Transfer hydrogenolysis of CFC-113a with aldehydes and metallic Fe or Ni

Article abstract of DOI:10.1016/S0022-1139(98)00334-0

Highly selective transfer hydrogenolysis of CFC-113a (CF₃CCl₃) to HCFC-123 (CF₃CHCl₂) was accomplished in the presence of metal powder (Fe or Ni) in THF at 90°C under 8 atm of He. Pressure effects on the catalytic activities depend on the nature of metal catalysts and this behavior can be explained by a different rate determining step in each system. Activation of the C-H bond of THF on metal powder aided by η² coordinated aldehydes is believed to occur first to produce electron-rich metal hydrides, which enhance the activation of the C-Cl bond of CFC-113a. Then reductive elimination follows to produce HCFC-123. This series of reactions was supported by experiments using deuterated THF and/or DMF and with p-substituted benzaldehydes.

Full text of DOI:10.1016/S0022-1139(98)00334-0

Journal of Fluorine Chemistry 94 (1999) 73±78
Transfer hydrogenolysis of CFC-113a with aldehydes
and metallic Fe or Ni
Sang Hyun Seoa, Seung-Pyo Honga, Chong-Yun Kwagb, Hyun-joo Leec,
HoonSik Kimc, Ik-Mo Leea,*
aDepartment of Chemistry, Inha University, Inchon, 402-751, South Korea
bResearch Center, Oriental Chemical Industries, Inchon, 402-040, South Korea
cPO Box 131 Chungyang, CFC Alternatives Technology Center, Korea Institute of Science and Technology, Dongdaemoon-ku,
Seoul, 130-650, South Korea
Received 17 November 1998; accepted 18 November 1998
Abstract
Highly selective transfer hydrogenolysis of CFC-113a (CF3CCl3) to HCFC-123 (CF3CHCl2) was accomplished in the presence of metal
powder (Fe or Ni) in THF at 908C under 8 atm of He. Pressure effects on the catalytic activities depend on the nature of metal catalysts and
this behavior can be explained by a different rate determining step in each system. Activation of the C±H bond of THF on metal powder
aided by ꢀ2 coordinated aldehydes is believed to occur ®rst to produce electron-rich metal hydrides, which enhance the activation of the
C±Cl bond of CFC-113a. Then reductive elimination follows to produce HCFC-123. This series of reactions was supported by experiments
using deuterated THF and/or DMF and with p-substituted benzaldehydes. # 1999 Elsevier Science S.A. All rights reserved.
Keywords: Transfer hydrogenolysis; CFC-113a; HCFC-123; Metal catalysts; Aldehydes
1. Introduction
a variety of hydrogen donors over many catalysts has been
extensively investigated [4]. Moreover, transformation of
the ¯uorinated hydrocarbons by incorporation of some
functional groups such as carbonyl groups would induce
the use of banned or to-be-banned chemicals such as Freons.
The results can be applicable to active research areas in the
®ne chemical pharmaceuticals and herbicides industries
where introduction of ¯uorine to biologically active com-
pounds has been extensively sought [5±9]. For these pur-
poses, aldehydes containing relatively active hydrogen and
carbonyl group were initially employed as hydrogen donors
but surprisingly protons in the solvents such as THF were
found to be introduced into the resulting HCFC compounds
instead and introduction of carbonyl groups was never
observed. Fujita and Hiyama [10] reported the stoichio-
metric reaction between aldehydes and CFC-113a in the
presence of Zn. They also produced HCFC-123 by a two-
step reaction, preparation of CF3CCl2ZnCl followed by
hydrolysis. Tamura and Sekiya [11] investigated the reaction
between HCFC-123 and aldehydes in the presence of Zn/
CuCl catalysts which yielded transfer hydrogenolysis pro-
ducts as well as alcohols and alkenes. In this paper, Fe and/or
Ni powders were found to catalyze transfer hydrogenolysis
reactions. Factors affecting the reaction rates are discussed.
