New Synthetic Approach to Polyfluorinated Carbonates

Article abstract of DOI:10.1134/S1070428020040120

Abstract: Transesterification of commercial titanium(IV) alkoxides with2,2,3,3-tetrafluoropropan-1-ol, followed by in situ transesterification of mixedtitanium(IV) alkoxides thus formed with diphenyl carbonate, afforded alkyl2,2,3,3-tetrafluoropropyl carb

Full text of DOI:10.1134/S1070428020040120

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 4, pp. 645–648. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Organicheskoi Khimii, 2020, Vol. 56, No. 4, pp. 607–612.
New Synthetic Approach to Polyfluorinated Carbonates
A. M. Semenovaa, M. A. Ezhikovaa, M. I. Kodessa,b, A. Ya. Zapevalova, and A. V. Pestova,b,*
a Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences,
Yekaterinburg, 620990 Russia
b Yeltsin Ural Federal University, Yekaterinburg, 620002 Russia
*e-mail: pestov@ios.uran.ru
Received December 16, 2019; revised February 18, 2020; accepted February 19, 2020
Abstract—Transesterification of commercial titanium(IV) alkoxides with 2,2,3,3-tetrafluoropropan-1-ol,
followed by in situ transesterification of mixed titanium(IV) alkoxides thus formed with diphenyl carbonate,
afforded alkyl 2,2,3,3-tetrafluoropropyl carbonates and bis(2,2,3,3-tetrafluoropropyl) carbonate in up to 60%
yield. The degree of transesterification decreased in the series (i-PrO)4Ti > (EtO)4Ti > (BuO)4Ti and did not
exceed 68%. The selectivity for alkyl 2,2,3,3-tetrafluoropropyl carbonates and bis(2,2,3,3-tetrafluoropropyl)
carbonate was found to change depending on the composition of mixed titanium(IV) alkoxide formed in situ.
Keywords: transesterification, titanium alkoxides, tetrafluoropropan-1-ol, dialkyl carbonates
DOI: 10.1134/S1070428020040120
Organic carbonates are among the most promising
“green” candidates for replacement of common toxic
solvents and fuel additives, as well as for the design of
innovative intermediate products in pharmaceutics,
lubricants, and polymers [1]. Fluorinated dialkyl car-
bonates are poorly studied compounds, but they attract
interest since introduction of fluorine into organic
molecules strongly affects physicochemical properties
of the latter [2]. The presence of fluorine atoms in
carbonates makes it possible to use them as solvents in
electrochemical power sources; fluorinated carbonates
have a high dielectric permittivity and a low viscosity
in comparison to hydrocarbon analogs, which favor
improved solubility of alkali metal salts as electrolyte
components. Furthermore, they are characterized by
extended operational temperature range [3–6]. Poly-
fluorinated carbonates are also important as highly
reactive intermediate products in the synthesis of other
derivatives, e.g., carbamates [7, 8].
dimethyl carbonate [12], which is a modern green
reagent [13], with 2,2,3,3-tetrafluoropropan-1-ol seems
experimentally more efficient since since it requires no
specific conditions. It was found that the best catalyst
for the synthesis of alkyl 2,2,3,3-tetrafluoropropyl
carbonates was tetramethylammonium hydroxide
which provided 81% selectivity for methyl 2,2,3,3-tet-
rafluoropropyl carbonate at 50% conversion of
dimethyl carbonate [12]. Titanium tetraethoxide
showed a low activity despite the known ability of
titanium(IV) alkoxides to catalyze transesterification
reactions [14, 15].
Taking into account successful use of stoichiometric
amounts of titanium(IV) alkoxides for the synthesis of
dialkyl carbonates [16], herein we propose a new
phosgene-free synthesis of polyfluorinated dialkyl
carbonates via successive transesterifications involving
titanium(IV) alkoxides.
We previously described cross-transesterification of
propylene carbonate with commercial titanium(IV)
alkoxides as an alternative phosgene-free method of
synthesis of dialkyl carbonates [16]. Titanium tetra-
kis(2,2,3,3-tetrafluoropropoxide) has not been reported
previously. Therefore, we initially tried to synthesize it
by transesterification of commercial Ti(IV) alkoxides
with 2,2,3,3-tetrafluoropropan-1-ol (Scheme 1). How-
ever, we failed to achieve complete transesterification
even with alcohols boiling at a lower temperature than
Dialkyl carbonates, including fluorinated ones, are
traditionally synthesized by reactions of the corre-
sponding alcohols with phosgene [9]. Alternative
methods such as reaction of 2,2,3,3-tetrafluoropropan-
1-ol with carbon tetrachloride in the presence of AlCl3
[10] and pyrolysis of ortho esters [11] have also been
reported. However, in both cases toxic, explosive, and
aggressive reagents are used, which adversely affect
the environment. In this connection, the synthesis of
polyfluorinated carbonates via transesterification of
645

