Note: Descriptions are shown in the official language in which they were submitted.
VAPOR PHASE CHLORINATION OF DIFLUOROMETHYL MEl~IYL ETHER
BACKGROUND OF l~E INVENTION
This invention relates in general to fluorinated dimethyl ethers and specifically to methyl
difluoromethyl ether as a starting material for the synthesis of fluorinated dimethyl ethers. Such
fluorinated dimethyl ethers, including bis(difluoromethyl)ether (CHF20CHF2), have u~lity has
CFC alternatives, particularly for use as refrigerants, blowing agents, etc.
Bis(difluoromethyl)ether has been prepared previously by chlorination of dimethyl ether
followed by isolation and fluorination of bis(dichloromethyl)ether. The chlorination step resulted
in a complex mixture of chlorinated dimethyl ethers, some of which were unstable, e.g. to
distillation, from which bis(dichloromethy1~ether was separated. Moreover, chloromethyl methyl
ether and bis(chloromethyl)ether are produced by this reaction, and are carcinogens.
Another approach to the synthesis of methyl difluoromethyl ether is disclosedby Hine and
Porter in Methvlene derivatives as int_rmediates in polar reaction VIII. Difluoromethvlene in the
Reaction of Chlorodifluoromethane with Sodium Methoxide, published in the Journal of the
American Chemical Society 79, 5493~ (1957). This article describes a reaction mechanism
wherein the desired difluoromethyl-methyl-ether is synthesized in a batch reaction in a fixed ratio
with the by-product trimethyl-orthoformate, while continuously refluxing the unreacted feed.
However, not only does this reaction produce large amounts of trimethylorthoformate, but also
the product itself breaks down to trimethylorthoformate, resulting in less than advantageous yields
of the desired difluoromethyl methyl ether.
U.S. Patent No. 5,185,474, the disclosure of which is hereby incorporated by reference,
discloses avoiding the production of such carcinogens and unstable compounds by using methyl
difluoromethyl ether as a starting material. The methyl difluoromethyl ether is chlorinated to
produce a reaction mixture including at least one compound of the formula CF2HOCH3.zClz,
wherein z is 1, 2, or 3. The mixture can then be fluorinated, or any one of the chlorination
- ~ 2 ~ 2 ~
compounds first separated from the mixture and separately fluorinated. ~;
However, during the chlorination of CF2HOCH3, it is difficult to control the distribution
of products. Although manipulation of the molar flow rates of Cl2 and CF2HOCH3 can give a ~ ~ ;
slight predominance of CF2HOCH2CI or CF2HOCHCI2, a sigmficant arnount of CF2HOCCI3 is
formed. If the desired product to be subsequently fluorinated is either CF2HOCH2CI or
CF2HOCHCI2, the formation of CF2HOCCI3 causes a considerable reduction in the efficiency of
the process.
Accordingly, it is an object of the present invention to provide an improved process for
the production of bis(difluoromethyl) ether.
It is an further object of the present invention to provide an improved process for the
production of bis(difluoromethyl) ether wherein the various required separations may be effected
by distillation without loss of yield and danger of explosion ~ue to marked instability of the
various intermediates.
It is a still further object of the present invention to provide a process for efficiently
producing difluoromethyl methyl ether.
SU~ARY OF THE INVENTION
The problems of the prwr art have been overcome by the present invention, which
provides a process for the production of difluoromethyl methyl ether. More specifically, the
process of the present invention includes means for preferentially inhibiting the formation of
CF2HOCCl3, and which does not produce carcinogens as intermediates.
The unstable complex mixture of chlorinated ethers, some of which are carcinogens, in
accordance with the prior art, is avoided in the present invention by employing methyl
difluoromethyl ether as a starting material. The methyl difluoromethyl ether ischlorinated to give
a chlorinated reaction mixture including at least one compound of the formula CF2HOCH3 zClz,
-
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wherein z is 1, 2 or 3, which compound can be readily separated from the chlorinated reaction
mixture. The chlorination of metbyldifluoromethyl ether would generally form only tbree
derivatives, i.e., z--l, z=2 and z=3. The dichloromethyl difluoromethyl ether (z=2) can be
readily separated from the chlorinated reaction mixture and is then fluorinated, with or without
such separation, to form the bis(difluorome&yl)ether. The production of CF2HOCC13 (z=3) can
be inhibited, and any produced also may be separated from the chlorination reaction product and
fluorinated. Alternatively, the chlorination reaction product itself may be fluorinated (without
prior separation) as follows:
CF2HOCH2CI ~ CF2HOCH2F (I)
~_, CF2HOCHCIF
CF2HOCHCk ~
--' CF2HOCHF2 (II)
CF2HOCCkF
CF2HOCCI3 - ~ CF2HOCCIF2
-- CF2HOCF3 (m)
All of the above would find utility as refrigerants, especially (I) monofluoromethyl difluoromethyl
ether and aI) bis(difluoromethyl)ether, which are considered to be substitutes for R-l 1 and R-l 14
refrigerants, respectively.
