Synthesis of trifluoromethyl fluoroformate from trifluoromethyl hypofluorite and carbon monoxide: Thermal and catalyzed reaction

Article abstract of DOI:10.1016/j.jfluchem.2009.07.004

New and improved routes to trifluoromethyl fluoroformate were developed. Sterically hindered halogenated olefins initiated the reaction of CF₃OF and CO under mild conditions, giving yields of up to 80%. The thermal reaction of CF₃OF

Full text of DOI:10.1016/j.jfluchem.2009.07.004

Journal of Fluorine Chemistry 130 (2009) 830–835
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis of trifluoromethyl fluoroformate from trifluoromethyl hypofluorite and
carbon monoxide: Thermal and catalyzed reaction
b
b
Libin Du a, Darryl D. DesMarteau a, , V. Tortelli , M. Galimberti
*
a Department of Chemistry, Clemson University, Clemson, SC 29634, USA
b Solvay Solexis, R&D Center, Viale Lombardia 20, 20021 Bollate (Milano), Italy
A R T I C L E I N F O
A B S T R A C T
Article history:
New and improved routes to trifluoromethyl fluoroformate were developed. Sterically hindered
halogenated olefins initiated the reaction of CF3OF and CO under mild conditions, giving yields of up to
80%. The thermal reaction of CF3OF and CO in a flow system was highly dependent on temperature and
the type of tubular reactor material. A PTFE reactor gave moderate conversion and high selectivity for the
formate at 120 8C.
Received 4 May 2009
Received in revised form 30 June 2009
Accepted 6 July 2009
Available online 14 July 2009
ß 2009 Elsevier B.V. All rights reserved.
Keywords:
Trifluoromethyl fluoroformate
Synthesis
Halogenated olefin
Radical chain reaction
Perfluoroalkyl hypofluorite
Carbon monoxide
Perfluorovinyl ether
1. Introduction
lymers have been used to formulate a series of novel fluoroelas-
tomers [15–20]. This vinyl ether, owing to the presence of the –
Trifluoromethyl fluoroformate, CF3OC(O)F 4, was first reported
by reaction of CF3OF 1 and CO 2 photochemically or thermally [1],
and then through a dimerization of COF2 in presence of catalysts
[2]. Its formation by other reactions as a minor or a side product
was also reported later [3–9]. Another two homologs in this series,
CF3CF2OC(O)F and (CF3)2CFOC(O)F, were prepared in low yield
through an oxidation of CF3CF55CFCF3 in presence of CF3OF [10]
and a reaction between (CF3)2CFOꢀCs+ and COF2 [11,12]. These
fluoroformates along with others, as a general formula of
RfOC(O)F, were probably among the products of the preparation
of some PFPE fluids through photochemical oxidation of hexa-
fluoropropene and/or tetrafluoroethylene [3,4,13,14]. However,
the products were mixtures of multiple homologs and the
preparation of a single fluoroformate through these reactions
was unlikely. The direct synthesis of the individual homolog in
this series, CF3(CF2)nOC(O)F (n ꢁ 2), has not been demonstrated.
Trifluoromethyl fluoroformate 4 is currently being used as the key
intermediate to the vinyl ether, CF3OCF2OCF55CF2, whose copo-
OCF2O– group adjacent to the vinyl group, is very effective in
lowering the glass transition temperatures of the corresponding
polymers [20], essential for selected low temperature applica-
tions [21]. Higher homologs of this vinyl ether with general
formula CF3O(CF2O)nCF2OCF55CF2 (n ꢁ 1) are also of interest [22].
An efficient route to 4 is an enabler for the commercialization of
these novel fluoroelastomers [23]. Recently, we have reported an
alternative synthesis of 4 at 22 8C through a radical reaction
between CF3OF and CO initiated by elemental fluorine [24].
