Dehalogenative aromatization of perchlorofluoroalicyclic compounds C6Cl6F6, C10Cl8F8 and C5Cl4F5N in the vapour phase or in solution

Article abstract of DOI:10.1016/j.jfluchem.2004.04.015

Dehalogenation of perhalogenated cyclohexanes C₆Cl₆F₆, 1-azacyclohexenes C₅Cl₄F₅N and bicyclo[4.4.0]dec-1(6)-enes C₁₀Cl₈F₈ in the vapour phase over iron fil

Full text of DOI:10.1016/j.jfluchem.2004.04.015

Journal of Fluorine Chemistry 125 (2004) 1431–1435
Dehalogenative aromatization of perchlorofluoroalicyclic compounds
C6Cl6F6, C10Cl8F8 and C5Cl4F5N in the vapour phase or in solution
Vadim V. Bardin*, Dmitrii V. Trukhin, Nicolay Yu. Adonin, Vladimir F. Starichenko
N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Academician Lavrentjev Avenue 9, 630090 Novosibirsk, Russia
Received 30 January 2004; received in revised form 15 April 2004; accepted 16 April 2004
Dedicated to Professor Hermann-Josef Frohn on the occasion of his 60th birthday.
Available online 25 June 2004
Abstract
Dehalogenation of perhalogenated cyclohexanes C6Cl6F6, 1-azacyclohexenes C5Cl4F5N and bicyclo[4.4.0]dec-1(6)-enes C10Cl8F8 in the
vapour phase over iron filings at 350–500 8C and in solution with Zn and additivities (Cu, NiCl2ꢀ6H2O þ bpy) at 80 8C (heterogeneous
reaction) or with P(NEt2)3 at 20 8C (homogeneous reaction) was studied. In all cases, perfluoroarenes, chloroperfluoroarenes and
dichloroperfluoroarenes (benzenes, naphthalenes and pyridines) were obtained in good overall yield.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Dehalogenation; Hexafluorobenzene; Octafluoronaphthalene; Pentafluoropyridine
1. Introduction
fluorocarbons C6ClnF12Àn with various n ¼ 5–7 was used
for dehalogenation [8,10–12]. The related syntheses of
polyfluorinated naphthalenes and pyridines from the corre-
sponding perchlorofluorocycloalkanes and perchlorofluoro-
cycloalkenes were not reported except of the defluorination
of perfluorinated materials [1].
Recently we described a simple and convenient method of
fluorine addition to perchloroarenes using vanadium penta-
fluoride [13]. Reaction of hexachlorobenzene with VF5 (bp
48 8C) occurred at 20–50 8C in chlorofluorocarbons (CFCl3,
C2Cl3F3) or without solvent and gave hexachlorohexafluor-
ocyclohexanes C6Cl6F6 (1) in a quantitative yield. Similarly,
tetrachloropentafluoro-1-azacyclohexenes C5Cl4F5N (2)
and octachlorooctafluorobicyclo[4.4.0]dec-1(6)-enes (3)
were prepared from pentachloropyridine and octachloro-
naphthalene, respectively, using standard laboratory equip-
ment. Herein dehalogenation of these compounds to
polyfluoroarenes in either the vapour phase or in solution
is reported.
Dehalogenation of perfluorinated alicyclic compounds
were studied intensively as a route to perfluoroarenes.
Initially these reactions were performed by passing of
vapour of perfluorinated material over heated (200–
500 8C) iron placed into a horizontal metal reactor [1].
During the last decade defluorinations of perfluorocycloalk-
anes in solution with the very strong reducing reagents Na–
benzophenone [2–4], Al–HgCl2–Cp2TiF2 [3,5], Mg–HgCl2
– Cp2ZrCl2 [5] and related reducing agents [6,7] were
reported.
