Fluorine addition to polychlorinated and polybrominated ethenes and arenes using vanadium pentafluoride

Article abstract of DOI:10.1016/j.jfluchem.2004.01.013

Reaction of vanadium pentafluoride with trichloroethene, tetrabromoethene, hexachlorobenzene, and octachloronaphthalene at -20 to 50°C gave products from fluorine addition, CFCl₂CFClH, C₂Br₄F₂, C₆Cl

Full text of DOI:10.1016/j.jfluchem.2004.01.013

Journal of Fluorine Chemistry 125 (2004) 1411–1414
Fluorine addition to polychlorinated and polybrominated ethenes
and arenes using vanadium pentafluoride
Vadim V. Bardin*, Svetlana G. Bardina
N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Academy Lavrentjev Avenue 9, 630090 Novosibirsk, Russia
Received 21 October 2003; received in revised form 12 December 2003; accepted 18 January 2004
Available online 25 August 2004
Abstract
Reaction of vanadium pentafluoride with trichloroethene, tetrabromoethene, hexachlorobenzene, and octachloronaphthalene at ꢀ20 to
50 8C gave products from fluorine addition, CFCl2CFClH, C2Br4F2, C6Cl6F6, and C10Cl8F8, respectively. The fluorine addition to
pentachloropyridine and hexabromobenzene was accompanied by the partial replacement of halogen atoms by fluorine and led to products
C5Cl4F5N and C6Br4F8, respectively.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Hexachlorobenzene; Octachloronaphthalene; Pentachloropyridine; Trichloroethene; Hexabromobenzene; Tetrabromoethene; Vanadium penta-
fluoride; Fluorine addition
1. Introduction
polychloropolyfluorocyclohexenes and/or polychloropoly-
fluorocyclohexanes which contained less than six chlorine
atoms. Similarly, both parallel fluorine addition and F for Cl
substitution occurred in reaction of polychloro- and poly-
chlorofluoroalkenes with elemental fluorine, very often
accompanied by oligomerisation of olefins [10].
Taking into account these circumstances, we studied the
reaction of vanadium pentafluoride with trichloroethene (1),
tetrabromoethene (2) and a series of perhalogenated arenes:
hexachlorobenzene (3), octachloronaphthalene (4), penta-
chloropyridine (5) and hexabromobenzene (6).
Vanadium pentafluoride is a powerful fluorinating agent
which had been used for the fluorine addition to polyfluori-
nated arenes, alkenes and cycloalkenes (see reviews [1,2]).
In general, these reactions has been carried out in chloro-
fluorocarbons or SO2FCl under mild conditions. Reactions
of VF5 with poly- and perchlorinated and perbrominated
olefins and arenes have been less investigated. Thus, an
addition of fluorine atoms to tetrachloroethene and hexa-
chloro-1,3-butadiene resulted in the formation of 1,2-
difluorotetrachloroethane and a mixture of two tetrafluor-
ohexachlorobutanes, respectively [3] (Eqs. (1) and (2)).
2. Results and discussion
CCl2¼¼CCl2 þ 2VF5 ! CFCl2CFCl2 þ 2VF4
CCl2¼¼CClCCl¼¼CCl2 þ 4VF5 ! CFCl2CFClCFClCFCl2
þ CF2ClCCl2CFClCFCl2 þ 4VF4 (2)
No replacement of chlorine atom(s) by fluorine(s) took place
in either case. Moreover, fluorine addition to halopentafluor-
obenzenes C6F5X (X: Cl, Br, I) proceeded without C–X
bond cleavage and gave halo-undecafluorocyclohexanes
C6F11X as final products [1]. In contrast, reactions of hexa-
chlorobenzene with elemental fluorine [4–6], chlorine tri-
fluoride [7], CoF3 [8] or SbF5 [9] always lead to a mixture of
(1)
We have found that trichloroethene reacted easily with
vanadium pentafluoride at ꢀ10 to 10 8C without solvent to
give 1,2,2-trichloro-1,2-difluoroethane (7). The formation of
significant amounts of 1,1-difluorotrichloroethane or highly
fluorinated products were not detected (Eq. (3)).
CCl2¼¼CHCl þ 2VF5ꢀ10 to 10 ꢁ
!