However, the single-cycle conversion in this reaction was low and
further improvements would be strongly dependent on
sophisticated reaction system [24].
a
In this paper, we report a revised version of the thermal route to
4 [1] in a flow system together with a novel synthesis of 4 from the
radical reaction between 1 and 2 initiated by some sterically
hindered olefins (3), at low temperatures. Higher yields, up to over
80%, were obtained in proper experimental conditions with both
routes.
The thermal reaction was revised trying to transform it from a
kinetic case [24] to a useful synthetic method: the previous batch
kinetic experiments became a flow reaction depending critically
upon reactor materials and temperatures but giving high
selectivity at reasonable conversion.
* Corresponding author. Tel.: +1 864 656 4705; fax: +1 864 656 2545.
E-mail addresses: fluorin@clemson.edu (D.D. DesMarteau),
vito.tortelli@solvay.com (V. Tortelli).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.07.004

L. Du et al. / Journal of Fluorine Chemistry 130 (2009) 830–835
831
Table 1
Reactions between 1 and 2 initiated by 3b.
Run 1 (mmol) 2 (mmol) 3b (mmol) Temp. (8C) Time Yield Recovered
(d)
(%)
1 (mmol)
1
2
3
4
5
6
7
2.3
4.5
4.9
5.2
5.4
5.4
5.8
2.7
4.6
5.1
5.6
5.5
5.5
5.9
2.9
0.6
0.5
1.0
0.5
0.5
0.7
22
22
22
22
40
40
51
1
2
7
5
1
2
2
56.5
0
55.6 1.8
77.6 1.1
86.5 0.9
74.1 1.4
85.7 0.7
91.4
–
All the reactions were run in a 150 ml one-piece glass reactor.
amount of 1 fed into the system (Run 1, Table 1). Apparently, the
reaction was initiated by 3b because neat thermal reaction
between 1 and 2 could not occur at 22 8C (Ref. [1] reports a
minimum reaction temperature of 90 8C but we had reaction at
82 8C. At 35 8C reaction was negligible). The reaction was
completed within 1 day as confirmed by the disappearance of 1.
The adducts of 1 to 3b were recovered as the major side products,
meaning that the addition reaction between 1 and 3b was
responsible for the relatively low yield. In the subsequent
reactions, the ratio of 3b to 1 was reduced to suppress this
addition reaction. However, the reaction rate for forming 4 seemed
to be suppressed too (Runs 2 and 3, Table 1). Especially in Run 3,
approximately 1/5 of 1 was still left intact after 7 days. The reaction
was apparently incomplete since a trace amount of 3b was also
untouched according to the analysis of the products. After doubling
the ratio of 3b (Run 4, Table 1), the reaction proceeded somewhat
faster with a higher conversion to 4, but the reaction was still
incomplete after 5 days. At the higher temperatures (Runs 5–7,
Table 1), the reaction rate was faster and completed with a yield
over 90% in 2 days.
All the reactions were run in a 150 ml one-piece glass reactor;the
main side products collected in some of the Runs are listed in Table 2
(see Scheme 2). Silicon tetrafluoride should be generated from the
slowetchingoftheglass wallby1. Its quantity maywellberelatedto
the residence time of 1 in the reactor. The generation of CF3(O)nCF3
(n = 2, 3) 9, due to the presence of traces of O2, and CF3OC(O)OCF3 10
as side products in this reaction indicates the generation of CF3Oꢂ 5
and CF3OC(O)ꢂ 6 radicals as the main intermediates during the
reaction. The formation of CF3OCR1R2CR3R4F 8 comes from the
fluorine transfer from 1 to CF3OCR1R2CR3R4 radical 7. The absolute
quantities of 8 in the reaction were not high in most cases compared
with the amounts of the dimer 3b fed initially as well as of the
desired product 4. The majority of 3b was still left intact after the
reaction. Surprisingly, higher temperatures did not result in higher
yields of 8b (Table 2), suggesting that the quantity of 8b was
determined by a competition between the desired reaction forming
4 and the side reaction forming 8b. This suggests that the reaction
rate can be increased while not sacrificing the yield to 4 using
elevated temperatures.
