Study of liquid-phase photolysis of perfluorinated ketones

Article abstract of DOI:10.1134/S1070427211060255

Liquid-phase photolysis of perfluorinated ketones under UV irradiation was examined.

Full text of DOI:10.1134/S1070427211060255

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 6, pp. 1046−1051. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © Yu.K. Starobin, V.V. Berenblit, N.V. Lebedev, V.A. Gubanov, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 6,
pp. 1025−1030.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Study of Liquid-Phase Photolysis
of Perfluorinated Ketones
Yu. K. Starobin, V. V. Berenblit, N. V. Lebedev, and V. A. Gubanov
Federal State Unitary Enterprise S.Y. Lebedev Research Institute for Synthetic Rubber, St. Petersburg, Russia
Received November 29, 2010
Abstract—Liquid-phase photolysis of perfluorinated ketones under UV irradiation was examined.
DOI: 10.1134/S1070427211060255
Perfluoropolyoxaalkanes being highly chemically
inert, heat resistant fluids are used as components in heat-
resistant fluoropolymer formulations and gas transporting
fluids in contemporary technology and medicine.
Interaction of radical I with radical III formed in
photolysis leads to formation of “crossed” products,
2-perfluoroackoxyalkane (IV), and to recombination of
perfluoroalkyl radical III to dimer V (Scheme 2).
Perfluoropolyoxaalkanes can be obtained by the anod-
ic dimerization according to Kolbe reaction in electrolysis
of perfluoro-2-methyl-3-oxaalkanoic acids in acetonitrile
medium [1–3] or by photolysis of perfluoroketones [4].
Mass ratio of photolysis products II, IV, and V in
a mixture for 1 h after the irradiation start at temperature
up to 50°С was 1 : 1 : 1, however, for 10 h after the end
of the process it reached 3 : 1 : 1. With increasing tem-
perature higher than 120°C yield of dimer V was 60 wt %.
Earlier pyrolysis of derivatives of perfluoro-2-methyl-
3
-oxaalkanoic acids was investigated and conditions for
Boiling points in a series of dimers II, IV, and V con-
taining oxygen in the structure decreased in increments of
30°. In particular, after photolysis of perfluoro-5,8,10,13-
tetramethyl-4,7,11,14-tetraoxaheptadecan-9-one (3)
obtaining the corresponding perfluoroketones in high
yield were found [5].
In this regard, a research of the liquid-phase photolysis
of perfluoroketones is promising in a wide temperature
range in order to find optimal conditions for obtaining
perfluoropolyoxaalkanes.
Scheme 1.
O
The liquid-phase decarbonylation of perfluoropoly-
oxaalkylketones under ultraviolet radiation at ambient
temperature is accompanied by recombination of radicals
formed and proceeds by Scheme 1.
hν
_CO
F
F
F
R OCFCCFOR
2 R OCF
F3C
CF3
CF3
1_
3
I
We found that at photolysis temperature higher than
3
0° decarbonylation was accompanied by abstraction of
CF3
trifluoroacetyl fluoride with formation of perfluoroalkyl
or perfluorooxaalkyl radicals [R ] :
·
F
F
R OCFCFOR ,
F
F3C
O
hν, T > 30°C
F
RF
II
2
R OCF
+
CF C
.
3
F
RF = CF CF CF – (1), CF OCF CF CF – (2),
CF3
3
2
2
3
2
2
2
I
III
CF CF CF OCFCF – (3).
3 2 2 2
1
046

