Synthesis and properties of di(polyfluoroalkyl) peroxydicarbonates

Article abstract of DOI:10.1134/S1070363211050100

Synthesis of di(polyfluoroalkyl)peroxydicarbonates [X(CF₂) _nCH₂OC(O)O]₂, where X = H, F; n = 1, 2, 4, 6 (yield 80%) involves the step of the chloroformate formation (yield up to 93%) via the phosgenation of polyfluorinated alcohols followed by the reaction with sodium peroxide. The rate constant of monomolecular decomposition k _term was found to decrease as the polyfluoroalkyl groups were incorporated into the peroxide: it equaled 3.30 and 3.10 s^-1 for X = H, n = 2 and 4, respectively, and 7.36 s^-1 for di-n- butylperoxydicarbonate. The new peroxides are a source of the polyfluoroalkoxy radicals and nano-modifiers of the polymers to improve their heat resistance and light stability. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1070363211050100

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 5, pp. 884–889. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.I. Rakhimov, L.A. Butkovskaya, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 5, pp. 795–800.
Synthesis and Properties of Di(polyfluoroalkyl)
Peroxydicarbonates
A. I. Rakhimov and L. A. Butkovskaya
Volgograd State Technical University, pr. Lenina 28, Volgograd, 400131 Russia
e-mail: organic@vstu.ru
Received April 29, 2010
Abstract—Synthesis of di(polyfluoroalkyl)peroxydicarbonates [X(CF2)nCH2OC(O)O]2, where X = H, F; n = 1,
2, 4, 6 (yield 80%) involves the step of the chloroformate formation (yield up to 93%) via the phosgenation of
polyfluorinated alcohols followed by the reaction with sodium peroxide. The rate constant of monomolecular
decomposition kterm was found to decrease as the polyfluoroalkyl groups were incorporated into the peroxide: it
equaled 3.30 and 3.10 s–1 for X = H, n = 2 and 4, respectively, and 7.36 s–1 for di-n-butylperoxydicarbonate.
The new peroxides are a source of the polyfluoroalkoxy radicals and nano-modifiers of the polymers to
improve their heat resistance and light stability.
DOI: 10.1134/S1070363211050100
Peroxydicarbonates are widely used for the poly-
merization of vinyl monomers [1]. A disadvantage of
these peroxides is their high explosiveness and a low
thermal stability. Introduction of polyfluoroalkyl
fragments in nano-amounts into the macromolecular
systems enhances the heat resistance and stability
against lightof the polymeric materials [2]. In this
connection the works on the synthesis of polyfluoro-
alkyl peroxycarbonates as the nano-modifiers of the
polymer systems are actual [3].
In this paper we consider a two-step synthesis of di-
(polyfluoroalkyl) peroxydicarbonates including a cata-
lytic phosgenation of polyfluorinated alcohols [4] and
their reaction with the freshly prepared aqueous solu-
tion of sodium peroxide.
Na2O2
COCl2, catalyst
[X(CF2)nCH2OC(O)O]2
X(CF2)nCH2OH
X(CF2)nCH2OC(O)Cl
Ia–VIa
Ib–VIIb
The phosgenation of the polyfluorinated alcohols
was performed in the presence of catalytic amounts of
pyridine, triethylamine or N,N-dimethylformamide (DMF)
(Table 1). These compounds show similar catalytic
activity that suggests common mechanism of the chloro-
formate formation. The associate A of the polyfluorina-
ted alcohol with amine or acids amide form a polar com-
plex B with phosgene leading to the chloroformate formation:
X(CF2)nCH2
H
O
COCl2
Ia−VIa + HN+(C2H5)3Cl−
X(CF2)nCH2OH N(C2H5)3
N(C2H5)3
C Cl
Cl
O
B
А
Triethylamine hydrochloride may also participate in
the catalysis of the reaction of polyfluorinated alcohol
with phosgene to form a polar six-membered struc-
ture C:
884

885
SYNTHESIS AND PROPERTIES OF DI(POLYFLUOROALKYL) PEROXYDICARBONATES
X(CF2)nCH2
H
O
O
COCl2
+
Iа−VIа + HCl + Cl− NH(C2H5)3
А
Cl
C
Cl
Cl NH(C2H5)3
+
C
The association of the polyfluorinated alcohols with
triethylamine or DMF was studied by means of the IR
and NMR spectroscopy [5–7]. Owing to high acidity
of alcohols, the hydrogen bonding in the associate is
rather strong. This facilitates the further complexation
with phosgene and the reaction proceeding. The
polyfluoroalkyl chloroformates yields are 83–93%.
