3,692,643 United States Patent Office Patented Sept. 19, 1972 2 tion of aromatic rings or other unsaturated structures 3,692,643 by addition of fluorine, such that a saturated acid fluoride ELECTROFLUORNATION PROCESS USENG product is obtained. The resulting product compound can THOESTERS be used to make a variety of useful perfluorocarbon de Dewey George Holland, Alientown, Pa., assignor to Air 5 rivatives. By way of example, the product can be hy Products and Chemicals, Inc., Allentown, Pa. drolyzed with water, reacted with ammonia to produce No Drawing. Filed May 17, 1971, Ser. No. 144,253 the corresponding amide, or can be reacted with an Ent. C. C07b 29/06, C07c5 1/58, 143/70 alcohol to produce an ester. The saturated fluorocarbon U.S. C. 204-59 R 18 Claims structure is highly stable and inert. When this structure 0. contains five or more carbon atoms it results in a ma terial with a fluorocarbon “tail” which is both hydro ABSTRACT OF THE DISCLOSURE phobic and oleophobic and which is characterized by The presence of a small amount of a thioester of marked surface active properties. Extensive industrial aromatic or aliphatic carboxylic acids in the electrolyte usage, however, of the resulting perfluorocarbon product during the electrofluorination of alkyl substituted or un compound has been hindered by the high cost of such substituted, aromatic or aliphatic, sulfonic or carboxylic, compound. Accordingly, any invention which will ma acid halides decreases the rate of electrode decomposition, terially reduce the cost of manufacturing such a com raises the yield of perfluorinated product and decreases pound is of significant economic importance. the formation of viscous materials. Three principal problems connected with electro 20 fluorination processes have been: (a) the rate of electrode decomposition, (b) low product yields and (c) the forma BACKGROUND OF THE INVENTION tion of undesirable viscous materials as a side reaction. This invention relates to an electrochemical process In spite of constant and continual efforts to overcome or for making fluorocarbon acid fluorides, and more particu minimize these problems, the problems have never been larly, the invention relates to a process for the electro 25 satisfactorily eliminated. fluorination of alkyl substituted or unsubstituted, aro Formation of tarry material is particularly prevalent matic or aliphatic, carboxylic or sulfonic, acid halides in a when an aromatic starting compound is employed. The cell containing an electrode pack having electrodes, a formation of such tarry material has resulted in relatively current conducting electrolyte solution comprising anhy short runs before it becomes necessary to shut down an drous liquid hydrogen fluoride and a small amount of a 30 operating cell in order to replace a fouled electrode pack thioester of an aromatic or an aliphatic carboxylic acid. or fouled electrolyte solution. Moreover, the formation The process for the electrofluorination of alkyl sub and presence of such tarry material renders it difficult to stituted or unsubstituted, aromatic or aliphatic, sulfonic recover the desired product compound in pure form. or carboxylic, acid halides is well known. Prior proce SUMMARY OF THE INVENTION dures have been described in U.S. Letters Patents Nos. 35 2,519,983; 2,717,871; and 2,732,398; and in the literature, It is an object of this invention to decrease the rate of e.g., in “Fluorine Chemistry,” volume I (Academic Press, electrode decomposition in electrofluorination processes. Inc., 1950). The conventional electrofluorination proc Another object of this invention is to increase the esses described by the prior art utilize an electrode pack, product yield obtained in electrofluorination processes comprising alternating, closely spaced (/8 inch to 4 40 per unit of electrical energy (electrical efficiency). inch) electrodes-generally iron cathode plates alter Still another object of this invention is to decrease the nating with nickel anode plates. A voltage is applied to formation of viscous material (i.e. tarry material) during the cell in the range of approximately 4 to 8 volts D.C. electrofluorination processes. The cell can be operated substantially at atmospheric Yet another object of this invention is to improve elec pressure and at a temperature between -20 and 19 de trofluorination processes by the incorporation of a grees C., although higher pressures and temperatures may thioester of an aromatic or an aliphatic carboxylic acid. be used. The organic starting material may suitably be It is