Catalytic fluorination of trichloroethene by anhydrous hydrogen fluoride in the presence of fluorinated chromia under static conditions. Synthesis of [18F]-labelled CF3CH2F and [36Cl]-labelled CF3CH2Cl. Catalytic dehydrofluorination of CF3CH2F and CF3CH2Cl

Article abstract of DOI:10.1016/S0022-1139(99)00289-4

Catalytic fluorination of trichloroethene by anhydrous hydrogen fluoride at 653K in the presence of fluorinated amorphous chromia under static conditions leads to a mixture of products in which partially halogenated olefins predominate. These are converted to mixtures containing CF₃CH₂F and CF₃CH₂Cl by a second fluorination using fresh catalyst. The results of product analyses from reactions carried out under various conditions have been used to design a synthesis of [¹⁸F]-CF₃CH₂F from CCl₂CHCl. It is proposed that [¹⁸F] labelling occurs via direct [¹⁸F]- for [¹⁹F] exchange rather than by a dehydrofluorination/hydrofluorination route. [³⁶Cl]-labelled CF₃CH₂Cl is readily prepared from CF₃CH₂F and H³⁶Cl in the presence of chromia catalysts. Enthalpies of dehydrofluorination of CF₃CH₂F and CF₃CH₂Cl in the vapour phase have been computed.Non-SI units employed: ?=10^-10m; a.u.≈4.36×10^-18 J≈6.27089×10²kcalmol^-1.¹

Full text of DOI:10.1016/S0022-1139(99)00289-4

Journal of Fluorine Chemistry 102 (2000) 279±284
Catalytic ¯uorination of trichloroethene by anhydrous hydrogen ¯uoride
in the presence of ¯uorinated chromia under static conditions. Synthesis
of [18F]-labelled CF3CH2F and [36Cl]-labelled CF3CH2Cl. Catalytic
dehydro¯uorination of CF3CH2F and CF3CH2Cl
a
b
c
a
È
Alan W. Baker , David Bonniface , Thomas M. Klapotke , Irene Nicol ,
John D. Scottb, William D.S. Scotta, Ronald R. Spencea,
Michael J. Watsonb, Geoffrey Webba, John M. Win®elda,*
aDepartment of Chemistry, University of Glasgow, Glasgow, G12 8QQ, UK
bResearch and Technology Department, ICI Klea, The Heath, Runcorn, WA7 4QD, UK
c
È
È
È
È
Institut fur Anorganische Chemie der Universitat Munchen, D-81377 Munchen, Germany
Received 9 July 1999; received in revised form 26 July 1999; accepted 27 August 1999
Dedicated to Professor Paul Tarrant on the occasion of his 85th birthday
Abstract
Catalytic ¯uorination of trichloroethene by anhydrous hydrogen ¯uoride at 653 K in the presence of ¯uorinated amorphous chromia
under static conditions leads to a mixture of products in which partially halogenated ole®ns predominate. These are converted to mixtures
containing CF3CH2F and CF3CH2Cl by a second ¯uorination using fresh catalyst. The results of product analyses from reactions carried out
under various conditions have been used to design a synthesis of [18F]-CF3CH2F from CCl2=CHCl. It is proposed that [18F] labelling occurs
via direct [18F]- for [19F] exchange rather than by a dehydro¯uorination/hydro¯uorination route. [36Cl]-labelled CF3CH2Cl is readily
prepared from CF3CH2F and H36Cl in the presence of chromia catalysts. Enthalpies of dehydro¯uorination of CF3CH2F and CF3CH2Cl in
the vapour phase have been computed.1 # 2000 Elsevier Science S.A. All rights reserved.
Keywords: Catalytic ¯uorination; Fluorine-18; Chlorine-36; Fluorinated chromia; ab initio computation
1. Introduction
¯uorinated chromia doped with zinc or nickel(II) in the
catalytic ¯uorination of CF3CH2Cl to CF3CH2F [13]. The
reactions involved in the multi-step catalytic ¯uorination of
CCl2=CHCl are complex and under ¯ow conditions ole®nic
biproducts are normally observed due to the propensity
of CF3CH2F, CF3CH2Cl and intermediates formed in
earlier ¯uorination steps to undergo dehydro¯uorination.