Fig. 1. Sterically hindered perhalogenated olefins used in the reaction.
2. Results and discussion
2.1. Synthesis of trifluoromethyl fluoroformate in presence of
sterically hindered halogenated olefins
A mixture (3a) of three hexafluoropropene (HFP) trimers (see
Fig. 1 for their structures) was attempted first. Another two HFP
trimers, F-2,4-dimethyl-3-ethyl-2-pentene and F-3-isopropyl-4-
methyl-2-pentene, have been used previously to make a persistent
radical by reacting with undiluted elemental fluorine [26]. The
resulting radical was stable to a number of strong oxidizers and
only reacted with elemental fluorine slowly forming the corre-
sponding perfluoroalkane. The mixture of the HFP trimers used in
this study (3a), though not the same isomers, formed the same
persistent radical after reacting with fluorine gas as confirmed by
EPR spectrum (supplementary materials). We initially expected
that 1, having similar reactivity as elemental fluorine, would react
with 3a slowly to form the persistent alkyl radical and the resulting
CF3O radical 5. Radical 5 is too bulky to react further with the alkyl
radical so that 5 can probably initiate a radical chain reaction with
CO to form 4. However, the reaction did not proceed as we
expected at room temperature. At higher temperature (47 8C), the
reaction was completed with a 95.7% yield after 4 days. According
to 19F NMR, we did not see evidence of the formation of the
persistent radical, so it appears to us that this reaction was only a
thermal version between 1 and 2 [1].
The unsaturated bond of the HFP dimer (3b) is less sterically
hindered than those of 3a (see Fig. 1), therefore it was expected to
be more accessible to the attack by 1. The neat reaction of two HFP
isomers (including 3b) with 1 was reported to be sluggish at room
temperature and elevated temperatures were necessary for the
completion of the reaction [27]. The addition reaction between 1
and 3b carried out in this study gave approximately 80%
conversion at room temperature after 5 days, and then completed
by reacting at 45 8C for 1 day. The regioselectivity of the reaction
was excellent as reported [27]. However, the ratio between the two
isomers (8b0/8b00) was 13/1 according to 19F NMR spectra rather
than the reported 24/1 at 45 8C. The stereochemistry of the
reaction and the absolute chirality of the products were not
determined (Scheme 1).
The slow reaction using 3b appears to be the result of steric
effects. In order to further accelerate the reaction, some less
sterically hindered halogenated olefins were tested as listed in
Table 2
When 2 was added into the reaction, the desired fluoroformate
4 was generated at 22 8C with a 56.5% yield calculated based on the
Side products in the reaction between 1 and 2 initiated by 3b.
Runa
CF3(O)nCF3
(mmol)
SiF4
8b (mmol)
Yield of
8bb (%)
CF3OC(O)OCF3
(mmol)
(mmol)
3
6
7
0.08
0.04
0.16
0.19
0.1
0.11
0.07
0.07
22.4
13.2
12.1
–
–
0.06
0.16
All the data were based on 19F NMR spectra.
a
As in Table 1.
b
Scheme 1. Reaction between 3b and 1.
Based on the amount of 3b used.

832
L. Du et al. / Journal of Fluorine Chemistry 130 (2009) 830–835
Scheme 2. Possible reaction paths for the formation of 4 and side products.
Table 3
Reactions between 1 and 2 initiated by other olefins.
Olefin
3 (mmol)
1 (mmol)
2 (mmol)
Time (days)
4 (mmol)
Yield (%)
Recovered 1 (mmol)
3c
3d
3e
3f
0.5
0.6
0.7
1.0
1.0
5.2
4.9
6.3
5.0
5.1
5.4
5.3
6.4
5.4
5.6
5
4
1
1
3
4.2
3.5
1.7
0
82.7
72.2
27.0
0
0.5
0.7
4.1a
4.9
2.2
3g
0
0
All the reactions were run in a 150 ml one-piece glass reactor at room temperature.
a
Contaminated with 4.