Depletion of the ozone layer apparently caused by CFC
compounds has induced tight restriction of the use and the
production of these compounds through the Montreal pro-
tocol and extensive studies for CFC alternatives have been
made during the past decade. HCFC-123 (CF3CHCl2) is one
of the promising alternatives and several processes for its
production have been proposed. Previously, we reported that
CFC-113a (CF3CCl3) can be selectively hydrogenolyzed to
give CF3CHCl2 by using transition metal complexes such as
RhCl(PPh3)3 [1]. Several factors affecting catalyst activity
and the mechanism for this reaction were also investigated
[2]. Polar solvent participation in the reaction with CFC-
113a catalyzed by alumina was also reported [3]. New
replacements for the hydrogen gas in the hydrogenolysis
reaction have been studied for the following reasons: hydro-
gen is rather dangerous and NMR tubes containing hydrogen
for the characterization of reaction intermediates are dif®-
cult to seal due to the possibility of explosion. Therefore,
transfer hydrogenolysis of various organic compounds with
*Corresponding author. Fax: +82-32-867-5604.
0022-1139/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
P I I : S 0 0 2 2 - 1 1 3 9 ( 9 8 ) 0 0 3 3 4 - 0

74
S.H. Seo et al. / Journal of Fluorine Chemistry 94 (1999) 73±78
2. Experimental
3. Results and discussion
2.1. Reagents
It has been reported that an aldehyde is able to function as
a hydrogen donor even though it is only used in limited
reactions [12,13]. Aromatic aldehydes and DMF serve as
hydrogen donors and transfer their formyl hydrogen to a, b-
unsaturated ketones in the presence of RuCl2(PPh3)3. Coor-
dination of formaldehyde on a metal center has been a
primary goal in metal-catalyzed C1 chemistry and Fischer±
Tropsch reactions [14]. With this in mind, we have carried
out the transfer hydrogenolysis reaction of CFC-113a with
aldehydes in a stainless steel reactor hoping to ®nd a better
process for the preparation of HCFC-123. Contrary to our
assumption of no catalysis by a reactor, we found that the
reaction of CFC-113a with aldehydes in THF produced
HCFC-123 even in the absence of catalysts. However, a
much slower reaction rate was observed when the reaction
was performed in a glass-lined pressure reactor even though
large excess of aldehydes were employed. After many trials,
we found that the stainless steel reactor itself is responsible
for the catalysis. Since the stainless steel is known to contain
iron, nickel, and chromium, we have conducted the transfer
hydrogenolysis reaction using these metals as catalysts. The
reaction did not proceed at all in benzene, unlike in THF,
indicating that the solvent is playing an important role in the
catalysis. In order to ®nd out the role of solvent, deuterium
labeling experiments were carried out in the presence of
metal and aldehyde. No scrambled products were obtained
both in the reaction employing DMF-d7/THF and one with
DMF/THF-d8 and slight reduction of the reaction rate was
caused by addition of a radical initiator such as AIBN
(azobisisobutylnitrile; up to 0.2 equivalent to aldehyde)
effectively excluding the possibility of a radical mechanism
in these reactions. In the reactions employing deuterated
compounds CF3CHCl2 or CF3CDCl2 were produced as a
main hydrogenated product in over 98% yield along with a
small amount of CF3CH2Cl or CF3CD2Cl showing that
protons in THF, not in aldehydes, actually replaced the
chlorines of CFC-113a. Such a high selectivity to CF3CHCl2
or CF3CDCl2 was attributed mainly to lower reactivity of
CF3CHCl2 than that of CF3CCl3 as mentioned elsewhere
[2]. H/D exchange between THF and DMF-d7 in the pre-
sence of metal catalysts was found to be negligible. In
MeOH, several side products were produced as reported
elsewhere [3]. Neither Brùnsted (HCl) nor Lewis acids
(AlCl3) altered the reaction rate and selectivity. However,
bases such as triethylamine and triphenylphosphines
depressed the reaction rate considerably. These results
may show that direct protonation from the hydrogen source
material does not occur or at least this step is not important
(HCl), and polarization of the C±Cl bond in the substrate
induced by AlCl3 does not occur effectively. The effect of
bases on the reaction rate might be attributed to the pre-
ferential coordination of bases on the surface of a metal
catalyst by effectively blocking the active sites where
activation of C±H bonds of the hydrogen source compounds
Solvents were all reagent grade and were distilled from
appropriate drying agents under a nitrogen atmosphere prior
to use. Other reagent grade chemicals were purchased from
Aldrich and used without further puri®cation. Fe (99.9%,
100±120 mm) and Ni (99.9%, 100±120 mm) powders were
purchased from Samchun. CFC-113a, obtained from the
rearrangement reaction of CFC-113 (Asahi Glass) with
AlCl3, was distilled under nitrogen before use.
