JPH06298693A - Method of vapor-phase chlorination of difluoromethyl methyl ether - Google Patents

Abstract

PURPOSE: To provide a preparation process of fluorinated dimethyl ether wherein the generation of carcinogenic CF₂HOCCl₃, as an intermediate is inhibited.

CONSTITUTION: A preparation process of fluorinated dimethyl ether of the formula: CF₂HOCCl_xF_yH_3-(x+y) (wherein _x is 0, 1 or 2; _y is 1, 2 or 3; and _(x+y) is 1, 2 or 3) is provided. In this process, methyl difluoromethyl ether is chlorinated in the presence of oxygen to form a chlorinated reaction product of formula: CF₂HOCH_3-zCl_z (wherein _z is 1 or 2) and the generation of CF₂HOCCl₃ is also inhibited, here. The obtained compound is subsequently fluorinated and then, separated to obtain a fluorinated reaction product containing the above- mentioned fluorinated dimethyl ether.

COPYRIGHT: (C)1994,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to fluorinated dimethyl ethers, and more particularly to methyldifluoromethyl ethers as a starting material for the synthesis of fluorinated dimethyl ethers. Such fluoromethyl ethers include bis (difluoromethyl) ether (CHF ₂ OCHF ₂ ), and are used as CFC substitutes, particularly as a cooling agent and a blowing agent.

[0002]

2. Description of the Related Art Conventionally, bis (difluoromethyl) ether has been produced by chlorinating dimethyl ether, followed by separation and fluorination of bis (dichloromethyl) ether. This chlorination step results in a complex mixture of chlorinated dimethyl ethers, some of which are unstable to distillation, for example when separating bis (dichloromethyl) ether. In addition, chloromethyl ether and bis (chloromethyl) ether are produced by this reaction, which are carcinogens.

Another method for the synthesis of methyl difluoromethyl ether is Hine and Porte.
r) by Journal of the Amer
ican Chemical Society 79,
5493-6 (1957), "Methylene Derivatives as Intermediates in Polar Reactions, VIII Difluoromethylene in the Reaction of Chlorodifluoromethane with Sodium Methoxide". In this paper,
A reaction mechanism is described in which the desired difluoromethyl methyl ether is synthesized with the by-product trimethyl orthoformate by a batch reaction at a predetermined ratio while continuously refluxing the unreacted feed. However, this reaction not only produces large amounts of trimethyl orthoformate, but the product itself decomposes to trimethyl orthoformate and as a result the desired difluoromethyl ether is not obtained in advantageous yields.

US Pat. No. 5,1 cited as a citation
No. 85,474 discloses the use of methyldifluoromethyl ether as a starting material to eliminate the formation of such carcinogens and labile compounds. The methyl difluoromethyl ether is chlorinated to form the formula CF ₂ HOCH _3-Z Cl _Z, where _Z is 1, 2
Or a reaction mixture containing at least one compound of 3) is produced. This mixture is then fluorinated, or any of the chlorinated compounds initially separated from this mixture are separated and fluorinated.

However, in the chlorination of CF ₂ HOCH ₃ , it is difficult to control the product distribution. By manipulating the molar flow ratio of Cl ₂ and CF ₂ HOCH ₃ , CF ₂ HOCH ₂ Cl or CF ₂
Although some advantage can be given to HOCHCl ₂ , a significant amount of CF ₂ HOCCl ₃ is produced. If the desired product to be fluorinated is then CF ₂ HOCH ₂ C
The formation of CF ₂ HOCCl ₃ , when either 1 or CF ₂ HOCHCl ₂ , causes a considerable reduction in the efficiency of the process.

[0006]

Accordingly, it is an object of the present invention to provide an improved process for the production of bis (difluoromethyl) ether. Another object of the invention is without compromising the yield and without the risk of explosion due to the marked instability of the various intermediates.
The various required separations are to provide an improved process for the production of bis (difluoromethyl) ethers by distillation. Yet another object of the present invention is to provide a process for effectively producing difluoromethyl methyl ether.

