Free Radical Hydrophosphorylation of Fluoroalkyl Vinyl Ethers: Synthesis of Fluoroalkyl Phosphonates

Article abstract of DOI:10.1134/S107036322004009X

Abstract: An effective method for the synthesis of dialkyl [2-(polyfluoroalkoxy)ethyl]phosphonates by free radical hydrophosphorylation of fluoroalkyl vinyl ethers with dialkyl (H)-phosphonates was developed. The reaction proceeds in the presence of catalytic amounts of azabisisobutyric acid dinitrile (AIBN) (150°C, 2 h, portionwise addition of AIBN) to afford the target fluoroalkyl phosphonates in up to 85% isolated yield.

Full text of DOI:10.1134/S107036322004009X

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 4, pp. 614–618. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Obshchei Khimii, 2020, Vol. 90, No. 4, pp. 551–556.
Free Radical Hydrophosphorylation of Fluoroalkyl Vinyl Ethers:
Synthesis of Fluoroalkyl Phosphonates
L. A. Oparinaa, M. Ya. Khil’koa, N. A. Kolyvanova, N. K. Gusarovaa, N. A. Nedolyaa,
V. N. Sapryginab, K. A. Apartsync, V. V. Kireevac, and B. A. Trofimova,*
a A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,
Irkutsk, 664033 Russia
b Irkutsk National Research Technical University, Irkutsk, 664074 Russia
c Irkutsk Scientific Center, Siberian Branch of the Russian Academy of Sciences, Irkutsk, 664033 Russia
*e-mail: boris_trofimov@irioch.irk.ru
Received November 25, 2019; revised November 25, 2019; accepted November 28, 2019
Abstract—An effective method for the synthesis of dialkyl [2-(polyfluoroalkoxy)ethyl]phosphonates by free radi-
cal hydrophosphorylation of fluoroalkyl vinyl ethers with dialkyl (H)-phosphonates was developed. The reaction
proceeds in the presence of catalytic amounts of azabisisobutyric acid dinitrile (AIBN) (150°C, 2 h, portionwise
addition of AIBN) to afford the target fluoroalkyl phosphonates in up to 85% isolated yield.
Keywords: dialkyl (H)-phosphonates, fluoroalkyl vinyl ethers, radical addition, atom-economic synthesis, fluo-
roalkyl phosphonates
DOI: 10.1134/S107036322004009X
Fluorine-containing organophosphorus compounds
have a wide range of useful properties and are used in
various fields of industry, agriculture, and medicine.
Among them, effective additives to the electrolytes of
lithium-ion batteries were found to increase their fire and
explosion safety [1–9]. A great deal of attention is also
paid to fluoroalkyl phosphonates [10, 11], among which
compounds have already been identified that are active
against various viral and retroviral DNAinfections, such
as hepatitis B and HIV [12–15], malignant tumors [16],
as well as anti-inflammatory effect [17]. Therefore, an
increasing interest in the development of the chemistry
of fluoroalkyl phosphonates and the development
of convenient approaches to their preparation is not
accidental.
the starting compounds were isolated from the reaction
mixture. Varying the initiator concentration (up to 3 wt %)
and the process duration (20 h) did not lead to a positive
result. Raising the reaction temperature to 120°C with a
single injection of AIBN also proved to be ineffective,
probably due to the rapid thermal destruction of the
initiator.
At the same time, we succeeded in carrying out the
process at 150°С with the portionwise addition of AIBN
and vinyl ether 1a to phosphonate 2a. The developed
technique involves the slow (1.5 h) dropwise addition of a
solution of 1.5 wt %AIBN (a mixture of 1 equiv. of ether
1a and 2 equiv. of phosphonate 2a was used as a solvent) to
phosphonate 2a (2 equiv.) heated to 150°С. This approach
provided a large excess of phosphorylating reagent 2a
with respect to substrate 1a, which made it possible
to suppress the telomerization of vinyl ether 1a and to
obtain the target dimethyl 2-(2,2,3,3-tetrafluoropropoxy)-
ethylphosphonate 3a in 85% yield. The reaction is of a
general nature: the target polyfluoroalkyl phosphonates
3b–3d were synthesized with a yield of 83, 66 and 67%,
respectively (Scheme 1). These data indicate that the
selectivity of the reaction decreases with increasing length
of the fluoroalkyl substituent in ether 1 (Scheme 1).
