Thermoanalytical and preparative investigations of the decomposition of potassium perfluoroorganyl(fluoro)borate salts, K[RFBF3] (RF = perfluoroalkyl, -alkenyl, -alkynyl, and -aryl groups) and K[(RF)2BF2] (RF = C 6F5 and C6F13)

Article abstract of DOI:10.1016/j.jfluchem.2013.11.006

Potassium perfluoroalkenyl(fluoro)borates, K[R_FBF₃], (R_F = CF₂C(CF₃), cis-CF₃CFCF, and cis-C₆F₁₃CFCF) decomposed at 208-225 C (T_max, dTG). The K[R_FBF₃] salts (R_F = C ₃F₇, C₆F₁₃, trans-CF ₃CFCF, and trans-C₄F₉CFCF) decomposed at 273-312 C (T_max, dTG). Both groups of salts formed volatile polyfluoroorganics and K[BF₄] as solid residue. The preparative thermolysis of selected prototypical salts K[R_FBF₃] showed that the polyfluoroorganics consisted of a mixture of internal perfluorohexenes, C₆F₁₂, and 1-H-tridecafluorohexane, C₆F₁₃H, in case of K[C₆F₁₃BF ₃], and of perfluorooctynes, C₈F₁₄, and cis-C₆F₁₃CFCFH in case of K[cis-C₆F ₁₃CFCFBF₃]. The salts K[(C₆F₅) ₂BF₂] and K[R_FBF₃] (R_F = CF₃CC, CF₃CFCFCC, C₆F₅CC, C ₆F₅, 2,3,5,6-C₅NF₄) decomposed in the temperature range 249-337 C (T_max, dTG) and mainly resulted in non-volatile polyfluoroorganics besides K[BF₄]. The reaction path of the thermolysis of perfluoroalkyl-, perfluoroalkenyl-, and perfluorophenyl(fluoro)borates is discussed and compared with that of perfluorocarboxylates.

Full text of DOI:10.1016/j.jfluchem.2013.11.006

Journal of Fluorine Chemistry 157 (2014) 73–78
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Thermoanalytical and preparative investigations of the decomposition
of potassium perfluoroorganyl(fluoro)borate salts, K[RFBF3]
(RF = perfluoroalkyl, -alkenyl, -alkynyl, and -aryl groups) and
K[(RF)2BF2] (RF = C6F5 and C6F13)
Vadim V. Bardin a, Inna K. Shundrina a, Hermann-Josef Frohn b,
*
a N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Acad. Lavrentjev Avenue 9, 630090 Novosibirsk, Russian Federation
b Inorganic Chemistry, University of Duisburg-Essen, Lotharstrasse 1, D-47048 Duisburg, Germany
A R T I C L E I N F O
A B S T R A C T
Article history:
Potassium perfluoroalkenyl(fluoro)borates, K[RFBF3], (RF = CF255C(CF3), cis-CF3CF55CF, and cis-
C6F13CF55CF) decomposed at 208–225 8C (Tmax, dTG). The K[RFBF3] salts (RF = C3F7, C6F13, trans-
CF3CF55CF, and trans-C4F9CF55CF) decomposed at 273–312 8C (Tmax, dTG). Both groups of salts formed
volatile polyfluoroorganics and K[BF4] as solid residue. The preparative thermolysis of selected
prototypical salts K[RFBF3] showed that the polyfluoroorganics consisted of a mixture of internal
Received 18 October 2013
Received in revised form 6 November 2013
Accepted 7 November 2013
Available online 15 November 2013
perfluorohexenes, C6F12, and 1-H-tridecafluorohexane, C6F13H, in case of K[C6F13BF3], and of
Keywords:
perfluorooctynes, C8F14, and cis-C6F13CF55CFH in case of K[cis-C6F13CF55CFBF3]. The salts K[(C6F5)2BF2]
and K[RFBF3] (RF = CF3CBB C, CF3CF55CFCBB C, C6F5CBB C, C6F5, 2,3,5,6-C5NF4) decomposed in the tempera-
ture range 249–337 8C (Tmax, dTG) and mainly resulted in non-volatile polyfluoroorganics besides K[BF4].
The reaction path of the thermolysis of perfluoroalkyl-, perfluoroalkenyl-, and perfluorophenyl-
(fluoro)borates is discussed and compared with that of perfluorocarboxylates.