still a further object of the present invention to initially present in admixture with the electrolyte solution improve the conductivity of electrolyte solution by the of hydrogen fluoride in an amount between about 0.5 inclusion of small amounts of a thioester of an aromatic percent and about 20 percent by weight, based on the or an aliphatic carboxylic acid in the electrolyte solution. weight of the hydrogen fluoride. Both the organic starting 50 In accordance with the present invention, electroflu material and the hydrogen fluoride electrolyte are re orination is accomplished by the addition to the elec plenished from time to time as required. A refrigerated trolytic solution of a thioester of an aromatic or an ali condenser is used to condense out most of the hydrogen phatic carboxylic acid having the following formula: fluoride vapors which are evolved with the exit gas mix ture, and the liquified hydrogen fluoride is then drained 55 back into the cell. The resulting fluorinated product of CnH2n+1 KLX-cosr the process is relatively insoluble in the hydrogen fluoride L b (Formula, ) electrolyte solution and either settles to the bottom of the where n is an integer from 0 to 10 when b is equal to 1 cell from which it can be drained or evolves from the cell and n is an integer from 1 to 10 when b is 0; b is an inte in admixture with the hydrogen and other gaseous 60 ger of 0 or 1; and R is a C1 to C alkyl group. The thio products, depending upon its volatility. ester of the aromatic or aliphatic carboxylic acid is ad Referring to the aforementioned patents, U.S. Letters vantageously present in an amount between about 0.5 Patent No. 2,717,871 relates particularly to the electro and about 6 percent by weight based on the weight of the chemical fluorination of carboxylic acid halides (com ge (starting compound) to the electrofluorination pounds containing one or more carbonyl halide groups); 65 CC. and U.S. Letters Patent No. 2,732,398 relates particularly DESCRIPTION OF THE PREFERRED to the electrochemical fluorination of sulfonic acid halides EMBODIMENT (compounds containing one or more sulfonyl halide The alkyl groups in the structure shown in Formula I groups). The electrochemical fluorination process results may have straight chains or branch chains and may be in perfluorination by replacement of all carbon bonded 70 primary, secondary or tertiary. When the aromatic ring hydrogen atoms by fluorine atoms, including the satura is present (i.e., b is 1), and CnH2n+1 hydrocarbon group 3,692,643 3 4. may be attached to the aromatic ring in either the ortho, Preferably, in the electrofluorination of the above start para or meta position. ing compounds, the electrolyte contains a Small amount Typical examples of thioester additives coming within of thioalkyl ester of the starting compound thus providing the scope of Formula I are the following materials: a relationship between charge and additive. While this is 5 not essential to the practice of the present invention, this CHCOSCH preferred practice affords a perfluorinated product of the CHCH2COS (CH2)2CH same structure as the main electrofluorination charge. CHCOS (CH2)4CH It is important to note that the described thioester addi CH3COS(CH2)5CH tives need only be present inthe electrolyte Solution. It 3-CH (CH-COS(CH3)2CH O has been found that these thioester additives are stable 4-CH3(CH2)(CH) COSCH and readily recoverable from anhydrous hydrogen fluo The preferred thioester compounds are thio (n-butyl)ben ride. They also are believed to possess the advantageous zoate; thio (n-butyl)butyrate and thio (n-butyl) octanoate. characteristic of not reacting in anhydrous hydrogen fluo A minor proportion by weight of the additive, relative to ride with the aromatic carboxylic or sulfonic acid fluorides the organic starting material, is employed. Initially, be present during the electrofluorination, nor are they believed tween 0.1 to 10 percent by weight of the thioester addi to react with the desired perfluorinated products which tive, based on the weight of hydrogen fluoride present, are present in the electrolyte solutions during the electro can be added to the cell. When the desired alkyl substituted fluorination process. or unsubstituted, aromatic or aliphatic, carboxylic or sul The invention will be further illustrated by the follow fonic, acid halide is added to the cell, additional thioester : ing specific examples, it being understood that there is no additive is placed in the cell such that between about 0.5 intention to be necessarily limited by any