G Model
CCLET 3697 1–4
2
Q. Geng et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
F
F F
CF3
O
F
F F
O
CF3
O
F3C
O
F3C
O
O
F
n
F
F
F
F
F F CF3
F
F
F
F F CF3
1
: HFPO trimer
2: HFPO oligomers (n = 2-10)
Fig. 1. Structure of HFPO trimer and HFPO oligomers.
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chemical used for the manufacture of Novec 1230 (3, Scheme 2)
[19], Heptafluoropropyl trifluorovinyl ether (PPVE) (4, Scheme 2)
[20], and HFPO dimer acid ammonium salt, namely GenX (5,
Scheme 2) [21] etc. Currently, there are two major ways reported
for the large-scale synthesis of PPF itself (Scheme 2): Electrolysis of
propionyl chloride (6, Scheme 2) in HF [22] or rearrangement of
hexafluoropropylene oxide (7, Scheme 2) catalyzed by KF
[23]. They both have their own drawbacks: the electrolysis
method is of low efficiency and uses HF as solvent whose leakage
could be lethal and disaster to natural environment; while the
rearrangement chemistry faces the high cost of starting material.
Herein, we report the degradation of HFPO trimer and
oligomers to PPF using CsF/tetraglyme as catalytic system both
under batch and autoclave conditions. These harmful chemicals
can produce PPF under the optimized conditions at 160 8C with
acceptable reaction rate in excellent yield (Scheme 3).
Scheme 2. Current reports on large-scale synthesis of PPF and representative
chemicals manufactured from it.
Scheme 3. Degradation of HFPO oligomers to PPF.
under vacuum. Fluoride salt, substrate, and solvent were quickly
transferred into the autoclave. The mixture was heated until the
pressure of the autoclave did not increase. The autoclave was
cooled to r.t. Product was collected in a dry ice trap. Analysis of the
product was performed in the same way as that in 2.1.
The detailed procedures are deposited in Supporting informa-
tion.
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2. Experimental
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NaF, KF, and CsF were dried at 200 8C under vacuum for 24 h.
Tetraglyme and diglyme were dried at 160 8C with CaH
2
under N
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3. Results and discussion
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protection for 24 h and vacuum distillated. Gas chromatographic
data were obtained using Agilent 7820 series gas chromatograph.
The reaction was monitored with an Agilent 7820 GC using a SE-30
capillary column. Temperature program was a hold at 40 8C and
then taken to 300 8C at 10 8C/min. Infrared spectra were obtained
on a Shimadzu FTIR-8400S Spectrometer. NMR spectra were
3.1. Degraduation of HFPO trimer to HFPO dimer and PPF in flask
First of all, we examined the degradation of HFPO trimer with
different alkali metal fluoride in either diglyme or tetraglyme
considering the host/guest effect of the solvents with alkali metal
ion enhancing the nucleophilicity of the fluoride ion (Table 1).
When NaF or KF was used as catalyst and diglyme as solvent, even
at reflux temperature of 113 8C for 12 h, nothing was collected in
the dry ice trap (entries 1,2). When the catalyst switched to CsF,
under otherwise same as above conditions, small amount of liquid
was collected in the dry ice trap, but the product distribution was
complex and no major product could be identified (entry 3).
However, while the solvent switched from diglyme to tetraglyme
and the reaction was performed at reflux temperature of 121 8C for
8 h, large amount of liquid product was collected in the dry ice trap.
After the liquid was transferred to methyl ester and analyzed using
GC SE-30 column, 65% PPF methyl ester, and 32% HFPO dimer
methyl ester were identified (Fig. S1 in Supporting information),
whose combined weight equaled to 97% weight of HFPO trimer.
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3
recorded on Bruker AM400 using neat 5 mm samples. CDCl is the
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references for the H and F NMR, respectively.
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2.1. Degradation reaction performed in flask
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A dry 250 mL flask equipped with a magneton, a thermocouple,
a reflux condenser into a dry ice trap protected under nitrogen was
set up. The equipment was dried by flame for three times under
nitrogen protection. Fluoride salt, substrate, and solvent were
quickly transferred into the flask. The mixture was heated to reflux
until no more liquid was collected in the dry ice trap. Methanol was
slowly dropped into dry ice trap to derive the product into
corresponding methyl ester. The methyl ester derivative was
washed three times with distilled water and then analyzed with
gas chromatography.
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.2. Complete degradation of HFPO oligomers to PPF in batch
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2.2. Degradation reaction preformed in batch autoclave
autoclave
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A 1 L batch autoclave equipped with a mechanical agitator, a
thermocouple, a heat booster was set up. It was dried by heating
In order to degrade HFPO trimer to PPF completely without
staying at the HFPO dimer stage, we examined the conditions to
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Scheme 1. Current commercial routes to consume HFPO trimer.
Please cite this article in press as: Q. Geng, et al., One stone two birds: Degradation of persistent organic pollutants to a valuable