In principle, conversion of CCl2FCH2Cl, formed from
CCl2CHCl ‡ HF, to CF3CH2F could occur by dehydro-
chlorination then hydro¯uorination pathways rather than
by direct F-for-Cl halogen exchange but the available evi-
dence [e.g. [1,4] suggests that the latter is preferred.
1,1,1,2-Tetra¯uoroethane is ®rmly established as an
important CFC-alternative refrigerant and, as a result, fun-
damental aspects of its catalytic synthesis from trichlor-
oethene and anhydrous hydrogen ¯uoride under
heterogeneous ¯ow conditions have been widely reported.
Chromia is the most widely-used catalyst precursor [1±5]
but other materials that have been investigated include
alumina-based aerogels [6] and ¯uorides containing alumi-
nium, chromium(III), magnesium and mixtures thereof [7±
12]. We have recently reported the behaviour of heavily
We now report the results of a study of the catalytic
¯uorination of CCl2=CHCl carried out under static condi-
tions in the presence of ¯uorinated chromia. This was
undertaken with the objective of preparing CF3CH2F and
CF3CH2Cl labelled with the radioisotopes [18F] and [36Cl],
respectively. Although the synthesis of [18F]-labelled
* Corresponding author. Tel.: ‡44-141-330-5134;
fax: ‡44-141-330-4888.
E-mail address: j.winfield@chem.gla.ac.uk (J.M. Winfield).
1 Non-SI units employed: A ˆ 10
10
18
Ê
m; a.u. ꢀ 4.36 Â 10
1
J ꢀ 6.27089 Â 102 kcal mol
.
0022-1139/00/$ ± see front matter # 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 9 9 ) 0 0 2 8 9 - 4

280
A.W. Baker et al. / Journal of Fluorine Chemistry 102 (2000) 279±284
CF3CH2F has been reported via the reactions of CF3CH2F or
CF3CH2OTs with [K(crypt)]18F [14], a synthesis based on
CCl2=CHCl would have the advantage of being applicable
also to a [14C]-labelled product. The target compounds have
been prepared and much useful information obtained con-
cerning the dehydro¯uorination behaviour of CF3CH2F and
its precursors. The results can be compared with the dis-
tribution of products obtained from catalytic ¯uorination of
CCl2=CHCl under ¯ow conditions [4].
2. Results and discussion
2.1. Product distribution studies
The distribution of products obtained from the ¯uorina-
tion of trichloroethene by anhydrous hydrogen ¯uoride,
mole ratio HF:CCl2CHCl ꢁ 4 : 1, at four different tempera-
tures in the range 373±653 K in the presence of lightly
¯uorinated amorphous chromia and under static conditions,
is shown diagrammatically in Fig. 1. Conversion of
CCl2CHCl increased with temperature and was essentially
complete at 653 K after 18 h. However, the major compo-
nents of the organic product mixture were partially ¯uori-
nated ole®ns and chloro-ole®ns, the ethanes, CF3CH2Cl and
CF3CH2F being ꢂ15% of the total organic fraction. The
distributions of saturated and ole®nic C2 compounds are
compared in Fig. 1(a, b); the major product was CF2=CHCl
and minor products were CF3CH2Cl, CF3CH2F and
CF2=CHF. The observed behaviour can be rationalised by
assuming that the dominant processes are catalytic ¯uor-
ination of CCl2=CHCl to give CF3CH2Cl and dehydro¯uor-
ination of CF3CH2Cl giving CF2=CHCl (Scheme 1). This is
in harmony with previous work under ¯ow conditions (e.g.
