MXPA97008684A - Process for the preparation of fluora aliphatic compounds - Google Patents

Abstract

A process for the preparation of a fluorinated aliphatic olefin having the formula: wherein a is 0 or the integer 1 or 2 and b is 0 or the integer 1, 2 or 3 is described. In the first step of the process, a chlorinated olefinic hydrocarbon of the formula: wherein c is 0 or the integer 1, and d is 0 or the whole number 1 or 2, is reacted with anhydrous hydrogen fluoride for a period of time and a sufficient temperature to form a chlorofluoroolefin of the formula: wherein e is 0 or the number 1 and f is 0 or the whole number 1 or 2. The chlorofluoroolefin produced in the first step is then reacted with anhydrous hydrogen fluoride in a second reaction, this second reaction is catalyzed with at least one compound which is metallic or metal halide. Mixtures of metal oxides, metal halides and metal oxides with metal halides can also be used. The metal part of such a compound is arsenic, antimony, tin, boron or is selected from a Group IVb, Vb, VIb, VIIb or VIIIb metal of the Periodic Table of the Elements. The desired fluorinated aliphatic hydrocarbon is subsequently separated and recovered. The process is particularly appropriate for the preparation of 1,1,1,3,3-pentafluoropropa

Description

PROCESS FOR THE PREPARATION OF FLUORITE ALIPHATIC COMPOUNDS FIELD OF THE INVENTION This invention relates to a process for the preparation of aliphatic compounds substituted with multiple fluorine atoms. In particular, this invention relates to the discovery that highly fluorinated aliphatic compounds can be prepared in high yield by a two-step process comprising a halogen / fluorine exchange, uncatalyzed, of a chlorinated olefin, followed by catalyzed hydrofluorination. and halogen / fluorine exchange of the resulting chlorofluoro intermediate.

BACKGROUND OF THE INVENTION The replacement of chlorofluorocarbons (CFCs) widely used in refrigerant compositions, propellants and cooling fluids as well as blowing agents, solvents and rinsing agents with environmentally acceptable alternatives, has produced an abundance of compounds that meet one or more of these REF: 25551 needs. The most acceptable replacement compounds are those that have little or no chlorine, since it is generally accepted that chlorinated aliphatic hydrocarbons lead to unacceptably reactive chlorine-containing radicals, when present in the upper atmosphere. It is thought that these radicals react with ozone in the stratosphere depleting it to dangerously low levels. One of the most promising alternatives for CFCs is the aliphatic compounds where the chlorine has been replaced with fluorine. These materials are known as hydrofluorocarbons (HFC's). Typical HFCs have atmospheric life times and global warming potentials that are a fraction of their chlorinated analogues. However, many of its other physical properties (low flammability and toxicity, sufficient volatility, etc.) are identical or similar to CFCs. Consequently, these are attractive replacements for chlorinated molecules. In the processes for the preparation of HFC's, a usual starting material is the chlorinated analogue of the desired fluorinated compound. Thus, U.S. Patent No. 2,787,646 discloses that SbF3Cl2 and / or SbF are useful for converting compounds of the formula CMZ, CX === - CHY, for example 3, 3, 3-trichloroprop-l-ene or 1 , 1,3-trichloroprop-1-ene to compounds of the formula CF.CX = ~~ CHY, for example 3, 3, 3-trifluoroprop-1-ene. U.S. Patent No. 2,549,580 describes the conversion of 1,1-dichloroprop-1-ene to 1,1,1-trifluoropropane by means of hydrogen fluoride at 120 ° C and 56.24 Kg / cm 2 (800 psi) pressure. The preparation of 1-chloro-1,3,3,3-pentafluoropropane and 1, 1, 1, 3, 3, 3-hexafluoropropane from 1, 1, 3, 3, 3-hexachloropropane in the liquid phase is described in the EPO publication No. 0,522,639 Al. While the preferred catalyst for the reaction is annotated as SbCl ^, other described catalysts are those chlorides, fluorides and chloride-fluorides of Group Illa, IVa, IVb metals , Va, Vb and VIb of the Periodic Table of the Elements. Compounds such as 1,1,1,3,3,3-hexafluoropropane are prepared by coupling two chlorine-containing reagents, for example 1,1,1-trichloro-2,2,2-trifluoroethane and dichlorodifluoromethane , in the presence of hydrogen and a first catalyst to form an olefin, for example, 1, 1, 1, 3, 3-pentafluoro-2-chloroprop-2-ene and then the olefin is hydrogenated in the presence of a second catalyst. See WO 95/05353.