Potassium perfluoroorganyl(fluoro)borates
Thermal decomposition
TA analysis
NMR spectroscopy
ß 2013 Published by Elsevier B.V.
1. Introduction
decomposition point of 84.9 8C [12], respectively. Zhou et al.
determined a temperature range of decomposition of 270–320 8C
The first representatives of perfluoroorganyl(fluoro)borates
were prepared more than 40 years ago. The majority of these
compounds were synthesized during the last two decades. There
are several reviews which cover the syntheses, chemical proper-
ties, spectral data, and application of these salts, e.g., in cross
coupling reactions, in electrolytes of lithium ion batteries, or in
supercapacitors for energy storage [1–7]. Data of their thermal
properties, especially their decomposition, are very limited and
usually reduced to their melting or decomposition points. In few
cases more information was presented, e.g., the salts M[CF3BF3]
decomposed in vacuum forming CF255CF2 and M[BF4] (M = K, 330–
350 8C; M = NH4; 175 8C) [8]. Chambers and Chivers reported that
the thermal decomposition of K[C6F5BF3] occurred in vacuum at
ca. 300 8C and produced K[BF4] and probably a mixture of
perfluoroterphenyls [9]. The same authors published melting
points of 324 8C for K[C6F5BF3] [9] whereas Molander reported
>250 8C [10]. The salts K[(C2F5)3BF] and K[(CF255CF)3BF] were
characterized either by a melting point of 174 8C [11] or a
for a series of perfluoroalkyl(trifluoro)borate salts M[CnF2n+1BF3]
(M = K, Et4N [13] (n = 2–4), cyclic quaternary ammonium [14],
and 1-alkyl(alkyl ether)-3-methylimidazolium [15]). The salts
M[CF3BF3]
(M = 1-alkyl(alkyl
ether)-3-methylimidazolium)
decomposed at lower temperatures (200–240 8C), presumably,
via elimination of difluorocarbene [15]. The decomposition of
those substances gave complex DSC data and products were not
analyzed [13–15].
Very recently we investigated the thermal property of neat [4-
FC6H4N2][RFBF3] (RF = C6F5, C6F13, trans-C4F9CF55CF, cis-C6F13CF55CF,
CF3CBB C) or their mixtures with NaF which gave the principal
product 1,4-C6F2H4 besides RFBF2 or Na[RFBF3], respectively, when
heated above 120–160 8C [16]. The thermolysis of [4-
FC6H4N2][(C6F13)2BF2] in NaF resulted in 1,4-C6F2H4, Na[(C6F13 2
)
BF2], the isomer Na[(C6F13)(C5F11)CFBF3], and Na[BF4]. Certainly,
that the decomposition proceeded in the manner of the Balz–
Schiemann reaction [16].
In the present work we report the thermal decomposition of a
representative series of potassium perfluoroorganyl(trifluoro)-
borates, K[RFBF3] (RF = perfluorinated alkyl, alkenyl, alkynyl, and
aryl group), and K[(RF)2BF2] (RF = C6F5, C6F13) by simultaneous
thermogravimetry and differential scanning calorimetry (TG/
*
Corresponding author. Tel.: +49 2152 7868.
E-mail address: h-j.frohn@uni-due.de (H.-J. Frohn).
0022-1139/$ – see front matter ß 2013 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.jfluchem.2013.11.006

74
V.V. Bardin et al. / Journal of Fluorine Chemistry 157 (2014) 73–78
DSC) and for selected salts, by visually controlled preparative
micro-scale thermolysis.
The visually controlled heating of K[trans-CF3CF55CFBF3]
showed changes of the crystals at 115–119 8C which were followed
by melting at 183–185 8C. These observations correspond to the
two endothermic solid–solid phase transitions at 107 and 112 8C
and the endothermic melting point at 171 8C (DSC). The molten
salt decomposed exothermically above 223 8C (T3%, dTG) with
Tmax = 273 8C (dTG). Notably, the sequence of individual steps
resembles that of the isomeric borate, K[CF255C(CF3)BF3], but all
steps in the latter proceed at ca. 30 8C lower temperatures. Thus,
there are two solid–solid phase transitions at 74 and 82 8C,
followed by subsequent melting at 142 8C, and decomposition at
209 8C (Tmax, dTG). The visual controlled mp of K[CF255C(CF3)BF3]
was found at 143–145 8C.
