Selective production of difluoromethyl methyl ether from chlorodifluoromethane using alkali metal carbonates

Article abstract of DOI:10.1016/S0022-1139(00)00392-4

CHF₂OCH₃ (HFE-152a), an important starting material for synthesizing various C₂ hydrofluoroethers and a prospective alternative to CH₃CF₂Cl (HCFC-142b), has been found to be effectively produced from the reaction of CHF₂Cl (HCFC-22) with alkali metal carbonates in methanol. Some alkali metal carbonates induce selective production of CHF₂OCH₃ with a small amount of CH(OCH₃)₃, a major side product. Activities of alkali metal carbonates for producing CHF₂OCH₃ are in the order of K₂CO₃ > Na₂CO₃ > Li₂CO₃, suggesting that the solubility and ionization tendency of alkali metal carbonate in methanol play important roles in the reaction.

Full text of DOI:10.1016/S0022-1139(00)00392-4

Journal of Fluorine Chemistry 107 (2001) 133±136
Selective production of di¯uoromethyl methyl ether from
chlorodi¯uoromethane using alkali metal carbonates
Hyunjoo Leea, Hoon Sik Kima, Sang Deuk Leea, Won Koo Leeb, Honggon Kima,*
aCFC Alternatives Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongrayng, Seoul 136-791, South Korea
bDepartment of Chemistry, Sogang University, Seoul 121-742, South Korea
Received 28 July 2000; accepted 29 September 2000
Abstract
CHF2OCH3 (HFE-152a), an important starting material for synthesizing various C2 hydro¯uoroethers and a prospective alternative to
CH3CF2Cl (HCFC-142b), has been found to be effectively produced from the reaction of CHF2Cl (HCFC-22) with alkali metal carbonates
in methanol. Some alkali metal carbonates induce selective production of CHF2OCH3 with a small amount of CH(OCH3)3, a major side
product. Activities of alkali metal carbonates for producing CHF2OCH3 are in the order of K2CO3 > Na2CO3 > Li2CO3, suggesting that
the solubility and ionization tendency of alkali metal carbonate in methanol play important roles in the reaction. # 2001 Elsevier Science
B.V. All rights reserved.
Keywords: Hydro¯uoroether; Di¯uoromethyl methyl ether; Chlorodi¯uoromethane; Alkali metal carbonate
1. Introduction
In this paper, we report a method to suppress effectively
the formation of the side product, CH(OCH3)3 by employing
alkali metal carbonates instead of using CH3ONa as a
base.
Hydro¯uoroethers (HFEs) are prospective candidates for
next generation alternatives of CFCs (chloro¯uorocarbons)
because HFEs do not produce ozone depletion and these
have very low impact on global warming [1±3]. Several
theoretical and experimental reports proposed that some
HFEs such as CHF2OCHF2, CF3OCH3, CF3CF2OCH3,
and CF3CF2CF2OCH3 have favorable physical and chemical
properties as do CFCs, HCFCs (hydrochloro¯uorocarbons)
and HFCs (hydro¯uorocarbons) [4±6].
Di¯uoromethyl methyl ether (CHF2OCH3, HFE-152a) is
considered a useful starting material for synthesizing various
higher-¯uorinated dimethyl ethers [7] and a possible alter-
native refrigerant to CH3CF2Cl (HCFC-142b) [8]. It has
been reported that CHF2OCH3 can be synthesized by the
reaction of CHF2Cl and CH3ONa in which, however, a large
amount of trimethylorthoformate, CH(OCH3)3, is produced
as a side product which is, however, economically valueless
[8±10]. Formation of CH(OCH3)3 requires competitive con-
sumption of the reactants, CHF2Cl and CH3ONa. In other
words, the formation of CH(OCH3)3 inevitably reduces the
yield of CHF2OCH3.
2. Experimental
CHF2Cl (purity > 98%) was supplied from Ulsan Che-
mical Co. Methyl alcohol, sodium methoxide, alkali metal
carbonates and other reagents used were purchased from
Aldrich Chemical Co. All chemicals were used without
further puri®cation.
Reactions were conducted in a 100 ml stainless steel high-
pressure reactor with a magnetic drive stirrer and an elec-
trical heating jacket. Base (50 mmol), methanol (25 ml) and
ethylene glycol dimethyl ether (1 g, internal standard)
were charged into the reactor. After the mixture was cooled
to 58C with a vigorous stirring, CHF2Cl (200 mmol) was
fed to the reactor through a sampling valve. The reactor
was then heated to a reaction temperature and the reactants
were stirred for 2 h. After cooling the reaction mixture to ±
788C, a sample of the liquid phase was analyzed using GC
(HP 6890, HP-1, 50 m  0:2 mm  10 um). The formation
of CHF2OCH3 was con®rmed by GC-Mass (HP 6890-5973
MSD) and 19F NMR (564.54 MHz, Varian INOVA-600)
[11].
* Corresponding author. Tel.: ‡82-2-958-5858; fax: ‡82-2-958-5859.
E-mail address: hkim@kist.re.kr (H. Kim).
0022-1139/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 0 ) 0 0 3 9 2 - 4