The easier removal of chlorine than fluorine from per-
chlorofluorocyclohexanes over heated iron was demon-
strated previously [8,9]. However, preparations of
perchlorofluorocyclohexanes by fluorine addition to per-
chloroarenes using elemental fluorine [10–12], chlorine
trifluoride [9] or cobalt trifluoride [8] are difficult to control,
and usually these resulted in a mixture of cyclohexanes
C6ClnF12Àn with an average number of chlorine atoms,
n ¼ 4–7. To our knowledge, dehalogenation of perchloro-
fluorocyclohexanes C6ClnF12Àn with definite number of
chlorine atoms, n ¼ 5, 6 and 7 was described only in
reference [9]. In other cases, a mixture of cyclic chloro-
2. Results and discussion
2.1. Dehalogenation in the vapour phase
* Corresponding author. Tel.: þ7-3832-34-1859; fax: þ7-3832-34-4752.
E-mail addresses: bardin@nioch.nsc.ru, vbardin@yandex.ru (V.V. Bardin).
The previously reported dehalogenation of C6Cl6F6 at
300 8C, by passing the vapour over iron gauze in a horizontal
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.04.015

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V.V. Bardin et al. / Journal of Fluorine Chemistry 125 (2004) 1431–1435
metal flow reactor gave C6F6, C6ClF5, C6Cl2F4 and C6Cl3F3
in 2, 39, 33 and 2% yield, respectively [9]. Brooke et al.
studied the dehalogenation of C6Cl6F6 (average composition)
over iron gauze and over fine iron filings at 330–340 8C and
obtained a better overall yield of C6F6 and C6ClF5 in the latter
case [10]. Following this, we dehalogenated compounds 1–3
at higher temperature by passage of their vapours in a stream
of nitrogen over fine iron filings packed in a vertical quartz
tube. Dehalogenation of C6Cl6F6 at 500 8C led to a quanti-
tative conversion in hexafluorobenzene, chloropentafluoro-
benzene and dichlorotetrafluorobenzenes in 30–32, 40–42
and 4–6% yields, respectively (Eq. (1)).
Reaction of C6Cl6F6 with zinc dust in refluxed dioxan
gave hexafluorobenzene, chloropentafluorobenzene and
dichlorotetrafluorobenzenes in 14, 32 and 10% yields,
respectively. However, dehalogenation proceeded slowly
and total conversion of 1 was achieved within 10 h (Eq. (4)).
Zn
C6Cl6F680À100 ꢁ
!
C6F6 þ C6ClF5 þ C6Cl2F4
(4)
C
1
Next, commercial zinc dust was treated with SOCl2 in
sulfolane at 20–25 8C for 30 min before 1 was added and the
reaction mixture was stirred for 5 h at 80 8. This modifica-
tion gave a better yields of both C6F6 and C6ClF5 (27 and
39%, respectively), while C6Cl2F4 remained the minor
component (Eq. (4)) (Table 1, entry 1). The activation of
zinc by preliminary reaction with CuSO4 (0.1 equivalent)
(formation of zinc–copper couple, Zn/Cu) and subsequent
reaction with 1 under the above conditions led to the slightly
increased yield of hexafluorobenzene and chloropentafluor-
obenzene (Table 1, entry 2). Dehalogenation of 1 with Zn/Cu
couple in diglyme gave a similar result (Table 1, entry 3).
Recently we described the reductive hydrodefluorination
and hydrodechlorination of polyfluoroarenes and polychlor-
oarenes with zinc catalyzed by complexes of NiCl2ꢀ6H2O
with bpy or NiCl2ꢀ6H2O with phen in aqueous DMF [14–
18]. It could be expected that the reaction of this system with
hexachlorohexafluorocyclohexanes C6Cl6F6 (1) will result
in the related hydrodehalogenation. However, treatment of 1
with zinc and complex (NiCl2ꢀ6H2O þ bpy) (5 mol%) in
anhydrous dimethylacetamide (DMA) at 80 8C gave C6F6,
C6ClF5 and C6Cl2F4 (Eq. (5)) (Table 1, entry 4). The same
result was obtained when complex (NiCl2ꢀ6H2O þ phen)
was employed (Table 1, entry 5). When reaction of 1 with Zn
and complex (NiCl2ꢀ6H2O þ bpy) was performed in DMF,
partial reduction of C6ClF5 in pentafluorobenzene took place
(Table 1, entry 6). The formation of highly chlorinated
benzenes C6ClnF6Àn (n ꢂ 3) as well as polychlorofluoro-
cycloalkenes was not detected (19F NMR, GLC).
