GB2211838A - Process for preparing chlorotrifluoroethylene telomers - Google Patents

Description

n 2211830 PROCESS FOR PREPARING CHLOROTRIFLUOROETHYLENE TELOMERS The

present invention relates to 6 process for prepering telomers of the formula F Br F F A 1 1 F- C C, Er F Cl t, j -:Jn where n is in the range of 1 to 10 r which telomers are saturatea, low molecular.'weight polymers useful for preparing non-flammable hydraulic-fluids.

Various methods of preparing chlorotrifluoroethylene ("CTFE") telomers are known and have been practiced commer cially for many years. An article by William 7. Miller, Jr. et al in Industrial and Engineering Chemistry, pages 333-337 (1947), entitled "Low Polymers of Chlorotrifluoroethylene", describes a process for producing low molecular weight polymers of CTFE by polymerization in a solution of chloroform using benzoyl peroxide as a polymerization pro M0ter. Other solvents disclosed in the reference as being useful for is this Ourpose include carbon tetrachloride and tetra chl oroethyl ene.

The solution is heated in a pressure vessel for 1-314 hours at 100% and the unreacted CTFE monomer and chloroform are removed by distil- lation, leaving a crude telomer of general formula CHCl 2 (CF 2CC 1F)nCls which can be further heated and distilled to yield products ranging from a light oil to a semi-solid wax or grease.

Another process for preparing low molecular weight CTFE polymers is described in U.S. Patent No. 2,788,375, issued April 9, 1957. This process comprises reacting CTFE with a saturated brominated compound in the presence of a source of radiation. Suitable brominated com pounds include 1,2-dibromo-2-chlorotri-fluoroethane (CF 2 BrCCUBr).

The saturated bromopolychlorofluoro compounds obtained by this process can then be distilled, and the isolated fractions reacted with chlor_ine to prepare polychlorofluorocompounds. The compounds are predominantly higher molecular weight telomers, i.e. n is greater than 4.

Czechoslovakian Patent No. 201,708, published August 15, 1982, discloses the reaction of CTFE with CBrClFU 2Br using a source of radiation at a temperature of from 2VC to 30C to prepare 1,4dibromo-2,3-dichlorohexafluorobutane and 1,6-dibromo-2,3, 5trichlorononafluorohexane as principal reaction products. These compounds are designated by the following structural formulas:

F F F F 1 1 1 1 br - L - C -C - C-Br (1) F LI C] F F F F F F F 1 1 1 1 1 1 Br - C - C -C-C- C- C - Br (2) f l 1 A 1 F Cl F Cl 11 h Both compounds (1) and (2) share the common feature of having the same end groups, i.e.,---CF2Br, as well as adjacent pairs of -CM- groups in the body of the telomer. Telomers having structures such as (1) and (2) are believed to be inherently more unstable and are less easily separated from impurities than the telomers of the present invention.

A more recent development in this field is described in a series of articles by Y. Pietrasanta et al entitled "Telomerization by Redox Catalysis" appearing in the Eruopean Polymer Journal, Vol 12 (1976). This technology involves the reaction of single carbon halogenated telogens, such as CC14 and CC] 3Br, with CTFE in the presence of benzoin and a suitable redox catalyst, such as ferric chloride. The telomerization reaction is suitably carried out in acetonitrile which is a common solvent for the reactants and catalysts. The telomerization reaction can be illustrated as follows:

FeCI 3 CC13 X + nCF 2= CM CC] 3 (CF 2 CM)nX (3) Benzoin where X is chlorine or bromine. The reference further discloses that the use of CC13Br as a telogen results in a lower degree of telomerization and a higher proportion of monoaddition product than would occur with 'the use of CC1 4 The redox process has the advantage of directly preparing low molecular weight products without the necessity of cracking or fractionating a higher molecular weight polymer.

A modification of the redox process is disclosed in commonly assigned U.S. application serial number 816,183, filed January 6, 1986.1n this modification, telomers of the structural formula F F F F 1 1 1 1 BrC-C-C-C-Br (4) 1 1 1 1 F cl F Cl;n where n is in the range of 1 to 10, are prepared by reacting chlorotrifluoroethylene with 1,2-dibromo-2-chlorotrifluoroethane MrClFU 2 Br) in the presence of a redox catalyst system. The redox catalyst system comprises a reducible metal halide selected from the group consisting of FeC13. FeBr 35 CuBr 29 Cucl 2 TiCl 49 VC] 3 and MC12..

and a reducing agent selected from the group consisting of Fe, Ni, Cu, Ti, V and benzoin. This process has the advantage of being able to prepare CTFE telomers which can be readily separated into relatively pure, stable, low molecular weight isomers, which can be further 5 chlorinated to prepare non-flammable hydraulic fluids.