134
H. Lee et al. / Journal of Fluorine Chemistry 107 (2001) 133±136
Conversion of the base was determined by acidimetric
concentration of CH3ONa. These results clearly indicate that
the formation of CH(OCH3)3 cannot be suppressed by
changing either the reaction temperature or the concentra-
tion of CH3ONa.
Two reaction mechanisms have been proposed for the
formation of CHF2OCH3 and CH(OCH3)3. Satoh et al.
proposed a reaction mechanism, where CHF2OCH3 and
CH(OCH3)3 are produced consecutively as in Eqs. (1)
and (2) [8].
titration of unreacted base left in the solution using 0.1N
aqueous HCl with an indicator. Yields of CHF2OCH3 and
CH(OCH3)3 were evaluated from gas chromatographic
results of the liquid sample containing internal standard
and the quantitative analysis of alkali metal chloride and
alkali metal ¯uoride. Yields of CHF2OCH3 and CH(OCH3)3
were de®ned as follows:
Percent yield of CHF2OCH3
CHF2Cl ‡ CH3ONa ! CHF2OCH3 ‡ NaCl
(1)
(2)
100  ‰CHF2OCH3 produced; mmolŠ
ˆ
‰baseintroduced; mmolŠ
CHF2OCH3 ‡ 2CH3ONa ! CHꢀOCH3† ‡ 2NaF
3
Percent yield of CHꢀOCH3†
3
They reported that the formation of CH(OCH3)3 is reduced
by removing CHF2OCH3 as soon as it forms.
100  ‰CHꢀOCH3†3 produced; mmolŠ
ˆ
On the other hand, Hine and Porter proposed a different
reaction mechanism in which CHF2OCH3 and CH(OCH3)3
were produced from the same di¯uorocarbene intermediate
F2 formed by the elimination of HCl from CHF2Cl as shown
in the following equations [9].
‰baseintroduced; mmolŠ
3. Results and discussion
3.1. Formation of CHF2OCH3 and CH(OCH3)3
CHF2Cl ‡ CH3ONa !: CF2 ‡ CH3OH ‡ NaCl
(3)
In order to ®nd out whether the variation of reaction
parameters can affect the formation of the side-product, the
reaction of CHF2Cl with CH3ONa was investigated at
various temperatures and CH3ONa concentrations. As
shown in Table 1, the yields of CHF2OCH3 and CH(OCH3)3
increased along with the temperature, but the product ratio
of CHF2OCH3/CH(OCH3)3 remained almost constant in the
range 3.6±3.7. On the other hand, the yield of CHF2OCH3
decreased as the concentration of CH3ONa increased. Even
though the formation of CH(OCH3)3 was suppressed by
lowering the concentration of CH3ONa, the amount of
CH(OCH3)3 was still high with respect to the formation
of CHF2OCH3. Furthermore, the net production of the target
compound, CHF2OCH3 also decreased with decrease in the
In order to have a better insight into the mechanism for the
formation of CH(OCH3)3, we have conducted a reaction of
CHF2OCH3 with CH3ONa. The reaction of CHF2OCH3 and
CH3ONa at 258C for 2 h produced only a trace amount of
CH(OCH3)3, strongly implying that CH(OCH3)3 is not
produced from CHF2OCH3.
Table 1
Effects of temperature and CH3ONa concentration on the production of CHF2OCH3 from CHF2Cl and CH3ONaa
Entry
CH3ONa (mmol)
Temperature (8C)
Conversion (%)b
Yield (%)
A
Product ratio (A/B)d
B
1
50
50
0
25
40
60
25
25
25
25
25
74.4
86.0
92.6
98.8
92.5
93.0
83.7
88.2
85.2
39.0
47.0
50.3
54.0
59.9
56.7
40.0
50.8
44.9
10.8
12.7
13.6
15.0
10.7
12.0
14.4
12.4
13.2
3.6
3.7
3.7
3.6
5.6
4.7
2.8
4.1
3.4
2
3
50
4
50
5
12.5
25
6
7
100
40
8c
9c
67
a Reaction condition: CH3ONa/CHF2Cl ˆ 1/4, methanol 25 ml, CH3OCH2CH2OCH3 (internal standard) 1 g, reaction time 2 h.
b Conversion of base.
c CHF2Cl ˆ 200 mmol.
d A: CHF2OCH3; B: CH(OCH3)3.