Fe
C6Cl6F6500 ꢁC;flow quartz reactor
!
C6F6 þ C6ClF5 þ C6Cl2F4
1
(1)
Dehalogenation of C5Cl4F5N under the same conditions
gave pentafluoropyridine in 40–43% yield, apart from 2-
chlorotetrafluoropyridine (11–12%) and 3-chlorotetrafluor-
opyridine (43–45%) (Eq. (2)). The formation of 4-C5ClF4N
and highly chlorinated polyfluoropyridines was not detected
(19F NMR).
Fe
C5Cl4F5N ! C5F5N þ 2-C5ClF4N þ 3-C5ClF4N
(2)
500 ꢁ
C
2
Octafluoronaphthalene, 1-chloroheptafluoronaphthalene,
2-chloroheptafluoronaphthalene and dichlorohexafluoro-
naphthalenes (isomer mixture) were obtained by passing
C10Cl8F8 vapour over heated iron filings (Eq. (3)). In con-
trast to the dehalogenation of 1 and 2, the yield of per-
fluorinated naphthalene did not exceed 9% with ca. 55%
overall yield of polyfluoronaphthalenes based on quantita-
tive conversion of 3.
Fe
C10Cl8F835!0 ꢁCC10F8 þ C10ClF7 þ C10Cl2F6
(3)
3
The yields of polyfluoroarenes were not optimized. How-
ever, the results obtained together with the recent availability
of the starting materials 1–3 demonstrate the possibility of
an alternative preparation of polyfluoroarenes from per-
chloroarenes.
Reaction of tetrachloropentafluoro-1-azacyclohexenes (2)
with commercial zinc dust in refluxed THF was complete
within 3 h and gave a mixture of pentafluoropyridine, 2-, 3-
and 4-chlorotetrafluoropyridines, 2,4- and 2,5-dichlorotri-
2.2. Dehalogenation in solution
Table 1
Dehalogenation of C6Cl6F6 (1) with zinc (80 8C, 5 h)
For a complete picture of the dehalogenation of 1, 2 and 3
under the different conditions, their reactions in the liquid
phase with zinc reagent or tris(diethylamino)phosphine were
studied.
Entry
Solvent
Yield (%) based on 1a
1
2
3
4
5
6
Sulfolaneb
Sulfolanec
Diglymec
DMAd
C6F6 (27), C6ClF5 (39), C6Cl2F4 (7)
C6F6 (35), C6ClF5 (42), C6Cl2F4 (7)
C6F6 (30), C6ClF5 (40), C6Cl2F4 (5)
C6F6 (34), C6ClF5 (44), C6Cl2F4 (7)
C6F6 (31), C6ClF5 (41), C6Cl2F4 (10)
C6F6 (30), C6ClF5 (34), C6Cl2F4 (5), C6F5H (12)
2.2.1. Dehalogenation with zinc dust
DMAe
In many cases, the quality of zinc affects significantly on
the result of dehalogenation [1]. We compared reaction of 1,
2 and 3 with commercial zinc dust, zinc dust pre-treated with
SOCl2, zinc dust dopped with freshly precipitated copper
(Zn/Cu), and zinc dust activated with complex (NiCl2ꢀ6H2O
þ bpy).
DMFd
a Determined by GLC.
b Zinc was activated with SOCl2.
c Zinc was activated with CuSO4.
d Zinc was activated with complex (NiCl2ꢀ6H2O þ bpy), 4 h.
e Zinc was activated with complex (NiCl2ꢀ6H2O þ phen), 4 h.