Salt K[trans-C4F9CF55CFBF3] melted at 184–187 8C (visually)
and 176 8C (Tonset, DSC). The decomposition occurred at 287 8C
(Tmax, dTG). In all four potassium perfluoroalkenyl(trifluoro)bo-
rates, the decomposition was accompanied by the elimination of
volatile perfluoroorganics according to Eq. (3) and K[BF4] resulted
as solid residue.
2. Results
2.1. Thermoanalytical investigation of potassium
perfluoroalkyl(fluoro)borates
Thermal decomposition data of K[C3F7BF3], K[C6F13BF3], and
K[(C6F13)2BF2] are summarized in Table 1. K[C3F7BF3] melted at
299 8C (Tonset, DSC) followed by decomposition at 312 8C (Tmax
,
dTG). The elongation of the perfluoroalkyl chain in K[C6F13BF3] was
accompanied by a decrease of the melting point to 285 8C and of
the decomposition temperature to 303 8C. In contrast, borate
K[(C6F13)2BF2] was thermally more stable and the melting at
354 8C overlapped remarkably with the decomposition at 363 8C.
Before melting, borates K[C6F13BF3] and K[(C6F13)2BF2] underwent
solid–solid phase transitions. In case of all three perfluoroalk-
yl(trifluoro)borate salts, the decomposition proceeded with the
formal elimination of the corresponding perfluoroalkene (Eqs. (1)
and (2)) and the formation of K[BF4] based on the TG data.
K½CnF2nꢁ1BF3ꢀ ! hCnF2nꢁ2i þ K½BF4ꢀ
(3)
K½CnF2nþ1BF3ꢀ ! hCnF2ni þ K½BF4ꢀ
K½ðC6F13Þ2BF2ꢀ ! h2C6F12i þ K½BF4ꢀ
(1)
(2)
2.3. Thermoanalytical investigation of potassium
perfluoroalkynyl(trifluoro)borates
The TG–DSC data of potassium perfluoroalkynyl(trifluoro)-
borates are summarized in Table 3. The decomposition of
K[C3F7CBB CBF3] started directly after melting (Tonset = 217 8C,
DSC) and went via two steps with Tmax = 228 and 272 8C (dTG).
2.2. Thermoanalytical investigation of potassium
perfluoroalkenyl(trifluoro)borates
A
similar picture was obtained for the isomeric borate
K[(CF3)2CFCBB CBF3] but with melting and decomposition ca. 20–
30 8C higher. The mass loss for both salts corresponded with the
elimination of ‘‘C5F6’’ and the formation of K[BF4] as solid residue
(Eqs. (4) and (5)).
The data of the thermal decomposition of the potassium
perfluoroalkenyl(trifluoro)borate salts are summarized in Table
2. The thermogram of K[cis-CF3CF55CFBF3] contained an endother-
mic effect at Tonset = 131 8C (DSC) which corresponds to the melting
point (proved by the visual melting point), two exothermic effects in
the range 208–228 8C and an endothermic effect at 294 8C. The
thermolysis was accompanied with a mass loss of 43% and ended
with the formation of K[BF4]. The latter was characterized with DSC
K½C3F7CBB CBF3ꢀ ! hC5F6i þ K½BF4ꢀ
(4)
(5)
K½ðCF3Þ2CFCBB CBF3ꢀ ! hC5F6i þ K½BF4ꢀ
by its endothermic phase transition from orthorhombic (
to cubic ( -K[BF4]) [17]. The phase transition data are in agreement
with that of neat K[BF4] (our data of an independent experiment).
a
-K[BF4])
Heating of K[CF3CBB CBF3] in a Koffler Block melting apparatus
between two glass disks showed a melting point at 183–187 8C and
parallel the formation of a dark brown solid. The DSC data reveal two
endothermic effects, a solid–solid phase transition (Tonset = 115 8C)
and melting (Tonset = 178 8C). Further heating caused an intensive
exothermic process (Tmax = 249 8C, dTG) which, however, was
accompanied by a remarkable small mass loss (only 7%).
Heating of borate K[CF3CF55CFCBB CBF3] was characterized by an
exothermic process (Tmax = 273 8C (dTG)) and was accompanied by
a partial eruption of the probe (initial mass 3.131 mg) through the
pierced lid. Using a smaller probe (1.983 mg) we measured a
remarkable small mass loss (9%). Notably, that a second heating
scan to 400 8C after cooling to 28 8C at the end of the first
measurement proceeded without mass loss and displayed only an
b
From DSC the decomposition temperature of K[cis-C6F13
CF55CFBF3] is only slightly lower than that of K[cis-CF3CF55CFBF3].
