FLUOROCARBONS AND PROCESS FOR PREPARING

SAME BY AQUEOUS ACID COUPLING OF

IODOFLUOROCARBONS USING Zn OR Cd

CROSS-REFERENCE TO EARLIER FILED APPLICATION

This application is a Continuation of patent application Serial No. 07/593,900 filed October 5, 1990, now abandoned.

FIELD OF THE INVENTION

The invention relates to a method of producing straight chain perfluoroalkanes and novel fluorohydroalkanes by dimerizing fluorohydroiodoalkanes, perfluorohydroiodoalkanes or mixtures thereof, with a dehalogenating metal in aqueous acid solution. Perfluormated organic compounds produced by this inventive process are of great industrial importance because of a combination of favorable electrical and physical properties, chemical inertness and thermal stability. In many instances, however, it is difficult or expensive to manufacture compounds having the requisite molecular size; or known methods of manufacture result in products which contain loosely bonded groups which detract from the inherent stability of the molecule. In addition, many of these materials, by nature of their manufacturing process, consist of mixtures of products with different molecular weights. A perfhioro organic compound having a greater molecular weight is most often desirable and can be prepared by coupling two iodoperfluoro organic molecules together, eliminating iodine and forming a molecule larger in size than either the original molecules. These coupled products have remarkable resistance to chemical and thermal attack and provide useful lubricants, solvents, plasticizers, heat transfer media and a host of other applications. lodoperfluoro compounds are currently coupled by any of several different methods.

DESCRIPTION OF RELATED ART

Previous techniques for carrying out such coupling reactions have in many cases involved the use of metallic mercury and ultraviolet radiation which is expensive and not well suited to industrial processes. The reaction of zinc or zinc/copper couples with perfluoro or perfluoro/halo carbons to produce dimers has been reported previously. The key difference is the present invention resides in the discovery that metallic Zn and Cd will couple Rfl to Rf-Rf in aqueous solution.

The earliest report of the reaction of zinc metal with perfluoroalkyl iodides was made by Haszeldine and Walaschewski in the Journal of the Chemical Society p.3607 in 1953. While their goal was the preparation of heptafluoropropyl zinc iodide (RfZnl), they report the following key features of the reaction: the solvent must be basic (in the Lewis acid sense) and an ether such as THF, Et ₂ 0, Bu ₂ 0, or dioxane. RfH, RfCF=CF ₂ , and Rf-Rf are by-products, the reaction is sensitive to the concentration of Rfl, it requires 1:5 Rf Solvent, higher temperatures give more Rf-Rf, RfZnl is decomposed by aqueous caustic or anhydrous acid to RfH, and RfZnl gives RfH quickly with hot water and slowly in cold.

U.S. Patent No.3,317,618 discloses both compositions of perhalogenated compounds and processes to make them. A myriad of methods are disclosed to produce coupled halogenated products. The processes pertinent to this reference include the use of a dehalogenating metal, such as zinc. When a dehalogenating metal is used, the reference maintains it is necessary to use a solvent, which it is reported should be organic, preferably a Lewis base. No mention of aqueous solvents for this use was made. Aqueous solvents were used, however, in conjunction with ultraviolet light to couple iodo compounds. These included aqueous potassium iodide, sodium thiosulphate, and sodium hydroxide. No mention of aqueous acids was made and no dehalogenating metals were used in combination with the aqueous solvents. In a series of three papers from 1977 to 1984, Blancou and

Commeyras reported investigating the reaction of zinc/copper couples with perfluorocarbons and with perfluorocarbon and additional substrates. The earliest paper discusses the reaction of perfluorocarbons alone, with Cu/Zn couple in dimethyl sulfoxide (DMSO) or DMSO with potassium

thiocyanate present. The products were RfH and isomers of the olefin resulting from loss of 'IF' from the perfluorocarbon. In acetone or DMSO with zinc alone, they report no reaction, while in dioxane, they report the organometallic. The second paper repeats the earlier reactions in the presence of methyl or ethyl iodide where they isolated the reduced product, the perfluoroalkyl coupled product, the zinc organometallic, and no olefins. When they replaced CH3I with CHC1 ₃ they obtained mainly RfH with a small amount of Rf-Rf, or with CH ₂ Br ₂ they observed RFH, Rf-R£ RfCH ₂ CH ₂ I, and finally with CCI ₄ they observe; RfH, Rf-Rf, RC1 and the corresponding perfluoro-mono-olefin. In the last paper they again repeated the earlier experiments but in the presence of CICOOEt in ethylene carbonate solvent. At low temperatures, 80° to 90°C they isolated Rf-Rf and RfC0 ₂ CH ₂ CH ₂ OH in good yields, while at 150°C they found only RfCOOH and Rf-Rf, again in good yields. Replacing ethylene carbonate with diethyl carbonate or diethyl at 80°C gave RfCOOEt and small amounts of Rf-Rf.