They are low-boiling liquids with a density of 1.48–
1.72 g cm–3 (Table 2).
In this work the polyfluoroalkyl chloroformates
were peroxygenated by the solution of sodium
peroxide freshly prepared from 30–50% aqueous
sodium peroxide and 13–17% aqueous sodium
hydroxide. To prevent the peroxydicarbonate decom-
position, the reaction temperature was maintained in
the initial period at about –5 to 0°С and then raised to
15–20°С. The organic layer was separated, washed
with water, dried with anhydrous sodium sulfate and
kept at a reduced pressure for 30–40 min. The
individuality of di(polyfluoroalkyl) peroxydicarbo-
nates obtained was established by TLC (Table 3). Note
that the yield of peroxydicarbonates decreases as the
length of perfluoroalkyl chain in the starting chloro-
formates increases. Di(polyfluoroalkyl)peroxydicar-
bonates are heavy liquids with the density 1.62 to
–1.78 g cm–3, except for trifluoroethyl peroxydicar-
bonate (1.43 g cm–3).
The nucleophilic substitution of tert-butylperoxy
groups in polyfluoroalkyl chloroformates with chlorine
have been described earlier [5]. The reaction of chloro-
formates with tert-butylhydroperoxide was carried out
in the presence of pyridine or sodium hydroxide at –5
to 0°С to obtain tert-butylperoxypolyfluoroalkyl car-
bonates in yields of 65–80%.
Table 1. Effect of the reactants ratio and the phosgenation parameters on the yield of polyfluoroalkyl chloroformates Ia–IIIa,
Va and VIa
Catalyst
Comp. no.
Alcohol:phosgene
T, оС
Time, h
Yield, %
compound
DMF
DMF
mol
0.07
0.05
0.1
0.03
0.1
0.1
0.08
0.04
1:1.4
1:1.2
1:1.5
1:1.2
1:1
1:1.2
1:1.3
1:1.25
50
90
95
80
80
90
70
90
3.0
1.5
2.0
2.5
3.0
1.5
2.0
2.0
90
86
93
87
83
88
88
87
Ia
IIa
DMF
Pyridine
Pyridine
DMF
TEA
TEA
IIIa
Va
VIa
Table 2. Polyfluoroalkyl chloroformates
Comp.
no.