Table 3. A perfluorinated 2-butene (3c) was first used. It has a
trifluoromethyl group, CF3–, in place of the isopropyl group of 3b,
so a faster reaction rate was expected [28]. Indeed, a higher yield
was obtained in a shorter reaction time using 3c (Run 1, Table 3)
compared with that using 3b (Run 3, Table 1), indicating the
reaction rate was faster. However, the absolute reaction rate
appeared to be still slow as approximately 10% of 1 remained after
reaction. Analysis of the final reaction mixture (see Table 4),
showed the majority of 3c was unreacted after 5 days.
With the even less hindered double bond of hexafluoropropene
(HFP, 3d) the reaction was completed within 4 days with a yield of
72.2% (Run 2, Table 3). Unreacted 1 left after the reaction was
apparently due to the complete consumption of 3d before 1 was
consumed (see Table 4). Using CCl255CCl2 3e, the reaction
proceeded even faster and was complete in 1 day. However, the
yield was further lowered, due to the main side reaction of the
addition 1 to 3e. The fast reaction also resulted in lower ratios of
some side products (see Table 4). Two cyclic perfluorinated olefins
(3f and 3g, Fig. 1), were explored but these did not result in the
formation of 4. Olefin 3f was unreactive and 3g led to unidentified
products and loss of 1.
Other hypofluorites in the series F(CF2)nOF (n = 2, 3),
(CF3)2CFOF, SF5OF and CF2(OF)2, were tested to see whether the
corresponding fluoroformates could be prepared. The fluorofor-
mate, SF5OC(O)F, was reported to form in the photochemical
reaction of SF5OF and 2 [29]. However, the thermal version of the
reaction generated only trace amount of SF5C(O)F along with other
products [30]. The compound (CF3)2CFOC(O)F was also prepared
earlier [10–12]. Compared with 1, these hypofluorites are all of
lower thermal stability and decomposition and other reactions
were anticipated. We attempted to react the above hypofluorites
with 2 in presence of 3c or 3d. However, only a trace amount of
CF3CF2OC(O)F was observed in the reaction of CF3CF2OF and 2 by
NMR spectroscopy. In all the other cases, the adducts of the
hypofluorites with the olefins were identified as minor products
along with a mixture of COF2, CF4 and the expected decomposition
products of the hypofluorite.
The side products generated in the reactions of 1 (Tables 2 and
4) suggest that the reaction path involves 5 as a key intermediate
(see Scheme 2). In the neat reaction between 1 and 3b [27] the
radical 7b has been detected using EPR spectroscopy, suggesting
the reaction path of Step I and IV shown in Scheme 2. In the case of
3b, it appears that the slow reaction between 5 and 3 allows 5 to
react with 2 forming 4. Radical 6 may also be present as an
intermediate in the reaction, as evidenced by the formation of a
side product 10 in some runs (Run 7 in Tables 1 and 2).
The proposed reaction path in Scheme 2 may indicate a way to
improve both the reaction rate and yield. Step II and III appear to be
Table 4
Side products in the reactions.
Olefin
CF3(O)nCF3 (mmol)
SiF4 (mmol)
8 (mmol)
Yield of 8a (%)
3c
3d
3e
0.06
0.05
–
0.04
0.01
–
0.18
0.6
34.0
100
0.7
100
All the data were based on 19F NMR spectra.
a
Based on the amount of olefin used.

L. Du et al. / Journal of Fluorine Chemistry 130 (2009) 830–835
833
Table 5
Reaction between 1.5 N l/h of 1, 2.0 N l/h of 2 and 3.0 N l/h of He at 170 8C.