The only report in the literature that describes the reaction of perfluoroalkyl iodides with zinc in aqueous acid is European Patent Publication No. 160577 Al published in 1985. This invention teaches a method for the production of acids of formula RfC0 ₂ H by reacting Rfl and trichloroethylene (αHC = CC1 ₂ ) to form RfCH = CC1 ₂ and subsequently oxidizing RfCH=CCl ₂ to RfCOOH. Thus the reaction involves an olefin. This reaction takes place by a vinyl radical (*CH=CC1 ₂ ) whereas the present invention involves an alkyl radical (*CH ₂ Rf) or (Rf*). Hence the reaction system is believed to be different from the present invention. The patent's main bulk of disclosure teaches using anhydrous organic acids as solvents for the reaction of Rfl and ClHC=CCl ₂ . However, they do state that "a dilute mineral acid (for example 10% hydrochloric acid)" will work. In their Example 5, they used 10% aqueous hydrochloric acid, zinc and a 2 fold molar excess of C1CH = Cl ₂ was used and they reported the following product distribution as determined by Fι ₉ Nmr.

30% C6F ₁₃ CH=CC1 ₂ (coupled compound of Rfl and trichloroethylene) 35% F13H (RfH compound) 33% Cli-aFa; (Rf-Rf compound) .

This process is similar to the related art teachings described herein since an organic solvent (excess of CHCl=CCl ₂ ) is present. Makromolekulare Chemie, 189(4), 911-25, 1988 and Polymer Preparation, 26(2), 234-5, 1985 presents fluorocarbons and fluorohydrocarbons of the form F(CF ₂ ) ₁₂ (CH ₂ ) _n H where n=0-20 and F(CF ₂ )„(CH ₂ ) _ιn (CF ₂ ) _n F where n= 10-12 and m=6, 8-20. Perfluoroalkyl olefins have also been synthesized as described in prior art such as Tetrahedron, 30(23/24), 4197-200.

The Academy of Sciences (USSR) Bui. Division Chem. Sci., (5), 1056-60, 1979 describes the synthesis of a mixture of fluorooctanes [CF ₃ CH ₂ CH(CF ₃ )] ₂ (95%, two diastereoisomers, separated by preparative GLC) from electrolysis of a solution of CF ₃ COOH-CF ₃ COONa and

3,3,3-trifluoropropene in aqueous MeCN at a current density of 2-4 A/ά ^~~~ and an increase in pressure with a yield of 42% based on current.

SUMMARY OF INVENTION The present invention relates to a process for dimerizing perfluoroiodoalkanes, perfluorohydroiodoalkanes and mixtures thereof with a dehalogenating metal in aqueous acid solution, as illustrated by the following equation:

Y(aq)

PI + P'l + M -> P-P' + MI ₂ where P and P' may be different or the same and are independently

Rf -, RfCH ₂ CH(Rf)- or RfCH ₂ CH(Rf)CH ₂ CH(Rf)- wherein Rf is OF*,* _! (n= 1 to

10),

M = Zn or Cd

Y = Dilute, aqueous HC1, acetic acid or any acid that would activate the surface of the zinc or cadmium.

This invention further pertains to novel perfluorohydroalkanes of formula P-P' where P and P' may be different or the same and are independently

Rf -, RfCH ₂ CH(Rf)- or RfCH ₂ CH(Rf)CH ₂ CH(Rf)- wherein Rf is C _n F _2ll+1 (n= 1 to

10), with the provisos

1) that P and P' may not simultaneously be Rf, and

2) P-P' cannot be [CF ₃ CH ₂ CH(CF ₃ )] ₂

The coupling reaction which have been described in previous references imply or state that the perfluoro organic zinc compound, once formed, should be decomposed quickly in aqueous HC1 to RfH. The finding that, metallic Zn and Cd will couple Rfl to Rf-Rf in an aqueous system without an organic solvent or excess organic reagent is novel, unexpected, and unprecedented. In addition, this is the first report of the coupling of a secondary perfluorohydro iodoalkane.

DETAILED DESCRIPTION OF INVENTION The perfluoroalkanes are prepared by heating an equal molar mixture of zinc or cadmium metal with a perfluoroalkyl iodide or hydrofluoroalkyl iodide in the presence of 10% HC1 as a solvent. The general reaction is:

HCl(aq) 2Rfl + Zn -* Rf-Rf + Znl ₂

A key feature of this invention is that this method greatly simplifies solvent removal. Unlike organic solvents, water is immiscible in the product and easily separates out from the organic product layer. More purification is accomplished depending on the physical state of the product. The product can be purified by hot filtration with low melting solids or dissolved in an easily removed solvent such as Freon ^® 113 and the organic layer is separated, filtered, and washed. The Freon ^® is removed by distillation.

