TECHNICAL FIELD AND BACKGROUND ART

Fluoromethy1-1,1,1,3,3,3-hexafluoroisopropyl ether, as described in U.S. Patent Nos. 3,689,571 and 3,683,092, is an anesthetic which is showing very promising results in clinical trial, being non-inflammable under conditions of use, and having advantages that appear to greatly out¬ weigh any minor disadvantages.

For clinical use, it is necessary of course to pro¬ duce the above ether material in large quantities, for ex¬ ample, by a synthesis technique as described in the above patents, and the abandoned original application, Serial No. 771,365, filed October 28, 1978, from which the above-cited U.S. patents claim priority.

Another currently preferred synthesis technique un¬ der consideration is the improvement as described in the patent application of Robert L. Simon, filed simultaneously with this present application and entitled "Method of Syn¬ thesizing Fluoromethylhexafluoroisopropyl Ether".

In many of these synthesis techniques, the corres¬ ponding alcohol, for example, 1,1,1,3,3,3-hexafluoroiso- propanol, is a reactant. Such material is currently very expensive, largely because the various byproducts produced with the material in the presently used commercial synthe¬ sis routes are difficult to separate from the acetone pre¬ cursor of the alcohol product.

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DISCLOSURE OF INVENTION In accordance with this invention, synthesis tech¬ niques are provided in which impure hexafluoroacetone mix¬ tures may be utilized as starting material, resulting in great cost savings, since the final expensive purification steps normally utilized in the commercial hexafluoroacetone reactant are rendered unnecessary..

In one instance, the resulting alcohol product is easily separable by simple distillation from its impurities, while in another case, the original impurity is also more easily separable, but may be utilized as a reactant for the desired further step of synthesis of the hexafluoroiso- propyl alcohol into the corresponding fluoromethyl ether. In accordance with this invention, hexafluoroiso- propanol can be synthesized from an impure mixture of hexa¬ fluoroacetone and certain impurities or byproducts result¬ ing from economical synthesis processes for the hexafluoro¬ acetone. The impure mixture is subjected to reducing con¬ ditions, to hydrogenate the hexafluoroacetone to a hexa- fluoroisopropanol product, with the impurities or byprod¬ ucts being either easily separable from the hexafluoroiso¬ propanol product, or used as reactants for the next syn¬ thesis step, which may be the synthesis of the fluoromethyl- hexafluoroisopropyl ether described above.

DESCRIPTION OF SPECIFIC EMBODIMENTS A. For example, the impure mixture utilized in this invention may comprise a mixture of hexafluoroacetone, ty¬ pically about 35 to 45 percent by weight, and hexafluoro- propylene in the order of about 45 to 55 percent by weight, plus small amounts of other byproduct materials. Such a reaction mixture may be manufactured in accordance with German Patent Publication No. 2,624,349, dated June 24, 1975, by means of the direct oxidation of hexafluoropro- pylene to hexafluoroacetone in the presence of aluminum oxide, a process commercially utilized by Daikin, a Japan¬ ese company.

In such a mixture, the hexafluoroacetone is sepa¬ rated only with substantial difficulty from the hexafluoro- propylene. Accordingly, purified hexafluoroacetone is much more expensive than the impure mixture.

In accordance with the teachings of the German Pa¬ tent Publication cited above, Example 1, the catalyst used herein may be prepared by introducing into a 28 mm. x 1000 mm. pyrex glass tube in an electric furnace granular, ac¬ tivated aluminum oxide in a particle size between 2.4 and 4.7 mm. (alumina gel) in the amount of 51.25 grams. De¬ hydration may be effected by heating for one hour in a stream of nitrogen to 500° C, then allowing the tempera- ture to drop to 200° C. Following this, an equimolar mix¬ ture of carbon tetrachloride and C 2CICFCI2 may be fed into the top of the reaction tube at the rate of 1 gram per min¬ ute. An immediate temperature rise to 270° C. is shown in the upper portion of the aluminum oxide column, which zone of high temperature migrates slowly to the lower layer until equilibrium is reached after about 40 minutes where the aluminum oxide layer exhibits a temperature of about 10° C. higher than its original temperature.

Following this, the desired temperature may be ad- justed to 250° C. while continuing to apply the halocarbon mixture to the column to possibly obtain a further hot spot moving through the column over the period of 45 minutes.