BRIEF DESCRIPTION OF THE INVENTION The process of the present invention for preparing a fluorinated aliphatic hydrocarbon uses a chlorinated olefinic hydrocarbon as the starting material. Olefin has the formula where c is 0 or the integer 1 and d is 0 or the whole number 1 or 2. In the first step of this process, the -define is reacted with anhydrous hydrogen fluoride (HF) for a sufficient time and temperature to form a second olefin, where some of the chlorine atoms in the initial material have been replaced with fluorine. The second olefin has the formula wherein e is 0 or the integer 1, and f is 0 or the integer 1 or 2. This second olefin is then reacted with anhydrous HF to form the desired fluorinated aliphatic hydrocarbon, for example, a compound of the formula CH. F ^ -CH-CH, F This reaction can be catalyzed with a catalytically effective amount of at least one metal oxide or at least one metal halide. Mixtures of these metal oxides, metal halides or metal oxides can also be advantageously used with metal halides.

DESCRIPTION OF THE PREFERRED MODALITIES The process of the present invention is particularly useful for producing highly fluorinated aliphatic compounds that are not easily prepared in typical fluorine-chlorine substitution reactions. Thus, for example, in the catalyzed reaction of 1, 1, 1, 3, 3-pentachloropropane with hydrogen fluoride, the substitution of fluorine for chlorine is accompanied by a lot of tar and by-products, so that the pentafluorinated compound is not form in commercially acceptable yields. Similarly, polychloro-olefins such as 1,1,3,3-tetrachloroprop-1-ene with anhydrous hydrogen fluoride and a typical catalyst fails to produce the desired pentafluoropropane in acceptable yields due to the extensive formation of tar residue. . The process of the present invention overcomes these and other disadvantages by the preparation in a first step of a partially fluorinated chloroolefin, of the formula where e is 0 or the integer 1, and f is 0 or the whole number 1 or 2, from the reaction of a polychlorinated compound of the formula CH Cl_- = CH-CH, C1 where c is 0 or the integer 1 and d is 0 or the whole number 1 or 2, with anhydrous hydrogen fluoride. The reaction is carried out for a time and at a temperature sufficient to produce the partially fluorinated chloroolefin, also referred to herein as a "chlorofluoro-olefin". In the first step described above, it is preferred that the polychlorinated compound is one where c is 0 or the integer 1, and d is the integer 1 or 2. More preferably, c is O and d is 1, oc is 1 and d is 0 At least three moles of anhydrous hydrogen fluoride are required to produce the partially fluorinated chloroolefin. However, an excess of hydrogen fluoride, preferably from about 2 to about 10 times the stoichiometric requirements, are typically used in this reaction to facilitate the formation of the fluorochloro-olefin. The reaction can be carried out as a batch or as a continuous process. In the batch mode, the initial polychloro-olefin material can be added first to the reaction vessel. The order of addition is not critical. The hydrogen fluoride is then introduced and the reaction vessel is heated, with stirring, at a temperature and in a period sufficient to produce the desired partially fluorinated olefin, for example, a temperature from about 70 ° C to about 120 ° C. , preferably from about 80 ° C to about 100 ° C, from about 15 minutes to about 24 hours. The pressure during this reaction step is maintained at 14.06-16.17 Kg / cpr (200-230 psia) by means of a back pressure regulator and the generated HCl is vented through a reflux condenser. The HF and the products taken along with the waste HCl are condensed and returned to the reactor. Accordingly, the reaction is run in the liquid phase for convenience although the reaction can be run in the vapor phase on an appropriate surface such as aluminum fluoride. This process is a conventional one and well known in the technique of fluorine chemistry. Upon completion of the reaction, the reaction vessel is cooled, typically to about 50 ° C and the partially fluorinated chloroolefin and the excess HF is then distilled instantaneously. The resulting mixture is used "as is" without further purification for the second step of the process of the present invention. The continuous mode requires continuous mixing at a flow rate and at a temperature sufficient to ensure contact times in the temperature range noted above. The continuous elimination of the product of fluorocloro and the gaseous byproducts with HF, it is of course required. As noted herein, the chlorofluoroolefin collected from the first reaction step is typically used without further purification in the second step of the process of the present invention. This second step may also require additional anhydrous hydrogen fluoride in the second reaction vessel which, in this step, contains a catalyst. As in the first step, the reaction that is carried out also in the liquid phase with the elimination of the HCl or under autogenous pressure, can be in the continuous mode or in batches. The catalyst is typically introduced into the reaction vessel before the partially fluorinated chloroolefin and the HF. A variety of catalysts (or catalyst mixtures) are useful for carrying out the second step of the reaction of the present invention. To a greater degree, many of these catalysts are equivalent and the choice depends on the cost, the availability and the solubility in the reaction mass. The catalysts are halides or metal oxides or mixtures of such compounds, the metals being selected from the group consisting of arsenic, antimony, tin, boron, and metals of Groups IVb, Vb, VIb, Vllb, or VHIb of the Periodic Table of the Elements. Preferably, the metal compound is a chloride or fluoride, more preferably a fluoride. This is preferably antimony, arsenic, tin, bismuth or Group IVb or VlIIb of the Periodic Table of the Elements. Preferably, the catalyst is selected from the antimony fluorides, tin, titanium and mixtures thereof. More preferably, the catalyst is a mixture of antimony (V) and titanium (IV). While molar proportions of antimony to titanium of from about 3 to about 5 can be used, it is especially preferred to use a molar ratio of antimony (V) to titanium (IV) in a 4 to 1 ratio. The amount of catalyst used in the reaction is sufficient to catalyze the reaction. This is at least 1 mmol and preferably from about 10 to about 200 mmol, per mole of partially fluorinated chloroolefin used in the batch operation. At very low catalyst concentrations, the reaction of the second step may be unacceptably low. A very high concentration of catalyst can lead to waste due to the fact that the solubility limit may have been reached in the reaction mass. Accordingly, the most preferred amount of catalyst is from about 10 to about 50 mmol, per mole of chlorofluoroolefin.