2.2. Instrumentation
1H NMR spectra were recorded on a Bruker AM-250
spectrometer operating at 250.133 MHz. These spectra were
referenced to internal standard tetramethylsilane (TMS).
Gas chromatographic analyses were made on a Young-In
680D gas chromatography equipped with a ¯ame ionization
detector and a 6 ft long stainless steel column packed with
liquid methyl silicone on chrom-W. Mass spectral analyses
were carried out employing a HP 5890A GC/HP 5917A MS
detector equipped with a 30 m-long capillary column
packed with liquid methyl silicone.
2.3. Kinetic study
Generally, in a 200 ml stainless steel high pressure reactor
®tted with a glass liner, 5.33Â10 2 mol of CFC-113a, 1 g of
n-hexane, 100 ml of THF and predetermined amounts of
catalysts and aldehydes were stirred magnetically at 908C
under 8 atm of He. Small amounts (ca. 1 ml) of samples
were taken every 30 min through a sampling port and
analyzed by gas chromatography. Between samplings, about
5 ml of fresh solution in the reactor was allowed to ¯ush the
sampling port. The observed 85% conversion rate was
determined by plotting the concentration of CFC-113a
versus time. The product composition was analyzed with
the use of internal standard, n-hexane. Plots of the kinetic
data were ®tted using a conventional linear regression
program (Microcal Origin version 4.10).
2.4. NMR tube experiment
Inside a dry box, mixed solvents [THF/DMF-d7 (DMF:
dimethylformamide,
volume
ratioˆ1:1,
mole
ratioˆ1.05:1), or THF/DMF-d7/CFC-113a (volume
ratioˆ1:1:1, mole ratioˆ1.05:1:0.65), or THF-d8/DMF/
CFC-113a (volume ratioˆ1:1:1, mole ratioˆ1.05:1:0.65)
(total volumeˆ2 ml)] and 5 mg of Fe or Ni powder were
placed in a 5 mm NMR tube equipped with a PTFE valve.
After the NMR tube was taken out of the dry box, it was
maintained at 908C in an oil bath for 2.5 h. The tube was
1
cooled down to room temperature for H NMR and MS
analyses.

S.H. Seo et al. / Journal of Fluorine Chemistry 94 (1999) 73±78
75
Table 1
Table 3
Effect of DMF content on the transfer hydrogenolysis reaction rates of
CFC-113a (no catalysts, He 8 atm, 908C, CFC-113a 10 g, hexane 1 g)
Variation of the transfer hydrogenolysis reaction rates of CFC-113a with
change of reaction conditions (Fe catalyst, 908C, CFC-113a 10 g, hexane
1 g)
Run no.
THF (ml)
DMF (g)
Timea
Run
no.
DMF
(g)
THF
(ml)
Fe
He
Conversion ratea
1
2
3
4
5
90
90
90
90
±
±
9 h
(g)
(atm)
0.39
3.9
39
6 h, 40 min
6 h
1
2
±
0.39
3.9
90
3.9
3.9
3.9
3.9
3.9
±
90
90
90
±
0.35
0.35
0.35
0.35
0.035
0.70
0.35
0.35
0.35
0.035
0.193
0.35
0.50
0.70
1.00
8
8
8
8
8
8
6
4
2
8
8
8
8
8
8
1.10 (5 h, 50 min)b
5 h, 40 min
8 h, 20 min
2.50
7.17
7.42 (50 min)b
90
3
4
aTime required for the 85% completion of the reaction.
5
90
90
90
90
90
90
90
90
90
90
90
14.83
6.72
6
7
13.42
and the C±Cl bond of CFC-113a take place. This also
represents active involvement of metal catalysts when
metals are present in these reactions. Even though the
transfer hydrogenolysis reaction catalyzed by metals pro-
ceeded fairly rapidly in THF or DMF, initial conversion
rates were always smaller than the later ones indicating that
substantial initial amount of active intermediate must be
formed. Further study is proceeding to clarify the mechan-
ism.