V.V. Bardin et al. / Journal of Fluorine Chemistry 125 (2004) 1431–1435
1433
Table 2
Dehalogenation of C5Cl4F5N (2) with zinc (80 8C, 5 h)
2.2.2. Dehalogenation with P(NEt2)3
The dehalogenations with zinc proceed under hetero-
geous conditions, and the observed domination of chloro
containing polyfluoroarenes could arise from the formation
of zinc difluoride, which is insoluble in organic solvents.
Trying to increase yield of perfluorinated arenes, we stu-
died the reaction of 1 and 3 with tris(diethylamino)pho-
sphine. Recently the latter was used successfully for
dehalogenation of some aliphatic perhalofluoroalkanes
RFCFXCYZR0F (X, Y, Z ¼ Cl, Br, I) [19], CF2BrCF2Br
[20] and 1,1,2-tribromopentafluorocyclobutane [19] to the
corresponding polyfluoroalkenes. Dehalofluorination did
not occur in any case.
Entry
Solvent
Yield (%) based on 2a
1
2
3
4
Sulfolaneb
Sulfolanec
Diglymec
DMAd
C5F5N (30), 2-C5ClF4N (8), 3-C5ClF4N (38)
C5F5N (38), 2-C5ClF4N (8), 3-C5ClF4N (34)
C5F5N (29), 2-C5ClF4N (9), 3-C5ClF4N (33)
C5F5N (34), 2-C5ClF4N (10), 3-C5ClF4N (36)
a Determined by GLC.
b Zinc was activated with SOCl2.
c Zinc was activated with CuSO4.
d Zinc was activated with complex (NiCl2ꢀ6H2O þ bpy), 4 h.
fluoropyridines in overall yield 80% although the yield of
C5F5N was only 18%. The use of zinc activated with SOCl2
in sulfolane 2 effected a higher yield of pentafluoropyridine
(30%), while dichlorotrifluoropyridines were not found
among products (Eq. (5)) (Table 2, entry 1).
However, the reaction of C6Cl6F6 with P(NEt2)3
(5–6 equivalents) in polar aprotic solvents (HMPA or
diglyme) gave hexafluorobenzene in lower yield than by
dehalogenation with zinc; chloropentafluorobenzene and
dichlorotetrafluorobenzene were major products besides
pentafluorobenzene (Eq. (7)). The reaction pathway was
not analysed but the 19F NMR spectrum of the final reaction
mixture (in diglyme) contained a signal assigned to
Zn
!
C5Cl4F5N
2
C5F5N þ 2-C5ClF4N þ 3-C5ClF4N (5)
80 ꢁC;4À5 h
Dehalogenation of 2 with zinc dust dopped with freshly
precipitated copper in sulfolane (Table 2, entry 2), in
diglyme (Table 2, entry 3) as well as with zinc and complex
(NiCl2ꢀ6H2O þ bpy) in DMA (Table 3, entry 4) gave the
same polyfluoropyridines in similar yields (Eq. (5)).
Similarly to 1 and 2, the results of dehalogenation of
octachlorooctafluorobicyclo[4.4.0]dec-1(6)-enes (3) were
practically independed of the method used to activate zinc.
Thus, reaction of 3 with zinc activated with SOCl2 in
sulfolane (Table 3, entry 1), with freshly precipitated copper
in sulfolane (Table 3, entry 2) or in diglyme (Table 3, entry
3) and with complex (NiCl2ꢀ6H2O þ bpy) in DMA (Table 3,
entry 4) led to the formation of octafluoronaphthalene (6–
9%), 1-chloroheptafluoronaphthalene (9–10%), 2-chloro-
heptafluoronaphthalene (18–19%) and dichlorohexafluoro-
naphthalenes (isomer mixture) (33–37%) (Eq. (6)).
1
P(NEt2)3FCl (d ¼ À79.3 ppm, d, JFP ¼ 955 Hz) beside
resonances due to polyfluorobenzenes.
PðNEt2Þ3
C6Cl6F6HMPA;20 ꢁC;1 h
!