Herein, we first reported the radical addition reaction
of dialkyl (H)-phosphonates to vinyl ethers of polyfluoro-
alkanols resulting in new representatives of fluoroalkyl
phosphonates.
Initial experiments showed that 2,2,3,3-tetrafluoro-
propan-1-ol vinyl ether 1a does not react with (H)-
phosphonate 2a under conditions typical for the
phosphorylation of alkyl vinyl ethers [18–21] (molar
ratio 1a : 2a = 1 : 4, 1.5 wt % AIBN, 80°C, 8 h): only
614

FREE RADICAL HYDROPHOSPHORYLATION OF FLUOROALKYL VINYL ETHERS
615
Scheme 1.
Scheme 2.
It should be noted that the excess of (H)-phosphonate
2 returns practically quantitatively when the reaction
mixture is fractionated.
Preliminary tests of fluoroalkyl phosphonates 3a–3d by
Samsung (Samsung SDI Co. Ltd.) using standard methods
[2, 3] showed the feasibility of further studying this
class of compounds to create new effective components
of Li-ion batteries that prevent their combustibility,
flammability and explosiveness.
Lowering the reaction temperature to 120°C leads to
a noticeable decrease (~ 1.5 times) in the yield of target
polyfluoroalkyl phosphonates 3, all other factors being
the same.
In conclusion, a convenient, efficient and atom-
economic method for the synthesis of previously unknown
dialkyl [2-(polyfluoroalkoxy)ethyl]phosphonates was
developed based on the AIBN-initiated reaction of
radical addition of dialkyl (H)-phosphonates to available
fluoroalkyl vinyl ethers. The obtained compounds are
promising additives for enhancing the thermal stability
of electrolytes, drug precursors, intermediates and
components for the design of innovative materials.
The experimental conditions found are: a temperature
of 150°С (contributing to the breaking of the P–H
bond, the dissociation energy of which is 365 kJ/mol
[22]), a portionwise addition of AIBN into the reaction
mixture (allowing its initiating activity to be preserved),
a portionwise addition of substrate 1; the use of excess
phosphorylating reagent 2 reduces a possibility of
telomerization of vinyl ether 1 and increases the efficiency
of the formation of polyfluoroalkyl phosphonates 3.
EXPERIMENTAL
1H, 13C, 19F, 31P NMR spectra were recorded on
Bruker DPX 400 and Bruker AV-400 spectrometers
(400.13, 101.61, 376.50 and 161.98 MHz, respectively),
internal standard—HMDS (1H, 13C), CFCl3 (19F), external
standard – 85% H3PO4 (31P). IR spectra were recorded
on a Bruker IFS 25 spectrometer from thin layer. Mass
spectra of electron ionization (70 eV) were obtained on
a GCMS-QP5050A Shimadzu instrument. Elemental
analysis was performed on a Flash EA 1112 Series
analyzer. Fluorine and phosphorus are determined by
combustion.
The starting fluoroalkyl vinyl ethers 1a and 1b were
synthesized according to a previously developed procedure
[23] by the direct vinylation of polyfluoroalkanols with
acetylene in the presence of the Cd(OAc)2–Bu3N catalyst
(Scheme 2).
The use of synthesized fluoroalkyl phosphonates
3a–3d as additives in electrolytes for Li-ion batteries
to increase their fire and explosion safety is promising
[2, 3]. These compounds dissolve well in organic solvents,
have a high dielectric constant ε (14–19), low viscosity η
(11–37 cP), high boiling point (> 250°С) and low glass
transition temperature (<−40°С), that is, they will not
significantly affect the physical characteristics of the
solvents used in electrolytes for Li-ion batteries [24].
Fluoroalkyl vinyl ethers were obtained according to
the procedure described in [23], dialkyl (H)-phosphonates
were obtained from Aldrich. As an electrolyte a 1 M
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616
OPARINA et al.
3
solution of LiPF6 in a mixture of ethylene carbonate and
methyl ethyl carbonate (3 : 7 by volume) with the addition
of 10 vol % phosphonate 3 was used.
spectrum (СDCl3), δ, ppm: 0.91 t (6Н, СН3, JHH
=
7.0 Hz), 1.70 d. t (2H, PCH2, 2JHP = 16.2, 3JHH = 7.0 Hz),
3
3
3.40 d. t (4H, OCH2CH3, JНР = 11.1, JНН = 7.0 Hz),
3.68 m (4H, OCH2), 5.56 t. t (1H, CF2H, 2JHF = 53.2, 3JHF
=
General procedure for the synthesis of dialkyl
[2-(trihydrofluoroalkoxy)ethyl]phosphonates 3a–3d.