[1,4,6]). Very active catalysts are required for the ¯uorina-
tion of CF3CH2Cl to CF3CH2F, a step which is thermo-
dynamically limited [2±4,8,10,13]. The origin of the `other
ole®ns' in Fig. 1(b) was not investigated but results from a
study under ¯ow conditions suggest that this component
may have been CClF=CHCl, formed from dehydrochlor-
ination of CCl2FCH2Cl or dehydro¯uorination of
CClF2CH2Cl [4]. Crucially, deactivation of the catalyst
was rapid and was accompanied by the apparent formation
of a black coating, possibly the result of oligomerization of
ole®nic products [cf. [15].
Fig. 1. Distribution of organic products, determined by G.C., from
catalytic fluorination of CCl2=CHCl under static conditions; (a)
CF3CH2Cl (133a) and CF3CH2F (134a) from a one step reaction; (b)
olefinic products from a one step reaction; (c) CF3CH2Cl (133a) and
CF3CH2F (134a) after a second step using fresh catalyst.
The results of a further HF treatment of the organic
product mixture in the presence of fresh ¯uorinated
chromia are illustrated in Fig. 1(c). This stage was char-
acterised by a marked reduction in CF2=CHCl and an
increase in CF3CH2F. The rationalisation is given in
Scheme 2. The ole®nic components, mainly CF2=CHF
and CF2=CHCl, could be removed by KOH treatment,
giving an organic product comprising CF3CH2F and
CF3CH2Cl in the mole ratio 3 : 1 as determined by G.C.
This two-step process, though somewhat laborious, gave
reproductible results.
2.2. Preparation of [18F]-labelled CF3CH2F and [36Cl]-
labelled CF3CH2Cl
Following the observations reported above, the behaviour
of [18F]-labelled anhydrous hydrogen ¯uoride towards a
mixture of CF3CH2F and CF3CH2Cl (3 : 1 mole ratio and
prepared as described) was examined under static condi-

A.W. Baker et al. / Journal of Fluorine Chemistry 102 (2000) 279±284
281
Table 1
18F] Activity expected in organic product depending on the pathway;
[
CF3CH2Cl/CF3CH2F(1 : 3) ‡ 5[18F]-HF
Reactant
Pathway
Expected [18F]-activity
in organic fraction/%
CF3CH2F
CF3CH2F
CF3CH2Cl
CF3CH2F‡
CF3CH2Cl
CF3CH2F‡
CF3CH2Cl
18F-for-F exchange
13
31
13
HF/‡H18
F
F
HF/‡H18
HF/‡H18
F
F
37
43
HF/‡H18
and 18F-for-F exchange
stoichiometry used, this route cannot be de®nitively
excluded for CF3CH2Cl. However, it is considered far more
likely that the [18F] incorporation observed in the organic
fraction is due predominantly to a direct 18F-for-F exchange
reaction on CF3CH2F. It is believed that dehydro¯uorina-
tion/hydro¯uorination pathways at the ¯uorinated chromia
surface are inhibited by the large excess of HF present on the
surface as indicated by the incorporation of [18F] by the
catalyst (see above).
This view is consistent with our recent [18F] measure-
ments on ¯uorinated chromia and metal(II) promoted chro-
mias under ¯ow conditions [13]. It is consistent also with
previous studies of catalytic ¯uorination under ¯ow condi-
tions, where partially ¯uorinated ole®nic products are
observed if HF levels are insuf®ciently high [4] or as a
catalyst looses its activity [2]. A dehydro¯uorination-hydro-
¯uorination pathway is feasible however, in the absence of
added HF which is the case in the previous synthesis of
[18F]-CF3CH2F [14] and in the related catalytic isomerisa-
tion of CHF2CHF2 to CF3CH2F [16±18].