8
11.88
9
10.24
8.86 (7 h, 10 min)b
10
11
12
13
14
15
±
2.05
1.10
1.18
0.74
0.63
±
±
±
±
aMole of CFC-113a converted/mole of Fe/time (h).
bTime required for the 85% completion of the reaction.
In order to understand the roles of the solvent (THF) and
aldehydes, transfer hydrogenolysis reactions of CF3CCl3
were performed in THF, DMF or DMF/THF solvent in the
absence of metal catalysts. DMF was chosen as a repre-
sentative aldehyde simply because the conversion rate in
DMF was the fastest in the preliminary experiments and
commercially deuterated compounds were easily accessi-
ble. Table 1 shows that the transfer hydrogenolysis reaction
proceeds faster in DMF than in THF. The reaction is
facilitated with the copresence of DMF and THF but the
effects of these compounds were not straightforward. These
results may suggest that there exist two different competing
mechanisms where each of THF and DMF participate. Both
iron and nickel powders are found to considerably accel-
erate the reaction rate conducted in DMF (run 7 in Table 1,
run 5 in Table 2, run 4 in Table 3). However, in THF, Ni and
Fe show different behaviors, i.e., Ni as an inhibitor (run 1
both in Tables 1 and 2) and Fe as an activator (run 1 both in
Tables 1 and 3). A more complicated situation was observed
when DMF and THF were used together in the presence of
Ni or Fe. With Ni, the rate of reaction increased with the
increasing amount of DMF in THF up to 39 g in 90 ml of
THF. This suggested that the promoting effect of DMF
overwhelmed the inhibiting effect of Ni or a new catalytic
cycle involving Ni and DMF worked more effectively. The
effectiveness of this cycle appeared to increase with the
amount of DMF. With Fe, conversion rate increased with the
amount of DMF and the effectiveness of this catalyst was
lower than that of Ni. Conversion rates generally decreased
with amount of catalysts, both Ni (runs 3,6,7,8 in Table 2)
and Fe (runs 5,2,6 in Table 3). This might be due to
incomplete dispersion of catalysts or the decreased substrate
concentration per unit site. Since Fe(CO)5, assumed homo-
geneous, was found to be inactive toward transfer hydro-
genolysis of CFC-113a, these reactions are believed to
proceed via heterogeneous pathways. Differences in beha-
vior between DMF and THF (Tables 1±3) re¯ect the differ-
ing ranges of interaction of DMF and THF with the metal
surfaces (in the presence of catalysts) and substrates (in the
absence of catalysts). Even though the nature of the inter-
actions is not clearly understood, there might be coordina-
tion (or adsorption) of THF and DMF to the surface metal
atoms and nucleophilic substitution of C±Cl bond in CFC-
113a by THF and DMF. In Tables 2 and 3, a pressure effect
on the reaction rates catalyzed by Ni and Fe powder was
shown. Rates increased with the increase of pressure in the
Ni catalyzed reaction (runs 3,9,10 in Table 2), while a
reverse trend was observed in the case of Fe catalyzed
reaction (runs 2,7,8,9 in Table 3). In an Ni system, activa-
tion of adsorbed substrates via oxidative addition may be the
slowest step and this step depends on the concentrations of
adsorbed substrates which, in turn, depend on the pressure
Table 2
Variation of the transfer hydrogenolysis reaction rates of CFC-113a with
change of reaction conditions (Ni catalyst, 908C, CFC-113a 10 g, hexane
1 g)
Run
no.
DMF
(g)
THF
(ml)
Ni
He
Conversion ratea
(g)
(atm)
1
2
±
90
90
90
90
±
0.031
0.031
0.031
0.031
0.031
0.062
0.31
8
8
8
8
8
8
8
8
4
2
5.22 (12 h, 40 min)b
0.39
3.9
39
10.50
15.38
17.67
12.19 (6 h)b
5.41
3
4
5
90
6
3.9
3.9
3.9
3.9
3.9
90
90
90
90
90
7
0.93
8
0.62
0.14
9
10
0.031
0.031
9.36
7.17
aMole of CFC-113a converted/mole of Ni/time (h).
bTime required for the 85% completion of the reaction.