SEMENOVA et al.
646
Scheme 1.
Ti(OR)4
HCF2CF2CH2OH
O
Ti(OR)4–n(OCH2CF2CF2H)n
–nROH
1a–1c
O
O
(PhO)2CO
–Ti(OPh)4
+
+
RO
OCH2CF2CF2H
2a–2c
HCF2CF2CH2O
OCH2CF2CF2H
RO
OR
3a
4a–4c
R = Et (a), i-Pr (b), Bu (c).
2,2,3,3-tetrafluoropropan-1-ol (Table 1). Analysis of
the distillate composition showed that 2,2,3,3-tetra-
fluoropropan-1-ol was distilled off from the reaction
mixture together with the corresponding aliphatic
alcohol, so that the degree of transesterification
decreased. In the case of titanium tetrabutoxide, there
were no reasons to increase the amount of 2,2,3,3-tetra-
fluoropropan-1-ol.
degree of transesterification. In the case of ethoxide 1a,
the amount of diethyl carbonate (4a) significantly
decreased, whereas the amount of diisopropyl car-
bonate (4b) almost did not change. Despite selective
formation of butyl 2,2,3,3-tetrafluoropropyl carbonate
2c, we failed to separate it from dibutyl carbonate (4c)
by fractional distillation.
Thus, we did not succeed in obtaining tetrakis-
(2,2,3,3-tetrafluoropropoxy)titanium(IV) by transes-
terification of titanium(IV) alkoxides with 2,2,3,3-tetra-
fluoropropan-1-ol. The degree of transesterification
decreases in the series (i-PrO)4Ti > (EtO)4Ti >
(BuO)4Ti, and it does not exceed 68%. Mixed titani-
um(IV) alkoxides 1a–1c generated in situ demonstrate
a high reactivity toward diphenyl carbonate, giving rise
to mixtures of dialkyl carbonates. Variation of the ratio
of 2,2,3,3-tetrafluoropropan-1-ol and aliphatic alcohol
moieties in titanium(IV) alkoxide 1a–1b makes it pos-
sible to control the selectivity for alkyl 2,2,3,3-tetra-
fluoropropyl carbonate and bis(2,2,3,3-tetrafluoro-
propyl) carbonate.
Mixed titanium(IV) alkoxide 1a–1c formed in situ
was treated with diphenyl carbonate (Scheme 1).
Propylene carbonate turned out to be effective in
transesterification with non-fluorinated titanium(IV)
alkoxides [16], but no dialkyl carbonates were formed
in its reactions with alkoxides 1a–1c. Presumably,
chelating properties of propane-1,2-diol as a weak
Brønsted acid do not compensate increased acidity of
2,2,3,3-tetrafluoropropan-1-ol. Phenol is a stronger
Brønsted acid than 2,2,3,3-tetrafluoropropan-1-ol and,
as follows from our results, is capable of replacing all
alcohols in mixed alkoxides 1a–1c. The reactions of
1a–1c with diphenyl carbonate afforded 80–90% of
mixtures of three products, alkyl 2,2,3,3-tetrafluoro-
propyl carbonate 2a–2c, bis(2,2,3,3-tetrafluoropropyl)
carbonate (3a), and dialkyl carbonate 4a–4c. The prod-
uct ratio (Table 1) depended not only on the composi-
tion of mixed alkoxide 1a–1c but also on the structure
of aliphatic alcohol. The overall amount of fluorinated
carbonates 2a–2c and 3a increased in parallel with the
In summary, we have developed procedures for the
synthesis of ethyl 2,2,3,3-tetrafluoropropyl carbonate
and bis(2,2,3,3-tetrafluoropropyl) carbonate by trans-
esterification of commercially available titanium(IV)
alkoxides with 2,2,3,3-tetrafluoropropan-1-ol, followed
by treatment of mixed titanium(IV) alkoxides formed
Table 1. Successive transesterifications of titanium(IV) alkoxides with 2,2,3,3-tetrafluoropropan-1-ol and diphenyl carbonate
Product ratio
HCF2CF2CH2OH–Ti(OR)4
molar ratio
Degree of
transesterification, %
R
2
3
12
25
56
39
42
58
2
4
21
14
4
18
16
20
58
54
51
Et
Et
Et
i-Pr
i-Pr
i-Pr
Bu
Bu
Bu
2:1
4:1
10:1
2:1
4:1
10:1
2:1
30
47
60
43
52
68
14
22
25
67
61
40
43
42
22
40
46
49
4:1
10:1
0
0
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 4 2020