The synthesis of [36Cl]-labelled CF3CH2Cl was achieved
in a straightforward manner from a reaction between equi-
molar quantities of CF3CH2F and anhydrous H36Cl in the
presence of un¯uorinated amorphous chromia at 673 K
under static conditions, conversions of CF3CH2F being
95% with minimal ole®n formation, after 1 h. However, a
more detailed examination of the reaction in the temperature
range 653±693 K in the presence of ¯uorinated or un¯uori-
nated chromias of varying degrees of crystallinity, in some
cases doped with zinc(II) [13], indicated a more complex
situation. Monitoring these reactions by G.C. at various
times led to a maximum in the concentration of CF3CH2Cl
being observed after 60±90 min. Thereafter, the proportion
of CF3CH2Cl in a reaction mixture decreased at the expense
of CF3CH2F. In some cases the process was followed over a
3 h period during which CF3CH2F ®rst decreased, then
increased, then decreased again. However, the proportion
of CF3CH2Cl never reached that observed after the ®rst
stage. Small quantities of ole®ns were formed during these
reactions but were never greater than 4% of the total organic
mixture. They, together with any hydrogen halide present,
were readily removed by treatment with moist NaOH pellets
and by careful adjustment of the time of reaction, pure
Scheme 1
tions at 653 K in the presence of fresh ¯uorinated chromia.
The contact time was 2 h, being determined by the short
half-life (110 min) of [18F]; under these conditions there
were no observable chemical reactions as indicated by G.C.
analyses before and after H18F treatment.
Under these conditions ca. 13% of the [18F] activity
originally present in H18F was detected in the organic
fraction while ca. 3%, equivalent to an uptake of H18F by
the ¯uorinated chromia catalyst of 2 mmol HF g 1, was
detected from the catalyst. The level to which [18F] was
incorporated in the organic enables an inference to be made
about the nature of the incorporation route. Some of the
possibilities are summarised in Table 1. Comparisons
between the data in Table 1 and the experimental value
of 13% suggest that under these conditions, labelling of
CF3CH2F via a dehydro¯uorination then hydro¯uorination
pathway is unlikely, since higher levels of [18F] incorpora-
tion would have been expected. Because of the reaction
Scheme 2

282
A.W. Baker et al. / Journal of Fluorine Chemistry 102 (2000) 279±284
Table 2
Computational results
CF3CH2F,
134a
CF3CH2Cl,
133a
CF2=CHF
CF2=CHCl
HF
Symmetry
State
Cs
1A0
Cs
1A0
Cs
1A0
Cs
1A0
C
1v
P
1
RHF/6-311G(d,p)
±E/a.u.
474.790272
834.837651
374.676325
734.729259
100.046904
NIMAG
zpe/kcal mol
0
31.0
0
29.86
0
20.14
0
19.14
0
6.45
1
RMP2/6-311G(d,p)
E/a.u.
NIMAG
475.878679
0
835.865285
0
375.549497
0
735.540873
0
100.267216
0
1
zpe/kcal mol
29.18
28.22
18.66
17.82
6.08
RMP4(SDQ)/6
311G(d,p)//
RMP2/6-311G(d,p)
E/a.u.
475.898373
835.894161
375.565673
735.565499
100.286106
CF3CH2Cl or CF3CH236Cl could be obtained. The beha-
viour observed here is consistent with our previous observa-
tions of labile, catalytically active ¯uoride on ¯uorinated
chromia surfaces [13,19]. This led to the development of an
halogen exchange model for the behaviour of chloro¯uor-
oethanes on ¯uorinated chromia [20] and it appears that a
similar model is applicable to the CF3CH2Cl, CF3CH2F
system.
CF3CH2F were calculated, which, after correction [21±23]
for zero-point energies (zpe, Table 2), differences in rota-
tional (DUrot ˆ ‡ RT) and translational (DUtr ˆ ‡ 3/2 RT)
degrees of freedom, and the work term (pDV ˆ ‡ RT), were
converted into the gas phase HF elimination enthalpy values
at room temperature. At all levels of theory applied, the
dehydro¯uorination of CF3CH2F is slightly more favourable
than that of CF3CH2Cl with the difference, D[DH2ꢃ98] ˆ
1
1
1
3.34 kcal mol
(HF), 2.84 kcal mol
(MP2) and
2.3. Ab initio computations of the dehydrofluorination
reactions of CF3CH2F and CF3CH2Cl
2.40 kcal mol (MP4). However, in real situations, the
small difference between the enthalpies for the HF elimina-
tion reactions is insigni®cant, for example it is comparable
to what might be expected from the effects of intermolecular
interactions that would be present in condensed phases. It is
considered that the data that result from calculations at the
MP2 or MP4//MP2 levels (Table 3) are far more reliable
than those from HF or semiempirical methods. For example,
the generally poor agreement between experimental data
and those from HF calculations for ¯uorine containing
molecules, demonstrates the great importance of electron
correlation for accurate predictions in non metal ¯uorides. A
previous computational study, using the semi-empirical
AM1 method, of ¯uorination and dehydrohalogenation
reactions in the CCl2=CHCl, CF3CH2Cl, CF3CH2F system
[4] should be regarded, therefore, as a useful guide rather
than being de®nitive. Notwithstanding, where overlap exists
the agreement is reasonable.