CFBF3]. At the visual melting point of 184–186 8C a liquid phase
appeared which above 190 8C showed bubbling of gas. According
to the TG data, the decomposition began at 173 8C (T3%, dTG) with
Tmax = 208 8C (dTG). The endothermic effect at 121 8C will be
-
attributed to
a preceding solid–solid phase transition. The
decomposition process is accompanied by a weak exothermic
peak at ca. 208 8C and resulted in the solid residue K[BF4]. The
amount of volatiles determined from TG agrees with the expected
mass loss.
Table 1
TG/DSC data of potassium perfluoroalkyl(fluoro)borates.
a
Compound
Ts1ꢁs
,
8C
Tmelting, 8C
Decomposition
b
c
T3%
,
8C
Tmax
,
8C
Heat effect of decomposition
Mass loss, %
mexp
d
D
Dmcalc
K[C3F7BF3]
–
255
327
299
285
354
303
271
290
312
303
363
Exothermic
Exothermic
Exothermic
57
72
89
54
71
83
K[C6F13BF3]
K[(C6F13)2BF2]
a
Temperature of solid–solid phase transition.
Temperature of 3% mass loss.
b
c
Temperature of the rate maximum of the decomposition.
Calculated from the residue for K[BF4].
d

V.V. Bardin et al. / Journal of Fluorine Chemistry 157 (2014) 73–78
75
Table 2
TG/DSC data of potassium perfluoroalkenyl(trifluoro)borates.
a
a
Compound
Ts1ꢁs
,
8C
Ts2ꢁs
,
8C
Tmelting, 8C
Decomposition
b
c
e
T3%
,
8C
Tmax
,
8C
Heat effect of
decomposition
Mass loss, %
mexp
Ts–s, 8C
d
D
Dmcalc
K[cis-CF3CF5CFBF3]
K[cis-C6F13CF5CFBF3]
K[trans-CF3CF5CFBF3]
K[trans-C4F9CF5CFBF3]
K[CF25C(CF3)BF3]
–
121
107
–
–
–
131
173
173
223
268
173
225
208
273
287
209
Exothermic
Exothermic
Exothermic
Exothermic
Exothermic
43
71
43
67
39
53
74
47
68
47
294
288
292
–
184–186f
171
112
–
176
74
82
142
287
a
Temperature of solid–solid phase transition.
Temperature of 3% mass loss.
b
c
d
e
f
Temperature of the rate maximum of the decomposition.
Calculated from the residue for K[BF4].
Solid–solid phase transition (
a
-K[BF4] !
b-K[BF4]).
Visually.
endothermic peak at 288 8C, which can be attributed to the
transition of -K[BF4] to -K[BF4]. In the case of K[CF3CBB CBF3]
thermal process except the solid–solid phase transition of K[BF4]
(Tonset = 288 8C, DSC).
a
b
which was also characterized by an unexpected low mass loss of
7%, the second heating scan of from 28 to 400 8C displayed a similar
result.
The DSC result of K[C6F5CBB CBF3] showed no thermal process
below 219 8C. Above that temperature DSC presented an ambigu-
ous result: which can be attributed to either two exothermic
maxima at 278 8C and 294 8C or one broad exothermic maximum
which has been superposed by an endothermic minimum at
284 8C. The endothermic effect may belong to the solid–solid phase
Borate K[(C6F5)2BF2] underwent a fast decomposition and the
TG diagram revealed that the mass loss proceeded in two steps at
327 and 332 8C (Tmax) with a total mass loss of 46% till 470 8C.
Two thermal processes were found in the DSC result of
K[2,3,5,6-C5NF4BF3]. The first was a solid–solid phase transition
(Tonset = 148 8C). Heating of the salt under visual control displayed
a change of the solid at 155–161 8C. The second process at
Tmax = 337 8C (dTG) was caused by decomposition and accompa-
nied by a 33% mass loss.
transition of obtained K[BF4]. The experimental mass loss
D
mexp
All studied potassium perfluoroaryl(fluoro)borates have in
commonthatnomeltingcouldbedetectedintheDSCmeasurement.
Furthermore, the thermal decomposition of all three salts is
(20%) was significantly lower than the calculated mcalc (58%)
D
which may indicate that thermally stable, non-volatile fluoroor-
ganic materials have resulted till 370 8C from borate
K[C6F5CBB CBF3].
characterized by a remarkable lower experimental mass loss
Dmexp
related to the calculated value based on the idealized Eq. (6).