CFCl2CHClF þ 2VF4
(3)
C
7
1
Unlike olefin 1, contact of tetrabromoethene 2 with liquid
VF5 caused a vigourous uncontrolled reaction. Therefore,
the fluorination was performed by an addition of VF5
dissolved in CFCl3 into a stirred suspension of 2 in CFCl3
at ꢀ25 8C. After 20 min stirring at ꢀ10 8C olefin 2 was
* 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).
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.01.013

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V.V. Bardin, S.G. Bardina / Journal of Fluorine Chemistry 125 (2004) 1411–1414
converted in 1,2-difluorotetrabromoethane (8a) and 1,1-
difluorotetrabromoethane (8b) (1:1) (ca. 50% conversion)
(Eq. (4)).
indicated the absence of the –CX¼¼CY– (X, Y: F, Cl)
moieties in molecule (cf. with IR spectra of perfluorinated
bicyclo[4.4.0]-1(2), -2 and -3-decene isomers [14]). Based
on the IR spectrum, analytical data and molecular mass
determination, product 10 was identified as octachloroocta-
fluorobicyclo[4.4.0]-1(6)-decene (a mixture of isomers
with cis- and trans-CFCl–CFCl and, probably, CF2–CCl2
fragments). For comparison, the fluorination of octafluor-
onaphthalene with VF5 led to perfluorobicyclo[4.4.0]-1(6)-
decene and the residual C¼C bond remained intact toward
the fluorine addition just at 250 8C [15].
CFCl3
CBr2¼¼CBr2 þ 2VF5ꢀ25 to ꢀ10 ꢁ CFBr2CFBr2 þ CF2BrCBr3
!
C
2
8a
8b
þ 2VF4
(4)
Easy fluorine addition to perchlorinated benzene, naphtha-
lene, pyridine and hexabromobenzene occurred under the
action of vanadium pentafluoride, but in every case the
reaction proceeded in a peculiar way.
Addition of VF5 (excess) in CFCl3 into stirred suspension
of hexachlorobenzene 3 in CFCl3 at 0–20 8C led to dissolu-
tion of 3 and precipitation of brown vanadium tetrafluoride.
After decantation of the liquid phase and subsequent eva-
poration of solvent and volatile VF5 (bp 48 8C), colourless
oil was obtained. It solidified within some hours to form a
glassy substance (mp 113–117 8C) which could be distilled
without decomposition at normal pressure. This substance
was also obtained by an addition of 3 to a solution of VF5 in
CF2ClCFCl2 or by the reaction with liquid vanadium
pentafluoride under reflux. Taking into account results of
fluorine addition to halogenated olefins CCl2¼¼CCl2,
CCl2¼¼CClCCl¼¼CCl2 [3], CCl2¼¼CHCl and CBr2¼¼CBr2,
we assumed the formation of hexachlorohexafluorocyclo-
hexanes (9) (Eq. (5)).
C2Cl3F3
C10Cl8 þ 8VF545ꢀ50 ꢁC
!
C10Cl8F8 þ 8VF4
(6)
4
10
While the fluorine addition to perhaloethenes 1, 2 and
perchloroarenes 3 and 4 gave compounds with the same
numbers of chlorine atoms as their precursors, the reaction
of pentachloropyridine 5 with vanadium pentafluoride in
C2Cl3F3 gave in the less chlorinated tetrachloropentafluoro-
1-azacyclohexenes C5Cl4F5N (11) (Eq. (7)). The 19F NMR
spectrum of 11 is very complex, although the resonances at
ꢀ38 to ꢀ60 ppm indicate the presence of N¼¼CF, CFCl–
N¼¼C and CF2–N¼¼C moieties [16]. This is not contradict to
results deduced from the IR spectrum where bands at
1746 cmꢀ1 (N¼¼CF) and 1677 cmꢀ1 (N¼¼CCl) are pre-
sented. Evidently, the IR spectrum of product C5Cl4F5N
obtained by the photochemical chlorination of pentafluor-
opyridine contains the band at 1734 cmꢀ1 (N¼¼CF) [17].
CFCl3 or C2Cl3F3
!