In order to obtain a greater understanding of the relation-
ships between CF3CH2X, X ˆ F or Cl, and their dehydro¯u-
orinated products, the structures and vibrational frequencies
of CF3CH2F, CF3CH2Cl, CF2=CH2 and CF2=CHCl were
computed quantum chemically at the HF and electron
correlated MP2 level of theory at a 6-311G(d,p) basis. In
addition, single point calculations were performed for all
species at the MP4(SDQ) level of theory employing again a
6-311G(d,p) basis. Details are given in Table 2.
The calculated total energies (Table 3) can be used to
predict theoretically the enthalpies for the HF elimination
reactions. The HF elimination energies of CF3CH2Cl and
Table 3
Reaction energies for the dehydrofluorination reactions
Dehydrofluorination Dehydrofluorination
of CF3CH2Cl
of CF3CH2F
3. Experimental
1a
DEeꢃl (HF)/kcal mol
DH298(HF)/kcal mol
42.05
39.71
38.86
36.49
29.22
26.85
38.57
36.37
35.90
33.65
26.70
24.45
1a
1a
3.1. Catalytic fluorination
DEeꢃl (MP2)/kcal mol
1a
DH298(MP2)/kcal mol
1b
DEeꢃl(MP4)/kcal mol
The chromia used in all the experiments, except when
noted below, was produced by the decomposition of ammo-
nium dichromate and then calcined for 3 h at 523 K under
dynamic vacuum. The chromia was ¯uorinated immediately
before use by opening the vessel to successive aliquots of
1b
DH298(MP4)/kcal mol
a MP2/6-311G(d,p)//MP2/6-311G(d,p).
b MP4(SDQ)/6-311G(d,p)//MP2/6-311G(d,p); zpe values taken from
the MP2 calculation (Table 2).

A.W. Baker et al. / Journal of Fluorine Chemistry 102 (2000) 279±284
283
HF vapour at room temperature with degassing between
aliquot addition. All ¯uorinations and reactions were per-
formed in stainless steel or Monel metal reaction vessels
attached to a Monel metal vacuum line.
counter by condensing a measured quantity (normally
0.5 mmol) onto dry CsF contained in an FEP counting tube,
and were in the range 600±5600 count s 1 mmol 1. Back-
ground and decay corrections were applied in all cases. The
initial [18F] activities supplied enabled the isotope to be used
over several half-lives.
A series of nine experiments was undertaken; some
experiments employed a single batch of catalyst, others
were performed in two stages, using a fresh batch of
¯uorinated chromia and more HF for the second stage.
The products were analysed, after removal of any HF
present, using a Varian 3400 gas chromatograph with a
SilicaPLOT 30 m capillary column. Product identities were
established by comparison with standards and relative sen-
sitivities were established for CF3CH2Cl and CF3CH2F
from experimentally determined calibration curves.
Step 1. Calcined (523 K) volcano chromia (0.2 g) which
had been ¯uorinated at room temperature with four succes-
sive aliquots (ca. 2 mmol each) of HF, was used; 2.2 mmol
of trichloroethene were reacted with 11 mmol HF over the
catalyst at 548 K for 3 h.
Step 2. The catalyst was prepared in a manner identical to
Step 1; 2 mmol of CCl2=CHCl were reacted with 8 mmol of
HF over the catalyst at 623 K overnight.
Step 3. As in Step 2 but heated to 573 K overnight.
