Synthesis of α,ω-dimethoxyfluoropolyethers: Reaction mechanism and kinetics

Article abstract of DOI:10.1016/j.jfluchem.2005.01.014

A new class of hydrofluoropolyethers, the α,ω- dimethoxyfluoropolyethers (DM-FPEs), characterized by the copolymeric structure CH₃O(CF₂CF₂O)_n(CF₂O) _mCH₃ has been recently developed. The synthesis of DM-FPEs here described, has been carried out via a new synthetic route which consists of the reaction of a perfluoropolyether diacyl fluoride with methyl fluoroformate in the presence of a metal fluoride. The reaction products are DM-FPEs and carbon dioxide. Several reaction conditions has been tested varying type of solvent, temperature, type and amount of metal fluoride. The best results were obtained using tetraglyme as solvent and CsF as metal fluoride.

Full text of DOI:10.1016/j.jfluchem.2005.01.014

Journal of Fluorine Chemistry 126 (2005) 633–639
www.elsevier.com/locate/fluor
Synthesis of a,v-dimethoxyfluoropolyethers:
reaction mechanism and kinetics
*
M. Avataneo , U. De Patto, M. Galimberti, G. Marchionni
*
Solvay Solexis R&D, Viale Lombardia 20, 20021 Bollate, Milan, Italy
Received 28 September 2004; received in revised form 21 January 2005; accepted 25 January 2005
Available online 25 February 2005
Dedicated to Prof. R.D. Chambers on the occasion of his 70th birthday.
Abstract
A new class of hydrofluoropolyethers, the a,v-dimethoxyfluoropolyethers (DM-FPEs), characterized by the copolymeric structure
CH3O(CF2CF2O)n(CF2O)mCH3 has been recently developed. The synthesis of DM-FPEs here described, has been carried out via a new
synthetic route which consists of the reaction of a perfluoropolyether diacyl fluoride with methyl fluoroformate in the presence of a metal
fluoride. The reaction products are DM-FPEs and carbon dioxide.
Several reaction conditions has been tested varying type of solvent, temperature, type and amount of metal fluoride. The best results were
obtained using tetraglyme as solvent and CsF as metal fluoride.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Dimethoxyfluoropolyethers; Hydrofluoropolyethers; Fluorinated fluids; Reaction rate; Methyl fluoroformate; Alkylation
1. Introduction
The synthesis of DM-FPEs here described has been carried
out via a new synthetic route which consists in the reaction
of a perfluoropolyether diacyl fluoride with methyl
fluoroformate in the presence of a source of fluoride ions,
generally metal fluoride (MF) [16]:
The a,v-dimethoxyfluoropolyethers (DM-FPEs), having
the copolymeric structure CH3O(CF2CF2O)n(CF2O)mCH3
(where ‘‘n’’ and ‘‘m’’ indicate the content of the various
moieties in the chain, whose distribution is random) are a new
class of compounds recently developed by Solvay-Solexis.
These chemicals are characterized by zero ozone depletion
potential and by low global warming potential [1–6].
MF
RfCOF þ CH3OCOFÀ! RfCF2OCH3 þ CO2
(1)
The reaction products are DM-FPEs and carbon dioxide.
The selection of the best conditions for this reaction
(Eq. (1)) is of primary importance for a possible application
to industrial practice. In the present paper the effects of
several reaction parameters on reaction rates are reported
and discussed. A kinetic study is presented for the more
promising reaction conditions.
Several synthetic routes to hydrofluoroethers and hydro-
fluoropolyethers are known, such as fluorination of ether
compounds [7–10], addition of alcohols to fluorinated
olefins [11,12], alkylation of fluorinated alkoxides with a
suitable alkylating agent (e.g. dialkylsulfate, alkyl- p-
toluensulfonate, alkyltriflate) [13] or with alkylfluoroviny-
lethers [14], and finally catalytic alkylation of acylfluoride
and ketones with Lewis acids and monofluoroalkanes [15].
2. Results and discussion
* Corresponding authors. Tel.: +39 02 3835 6672 (M. Avataneo)/+39 02
3835 6289 (G. Marchionni); fax: +39 02 3835 6355 (M. Avataneo)/+39 02
3835 2152 (G. Marchionni).