The second step of the reaction is conducted for a sufficient time and temperature to form the desired aliphatic, fluorinated hydrocarbon.

This is typically in the range of about 25 ° C to about 150 ° C for about minutes to approximately 24 hours.

Preferably, the reaction temperature is from about 75 ° C to about 175 ° C, more preferably from 80 ° C to about 100 ° C for about 45 minutes to about 6 hours. Higher temperatures are required (above 200 ° C) for a reaction in the vapor phase.

During the second step of the reaction, a reaction mass is produced which is essentially a mixture of the desired product (the fluorinated aliphatic hydrocarbon), hydrogen fluoride, catalyst and very small amounts of unreacted starting material from step I) and the step ii). The components of the mixture are not easily separated from the end product of fluorinated aliphatic hydrocarbon, by conventional methods.

For example, conventional distillation does not result in a separation of the final product from hydrogen fluoride because these materials have similar boiling points. The separation of liquid / liquid phase is not practical, since the two materials are miscible. The standard method to induce phase separation (addition of a non-reactive solvent that dissolves the fluorinated hydrocarbon, but not hydrogen fluoride) is not efficient.

It has now been discovered that the fluorinated aliphatic hydrocarbon can be easily separated from a mixture of hydrogen fluoride, as exemplified by the reaction mixture formed in step ii), by the addition to such a mixture of an organic or inorganic which dissolves preferentially in hydrogen fluoride and causes an insoluble liquid phase substantially enriched with fluorinated aliphatic hydrocarbon to be separated.

In order to be effective in this separation process, the organic or inorganic salt must be non-reactive for the components of the reaction mixture, sufficiently soluble in hydrogen fluoride, for example, the reaction mixture, to cause the phase enriched with the fluorinated aliphatic hydrocarbon is separated as a separate phase easily recovered, relatively insoluble in the final product of fluorinated hydrocarbon, and easily separated from the resulting residual mixture after the fluorinated aliphatic hydrocarbon has been separated.