Step 4. The product mixture from Step 3 was heated to
623 K overnight over a fresh sample of the same catalyst.
Step 5. The catalyst and reagents were exactly as in Step
2, but heated to 653 K overnight.
1,1,1,2-Tetra¯uoroethane labelled with [18F] was pre-
pared from CCl2=CHCl by the following procedure, the
quantities given being typical of those used. To a Monel
metal pressure vessel containing chromia (0.2 g), previously
¯uorinated at room temperature with four successive ali-
quots (2.0 mmol) of anhydrous HF, was added CCl2=CHCl
(8.0 mmol) then anhydrous HF (20.0 mmol). The mixture
was allowed to react at 653 K overnight. Volatile material
was condensed onto KOH pellets contained in a stainless
steel vessel and stored at room temperature for 2 h. The
organic material isolated (3.0 mmol) was a mixture of
CF3CH2F and CF3CH2Cl (3 : 1) as determined by GC,
and was added by distillation to a second Monel metal
pressure vessel containing ¯uorinated chromia followed by
H18F (15.0 mmol). The contents were heated to 653 K for
2 h then, after cooling, treated with KOH for 0.5 h at room
temperature. The organic fraction (1.78 mmol) was trans-
ferred to a Pyrex counting vessel; its speci®c count rate,
determined in the frozen state, was 378 count s 1 mmol
1
.
For comparison, the initial speci®c count rate of H18F in this
1
experiment was 563 count s 1 mmol
and that of the
Step 6. Repeat Step 5.
¯uorinated chromia catalyst after reaction was 1143
count s 1 g 1. Analysis of the organic fraction by GC after
complete decay of [18F] indicated that its chemical compo-
sition was unchanged by the H18F treatment.
Step 7. The products from Step 6 were condensed onto
fresh ¯uorinated chromia, prepared as before, and the
mixture heated to 523 K overnight.
Step 8. The product mixture from Step 7 was heated to
653 K, over the same catalyst, for 1 h.
3.2.2. [36Cl]-labelling
Step 9. Trichloroethene (3.0 mmol), HF (10.0 mmol) and
of chromia (0.2 g prepared as before) were allowed to react
overnight at 653 K. The product mixture was condensed
onto fresh ¯uorinated chromia and reacted at 653 K for 1 h.
The product mixture from this second stage was then
condensed onto NaOH pellets before CG analysis.
2-Chloro-1,1,1-tri¯uoroethane, labelled with [36Cl] was
prepared from the reaction of CF3CH2F with anhydrous
H36Cl in the presence of un¯uorinated amorphous chromia
at 673 K. Anhydrous H36Cl was prepared by a modi®ed
literature procedure [24] from conc. H2SO4 and aqueous
[36Cl]-chloride ion using a Pyrex reaction vessel ®tted with a
pressure-equilibrated dropping funnel and a series of traps
containing P4O10 and cooled in CO2/CH2Cl2 and liq. N2/
isopentane baths. The collection trap was ®tted with PTFE/
Pyrex stop-cocks enabling it to be transferred to a Pyrex
vacuum line for subsequent storage (in a Monel metal vessel
over P4O10).
3.2. Preparation of labelled compounds
3.2.1. [18F]-labelling
Fluorine-18 was supplied by the John Mallard Scottish
PET Centre, Grampian University Hospitals Trust, Aberd-
een as an effectively `no carrier added' aqueous solution
(activities supplied were in the range 50±450 MBq). After
transfer to Glasgow, an [18F] solution was added to aqueous
CsOH (1.0 g, in 5±10 cm3) and the mixture carefully neu-
tralised with aqueous HF (40%). Usually ca. 2 cm3 were
required. Solid Cs18F was obtained by evaporation and
drying, then transferred to a Monel metal vessel attached
to a Monel vacuum line and evacuated. Anhydrous HF (up
to 15 mmol) was labelled with [18F] by exchange with Cs18F
at 523 K for 0.5 h. Speci®c count rates of each sample of
H18F prepared were determined using a well scintillation
Aqueous [36Cl] sodium chloride (6750 MBq, 1.0 cm3;
Amersham International) was diluted with conc. HCl
(9.0 cm3) and aliquots of this solution were added dropwise
to H2SO4 contained in the reaction vessel. Typical [36Cl]
count rates of H36Cl prepared by this procedure, measured
using a Pyrex Geiger MuÈller direct monitoring cell [25],
1
were ca. 1000 count min
.