Following this, the temperature may be raised to 300° C. for 40 minutes, after which the catalyst may be removed from the furnace and cooled.

The resulting catalyst obtained in this manner may have a fluorine assay of about 9.9 percent by weight.

Fifty grams of this catalyst may be placed in a re¬ action tube made of Hastalloy -C ^~ having an interal dia¬ meter of 18 mm. and a length of one meter.

A reactant gas mixture of hexafluoropropylene (CF3CF=CF£) and oxygen in the molar ratio of 1 to 0.7 may be introduced to the tube to a pressure of 5.9 bar at 170° C. The reactant gas is fed into the tube at a rate of 100 ml./min. at 25° C, arriving with a pressure of 0.99 bar and introduced until the desired pressure in the tube is achieved.

The tube is then sealed and allowed to stand at 170° G. for three hours. Following this, the gas is removed from the tube, and may be found to contain 65.6 mole per¬ cent of hexafluoropropylene and 15.9 mole percent of hexa- fluoroacetone, as well as certain other fluorinated com¬ pounds which are relatively easily separated from the bulk of the reaction mixture. However, the hexafluoropropylene is separated only with difficulty from the hexafluoroace¬ tone. Accordingly, in accordance with this invention, one may subject the impure mixture to reducing conditions, to hydrogenate the hexafluoroacetone to hexafluoroisopropanol product, which is easily separated from the residual hexa¬ fluoropropylene.

A yield of 18.0 mole percent of hexafluoroacetone can be obtained in accordance with the above cited German Patent Publication when the same catalyst is brought to a temperature of 145° C. and the ratio of the hexafluoropro¬ pylene molar concentration to the oxygen molar concentra¬ tion is 0.9, with the Hastalloy -C tube being filled to a pressure of 4.32 bar and the gas flow being 40 ml. per minute (See Example 8) .

B. Alternatively, the impure mixture used in this invention may comprise hexafluoroacetone and hydrogen flu¬ oride, with the hydrogen fluoride preferably being present in the range of 5 to 50 percent by weight of the impure mixture.

This impure mixture may be the product of the cata¬ lytic reaction of hydrogen fluoride and hexachloroacetone as described, for example, in the DuPont French Patent No. 1,372,549 or the Rhone-Progil German Patent Publication No. 2,221,844.

In the product of these reactions, while the by¬ product hydrogen chloride is easily removed, and prefer¬ ably is so removed, hydrogen fluoride is quite difficult to separate from the hexafluoroacetone, apparently because it forms a complex with the product. Accordingly, as be¬ fore, purified hexafluoroacetone from these processes is much more expensive then the impure products of the re¬ actions.

A specific example of the catalytic reaction of hy- drogen fluoride and hexafluoroacetone is as described in

Example 1 of the cited German Patent Publication No. 2,221,844. There, a stainless steel tube reactor is used, which may be heated from the outside with three heating elements inde¬ pendently operable from each other, having an internal dia- meter of 3.56 cm. and a length of 1.5 meters.

Achromium hydroxide gel which had been precipitated at a continuously rising temperature has been treated with anhydrous hydrogen fluoride. After the treatment and the agglomeration of the gel into granules about 5 mm. in dia- meter, a catalyst having a specific surface area of 186 sq. meters per gram was formed. The stainless steel tube reactor was filled, and maintained in a vertical position containing, from the bottom toward the top, a sequence of the following layers: (1) a layer, 7 cm. high, of aluminum oxide spheres of lamellar structure, which material is relatively imper¬ vious to hydrogen fluoride; -_ _nS

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(2) a 33.5 cm. layer of the above catalyst compris¬ ing the third catalyst zone;

(3) a 7 cm. layer of more of the same type of al¬ uminum oxide spheres; (4) a 36.5 cm. layer of the above catalyst which serves as the second catalyst zone;

(5) a 7 cm. layer of the same type of aluminum ox¬ ide spheres;

(6) a 50 cm. layer of the chromium oxide catalyst to function as the first catalyst zone;

(7) a 6 cm. layer of the same type of aluminum ox¬ ide spheres.

The weight of catalyst used in the tube was 0.84 kg. A gas mixture was fed through the tube, passing from the first through the third catalyst z.ones. The feed mix¬ ture was adjusted to include a flow of 0.94 mole per hour hexachloroacetone and 8.4 mole per hour of anhydrous hydro¬ gen fluoride, which is a 48.8 percent stoichiometric excess of hydrogen fluoride. The pressure inside the reactor was kept constant at 1.3 bar, and the temperatures of catalyst zones 1 through 3 were maintained respectivelyat 236°, 265° and 310° C.