Organic salts useful in effecting such separation include ammonium fluoride and (lower alkyl) ammonium fluorides, for example, ammonium fluoride and mono-, di-, tri- or tetra- (linear or branched alkyl fluoride from 1 to 3. carbon atoms) -ammonium. Preferably, such salts include ammonium fluoride, mono- and dimethylammonium fluoride and mono- and diethylammonium fluoride. Particularly useful is ammonium fluoride.

Inorganic salts useful in effecting such a separation process include the fluorides and bifluorides (sometimes referred to as "acid fluorides") of the Group metals that of the Periodic Table of the Elements. Preferably, the fluorides and the fluorides of lithium, sodium and potassium acid are used in this process. More preferred are sodium and potassium fluorides.

The amount of the organic or inorganic salt added to the reaction mass is directly proportional to the amount of fluorinated aliphatic hydrocarbon that appears in the separated liquid, enriched phase. Thus, as little as 0.01 mole of salt per mole of hydrogen fluoride (calculated) is sufficient to result in the separation of a second liquid phase. If more than 0.25 mole of salt is used per mole of hydrogen fluoride (calculated), then crystallization of the reaction mixture can occur, (a crystalline complex forms between the salt and hydrogen fluoride) which interferes with the separation of the desired product. Preferably, the salt is used in an amount of 0.02 to about 0.20 mole per mole of hydrogen fluoride (calculated), more preferably from about 0.05 to about 0.10 mole.

In the following examples, the specific embodiments of the process of the present invention are described. These are not included as limitations of the process, but for purposes of illustration only. Unless stated otherwise, temperatures are in degrees centigrade.

EXAMPLES EXAMPLE 1 i. (Not catalyzed) Preparation of l-chloro-3, 3, 3-trifluoropropene from 1, 1, 3, 3-tetrachloropropene A 450 ml nickel-iron-molybdenum alloy autoclave, equipped with a condenser and back pressure regulator, was evacuated and cooled in a dry ice / acetone bath. The condenser was maintained at 0 ° C. The reactor was charged with 120 g (6 moles) of anhydrous HF. The reactor was then charged with 180 g (1 mol) of 1,1,3,3-tetrachloropropene. The reactor was heated to 80 ° C and the pressure was maintained at 14.06 Kg / cm '(200 psi) by venting the HCl through the pressure regulator. When the evolution of HCl ceased, the reactor was cooled to 50 ° C and discharged through a KOH scrubber and into a separatory funnel filled with ice. The product was decanted as the densest layer towards a cooled bottle. An average isolated yield of 107 g (80 °) was achieved for each of the 4 consecutive runs. For each run, approximately 19 g of the oligomeric material were recovered from the reactor ii. (Catalyzed Preparation of l-chloro-3, 3, 3-trifluoropropene from 1, 1,3,3-tetrachloropropene (catalyzed with SbCl?) A 450 ml nickel-iron-molybdenum alloy autoclave, equipped with a condenser and pressure regulator, was evacuated and cooled in a dry ice / acetone bath. The condenser was maintained at 0 ° C. The reactor was charged with 3 g (0.01 mol) of SbCl; and 136 g (6.8 mol) of HF. The reactor was heated at 90 ° C for 1 hour. The reactor was then cooled to 20 ° C and the HCl pressure was released. The reactor was then cooled in a dry ice / acetone bath and loaded with 152 g (0.84 mol) of 1,1,3,3-tetrachloropropene. The reactor was maintained at 80 ° C and the pressure was maintained at 14.06 Kg / cm2 (200 psi) by venting the HCl through the pressure regulator. When the evolution of HCl ceased, the reactor was cooled to 50 ° C and discharged through a KOH scrubber and into a separatory funnel filled with ice. The product was decanted as the densest layer towards a cooled bottle. A total of 3 g (2.6%) of 1-chloro-3,3,3-trifluoropropene was isolated. After washing. 109 g of oligomeric material was recovered from the reactor. Similar results were obtained using fluorosulfonic acid (HOSO-, F) or SnCl 4, instead of SbCl 5. iii. (Solvent of sulfolane) Preparation of l-chloro-3, 3, 3-trifluoropropene from 1, 1,3,3-tetrachloropropene A 450 ml nickel-iron-molybdenum alloy autoclave, equipped with a condenser and pressure regulator, was evacuated and cooled in a dry ice / acetone bath. The condenser was maintained at 0 ° C.