[0007]

The above-mentioned problems of the prior art have been overcome by the present invention which provides a process for the production of difluoromethyl methyl ether. In particular, the process of the present invention includes means for selectively preventing the formation of CF ₂ HOCCl ₃ and not producing carcinogens as intermediates.

In the present invention, the use of methyldifluoromethyl ether as a starting material eliminates an unstable complex mixture of chlorinated substances, which in the prior art is said to be a carcinogen. This methyl difluoromethyl ether is chlorinated and has the formula CF
A chlorination reaction mixture containing at least one compound of ₂ HOCH _3-Z Cl _{Z, where Z} is 1, 2 or 3 is provided. This compound can be easily separated from the chlorination reaction mixture. Chlorination of methyl difluoromethyl ether is generally accomplished by three derivatives, namely z = 1, z = 2 and z =
Only the derivative of 3 is produced. Dichloromethyldifluoromethyl ether (z = 2) can be easily separated from this chlorination reaction mixture, but is then fluorinated without such separation or separation to produce bis (difluoromethyl) ether. It CF ₂ HOCCl
It is possible to prevent the generation of ₃ (z = 3). The product can likewise be separated from the chlorination reaction product and fluorinated. Alternatively to the above, the chlorination reaction product itself can be fluorinated as follows. (Without separation in advance).

[0009]

[Chemical 1]

All of the above can be used as coolants or refrigerants, in particular (I) monofluoromethyldifluoromethyl ether and (II) bis (difluoromethyl) ether are R-11 and R-1 respectively.
It is considered to be an alternative to 14. Methyldifluoromethyl ether, which is regarded as a starting material in the method of the present invention, is a known compound, and is described in Journal of the
American Chemical Society
Hine and Porter described in
er) method. Especially difluoromethyl ether is sodium methoxide (NaOM
prepared by reaction of e) with chlorodifluoromethane (CF ₂ HCl), which reaction is represented as:

[0011]

[Chemical 2]

Briefly, this method produces an alcoholic solution of sodium methoxide and slowly blows chlorodifluoromethane into the reaction mixture to obtain methyldifluoromethyl ether as a residue in the reaction mixture. . Some product is unreacted CF ₂ H
Since it is contained together with Cl, it can be separated by a distillation operation.

CHF ₂ OCH, the starting ether
₃ first reacts NaOH with CH ₃ OH to give CH ₃ O
It can be similarly prepared by making Na and then reacting it with CF ₂ HCl. However, water is produced during the NaOH / CH ₃ OH. The produced water produces CHF ₂ OCH ₃ in the next reaction, and C
It reduces the yield of HF ₂ OCH ₃ . The chlorination and fluorination steps of the present invention are represented as follows.

[0014]

[Chemical 3]

The present inventors have found that CF _{2 in the} above reaction formula
HOCH _3-Z Cl _Z source of oxygen (where _Z = 3) generated vapor phase reaction medium, preferably have found that either prevented by the addition of air, or removal is even possible. Regardless of equally preventing the three chlorinated products,
It is surprising that the addition of oxygen preferentially prevents the formation of CF ₂ HOCCl ₃ . Although the inventors are not limited to the theory of reaction mechanism,
This prevention appears to be the result of oxygen forming a complex with activated chlorine molecules, with reaction kinetics such that the trichloro derivative is preferentially prevented. Any oxygen source may be used as long as it is not harmful to the formation of the desired compound, and an oxygen-containing compound that releases oxygen at that location is also included in this.

Oxygen should be present in an amount that produces the desired inhibitory effect. In the case of air, it is preferably added in an amount of about 1.5 to about 5.5% of the total gas flow rate. It will be appreciated by those skilled in the art that when pure oxygen is used, its amount is about one fifth of the amount of air. This oxygen source is preferably added to the reaction medium as long as chlorine gas is flowing.