Analysis showed that the gas mixture leaving the third catalyst zone contained 96.8 percent hexafluoroace- tone, based on the organic materials, plus minor amounts of other halogenated carbon compounds. Inorganic products included unused hydrogen fluoride reactant and hydrogen chloride.

While the hexafluoroacetone is relatively easily separated from the hydrogen chloride, it is only separated with substantial difficulty from the hydrogen fluoride. Accordingly, in this present invention, the mixture of hexafluoroacetone and hydrogen fluoride may be subjected to reducing conditions, to hydrogenate the hexafluoroace- tone to a hexafluoroisopropanol product, specifically 1,1,1,3,3,3-hexafluoroisopropanol.

After this reducing reaction, the hexafluoroiso-

propanol, which has a much higher boiling point than the hexafluoroacetone, which may be readily collected, being separated with ease from the residual hexafluoroacetone and the hexafluoropropylene, if present, which can outgas easily at about room temperature, for example, and may be recycled for the production of more hexafluoroacetone and alcohol.

Similarly, the product hexafluoroisopropanol is not as strongly bonded with the hydrogen fluoride as the hexa¬ fluoroacetone, so the alcohol may be easily separated from the remaining hydrogen fluoride in the reaction mixture, if desired.

However, such is preferably unnecessary, and the hydrogen fluoride can "ride" through the hydrogenation step, if desired, to serve as a reactant in the next step for synthesizing the ether product described below.

The step of hydrogenation of the hexafluoroacetone to form the alcohol may take place in presence of strong hydrogenating agents, for example, sodium borohydride in the presence of preferably methanol solvent, lithium alum- inum hydride, calcium hydride, or sodium hydride, generally in the presence of an oxygen-containing, reaction-promoting solvent such as diethyl ether, methanol, isopropanol, or tetrahydrofuran.

Alternatively, the hydrogenation conditions for the hexafluoroacetone may be provided by a direct hydrogena¬ tion process in the presence of a catalyst such as Raney nickel, or various forms of platinum or palladium, such as platinum on charcoal or barium sulfate, or palladium on aluminum oxide or barium sulfate, for example as in U.S. Patent Nos. 3,468,964 and 3,702,872.

Another hydrogenation reaction which can be used is to subject the impure mixture of hexafluoroacetone and hexafluoropropylene to aluminum triisoproproxide in the presence of a suitable solvent such as isopropyl alcohol. The reaction product is hexafluoroisopropyl alcohol and acetone, with the hexafluoropropylene being nonreactive.

Hexafluoroacetone may be converted to hexafluoro-

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isopropyl alcohol in accordance with the Allied Chemical French Patent No. 2,133,126 in the presence of hydrogen, in which palladium on charcoal with sodium carbonate added may be used as a catalyst. Similarly, the reaction condi- tions of German Patent Publication No. 2,113,551 may be used. Likewise, the teachings of U.S. Patent No. 3,356,742 may be used to convert hexafluoroacetone in a silver-lined vessel in the presence of isopropyl alcohol into hexafluoro- isopropyl alcohol. It is preferable in the case of the acidic impure mixtures used herein to use the direct hydrogenation type of process, with a catalyst such as platinum or palladium.

Preferably, the resulting hexafluoroisopropyl al¬ cohol product may be reacted with hydrogen fluoride and formaldehyde, preferably paraformaldehyde, in the presence of sulfuric acid and at a temperature of about 65° C. to produce fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether. The hexafluoroisopropanol may be added dropwise, and the product collected in a distillation column, as taught in the previously cited application of Robert L. Simon, en¬ titled "Method of Synthesizing Fluoromethylhexafluoroiso- propyl Ether".

Alternatively, other synthesis techniques may be utilized to preferably convert the alcohol product into the preferred product fluoromethyl-1,1,1,3,3,3-hexafluoro¬ isopropyl ether.

The resulting product may be purified for use as a clinical anesthetic, having been produced in economical manner from inexpensive, impure mixtures of hexafluoro- acetone, which are purified only with substantial diffi¬ culty and economic cost.

The above has been offered for illustrative pur¬ poses only, and is not intended to limit the invention of this application, which is as defined in the claims below.