Compound
bp, °С (mm Hg)
n2D0
d420
2,2,2-Trifluoroethyl chloroformate
40 (165)
35 (32)
50 (11)
36 (15)
59 (13)
63 (3)
1.3210
1.3510
1.3376
1.3182
1.3188
1.3338
1.4896
1.5179
1.6475
1.6200
1.7105
1.7240
Ia
IIa
IIIa
IVa
Va
1,1,3-Trihydroperfluoropropyl chloroformate
1,1,5-Trihydroperfluoropentyl chloroformate
1,1-Dihydroperfluoropentyl chloroformate
1,1-Dihydroperfluoroheptyl chloroformate
1,1,7-Trihydroperfluoroheptyl chloroformate
VIa
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RAKHIMOV, BUTKOVSKAYA
Table 3. Di(polyfluoroalkyl) peroxydicarbonates Ib–VIba
MRD
Elemental analysis
Formula
X(CF2)nCH2
Rf
d420
n2D0
Found, %
F
Calculated, %
found calculated
С
Оact
C
F
Oact
CF3CH2
75
78
80
66
68
79
0.73
0.75
0.78
0.76
0.77
0.79
1.4338 1.3298 40.53
1.6214 1.3548 47.01
1.7167 1.3362 66.47
1.7110 1.3192 67.82
1.7330 1.3095 87.41
1.7828 1.3308 86.16
40.62 24.91 39.82 5.57 C6H4O8F6
46.98 27.40 43.37 4.56 C8H6O6F8
25.17 39.86 5.59
27.42 43.42 4.57
66.57 25.87 55.07 2.78 C12H6O6F16 26.18 55.27 2.90
67.82 24.04 58.16 2.64 C12H6O6F18 24.57 58.36 2.73
87.41 24.13 62.80 1.97 C16H4O6F26 24.42 62.84 2.03
86.16 25.01 59.27 2.10 C16H6O6F24 25.60 60.08 2.13
Ib
H(CF2)2CH2
H(CF2)4CH2
F(CF2)4CH2
F(CF2)6CH2
H(CF2)6CH2
IIb
IIIb
IVb
Vb
VIb
a
Ib, di(2,2,2-trifluoroethyl) peroxydicarbonate, IIb, di(1,1,3-trihydroperfluoropropyl) peroxydicarbonate, IIIb, di(1,1,5-trihydro-
perfluoropentyl) peroxydicarbonate, IVb, di(1,1-dihydroperfluoropentyl) peroxydicarbonate, Vb, di(1,1-dihydroperfluoroheptyl) per-
oxydicarbonate, VIb, di(1,1,7-trihydroperfluoroheptyl) peroxydicarbonate.
In the IR spectra of di(polyfluoroalkyl) peroxydi-
constants, half-life (τ1/2) and activation energy for IIb
and IIIb in comparison with a widely used di(n-butyl)
peroxydicarbonate VII are presented in Table 4. The
introduction of perfluorinated carbon chains into the
dialkyl peroxydicarbonate IIb structure and the
elongation of this chain by more than two times in IIIb
reduce the rate constant of thermolysis in benzene
compared with the unsubstituted peroxide VII: kterm at
70°C for IIb, IIIb and VII are 3.30, 3.10, and 7.36 s–1,
respectively. The half-life of the peroxide at 70°C
varies in the following order: IIb 35 min, IIIb 38 min,
VII 16 min.
carbonates there are two absorption bands at 1778±2
and 1807±3 cm–1, corresponding to the stretching
vibration of carbonyl group in the unsubstituted
peroxydicarbonates [1, 3]. This indicates that the
polyfluoroalkyl groups located in β-position relative to
the peroxydicarbonate group do not affect appreciably
the spectral characteristics of the latter. The stretching
vibrations of the О–О bond in di(polyfluoroalkyl)
peroxydicarbonates appear in the range of 845–
850 cm–1. The stretching vibrations of the С–О–О–С
fragment are observed at 1041–1094 cm–1, which
corresponds to the published data [8].
The half-life, rate constant of the monomolecular
decomposition, and the activation energy in going
from benzene to ethylbenzene are significantly dif-
ferent (Table 4): the activation energy of thermolysis
decreases from 115 to 96–97 kJ mol–1. The rate con-
stants of peroxides thermolysis differ the most signi-
ficantly at 50°C: IIb 0.35 s–1 (benzene) and 0.69 s–1
(ethylbenzene), IIIb 0.25 s–1 (benzene) and 0.68 s–1
(ethylbenzene). The increase in the rate constants of
peroxydicarbonates thermolysis in passing from
benzene to ethylbenzene (at 50°C) almost 2-fold (IIb)
and 2.7-fold (IIIb) is due to the abstraction of a
hydrogen atom from ethylbenzene by polyfluoro-
alkoxy radicals. The phenylethyl radicals formed in
this case attack the peroxide groups of peroxydi-
carbonate:
In the 1H NMR spectra of all synthesized
peroxydicarbonates [X(CF2)nCH2OC(O)O]2 the signal
of terminal proton of HCF2-group appears as a triplet
of triplets at 5.8±0.05 ppm (αJHF 52 Hz), each
component of which is split into a triplet with a spin-
β
spin coupling constant with the β-fluorine atom JHF
5.5 Hz. The signal of two СF2CH2-protons is seen as a
well-resolved triplet at 4.6±0.03 ppm with the spin-
spin coupling constant JHF 5.5 Hz.