The reactor was charged with 75 ml of tetramethylene sulfone (sulfolane) The reactor was then cooled in a dry ice / acetone bath and charged with 134 g (6.7 mol) of HF and 180 g (1.0 mol) of 1,1,3,3-tetrachloropropene. The reactor was heated to 100 ° C and the pressure was maintained at 16.17 Kg / cm- (230 psi) by the HCl ventilation through the back pressure regulator. When the evolution of HCl ceased, the reactor was cooled to 70 ° C and discharged through a KOH scrubber and into a separatory funnel filled with ice. The product was decanted as the densest layer towards a cooled bottle. An average performance of the isolate of 115 g (86%) for each of the 4 consecutive runs. After washing, 2.3 g of the oligomeric material was recovered from the reactor in each run.

EXAMPLE Ib i. Preparation of 1, 1, 1, 3, 3-pentafluoropropane from l-chloro-3, 3, 3-trifluoropropene ^ catalyzed with SbCl = A 300 ml nickel-iron-molybdenum alloy autoclave was charged with 35 g (0.12 mol) of SbCl- and 48 g (2.4 mol) of HF. The reactor was heated to 80 ° C for 1 hour. The reactor was then cooled to 20 ° C and the HCl pressure was released. The reactor was then cooled in a dry ice / acetone bath and charged with 68 g (3.4 moles) of HF and 140 g (1.04 moles) of 1-chloro-3, 3, 3-trifluoropropene. The reactor was heated to 80 ° C. After an initial exotherm and a subsequent ease in pressure, the reactor was cooled to 50 ° C and discharged through a KOH scrubber and into a separatory funnel filled with ice. The product was decanted as the densest layer in a cooled bottle, an average of 112 g (76%) was isolated from 1, 1, 1, 3, 3-pentafluoropropane (71% purity) for each of the 2 consecutive runs, after which the catalyst appeared to be inactive. 4 g of oligomer were observed on this catalyst. ii. (Catalyzed) Preparation of 1, 1, 1, 3, 3-pentafluoropropane from l-chloro-3, 3, 3-trifluoropropene (catalyzed with SbC TiCl A 300 ml nickel-iron-molybdenum alloy autoclave was charged with 45 g (0.15 mol) of SbCl, 7 g (0.04 mol) of TiCl 4 and 24 g (1.2 mol) of anhydrous HF. The reactor was heated at 90 ° C for 1 hour. The reactor was then cooled to 20 ° C and the HCl pressure was released. The reactor was then cooled in a dry ice / acetone bath and charged with 60 g (3.0 mol) of HF and 134 g (1.0 mol) of l-chloro-3,3,3-trifluoropropene. The reactor was heated to 90 ° C. After an initial exotherm and a subsequent increase in pressure, the reactor was cooled to 50 ° C and discharged through a KOH scrubber and into a separatory funnel filled with ice. The product was decanted as the densest layer inside a cooled bottle. An average of 131 g (95%) of 1, 1, 1, 3, 3-pentafluoropropane was isolated for each of the 2 consecutive runs. No oligomeric material was observed in the reactor. iii. (Mixed substrates) Preparation of 1, 1, 1, 3, 3-pentafluoropropane from a mixture of 1, 1, 3, 3-tetrachloropropene and 1,3,3,3-tetratrioropropene A 450 ml nickel-iron-molybdenum alloy autoclave (reactor # 1) equipped with a condenser and pressure regulator was evacuated and cooled in a dry ice / acetone bath. The condenser was maintained at 0 ° C. The reactor was charged with 50 ml of tetramethylenesulphone (sulfolane). The reactor was then cooled in a dry ice / acetone bath and charged with 134 g (6.7 mol) of HF and 180 g (1.0 mol) of approximately a 4 to 1 mixture of 1,1,3,3 and 1, 3,3,3-tetrachloropropene. The reactor was heated to 100 ° C and the pressure was maintained at 16.17 Kg / cm2 (230 psi) by means of HCl ventilation through the pressure regulator. When the evolution of HCl ceased, the reactor was cooled to 50 ° C. A 300 ml nickel-iron-molybdenum alloy autoclave (reactor # 2) was charged with 45 g (0.15 mol) of SbClf, 7 g (0.04 mol) of TiCl 4 and 24 g (1.2 mol) of anhydrous HF. The reactor was heated at 90 ° C for 1 hour. The reactor was then cooled to 20 ° C and the HCl pressure was released. The reactor was then cooled in a dry ice / acetone bath. The 300 ml reactor was charged directly with the 450 ml reactor contents (approximately 204 g). Any deficit in weight was reconstituted with anhydrous HF. The reactor was heated to 90 ° C. After an initial exotherm and a subsequent increase in pressure, the reactor was cooled to 50 ° C and discharged through a KOH scrubber and into a separatory funnel filled with ice.