76
S.H. Seo et al. / Journal of Fluorine Chemistry 94 (1999) 73±78
Table 4
are also suggested as possible intermediate species to
play a role in enhancing the rate of reaction by assisting
the oxidative addition of CFC-113a. Enhanced reaction
rate in the late stage can be rationalized by the effect of
increased electron density (negative charge) at the active
sites, originating from the formation of metal hydrides, on
the oxidative addition of CF3CCl3 as reported in the
RhCl(PPh3)3-catalyzed hydrogenolysis of CFC-113a [2].
Slower rates in the reactions employing aldehydes having
electron withdrawing groups can be interpreted by the
reduction in both negative charge (or electron density on
the surface) and nucleophilicity of the active species. This
interpretation requires the coordination of aldehydes to
the metal. The observation of no H/D exchange between
aldehydes and THF in the presence of metal powder
strongly indicates that aldehydes simply coordinate to the
surface metal atoms without transformation and control
the electron density of active sites. Small change (less
than 5%) in the amount of aldehydes during the reaction
supports this explanation. It is believed that aldehydes
adsorb (or coordinate) via an ꢀ2 mode (side-on coordina-
tion) [15±19] due to the electron-rich nature of late transi-
tion metals and the transfer of electron density from the
surface metal atoms (®lled dꢁ orbital) to aldehydes (empty
ꢁ*(CO) orbital) occurs through ꢁ-back bonding. Reduced
electron density on metal by ꢁ-back bonding promotes the
coordination of THF and formation of metal hydride spe-
cies. Sterically bulky aldehydes were generally found to
retard reaction rates. This can be rationalized from the fact
that the ꢀ2 bonding mode is destabilized by the steric
bulkiness of the ligand [19]. Alkyl aldehydes with electron
donating possibilities showed slower rates than aromatic
aldehydes probably due to destabilization of ꢁ* orbital of
CO group and less ꢁ-back bonding. The effect of electro-
negative atoms such as N and O a to carbonyl groups is
expected to increase reaction rate on the basis of above
discussion. However, experiments showed complicated
trends; formamides increased rates while formates
decreased rates. This may be rationalized by the differences
in coordinating ability, possibly originating from the relative
stabilities of zwitterionic forms as shown in Scheme 1. The
canonical form B of formamides (the ®rst row in Scheme 1)
is expected to be more stable than that of formates (the
second row) on the basis of electronegativities of the ele-
ments. Positive charge on the more electronegative element
would destabilize the system. Electronegative atoms located
a to carbonyl groups could stabilize the ꢁ electrons of
carbonyl groups, and therefore reduce the ꢁ basicity and
coordinating ability via an ꢀ2 bonding mode. However, a
more stable zwitterion (form B) could coordinate to a metal
via an ꢀ1 mode initially through O atom and then convert to
an ꢀ3 mode for THF to be coordinated and activated. This
kind of change in bonding mode could occur at one metal
center as shown in Scheme 1 or at two close metal centers.
This was supported by the slightly faster conversion rate
with N,N-dimethylformamide (DMF) than with N-methyl-
Dependence of time required for 85% conversion of CFC-113a on the
aldehydes (CFC-113a 10 g, aldehydes, 0.053 mol, He 8 atm, 908C, hexane
1 g, THF 90 ml)
Aldehydes
Time
p-Nitrobenzaldehyde
p-Cyanobenzaldehyde
p-Chlorobenzaldehyde
Benzaldehyde
38 h
8 h, 15 min
7 h
4 h, 40 min
7 h, 30 min
6 h, 30 min
5 h, 10 min
No reaction
7 h
p-Tolualdehyde
p-Methoxybenzaldehyde
Acetaldehyde
Acetaldehydea
Paraformaldehyde
Propionaldehyde
4 h, 40 min
7 h, 30 min
6 h, 40 min
9 h, 10 min
11 h
2-Methylvaleraldehyde
Phenylacetaldehyde
Trimethylacetaldehyde
Methylformate
Ethylformate
9 h, 40 min
1 h, 30 min
1 h, 20 min
N-Methylformamide
N,N-Dimethylformamide
aThe reaction was run in benzene (90 ml).
of He. In an Fe system, activation of adsorbed substrates
depends on the concentrations at the catalyst surface up to
6 atm but at the higher pressure (8 atm) desorption and
diffusion of the products to the bulk solution could be the
rate determining step, which might depend inversely on the
pressure. Therefore, reduced reaction rates were observed.