0
2.4. Thermoanalytical investigation of potassium
perfluoroaryl(fluoro)borates
K½RFBF3ꢀ ! hRF i þ K½BF4ꢀ
(6)
The TG data of potassium perfluoroaryl(fluoro)borates are
summarized in Table 4. The DSC curve of K[C6F5BF3] contained two
weak endothermic effects at 170 and 210 8C (Tonset) which
correspond to phase transitions. Those assignments were con-
firmed by heating under visual control. At 327 8C (Tmax, DSC) an
exothermic process took place. The process was accompanied by a
gradual mass loss which achieved 19% at 410 8C. Cooling to 28 8C
followed by a second heating to 400 8C showed no mass loss and no
2.5. Preparative thermolysis of selected potassium
perfluoroorganyl(trifluoro)borates
The TA data display the range of thermal stability of
perfluoroorganyl(fluoro)borates but give neither information of
the routes of decomposition nor of the nature of the polyfluoro-
organic products. To get insight into the kind of products, we
performed preparative thermolysis reactions of three selected
Table 3
TG/DSC data of potassium perfluoroalkynyl(trifluoro)borates.
a
Compound
Ts1ꢁs
,
8C
Tmelting, 8C
Decomposition
b
c
e
T3%
,
8C
Tmax
,
8C
Heat effect of
decomposition
Mass loss, %
T
, 8C
–
a b
d
Dmexp
Dmcalc
K[CF3CBB CBF3]
115
–
178
–
242
–
249
–
Exothermic
–
7
0
49g
54g
9
37
–
296
289
286
284
–
K[CF3CBB CBF3]f
K[C3F7CBB CBF3]
–
217
245
–
228
255
262
–
228, 272
258, 283, 290
273
Exothermic
Exothermic
Exothermic
–
58
58
52
–
K[(CF3)2CFCBB CBF3]
K[CF3CF5CFCBB CBF3]
K[CF3CF5CFCBB CBF3]f
K[C6F5CBB CBF3]
–
161
–
–
–
0
288
284h
–
–
222
241, 293
Exothermic
20
58
a
Temperature of solid–solid phase transition.
Temperature of 3% mass loss.
b
c
d
e
f
Temperature of the rate maximum of the decomposition.
Calculated from the residue for K[BF4].
Solid–solid phase transition (
a
-K[BF4] !
b-K[BF4]).
The sample was cooled after the first scan to 28 8C and again heated to 400 8C.
g
h
Heating up to 400 8C.
Proposed assignment.

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V.V. Bardin et al. / Journal of Fluorine Chemistry 157 (2014) 73–78
Table 4
TG/DSC data of potassium perfluoroaryl(fluoro)borates.
b
b
Compounda
Ts1ꢁs
,
8C
Ts2ꢁs
,
8C
Decomposition
c
d
f
T3%
,
8C
Tmax
,
8C
Heat effect of
decomposition
Mass loss, %
mexp
T
,
8C
–
a b
e
D
Dmcalc
K[C6F5BF3]
170
–
210
–
328
–
329
–
Exothermic
–
19g
0
46i
33
54
–
–
K[C6F5BF3]h
288
–
K[(C6F5)2BF2]
K[2,3,5,6-C5NF4BF3]
–
–
315
316
327, 332
337
Exothermic
Exothermic
70
51
148
–
–
a
No melting was detected.
b
Temperature of solid–solid phase transition.
Temperature of 3% mass loss.
c
d
e
f
Temperature of the rate maximum of the decomposition.
Calculated from the residue for K[BF4].
Solid–solid phase transition (
a
-K[BF4] !
b-K[BF4]).
g
h
i
Heating up to 410 8C.
The sample was cooled after the first scan to 28 8C and again heated to 400 8C.
Heating up to 470 8C.
potassium perfluoroorganyl(trifluoro)borates: K[C6F13BF3], K[cis-
C6F13CF55CFBF3], and K[C6F5BF3], with a thermal behavior which is
typical for groups of borates. Reactions were performed in flame-
dried sealed glass ampoules at decomposition temperatures
slightly exceeding Toffset obtained from DSC measurements.