Reactor
Conversion
CF3OF
Selectivity
CF3OCOF
Selectivity
COF2
0.25 l nickel
0.25 l, copper
0.14 l, AISI316
0.14 l, not passivated
AISI316
45%
41%
23%
23%
1%
7%
99%
93%
70%
6%
30%
94%
0.16 l, PTFE
33%
18%
97%
96%
3%
4%
0.08 l, glass
Fig. 2. Possible radicals of the olefins generated in the reactions of 1.
independent of the olefin, so the effect of olefin on reaction rate
should occur mainly in Step I. We have shown that the less
sterically hindered olefin was usually associated with a faster
reaction (see Table 3), but with a lower yield of 4 (Step IV was
faster). An olefin like 3h (Fig. 2) could be more reactive than 3b and
c with CF3O radical, its corresponding tertiary radical (7h), being
more sterically hindered than 7b and c. This could result in a
slower abstraction of fluorine from CF3OF (Step VII). Therefore,
both a fast reaction (as in the case of 3d and e) and a high yield (as
with 3b and c) may be possible if an olefin of this type is used.
In Table 5 the influence of the reactor material on conversion
and selectivity is shown.
The conversion of 1, having fixed the ratio of reagents, their
concentration and the reaction temperature, depends on the
volume of the reactor and hence is a function of the residence time.
The selectivity of 4 strictly depends on the reactor material and on
the ‘‘history’’ of the reactor: different materials give different
selectivity. Metal reactors (Stainless Steel 316, Copper, Nickel, etc.)
used for reaction with fluorine or hypofluorites have to be
passivated before use to prevent highly exothermic side reactions
or even explosions promoted by the metal surface. The internal
walls have to be previously treated gradually with the diluted
oxidant to form a protective layer of metal fluoride. Due to the
presence of this fluoride layer, the selectivity of the fluoroformate
decreases significantly along time with simultaneous formation of
COF2 due to the known fluoride induced decomposition of
fluoroformate [2]. The equilibrium between 4 and COF2 in the
presence of metal fluorides allows the synthesis of 4 starting from
COF2 at very low temperature [2] but causes the irreversible
decomposition of 4 at high temperature, even in gas phase.
Nonetheless it is possible to get 4 in decent yield and good
selectivity, even in metal reactors, playing on residence time,
temperature and concentration. The effect of reaction temperature
and dilution of the reactants are shown in Tables 6 and 7,
respectively.
As expected, an increase in temperature increased the
conversion of 1 and the decomposition of 4 due to the enhanced
catalytic effect of the reactor internal surface (Table 6). More
concentrated reagents, i.e. no dilution with inert gas, favour
conversion to 4 and conversely cause greater decomposition of 4 to
carbonyl difluoride (Table 7).
At T > 220 8C we observed some micro-explosions during the
reaction: to see what happens at higher temperature a reactor
having only 1 ml volume was used to minimize the risks. In these
conditions the conversion of the reagents was very low (<5%) up to
2.2. Thermal synthesis of trifluoromethyl fluoroformate
According to the literature [1,25], no significant attempts to
obtain 4 by thermal reaction between 1 and 2 at T > 110 8C have
ever been tried. The technical difficulties involved in managing
strong oxidizers like hypofluorites in the presence of a reducer like
2, at high temperatures, probably discouraged such experiments.
Leveraging on our experience in the proper and safe use and
reaction of perfluoroalkyl hypofluorites [31] this thermal reaction
was carried out in a continuous flow system with monitoring.
The reaction path proceeds through the typical steps of a radical
reaction:
Initiation:
CF3OF þ CO ! CF3Oꢂ þ FCOꢂ
FCOꢂ þ CF3OF ! COF2 þ CF3Oꢂ
Propagation:
CF3Oꢂ þ CO ! CF3OCOꢂ
CF3OCOꢂ þ CF3OF ! CF3OCOF þ CF3Oꢂ
Termination:
2CF3Oꢂ ! CF3OOCF3
2CF3OCOꢂ ! CF3OCðOÞCðOÞOCF3
CF3OCOꢂ þ CF3Oꢂ ! CF3OCðOÞOCF3
CF3Oꢂ þ FCOꢂ ! CF3OCOF
Table 6
Reaction between 1.5 N l/h of 1, 1.5 N l/h of 2 and 4.5 N l/h of He in a 0.20 l SS 316
reactor.