C6F6 þ C6ClF5 þ C6Cl2F4 þ C6F5H
18% 32% 14% 7%
(7)
Dehaloganation of C10Cl8F8 with P(NEt2)3 in dichloro-
methane proceeded in a similar way to form octafluoro-
naphthalene (16%), chloroheptafluoronaphthalenes (42%),
dichlorohexafluoronaphthalenes (24%) and trichloropenta-
fluoronaphthalenes (15%) (Eq. (8)).
PðNEt2Þ3
CH2Cl2;20 ꢁC;1 h
C10Cl8F8
!
C10F8 þ C10ClF7 þ C10Cl2F6
þ C10Cl3F5 (8)
Zn
C10Cl8F880 ꢁ4À5 h
!
C10F8 þ 1-C10ClF7 þ 2-C10ClF7
The picture obtained of dehalogenation of hexachlo-
rohexafluorocyclohexanes (1), tetrachloropentafluoro-1-
azacyclohexenes C5Cl4F5N (2) and octachlorooctafluorobi-
cyclo[4.4.0]dec-1(6)-enes (3) either in the vapour phase over
iron filings or in solutions with zinc or with tris(diethyla-
mino)phosphine showed the facile conversion of these
perhalogenated materials in perfluorinated and chlorofluori-
nated arenes. It should be noted that 1, 2 and 3 are mixtures
of cis and trans isomers with –CFCl–CFCl– fragments and,
probably, of isomers with –CF2–CCl2– fragments [13].
Despite this circumstance, dehalogenation of 1–3 under
significantly different conditions is characterised by a
remarkable similarity. Thus, dehalogenation of 1 in the
vapour phase over heated iron and in the liquid phase with
zinc and additivities gave closely related yields of hexa-
fluorobenzene, chloropentafluorobenzene and dichlorotetra-
3
þ C10Cl2F6
(6)
Table 3
Dehalogenation of C10Cl8F8 (3) with zinc (80 8C, 8 h)
Entry
1
Solvent
Yield (%) based on 3a
Sulfolaneb
C10F8 (9), 1-C10ClF7 (10), 2-C10ClF7
(19), C10Cl2F6 (33)
2
3
4
Sulfolanec
Diglymec
DMAd
C10F8 (6), 1-C10ClF7 (9), 2-C10ClF7 (19),
C10Cl2F6 (37)
C10F8 (7), 1-C10ClF7 (10), 2-C10ClF7
(19), C10Cl2F6 (34)
C10F8 (7), 1-C10ClF7 (9), 2-C10ClF7 (18),
C10Cl2F6 (35)
a Determined by GLC.
fluorobenzenes. A similar situation is observed for
dehalogenation of 2 and 3 with iron and zinc. Dehalogena-
tion with P(NEt2)3 gave a somewhat different molar ratio of
b Zinc was activated with SOCl2.
c Zinc was activated with CuSO4.
d Zinc was activated with complex (NiCl2ꢀ6H2O þ bpy), 6 h.

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V.V. Bardin et al. / Journal of Fluorine Chemistry 125 (2004) 1431–1435
perhalogenated arenes derived from 1 and 3. Unlike the
metal used, P(NEt2)3 can react partially with intermediate
cycloalkenes at the C–F and C–Cl bonds of olefinic moiety
[21] to decrease yields of desirable polyfluoroarenes.
43, 11–12 and 43–45% yield, respectively (GLC). Identifi-
cation of 2-C5ClF4N and 3-C5ClF4N and determination of
their molar ratio was performed by the 19F NMR spectro-
scopy [23].
3.1.3. Dehalogenation of
3. Experimental
octachlorooctafluorobicyclo[4.4.0]dec-1(6)-enes (3)
Vapour-phase dehalogenation of 3 (2.3 g, 4 mmol) at
350 8C gave C10F8, C10ClF7 and C10Cl2F6 in 7–9, 39–40
and 46–48% yield, respectively (GLC).