The product was decanted as the densest layer in a cooled bottle. An average of 126 g (85%) of 1, 1, 1, 3, 3-pentafluoropropane (75% purity) for each of 8 consecutive runs. The remainder was 1-chloro-1,3,3,3-tetrafluoropropane and 1,1-dichloro-3,3,3-trifluoropropane (so-called subfluorinated materials).

Reactor # 1 contained a total of 45 g of oligomers after the 8 runs. Reactor # 2 showed no evidence of tars.

Comparative Example Reaction of Subfluorinated Materials A 300 ml nickel-iron-molybdenum alloy autoclave, equipped with a condenser and pressure regulator, was charged with 45 g (0.15 mole) of SbCJ, 7 g (0.04 mole) of TiCl4 and 48 g (2.4 mole) of anhydrous HF. The reactor was heated to 90 ° C. The reactor was then cooled to 20 ° C and the HCl pressure was released. The reactor was then cooled in a dry ice / acetone bath and charged with 136 g through the pressure regulator. When the evolution of HCl ceased, the reactor was cooled to 60 ° C and discharged through a KOH scrubber and into a separating funnel filled with ice. The product was decanted as the densest layer inside a cooled bottle.

An average of 200 g (93%) of 1, 1, 1, 3, 3-pentafluoropropane (98% purity) was isolated for each of 3 consecutive runs. No oligomeric material was observed in the reactor after the 3 runs.

EXAMPLE 2 Separation of the 1,1,1,3,3-pentafluoropropane / hydrofluoric acid mixture A solution of 20 g of HF and 20 g of 1,1,1,3,3-pentafluoropropane was made in a Teflon separating funnel. The solution was cooled in an ice bath and small amounts (see table below) of sodium fluoride powder were added slowly. The funnel was stirred and allowed to settle. The lower organic layer was removed, weighed and titrated with 0.5 N sodium hydroxide solution using phenolphthalein as the indicator.

Amount of 0.42 0.84 1.26 1.68 2.10 NaF added (grams) Weight of 0 0 < 1 7.10 10.60 13.40 Organic layer (grams) HF in the - - - 0.72 0.73 0.35 Organic Cloak It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (13)

1. A process for the preparation of a fluorinated aliphatic hydrocarbon of the formula where a is 0 or the integer l or 2, and b is 0 or the integer 1, 2 or 3, characterized in the process because it comprises: i) the reaction of a chlorinated olefinic hydrocarbon of the formula wherein c is 0 or the integer 1 6 2, and d is 0 or the integer 1 or 2, with anhydrous hydrogen fluoride at a temperature and for a time sufficient to form a chlorofluoroolefin of the formula CH »Cl ^ - = CH-CH > F, .t where e is 0 or the integer 1 or 2, and f is 0 or the integer 1 or 2, where the reaction is not catalyzed; F, ii) the reaction of the chlorofluoroolefin with anhydrous idrogen fluoride and in the presence of a catalytically effective amount of at least one of a metal oxide or at least one of a metal halide or mixtures of at least one metal oxide with at least one metal halide , for a time and at a temperature sufficient to form a reaction mixture containing the fluorinated aliphatic hydrocarbon; and iii) the separation of the fluorinated aliphatic hydrocarbon from the reaction mixture.

