PROCESS FOR THE PREPARAΗON OF PERFLUOROALKYL IODIDE

BACKGROUND OF THE INVENTION

This invention concerns a process for the preparation of perfluoroalkyl iodides, especially pentafluoroethyl iodide, by reaction of perfluorinated compounds which contain a carbon carbon double bond, with ICl and HF in excess HF solvent in the presence of Lewis acid catalysts. The perfluoroalkyl iodides are used as telogens for the telomerization of tetrafluoroethylene to long-chain perfluoroalkyl iodides. Telomerization is a free radical chemical reaction in which one or more molecules of a polymerizable substance (tetrafluoroethylene) combine with another molecule (perfluoroalkyl iodide) called the telogen.

Perfluoroalkyl iodides are known compounds useful for making articles of commerce. Pentafluoroethyl iodide (PFEI) is a commercial product widely used as a telogen for preparation of long-chain perfluoroalkyl iodides. The known methods of preparation of PFEI are based on reaction of IF5 with a mixture of tetrafluoroethylene (TFE) and iodine. Another method of preparation of PFEI is a two-step operation, in which tetrafluorodiiodoethane is first prepared from tetrafluoroethylene and iodine and then converted to pentafluoroethyl iodide by reaction with iodine pentafluoride. These processes have the disadvantage of requiring IF5, which is prepared from elementary fluorine. Fluorine, as well as iodine pentafluoride, are substances dangerous to handle and expensive.

According to United States Patent No. 3,829,512, PFEI can be prepared by the reaction of TFE or tetrafluorodiiodoethane with the mixture of I2/CI2 and HF at temperatures of 50-170 °C. The reaction is catalyzed by antimony pentafluoride or other pentavalent antimony halides. No mention is made of the use of catalysts other than SbXs (X is halogen), or of operation at temperatures below 50 °C.

SUMMARY OF THE INVENTION This invention provides a process for the preparation of RCFICF2X where R is selected from the group consisting of F and C _n F2n+ _l , n has a value of 1- 10, X is selected from the group consisting of F and OR', and R' is perfluoroalkyl containing up to about 10 carbon atoms, branched or straight, optionally containing in-chain ether oxygen, and having F, SO2F or CO2CH3 as an end group, provided that when X is OR', R is F, which process comprises reacting a compound of the formula RCF=CFX, where R, X and n are as defined above, with an IC1/HF

mixture in the presence of a Lewis acid catalyst which increases the Ho acidity of HF from -11 to at least -13, provided the Lewis acid catalyst is not an antimony compound, at a temperature of from about 0 to about 200°C.

This invention further provides a process for the preparation of RCFICF2X where R and X are as defined above, which process comprises reacting a compound selected from a compound of the formula RCF=CFX, where R and X are as defined above, with an IC1/HF mixture in the presence of a Lewis acid catalyst which increases the Ho acidity of HF from -11 to at least -13, at a temperature of from about 0 to about 45°G DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention concerns the preparation of perfluoroalkyl iodides, especially perfluoroethyl iodide.

Starting materials for the process comprise compounds of the general formula RCF=CFX, where R is selected from the group consisting of F and C _n F2n ₊ ι. n has a value of 1-10, X is selected from the group consisting of F and OR'; and R' is a perfluoroalkyl, branched or straight, containing up to about 10 carbon atoms, optionally containing one or more, preferably 1-5, more preferably 1 in-chain ether oxygens, and having F, SO2F or CO2CH3 as an end group, provided that when X is OR', R is F. Preferred R substituents are C _n F2n ₊ ι. where n is from 1 to 5, or fluorine. Most preferred is where R is fluorine.

Preferred X substituents are OR' where R' is a perfluoroalkyl wherein the alkyl moiety contains from 1 to 3 carbon atoms, or fluorine. Most preferred is where X is fluorine. Two more preferred compounds of the general formula RCF=CFX are FSO2CF2CF2OCF(CF3)CF2OCF=CF2 and CH ₃ OC(=O)CF2CF2θCF(CF3)CF2θCF=CF2.

The term "perfluoroalkyl" is defined as an alkyl compound in which the hydrogen direcdy attached to the carbon atoms is completely replaced by fluorine.

In the term "perfluoroalkyl", the term "alkyl" denotes straight or branched alkyl such as methyl, ethyl, n-propyl, isopropyl, and the different butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl isomers.

The perfluoroalkyls of the R' designation optionally contain in-chain ether oxygen. For example CF3OCF2CF2-, CF3CF2OCF(CF3)CF2-, and CF ₃ CF2θCF(CF3)CF2θCF ₂ CF2-.

Compounds of the general formula RCF=CFX, which contain a carbon carbon double bond are herein generally referred to as "olefins." These compounds

are specifically referred to as "olefins" when X is F. However, when X is OR' the olefinic compounds formed are herein also referred to as "vinyl ethers."