The decomposition of K[C6F13BF3] at 300–310 8C (bath) was not
melts and undergoes subsequently decomposition into volatile
perfluoroorganic products and a solid residue which consists of
K[BF4]. In some cases Tmp and Tdec are very close together. The first
group is typical for perfluoroalkyl(fluoro)borates, perfluoroalk-
enyl(trifluoro)borates, and perfluoroalkynyl(trifluoro)borates (ex-
cept for K[CF3CF55CFCBB CBF3] and K[C6F5CBB CBF3]). Within this
group perfluoroalkyl(trifluoro)borates are thermally more stable
than alkenyl(fluoro)borates. Within the subgroup of perfluoroalk-
enyl(fluoro)borates trans-perfluoroalkenyl(trifluoro)borates are
more stable than their cis-isomers. The subgroup of potassium
perfluoroalkynyl(trifluoro)borates, K[RFCBB CBF3] (RF = CF3, C3F7,
(CF3)2CF), decompose in the temperature range of 228–290 8C.
The present investigation allows giving a sequence of the
temperature of the rate maximum of decomposition (Tmax, dTG) of
K[RFBF3] salts: K[2,3,5,6-C5NF4BF3] (337 8C) ꢂ K[C6F5BF3]
(329 8C) > K[C3F7BF3] (312 8C) ꢂ K[C6F13BF3] (303 8C) > K[trans-
completed within 40 min and gave
a mixture of internal
perfluorohexenes and 1-H-tridecafluorohexane. Perfluorohex-1-
ene was not detected (Scheme 1).
The decomposition of K[cis-C6F13CF55CFBF3] occurred incom-
pletely at 215–225 8C (bath) within 1.5 h and gave cis-
C6F13CF55CFH, C6F13CBB CF, and C5F11CBB CCF3 besides not identified
perfluoroorganics. According to 19F NMR and GC–MS data, the
latter may be dimers of perfluorooctyne. The compounds trans-
C6F13CF55CFH, C5F11CF55CFCF2H, and C5F11CF55C55CF2 were not
formed (Scheme 2).
Thermolysis of K[C6F5BF3] at 325–335 8C (bath) for 40 min gave
a black solid which was extracted with DMF. The 19F NMR
spectrum of the extract contained signals of K[BF4], C6F5H (trace),
and three groups of resonances at ꢁ136 to ꢁ140, ꢁ149 to ꢁ151 and
ꢁ161 ppm in the ratio 100:15:65. The latter compound(s)
probably represent(s) perfluorinated polyphenyl derivatives such
as K[C6F5(C6F4)nBF3]. In the proposed assignment the resonances of
the BF3 group are overlapping with aryl fluorine signals at 136–
140 ppm. Such an overlap is observed for K[C6F5BF3] in DMF [18].
The insoluble part of the reaction mixture was not studied in detail.
C4F9CF55CFBF3]
(287 8C) > K[trans-CF3CF55CFBF3]
(273 8C)
ꢂ K[CF3CF55CFCBB CBF3] (273 8C)–K[C3F7CBB CBF3]
(272 8C) >
K[(CF3)2CFCBB CBF3] (258 8C) ꢂ K[CF3CBB CBF3] (249 8C) ꢂ K[C6F5C
BB CBF3](241 8C) > K[cis-CF3CF55CFBF3] (225 8C) > K[CF2 55C(CF3)
BF3] (209 8C) ꢂ K[trans-C6F13CF55CFBF3] (208 8C).
The reaction pathway of the first group can be described by the
sequence: (a) heterolytic cleavage of C–B bond, (b) elimination of
fluoride from the perfluoroorganyl anion in hK[RF]i, (c) fluoride
transfer from KF to BF3. Final products are simplified perfluoroalk-
enes (from perfluoroalkyl(trifluoro)borates) and perfluoroalkynes
(from perfluoroalkenyl(trifluoro)borates) besides K[BF4]. This
generalization and idealization is supported by the results of the
preparative thermolysis of K[C6F13BF3] and K[cis-C6F13CF55CFBF3].
hK[RF]i eliminates KF spontaneously to give the terminal per-
fluoroalkene. Isomerization of the latter ends up in the observed
3. Discussion
The investigated potassium perfluoroorganyl(fluoro)borates
can be subdivided into two groups. The first group of borates
300–310 °C, 40 min
K[C6F13BF3] ⎯⎯⎯⎯⎯⎯⎯⎯→ cis-C3F7CF=CFCF3 + trans-C3F7CF=CFCF3 +
26% conversion
trans-C2F5CF=CFC2F5 + C6F13H + K[BF4]
Scheme 1.
Scheme 2.