19F NMR spectra were measured on a BRUKER WP 200
SY spectrometer at 188.28 MHz in CDCl3. The chemical
shifts are referenced to CCl3F with C6F6 as secondary
reference (À162.9 ppm). GC–MS analyses were performed
on Hewlett Packard G1800A and Hewlett Packard GS6890
instruments. GLC analyses were performed on LKhM 72
chromatograph (25% SKTFT-50 on chromosorb W, gas-
carrier He, 60 mL per min).
Organic solvents (DMF, DMA, THF, HMPA, sulfolane,
diglyme, dioxan and dichloromethane) were purified by
standard procedures. Zinc dust (purum), NiCl2ꢀ6H2O
(purum), 1,10-phenanthroline (phen) (purum for analysis)
and 2,20-bipyridyl (bpy) (Aldrich) were used as supplied.
Tris(diethylamino)phosphine was prepared from PCl3 and
HNEt2 in hexane [22] and distilled in vacuum. Thionyl
chloride was freshly distilled before use. Preparation of 1,
2 and 3 was described in reference [13]. If not specified
otherwise, the compositions of isomer mixtures of C6Cl2F4,
C5ClF4N, C5Cl2F3N, C10ClF7, C10Cl2F6 and C10Cl3F5, were
not determined.
3.2. Dehalogenation of 1, 2 and 3 in solution
3.2.1. Dehalogenation of 1 with zinc dust
Zinc dust (80 g, 1.23 mol) and dioxan (150 mL) were
charged into a 1 L three-necked flask equipped with stirrer,
reflux condenser and dropping funnel and were heated to
reflux. Then solution of C6Cl6F6 (20 g, 50 mmol) in dioxan
(20 mL) was added dropwise within 1 h. After 10 h, GLC
monitoring showed the total consumption of 1. The hot
reaction mixture was filtered under a slight pressure of argon
to prevent losses of volatile fluorinated benzenes and the
filtrate was diluted with water (1 L). The organic phase was
separated and dried with MgSO4 to give a mixture of 6.5 g of
C6F6, C6ClF5 and C6Cl2F4 (yields 14, 32 and 10%, respec-
tively) (GLC).
3.2.2. Dehalogenation of 2 with zinc dust
Zinc dust (1.0 g, 15 mmol) and THF (5 mL) were heated
to reflux with stirring. A solution of C5Cl4F5N (1.4 g,
4.5 mmol) in THF (1 mL) was added dropwise and the
reaction mixture was stirred under reflux for 3 h. After
cooling to 22–25 8C, the formation of C5F5N (18%), 2-
C5ClF4N (11%), 3-C5ClF4N (27%), 4-C5ClF4N (4%), 2,4-
C5Cl2F3N (2%), and 2,5-C5Cl2F3N (18%) was detected by
19F NMR spectroscopy [23] (yields were determined using a
quantitative internal reference C6H5CF3).
3.1. Dehalogenation of 1, 2 and 3 in the vapour phase
A quartz tube (30 mm diameter, 750 mm length) equipped
with an internal quartz pocket for a thermocouple, pressure
equilized dropping funnel with nitrogen inlet on top and with
two sequentally connected traps cooled with ice and liquid
nitrogen, respectively, was charged with iron filings (0.2–
1 mm size) and placed into a vertical cylindric electric
furnace. The reactor was flushed with nitrogen (100–
150 mL per min) at 400 8C for 2 h and then at the working
temperature for 20–30 min. Dehalogenation was performed
by an addition of 1 (2 or 3) under a slight pressure of nitrogen
(2–5 mL per min) (time of contact ꢃ25 s). At the end, the
reactor was flushed with nitrogen (10–15 mL per min) for
10–15 min. Products from both traps were combined,
weighed and analysed by GLC.