The iodine monochloride reagent, ICl, may be used as such or prepared in situ from equimolar amounts of iodine and chlorine as described in "Synthesis of Fluoroorganic Compounds," edited by L. Knunyants and G. G. Yakbson, Springer- Verlag, Berlin, 1985. HF serves as solvent as well as reagent. It dissolves ICl and at least partially dissolves the olefinic starting material. The proportion of ICl used is 0.01-1 mole per mole of HF, preferably 0.03-0.07 mole, and the ratio of ICl to olefin is preferably 1:1. The Lewis acid catalyst is selected from the group of Lewis acid catalysts capable of enhancing the acidity, as measured by the HQ value, of hydrofluoric acid from its value of -11 to -13 or less. The acidity function, Ho, is defined as in the monograph "Superacids," G. A. Olah, G. K. S. Prakash and J. Sommer, pages 1-10, John Wiley and Sons, New York, 1985. This acidity enhancement is necessary to avoid the alternate reaction available to ICl of direct addition of ICl across the olefinic double bond to yield products of the type RCFCICFXI or RCFICF2CI which are undesirable impurities in the preparation of RCFICF2X. Lewis acids suitable for this invention include boron trifluoride, niobium pentafluoride, tantalum pentafluoride, bismuth pentafluoride, and antimony. pentafluoride (this latter at temperatures of from 0 to 45 °C), preferably boron trifluoride, niobium pentafluoride and tantalum pentafluoride; more preferably boron trifluoride and niobium pentafluoride. The most preferred Lewis acid catalyst is boron trifluoride. Other metal derivatives such as oxides, chlorides and alkoxides, which can be converted into fluorides under reaction conditions in HF, and which give appropriate Ho acidities, can be employed. The proportion of the catalyst used may be from 0.0001 mole to 10 mole per mole HF, preferably 0.05-1. It is possible to use a higher ratio, but this results in only a slight yield increase.

Compared to the pentavalent antimony compounds, boron trifluoride offers cleaner conversions, i.e., fewer side reactions due to the fact that pentavalent antimony compounds can also function as oxidation agents in addition to their being Lewis acids. No reaction residues remain when BF3 is used and any waste or by¬ products are less toxic and easier to treat or dispose of as opposed to reaction residues obtained with the use of heavy metal antimony compounds.

The reaction can be carried out conveniendy at temperatures of from 0 to 200 °C. Preferably, the reaction is carried out at temperatures from 20 to 100 °C. More preferably, the reaction is carried out at temperatures from 50 to 100 °C. The reaction can be carried out in batch, semi-batch, semi-continuous or continuous modes in one or in a plurality of reaction vessels. On a laboratory scale, the reaction can be caπied out in shaker tubes, where all reagents are combined before the reaction vessel is sealed and die reaction commenced. It can also be carried out in agitated autoclaves where all reactants except the olefin are combined and the olefin is fed in a controlled manner. In the case where pentafluoroethyl iodide (PFEI) is the desired product,

PFEI can be easily separated from HF by distillation allowing reuse of the HF and Lewis acid catalyst in subsequent preparations.

Agitation during the course of the reaction is preferred. Agitation can be carried out in any of the commonly used methods including stirring, shaking, and reagent introduction.

The proportion of HF used is from 2 to 40 moles per mole of olefin, preferably 5-25 mole.

Product may be isolated by any of the methods customary in organic synthetic chemistry. Fractional distillation is usually employed with liquid . products. It is convenient to contact the reaction mixture with water prior to product isolation to extract ICl, HF and catalyst.

Pressure is not usually a critical variable. The reaction is typically carried out at 1 to 100 atmospheres pressure. It is convenient to start out below 1 atmosphere and allow evolved HC1 build up the pressure in the reaction vessel. Reaction time can vary from several minutes to several hours, depending on such variables as catalyst concentration, pressure, and temperature.

EXAMPLES General Procedures Olefins are commercial grade materials and are used as obtained. Tetrafluoroethylene and hexafluoropropene are obtained from PCR, Inc. in

Gainsville, Florida. Hydrofluoric acid anhydrous, 99.5% is obtained from Allied Signal. Lewis acid catalysts are common laboratory grade materials. Iodine monochloride is purchased from Aldrich Chemical Co., Milwaukee, WI.

EXAMPLE 1 Preparation of Pentafluoroethyl Iodide A 400 mL Hastelloy shaker tube was loaded with 48 g (0.3 mole of ICl, evacuated, cooled down to -30 °C and then charged with 100 g (5 mole) of anhydrous HF, 5 g (0.074 mole) BF3 and 30 g (0.3 mole) of tetrafluoroethylene (TFE). The reaction vessel was shaken 8 h at 50 °C and 10 h at 20 °C. The gaseous products were then bled from the reaction vessel at 25-40 °C. These gases containing HC1, HF, and pentafluoroethyl iodide (PFEI) were passed through a washing vessel containing 1000 mL of water to remove the HF and HC1, and the product was collected in a cooled trap (-78 °C). Distillation of crude product through a low temperature column gave 57 g (78%) of PFEI with b.p. 11-13 °C; 99% purity, according to GC and NMR ¹⁹ F. The residue in the distillation pot, 3.5 g, was according to GC and NMR data, a mixture of 80% of PFEI and 20% CF2CI CF2I (calculated yield 1%). EXAMPLE 2