C6Cl6 þ 6VF5
C6Cl6F6 þ 6VF4
(5)
0 to 50 ꢁC
3
9
C2Cl3F3
1
2
C5Cl5N þ 5VF545ꢀ50 ꢁC
!
C5Cl4F5N þ 5VF4 þ Cl2
(7)
Indeed, analytical data (contents of C, Cl, F) and the
molecular mass determination of 9 correspond to C6Cl6F6.
Neither the less or the highly fluorinated compounds
C6ClnF12ꢀn, C6ClnF10ꢀn (n ¼ 6) were detected by GC–
MS analysis of 9. Infrared spectrum of 9 does not contain
bands at 1600–1750 cmꢀ1 due to the C¼C bond of poly-
halogenated cyclohexadienes and cyclohexenes. The 19F
NMR spectrum of 9 is too complex for analysis and contains
the numerous resonances at ꢀ80 to ꢀ140 ppm (cf. with
spectra of polychloropolyfluorocyclopentanes [11]). The
13C NMR spectrum of 9 displayed signals between 108
and 120 ppm (CFCl and CF2 moieties) and the resonance at
90 ppm which was assigned to CCl2 fragment of polyhalo-
genated carbon chain [12]. Because GC–MS analysis of 9
showed the presence at least four components with the close
retention times, product 9 was assumed to be a mixture of
isomers C6Cl6F6 with cis- and trans-CFCl–CFCl and CF2–
CCl2 fragments. Noteworthy, that compounds C6Cl6F6 were
previously isolated from the reaction mixtures obtained by
the fluorination of 3 with elemental fluorine [4–6], ClF3 [7],
or CoF3 [8] or prepared by the chlorine addition to C6F6
under UV irradiation [13]. In any cases, these products were
characterised only by analytical data (C, Cl, F) and melting
and/or boiling points [6,7,13].
5
11
An addition of six fluorine atoms as well as replacement of
two bromine atoms by fluorine atoms, took place in reaction
of hexabromobenzene 6 with vanadium pentafluoride
(excess) which gave tetrabromooctafluorocyclohexanes
(12) (Eq. (8)).
C6Br6 þ 8VF55!0 ꢁ C6Br4F8 þ 8VF4 þ Br2
(8)
C
6
12
In contrast to perhalogenated arenes 3, 4, 5 and 6, com-
pounds 9–12 are readily soluble in CFCl3, CF2ClCFCl2 and
in common organic solvents (pentane, hexane, benzene,
acetone, ethanol, ether, diglyme, THF, dioxane, MeCN
and DMF), partially chlorinated hydrocarbons (CH2Cl2,
CHCl3, CH2ClCH2Cl) and perhalocarbons (CCl4, CF2-
BrCF2Br, C6F6, C6F5Cl).
3. Experimental
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 (ꢀ162.9 ppm). IR spectra were recorded on a
BRUKER Vector 22 spectrometer. GC-MS analyses were
performed on HEWLETT-PACKARD G1800A and HEW-
LETT-PACKARD GS6890 instruments.
Reaction of octachloronaphthalene 4 with VF5 in C2Cl3F3
gave the product of composition C10Cl8F8 (10) (Eq. (6)). The
absence of bands at 1600–1750 cmꢀ1 in the IR spectrum

V.V. Bardin, S.G. Bardina / Journal of Fluorine Chemistry 125 (2004) 1411–1414
1413
Hexachlorobenzene, trichloroethene, hexabromobenzene,
CFCl3 and CF2ClCFCl2 were commercial products. Octa-
chloronaphthalene (94%) and pentachloropyridine (94%)
were prepared in Novosibirsk Institute of Organic Chem-
istry. Tetrabromoethene was purified by crystallisation from
ethanol. Vanadium pentafluoride (Siberian Chemical Enter-
prise, Russia) was prepared by fluorination of vanadium with
elemental fluorine at 300–350 8C and distilled over NaF
before use. All manipulations with VF5 were performed in a
Pyrex equipment under atmosphere of dry argon.
Vanadium tetrafluoride formed in above reactions was
fine brown powder (Anal. Calcd. for VF4: F, 59.9. Found: F,
59.2). It dissolved rapidly in water yielding an acidic solu-
tion with the characteristic rich blue colour of vanadium(IV)
[18].