3.2.3. Dehalogenation of 1, 2 and 3 with zinc activated
with SOCl2
Zinc dust (n ꢄ 15 mmol; n ¼ 6, 8 and 4 for C6Cl6F6,
C10Cl8F8 and C5Cl4F5N, respectively) and sulfolane
(10 mL) were charged into a three-necked flask equipped
with magnetic stirrer, reflux condenser, thermometer and
dropping funnel. With vigorous stirring, thionyl chloride
(0.1 mL) was added. After 30 min, C6Cl6F6 (1) (10 mmol)
was added and stirred at 80 8C till consumption of 1 (19F
NMR). The reaction mixture was cooled to 20–25 8C,
filtered and diluted with water. Products were steam dis-
tilled, the organic phase was separated, dried with MgSO4
and analysed by GLC (Table 1, entry 1). C5Cl4F5N (2)
(Table 2, entry 1) and C10Cl8F8 (3) (Table 3, entry 1) were
dehalogenated in a similar way. In the latter case, after steam
distillation polyfluoronaphthalenes were extracted with
ether, the extract was dried and solvent was removed under
reduced pressure.
3.1.1. Dehalogenation of
hexachlorohexafluorocyclohexanes (1)
Vapour-phase dehalogenation of 1 (2.0 g, 5 mmol) at
500 8C gave C6F6, C6ClF5 and C6Cl2F4 in 30–32, 40–42
and 4–6% yield, respectively (GLC).
3.1.2. Dehalogenation of tetrachloropentafluoro-1-
azacyclohexenes C5Cl4F5N (2)
Vapour-phase dehalogenation of 2 (1.6 g, 5 mmol) at
500 8C gave C5F5N, 2–C5ClF4N and 3–C5ClF4N in 40–

V.V. Bardin et al. / Journal of Fluorine Chemistry 125 (2004) 1431–1435
1435
3.2.4. Dehalogenation of 1, 2 and 3 with zinc activated
with CuSO4
3.2.8. Dehalogenation of 3 with
tris(diethylamino)phosphine
Zinc dust (n ꢄ 15 mmol; n ¼ 6, 8 and 4 for C6Cl6F6,
C10Cl8F8 and C5Cl4F5N, respectively) and sulfolane or
diglyme (10 mL) were charged into a three-necked flask
equipped with magnetic stirrer, reflux condenser, thermo-
meter and dropping funnel. Under vigorous stirring, anhy-
drous CuSO4 (n ꢄ 1.5 mmol) was added. The further
manipulations were performed as above (see 3.2.3)
(Tables 1–3, entries 2 and 3).
P(NEt2)3 (2.3 g, 9.3 mmol) was added dropwise into a
stirred solution of C10Cl8F8 (1.0 g, 1.8 mmol) in CH2Cl2
(10 mL) under cooling with cold water (5–10 8C). The
formed solution was stirred at 20–25 8C for 1 h, washed
with concentrated H2SO4 (3 mL), water and dried with
CaCl2. Solvent was distilled off and 0.6 g of a mixture of
C10F8 (16%), C10ClF7 (13 and 29%), C10Cl2F6 (7 and 17%)
and C10Cl3F5 (4, 5 and 6%) was obtained (yields of isomers
were determined by GC–MS).
3.2.5. Dehalogenation of 1, 2 and 3 with zinc activated
with complex (NiCl2ꢀ6H2O þ bpy)
References
NiCl2ꢀ6H2O (120 mg, 0.5 mmol), 2,20-bipyridyl (bpy)
(78 mg, 0.5 mmol) and anhydrous DMF (or DMA)
(10 mL) were charged into a three-necked flask equipped
with magnetic stirrer, reflux condenser, thermometer and
dropping funnel. Reaction mixture was stirred at 80 8C for
30–40 min until green solution was formed. Addition of zinc
dust (n ꢄ 15 mmol; n ¼ 6, 8 and 4 for C6Cl6F6, C10Cl8F8 and
C5Cl4F5N, respectively) caused the deep coloration of solu-
tion after that substrate 1 (2 or 3) (10 mmol) was added in
one portion. The further manipulations were performed as
above (see 3.2.3). Composition of products was determined
by GC–MS and 19F NMR spectroscopy (Tables 1–3).
ˇ
[1] J. Kvicala, O. Paleta, Dehalogenation, in: B. Baasner, H. Hagemann,
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(1962) 267–271.