2.1. Synthesis of methyl fluoroformate
The methyl fluoroformate used in our experiments was
prepared by bubbling, at low temperature (À65 Æ 5 8C), an
E-mail addresses: marco.avataneo@solvay.com (M. Avataneo), giusep-
pe.marchionni@solvay.com (G. Marchionni).
0022-1139/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2005.01.014

634
M. Avataneo et al. / Journal of Fluorine Chemistry 126 (2005) 633–639
excess of carbonyl difluoride (COF2) into a mixture of
methanol and anhydrous sodium fluoride. The reaction
products are methyl fluoroformate and hydrogen fluoride
(Eq. (2)), that is rapidly scavenged by sodium fluoride
(Eq. (3)):
In the second step (Eq. (6)) the alkoxide reacts with
methyl fluoroformate leading to the introduction of a
methoxy group at the end of the perfluoropolyether chain, to
the formation of carbon dioxide and to the release of fluoride
ion, which can react with another acylfluoride group.
The reaction system must be completely anhydrous to
avoid the hydrolysis of the acyl fluoride group and the
consequent formation of hydrogen fluoride. In the presence
of MF, hydrogen fluoride forms MHF2 which does not react
with the acylfluoride to form the alkoxide. To avoid the
generation of HF, the metal fluorides were thermally treated
under nitrogen flow at 350 8C for at least 3 h and the solvents
were stored in the presence of molecular sieves. DAF and
methyl fluoroformate were also stored in the presence of
sodium fluoride to scavenge the HF, possibly present, as
NaHF2.
COF2 þ CH3OH ! CH3OCOF þ HF
HF þ NaF ! NaHF2
(2)
(3)
The conversion of methanol is complete and the molar yield
in CH3OCOF is higher than 95%. The only by-product
detected is methyl carbonate, CH3OC(O)OCH3, which is
formed by reaction of methyl fluoroformate with methanol
(Eq. (4)):
CH3OCOF þ CH3OH ! CH3OCðOÞOCH3 þ HF
(4)
The relatively low yield of methyl carbonate can be
explained considering the different reactivity of COF2 and
CH3OCOF toward CH3OH. The substitution of a fluorine
atom with a methoxy group in methyl fluoroformate
decreases the positive charge on the carbon of the carbonyl
group, slowing down the reaction with methanol (Eq. (4)),
especially at these low temperatures.
The reactions of alkylation reported in the following
paragraphs are described in details in Section 3.3.
2.2.1. Effect of solvents
Polar aprotic solvents are the most suitable for the
synthesis of hydrofluoropolyethers and hydrofluoroethers
when metal fluorides are required in the synthesis
[13,16,22,23]. The solvents here investigated are tetraglyme,
diglyme, acetonitrile, dimethylcarbonate, tetrahydrofuran,
dimethylformamide, ethylene carbonate and methyl fluor-
oformate (this latter might act both as a solvent and as
alkylating agent). They were all tested in the presence of
cesium fluoride.
The difference of boiling points between methyl
fluoroformate (35 8C [17–20]) and methyl carbonate
(90 8C) is high enough to enable, through a simple
distillation, the recovery of the alkylating agent with a
purity higher than 99% molar.
2.2. Synthesis of DM-FPEs
The rates of the two steps of the alkylation (Eqs. (5) and
(6)) can be defined as:
The perfluoropolyether diacyl fluorides (DAFs) having
the structure
d½RfOCF2CF2OMŠ
¼ k1½RfOCF2COFŠ½MFŠ
dt
FOCCF2OðCF2CF2OÞpðCF2OÞmCF2COF
are the starting reactant for the synthesis of DM-FPEs:
À kÀ1½RfOCF2CF2OMŠ
À k2½RfOCF2CF2OMŠ½CH3OCOFŠ
(7)
CH3OðCF2CF2OÞnðCF2OÞmCH3
where p, m and n are well defined values indicating the
content of the various moieties in the chain and n = p + 2.
The DM-FPEs are obtained by reacting, in a polar aprotic
solvent, DAF (here indicated as RfOCF2COF to emphasize
the acylfluoride end groups) with methyl fluoroformate and a
metal fluoride (MF).
d½RfOCF2CF2OCH3Š
¼ k2½RfOCF2CF2OMŠ½CH3OCOFŠ
dt
(8)
where k1 and kÀ1 are respectively the direct and the reverse
rate constant for the formation of the alkoxide
RfOCF2CF2OÀM+ (Eq. (5)), k2 is the rate constant for the
reaction between the alkoxide and methyl fluoroformate
(Eq. (6)).
