Reactivity of antimony mixed halides for the flourination of tetrachlorethene (PCE) in liquid phase

Article abstract of DOI:10.1016/S1381-1169(98)00293-3

The active species for the liquid phase fluorination of tetrachloroethene (PCE) was produced by in situ reaction between HF and SbCl₅. By comparison with various commercial antimony mixed halides (SbCl₄F, SbCl₃F₂, SbCl₂F₃ and SbClF₄), the active species, produced in situ in our conditions, could be composed by SbCl₄F or/and SbCl₃F₂ or a mixture of both.

Full text of DOI:10.1016/S1381-1169(98)00293-3

Journal of Molecular Catalysis A: Chemical 142 Ž1999. 183–186
Reactivity of antimony mixed halides for the fluorination of
ž
/
tetrachlorethene PCE in liquid phase
)
S. Brunet , C. Batiot, P. Moriceau, N. Thybaud
UniÕersit e´ de Poitiers, Catalyse en chimie organique, UMR 6503 CNRS, 40, aÕenue du Recteur Pineau, 86022 Poitiers Cedex, France
Received 4 May 1998; received in revised form 24 August 1998
Abstract
The active species for the liquid phase fluorination of tetrachloroethene ŽPCE. was produced by in situ reaction between
HF and SbCl . By comparison with various commercial antimony mixed halides ŽSbCl F, SbCl F , SbCl F and SbClF .,
5
4
3
2
2
3
4
the active species, produced in situ in our conditions, could be composed by SbCl F orrand SbCl F or a mixture of both.
4
3 2
q 1999 Elsevier Science B.V. All rights reserved.
Keywords: Fluorination; Tetrachlorethene; Lewis acid; Antimony
1
. Introduction
value of x depends naturally on the temperature
Ž
1FxF4
. and on the amount of HF w3–9x. It is
The catalytic fluorination in liquid phase of
possible in fact that a mixture of these halides is
chloro compounds is currently carried out in
liquid hydrogen fluorine in the presence of SbCl5
w1–3x. This antimony halide is the starting mate-
obtained. The reaction is accompanied by a
reduction of Sb
Ž
V
.
into Sb
Ž
III
.
. This side reac-
III halides
tion is a major drawback because Sb
Ž
.
rial for the in situ formation of the catalyst.
are unreactive and, unless an amount of Cl is
2
For example, the preparation of CHCl CClF2
added continuously, the catalytic activity de-
creases drastically.
2
and CHCl CF involves the addition of HF on
2
3
tetrachloroethene followed by a ClrF exchange.
CCl 5CCl qHF™CHCl –CCl F
It was, therefore, interesting to use prepre-
pared antimony mixed halides and to compare
their activity, their selectivity towards the for-
mation of CF ClCHCl and their stability.
2
2
2
2
HF
HF
2
2
™
CHCl CClF ™ CHCl CF
2
2
2
3
It has been suggested that the catalyst is an
antimony mixed halide SbCl5yx Fx , nHF. The
2
. Experimental
All the experiments were carried out in a 100
ml Teflon autoclave at 908C in liquid HF at a
)
Corresponding author.
1
381-1169r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
PII: S1381-1169Ž98.00293-3