To a Monel metal pressure vessel containing amorphous
un¯uorinated chromia (2.0 g), previously calcined at 523 K
in vacuo, was added a mixture of CF3CH2F (6.1 mmol) and
H36Cl (6.0 mmol) by vacuum distillation. The mixture was

284
A.W. Baker et al. / Journal of Fluorine Chemistry 102 (2000) 279±284
[2] S. Brunet, B. Requieme, E. Matouba, J. Barrault, M. Blanchard, J.
Catal. 152 (1995) 70.
allowed to react at 673 K for 1 h. After cooling to room
temperature, the volatile material was condensed onto moist
NaOH pellets, the process being repeated until there was no
evidence for either HCl or HF in the IR spectrum of the
fraction. Analysis by GC indicated that the ratio CF3CH2Cl:
CF3CH2F was ꢁ95 : 5. Longer reaction times led to product
mixtures containing higher proportions of CF3CH2F.
Other catalysts, partially crystalline chromias both
un¯uorinated and ¯uorinated and zinc(II)-doped ¯uorinated
chromias [13], were evaluated for use in this reaction.
Generally they were less active, although pre-¯uorination
was bene®cial for the partially crystalline materials as was
Zn(II) doping. The [36Cl]- count rates of CF3CH236Cl
[3] S. Brunet, B. Requieme, E. Colnay, J. Barrault, M. Blanchard, Appl.
Catal. B 5 (1995) 305.
[4] A. Kohne, E. Kemnitz, J. Fluor. Chem. 75 (1995) 103.
[5] S. Brunet, B. Boussand, A. Rousset, D. Andre, Appl. Catal. A 168
(1998) 57.
[6] T. Skapin, J. Mater. Chem. 5 (1995) 1215.
[7] J.N. Armor, Chem. Mater. 6 (1994) 730.
[8] H. Kim, H.S. Kim, B.G. Lee, H. Lee, S. Kim, J. Chem. Soc. Chem.
Commun. (1995) 2383.
[9] H.-d. Quan, Z. Li, Z.-x. Zhao, H.-e. Yang, J. Lu, J.-g. Ren, S.-k.
Chen, H.-f. Li, H.-l. Li, Appl. Catal. B 8 (1996) 209.
[10] J.A. Lu, H. Yang, S.K. Chen, L. Shi, J.G. Pen, H.L. Li, S.Y. Peng,
Catal. Lett. 41 (1996) 221.
[11] H. Lee, H.D. Jeong, Y.S. Chung, H.G. Lee, M.J. Chung, S. Kim, H.S.
Kim, J. Catal. 169 (1997) 307.
1
prepared in this way were ca. 4000 count min as deter-
mined by the Geiger MuÈller direct monitoring method [25]
at 100 Torr pressure.
[12] Y.S. Chung, H. Lee, H.D. Jeong, Y.K. Kim, H.G. Lee, H.S. Kim, S.
Kim, J. Catal. 175 (1998) 220.
[13] D.W. Bonniface, J.R. Fryer, P. Landon, J.D. Scott, W.D.S. Scott, M.J.
Watson, G. Webb, J.M. Winfield, Green Chem. 1 (1999) 9.
[14] F.I. Aigbirhio, V.W. Pike, S.L. Waters, R.J.N. Tanner, J. Fluor. Chem.
70 (1995) 279.
3.3. Computational studies
Preliminary geometries for all compounds, CF3CH2F,
CF3CH2Cl, CF2=CH2, CF2=CHCl and HF, were calculated
semiempirically (PM3) [26] in C1 symmetry with the
program package HyperChem [27] and were optimized to
[15] A. Bendada, D.W. Bonniface, F. McMonagle, R. Marshall, C.