Preparation of Pentafluoroethyl Iodide In a test as described in Example 1, 10 g (0.147 mole) BF3 was used. The reaction vessel was shaken 18 h at 20 °C. The reaction mixture was worked up as described. The yield of PFEI was 91%, the yield of CF ₂ CI CF2I was <1%. EXAMPLE 3

Preparation of Pentafluoroethyl Iodide In a test as in Example 1, 15 g (0.069 mole) SbFs was used in place of die boron trifluoride. The reaction vessel was shaken 18 h at 20 °C. The yield of PFEI was 77%, the yield of CF2CICF2I was 4%. EXAMPLE 4

Preparation of Pentafluoroethyl Iodide In a test as in Example 1, 2 g (0.011 M) NbFs was used in place of the boron trifluoride. The reaction vessel was shaken 8 h at 5 °C and 10 h at 20 °C . The yield of PFEI was 86%, the yield of CF2CICF2I was <1%. EXAMPLE 5

Preparation of Pentafluoroethyl Iodide In a test as in Example 1, 1.15 g (0.006 mole) of TaFs was used in place of the boron trifluoride. The reaction vessel was shaken 8 h at 50 °C and 10 h at 20 °C. The yield of PFEI was 53%, the yield of CF2CICF ₂ I was 9%.

EXAMPLE 6 Preparation of Pentafluoroethyl Iodide In a test as in Example 1, 2 g (0.0065 M) of B-F5 was used in place of the boron trifluoride. The reaction vessel was shaken 18 h at 40 °C. The yield of PFEI was 24%, the yield of CF2CICF2I was 12%.

EXAMPLE 7 Preparation of Pentafluoroethyl Iodide In a test as in Example 1, 6 g (0.02 M) of SbG.5 was used in place of the boron trifluoride. The reaction vessel was shaken 8 h at 50 °C and 10 h at 20 °C. The yield of PFEI was 79%, the yield of CF2CICF2I was 2%.

EXAMPLE 8 Preparation of 2-Iodoheptafluoropropane In a test as in Example 1, 10 g (0.147 M) BF3 and 45 g (0.3 M) of hexafluoropropene (in place of TFE) were used. The reaction vessel was shaken 18 h at 50 °C. The product was isolated as above. After distillation it was isolated. 70 g (79% yield) of (CF3)2CFI (purity >98%, GC, NMR) was obtained. Boiling point was 37-38 °C.

EXAMPLE 9 Preparation of ICF2CF2OCF3 In a test as in Example 1, 10 g (0.147 M) BF3 and 50 g (0.3 M) of perfluoromethylvinyl ether were used. The reaction vessel was shaken 18 h at

50 °C. The product was isolated as above. After distillation was obtained 79 g

(84%) of ICF2CF2OCF3, b.p. 43-44 °C.

EXAMPLE 10 Preparation of ICF2CF2OCF2CF2CF3

In a test as in Example 1, 10 g (0.147 M) BF3 and 78 g (0.3 M) of perfluoro-n-propylvinyl ether were used. The reaction vessel was shaken 18 h at 70 °C. The product was isolated as above. After distillation was obtained 101 g (82%) of ICF2CF2OCF2CF2CF3, b.p. 84-85 °C. EXAMPLE 11

Preparation of Pentafluoroethyl Iodide A 1000 mL Hastelloy autoclave with stirrer was charged with 78 g (0.48 mole) of ICl, evacuated, cooled down to -30 °C and then charged with 225 g (11.25 mole) of anhydrous HF, 23 g (0.11 mole) of SbFs, and 40 g (0.4 mole) of TFE. The reaction mixture was stirred at 40 °C for 8 h and then

10 h at 20 °C. The gaseous products were tiien bled from reaction vessel at

20 °C. These gases were passed dirough a washing vessel containing 1500 mL of water and the product was collected in a cooled trap (-78 °C). The autoclave was recharged with the same amount of IQ and TFE and the reaction was repeated under die same conditions. Four cycles were made in total. After the fourth run, the autoclave was completely discharged as described above at 40 °C. The total yield of PFEI was 299 g (68% yield). The calculated yield of CF2CICF2I was

10% (GC).

EXAMPLE 12 Preparation of FSQ2CF2CF2θCF(CF )CF ₂ OCF2CF2l

In a test as in Example 1, 4 g (0.059 M) BF3, 45 g (0.1 M) of FSO ₂ CF ₂ CF2θCF(CF3)CF ₂ OCF=CF2, 16 g (0.1 M) of ICl and 50 g of HF were used. After 18 h at 70°C, 200 ml of water was injected into the shaker tube to dilute the HF. The product (lower layer) was separated, washed twice with water, dried over P2O5 and distilled giving 49 g (82%) of

FSO ₂ CF ₂ CF2θCF(CF3)CF2θCF2CF2l, b.p. 130-132°C/200 mm Hg.