1
84
S. Brunet et al.rJournal of Molecular Catalysis A: Chemical 142 (1999) 183–186
The transformation of CFCl CHCl was also
2
2
studied under the same conditions
bar
Ž
908C, 10
.
with preprepared SbCl during 4 h.
5
3
. Results
The catalytic activity of SbCl preprepared
5
Fig. 1. Influence of the amount of HF for the in situ fluorination
with various amounts of HF for the PCE trans-
formation is reported in Fig. 1. No significant
effect of the amount of HF on the conversion of
PCE could be observed. However, a small in-
crease of the selectivity towards CHCl CClF
of SbCl5 on the conversion of PCE. SbCl s0.027 mol; PCEs
5
0
.25 mol, HFs1.3 mol; T s908C, Ps10 bar N2.
2
2
pressure of 10 bar. The catalyst was prepared,
prior to reacting PCE with HF. For this, SbCl5
and a small decrease of CHCl CCl F and of
2 2
other products down to 1 mol of HF could be
observed Fig. 2 . Below this value, all the
performances were constant. A large reduction
of Sb into Sb III can be noticed.
Ž
0.027 mol
.
was reacted with HF. After 1 h, the
Ž
.
autoclave was cooled down and vented with dry
dinitrogen in order to eliminate the HCl and the
Ž
V
.
Ž
.
HF in excess. PCE
Ž
0.25 mol
.
, and HF
Ž
1.3
To identify the active species for the fluorina-
tion of PCE under our conditions, the reactivity
of various commercial antimony mixed halides
mol were then added. The reaction was carried
.
out for 4 h at 908C under 10 bar of dinitrogen.
We checked that CF CHCl was not vented
Ž
SbFCl , SbCl F , SbCl F and SbClF was
.
3
2
4 3 2 2 3 4
under these conditions. The contents were
quenched with 20 ml 6 M H SO . The organic
tested for the transformation of the PCE. The
catalytic activity of these antimony mixed
halides was compared in Table 1 to the in situ
SbCl preprepared with HF and to SbCl with-
2
4
phase was dried and analyzed by temperature
programmed GC with a BP1 column 40 to
508C . The products were identified by GC-
MS.
Since the reaction was accompanied by a
partial reduction of Sb into Sb III , the
Ž
5
5
1
.
out prefluorination. First, the prefluorination of
SbCl5 increases the total conversion and the
selectivity towards CF ClCHCl . Similar con-
2
2
Ž
V
.
Ž
.
version and selectivities are obtained with pre-
fluorinated SbCl , SbCl F and SbCl F . The
amounts of these two species were determined
by titration of the aqueous phase. Both Sb
species were measured by atomic adsorption.
5
4
3 2
great activity and selectivity towards fluorina-
The amount of Sb III was determined by oxida-
Ž .
tion with a KMnO solution. In some cases the
4
y
residual amount of Cl was measured by titra-
tion with AgNO in the presence of K CrO .
3
2
4
In another series of experiments, the catalyst
SbCl5 or antimony mixed halides , HF 1.3
mol and PCE 0.25 mol were added sequen-
Ž
.
Ž
.
Ž
.
tially and the mixture was heated at 908C. The
reaction was carried out as mentioned above.
The different antimony mixed halides
Ž
SbFCl4,
Fig. 2. Influence of the amount of HF in the in situ fluorination of
SbCl5 on the different selectivities and on the reduction of SbŽV..
SbCl F , SbCl F and SbClF were purchased
Ž
an Elf Atochem North
America, Subsidiary with a purity )99.5.
.
4
3
2
2
3
SbCl s0.027 mol; PCEs0.25 mol, HFs1.3 mol; T s908C,
5
at the Ozarvi-Mahoning
Ps10 bar N . Others: CCl CCl , CCl CCl F, CCl CCl H,
2
3
3
3
2
3
2
.
CCl FCCl F.
2 2