The kinetics of thermal decomposition of di(poly-
fluoroalkyl)peroxydicarbonates in benzene and ethyl-
benzene was studied at the initial peroxide
concentration of 4×10–2 mol l–1, which allows mini-
mizing the induced decay processes involving the free
radicals from the peroxide. The thermolysis rate
X(CF2)nCH2OH + C6H5CHCH3
C2H5CH2CH3 + X(CF2)nCH2O
peroxide
X(CF2)nOC(O)OCH(CH3)C6H5 + CO2 + X(CF2)nCH2O
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SYNTHESIS AND PROPERTIES OF DI(POLYFLUOROALKYL) PEROXYDICARBONATES
Table 4. Kinetic parameters of di(polyfluoroalkyl) peroxydicarbonates thermolysis (4×10–2 mol l–1) in comparison with
thermolysis of di(n-butyl) peroxydicarbonate VII (1×10–2 mol l–1)
Peroxide
Solvent
Benzene
Temperature, °С
k×10–4, s–1
τ1/2, min
Еa, kJ mol–1
50
60
70
50
60
70
50
60
70
50
60
70
50
60
70
0.35±0.04
1.20±0.02
3.30±0.02
0.69±0.04
1.96±0.04
4.38±0.02
0.25±0.06
1.00±0.05
3.10±0.02
0.68±0.03
1.90±0.06
4.36±0.04
0.62±0.05
2.20±0.05
7.36±0.04
320
100
35
183
60
115±3
IIb
Ethylbenzene
Benzene
96±3
115±4
97±3
28
IIIb
VI
462
115
38
172
60
28
186
52
Ethylbenzene
Benzene
113±5
16
The formation of polyfluoroalkoxy radicals is con-
firmed by a high content of 1,1,3-trihydroperfluoro-
propanol (1.27 mol per 1 mol of peroxide), carbon
dioxide (1.58 mol per 1 mol of peroxide), and
carbonate (0.28 mol 1 mol peroxide) in the thermolysis
products of peroxide IIb in ethylbenzene at 70°C:
0.28 carbonates
2 HCF2CF2CH2O(СO)O
[HCF2CF2CH2OC(O)O]2
1.58 HCF2CF2CH2O + 1.58 CO2
C6H5C2H5
1.27 HCF2CF2CH2OH + 0.31 CH2=O + HCF2CF2
The carbonate radicals formed during the mono-
molecular decay of peroxydicarbonate IIb at the О–О
bond transform into the tetrafluoropropoxy radicals
and CO2 (1.58 mol of CO2 found per 1 mol of the de-
composed peroxide). The main part of the tetrafluoro-
propoxy radicals (1.27 mol per 1 mol of the de-
composed peroxide) reacts with ethylbenzene resulting
in 1,1,3-trihydroperfluoropropanol (1.27 mol per 1 mol
of the decomposed peroxide). A small part of these
radicals (0.31 mol per 1 mol of the decomposed
peroxide) undergoes β-decay, which is consistent with
the amount of the formaldehyde detected.
