Imidazolium salt assisted hydrolysis of 1-chloro-2,2,2-trifluoroethane

Article abstract of DOI:10.1016/j.jfluchem.2003.10.014

The use of imidazolium-based ionic liquids as promoters was found to be highly effective for the hydrolysis reaction of CF3CH2Cl with aqueous potassium acetate to produce 2,2,2-trifluoroethanol (TFE). Among ionic liquids tested, 1-butyl-3-methylimidazoliu

Full text of DOI:10.1016/j.jfluchem.2003.10.014

Journal of Fluorine Chemistry 125 (2004) 95–97
Imidazolium salt assisted hydrolysis of 1-chloro-2,2,2-trifluoroethane
*
Hyunjoo Lee, Kyung Hwan Kim, Honggon Kim, Sang Deuk Lee, Hoon Sik Kim
Reaction Media Research Center, Korea Institute of Science and Technology, 39-1 Hawolkogdong, Seoul 136-791, South Korea
Received 1 September 2003; received in revised form 28 October 2003; accepted 31 October 2003
Abstract
The use of imidazolium-based ionic liquids as promoters was found to be highly effective for the hydrolysis reaction of CF
aqueous potassium acetate to produce 2,2,2-trifluoroethanol (TFE). Among ionic liquids tested, 1-butyl-3-methylimidazolium chloride
[bmim]Cl) showed the highest yield of TFE, over 90%, which is almost two times higher than that obtained in the absence of an ionic liquid.
3 2
CH Cl with
(
1
The integrity of imidazolium salt was maintained during the reaction, which was confirmed from the recycling studies and H NMR
spectroscopy.
#
2003 Elsevier B.V. All rights reserved.
Keywords: 2,2,2-Trifluoroethanol; 1-Chloro-2,2,2-trifluoroethane; Hydrolysis; Ionic liquid; Phase transfer catalyst
1
. Introduction
,2,2-Trifluoroethanol (TFE) is widely used in many
has been demonstrated as catalyst and solvent for the con-
version of an alcohol to an alkyl halide [7,8]. With a hope
that ionic liquids could also find a role in promoting the
hydrolysis reaction of alkyl halides containing highly elec-
2
branches of chemistry and engineering as a working sub-
stance for heat pumps, a versatile solvent, and a raw material
for further organic synthesis [1–4]. TFE is also considered to
be a promising intermediate for non-chlorine containing
CFC alternatives, such hydrofluorocarbon ethers, which
have low global warming and zero ozone depleting poten-
tials.
tron withdrawing functional groups like CF , various ionic
3
liquids were prepared and tested for their effects on the
hydrolysis of CF CH Cl. Here we report that the use of
3
2
imidazolium-based ionic liquid enhances significantly the
reactivity of aqueous potassium acetate with CF CH Cl to
give TFE in high yield.
3
2
TFE can be prepared by the hydrolysis reaction of 1-
chloro-2,2,2-trifluoroethane (HCFC-133a) in the presence
of an aqueous alkali metal hydroxide or alkali metal salt of
carboxylic acid as shown in Eqs. (1) and (2) [5,6].
2. Results and discussion
To investigate the role of ionic liquids, the hydrolysis
reactions of CF CH Cl with aqueous potassium acetate were
CF CH Cl þ MOH ðaqÞ ! CF CH OH þ MCl
(1)
3
2
3
2
3
2
CF CH Cl þ RCH CO M ðaqÞ
performed in DMF in the presence of various ionic liquids.
As shown in Table 1, the hydrolysis reactions of CF CH Cl
3
2
2
2
!
CF3CH2OH þ RCH2CO2H þ MCl
(2)
3
2
produced TFE only in 42.7% yield together with the for-
mation of 1.3% of trifluoroethyl acetate, an intermediate to
TFE. Surprisingly, however, the use of small amounts of
imidazolium-based ionic liquid increased the yield of TFE
up to two times, depending on the types of ionic liquid
employed. The ionic liquid added may act as a phase transfer
catalyst, thereby facilitating the contact between CF CH Cl
where M ¼ K, Na.
However, unlike the hydrolysis reaction of an alkyl halide
to give the corresponding alcohol, the hydrolysis reaction of
CF CH Cl, proceeds slowly, even at elevated temperatures,
3
2
due to the presence of an highly electron withdrawing CF3
group.
Recently, the use of ionic liquids such as 1-butyl-3-
3
2
and the potassium acetate [9,10]. The hydrolysis reaction
was not affected by the variation of the cation, but strongly
dependent on the type of anion. Among 1-butyl-3-methyli-
midazolium (bmim) salts, [bmim]Cl gave much higher
yields of TFE in comparison with other imidazolium salts.
methylimidazolium hexafluorophosphate ([bmim][PF ])
6
*
Corresponding author. Tel.: þ82-2-958-5855;
fax: þ82-2-958-5859.
E-mail address: khs@kist.re.kr (H.S. Kim).
0022-1139/$ – see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2003.10.014