2FCOꢂ ! FCðOÞCðOÞF
CF3OCOꢂ þ FCOꢂ ! CF3OCðOÞCðOÞF
Temperature
Conversion CF3OF
Selectivity CF3OCOF
Selectivity COF2
160 8C
180 8C
200 8C
220 8C
18%
29%
42%
49%
86%
85%
84%
80%
14%
15%
16%
20%
The on-line GC analysis of the gaseous compounds exiting the
thermal reactor showed the presence of starting reagents 1 and 2,
product
CF3OOCF3, CF4 and CO2 were detected only in trace amounts.
In typical run, carbon monoxide and trifluoromethyl
4 and COF2 as main byproduct. Other byproducts
Table 7
a
Reaction between 1.5 N l/h of 1, 1.5 N l/h of 2 in a 0.20 l 316 SS reactor.
hypofluorite 1 were fed continuously to the reactor maintained
at the desired temperature. The exit gases, after GC analysis, were
quenched in a cold solution containing 1,2-dichloro 1,2-difluor-
oethylene to consume the residual hypofluorite and forming
CF3OCFClCF2Cl [31].
Temperature
Conversion CF3OF
Selectivity CF3OCOF
Selectivity COF2
180 8C
200 8C
220 8C
75%
81%
83%
76%
68%
62%
24%
32%
38%

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L. Du et al. / Journal of Fluorine Chemistry 130 (2009) 830–835
Table 8
240 8C while the selectivity of 4 was very high (>95%); at
T > 250 8C total conversion of the reagents was achieved with
quantitative selectivity to COF2. During the reaction if the
temperature was decreased below 230 8C, decomposition stopped
and reaction ceased. This phenomena cannot be explained by a
Reaction between 1.0 N l/h of CF3CF2OF, 1.0 N l/h of 2 and 8.0 N l/h of He in
a
0.16 l PTFE reactor or
a 0.85 l glass reactor.
Reactor
Temperature
Conversion CF3CF2OF
100 8C
100 8C
120 8C
140 8C
160 8C
160 8C
6%
60%
24%
48%
70%
7%a
total conversion of the reagents to
4 and its subsequent
decomposition to COF2, because a more gradual change would
have been expected. The observed discontinuity may be tenta-
tively related to a different mechanism. It is known [32] that
hypofluorite 1 may decompose to COF2 and fluorine at high
temperature; in the presence of 2 a possible mechanism explaining
the selective formation of COF2 may be the following:
Initiation:
a
In absence on CO.
ꢂ
CF3OF þ CO ! CF3Oꢂ þ FCOꢂ
CF3 þ CF3CF2OF ! CF4 þ CF3CF2Oꢂ
Propagation:
CF3Oꢂ ! COF3 þ Fꢂ
Fꢂ þ CO ! FCOꢂ
FCOꢂ þ CF3OF ! COF2 þ CF3Oꢂ
Termination:
ꢂ
2CF3 ! CF3CF3
The role of carbon monoxide to initiate the reaction is outlined
by the low decomposition of CF3CF2OF in the absence of CO at
160 8C (7%) compared to the 60% decomposition at 100 8C in the
presence of CO (Table 8).
Termination:
Fꢂ þ FCOꢂ ! COF2
Summarizing, we have developed two convenient synthetic
routes to trifluoromethyl fluoroformate by reacting trifluoro-
methyl hypofluorite with carbon monoxide: at or near room
temperature, initiated by sterically hindered olefins and at higher
temperatures (T > 150 8C) in a proper tubular reactor. Both
syntheses allow the preparation of reasonable amounts of
trifluoromethyl fluoroformate on a laboratory scale.
This mechanism is supported by the measurement of the
temperature at the point were the two reagents meet with a
thermocouple inserted just inside the small metal reactor. When
the decomposition to COF2 started,
temperature was observed (370–400 8C,
a
D
sudden increase of
T > 120 8C).