To 0.1 mol of dialkyl (H)-phosphonate 2 heated to
150°C was added dropwise with stirring a mixture of
vinyl ether 1 (0.05 mol), dialkyl (H)-phosphonate 2
(0.1 mol) and 0.5–0.8 g (1.5 wt %) AIBN within ~ 1.5 h.
The reaction mixture was stirred for another 0.5 h at the
same temperature, then it was cooled and the desired
phosphonates 3 were obtained by distillation in vacuum.
4.2 Hz). 13С NMR spectrum (СDCl3), δС, ppm: 16.1 d
(CH3, JCP = 5.7 Hz), 26.7 d (PCH2, 1JCP = 141.0 Hz),
3
61.5 d (CH2Me, 3JCP = 6.2 Hz), 66.5 (CH2O), 67.7 t
(CH2CF2, 2JCF = 30.1 Hz), 109.0 t. t (HCF2, 1JCF = 249.2,
1
2
2JCF = 33.9 Hz), 114.8 t. t (CF2, JCF = 249.9, JCF
=
27.1 Hz). 19F NMR spectrum (СDCl3), δF, ppm: –140.2 d
(HCF2, JHF = 53.2 Hz), –125.43 (CF2). 31P NMR
2
spectrum (СDCl3): δP 28.54 ppm. Mass spectrum, m/z (Irel,
%): 251 (11) [М – EtO]+, 181 (89) [М – CH2CF2CF2H]+,
138 (52) [(EtO)2P(O)H], 137 (27) [(EtO)2P(O)]+, 109
(100) [138 – Et]+, 93 (26) [138 – EtO]+. Found, %: C
36.02; H 5.78; F 24.86; P9.98. C9H17F4O4P (M 296.196).
Calculated, %: C 36.49; H 5.79; F 25.66; P 10.46.
Dimethyl [2-(2,2,3,3-tetrafluoropropoxy)ethyl]-
phosphonate (3a). Yield 11.38 g (85%), clear colorless
20
liquid, bp 113–115°C (2 mmHg), d420 1.4336, nD
1.3940, ε 19.6±0.1, η 1.69×10–3 Pa s. IR spectrum, ν,
cm–1: 3005 w (CH–F), 2960 s, 2929 m, 2893 m, 2856 m
(CH2, CH3), 1463 m, 1453 sh, 1414 w, 1403 w, 1382 w
[δ(CH3, CH2)], 1254 s, 1237 s [P=O, δ(CF2)], 1205 s,
1189 s (P–O–C), 1137 sh, 1116 s, 1104 s, 1059 s, 1033 s
(C–O–C), 1001 sh [δ(C–O, P–O)], 938 m, 833 m, 800 sh
[δ(CH2), C–C], 742 w, 684 w (P–O), 592 w, 557 sh, 541 w,
469 w [δ(P–O–C, O–P=O)]. 1Н NMR spectrum (СDCl3),
δ, ppm: 2.08 d. t (2H, PCH2, 2JHP = 18.6, 3JHH = 7.0 Hz),
3.70 d (6H, OCH3, 3JHP = 11.0 Hz), 3.82 m (4H, OCH2),
Dimethyl [2-(2,2,3,3,4,4,5,5-octafluoropentyloxy)-
ethyl]phosphonate (3c). Yield 12.15 g (66%), clear
colorless liquid, bp 130–132°C (2 mmHg), d420 1.4879,
nD20 1.3798, ε 16.2±0.1, η 3.72×10–3 Pa s. IR spectrum, ν,
cm–1: 3011 w (CH–F), 2961 s, 2931 m, 2896 m, 2857 m
(CH2, CH3), 1464 m, 1452 sh, 1402 m, 1381 m [δ(CH3,
CH2)], 1253 s, 1237 sh [P=O, δ(CF2)], 1171 s, 1128 s,
1062 s, 1035 s (C–O–C), 994 sh [δ(C–O, P–O)], 929 sh,
901 s, 841 sh, 809 s [δ(CH2), C–C], 766 m, 708 m (P–O),
2
3
5.93 t. t (1H, CF2H, JHF = 53.0, JHF = 5.0 Hz). 13С
1
NMR spectrum (СDCl3), δС, ppm: 25.7 d (PCH2, 1JCP
=
608 w, 544 m, 470 w [δ(P–O–C, O–P=O)]. Н NMR