Residue was extracted with 1,1,2-trichlorotrifluor-
oethane (2 ꢂ 250 ml) and combined extracts were
evaporated. Initially formed colourless oil was solidified
within some hours to yield glassy product 9 (152 g,
76%). Yield of VF4 was 384 g (3.0 mol).
2. Hexachlorobenzene (6 g, 0.021 mol) was added to
refluxed (bp 48 8C) vanadium pentafluoride (36 g,
0.24 mol) under stirring. The reaction mixture was kept
at 50 8C (bath) for 1.5 h, cooled below 30 8C and reflux
condenser was replaced with distillation head. Excess of
VF5 (14 g) was distilled-off and residue was extracted
with 1,1,2-trichlorotrifluoroethane (2 ꢂ 40 ml). After
evaporation of C2Cl3F3 from the combined extracts,
initially formed, a colourless oil was solidified within
3 h to yield glassy product 9 (6.2 g, 74%). Yield of VF4
was 21 g.
3.1. Fluorination of trichloroethene (1)
3. Solution of VF5 (277 g, 1.9 mol) in CFCl3 (180 ml) was
added dropwise into stirred suspension of hexachlor-
obenzene (55 g, 0.19 mol) in CFCl3 (400 ml) at 0–
20 8C. The reaction mixture was stirred at 20–24 8C for
3 h and cooled to 0–4 8C. Vanadium tetrafluoride was
filtered-off and washed with CFCl3 (20 ml). Solvent (bp
24 8C) and excess of VF5 (91 g, 83%) were evaporated
to give 9 (62 g, 81%). Yield of VF4 was 148 g.
Trichloroethene (8.2 g, 0.062 mol) was added dropwise to
vanadium pentafluoride (32 g, 0.22 mol) at ꢀ10 to 10 8C
under stirring. The reaction mixture was kept at 0–5 8C for
30 min and all volatile product were distilled into receiver
filled with ice water. The organic layer was separated,
washed with water and dried with MgSO4. The colourless
liquid obtained (5.2 g) contained 80% of trichlorodifluor-
oethane 7 (19F NMR) beside unknown components (content
of each did not exceed 2–5%).
Hexachlorohexafluorocyclohexanes (9): mp 113–
117 8C (lit. mp 94–96 8C [6], 101–102 8C [13]), bp
241 8C (lit. bp 137 8C at 30 mmHg [7], 248 8C [13]).
Anal. Calcd. for C6Cl6F6: M 399; C, 18.0; Cl, 53.3; F,
28.6. Found: M 399; 402 (in CHCl3); C, 18.0; Cl, 53.0;
F, 29.2. IR (CCl4): n 1229, 1197, 1178, 1147, 1128,
1100, 1074, 1044, 977, 959, 905, 890, 841, 826, 803,
3.2. Fluorination of tetrabromoethene (2)
Solution of VF5 (38 g, 0.26 mol) in CFCl3 (50 ml) was
added to cold (ꢀ25 8C) stirred suspension of tetrabro-
moethene (34.4 g, 0.10 mol) in CFCl3 (100 ml) within
20 min. After additional 20 min stirring at ꢀ10 8C, the
reaction mixture was poured onto ice cooled with liquid
nitrogen. Red organic phase was separated and aqueous one
was extracted with CFCl3 (30 ml). Combined extract was
washed with aqueous K2S2O5, with water and dried with
CaCl2. Solvent was distilled off to give a liquid (34.4 g)
which contained C2Br4 (52%) and C2Br4F2 (43%) (GLC).
The 19F NMR spectrum displayed two single resonances at
ꢀ55.8 ppm (olefin 8a) and ꢀ64.7 ppm (olefin 8b) of equal
intensity. GC–MS analysis showed the presence of two
isomers C2Br4F2 [Mþ 378 (79Br)] with the different frag-
mentation routes beside olefin 2.
792, 768, 749, 730, 712, 619 cmꢀ1
.