2. A process for the separation of a fluorinated aliphatic hydrocarbon from the formula CH.F -.- a-CHí-CH.Fj- ,, wherein a is 0 or the integer 1 or 2, and b is 0 or the integer 1, 2 or 3, from a reaction mixture containing hydrogen fluoride, characterized the separation process because it comprises: a) the adding an organic or inorganic salt to the reaction mixture, whereby a mixture containing a separate phase enriched with aliphatic fluorinated hydrocarbon is formed and then the phase enriched with the aliphatic fluorinated hydrocarbon is separated from said mixture, the organic salt being or inorganic I) nc reactive to the components contained in the reaction mixture; ii) substantially insoluble in the separate phase which is enriched with the fluorinated aliphatic hydrocarbon; and iii) separable from the mixture that is formed after the phase separation of the enriched fluorinated aliphatic hydrocarbon, and b) the separation of the fluorinated aliphatic hydrocarbon from the phase enriched in the fluorinated aliphatic hydrocarbon.

3. The process according to claim 2, characterized in that the organic salt is ammonium fluoride or a fluoride of (lower alkyl) ammonium.

4. The process according to claim 3, characterized in that the organic salt is ammonium fluoride or is selected from the group consisting of straight or branched mono-, di-, tri- or tetra-alkyl fluoride of 1 to 3 carbon atoms. carbon) -ammonium.

5. The process according to claim 4, characterized in that the organic salt is ammonium fluoride, monomethylammonium fluoride, and dimethylammonium fluoride, monoethylammonium fluoride, and diethylammonium fluoride.

6. The process according to claim 5, characterized in that the organic salt is ammonium fluoride.

7. The process according to claim 2, characterized in that the inorganic salt is a fluoride or a bifluoride of the Group metals that of the Periodic Table of the Elements.

8. The process according to claim 7, characterized in that the inorganic salt is a fluoride or an alkali metal bifluoride selected from the group consisting of lithium, sodium and potassium.

9. The process according to claim 8, characterized in that the inorganic salt is a sodium or potassium fluoride.

10. The process according to claim 2, characterized in that the amount of organic or inorganic salt added to the reaction mixture is directly proportional to the amount of fluorinated aliphatic hydrocarbon that appears in the separated, enriched liquid phase.

11. The process according to claim 10, characterized in that the amount of organic or inorganic salt is about 0.01 mole of salt per mole of hydrogen fluoride to about 0.25 mole of salt per mole of hydrogen fluoride.

12. The process according to claim 11, characterized in that the amount of organic or inorganic salt is about 0.02 mole of salt per mole of hydrogen fluoride to about 0.20 mole of salt per mole of hydrogen fluoride.

13. The process according to claim 12, characterized in that the amount of organic or inorganic salt is about 0.05 mole of salt per mole of hydrogen fluoride to about 0.10 mole of salt per mole of hydrogen fluoride. SUMMARY OF THE INVENTION A process for the preparation of a fluorinated aliphatic olefin having the formula is described where a is 0 or the integer I or 2 and b is 0 or the integer 1, 2 or 3. In the first step of the process, a chlorinated olefinic hydrocarbon of the formula: wherein c is 0 or the integer 1, and d is 0 or the integer 1 or 2, is reacted with anhydrous hydrogen fluoride for a period of time and at a temperature sufficient to form a chlorofluoroolefin of the formula: where e is 0 or the integer 1 and f is 0 or the whole number 1 or 2. The chlorofluoroolefin produced in the first step is then reacted with anhydrous hydrogen fluoride in a second reaction, this second reaction is catalyzed with at least one compound which is a metal oxide or metal halide. Mixtures of metal oxides, metal halides and metal oxide with metal halides can also be used. The metal part of such a compound is arsenic, antimony, tin, boron or is selected from a Group IVb, Vb, VIb, Vllb or VHIb metal of the Periodic Table of the Elements. The desired fluorinated aliphatic hydrocarbon is subsequently separated and recovered. The process is particularly suitable for the preparation of 1, 1, 1, 3, 3-pentafluoropropane.