The reaction takes place trough the following two steps:
k1
RfOCF2COF þ MF @ RfOCF2CF2OÀMþ
(5)
k
À1
According to Eqs. (7) and (8), the determination of the
rate constants requires the measurement of the concentration
of MF and RfOCF2COF during the reaction. But, being MF
and RfOCF2COF in equilibrium with RfOCF2CF2OÀM+, the
19F-NMR spectra of the reaction mixture show, generally,
only a single broad signal and, consequently, their
concentration cannot be directly measured with this
technique. Therefore, our first approach was to evaluate
the effect of solvents only on the basis of the conversion,
calculated from the 19F-NMR spectra, at different times.
k2
RfOCF2CF2OÀMþ þ CH3OCOFÀ!RfOCF2CF2OCH3
þ CO2 þ MF
(6)
In the first step (Eq. (5)) the acylfluoride group reacts with
the metal fluoride to form the metal alkoxide
RfOCF2CF2OÀM+ whose stability depends on the nature
of the metal fluoride, on the temperature (an increase of
temperature shifts the equilibrium to the left) [21] and on the
type of solvent.

M. Avataneo et al. / Journal of Fluorine Chemistry 126 (2005) 633–639
635
where K0 = k2 [CH3OCOF].
Table 1
Effect of solvent on conversion (Boiling points of the solvents and reaction
temperatures are also reported)
By integration between the initial time t0 and the final
time t, Eq. (10) becomes:
Solvent
Bp (8C) Reaction
Molar conversion
ꢀ
ꢁ
temperature (% of RfOCF2COF
½RfOCF2CF2OMŠ
½RfOCF2CF2OMŠ
where [RfOCF2CF2OM]0 is the concentration at the time t0.
¼ K0t
(11)
(8C)
groups)
1 h
Àln
0
2 h 3 h 4 h
Tetraglyme
276
162
153
90
75
75
75
75
65
55
55
30
22
6
31
9
40
10
19
0
48
11
22
0
If the formation of the alkoxide is instantaneous:
Diglyme
Dimethylformamide
Dimethylcarbonate
Acetonitrile
6
13
0
½RfOCF2CF2OMŠ ¼ ½RfOCF2COFŠ0;
0
0
82
0.5
4
1
1
2
½RfOCF2CF2OMŠ ¼ ½RfOCF2COFŠ0 À ½RfOCF2CF2OCH3Š
and Eq. (11) becomes:
Ethylene carbonate
Tetrahydrofuran
Methyl fluoroformate
244
66
6
8
–
0
0
0
0
35
0
0
0
0
ꢀ
ꢁ
½RfOCF2COFŠ0 À ½RfOCF2CF2OCH3Š
À ln
¼ K0t
½RfOCF2COFŠ
0
The reactions were performed when possible at 75 8C,
except for low boiling solvents such as acetonitrile,
tetrahydrofuran, methyl fluoroformate, and for ethylene
carbonate, which decomposes in the presence of fluorides at
temperature above 70 8C (inorganic carbonates and CO2
were observed). Reaction temperatures and conversions are
reported in Table 1.
(12)
or
ꢀ
ꢁ
½RfOCF2CF2OCH3Š
Àln 1 À
¼ Àlnð1 À CÞ
½RfOCF2COFŠ
0
ꢂ
ꢃ
1
¼ ln
¼ K0t (13)
1 À C
The highest conversions were obtained with tetraglyme
(about 50% after 4 h) and this good result can be explained
considering its coordinative effect toward metallic cations,
which is similar to crown ethers [24,25]. Relatively high
conversions were also obtained with diglyme, whose
structure is similar to that of tetraglyme, and with
dimethylformamide which is a highly polar solvent.
In the trial with tetraglyme the 19F-NMR spectrum of the
reaction mixture showed, after a few minutes, two new
narrow signals at À36 and À86 ppm which can be assigned
respectively to RfOCF2CF2OÀCs+ and RfOCF2CF2OÀCs+.