From the experimental results, it is suggested that Ni or
Fe-catalyzed transfer hydrogenolysis reaction proceeds via
several independent pathways. The transfer hydrogenolysis
reaction in THF yielded 1-butenal and viscous products in
addition to CF3CHCl2. The viscous organic product is
believed to be formed from the oligomerization of 1-bute-
nal. The effect of substituents in para-substituted benzal-
dehydes was also examined to investigate the electronic
effects on the rate. As shown in Table 4 and Fig. 1, electron
withdrawing groups generally reduced the rates of reaction,
while the rates were increased by electron donating groups.
An attempt to correlate Hammett constants with the reaction
rates was not successful. Benzaldehyde and p-chloroben-
zaldehyde especially showed the largest deviation from
linearity. Aldehydes showed a similar reaction pro®le,
i.e., a slower reaction rate in the early stage (or induction
periods). This strongly indicated that conditioning of the
surface occurred. It is also possible that highly active sur-
face adsorbed intermediate species might be formed during
the early stage and that intermediate species actively parti-
cipate in the reaction in the later stage of reaction. Metal
hydride species, presumably formed by the activation of a
C±H bond in THF on the surface of metal powder (Eq. (1)),
ꢀ1†

S.H. Seo et al. / Journal of Fluorine Chemistry 94 (1999) 73±78
77
Fig. 1. A plot of [CFC-113a] against time with various p-substituted benzaldehydes at 908C under 8 atm of He.
4. Conclusions
Metal powder (Fe or Ni) was found to catalyze transfer
hydrogenolysis of CFC-113a to produce HCFC-123
in high yield and selectivity from THF at 908C under
8 atm of He. Pressure effects on the catalytic activities
depend on the nature of metal catalysts and this be±
havior can be explained by the different rate determin-
ing step in each system. Activation of the C±H bond of
THF on the metal powder is believed to occur ®rst to
produce electron-rich surface metal hydrides, which
enhance the activation of C±Cl bond of CFC-113a and
then reductive elimination follows to produce HCFC-123.
In the reactions in THF, aldehydes seem to function as
cocatalysts assisting coordination and activation of
THF. However, aldehydes are also able to function as
hydrogen donors in the absence of THF. Experiments
using deuterated THF and/or DMF revealed that THF acted
as hydrogen donor and radical pathways were not adopted.
A series of experiments with p-substituted benzaldehydes
showed the electronic effects of substituents. Reduced
electron density at the active sites by ꢁ-back bonding to
Scheme 1.
formamide (Table 4). The presence of more alkyl groups
would stabilize the positive charge on nitrogen atom in a
zwitterion.

78
S.H. Seo et al. / Journal of Fluorine Chemistry 94 (1999) 73±78
[6] R. Filler, Biochemistry Involving Carbon±Fluorine Bond, American
Chemical Society, Washington, DC, 1976.
coordinated (or adsorbed) aldehydes might rationalize the
results of these reactions.
[7] R. Filler, Y. Kobayashi (Eds.), Biomedical Aspects of Fluorine
Chemistry, Elsevier, Amsterdam, 1982.
[8] F.A. Smith, CHEMTECH (1973) 422.
Acknowledgements
[9] R. Filler, CHEMTECH (1974) 752.
[10] M. Fujita, T. Hiyama, Bull. Chem. Soc. Jpn. 60 (1987) 4377.
[11] M. Tamura, A. Sekiya, J. Fluorine Chem. 71 (1995) 119.
[12] R.M. Kellogg, in: B.M. Trost, I. Fleming (Eds.), Comprehensive
Organic Synthesis, vol. 8, Pergamon Press, New York, 1991, p. 86.
[13] E. Keinan, N. Greenspoon, in: B.M. Trost, I. Fleming (Eds.),
Comprehensive Organic Synthesis, vol. 8, Pergamon Press, New
York, 1991, p. 557.
Financial support from Inha University (1995) and Korea
Science and Engineering Foundation (94-0501-06-01-3) are
appreciated.
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