3.4. Fluorination of octachloronaphthalene (4)
1. Octachloronaphthalene (10 g, 0.025 mol) was added in
portions to a stirred solution of vanadium pentafluoride
(39 g, 0.27 mol) in CF2ClCFCl2 (40 ml) at the tempera-
ture below 40–45 8C. Suspension was refluxed for 3 h,
the mother liquor was decanted and residue was
extracted with CF2ClCFCl2 (3 ꢂ 20 ml). After the
evaporation of solvent and excess of VF5, product 10
(colourless oil; 11g, 85%) was obtained. Yield of VF4
was 28 g.
2. Octachloronaphthalene (8 g, 0.02 mol) was fluorinated
with VF5 (32 g, 0.22 mol) in CF2ClCFCl2 (40 ml) as
above. After cooling to 20 8C, excess of VF5 was
quenched by addition of trichloroethene (3 ml) and
formed vanadium tetrafluoride (28 g) was filtered-off.
Filtrate was evaporated to give product 10 (10 g, 92%).
Octachlorooctafluorobicyclo[4.4.0]-1(6)-decenes (10):
bp 150–160 8C (2 mmHg). Anal. Calcd. for C10F8Cl8: M
556; C, 21.6; Cl, 51.0; F, 27.3. Found: M 559, 560 (in
CHCl3); C, 21.6; Cl, 51.1; F, 26.6. IR (CCl4): n 1224,
1187, 1140, 1026, 976, 944, 864, 804, 781, 746, 712,
3.3. Fluorination of hexachlorobenzene (3)
1. A 1 l, three-necked round-bottom Pyrex flask equipped
with mechanic stirrer, thermometer and reflux condenser
was charged with vanadium pentafluoride (650 g,
4.5 mol) and 1,1,2-trichlorotrifluoroethane (300 ml).
Hexachlorobenzene (142 g, 0.5 mol) was added in small
portions so the temperature was kept below 25–30 8C.
The mixture was stirred at this temperature for 1.5 h and
volatile substances (C2Cl3F3 and VF5) were distilled-off.
621, 600 cmꢀ1
.

1414
V.V. Bardin, S.G. Bardina / Journal of Fluorine Chemistry 125 (2004) 1411–1414
3.5. Fluorination of pentachloropyridine (5)
Tetrabromooctafluorocyclohexanes (12): Anal. Calcd. for
C6Br4F8: M 544; C, 13.3; Br, 58.8; F, 28.0. Found: M 553,
556 (in CHCl3); C, 13.3; Br, 58.0; F, 28.5. IR (KBr): n 1230,
1205, 1185, 1165, 1125, 1110, 1040, 970, 955, 915, 895,
1. Pentachloropyridine (10 g, 0.025 mol) was added in
portions into stirred solution of VF5 (39 g, 0.27 mol) in
CF2ClCFCl2 (40 ml) and kept at 45–50 8C for 4 h.
Solution was decanted at 20ꢀ25 8C and precipitate was
washed with CF2ClCFCl2 (3 ꢂ 40 ml) to give vanadium
tetrafluoride (33 g). Combined extract was evaporated
and product 11 (colourless oil; 11 g, 85%) was obtained.
2. Reaction of pyridine 5 (25 g, 0.01 mol) with VF5 (89 g,
0.61 mol) in CF2ClCFCl2 (80 ml) was performed in
similar way. After cooling to 18–20 8C, excess of VF5
was reacted with trichloroethene (5 ml) to give insoluble
vanadium tetrafluoride. The reaction mixture was
filtered, cake was washed with CF2ClCFCl2
(2 ꢂ 35 ml) and combined extract was evaporated to
give product 11 (23 g, 74%). Vanadium tetrafluoride
was isolated in 90% yield (70 g).
865, 830, 790, 770, 690, 600 cmꢀ1
.
References
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Hexabromobenzene (5.5 g, 0.01 mol) was added in por-
tions to the stirred refluxed vanadium pentafluoride (30 g,
0.20 mol). The reaction mixture was refluxed for 1.5 h,
cooled to 25 8C and suspended in dichloromethane
(25 ml). Suspension was poured onto ice, brown organic
phase was separated and aqueous one was extracted
with CH2Cl2 (25 ml). Combined extract was washed in
sequence with aqueous Na2S2O5 and water and dried with
CaCl2. After evaporation of solvent, the colourless oil was
solidified within some days to give soft solid 12 (1.6 g,
29%).
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