STUDY OF LIQUID-PHASE PHOTOLYSIS OF PERFLUORINATED KETONES
1047
Scheme 2.
F
RF
F
R OCFRF
RF
F
R OCF
+
+
R .
CF3
F3C
I
III
IV
V
perfluoro-5,8,9,12-tetramethyl-4,7,10,13-tetraoxahexa-
decane (II ), bp 216°C, perfluoro-5,8,10-trimethyl-
surface by various radicals.
3
In an enlarged experience of decarbonylation of per-
fluoro-7,9-dimethyl-2,6,10,14-tetraoxapentadecan-8-one
(2) at 40°C by the reaction on Scheme 3 a yield of dimer
4
,7,11-trioxatetradecane (IV ), bp 186°C, and
3
perfluoro-5 ,7-dimethyl-4 ,8-dioxadodecane (V3),
bp 156°C were isolated by distillation and identified.
II reached 95 mol %, whereas a total yield of dimers
2
Unlike Kolbe cross-synthesis [1, 2], when both the
dimerization of each of the radicals and their recom-
bination to form an asymmetric dimer are revealed in
the electrolysis products with comparable yields, in the
asymmetric photolysis of the ketone 4 at 25°C almost
exclusively asymmetric dimer is produced, which coin-
IV and V under these conditions was only 5 mol %.
2
2
Figure 1 shows dependence of a composition of the
products of photolysis of ketone 2 in the reaction mixture
on time according to GLC data obtained by sampling in
the course of the process.
Tables 1–3 show the structures, boiling temperatures
cides with IV by the structure:
3
1
9
and F NMR spectra of the photolysis products, which
reflect stereoisomerism of dimers II and IV associated
with the presence of asymmetric fluoromethine carbon
atoms with lateral trifluoromethyl groups.
O
CF CF OCFCCFOCF CFOCF CF CF
3
2
2
CF3
4
2
2
3
F3C
CF
3
EXPERIMENTAL
CF3
To study the photolysis reaction of perfluoroketones
hν, 25°C
_CO
we used photochemical reactors with a capacity of 0.3 and
CF CF CF OCFCFOCF CFOCF CF CF .
3
2
2
2
2
2
3
2
liters. A reactor (Fig. 2) consisted of a quartz cylindri-
F3C
CF3
cal vessel with double walls with a height of 150 mm,
an inner diameter of 50 mm, and an outer diameter of
IV3
1
40 mm equipped with a thermocouple and a reflux con-
Recombination of radicals in the liquid phase takes
place as if in a “cage,” directly in decarbonylation pro-
cess, while in Kolbe electrosynthesis a mechanism of
electrochemical desorption dictates the output of various
products depending on the degree of filling of an anode
denser connected to a nozzle for discharging the reaction
gases. In the center of the reactor a high pressure mercury
lamp (radiation in the ultraviolet region of 100–400 nm)
was coaxially placed, which was cooled by air flow. The
Scheme 3.
_
hν, 30 40°C,
00 h
O
CF3
1
CF OCF CF CF OCFCCFOCF CF CF OCF
CF OCF CF CF OCFCFOCF CF CF OCF
3
2
2
2
2
2
2
3
3
2
2
2
2
2
2
3
_
_
CO, CF COF
3
F3C
CF3
F3C
II2 96%
CF3
+
CF OCF CF CF CFOCF CF CF OCF
+
CF OCF CF CF CF CF CF OCF
3 2 2 2 2 2 2 3
3
2
2
2
2
2
2
3
IV2 4%
V2 1%
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 6 2011