This indicates that the equilibrium 5 is completely shifted to
the right (k1 ꢀ kÀ1) and that all the acylfluoride groups
have been converted to cesium alkoxides. Using solvents
which resulted in zero or near zero conversion (see Table 1),
the 19F-NMR analyses evidenced only a broadening of the
RfOCF2COF signal at +12 ppm: in this case the equilibrium
5 is shifted to the left (k1 < kÀ1) and the concentration of the
alkoxide in the solution is presumably low.
½RfOCF2CF2OCH Š
where C is
3 , i.e. the relative conversion.
½RfOCF2COFŠ
To summarize, Eqs. (11)–(13) are valid if:
0
ꢁ k1 ꢀ kÀ1, i.e. all the acylfluoride is rapidly converted to
metal alkoxide.
ꢁ The initial concentration of RfOCF2COF is known.
ꢁ The concentration of RfOCF2CF2OÀM+ (or RfOCF2C-
F2OCH3) at different reaction times is known.
ꢁ The concentration of CH3OCOF is constant and known.
À
Á
1
1ÀC
In Fig. 1 the plot of ln
versus reaction time for
tetraglyme is reported. The concentrations of CH3OCOF,
RfOCF2CF2OCH3 and RfOCF2CF2OÀCs+ were determined
by means of 19F-NMR analyses (Ref. CFCl3):
ꢁ CH3OCOF: d À19.0 ppm.
ꢁ RfOCF2CF2OCH3: À94.4 ppm.
ꢁ RfOCF2CF2OÀCs+: À36 ppm.
ꢁ RfOCF2CF2OÀCs+: À86 ppm.
When tetraglyme is used as solvent, all the acylfluoride is
rapidly converted to alkoxide and its concentration can be
directly measured via 19F-NMR (signals at À36 and
À86 ppm). In this specific case, the reaction rate can be
simplified as following:
The experimental points were fitted with a straight line
whose slope is K0. Dividing K0 by the concentration of
CH3OCOF a value of k2 equal to 4 Æ 0.3 ꢂ 10À5 l mol-
molÀ1 sÀ1 was obtained (the molar concentration is relative
to the end groups).
d½RfOCF2CF2OCH3Š
dt
d½RfOCF2CF2OMŠ
dt
¼ À
¼ k2½RfOCF2CF2OMŠ½CH3OCOFŠ
(9)
2.2.2. Effect of temperature
The effect of temperature was evaluated, using tetra-
glyme and CsF, in the range between +30 and +150 8C. At
higher temperatures degradation was observed, probably
due to the decomposition of methyl fluoroformate in the
presence of metal fluoride.
and, if the concentration of CH3OCOF is constant or can be
considered constant (when it is used in large excess):
d½RfOCF2CF2OMŠ
À
¼ K0½RfOCF2CF2OMŠ
(10)
dt

636
M. Avataneo et al. / Journal of Fluorine Chemistry 126 (2005) 633–639
À
Á
1
1ÀC
Fig. 1. ln
, where C is the relative conversion, plotted as a function of
Fig. 3. Arrhenius plot for the reaction in tetraglyme as solvent and CsF as
the reaction time using CsF as metal fluoride and tetraglyme as solvent at
75 8C.
metal fluoride.
2.2.3. Effect of metal and organic fluorides
Fluorinated alkoxides can be prepared by reacting acyl
fluoridewithanhydrouscompoundswhichcanreleasefluoride
ions. Among these, the metal fluorides are the most common
even if organic compounds, such as phosponium salts or
quaternary ammonium salts, have also been successfully
employed for their higher solubility in the reaction media. In
the present investigation, NaF, KF and CsF were tested in
stoichiometric amount (molar ratio KF/RfOCF2COF = 1).
In addition, the organic complex Et3NꢃHF, whose use is
reported in the literature for alkylation reactions on
acylfluoride [26], was tested. The reaction conditions and
the determined k2 values are reported in Table 3.
À
Á
1
1ÀC
Fig. 2. ln
reported as a function of the reaction time for different
At 50 8C CsF and KF present similar values of k2. As in
case of CsF, the 19F-NMR spectra of the reaction mixture
with KF show two narrow signals at À38 ppm
(RfCF2CF2OÀK+) and at À86 ppm (RfCF2CF2OÀK+). No
reaction product was observed with NaF and the 19F-NMR
analyses show only a slightly broad signal of the acyl
fluoride RfCOF at +12 ppm (no significant formation of the
alkoxide). These results can be interpreted in terms of the
lattice energy of the salts, because the larger the lattice
energy of the alkali metal fluorides, the more difficult is the
formation of adducts [21]. The lattice energy of NaF
temperatures using CsF as metal fluoride and tetraglyme as solvent.