CHF₂OCH₃Is CHF₂OCH₃To
Liquefaction and react with chlorine gas while irradiating with a visible light source
It was found that the
Was issued. Instead of the visible light mentioned above, UV or heat
Use other light sources, such as a catalyst or catalyst to aid the reaction.
Free radical initiators may also be used. CHF₂OCH ₃
The chlorinated products of E. coli can be easily separated before fluorination
Or fluorination without separation of the reaction mixture
Can be CF₂HOCCl₂F, CF ₂HOC
F₂Cl, CF₂HOCH₂F, CF₂HOCFHC
l, CF₂HOCF₂A mixture of H is given. All of these
All separations can be carried out by fractional distillation.

[0018] CHF ₂ OCH ₃ in the preferred method of chlorination is to hold the CHF ₂ OCH ₃ in the vapor phase, a light source, preferably be reacted with chlorine gas under visible or ultraviolet light. Instead of light in the chlorination reaction, other reaction aids such as catalysts, heat or free radical initiators may be used. In the preferred fluorination step, the chlorination reaction product is reacted with anhydrous hydrogen fluoride (HF). This reaction is represented as follows.

[0019]

[Chemical 4]

By using the above reaction with hydrogen fluoride, the inventor has found that with a small amount of CF ₂ HOCFCl ₂ ,
A high yield such as 8% CF ₂ HOCF ₂ Cl was obtained. This was an unexpected result because HF itself usually does not displace halogens such as chlorine except at very high temperatures. However, it may be fluorinated by continuous regeneration of a fluorinating agent such as SbCl _5-y F _y (eg SbF ₃ ) or SbF ₃ Cl ₂ . It is clear that the difluoromethoxy group activates chlorine on the alpha carbon atom and reacts readily with HF.

Alternatively to the above, HF is a dipolar aprotic such as an organic solvent, preferably methylpyrrolidone, to reduce fission of the fluorinated material.
You may dilute with a solvent. This allows the desired product to be obtained in high yield with less by-product formation. Other fluorine sources for the fluorination process include KH
_{F 2, NaHF 2, LiHF 2} , NH 4 HF 2, HF , such as equal ^- metal fluoride capable of generating an anion of salt, containing pyridine salt of HF, NaF and KF (a suitable solvent).

The resulting fluorinated product may be isolated by distillation or by the method taught in the cited US Pat. Nos. 4,025,567 or 3,887,439. it can. The present invention will be described in more detail with reference to the following examples.

[0023]

【Example】

Example 1 a) Preparation of CF ₂ HOCH ₃ A 25 wt% solution of sodium methoxide in methanol (1533.1 g) containing 7.1 mol sodium methoxide in a 4 liter jacket equipped with a thermometer, pressure gauge and dip leg. It was placed in an autoclave. This container is 0
Cooled to -5 ° C and stirred for 2.5 hours over chlorodifluoromethane (318.2g, 3.
70 mol) was added. When the gas addition is complete,
Slowly heat the autoclave to about 60 ° C, while
The gaseous product was discharged through a water cooled condenser into a collection trap cooled to about -70 ° C.

When all the volatiles were collected, the unreacted CHF ₂ Cl was removed at -20 ° C and the remaining CF ₂ HOCH ₃ was transferred to a metal cylinder. This recovered difluoromethyl methyl ether (150.0
g, 1.83 mol) showed a yield of 49.4% based on CF ₂ HCl. _{b) CF 2 HOCH CF 2 HOCH} 3 in a chlorinated chlorine and gas phase ₃ is passed through a separation capacitor cooled to 0 ° C., then combined gas stream,
It is passed through one arm of a U-shaped reactor illuminated with visible light or UV. Both arms of the reactor are jacketed and water cooled.

An outlet is provided at the bottom of the U-shape, and a product collection flask is attached to the outlet. -50 ° C
The Dewar-type condenser cooled to
A cold trap and H attached to the U-shaped second arm for trapping unreacted chlorine
A NaOH scrubber for removing Cl is connected in series. The reaction is usually carried out at atmospheric pressure, although lower or higher pressures can be used.
The temperature inside the reactor is about 50 ° C to avoid glass erosion
Do not raise too much.