V.V. Bardin et al. / Journal of Fluorine Chemistry 157 (2014) 73–78
77
– BF3
K[C6F13BF3] ⎯⎯→ <C4F9CF2CF2K> ⎯⎯→ C4F9CF=CF2 ⎯⎯⎯→ C6F12
isomers
– KF
H+
C4F9CF2CF2K ⎯→ C6F13H + K+
KF + BF3
⎯→ K[BF4]
Scheme 3.
Scheme 4.
K[C6F5BF3]
K[C6F5BF3] ⎯⎯⎯→ BF3 + <C6F5K> ⎯⎯⎯→ K[C6F5C6F4BF3] ⎯→ ⎯→
K[C6F5(C6F4)nBF3] and/or K[(C6F5)nC6F5-nBF3]
Scheme 5.
internal perfluorohexenes. In a side-reaction, the perfluorocarb-
anion in hK[RF]i reacts with an H+-donor (glass wall, etc.) to yield 1-
H-perfluoroalkane (Scheme 3).
The thermal decomposition of potassium perfluoroalkenyl(tri-
fluoro)borates can formally be described in a similar manner
(Scheme 4).
Notably, that RFH which derived from the corresponding key
carbanion intermediate [RF]ꢁ was unambiguously proved in both
cases.
The thermolysis reactions of potassium perfluoroalkyl(tri-
fluoro)borates and perfluoroalkenyl(trifluoro)borates are for-
mally related to the known thermal decarboxylation of
potassium perfluoroalkylcarboxylates and perfluoroalkenylcar-
boxylates where perfluoroalkenes and a mixture of perfluor-
oalkynes and perfluoroalkadienes were produced, respectively
[19]. In the thermolysis of potassium perfluoroalkylcarbox-
ylates, K[RFCO2], potassium perfluoroalkalide, K[RF], is the
proposed intermediate.
The decomposition of salts which belong to the second
group (without melting point), such as K[CF3CF55CFCBB CBF3],
K[C6F5CBB CBF3], K[C6F5BF3], K[(C6F5)2BF2], and K[2,3,5,6-
C5NF4BF3] is characterized by a significantly lower amount
of volatile fluoroorganics than expected. But K[BF4] was formed
too. The result of the preparative thermolysis of K[C6F5BF3]
allows to assume the formation of perfluoropolyphenyl(tri-
fluoro)borates, K[C6F5(C6F4)nBF3] and/or K[(C6F5)nC6F5ꢁnBF3],
at least in the DMF soluble fraction of the reaction extract (cf.
[9]). Their formation can be explained by the generation of the
pentafluorophenyl anion via the heterolytic carbon–boron
bond cleavage and a successive nucleophilic polyarylation
(Scheme 5).
4. Conclusion
The reaction path of the thermolysis of K[RFBF3] salts depends
on the nature of RF. In case of RF = perfluoroalkyl and perfluoroalk-
1-en-1-yl perfluoroalkenes and -alkynes are formed as volatile
products, respectively, besides K[BF4] as solid residue. In case of
RF = perfluoroaryl, thermolysis proceeds without melting with a
low amount of volatile products and nucleophilic pentafluoro-
phenylation products (RF = C6F5) of the starting salt besides
K[BF4]. The thermolysis of K[RFCBB CBF3] salts is more complex and
depends on the substituent RF. It is scientifically interesting to
compare the reaction path of the thermolysis of K[RFBF3] salts
with that of the perfluoroorganylcarboxylates, K[RFCO2]. The
thermolysis of the perfluoroalkyl(fluoro)borates resembles
strongly that of perfluoroalkylcarboxylates. In case of perfluoro-
alkylcarboxyles perfluoroalkenes are formed besides KF and CO2.
In both cases cleavage of the strong C–C or C–B proceeds in the first
step. The experimental finding that in case of fluoroorganyl-
(fluoro)borate salts the thermal cleavage of the C–B bond is
favored over fluoride abstraction from the B–F moiety allows to
conclude that despite of the strong electrostatic interaction of the
negatively charged BF3ꢁ moiety and K+ the fluoroorganyl(fluoro)-
borate anion in the salt decomposes as expected for the gas phase.