H. Lee et al. / Journal of Fluorine Chemistry 107 (2001) 133±136
135
Table 2
Effect of bases on the production of CHF2OCH3 from CHF2Cl and methanola
Entry
Baseb
Temperature (oC)
Conversion (%)c
Yield (%)
A
Product ratio (A/B)d
B
1
2
3
4
5
6
KOH (15.7)
25
60
82.4
99.5
70.5
8.4
40.4
51.8
64.0
8.0
12.9
15.6
1.7
±
3.1
3.3
37.6
±
NaOH (15.7)
K2CO3 (10.3)
KHCO3 (6.35)
NaHCO3 (6.35)
CH3CO2Na (5)
60
100
100
100
3.5
1.6
3.2
1.5
±
±
±
±
a Reaction condition: base 50 mmol, CHF2Cl 200 mmol, methanol 25 ml, CH3OCH2CH2OCH3 (internal standard) 1 g, reaction time 2 h.
b The values in parenthesis are pKa's of conjugate acids [12].
c Conversion of base.
d A: CHF2OCH3; B: CH(OCH3)3.
3.2. Reactions of chlorodifluoromethane with various
bases
On the contrary, the reaction of less basic K2CO3 with
CHF2Cl gave the highest yield of CHF2OCH3 and the lowest
formation of CH(OCH3)3. In the case of much weaker base,
KHCO3 or CH3CO2Na, only a few percent conversion were
obtained at 1008C. These results indicate that basicity is
important in enhancing the yield of CHF2OCH3 and in
preventing the formation of CH(OCH3)3.
Table 3 shows that the reactivity of alkali metal carbonate
for the production of CHF2OCH3 is in the order of
K2CO3 > Na2CO3 > Li2CO3. The same trend is observed
with alkali metal bicarbonates: KHCO3 > NaHCO3
(Table 2). These indicate that, in addition to the basicity,
solubility and ionization tendency of alkali metal carbonate
in methanol play important roles in determining the yield of
CHF2OCH3.
In an attempt to ®nd a more ef®cient base system to
replace CH3ONa, several bases having different basicities
were tested for the production of CHF2OCH3. According to
the carbene mechanism, the side product, CH(OCH3)3 can
be produced only in the presence of methoxide anion.
Therefore, if the base to be used has a basicity that is
enough to abstract hydrogen from CHF2Cl but too weak
to form CH3O from CH3OH, then a higher yield of
CHF2OCH3 and less formation of CH(OCH3)3 can be
achieved.
Table 2 shows that KOH and NaOH exhibit similar
behavior to CH3ONa for the production of CHF2OCH3
and CH(OCH3)3. The formation of large amounts of
CH(OCH3)3 can be ascribed to the methoxide anion
(CH3O ) formed by the equilibrium reaction between
OH and CH3OH.
The effect of temperature on the reaction of CHF2Cl with
alkali metal carbonate was investigated. Unlike in the case of
CH3ONa (Table 1), the yield of CH(OCH3)3 decreased with
rise in reaction temperature (Table 3). However, the forma-
tion of CHF2OCH3 increased with the temperature rise,
giving higher product ratio of CHF2OCH3/CH(OCH3)3.
OH ‡ CH3OH„H2O ‡ CH3O
Keq ꢁ 0:50
(6)
Table 3
a
Effect of alkali metal carbonates on the production of CHF2OCH3
Entry
Base
Temperature (8C)
Conversion (%)b
Yield (%)
A
Product ratio (A/B)d
B
1
2
3
4
5
6
7
Li2CO3
Na2CO3
Na2CO3
K2CO3
K2CO3
K2CO3
100
60
12.5
5.9
12.1
5.7
±
±
±
±
100
25
40.4
42.5
71.2
78.6
87.7
41.2
30.6
64.0
74.8
84.2
±
±
3.6
2.1
1.2
0.8
8.5
30.5
62.3
105.3
60
100
100
c
K2CO3
a Reaction condition: alkali metal carbonate 50 mmol, CHF2Cl 200 mmol, methanol 25 ml, CH3OCH2CH2OCH3 (internal standard) 1 g, reaction time
2 h.
b Conversion of base.
c K2CO3: 25 mmol.
d A: CHF2OCH3; B: CH(OCH3)3.