DETAILED DESCR~IION OF TEIE lNVENTION
The methyl difluoromethyl e~her which is regarded as the starting material for the process
of the present invention is a known compound which may be prepared in the manner reported by
. ` 2 ~
Hine and Porter in their aforementioned article published in the Journal of the American Chemical
Societv. Specifically, difluoromethyl methyl ether is produced by reaction of sodium methoxide
(NaOMe) with chloro~difluoromethane (CF2HCl), which reaction may be represented as follows~
.. ~ .
CF2HCl + CH30Na~ CF2HOCH3 + NaCI
Briefly, the method involves forming an alcohol solution of sodium methoxide and bubbling the
chlorodifluoromethane slowly into the reaction mixture to obtain the methyldifluoromethyl ether
as a residue in the reaction mix~ure. Some product is entrained with unreacted CF2HCI and can
be separated from it in a distillation operation.
The starting ether, CHF20CH3, also might be prepared by first reacting NaOH with
CH30H, in effect rnaking CH30Na, and then reacting it with CF2HCI. However, water is also
formed in the NaOH/CH30H reaction. The effect water has on the subsequent reaction to form
CHF20CH3 is to reduce the yield of CHF20CH3.
The chlorination and fluorination steps of this invention can be represented as follows:
zCl2
CHF20CH3 ~> CF2HOCH3~zClz + zHCI (where~n z = 1, 2, or 3)
F
CF2HOCH3 zClz ~----> CF2HOCH3~Clz yFy
(whe~ein z = 1, 2, or 3
y= 1,2,or3
y S z)
The inventors of the present invention have found that the formation of CF2HOCH3 zClz
wherein z = 3 in the above reaction scheme can be inhibited or even eliminated upon the addition
of an oxygen source, preferably air, to the vapor phase reacdon medium. Rather than inhibiting
the three chlorination products equally, the addition of oxygen surprisingly preferentially inhibits
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the formation of CF2HOCC13. Although the inventors of the present invention are not to be
limited by any mechanism theory, it is believed that the inhibition is caused as a result of oxygen
forming a complex w,lth the activated chlorine molecule, with the kinetics of the reaction being
such that the trichloro derivative is preferentially inhibited. Any oxygen source not deleterious
to the production of the desired compounds could be used, including oxygen-containing
compounds which liberate oxygen in si~u.
The oxygen should be present in an amount effective for the desired inhibition. In the case
of air, preferably tbe air is added in an amount from about 1.5 to about 5.5% of the total gas
flow. Those skilled in the art will recognize that where pure oxygen is used, the amounts will be
about 1/5 that of air. Preferably the oxygen source is added to the reaction medium for as long
æ the chlorine gæ is flowing.
It hæ been found tbat CHF20CH3 may be suitably chlorinated by liquefying the
CHF20CH3 and reacting it with chlorine gas while irradiating with a source of visible light.
Alternatively, one may use other light sources such as ultraviolet light or heat, a catalyst or a free
radical initiator to aid in the reaction. The chlorirlation products of CHF20CH3 can be readily
separated prior to fluorination or the reaction mixture can be fluorinated without separation to give
an admixture of CF2HOCCI2F, CF2HOCF2CI, CF2HOCH2F, CF2HOCFHCI, CF2HOCF2H. All
separations may be effected by fractional distillation.
A preferred method of chlorinating the CHF20CH3 is to maintain &e CHF20CH3 in a
vapor phæe and react it with chlorine gæ while subjecting the chlorination reaction to a source
of light, preferably visible orultraviolèt light. Alternatively, other reaction aids such as a catalyst,
heat or a free radical initiator rnay be used instead of light in the chlorination reaction.