Shortman, R.R. Spence, J. Thomson, G. Webb, J.M. Winfield, N.
Winterton, Chem. Commun. (1996) 1947.
[16] E. Kemnitz, K.-U. Niedersen, J. Catal. 155 (1995) 283.
[17] K.-U. Niedersen, E. Schreier, E. Kemnitz, J. Catal. 167 (1997) 210.
[18] E. Kemnitz, K. -U Niedersen, J. Fluor. Chem. 79 (1996) 111.
[19] J. Kijowski, J.M. Winfield, G. Webb, Appl. Catal. 27 (1986) 181.
[20] L. Rowley, J. Thomson, G. Webb, J.M. Winfield, A. McCulloch,
Appl. Catal. A 79 (1991) 89.
CS (CF3CH2F, CF3CH2Cl, CF2=CH2, CF2=CHCl) or C
1n
(HF) symmetry, respectively. The structures, vibrational
frequencies and zero point energies (zpe) for all molecules
were then optimized within Cs or C1n symmetry with the ab
initio method at the RHF level of theory at the 6-311G(d,p)
basis with the program package Gaussian 98 (Revision A.3)
[28]. Electron correlation was taken into consideration
(structure optimization, vibrational frequencies and zpe
values at the 6-311G(d,p) basis) by applying perturbation
theory according to Mùller-Plesset (MP) which takes higher
excitations into account by using a perturbation operator and
È
[21] T.M. Klapotke, A. Schulz, Quantenmechanische Methoden in der
Hauptgruppenchemie, Spektrum, Heidelberg, 1996, p.92.
È
[22] T.M. Klapotke, A. Schulz, R.D. Harcourt, Quantum Chemical
Methods in Main-Group Chemistry, Wiley, Chichester, 1998, p. 89.
[23] J.B. Foresman, A. Frisch, Exploring Chemistry with Electronic
Structure Methods, 2nd Edition, Gaussian, Pittsburgh, USA, 1993.
[24] R.N. Maxson, Inorg. Synth. 1 (1939) 147.
[25] A.S. Al-Ammar, G. Webb, J. Chem. Soc. Faraday Trans. 1 74 (1978)
195.
È
using Rayleigh-Schrodinger perturbation theory to obtain a
[26] J.J.P. Stewart, J. Comp. Chem. 10 (1989) 221.
[27] HyperChem 5.1, Molecular Visualization and Simulation Program
Package, Hypercube,Gainesville, FL 32601, 1998.
better wave function and energies (second order, notation
MP2) [29±32]. In addition, single point calculations were
performed for all species at the MP4(SDQ) level of theory
which accounts for single, double and quadruple substitu-
tions [33] employing a 6-311G(d,p) basis.
[28] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuscria, M.A. Robb,
J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery, Jr., R.E.
Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels,
K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi,
R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J.
Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K.
Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslows-
ki, J.V. Ortiz, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I.
Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-
Laham, C.Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe,
P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C.
Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98,
Revision A3, Gaussian, Inc., Pittsburgh PA, 1998.
Acknowledgements
We are grateful to EPSRC, ICI Klea, the University of
Munich and the Fonds der Chemischen Industrie for support
of this work. Staff at the John Mallard Scottish PET Centre,
Aberdeen are thanked for assistance with [18F] preparation.
[29] C. Mùller, M.S. Plesset, Phys. Rev. 46 (1934) 618.
[30] R.J. Bartlett, D.M. Silver, J. Chem. Phys. 62 (1975) 3258.
[31] J.A. Pople, J.S. Binkley, R. Seeger, Int. J. Quant. Chem. Quant.
Chem. Symp. 10 (1976) 1.
References
[32] J.A. Pople, R. Seeger, R. Krishnan, Int. J. Quant. Chem. Quant.
Chem. Symp. 11 (1977) 149.
[1] D.M.C. Kavanagh, T.A. Ryan, B. Mile, J. Fluor. Chem. 64 (1993)
167.
[33] R. Krishnan, J.A. Pople, Int. J.Quant. Chem. 14 (1978) 91.