À
Á
1
1ÀC
The graph of ln
versus reaction time for all the trials
is reported in Fig. 2. The experimental points are well
interpolated by a linear equation (R2 > 0.97) whose slopes
were divided by [CH3OCOF] to obtain k2.
The k2 values, calculated at different temperature, are
reported in Table 2. It is evident an increase of one order of
magnitude every 20–30 8C increase of temperature. By
introducing these data into the Arrhenius equation:
ꢂ
ꢃ
ÀEact
(215 kcal molÀ1
) is much higher than that of KF
k ¼ A exp
(14)
RT
(192 kcal molÀ1) and CsF (176 kcal molÀ1) and the forma-
tion of the alkoxide by reaction with DAF is more difficult.
Also in case of Et3NꢃHF the degree of conversion was
zero. Differently from NaF, the signal of acyl fluoride
i.e. by plotting Àln k2 as a function of 1/T (Fig. 3), an
activation energy (Eact) of 17 kcal molÀ1 has been deter-
mined (R2 = 0.99).
Table 3
Table 2
Effect of some metal and organic fluoride on the rate constant k2 using
Effect of temperature on the rate constant k2 using CsF as metal fluoride and
tetraglyme as solvent
tetraglyme as solvent
Fluoride
Temperature (8C)
k2 (l molÀ1 sÀ1
)
Temperature (8C)
k2 (l molÀ1 sÀ1
)
NaF
50
50
0
30
50
6 Æ 0.2 ꢂ 10À7
6 Æ 0.5 ꢂ 10À6
4 Æ 0.3 ꢂ 10À5
4 Æ 0.3 ꢂ 10À4
1 Æ 0.4 ꢂ 10À3
KF
6 Æ 0.7 ꢂ 10À6
6 Æ 0.5 ꢂ 10À6
0
CsF
50
75
[Et3NꢃHF]
KF
50
110
110
5 Æ 0.8 ꢂ 10À5
110
150
CsF
4 Æ 0.3 ꢂ 10À4

M. Avataneo et al. / Journal of Fluorine Chemistry 126 (2005) 633–639
637
Table 4
RfOCF2COF at +12 ppm disappeared and a new very broad
signal appeared at about À60 ppm (the base of the signals
covers a range of about 40 ppm). This seems to be indicative
of a partial conversion of the acylfluoride to the alkoxide.
The low concentration of the alkoxide together with the
steric hindrance of the counterion Et3NH+ could explain the
difficulty of the reaction with methyl fluoroformate. To
confirm the presence of the alkoxide another experiment was
carried out with Et3NꢃHF using the same reaction conditions
except for the alkylating agent. By substituting the methyl
fluoroformate with a more reactive alkylating agent, the
methyl paratoluensulfonate, all the acyl fluoride end groups
were converted to RfCF2CF2OCH3 in less than 30 min,
confirming the existence of RfCF2CF2OÀEt3NH+. The
reactivity of Et3NꢃHF is intermediate between NaF and
CsF and requires an alkylating agent more reactive than
methyl fluoroformate.
Effect of the amount of KF on the rate constant k2 at 50 8C using tetraglyme
as solvent
Amount of KFa
k2 (l molÀ1 sÀ1
)
1.00
0.75
0.50
0.38
0.25
0.13
6 Æ 0.7 ꢂ 10À6
6 Æ 0.2 ꢂ 10À6
7 Æ 0.2 ꢂ 10À6
7 Æ 0.1 ꢂ 10À6
6 Æ 0.1 ꢂ 10À6
5 Æ 0.2 ꢂ 10À6
a
Molar ratio KF/RfOCF2COF at time zero.
By plotting the concentration of RfOCF2CF2OCH3 versus
the reaction time straight lines were obtained. Their slopes,
divided by [RfOCF2CF2OM] and by [CH3OCOF], give the
k2 values.
KF and CsF were also tested at 110 8C. At this
temperature a moderate difference of reactivity was
observed between the two salts, being the value of k2 of
CsF about eight times higher than that of KF.