The electrophilic properties of polifluoroalkoxyl
radicals generated from polyfluoroalkylperoxydi-carbo-
nate during polymerization of vinyl chloride facilitate
the attack of the vinyl chloride H2C group in compari-
son with the unsubstituted alkoxy radicals generated
from dialkyl diperoxycarbonates. This reduces defects
in the macromolecular chain of polyvinyl chloride [2]
and results in its simultaneous nano-modification:
HCF2CF2CH2OCH2CHCl
А
CH2=CHCl + HCF2CF2CH2O
CH2CH(Cl)OCH2CF2CF2H
B
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RAKHIMOV, BUTKOVSKAYA
Radical A by 0.310 eV is more stable than B, which
(2 parallel samples), cooled and opened, and the
amount of remaining peroxide was determined by the
iodometric titration [1].
explains the preference of its formation. Therefore, the
polyvinyl chloride suspension prepared using di(poly-
fluoroalkyl)peroxydicarbonates has a more ordered
structure, contains less labile groups, and so is more
thermally stable than in the case of the use of di(n-
butyl) peroxydicarbonate [2].
The composition of the thermolysis products of
peroxydicarbonate in ethylbenzene solution was deter-
mined after keeping the samples at 70°C for at least 10
half-life periods in the ampules of 15 ml volume each.
The gaseous products were analyzed on a Tsvet-104
chromatograph with a stainless steel column 300×
0.4 cm, sorbent activated carbon AG-3. The column
temperature 227°C, detector temperature 250°C,
evaporator temperature 300°C. Carrier gas helium,
pressure 25 kg cm–3. The qualitative composition of
the gases was determined by comparing the retention
times of the pure samples and the reaction mixture
components, the amount was determined by a simple
normalization method.
EXPERIMENTAL
1
The H NMR spectrum (CCl4) was registered on a
Varian Mercury instrument (300 MHz), internal
reference HMDS. The IR spectra were recorded on a
Specord-M82 instrument (from films).
Synthesis of di(1,1,3-trihydroperfluoropropyl)-
peroxydicarbonate (IIb). Into a three-neck reactor
equipped with a stirrer, thermometer, and dropping
funnel were placed 33.0 g (0.25 mol) of 1,1,3-
trihydroperfluoropropanol, 0.57 g (0.0078 mol) of
N,N-dimethylformamide, and 8.14 g (0.15 mol) of
liquid phosgene at –5 to 0°С. Then the temperature
was raised to 90°C and 14.85 g (0.15 mol) of gaseous
phosgene was passed through the reaction mixture for
2.5 h. As the reaction completed, hydrogen chloride
and unreacted phosgene were removed from the
reactor by blowing the dry nitrogen. The product was
distilled at the reduced pressure to give 1,1,3-tri-
hydroperfluoropropyl chloroformate IIa. Yield 45.2 g
(93%).
Liquid products in the reaction mixture were
identified and quantitatively determined on a Tsvet-
134 chromatograph, column 300×0.4 cm, adsorbent
SE-30 (5%) on Chromaton N-AW. The column
temperature 60°C, detector temperature 110°C,
evaporator temperature 270°C. Carrier gas helium, the
rate 20 cm3 min–1, the diagram sweep rate 600 mm h–1.
The identification of the liquid products was carried
out by comparing the retention times of the pure
samples, the reference substances in ethylbenzene and
the components of the reaction mixture. The quanti-
tative measurements were made using an internal
reference method [8].
To the cooled chloroformate IIa (45.2 g, 0.23 mol)
was added sodium peroxide prepared from 17%
aqueous solution of sodium hydroxide containing 9.2 g
(0.23 mol) of NaOH, and 4.4 g of 30% hydrogen
peroxide, at –5 to 0°С under vigorous stirring. The
reaction mixture was stirred for 2 h with the gradual
warming to 15–20°C. Then the organic layer was
separated and washed with distilled water, dried with
anhydrous sodium or magnesium sulfate, and kept at a
reduced pressure for 30–40 min. Yield 31.7 g (78%).
Peroxide IIb is a liquid with a characteristic odor. Rf
0.75 (silufol, acetone–diethyl ether–hexane, 0.5:1:1).
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SYNTHESIS AND PROPERTIES OF DI(POLYFLUOROALKYL) PEROXYDICARBONATES
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