96
H. Lee et al. / Journal of Fluorine Chemistry 125 (2004) 95–97
Table 1
Table 2
a
Effect of ionic liquids on the hydrolysis of CF
a
potassium acetate
3
CH
2
Cl with aqueous
3 2
Reuse of the [bmim]Cl for the hydrolysis of CF CH Cl
Number of reaction
Yield (%)
TFE
Entry
Ionic liquid
Yield (%)
3 2
CF CH OAc
TFE
3 2
CF CH OAc
1
2
3
4
5
91.3
92.1
91.4
90.4
89.8
2.6
1.4
2.0
2.8
1.8
1
2
3
4
5
6
7
–
42.7
91.3
87.3
87.1
60.5
61.4
59.2
92.7
67.4
72.2
1.3
2.6
2.4
1.8
2.1
2.4
2.0
1.7
2.1
1.7
[bmim]Cl
[emim]Cl
[dmim]Cl
[bmim][BF
[bmim][OTf]
[bmim][PF
[bmim][OAc]
4
]
a
3 2 3 2
CF CH Cl, 50 mmol; CH CO K, 75 mmol; [bmim]Cl, 10 mmol;
2
H O, 75 mmol; DMF, 30 ml, 180 8C, 3 h.
6
]
b
8
9
Bu
Bu
4
NCl
PBr
volatile organic compounds, CF CH Cl, TFE, acetic acid
3 2
1
0
4
and 2,2,2-trifluoroethyl acetate, at 40 8C under vacuum, the
resulting solution containing [bmim]Cl was reused for a
further hydrolysis reaction with a fresh charge of CF CH Cl,
potassium acetate, and water. As can be seen in Table 2, the
yield of TFE remained almost unchanged even after five
times of reuse, indicating that [bmim]Cl is, indeed, recycl-
able.
a
CF
3 2 3 2
CH Cl, 50 mmol; CH CO K, 75 mmol; ionic liquid, 10 mmol;
H O, 75 mmol; DMF, 30 ml, 180 8C, 3 h. [bmim], 1-butyl-3-methylimi-
dazolium; [emim], 1-ethyl-3-methylimidazolium; [dmim], 1,3-dimethyli-
2
3
2
midazolium.
b
[
bmim][OAc], 75 mmol. The hydrolysis reaction was conducted in
the absence of CH CO K.
3
2
The hydrolysis reaction of CF CH Cl was influenced
3
2
It is likely that [bmim]Cl reacts with potassium acetate to
give [bmim][OAc], which in turn reacts with CF CH Cl and
H O to produce TFE, as shown in Eqs. (3)–(5).
greatly by the amounts of [bmim]Cl used. Fig. 1 shows that
the yield of TFE increased continuously with increasing
amounts of [bmim]Cl up to the molar ratio of [bmim]Cl/
CF CH Cl ¼ 0:4, and remained unchanged thereafter. The
3
2
2
3
2
½
bmimꢀCl þ CH3CO2K ! ½bmimꢀ½OAcꢀ þ KCl
(3)
formation of trifluoroethyl acetate was not affected greatly
by the variation of the molar ratio of [bmim]Cl/CF CH Cl,
3
2
CF3CH2Cl þ ½bmimꢀ½OAcꢀ ! ½bmimꢀCl þ CF3CH2OAc
suggesting that the reaction of trifluoroethyl acetate with
water to produce TFE is an equilibrium reaction.
(4)
As can be seen in Table 3, the amount of potassium acetate
also affected the hydrolysis of CF CH Cl. As the amount of
CF3CH2OAc þ H2O ! CH3CH2OH þ CH3CO2H
(5)
3
2
In fact, the hydrolysis reaction of CF CH Cl with aqueous
2
potassium acetate increased from 1 to 5 molar equivalents of
CF CH Cl, the yield of TFE increased from 75.7 to 97.7%.
3
[
bmim][OAc] produced TFE in an high yield of 92.7% even
3
2
in the absence of potassium acetate (Table 1, entry 8).
The conventional phase transfer catalyst, tetrabutylam-
monium chloride also exhibited some promotion effect for
the hydrolysis reaction. However, it was observed that a
large portion of the tetrabutylammonium chloride added was
decomposed into tributylamine and butyl chloride under
experimental conditions, thereby making the purification
step more costly and prohibiting the recycling of tetrabu-
tylammonium chloride [11]. Tetrabutylphosphonium bro-
mide showed similar behavior to tetrabutylammonium
chloride, decomposing into tributylphosphine and 1-bromo-
butane. The decomposed products, 1-chlorobutane and 1-
bromobutane, were easily converted to 1-butanol by reacting
with aqueous potassium acetate.
The effect of solvents was investigated in the presence of
[bmim]Cl and the results are listed in Table 4. Much higher
yields of TFE were obtained in DMF, DMSO and 1-methyl-
2-pyrrolidinone (NMP) than in g-butyrolactone and CH CN.
3
The lower TFE yields in g-butyrolactone and CH CN
3
can be ascribed to the low solubility of potassium acetate
in these solvents. However, the promoting effect of
[bmim]Cl was found to be more pronounced in g-butyro-
lactone and CH CN when comparing TFE yields in the
presence of [bmim]Cl with the one in the absence of the salt.
3
Table 3
a
Effect of CH
3
CO
2
3 2
K on the hydrolysis of CF CH Cl
b
Entry
Molar ratio
Yield (%)
TFE
In contrast, imidazolium-based ionic liquids exhibited a
1
3 2
CF CH OAc
remarkably high thermal stability. H NMR spectra of the
reaction mixtures containing [bmim][BF ], [bmim][OTf] or
1
2
3
4
5
1
75.7
89.3
91.6
95.3
97.7
2.1
2.6
1.8
2.2
2.0
4
1.5
2
[
bmim]Cl (not shown here) revealed that the ionic liquid
remained unchanged after the reaction. The stability of
the imidazolium-based ionic liquid was confirmed further
by recycling studies. Experiments were conducted using
3
5
a
3 2 2
CF CH Cl, 50 mmol; [bmim]Cl, 10 mmol; H O, 75 mmol; DMF,
[bmim]Cl at 180 8C for 3 h, after which time the reaction
mixture was filtered off to remove KCl. After removing
3
0 ml, 180 8C, 3 h.
Molar ratio: [CH CO K]/[CF CH Cl].
b
3
2
3
2