In practice, the device was flushed with nitrogen,
The ratio of chlorine and CHF ₂ OCH ₃ chlorine flow to ether flow is then the optimum result, ie CF ₂ HO.
The reactor is fed at a rate such that it is maintained at about 2.5: 1 to give the highest yield of CHCl ₂ . A preferential amount of any of the three products can be obtained by varying the gas flow ratio.

2.3 mol of chlorine and 0.9 mol of CHF ₂
After passing OCH ₃ , 136.6 g of product were recovered. GC analysis of the product mixture showed CF ₂ HOCH ₂ C
1: 10.0%, CF ₂ HOCHCl ₂ : 62.4%,
And CF ₂ HOCCl ₃ : 22.2%. c) Fluorination of CHF ₂ OCHCl ₂ with HF Chlorinated CHF containing 46.1% CF ₂ HOCHCl _2.
2 OCH ₃ (40.0 g) was cooled with ice in a stainless steel cylinder, then anhydrous HF (30.0 g) was added. The cylinder was sealed with a valve and pressure gauge and placed in a 60 ° C. water bath for 3 hours. The cylinder was then evacuated through a NaOH scrubber and volatile products collected in a trap cooled to -70 ° C.
The weight of product recovered from the trap was 16.8 g. According to GC analysis, this product contains 71.8% C
It contains F ₂ HOCF ₂ H, which corresponds to a yield of CF ₂ HOCF ₂ H of 83.8%. When performed with a large skeleton (eg 5 gallons), CF ₂ HOCF
A quantitative yield of ₂ H (based on CF ₂ HOCHCl ₂ ) was obtained.

Example 2 A sample of a chlorinated difluoromethyl ether mixture (25 g) containing 50% CF ₂ HOCCl ₃ was taken as an inlet tube of nitrogen as carrier gas, NaOH solution (10%).
) Was placed in a polyethylene flask with an outlet tube leading to a second polyethylene flask.
The outlet tube of this flask is equipped with a dry tube and a trap cooled with dry ice / MeOH.

Excess anhydrous hydrogen fluoride becomes chlorinated ether
Is added and the mixture is stirred with a magnetic stirrer
It was No heat was applied and the temperature was maintained at about 20 ° C. You
This mixture may be added, if necessary, until all organic substances have reacted.
Further hydrogen fluoride was added to. Cold trap
The amount of substance collected from the above was 9.5 g. By GC
According to analysis of the product recovered from
3% CF ₂HOCF₂It consists of Cl and its yield is chlorine
CF of chemical mixture₂OCCl₃78% based on the content
It was A small amount of CF₂HOCFCl₂Exists as well
It was

Example 3 A chlorination apparatus is a U-tube type jacket with two vertical lengths connected by a short length, unjacketed, 2 inch ID tube to the lower end. It consists of a glass tube (4 feet long x 2 inches inside diameter). The drain tube is led from the lowest point of the U-tube arrangement so that the product can be collected when it is produced and continuously removed from the device or stored in a receiver. There is. Three 150 watt incandescent flood lamps were placed along the length of each tube.

Gas was fed into the upper end of one arm of the U-tube arrangement. Flow rate was measured by a corrected mass flow meter. Unreacted E-152a (methyldifluoromethyl ether) and chlorine were returned to the reaction zone during irradiation from the low temperature condenser at the outlet of the second arm of the U-tube. The hydrogen chloride byproduct and air were passed through a condenser into a water scrubber where hydrogen chloride was removed.

A mixture of methanol and water cooled to 0-5 ° C. was circulated through the cooling jacket of the device. In a typical method, refrigerant at a temperature of 0 to 5 ° C is circulated through a cooling jacket, a flood lamp is turned on, and dry ice is placed in a low temperature condenser. Chlorine is introduced into the apparatus and then difluoromethyl ether and air in the desired ratio. The product was intermittently removed from the receiver and washed with saturated NaHCO ₃ to remove HCl. Since the reaction is continuous, it can be allowed to proceed for a desired length of time. At the end of the reaction, the gas flow was stopped and the product was dripped into the receiver through a vertical reactor tube.