spectrum (СDCl3), δ, ppm: 2.12 d. t (2H, PCH2, 2JHP
=
141.5 Hz), 52.2 d (OCH3, 2JCP = 6.3 Hz), 66.2 (CH2O),
18.6, 3JHH = 7.1 Hz), 3.72 d (6H, OCH3, 3JHP = 11.0 Hz),
3.83 d. t (2H, OCH2, 3JHP = 14.2, 3JHH = 7.1 Hz,), 3.92 t
67.7 t (CH2CF2, 2JCF = 32.1 Hz), 109.0 t. t (HCF2, 1JCF
249.1, 2JCF = 34.3 Hz), 114.8 t. t (CF2, 1JCF = 249.9, 2JCF
=
=
(2H, OCH2CF2, 3JHF = 13.9 Hz), 6.05 t. t (1H, CF2H, 2JHF
=
26.9 Hz). 19F NMR spectrum (СDCl3), δF, ppm: –140.24 d
52.0, JHF = 5.5 Hz). 13С NMR spectrum (СDCl3), δС,
3
(HCF2, JHF = 53.0 Hz), –125.55 (CF2). 31P NMR
2
1
ppm: 25.4 d (PCH2, JCP = 141.2 Hz), 51.8 d (OCH3,
spectrum (СDCl3): δP 31.11 ppm. Mass spectrum, m/z (Irel,
%): 153 (75) [М – CH2CF2CF2H]+, 137 (17) [153 − Me],
110 (80) [(MeO)2P(O)H], 109 (100) [(MeO)2P(O)]+, 79
(56) [110 – MeO]+. Found, %: C 31.44; H 4.99; F 28.31;
P 10.92. C7H13F4O4P (M 268.143). Calculated, %: C
31.35; H 4.89; F 28.46; P 11.56.
2
2JCP = 6.2 Hz), 66.4 (CH2O), 67.4 t (CH2CF2, JCF
=
25.4 Hz), 107.2 t. t (HCF2, 1JCF = 254.0, 2JCF = 30.2 Hz),
1
109.7–113.4 m (CF2CF2), 115.2 t. t (CF2СН2, JCF
=
256.5, JCF = 30.6 Hz). 19F NMR spectrum (СDCl3),
2
2
δF, ppm: –137.37 d (HCF2, JHF = 52.0 Hz), –130.36
(CF2), –125.69 (CF2), –119.86 (CF2). 31PNMR spectrum
(СDCl3): δP 30.98 ppm. Mass spectrum, m/z (Irel, %):
153 (100) [М – CH2(CF2)4H]+, 137 (34) [153 − Me], 110
(89) [(MeO)2P(O)H], 109 (96) [(MeO)2P(O)]+, 79 (56)
[110 – MeO]+. Found, %: C 28.83; H 3.73; F 41.87; P
8.36. C9H13F8O4P (M 368.158). Calculated, %: C 29.36;
H 3.56; F 41.28; P 8.41.
Diethyl [2-(2,2,3,3-tetrafluoropropoxy)ethyl]-
phosphonate (3b). Yield 12.35 g (83%), clear colorless
liquid, bp 119–121°C (2 mmHg), d420 1.2583, nD20 1.3970,
ε 16.0±0.1, η 1.17×10–3 Pa s. IR spectrum, ν, cm–1: 2986 s,
2934 s, 2912 s (CH2, CH3), 1482 m, 1460 m, 1446 m,
1394 m, 1371 m [δ(CH3, CH2, C–F)], 1270 sh, 1251 s,
1236 s (P=O), 1206 s, 1164 s (C–F, P–O–C), 1133 sh,
1116 s, 1103 s, 1058 s, 1028 s (C–O, C–F), 994 s, 963 s,
832 s, 793 m [δ(CH2), C–C], 742 m, 684 m (P–C), 592 w,
Diethyl [2-(2,2,3,3,4,4,5,5-octafluoropentyloxy)-
ethyl]phosphonate (3d). Yield 13.27 g (67%), clear
colorless liquid, bp 133–135°C (2 mmHg), d420 1.3690,
1
557 sh, 541 m, 485 w [δ(P–O–C, O–P=O)]. Н NMR
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FREE RADICAL HYDROPHOSPHORYLATION OF FLUOROALKYL VINYL ETHERS
617
nD20 1.3840, ε 14.2±0.1, η 2.37×10–3 Pa s. IR spectrum, ν,
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