1048
STAROBIN et al.
Air
Carbon
monoxide
Cooling agent
Fig. 1. Composition of the products of the photolysis of (1)
perfluoro-7,9-dimethyl-2,6,10,14-tetraoxapentadecan-8-one (2)
in the reaction mixture as function of a time τ of the synthesis
according to GLC data. (М) Content of the photolysis products
~220 V
Cooling agent
(wt %), (τ) time (h). Compound: (2) II, (3) IV, (4) V.
reactor was thermostated by water supply to the jacket.
The reactor of the 0.3 l capacity was used for selection
of the process temperature in the photolysis of perfluoro-
ketones. The reactor of 2-liter capacity was used for the
experiment enlarged.
Fig. 2. Photochemical reactor. (1) Photochemical reactor made
of quartz glass, (2) cooling jacket, (3) UV lamp, (4) device
DRL-250 (SIP) for launching and controlling, (5) inlet of the
cooling agent, (6) outlet of cooling agent, (7) fitting for carbon
monoxide discharging, (8) inlet fitting for air, (9) thermocouple.
Initial perfluoroketones, perfluoro-2,4-dipropoxy-
pentan-3-one (1) and perfluoro-5,8,10,13-tetramethyl-
Table 1. 19F NMR spectra of the products of the photolysis of perfluoro-2,4-dipropoxypentan-3-one (1)
Compound structure
Atom no. –δ
, ppm Multiplet
JF–F*, Hz
СCl F
2
Perfluoro-5,6-dimethyl-4,7-dioxadecane (II ) (bp 129–130°С)
1
2
76.6
78.2
d
d
J1–10 8.5
J2–9 8.5
1
2
F5
CF CF C
F9 CF3
F5
3
4
5
6
7
8
9
80.1
80.6
t
J3–5;6 9.0
3
7
8
4
t
J4–5;6 9.0
O
C
C
O
CCF CF
3
2
2
3
84.2
d.d.q
J5–6 150; J5–9 15; J5–3 9.0
J6–5 150; J6–9 15
F
CF F
F
3
6
1
10
6
84.8
d.d
s
127.8
128.3
137.7
138.9
77.1
s
m
m
t
1
0
Perfluoro-5-methyl-4-oxaoctane (IV ) (bp 99–100°С)
1
J1–6;7 8.5
1
2
3
4
5
6
80.7
81.2
t
J2–6;7 8.7
J3–4;5 9.0
J4–5148
F5
CF CF C
F10 F7
3
8
9
2
84.1
O
C
CCF CF3
3
2
2
84.8
J5–4 148
J6–7 286
F
CF
F
3
4
1
6
117.2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 6 2011

STUDY OF LIQUID-PHASE PHOTOLYSIS OF PERFLUORINATED KETONES
1049
Table 1 (Contd.)
Compound structure
Atom no. –δ
, ppm Multiplet
JF–F*, Hz
J7–6 286
СCl F
2
7
8
120.1
127.5
d.m
s
9
128.6
137.9
82.0
s
m
t
1
0
Perfluorohexane (V ) (bp 58–60°С)
1
J1–3 9.5
J2–4 8.5
J3–1;5 9.0
1
1
2
3
4
5
1
2;5
;4
127.3
123.4
t
CF CF CF CF CF CF
3
2
2
2
2
3
3
sext
Table 2. 19F NMR spectra of the products of the photolysis of perfluoro-7,9-dimethyl-2,6,10,14-tetraoxapentadeca-8-one (2)
Compound structure
Atom no. –δ
, ppm Multiplet
JF–F*, Hz
J1–4(5) 10.0
СCl F
2
Perfluoro-7,8-dimethyl-2,6,9,13-tetraoxatetradecane (II ) (bp 172°С)
1
2
3
4
5
6
7
8
9
54.7
76.5
t
d
2
3
J2–11 8.6
J3–10 8.6
J4–1;6;7 9.0
J5–1;6;7 9.0
J6–7 147
J7–6 147
F7
CF OCF CF C
F10 CF3
F7
78.1
83.4
d
1
4
8
9
5
1
O
C
C
O
CCF CF OCF
3
2
2
2 2 3
sext
sext
d.m
d.m
s
F
CF F
F
83.6
3
6
2
11
6
84.2
84.9
127.8
128.3
137.7
138.9
s
1
0
1
m
1
m
Perfluoro-7-metyl-2,6,11-trioxadodecane (IV ) (bp 142°С)
1
54.5
t
J1–4 10.0
2
2
5
2
3
4
5
6
7
8
9
54.9
78.4
t
t
J2–5 F –F 9.8
J3–8;9 8.7
J4–1;6;7 9.0
J5–1;8;9 9.2
J6–7147
F7
F12 F9
1
4
11
10
5
2
83.0
sext
sext
d.m
d.m
d.m
d.m
s
CF OCF CF C
O
C
CCF CF OCF
3
2
2
2 2 3
83.8
F
CF
F
3
6
3
8
84.2
84.7
J7–6 147
117.2
120.1
127.5
128.6
137.9
54.9
J8–9284
J9–9 284
1
0
11
s
1
2
m
Perfluoro-2,9-dioxadecane (V ) (bp 112°С)
1
t
J1–2 9.8
J2–1;3 9.0
J3–2;4 8.5
J4–3 8.5
2
2
3
4
83.9
sext
q
1
2
4
3
3' 4'
2
1
CF OCF CF CF CF CF CF OCF
122.4
123.8
3
2
2
2
2
2
2
3
t
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 6 2011