3.2.6. Dehalogenation of 1 with zinc activated with
complex (NiCl2ꢀ6H2O þ phen)
[9] R.D. Chambers, J. Heyes, W.K.R. Musgrave, Tetrahedron 19 (1963)
891–900.
Reaction was performed as mentioned above (3.2.5) using
phen (0.5 mmol) instead of bpy (Table 1, entry 6).
[10] G.M. Brooke, R.D. Chambers, J. Heyes, W.K.R. Musgrave, J. Chem.
Soc. (1964) 729–733.
[11] L.A. Bigelow, J.H. Pearson, J. Am. Chem. Soc. 56 (1934) 2773–
2774.
3.2.7. Dehalogenation of 1 with
tris(diethylamino)phosphine
[12] V. Grakauskas, J. Org. Chem. 34 (1969) 2835–2839.
[13] V.V. Bardin, S.G. Bardina, J. Fluorine Chem. 125 (2004) 1411–1414.
[14] D.V. Trukhin, N.Yu. Adonin, V.F. Starichenko, Zh. Org. Khim. 38
(2002) 942–943;
3.2.7.1. In HMPA. Solution of P(NEt2)3 (18.5 g, 75 mmol)
in HMPA (20 mL) was added dropwise into a stirred solution
of C6Cl6F6 (5.0 g, 12.5 mmol) in HMPA (20 mL) under
cooling with cold water (5–10 8C). The formed solution
was stirred at 20–25 8C for 1 h, diluted with water (40 mL),
and products were steam distilled. The organic phase was
separated and dried with MgSO4 to give 1.65 g a mixture of
C6F6, C6ClF5, C6Cl2F4 and C6F5H (yields 18, 32, 14 and 7%,
respectively) (19F NMR, quantitative internal reference
C6H5CF3).
D.V. Trukhin, N.Yu. Adonin, V.F. Starichenko, Russ. J. Org. Chem.
38 (2002) 900–901. English Translation.
[15] D.V. Trukhin, N.Yu. Adonin, V.F. Starichenko, Zh. Org. Khim. 36
(2000) 143–144;
D.V. Trukhin, N.Yu. Adonin, V.F. Starichenko, Russ. J. Org. Chem.
36 (2000) 132–133. English Translation.
[16] D.V. Trukhin, N.Yu. Adonin, V.F. Starichenko, Zh. Org. Khim. 36
(2000) 1261–2162;
D.V. Trukhin, N.Yu. Adonin, V.F. Starichenko, Russ. J. Org. Chem.
36 (2000) 1227–1228. English Translation.
[17] N.Yu. Adonin, V.F. Starichenko, J. Fluorine Chem. 101 (2000) 65–
67.
3.2.7.2. In diglyme. Solution of P(NEt2)3 (17.0 g,
68 mmol) in diglyme (20 mL) was added dropwise into
a stirred solution of C6Cl6F6 (5.1 g, 12.7 mmol) in diglyme
(30 mL) under cooling with cold water (5–10 8C). The
formed solution was stirred at 20–25 8C for 1 h. The 19F
NMR showed the presence of C6F6, C6ClF5, and
C6F5H (yields 14, 56, and 15%, respectively) beside
P(NEt2)3ClF (ca. 30% yield) (quantitative internal
reference C6H5CF3).
[18] N.Yu. Adonin, V.F. Starichenko, Mendeleev Commun. (2000) 60–61.
[19] V. Montanari, D. DesMarteau, J. Org. Chem. 57 (1992) 5018–5019.
[20] V.V. Bardin, Synth. Commun. 23 (1993) 1409–1413.
[21] V.V. Bardin, L.S. Pressman, V.F. Cherstkov, Synth. Commun. 25
(1995) 2425–2433.
[22] C. Stuebe, H.P. Lankelma, J. Am. Chem. Soc. 78 (1956) 976–977.
[23] S. Berger, S. Braun, H.-O. Kalinowski, NMR-Spektroskopie von
Nichtmetallen. Bd 4. 19F-NMR-Spektroskopie. Thieme, Stuttgart,
1994, S. 50.