In Table 4 the amounts of KF are reported together with
k2. As we can see, there is a narrow variation of the
calculated values of k2 with the amount of metal fluoride:
this confirms that k1 is much higher than k
.
À1
To increase the rate of alkylation, the trial with KF in
tetraglyme at 50 8C was repeated in the presence of dibenzo-
18-crown-6-ether (2.5% of the molar amount of KF). This
crown ether strongly interacts with the potassium cation
whereas the fluoride anion remains free and might react
more easily with the acylfluoride. However, no noticeable
variation of the reaction rate was observed and this could
probably be explained taking into account the effect of the
solvent tetraglyme which, acting in the same way as a crown
ether, could hide the effect of the crown ethers.
3. Experimental
DAFs are not commercially available products and they
were synthesized according to the below reported descrip-
tion. Carbonyl difluoride were purchased from Apollo
Scientific Ltd. whereas all the other reagents were purchased
from Aldrich Chemical Co.
3.1. Synthesis of DAFs
2.2.4. Effect of the amount of metal fluoride
For Eqs. (11)–(13) we have assumed that the equilibrium
between MF and RfOCF2COF is completely shifted to right,
i.e. k1 ꢀ kÀ1. If this is true, the equilibrium should not be
appreciably affected by the variation of the concentrations of
the acylfluoride and of the metal fluoride and, when the
concentration of the metal fluoride is lower than its
stoichiometric value, we can write:
DAFs can be obtained in a two steps process. The first
(Eq. (18)) includes the oxidative polymerization of
tetrafluoroethylene at low temperature in a suitable
fluorinated solvent. Elemental fluorine or UV light are used
to generate radicals [27–29]. A peroxide polymeric
precursor is formed as a result of the polymerization
reaction:
½RfOCF2CF2OMŠ ¼ ½MFŠ
(15)
0
0
CF2 ¼ CF2 þ O2
Some tests were carried out to confirm that k1 ꢀ kÀ1. In
these tests the molar ratio KF/RfOCF2COF was varied from
0.75 to 0.13 and 19F-NMR analyses of the reaction mixture
were performed in the range of conversion between 0 and
15% molar. If k1 ꢀ kÀ1, in this range of conversions:
fluorine or UV
À!
TOÀðCF2CF2OÞqÀðCF2OÞrÀðOÞsÀT0
< À40 ꢄC;solvent
ðAÞ
(18)
whose constituents are fluoroether repeating units
(–CF2CF2O– and –CF2O–) interspersed with peroxy units
(–CF2CF2OO– and –CF2OO–). The end groups T and T0 are
perfluorinated (–CF3 and –CF2CF3). Compositions of the
polymer and reaction yields (>90% molar) depend on
temperature and TFE concentration. Carbonyl difluoride
and tetrafluoroethylene oxide are the main by-products.
The peroxy groups of the perfluoropolyether-polyper-
oxide (A) can be cleaved by reaction with hydrogen over a
½RfOCF2CF2OMŠ ¼ ½MFŠ ¼ constant
(16)
0
and, if the concentration of CH3OCOF is constant, the
alkylation rate is constant too:
d½RfOCF2CF2OCH3Š
¼ k2½RfOCF2CF2OMŠ
dt
ꢂ ½CH3OCOFŠ
¼ constant
(17)

638
M. Avataneo et al. / Journal of Fluorine Chemistry 126 (2005) 633–639
suitable catalyst to yield substantially bifunctional acyl
fluorides [30]:
3.3.3. Reaction at 150 8C
The procedure is the same reported in Section 3.3.2 but a
higher boiling point fraction of DAF was used (MW = 824,
Bp > 190 8C) to avoid the evaporation of this reactant.
Periodic samples of about 1 ml were taken to determine the
concentration of methyl fluoroformate (which was constant
and equal to 0.2 mol lÀ1) and of the other reagents.