Decomposition of 4 to COF2 may become a serious problem
when it is stored (pure or diluted) in a cylinder: 4 has a vapor
pressure of about 6 bar at room temperature, while COF2 exhibits a
critical temperature of 22.8 8C and a vapor pressure of 55.4 bar at
21 8C [33]. Hence, the uncontrolled decomposition of 4 would lead
to a dangerous increase in pressure inside the cylinder. Some tests
were carried out storing 4 in a cylinder containing a powder
constituted of metal fluorides (about 160 mg of powder per
1000 mg of 4) deriving from a fluorine passivated SS 316 reactor
(mainly nickel, chromium and iron fluorides) and monitoring the
pressure continuously. After 90 h at room temperature a 47%
decomposition was achieved. For comparison, a similar test using
KF or KHF2 (respectively 95 and 150 mg per 1000 mg of 4) showed
a 100% decomposition in 40 min.
No problems were experienced in storing small amounts of 4
even in the liquid phase, for several days, in clean, new (not
passivated) SS 316 cylinders.
As in the olefin promoted reaction, attempts to carry out
thermal carbonylation of higher perfluoroalkyl hypofluorites and
particularly perfluoroethyl hypofluorite were unsuccessful.
3. General experimental procedures
3.1. Instruments
19F NMR spectrum was recorded on a Joel 300 MHz or a Varian
200 MHz FT/NMR.
The samples were sealed in a 4 mm glass tube with CCl4 as
solvent and CFCl3 as reference. The tube was inserted into a regular
5 mm NMR tube during the measurement. Deuterated oxide, D2O,
was added in the outer tube for locking the signal. Infrared spectra
are recorded on a PerkinElmer Spectrum 2000 series FTIR. The
sample was analyzed in a 10 cm path length glass gas cell fitted
with a Kontes–Teflon valve using AgCl window attached with
Halocarbon 1500 wax. Gas chromatograms were recorded on a GC
8000 Top Carlo Erba gas chromatograph employing either a
capillary 0.54 mm, 25 m silicone column (no hypofluorites present
in the samples) and a 8 m PTFE column filled with Kel-F (20%) on
PTFE microspheres for on-line analysis. Mass spectra were
recorded on a Finnigan MAT SSQ700 chromatograph using a
50 m methyl silicone CPSIL (Varian-Chrompack) column.
CF2CF2OF þ CO CF2CF2OCOF
3.2. Apparatus and reagents
Perfluoroethylhypofluorite is less stable than 1 and it is more
stable conversely than higher homologues [34]. No trace of the
desired perfluoroethyl fluoroformate was detected and only CF4
and COF2 (Table 8) were observed.
In the presence of 2 the only reaction occurring is the
decomposition of CF3CF2OF: the reaction was initiated by 2, then
the oxyradical so formed decomposes rather then adding to carbon
monoxide.
The glassware used for olefin-initiated reaction was dried at
100 8C in an oven followed by an overnight (about 12 h) evacuation
on a standard glass vacuum line. The chemical transformation and
fractional separation were all performed on a glass vacuum line
containing 4 U-traps [23]. Trifluoromethyl hypofluorite as well as
the other hypofluorites, F(CF2)nOF (n = 2, 3), (CF3)2CFOF, SF5OF and
CF2(OF)2, were prepared according to literature procedures [35–
38]. The olefins and CO were all purchased from commercial
sources and used as received.