136
H. Lee et al. / Journal of Fluorine Chemistry 107 (2001) 133±136
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4. Conclusion
[3] D.L. Cooper, T.P. Dunningham, Atmos. Environ. 27A (1993)
117.
CHF2OCH3 (HFE-152a) can be produced by the reaction
of CHF2Cl (HCFC-22) and methanol with base. Experi-
mental studies revealed that the formation of the valueless
side-product CH(OCH3)3 was inevitable in the reaction of
CHF2Cl with CH3ONa. Alkali metal carbonates showed
remarkable activities and selectivities for CHF2OCH3 by
suppressing the formation of CH(OCH3)3. Activities of alkali
metal carbonates for producing CHF2OCH3 were in the order
K2CO3 > Na2CO3 > Li2CO3, suggesting that solubility and
ionization tendency of alkali metal carbonate in methanol
play important roles in determining the yield of CHF2OCH3.
[4] E.A. Vineyard, J.R. Sand, T.G. Statt, Selection of ozone-safe,
nonazeotropic refrigerant mixtures for capacity modulation in
residential heat pumps, in: CFCs Ð Time of Transition, American
Society of Heating, Refrigerating and Air-Conditioning Engineers,
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119:116795).
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(1998) 211.
[9] J. Hine, J.J. Porter, J. Am. Chem. Soc. 20 (1957) 5493.
[10] F.B. Popper, European Patent Application 0 603 002A1 (1993)
(Chem. Abs. 121:82513).
References
‡
[11] Mass fragmentation pattern: 82 (M ), 81 (100%), 63, 51, 15. 19F
NMR (ref. CFCl3): 86.91 ppm (d, J ˆ 75:5 Hz).
[12] A.J. Gordon, R.A. Ford, The Chemist's Companion, Wiley, New
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