S. Brunet et al.rJournal of Molecular Catalysis A: Chemical 142 (1999) 183–186
185
Table 1
Catalytic activity of different antimony mixed halides compared to SbCl5 Žwith and without prefluorination.
Othersa
Sb
3q
Catalyst
Conversion
CHCl –CClF
CHCl –CCl F
2
2
2
2
Žmolar %.
Žmolar %.
Žmolar %.
Žmolar %.
Žmolar %.
SbCl5
47
46
38
16
71
without prefluorination
SbCl5 prefluorinated
57
58
52
70
70
57
54
53
67
66
31
33
37
25
26
12
13
10
8
60
72
64
60
40
SbCl F
4
SbCl F
3
2
SbCl F
2
3
SbClF4
8
Ts908C. Ps10 bar of N . Catalysts0.027 mol. PCEs0.25 mol. HFs1.2 mol.
2
a
CCl CCl , CCl CCl F, CCl CCl H, CCl FCCl F.
3
3
3
2
3
2
2
2
Table 2
Fluorination of CFCl CHCl with SbCl5
2
2
Catalyst
SbCl5
SbŽIII. after
reaction Žmolar %.
Conversion
Žmolar %.
CCl 5CCl
Žmolar %.
CF ClCHCl
Žmolar %.
Othersa
Žmolar %.
2
2
2
2
27
98
0.3
97.7
2
SbCl s0.0135 mol, HFs0.3 mol. CFCl CHCl s0.0625 mol. HFs0.3 mol. Ts908C. Ps10 bar N .
5
2
2
2
a
CCl CCl , CCl CCl F, CCl CCl H, CCl FCCl F.
3
3
3
2
3
2
2
2
tion can be observed with the antimony mixed
halides which contain a high degree of fluorina-
products are presented in the Scheme 1. Differ-
ent mechanisms electrophilic and nucleophilic
could be involved for both reactions the addi-
tion of HF and the ClrF exchange
. w3,7,10,11x.
Ž
.
tion
Ž
SbCl F and SbClF . In every case, a
.
V
Ž
2
3
4
significant reduction of Sb
Ž
.
into Sb
Ž
III
.
oc-
curs.
But in our conditions, we could not separated
these two mechanisms.
The reactivity of preprepared SbCl5 under
the same conditions Ts908C was also tested
for the CFCl CHCl fluorination which in-
Ž
.
Under these conditions 908C, 10 bar , the
Ž .
amount of HF during the fluorination of SbCl5
did not really modify the selectivity towards
fluorination and the conversion of PCE. The
main product corresponds to the formation of
CF ClCHCl . A significant selectivity towards
2
2
volved only a ClrF exchange
Table 2 . After 4
Ž .
h of reaction, the conversion of CFCl CHCl is
2
2
9
8%, the main product being CF ClCHCl . A
2
2
reduction of Sb
noticed.
Ž
V
.
into Sb
Ž
III
.
can be also
2
2
fluorination was observed with a high degree of
fluorination of antimony SbCl F and SbClF
Ž
.
.
4
2
3
This corresponds also to the decrease of the
4
. Discussion
The fluorination of PCE with HF–SbCl in-
5
volved two reactions: the addition of HF and the
ClrF exchange to produce ClF CCHCl and
2
2
Cl FCCHCl . Other products resulting from the
2
2
addition of Cl2 and of HCl on CCl 5CCl2
2
were observed. HCl was formed ‘in situ’ during
the ClrF exchange and Cl was produced by
2
the reduction of Sb
Ž
V
.
into Sb
Ž
III
.
. All the
Scheme 1. Transformation of PCE with HF–SbCl5.

1
86
S. Brunet et al.rJournal of Molecular Catalysis A: Chemical 142 (1999) 183–186
Scheme 2. Change of the catalyst during the reaction of addition of HF on PCE.
addition of HF to CCl 5CCl , which involved
2
2
a electrophilic or a nucleophilic mechanism,
does not seem to reduce Sb . The
. ŽScheme 2
Ž
V
.
catalyst would be regenerated after the addition
of HF, without having suffered any reduction.
We suggest that the reduction of Sb
occur as described in this cycle Scheme 3 .
.
V could
Ž .
Ž
This catalytic cycle explains the formation of
Cl from antimony mixed halides. The addition
2
of Cl to CCl 5CCl favours the Sb V reduc-
Ž .
2
2
2
tion. It would be difficult to obtain a good
fluorinating activity and a good selectivity to-
Ž .
wards fluorination without a reduction of Sb V .
Scheme 3. Catalytic cycle of the reduction of SbŽV..
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lar performances to the antimony mixed halides
5
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4
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Ž
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.
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Ž
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.
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w x
S. Brunet, C. Batiot, M. Calderon, J. Mol. Catal. A: Chem.
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08 Ž1996. 11–14.
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2
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