dried over sodium. H, 31P and 19F NMR spectra were
J. Chem. Soc., Perkin Trans. 1, 1998
839

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recorded on a Varian 400 MHz superconducting NMR spectro-
n-C3H7POF2: δH(400 MHz, CDCl3) 2.13 (m, J 7.3), 1.77 (m,
1
meter. TMS (internal) for H, 85% phosphoric acid (external)
J 6.3), 1.09 (t, J 5.3); δP(400 MHz, CDCl3) 23.68 (tm, includ-
ing J 1135, 18.4); δF(400 MHz, CDCl3) Ϫ65.15 (d, JF–P 1134).
p-NO2PhOPOF2: δH(400 MHz, CDCl3) 8.12 (d, J 9.03), 6.94
(d, J 9.03); δP(400 MHz, CDCl3) Ϫ20.04 (t, JP–F 1012).
for 31P and CFCl3 (external) for 19F NMR spectra were used as
references.
General procedure of fluorination of organodichlorophosphorus
compounds
CBr3CH2OPOF2: δP(400 MHz, CDCl3) Ϫ19.63 (t, JP–F 978).
To 2 g (10.3 mmol) phenylphosphonic dichloride was added
2.1 g (11.2 mmol) sodium hexafluorosilicate and the mixture
was heated to about 200 ЊC for 1.5 h. The distillate collected
within bp 55–65 ЊC/0.5 Torr consisted of phenylphosphonic
difluoride in 98% purity. Redistillation gave the product in 44%
yield [bp 55–60 ЊC/0.5 Torr (lit.,10a,b 78 ЊC/15 mmHg, 69 ЊC/10
mmHg)]. Reaction in the presence of tetraglyme was similarly
carried out for 15 min to obtain the product in 61% yield. The
product was identified by comparison of its NMR spectra with
those of an authentic sample.10a Reactions of other organo-
dichlorophosphorus compounds were similarly carried out and
analyzed. The NMR spectra of various organofluorophos-
phorus compounds are as follows.†
PhPOF2: δH(400 MHz, CDCl3) 7.76 (2H, ddd, J 15, 7.0, 1.4),
7.63 (1H, dt, J 8.0, 1.2), 7.47 (2H, dq, J 6.5, 1.2); δP(400 MHz,
CDCl3) 10.64 (t, JP–F 1103) [lit.,11 10.82 (JP–F 1103)]; δF(400
MHz, CDCl3) Ϫ65.41 (d, JP–F 1104) [lit.,2a Ϫ65.40 (JP–F 1107)].
PhOPOF2: δH(400 MHz, CDCl3) 7.34 (t, J 8), 7.22 (t, J 6.2),
7.16 (d, J 7.8); δP(400 MHz, CDCl3) Ϫ28.3 (t, JP–F 1032) [lit.,12
Ϫ27.1 (JP–F 1030)]; δF(400 MHz, CDCl3) Ϫ83.70 (d, JF–P 1032)
[lit.,10a Ϫ84.1 (JF–P 102)].
References
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EtOPOF2: δH(400 MHz, CDCl3) 1.11 (t, J 5.3), 4.38 (q, J 7.2);
δP(400 MHz, CDCl3) Ϫ21.35 (t, JP–F 1014) [lit.,10a Ϫ20.2 (JP–F
1014)]; δF(400 MHz, CDCl3) Ϫ84.6 (JF–P 1034) [lit.,10a Ϫ85.0
(JF–P 1008)].
Paper 8/00243F
Received 8th January 1998
Accepted 8th January 1998
† J Values are given in Hz.
840
J. Chem. Soc., Perkin Trans. 1, 1998