The results are shown in Table 1 below. Example 6-
29-1 to 6-29-7 represent the product distributions normally obtained without the addition of air to the gas stream. Example 7-
Nos. 73 to 7-8-6 show the effect of reducing the addition of air according to the present invention.

[0034]

EFFECT OF THE INVENTION CF ₂ H which is a carcinogen as an intermediate
A method for producing fluorinated dimethyl ether that prevents the formation of OCCl ₃ is provided.

[0035]

[Table 1]

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Robert Jay. Burka, Hutchinson Road, Merrimack, 03054 New Hampshire, USA 9

Claims (11)

[Claims] 1. CHF ₂ OCH ₃ is reacted with chlorine in the presence of oxygen to give a compound of the formula CF ₂ HOCH _3-Z Cl _z.
A chlorinated mixture containing at least one compound of formula (wherein _Z is 1 or 2) and preventing the formation of CF ₂ HOCCl ₃ and having the formula CF ₂ HO
The CH _3-Z Cl wherein at least one compound of _Z, in the absence of a catalyst, hydrogen fluoride, anhydrous hydrogen fluoride, HF ₂ ^-
Fluorinated with a fluorine source selected from the group consisting of pyridine salts of NaF, KF and HF of the formula CF ₂ HO.
A fluorinated mixture containing at least one compound of CH _3-z FyCl _zy is obtained, the formula CF ₂ HOCClXF _y H
_A method for producing a fluorinated dimethyl ether represented by _{3- (x + y)} (where _X is 0, 1 or 2, _y is 1, 2 or 3, and _{X + y} is 1, 2 or 3). 2. A process according to claim 1, wherein the chlorination step occurs in either the gas or liquid phase and the chlorine is in liquid or gas form. 3. The method according to claim 1, wherein the chlorination step is in a liquid phase and chlorine is in a gaseous state. 4. The method according to claim 1, wherein the hydrogen fluoride is selected from the group consisting of hydrogen fluoride anhydride and hydrogen fluoride in an organic solvent. 5. The formula CF ₂ HOCH _3-Z Cl _Z is CF ₂ H.
OCHCl ₂ and the fluorination reaction product is CF ₂
The method of claim 1 comprising HOCF ₂ H and CF ₂ HOCHFCl. 6. The at least one compound of formula CF ₂ HOCH _3-Z Cl _Z is CF ₂ HOCHCl ₂ and said at least one compound of formula CF ₂ HOCClXF _y H _{3- (x + y).}
The method of claim 1, wherein one compound is CF ₂ HOCF ₂ H, and further comprising separating and recovering the CF ₂ HOCF ₂ H from the fluorinated mixture. 7. The method of claim 1 wherein said chlorination is carried out at a temperature and pressure sufficient to maintain said CF ₂ HOCH ₃ in a gaseous state. 8. The method of claim 1, further comprising reacting CHF ₂ Cl with an alkali metal methoxide in a solvent solution to produce the CHF ₂ OCH ₃ . 9. The method of claim 1, wherein the oxygen source is air. 10. The formula CF ₂ HOCCl _x F _y H _{3- (x + y).}
(Where _x is 0, 1 or 2, _y is 1, 2 or 3,
_{x + y} is chlorinated by reacting CHF ₂ OCH ₃ with chlorine in the method for producing a fluorinated dimethyl ether represented by 1, 2 or 3), and has the formula CF ₂ HOCH _3-Z C
a chlorinated mixture containing at least one compound of 1 _Z (where _Z is 1 or 2) and having the formula CF ₂ HO
The CH _3-Z Cl wherein at least one compound of _Z, hydrogen fluoride in the absence of a catalyst, anhydrous hydrogen fluoride, HF ₂ ^- metal salt, selected from the group consisting of pyridine salt of NaF, KF and HF Fluorinated with a fluorine source of formula CF ₂ HOC
Fluorinating to obtain a fluorinated mixture containing at least one compound of H _3-z F _y Cl _zy , and preventing the formation of CF ₂ HOCCCl ₃ by performing the chlorinating step in the presence of oxygen. Method for producing dimethyl ethers. 11. The method of claim 10, wherein the oxygen source is air.