Although telomers produced according to this latter process represent a significant advance over the prior art, there is still a need to increase the yield of the more desirable low molecular weight species using milder reaction conditions.

SUMMARY OF THE INVENTION

In accordance with the present invention, a distribution of telomers of the structural formula F Br F F 1 1 1 1 F-C-C--C-C--Br (5) F Cl -F Cl n where n is in the range of 1 to 10, are prepared by reacting chlorotrifluoroethylene with 1,1-dibromo-l-chlorotrifluoroethane (CF3 C0Br 2) in the presence of a redox catalyst system. The redox catalyst system comprises a reducible metal halide selected from the group consisting of FeC13, FeBr3, Fe2(S04)3 CuBr2, CuC12, TiC141 VC13 and NiC] 23 and a reducing agent selected from the group consisting of Fe, Ni, Cu, Ti, V and benzoin. Alternatively, the catalyst system can comprise a metal halide in reduced form without a reducing agent. Suitable reduced metal halides include FeCl 2. FeBr21 FeS04, CuBr and CuC]. The reaction is conducted in a common solvent for the reactants and catalysts, preferably acetonitrile, and the preferred catalyst system is ferric chloride and nickel.

The telomerization reaction of the present invention occurs at relatively lower temperatures of from about 700C to about 1500C, and the reaction produces a relatively high yield of low molecular weight species.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The telomerization process of the present invention involves the reaction of chlorotrifluoroethylene with 1,1-dibromo-l-chlorotrifluoroethane in a solvent, such as acetonitrile, in the presence of a catalytic amount of a reducible metal halide and a suitable metal, or a reduced metal halide alone. This process can be illustrated as follows:

K U 3 CC1Br + nCF 2= CK1)CF 2 BrUCI(U 2 CK1) n Br (6) where n is in the range of 1 to 10.

In reaction (6), K can be a redox catalyst system comprising a reducible metal halide selected from the group consisting of FeCl 32 FeBr 3$ Fe 2 (SO 4)31 CuBr 2. CuC12, TiC] 49 W 3 and NiCl 35 and a reducing agent selected from the group consisting df iron, nickel, copper, titanium, vanadium and benzoin, where the reducing agent must be capable of reducing the metal halide selected. Typical combinations of metal halides and reducing agents which are operable include FeC13 or FeBr 3 and Fe or Ni, TW4 and Ti, CuC] 2 or CuBr 2 and Cu, NiCl 3 and Ni, W13 and V, and preferably FeC] 3 and Ni. Mixtures and alloys of the metal reducing agents are also operable in this invention. Alter- natively, K can comprise a reduced metal halide without a reducing agent, the reduced metal halide comprising FeCI 2$ FeBr 29 FeSO 49 CuBr and CuC]. Reaction (6) is conducted in a common solvent such as acetonitrile, benzonitrile or propionitrile, and preferably acetonitrile.

Reaction (6) results in the preparation of a mixture or distribution of individual telomer species having molecular weights corresponding to n values of from 1 to 10, rather than pure isomers having a discrete structure, i.e. a single n value. Separation of the individual telomer species from the mixture is accomplished by distillation using procedures well known to those skilled in this art.

The lighter molecular weight telomers i.e., telomers having an n value of 4 or less, generally predominate in reaction (6). Some of the lighter weight materials, such as the telomer corresponding to an n value of 1, have no known commercial value. However, this telomer can be readily returned or recycled to the telomierzation reaction, and thereby converted into useful telomer products of higher molecular weight, thus increasing the overall efficiency of the reaction. Other telomers are of considerable current interest. For instance, nonflammable hydraulic fluids require an average molecular weight corre- sponding to an n value intermediate between 2 and 4. These fluids can be produced by first preparing individual stabilized, i.e. chlorinated, telomers having n values between 2 and 4, and blending these telomers to obtain the desired viscosity. Control of the molecular weight distribution in reaction (6) is therefore essential since the most desirable products require a narrow molecular weight distribution. This can be achieved by maintaining the concentration of metal halide (reducible or reduced) in the reaction mixture in the range of from about 0.01% to about 2% by weight of CTFE, and also maintaining the concentration of reducing agent in the reaction mixture in an amount of from about 0.5% to about 10% by weight of CTFE. Following the process of this invention, yields of telomer having an n value of 2 to 4 of 50 percent or more can be achieved.