1050
STAROBIN et al.
Table 3. 19F NMR spectra of the products of the photolysis of perfluoro-5,8,10,13-tetrametyl-4,7,11,14-tetraoxaheptadecan-9-
one (3)
Compound structure
Atom no. –δ
, ppm Multiplet
JF–F*, Hz
СCl F
2
Perfluoro-5,8,9,12- tetrametyl -4,7,10,13- tetraoxaheptadecane (II3)
1
2
3
4
5
6
7
8
9
76.4
76.5
br.s
d.m
br.s
d.m
br.s
br.s
d.m
d.m
br.s
d.m
d.m
br.s
d
(bp 216°С)
J2–8 ~ 150
3
6
77.1
77.3
F7
F15 F8
F13 CF3 F10 CF
F7
3
J4–7 ~ 150
9
12
12
9
CF CF CO
C
CO
C
C
OC
C
OCCF CF3
3
2
2
78.4
78.5
F
CF
F
CF
F
F
F
F
3
3
1
1
5
2
1
16
11
1
4
4
78.7
J7–4 ~ 150
J2–8 ~ 150
80.0
80.3
1
0
81.5
J10–11 ~ 150
J11–10 ~ 150
11
82.7
12
13
14
15
16
1
128.2
130.5
138.2
142.5
142.8
76.6
J13–х 19
J14–х 19
J15–х 24
J16–х 24
J1–5 ~ 150
d
t
t
Perfluoro-5,810-trimethyl-4,7,11-trioxatetradecane (IV ) (bp 186°С)
d.m
3
3
2
3
4
5
6
7
8
9
0
77.1
78.2
br.s
br.s
d.m
d.m
br.s
d.m
d.m
d.m
br.s
t
F7
F11 F5
F12 F9 CF3 F7
6
10
10
6
CF CF CO
C
CO
C
C
C
OCCF CF
3
2
2
3
78.7
J4–7 ~ 150
J5–1 ~150
F
CF
F
CF F
F
F
3
3
80.0
4
2
1
3
8
4
1
1
80.3
81.5
J7–4 ~ 150
J8–9 ~ 290
J9–8 ~ 290
118.0
120.5
128.2
142.3
142.8
78.2
1
11
J11–x24
1
2
1
t.d
J12–х24; J12–х 18
Perfluoro-5,7-dimethyl-4,8-dioxadodecane (V ) (bp 156°С)
br.s
3
1
2
3
4
5
6
7
8
78.7
80.3
d.m
br.s
d.m
d.m
d.m
br.s
t.d
J2–4~150
F2
CF CF CO
F8 F5 CF3 F2
3
7
7
3
C
C
C
OCCF CF3
3
2
2
81.5
J4–2~150
J5–6~290
J6–7 ~290
F
CF
F
F
F
3
118.0
120.5
127.9
143.0
4
1
6
4
8
J8–х24; J8–х 18
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 6 2011