Initiation:
CF3CF2OF þ CO ! CF3CF2Oꢂ þ FCOꢂ
CF3CF2OF þ FCOꢂ ! CF3CF2Oꢂ þ COF2
The tubular reactors of different materials and appropriate
volume, as reported in the text, were pretreated with diluted
fluorine gas to remove any impurity and, for metal reactors, to
passivate it. They were thermostated to the desired temperature
Propagation:
ꢂ
CF3CF2Oꢂ ! COF2 þ CF3

L. Du et al. / Journal of Fluorine Chemistry 130 (2009) 830–835
835
by electric resistance heating. The flow of gaseous reagents was
measured by thermal mass flowmeters. The flow coming out of the
reactor was condensed in a trap maintained at ꢀ110 8C and
containing 15 g of CFCl55CFCl to remove the residual hypofluorite
as CF3OCFClCF2Cl, then distilled to separate 4.
furnace. The flow was maintained for 4 h. The gas coming out of the
reactor was condensed in a cold trap (ꢀ110 8C) containing 15 g of
CFCl55CFCl. After fractional distillation of the resulting mixture
11.3 g of 99.8% pure 4 were collected (conversion CF3OF: 33%;
selectivity CF3OCOF: 97%).
3.3. Reactions of 1
Acknowledgement
3.3.1. A typical procedure is described for the reactions of 1
L. Du and D.D.D. gratefully acknowledge the financial support of
Solvay Solexis.
3.3.1.1. Thermal reaction between 1 and 3b. A pre-dried 150 ml
one-piece Pyrex reactor equipped with a Kontes glass-Teflon valve
was used. First, the olefin 3b (1.0 mmol) was added, followed by 1
(1.1 mmol). The reactor was warmed up slowly from ꢀ196 8C in a
cold dewar and remained at room temperature for 5 days. The
separation was done through trap-to-trap distillation using ꢀ100
and ꢀ196 8C traps. Unreacted 1 (0.3 mmol) was collected in
ꢀ196 8C trap, while addition product 8b contaminated with intact
3b (1.0 mmol) were collected in ꢀ100 8C trap. Further separation
using ꢀ80 and ꢀ196 8C traps collected 8b (0.8 mmol, 80%) in
ꢀ80 8C trap and 3b (0.2 mmol) in ꢀ196 8C trap. The characteristic
properties and spectral values of 8b match with those described in
earlier report [28].
References
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3.3.1.2. Reaction between 1 and 2 initiated by 3b. A pre-dried
150 ml one-piece Pyrex reactor equipped with a Kontes glass-
Teflon valve was used. The hypofluorite
1 (5.2 mmol) was
condensed under vacuum on the bottom of the flask followed
by 3b (1.0 mmol) on the upper glass wall. Gaseous 2 (5.6 mmol)
was then added. The reactor was warmed up slowly from ꢀ196 8C
in a cold dewar and remained at room temperature for 4 h. The
separation was done through trap-to-trap distillation using three
traps with the temperatures set at ꢀ196, ꢀ130 and ꢀ100 8C.
Unreacted 1 contaminated with a little 4 and SiF4 (4.9 mmol) was
collected in the ꢀ196 8C trap. The desired product, 4 (0.4 mmol)
was collected in ꢀ130 8C trap. Unreacted 3b (1.0 mmol) was
collected in ꢀ100 8C trap. All the trapped chemicals were then
returned to the reactor at ꢀ196 8C and more 2 (5.6 mmol) was
added. The reactor was allowed to warm to 22 8C in the air and let
stand for 5 days. The separation was repeated as above. Pure 4
(4.3 mmol, 82.7%) was collected in ꢀ135 8C trap. A mixture
(1.2 mmol) was collected in ꢀ196 8C trap which contained 1
(0.9 mmol),
4 (0.2 mmol), and CF3OOCF3 and CF3OOOCF3
(0.1 mmol) based on 19F NMR spectra. A mixture of 3b and 8b
(0.9 mmol) was collected in ꢀ100 8C trap. The overall yield of 4 was
86.5%. The characteristic properties and spectral values of 4 match
with those described in the earlier reports [1,8].
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3.3.1.3. Thermal reaction between 1 and 2. As an example the
reaction in a PTFE reactor is described.
A gaseous flow of 1.5 N l/h of 1, 2.0 N l/h of 2 and 3.0 N l/h of He
was fed into a tubular PTFE reactor, having an internal diameter of
4 mm and length of 13.2 m, maintained at 170 8C by an electric