The preferred metal reducing agent is nickel and nickel alloys such as Hastelloy C (Hastelloy is a registered trademark of the Union Carbide Corporation). The metal may be physically present in the reaction mixture in a variety of forms, such as a powder, particles of various sizes, wires, plates, or as a cladding material on the internal surface of the reactor. The preferred form is a finely divided powder which is uniformly dispersed in the reaction vessel by means of mechanical agitation, such as in a stirred reactor.

The telomerization reaction is preferably conducted in a stirred reactor under elevated temperature and pressure conditions, with temperatures generally ranging from about 700C to about 150% and pressures generally in the range of from about 75 psi to about 450 psi.

The products of reaction (6) are distinguished by the distribution of -CF 2 - -CM- and -CBrC]- groups in the telomer chain, and by the presence o; one -CF 3 and one -CF0Br end group. These telomers can be represented by the following structure:

F Br F F F-C- C --C-C-- Br (5) F cl F cl n The telomers of formula (5) have a bromine atom on the terminal carbon atom, as well as a bromine on the second carbon of the opposite end of the chain. Both of these bromines are sufficiently reactive to participate in a reinitiation reaction, although the secondary bromine is somewhat less reactive than the primary bromine. Reinitiation of the secondary bromine frequently occurs when FeC] 3 is selected as the reducible metal halide of choice, and results in a chain that has a trifluoromethyl branch as follows:

FeC] 3 CF 3 CF3MBr(CF2M1) n Br+U 2= CM PBr(CMU 2)aCCl(CF2CM)b Br (7) where the sum of a and b is not more than 10. Consequently, the products of reaction (6) can consist of both straight chain and branched isomers which can be present in the final product in varying degrees.

The following examples are intended to further illustrate the various embodiments and advantages of the present invention without limiting it thereby. These examples illustrate the preparation of CTFE telomers using various telogens and telomerization processes.

EXAMPLE 1

100 9. of CF 3 CC1Br 25 60 9. acetonitrile, 1.5 g. FeC] 39 and 2.0 9.

Ni powder were placed into the glass liner of a 600 m]. stirred autoclave. After pressure checking and flushing with N2 120 9. of CTFE was added. The autoclave was closed and slowly heated to 120'C. The reaction was maintained at this temperature for 4 hours. The maximum pressure reached was 215 psig. As the reaction progressed, an addi- tional 47 9. of CTFE was added from a heated reservoir. The reactor was then cooled to room temperature, and unreacted CTFE vented off.

Upon opening the autoclave, 123 grams of reaction mixture was obtained which consisted of two liquid phases. This product was -washed with dilute HCl and then with water. GC analysis of the washed product indicated that approximately 60 percent of the CF 3 CC1Br 2 had reacted. The four (4) carbon telomer made up about 52% of the product, and appeared to be composed of a single isomer. The six (6) carbon telomer consisted of two isomers, one straight chain, the other branched. More of the branched isomer than the straight chain isomer was present. Some resuffling of the bromine and chlorine on the telogen was observed. Both CF 3 CBr 3 and CF 3 cc] 2 Br were found in the product, along with a minor amount of each telomer series based upon each of these materials.

EXAMPLE 2

100 9. of CF 3 CC1Br 2 60 9. acetonitrile, 3.0 FeC] 33 and 3.0 9. Fe powder was placed into the glass liner of a 600 ml. stirred autoclave.

After pressure checking and flushing with N 25 111 g. of CTFE was added. The autoclave was closed and slowly heated to 120'C. The re action was maintained at this temperature for 4 hours. The maximum pressure reached was 200 psig. As the reaction progressed, an additional 59 9. of CTFE was added from a heated reservoir. The reactor was then cooled to room temperature, and unreacted CTFE vented off.

Upon opening the autoclave, 169 grams of reaction mixture was obtained. The product was washed with dilute HCl and then with water, GC analysis of the washed product indicated that approximately 70% of the CF 3 CC1Br2 had reacted. The four (4) carbon telomer made up about 42% of the product, and appeared to be composed of a single isomer. A larger amount of the resuffled telogens were found in this product than in the product of Example 1.