5. Experimental
The NMR spectra were recorded on a Bruker AVANCE 300
spectrometer (1H at 300.13 MHz, 19F at 282.40 MHz). The chemical
shifts are referenced to TMS (1H), and CCl3F (19F) [with C6F6 as a
secondary reference (ꢁ162.9 ppm)]. The composition of the
reaction mixtures and the yield of products were determined by

78
V.V. Bardin et al. / Journal of Fluorine Chemistry 157 (2014) 73–78
19F NMR spectroscopy using C6F6 as an internal quantitative
standard. TG-DSC analyses were performed using a Netzsch
STA409 instrument with a heating rate of 10 K/min under He
flow. The solid samples (2–4 mg) were weighed into aluminum
pans which were closed by a pierced aluminum lid. To support the
assignment of endothermic processes (solid–solid phase transi-
tions or melting) of DSC scans in addition the salts were analyzed
visually using a Koffler melting point apparatus. Temperatures of
phase transitions (Ts–s, Tmelting) were determined from DSC curves
as Tonset. Temperature of maximal rate of decomposition (Tmax) was
determined from the dTG diagrams.
BoratesK[C3F7BF3], K[C6F13BF3][20], K[(C6F13)2BF2][16], K[trans-
C4F9CF55CFBF3] [21], K[cis-C6F13CF55CFBF3] [21], K[cis-CF3-
CF55CFBF3],, K[trans-CF3CF55CFBF3] [22], K[CF255C(CF3)BF3] [23],
K[CF3CꢃCBF3], K[C3F7CꢃCBF3], K[(CF3)2CFCꢃCBF3], K[CF3CF55CF-
CꢃCBF3], K[C6F5CꢃCBF3] [24], K[C6F5BF3] [25], K[2,3,5,6-C5NF4BF3]
[18], and K[(C6F5)2BF2] [26] were prepared as described.
products were extracted with DMF (2 mL ꢄ 0.5 mL). The extract
was filtered through wool and gave a dark brown solution. The 19
NMR spectrum contained the resonances of C6F5H (trace), K[BF4],
and three groups of resonances at ꢁ136 to ꢁ140, ꢁ149 to ꢁ151,
and ꢁ161 ppm in the ratio 100:15:65 besides weak multiplets at
ꢁ55 and ꢁ127 ppm.
F
Appendix A. Supplementary data
Supplementary material related to this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jfluchem.
2013.11.006.
References
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The salt K[C6F13BF3] (231 mg, 0.54 mmol) was sealed in a glass
ampoule and deposited in a pre-heated (300 8C) metal bath. After
40 min at 300–310 8C the ampoule was cooled to 25 8C. The
content, a gray powder, was extracted with CHCl3 (0.8 mL). The 19
F
NMR spectrum contained the resonances of cis-C3F7CF55CFCF3 [27],
trans-C3F7CF55CFCF3 [27], trans-C2F5CF55CFC2F5 [27], and C6F13
H
[28] (molar ratio 21:49:1:29). After extraction with CHCl3 the
residue was dried on air and extracted with DMF (1.5 mL). The
extract contained K[C6F13BF3] (0.40 mmol, 26% conversion)
besides K[BF4] (0.03 mmol) (19F NMR).
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The salt K[cis-C6F13CF55CFBF3] (212 mg, 0.43 mmol) was sealed
in a glass ampoule and deposited in a pre-heated (210 8C) metal
bath. After 1.5 h at 215–225 8C, the ampoule was cooled to 25 8C
and the organic products were extracted with CHCl3 (0.8 mL). The
19F NMR spectrum contained resonances of cis-C6F13CF55CFH
(0.14 mmol), C6F13CBB CF (0.02 mmol), and C5F11CBB CCF3
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(0.04 mmol). Products with resonances at
d
ꢁ82, ꢁ105 to ꢁ112,
ꢁ119, ꢁ122 to ꢁ124, and ꢁ127 ppm could not be identified. The
GC–MS analysis showed the presence of 3 products (ratio 1:1.5:2)
with equal mass-spectra which may be isomers of the dimers of
perfluorooctyne (M+ 724, C16F28). After extraction with CHCl3 the
residue was dried on air and extracted with DMF (1.5 mL). The
extract contained K[cis-C6F13CF55CFBF3] (0.18 mmol) besides the
soluble part of K[BF4].
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5.3. Thermolysis of K[C6F5BF3]
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59 (1992) 9–14.
The salt K[C6F5BF3] (313 mg, 1.14 mmol) was sealed in a glass
ampoule and deposited in a pre-heated (325 8C) metal bath. After
40 min at 325–335 8C the ampoule was cooled to 25 8C. The inner
wall of the ampoule was coated with a dark solid material. The