H. Lee et al. / Journal of Fluorine Chemistry 125 (2004) 95–97
97
Fig. 1. Effect of molar ratio of [bmim]Cl/CF CH
3
2
Cl on the hydrolysis of CF
3
CH
2
Cl. Conditions: CF
3
CH Cl, 50 mmol; CF
2
3
CO
2
K, 75 mmol; H
2
O, 75 mmol;
DMF, 30 ml, 180 8C, 3 h.
Only trace amounts of TFE were formed in toluene and
CH Cl , indicating the importance of solvent polarity in the
hydrolysis reaction.
Hydrolysis reactions were conducted in a 100 ml stainless
steel high pressure reactor with an electrical heating band.
Potassium acetate (75 mmol), solvent (30 ml), H O (1.35 g,
2
2
2
In summary, we have demonstrated the facile hydrolysis
of CF CH Cl to produce TFE using aqueous potassium
acetate in the presence of an imidazolium-based ionic liquid.
The ionic liquids tested were stable enough to be recycled
for further hydrolysis reaction.
75 mmol), 2-methyl pentanone (1 g, internal standard) and
ionic liquid were charged into the reactor. After the mixture
was cooled to 0 8C, CF CH Cl (50 mmol) was fed into
3
2
3
2
the reactor through a sampling valve. The reactor was then
heated to 180 8C and the reactants were stirred for 3 h. After
cooling the reaction mixture to 0 8C, a sample of the liquid
phase was analyzed using GC (HP 6890, FFAP, 25 m ꢁ
0:32 mm ꢁ 5 um). The yields of TFE and CF CH OAc were
3
. Experimental
3
2
determined by GC using an internal standard method. For the
identification of the products, GC–MS (HP 6890N-5973
MSD) and NMR (Varian UNITYplus-300) were employed.
CF CH Cl (1-choro-2,2,2-trifluoroethane) was purchased
3
2
from Halocarbon Product Corp. Solvents, potassium acetate,
tetrabutylammonium chloride, tetrabutylphosphonium bro-
mide, and other reagents were obtained from Aldrich and
used as received. Ionic liquids were prepared as described in
the literature [12,13].
References
[
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[
[
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a
3 2
Effect of solvent on the hydrolysis of CF CH Cl
b
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Solvent
Yield (%)
TFE
CF CH
3
2
OAc
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1
2
3
4
5
6
7
DMF
89.3 (42.7)
80.9 (36.4)
81.3 (35.0)
51.1 (20.3)
18.8 (5.6)
Trace
2.6 (1.3)
2.3 (2.4)
3.5 (2.7)
3.7 (2.6)
1.6 (2.0)
–
c
NMP
DMSO
(
[
[
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[
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p. 73.
2
2
Trace
–
a
3 2 3 2
CF CH Cl, 50 mmol; CH CO K, 75 mmol; [bmim]Cl, 10 mmol;
H
2
O, 75 mmol; solvent, 30 ml, 180 8C, 3 h.
The numbers in parentheses are the results of the reactions conducted
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Gratzel, Inorg. Chem. 35 (1996) 1168.
b
in the absence of [bmim]Cl.
c
NMP, 1-methyl-2-pyrrolidinone.
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Wiley-VCH, Weinheim, 2003.