STUDY OF LIQUID-PHASE PHOTOLYSIS OF PERFLUORINATED KETONES
1051
1
9
4
,7,11,14-tetraoxaheptadecan-9-one (3), were synthesized
(bp 70.5–71.5°C/22 mm Hg) identified by F NMR spec-
trum. From a head faction was isolated 25 g of perfluoro-
from the dimer and trimer of hexafluoropropenoxide
respectively, perfluoro-7,9-dimethyl-2,6,10,14-tetraoxa-
pentadecan-8-one (2) was obtained from perfluoro-2-
2,9-dioxadexane (V ) (bp 112°C/760 mm Hg) and from
an intermediate fraction, 100 g of perfluoro-7-methyl-
2
(
3-metoxy,propoxy)propionylfluoride [5]. Asymmetric
perfluoro-5,7,10-dimethyl-4,8,11-trioxatetradecan-6-one
4) was obtained by condensation of the trimer of hexa-
2,6,11-trioxadodecane (IV ) (bp 142°C/760 mm Hg).
2
(
CONCLUSIONS
fluoropropenoxide with perfluoropropylvinyl ether in the
presence of potassium fluoride in diglyme.
(1) Under the influence of UV irradiation at a tem-
perature below 25°C, decarbonylation of perfluoro-2,4-
dialkoxypentan-3-ones is accompanied by recombination
of the resulting secondary perfluoroalkoxyethyl radicals
to form the corresponding perfluoropolyoxaalkanes.
IR spectra were recorded on a spectrometer Perkin-
Elmer FT Spectrum BX, UV spectra, on a spectrophotom-
eter Perkin-Elmer Lambda 35 in a range of 50–400 nm.
The structure of the photolysis products were determined
19
by F NMR spectra with a spectrometer Bruker Spec-
trospin AM-500 with a frequency of 470.6 MHz with
hexafluorobenzene as an internal standard. Composition
of the photolysis products were analyzed by gas-liquid
chromatography (GLC) in a chromatograph LHM-8MD
(2) When increasing the temperature of the photolysis
decarbonylation of perfluoro-2,4-dialkoxypentan-3-ones
accompanied by abstraction of trifluoroacetyl fluoride
with the formation of the recombination products of
perfluororadikals being formed.
(
Model 5, the thermal conductivity detector, temperature
(
3) The photolysis of the asymmetric perfluoro-2,4-
–
1
programming 30–200°C at 6 deg min ) with a column
diameter d = 3 mm, length l = 3 m on a solid support
Silohrom-2 (0.16–0.20 mm) with the stationary phase
dialkoxypentan-3-ones at 25°C leads to the formation of
only asymmetric perfluoropolyoxaalkanes.
–
1
5
F4E (15 wt %), carrier gas helium, 40 ml min .
ACKNOWLEDGMENTS
In the 0.3 l reactor we charged 300 g of perfluoroketone,
launched a temperature control of the reactor (a cooling
agent temperature was set by setting its value on the ther-
mostat) and cooling of the UV lamp by air flow supplied
from a compressor. Then we switched on UV irradiation
and monitored the process by the sampling from the reactor
until complete disappearance in the products of the photoly-
sis by IR spectrum of a band at 1780 cm corresponding to
the carbonyl group of perfluoroketone or by UV spectrum
by disappearance of the absorption band of carbonyl group
at 350 nm. The photolysis proceeded up to 10 hours, the
temperature range was 30–120°C.
This work was supported by theFederalAgency forSci-
ence and Innovation, State Contract no. 02.523.12.3027.
REFERENCES
1. Levin, A.I., Sokolov, S.V., Chechina, O.N., and
Bil’dinov, K.N., Zh. Obshch. Khim., 1969, vol. 39, no. 2,
pp. 440–442.
–1
2. USSR Inventor’s Certificate 1262890; SSSR Byull. Izobr.,
no. 1262890.
3. Cherstkov, V.F., Grinberg, V.A., Sterlin, S.R. et al.; Izv. Akad.
Nauk SSSR, Ser. Khim., 1990, no. 10, pp. 2448–2449.
In the enlarged experiment, in the 2 l reactor 2900 g
of perfluoro-7,9-dimethyl-2,6,10,14-tetraoxapentadecan-
4
. German Patent 2531511. Verfahren zur Herstellung von
Perfluoraethern.
8
-one (2) was charged and irradiated at 40°C with UV
light for 100 hours. By distillation of 2800 g of the
mixture of photolysis products we isolated 2650 g of
perfluoro-7,8-dimethyl-2,6,9,13-tetraoxatetradecane (II2)
5. Lebedev, N.V., Berenblit, V.V., Starobin, Yu.K., and
Gubanov, V.A., Zh. Prikl. Khim., 2005, vol. 78, no. 10,
pp. 1668–1673.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 6 2011