In t&e preferred fluorination procedure, the chlorinated reaction product is reacted with
anhydrous hydrogen fluoride (HP), which reaction may be represented as follows:
2CF2HOCCI3 + 3HF~--> CF2HOCFCl2 + CF2HOCF2CI + 3HCI
~' ~
Utilizing the above reaction with hydrogen fluoride t'ne inventor has obtained a yield as high as
78% CF2HOCF2Cl with a small amount of CF2HOCFC12. This was an unexpected result since
HF by itself does not normally replace a halogen such as chlorine, except perhaps at very high
temperatures, but instead fluorinates by continuous regeneration of a fluorinating agent such as
SbCI5qFy7 such as SbF3, or SbF3C12. Apparently, the difluoromethoxy group activates the chlorine
on the alpha-carbon atom, aDowing it to react readily with HF.
Alternatively, the HF may be diluted with an organic solvent, preferably a dipolar aprotic
solvent such as metbyl pyrrolidone, in order to reduce fragmentation of the fluorinated material,
resulting in higher yields of desired product with less by-product generation. Other sources of
fluorine for the fluorination step include metal fluorides that can form salts of the HF2e anion,
such as KHF2, NaHF2, LiHF2, NH4HF2, etc., and pyridine salts of HF and NaF and KF in
suitable solvents.
The resultant fluorinated products may be separated by distiDation or by the process as
taught in U.S. Patent 4,025,567 or U.S. Patent 3,887,439 which are incorporated herein by
reference in their entirety.
The present invention will now be further iDustrated by the foDowing examples.
EXAMPLE 1
a) Preparation of CF2HOCH3
A 25 wt ~ solution of sodium methoxide in methanol (1533. lg) containing 7.1 moles of
sodium methoxide was placed in a 4 liter jacketed autoclave fitted with a temperature sensor, a
pressure gauge and a dipleg. The vessel was cooled to 0 to 5C and chlorodifluoromethane
(318.2g, 3.70 moles) added over a period of 2.5 hours with agitation. When the addition of gas
had been completed, the autoclave was s1Owly warmed to about 60C while venting gaseous
products through the water-cooled condenser into a coDection trap cooled to about -70C.
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When all volatile material had been collected unreacted CHF2CI was removed at ^20C
and the remaining CF2HOCH3 transferred to a metal cylinder. The recovered difluoromethyl
methyl ether (150 0g, 1.83 moles) represented a yield of 49.4% based on CF2HCI.
b) Chlorination of CF2HOCH3
Chlorine and CF2HOCH3 in a gaseous phase are passed through separate condensers cooled
to 0C and then the gas strearns combine and pass into one arm of a U-shaped reactor, irradiated
with visible light or W. Both anns of the reactor are jacketed and cooled with water.
There is an outlet at the bottom of the U to which is attached a product collection flask.
A Dewar-type condenser cooled to -50C is attached to the outlet of the second arm of the U-tube
and, in turn, it is connected in series wi& a cold trap to collect unreacted chlorine and an NaOH
scrubber to remove HCI. The reaction is normally carried out at atmospheric pressure, but higher
or lower pressure can be used. Temperature should not be allowed to rise much above 50C in
the reactor to avoid attack on the glass.
In practice, the apparatus is flushed with nitrogen and then chlorine and CHF2OCH3 are
fed to the reactor at rates such that the ratio of the flow of chlorine to that of the ether is
maintained at about 2.5:1 for optimum results, i.e., yield of CF2HOCHCI2. A predorninant
amount of any one of the three products can be obtained by changing t~e ratio of the gas flows.
After the passage of 2.3 moles of chlorine and 0.9 moles of CHF2OCH3, 136.6g of
product were recovered. GC analysis of the product n~ixture showed CF2HOCH2Cl 10.0%,
CF2HOCHCl2 62.4%, and CF2HOCCI3 22.2%.
c) Fluorination of CHF2OCHCl2 with HF
The chlorinated CHF2OCH3 (40.0g) containing 46.1% CF2HOCHCl2 in a stainless steel
cylinder was then cooled in ice before adding anhydrous HF (30.0g). The cylinder was closed
with a valve and pressure gauge and then was placed in a water bath at 60C for 3 hours. The
cylinder was then vented through a NaOH scrubber and volatile products collected in a trap cooled
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at -70C. The weight of product recovered from the trap was 16.8g. It contained 71.8%
CF2HOCF2H by GC analysis, corresponding to a yield of 83.8% of CF2HOCF2H.
When conducted on a larger scale (e.g., 5 gallons), almost quantitative yields of
CF2HOCF2H (based on CF2HOCHCI2) were obtained.