Perfluoroalkyl iodides and certain fluorohydroalkyl iodides have been found to couple using this process. For example, both C F ₉ CH ₂ CHIC ₄ F ₉ and both can be coupled using this process.

The reactions tend to be fairly insensitive to both concentration and strength of the acid solvent. Reducing the 10% strength of the HC1 solution to 2% did not change the yield of the coupled product. Also, diluting the reaction mixture by adding 100 ml of 10% HC1 rather than the usual 5 fold did not affect the yield. With respect to the Rfl/Zn ratio as expected, the conversion of Rfl to products decreases as the ratio of Rfl/Zn increases. With respect to the metal used, while both zinc and cadmium work, zinc is preferred. Copper, a commonly used coupling agent, and mercury were tested but do not work.

Generally the reaction is carried out at 70° to 110°C. "Yield" and "conversion" which are used below are defined as follows. Conversion is molar % of Rfl consumed. Yield is molar % of Rfl converted to dimer divided by conversion x 100%.

Except where noted, the Examples were run as follows: A 3-necked flask is fitted with a reflux condenser, a magnetic stirrer, and a heating mantel with a Thermowatch ^® temperature controller. The desired amount of metal (Zn or Cd) is introduced, followed by the desired amount of perfluoroalkyl iodide or hydrofluoroalkyl iodide. Then the desired amount of aqueous HC1 is added and the mixture is heated to reflux. Samples are taken periodically, usually after 1 hour, 2 hours, 4 hours, 7 hours and overnight until the GC analysis shows that the Rfl has been completely reacted or has stopped reacting. The mixture is then cooled, sufficient 10% H ₂ S0 ₄ is added to dissolve the Znl ₂ . Liquid samples are then filtered to remove any remaining metal., and the immiscible liquids separated and resulting product is weighed. When the product is a solid, the mixture can be hot filtered to remove unreacted metal, cooled to precipitate the product and subsequently filtered to remove the aqueous layer. Alternately, sufficient easily removed solvent like Freon 113 ^® can be added to dissolve the product, the mixture filtered to remove any remaining metal, and the immiscible liquids separated, and the Freon 113 ^® removed by distillation or evaporation. The resulting solid is weighed.

TABLE 1

JΔBLΣ LΔ

Yield (%)

TABLE IB

Example Starting Rfl ProdlKt R-Rf

1 C ₄ F9CH ₂ CH(C ₄ F ₉ )CH2CHIC ₄ F9 [C ₂ F ₉ CH ₂ CH(C ₄ F ₉ )CH ₂ CH(C ₄ F9)] ₂

C ₄ F ₉

C F CH CHCH CHC F

4 9 2 2 4 9

C F CH CHCH CHC F

4 9 2 2 4 9

CF

4 9

CF I CF -CF

6 13 6 13 6 13

3 CF I CF -CF 6 13 6 13 6 13

C 6F 13 I&C 4F9CH2CHIC 4F9 C 4F9CH2CH(C 4F 9)C6F 13

In Example 4, not only is the desired product, C ₄ F ₉ CH ₂ CH(C ₄ F ₉ )C ₆ Fι ₃ , obtained in 14.7% yield, but the products expected from the individual reactions as well. The product and yields, in parenthesis, from the individual reactions are; (14.7%), FisH (33.4%), Ci ₂ F ₂ 6 (9.0%), C ₄ F ₉ CH ₂ CH ₂ C ₄ F,, (323%), and [Cφ-CH-CH(( F-)h (20.7%).

EXAMP E 5 Example 1 was repeated except the concentration of the HC1 solution was 2% rather than 10%. Also, after the reaction was run, 10 ml of 10% sulfuric acid was added to the flask. The mixture was then filtered and worked up in the same way as above.

TABIE2

Time(hrs)/

Example Metal(g> Rfl(g) 2% Hq(g) Tgπφ,(°C) 5 Zn 3 7 22.3 20 5.5/100

TABLE 2A

Yield (%)

Example Rf-Rf RfH Conversion 5 41.8 5.0 100

Example Starting Rfl Product Rf-Rf 5 F ₁₃ I Fi Fis

The reaction of C ₆ F ₁₃ I (Rfl in Table 3) with Zn in HC1 was studied with respect to the mole ratio of zinc. The range chosen for study was from a 0.1 to a 2 fold molar excess of zinc. The data is given in Table 3 below. It shows that as the molar % of zinc decreases so does the conversion of the Rfl to products, but the yield of coupled product is independent of the relative amount of zinc.

TABLE 3

Molar Ratio Time Temp Yield

Ex.- Rfl/Zn Hrs J£ Rf-Rf RfH Conversion

2 1:2 6 90 38.4 Trace 99.9 6 1:1 12 75 36.7 None* 100

* Early GC traces show RfH - None recovered