ðAÞ þ H2
Pd catalyst
À! FOCCF2OÀðCF2CF2OÞpðCF2OÞmÀCF2COF
100À200 ꢄC
ðBÞ
(19)
3.3.4. Reaction with triethylamine hydrofluoride
(Et3NꢃHF)
3.2. Synthesis of methyl fluoroformate
An amount of 7 mmol of triethylamine trihydrofluoride
was charged in a 50 ml three necked glass flask equipped
with a condenser, a stirring bar and two rubber septa. After
cooling the system at 0 8C with an ice bath, 14 mmol of
triethylamine were slowly added in the flask. After the
addition was complete, the reaction mixture was allowed to
warm slowly to room temperature and 14 g of tetraglyme,
10.5 mmol of DAF (MW = 474, Bp = 112–114 8C) and
50 mmol of methyl fluoroformate were added. The mixture
was kept under stirring at room temperature for 30 min and
then warmed up to 50 8C. Periodical samples of about 1 ml
were taken and analysed.
An amount of 80 g of carbonyl difluoride was gradually
bubbled in a mixture of 45 g of NaF (dried at 320 8C under
high vacuum for 3 h) and 30 g of methanol previously
charged in a 100 ml three necked glass flasks equipped with
a stirring bar. The reaction mixture was kept cool in dry-ice
bath at À70 8C. After the addition of COF2 was complete,
the reaction mixture was allowed to warm up to room
temperature. The methyl fluoroformate was distilled and
recovered. Purity by 19F-NMR and 1H-NMR: >99.5%
molar.
3.3. Typical procedure for the alkylation reaction
3.4. 19F-NMR analysis
19F-NMR spectra were recorded on Variant Mercury
200 MHz spectrometer using CFCl3 as internal standard.
3.3.1. Reactions at temperatures between 25 and 75 8C
An amount of 21 mmol of cesium fluoride (dried at
320 8C under high vacuum for 3 h), 14 g of solvent
(tetraglyme or one of the other solvents reported in
Table 1), 10.5 mmol of DAF (MW = 474, Bp = 112–
114 8C) and 50 mmol of methyl fluoroformate were charged
in a 50 ml three necked glass flask equipped with a
condenser, a stirring bar and two rubber septa. The mixture
was kept under stirring at room temperature for 30 min and
then warmed up to the reaction temperature. All the
reactions were stopped at degree of conversion lower than
50% so that the variation of concentration of methyl
fluoroformate could be considered approximately constant.
For the calculation of k2 we assumed that [CH3OCOF]
during the reaction was equal to its initial value
[CH3OCOF]0.
4. Conclusion
DM-FPEs were obtained by alkylation of DAF with
methyl fluoroformate in the presence of a fluoride anion
source in solvent. Several conditions were tested; among
them are type of solvent, temperature, type and amount of
the fluoride source. The best results were obtained using
tetraglyme as solvent and CsF as fluoride metal source.
The estimated rate constant k2 using CsF in tetraglyme
ranges between 10À7 l molÀ1 sÀ1 at 30 8C and 10À3 l molÀ1
s
À1 at 150 8C. The Arrhenius plot well fits the experimental
data, yielding an activation energy of 17 kcal molÀ1. Good
results were also obtained with tetraglyme and KF, being the
reaction rate at 50 8C comparable with that obtained with CsF,
whereas at 110 8C a slight difference was observed. For the
industrial practice, KF might be more advantageous for its
lower commercialcostcomparedtoCsFand for the possibility
to regenerate the deactivated form (KHF2) by thermal
treatment.
Periodic samples of about 1 ml were taken by using a
syringe and analysed via 19F-NMR.
3.3.2. Reaction at 110 8C
An amount of 21 mmol of metal fluoride (dried at 320 8C
under high vacuum for 3 h), 14 g of tetraglyme and
10.5 mmol of DAF (MW = 474, Bp = 112–114 8C) were
charged in a 50 ml three necked glass flask, a stirring bar and
two rubber septa. The mixture was kept under stirring at
room temperature for 30 min and then warmed up to 110 8C.
At this temperature methyl fluoroformate was fed into the
mixture (80 mmol hÀ1). Periodic samples of about 1 ml
were taken and analysed via 19F-NMR. The concentration of
methyl fluoroformate was found to be constant during all the
reaction (0.3 mol lÀ1).
Acknowledgements
The authors wish to thank Renzo Bartolini for the
syntheses, the Analytical and Material Science Department
for the analytical characterizations and Solvay Solexis for
permission to publish this work.

M. Avataneo et al. / Journal of Fluorine Chemistry 126 (2005) 633–639
[14] F.E. Behr, Y. Cheburkov, US Patent 6023002 (2000).
639
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