EXAMPLE 3 g. of CF 3 CC1Br 29 30 g. acetonitrile, and 2.0 9. FeC12 were placed into the glass liner of a 600 ml. stirred autoclave. After pressure checking and flushing with N21 112 g. of CTFE was added. The autoclave was closed and slowly heated to 100'C. The reaction was maintained at this temperature for 4 hours. The maximum pressure reached was 220 psig. As the reaction progressed, an additional 22 9.

of CTFE was added from a heated reservoir. The reactor was then cooled to room temperature, and unreacted CTFE vented off.

Upon opening the autoclave, 75 grams of reaction mixture was obtained. This product was washed with dilute HCl and then with water. GC analysis of the washed product indicated that approximately 57% of the CF 3 CC1Br 2 had reacted. The four (4) carbon telomer made up about 36% of the product, and appeared to be composed of a single isomer. The straight chain isomer made up the major portion of the six (6) carbon telomer. A smaller amount of resuffled products were present than in the two preceeding examples.

EXAMPLE 4

9. of CF 3 CC1Br 29 75 g. acetonitrile, 7.5 9. Fe 2("4)3 and 5 9. benzoin were placed into the glass liner of a 600 m]. stirred auto clave. After pressure checking and flushing with N 29 254 g. of CTFE was added. The autoclave was closed and slowly heated to 1150C. The reaction was maintained at this temperature for 4 hours. The maximum pressure reached was 360 psig. The reactor was then cooled to room temperature, and unreacted CTFE vented off. Upon opening the auto clave, 125 grams of reaction mixture was obtained. This crude product was washed with dilute HCI and then with water. GC analysis of the washed product indicated that approximately 54% of the CF 3 CC1Br 2 had reacted. The product was composed of:

Four (4) Carbon Telomer 39% 1; Six (6) Carbon Telomer 26% 1 Eight (8) Carbon Telomer 19% t Ten (10) Carbon Telomer 6% C

Claims (12)

1. A process for preparing brominated chlorotrifluoroethylene telomers which comprises reacting chlorotrifluoroethylene with W 3 CC1Br 2 in the presence of a catalyst system comprising at least one reducible metal halide selected from FeCl 3, FeBr 3, Fe 2(S04)31 CuBr 2. CuC12' TiCl 41 VC13 and Ni C13, and at least reducing one agent capable of reducing the metal halide in the reaction mixture and selected from iron, nickel, copper, titanium, vanadium and benzoin, said reaction being conducted in a common solvent for the reactants and catalyst system.

2. A process according to claim 1 wherein the brominated chlorotrifluoroethylene telomers comprise straight-chain telomers of formula CF 3 CC1Br(W 2WC1) n Br and branched isomers of formula Br(CFC1CF 2) a CC1CF 3 (CF 2 CK1) b Br where n, a and b are from 1 to 10, and the sum of a and b is not more than 10.

3. A process according to claim 2 wherein telomers having an n value of between 2 and 4 are present in at least percent by weight in the reaction product.

4. A process according to claim 1, 2 or 3 wherein the common solvent is acetonitrile.

5. A process according to claim 4 wherein the catalyst system comprises FeCl 3 and nickel.

6. A process according to claim 5 wherein the FeCl 3 is present in the reaction mixture in an amount of from 0.01% to 2% by weight of chlorotrifluoroethylene.

7. A process according to any one of the preceding claims wherein the reducing agent is present in the reaction mixture in an amount of from 0.5% to 10% by weight of chlorotrifluoroethylene.

8. A process according to any one of the preceding claims wherein the telomerization reaction is conducted at from 70 0 C to 150 0 C and at a pressure of from 0.52 to 3.1 MPa (75 to 450 psi).

9. A process for preparing brominated chlorotrifluoroethylene telomers which comprises reacting chlorotrifluoroethylene with W 3 CC1Br 2 in the presence of a catalyst comprising at least one reduced metal halide selected from FeCl 2, FeBr 21 Fe S04' CuBr and CuCl, said reaction being conducted in a common solvent for the reactants and catalyst.

10. A process according to claim 9 wherein the common solvent is acetonitrile.

11. A process according to claim 10 or 11 wherein the catalyst is PeCl 2

12. A process according to claim 1 or 9 substantially as described with reference to any one of the Examples.

Published 1989 atThe Patent Office, State House. 6671 High Holborn, LondonWC1R 4TP. Further copies maybe obtained from The Patent O=ce. Sales Branch, St Maxy Cray. Orpington. Kent BR5 3RD Printed by Multiplex tecbiuques ltd- St Mary Cray, Kent, Con. 1187