NEW SYNTHETIC APPROACH TO POLYFLUORINATED CARBONATES
647
in situ with diphenyl carbonate. Isopropyl 2,2,3,3-tet-
rafluoropropyl carbonate and butyl 2,2,3,3-tetrafluoro-
propyl carbonate could not be isolated from the
reaction mixtures. The proposed approach based on
successive transesterifications can be regarded as an al-
ternative phosgene-free method of synthesis of dialkyl
carbonates, including fluorinated ones.
carbonate was isolated from the product mixture by
fractional distillation.
Ethyl 2,2,3,3-tetrafluoropropyl carbonate (2a).
Yield 58%, colorless liquid, bp 155–156°C, nD20
=
1.340. IR spectrum (KBr), ν, cm–1: 2990 (C–H), 1762
1
(C=O), 1271 (C–F), 1108 (C–O). H NMR spectrum,
δ, ppm: 1.24 t (3H, CH3, J = 7.1 Hz), 4.20 q (2H,
OCH2CH3, J = 7.1 Hz), 4.65 t (2H, OCH2CF2, J =
14.2 Hz), 6.61 t.t (1H, CF2H, J = 51.8, 5.2 Hz).
19F NMR spectrum, δF, ppm: 23.89 d.t (2F, CF2H, J =
51.8, 5.2 Hz), 37.5 t.q (2F, OCH2CF2, J = 14.2,
5.2 Hz). 13C NMR spectrum (126 MHz), δC, ppm:
13.79 (CH3), 62.38 t (OCH2CF2, J = 26.8 Hz), 64.78
(OCH2CH3), 109.23 t.t (CF2H, J = 248.0, 33.3 Hz),
114.27 t.t (OCH2CF2, J = 249.4, 26.7 Hz), 153.62
(CO). Found, %: C 35.10; H 3.95; F 37.03. C6H8F4O3.
Calculated, %: C 35.31; H 3.95; F 37.23.
EXPERIMENTAL
2,2,3,3-Tetrafluoroprpropan-1-ol (98%, manufac-
tured by GaloPolimer Perm) and other commercially
available reagents (Alfa Aesar) were used without
further purification.
The 1H, 19F, and 13C NMR spectra were recorded in
DMSO-d6 on Bruker Avance-500 and DRX-400 spec-
1
trometers. The H and 19F NMR chemical shifts were
measured relative to tetramethylsilane and hexafluoro-
benzene, respectively, used as internal standards; the
13C chemical shifts were measured relative to the
solvent signal (δC 39.5 ppm). The IR spectra were
recorded in the range 400–4000 cm–1 on a Nicolet 6700
spectrometer with Fourier transform equipped with
a diamond ATR accessory. The elemental compositions
were determined with a Perkin Elmer 2400 automated
CHN analyzer. Chromatographic analyses were carried
out on a Shimadzu GC2010 gas chromatograph
equipped with a flame ionization detector and a ZB-5
capillary column, 30 m×0.25 mm, film thickness
0.25 μm; carrier gas nitrogen, split ratio 1:30; oven
temperature programming from 40°C (3 min) at a rate
of 10 deg/min to 280°C (15 min); injector temperature
250°C, detector temperature 300°C.
Bis(2,2,3,3-tetrafluoropropyl) carbonate (3a).
Yield 51%, colorless liquid, bp 181–182°C, nD20
=
1.335. IR spectrum (KBr), ν, cm–1: 2983 (C–H), 1778
1
(C=O), 1279 (C–F), 1108 (C–O). H NMR spectrum,
δ, ppm: 4.77 t (2H, OCH2CF2, J = 14.2 Hz), 6.63 t.t
(1H, CF2H, J = 51.8, 5.2 Hz). 19F NMR spectrum, δF,
ppm: 23.95 d.t (2F, CF2H, J = 51.8, 5.2 Hz), 37.55 t.q
(2F, OCH2CF2, J = 14.2, 5.2 Hz). 13C NMR spectrum
(126 MHz), δC, ppm: 63.41 t (OCH2CF2, J = 26.7 Hz),
109.22 t.t (CF2H, J = 248.1, 33.2 Hz), 114.14 t.t
(OCH2CF2, J = 249.7, 26.9 Hz), 152.97 (CO).
Found, %: C 28.95; H 2.07; F 52.21. C7H6F8O3. Cal-
culated, %: C 28.98; H 2.08; F 52.39.
ACKNOWLEDGMENTS
General procedure for the synthesis of alkyl
2,2,3,3-tetrafluoropropyl carbonates. A mixture of
2,2,3,3-tetrafluoropropan-1-ol (0.38 mol) and tetraethyl
or tetraisopropyl titanate (0.19 mol) was heated to
the boiling point with simultaneous removal of the
liberated alcohol by distillation. Diphenyl carbonate
(0.32 mol) was added to the residue, and the mixture
was heated to the boiling point while distilling off the
resulting carbonates which were then separated by
fractional distillation.
The spectral and analytical data were obtained using the
facilities of the Spectroscopy and Analysis of Organic
Compounds joint center.
FUNDING
This study was performed in the framework of state task
to the Postovskii Institute of Organic Synthesis, Ural Branch,
Russian Academy of Sciences (project nos. AAAA-A19-
119012490006-1, AAAA-A19-119012290116-9).
General procedure for the synthesis of bis-
(2,2,3,3-tetrafluoropropyl) carbonate. A mixture of
2,2,3,3-tetrafluoropropan-1-ol (0.95 mol) and tetraethyl
or tetraisopropyl titanate (0.095 mol) was heated to the
boiling point with simultaneous removal of the
liberated alcohol by distillation. Diphenyl carbonate
(0.162 mol) was added to the residue, and the mixture
was heated to the boiling point while distilling off the
resulting carbonates. Bis(2,2,3,3-tetrafluoropropyl)
CONFLICT OF INTEREST
The authors declare the absence of conflict of interest.
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