EXAMPLE 2
A sample of chlorinated difluoromethyl ether rLuxture (25g) containing 50% CF2HOCCI3,
was placed in a polyethylene flask fitted with an inlet tube for nitrogen as carrier gas, an outlet
tube leading to a secondpolyethylene flæk containing NaOH solution (10%), followed by a drying
tube and a trap cooled in Dry Ice/MeOH.
An excess of anhydrous hydrogen fluoride was added to the chlorinated ether and the
mixture stirred with a magnetic stirrer. Heat was not applied, the temperature remaining at about
20C. More hydrogen fluoride was added to the mixture as needed until all the organic material
had reacted. The weight of material collected from the cold trap was 9.5g.
Analysis of the recovered product by GC showed it to consist of 84.3 % CF2HOCF2CI, a
yield of 78% bæed on the CF2OCCI3 content of the chlorinated mixture. A small amount of
CFzHOCFCl2 wæ also present.
~ ~ .
EXAMPLE 3
The chlorination apparatus consisted of two vertical lengths of jacketed glass tubing, 4 feet
long by 2 inches I.D., connected at the lower ends in a U-tube fæhion by a short length of
unjacketed 2 inch I.D. tubing. A drain tube led from the lowest point of the U-tube arrangement
so that product could be collected as it forrned and removed continuously from the apparatus or
alternatively allowed to accumulate in a receher. Three 150 watt incandescent flood lamps were
arranged along the length of each tube.
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The gases were fed into the upper end of one arm of the U-tube arrangement. Flow rates
were measured by calibrated mass flowmeters. A low temperature condenser on the ou~det of the
second arm of the U-tube returned unreacted E-152a and chlorine to &e illuminated reaction zone.
Hydrogen chloride by-product and air passed through the condenser into a water scrubber where
the hydrogen chloride was removed.
A mixture of methanol and water, cooled to O to 5C was circulated &rough &e cooling
jackets of &e apparatus.
In a typical run, coolant at a temperature of O to 5C is circulated through &e cooling
jackets, &e flood lamps were turned on and dry ice placed in the low ternperature condenser.
Chlorine was introduced into the apparatus first, followed by difluorome&yl ether and air in the
desired ratios. Product was removed at illtervals from &e receiver and washed with saturated
NaHC()3 solution to remove HCl. Since the reaction was continuous, it could proceed for any
length of time desired. At the end of the reaction, gas flows were stopped and product allowed
to drain froIn &e vertical reactor tubes into the receiver.
The results are tabulated in Table 1 below. Examples 6-29-1 to 6-29-7 show ~he
distn~ution of products normally obtained without the addition of air to &e gas stream. Examples
7-7-3 through 7-8~ show the effect of the addition of air in dirninishing arnounts, in accordance
wi& the presentinvention.
TABLE 1
--Flow Rates-- hod=l --P~oduct Distributioo----Moles-- Mob Ratio m T:ral Air m
E1DIYQ C80 ~ 152a A~ ~Y~ ~SQ~Q r~ Tn S~2 E~2a C~2oe~2~ Ch5~0w S~lQi
(mlshDiD) (gms) (%) (%) (%) ~0) (%)
6-29-1 500 273 _ 69.6 6.0 42.5 33.60.0203 0.0111 1.83 .
6-29-2 500 280 _ 95.6 8.2 42.5 30.40.0203 0.0114 1.~8 .
6-29-6 510 270 - 81.4 22.5 38.5 33.70.0207 0.0110 1.88 .
6-29-7 500 280 - 79.1 23.2 42.3 37.20.0203 0.0114 1.~8 _
7-7-3 870 380 6~ 69.3 55.0 32.9 2.80.0353 0.0154 2.29 5.4 7.~
4 850 440 65 96.8 56.8 37.0 3.50.0345 0.01~9 1.93 5.1 ~.6
~-~-5 900 405 63 119.3 48.3 42.4 5.20.0365 0.0164 2.23 4.8 7.0
~ 900 405 60 116.0 54.3 39.8 4.50.0365 0.0164 2.23 4.6 6.~
7-~-8 930 405 62 111.5 52.5 36.2 3.30.0378 0.0164 2.30 4.6 6.7
~-8-2 1430 600 55 198.6 43.0 45.2 ~.20 0581 0 0244 2 38 2.~ 3.8
~-8-3 1850 ~50 54 202.4 42.8 46.5 5.00 0~51 0 0305 2 46 2 1 2 9
7-8-6 2200 1030 51 213 0 33.6 56.9 7 ~0.0893 0.0418 2.14 1 3 Z-3
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