details thereof and about 6 percent by weight of thioester additive based since variations can be made within the scope of the inven on the acid halide charge is present in the cell at all tion. In each of the examples set forth below, Cell I refers times during the process. Thus, while large amounts of to a 6,500 cc. Monel Cell containing A6 inch thick nickel the thioester additive can be incorporated initially with anodes and cathodes in which an outer body glycol re either the electrolyte or starting compound, the preferred frigerant is used to maintain the Cell at an operating procedure is to add a small amount initially to the elec temperature of from 50 to 67 degrees F. and in which the trolyte and then continue to add additive to the elec Monel reflux condenser is operated at from -40 to -60 trolyte during the process. Continuous addition of the ad degrees F. Cell II is a cell of identical construction to ditive is required since the additive is fluorinated during 30 Cell I except that the electrolyte volume is 4,500 cc. The the operation of the process; making it necessary to re organic and electrical yields set forth in the following plenish the additive from time to time during an extended examples are based on the theoretical equations for the run in order to maintain the concentration of starting charge and the assumption that the molecular weight of compound and additive within the desired range. Othe the fluorinated product is essentially the weight of the method of insuring that there is sufficient additive present perfluorinated saturated carboxylic or sulfonic acid fluo in the electrolyte solution during operation of the process ride corresponding to the skeletal structure of the charge. is to monitor its concentration in the electrolyte by vapor Subsequent to the initial charging of the cell, additional phase chromatography. starting compound and additive are replaced based on the Pure anhydrous liquid hydrogen fluoride is nonconduc consumption of starting compound according to the tive. Due to this fact, it has previously been necessary to 40 amount of current consumed and the theoretical electro add sodium fluoride, or some other carrier electrolyte, to fluorination equation. These subsequent additions are per the cell in order to provide a conductive solution. Since formed at twenty-four (24) hour intervals. the additive of the present invention also serves as a car rier electrolyte, the thioester additive makes it unneces EXAMPLE 1. sary to employ a carrier electrolyte such as sodium fluo (A) The electrofluorination of benzene sulfonyl chlo ride (which promotes extensive electrode decomposition) ride was conducted in Cell I. The anode-cathode elec for the electrochemical fluorination process. trode pack had /8 inch spacing and a total anode area of The alkyl Substituted or unsubstituted, aromatic or ali 4.245 square feet. An initial charge of 450 grams of ben phatic, carboxylic or sulfonic, acid halide starting com zene sulfonyl chloride was added to the anhydrous hydro pound which can be employed in the practice of the pres gen fluoride. The run was conducted at from 6.8 to 8.6 ent improved process includes starting compounds having 50 volts for a period of 371.6 Faradays, at an average current the following general formula: density of 10.8 amperes per square foot. The initial charge and subsequent additions totaled 14.2 moles of benzene sulfonyl chloride. The liquid fluorinated product obtained CnH2n+1 k >YZ from the bottom of the cell was 2,970 grams. This rep L (Formula II) 55 resents a 37.4% electrical efficiency and a 58.3% organic where n is an integer between 0 and 10 when b is 1 and in efficiency. The rate of loss of nickel from the electrode is an integer between 1 and 10 when b is 0; b is either 0 or pack was in excess of 25 grams/1,000 ampere hours. 1; and Y is CO or SO2 and Z is C1 or F. Examples of (B) When the above experiment is repeated and 2%, starting materials defined by Formula II include the fol by weight, of thio (n-propyl) butyrate is added along lowing compounds: 60 with the organic charge, the electrical and organic yields is increased to about 60% and the loss of nickel from the CHCOF electrode pack is decreased to less than 1 gram/1,000 CHSOC1 ampere hours. The current density is increased to 20 am CH56CH-COF peres per square foot at 7.5 volts. CHCH-SOF 65 CoH2COCl EXAMPLE 2 (CH3)2CHCCHA)SOCI (A) The electrofluorination of p-isoheptylbenzoyl chlo Thus, starting compounds defined by Formula II include ride was conducted in the apparatus described in Example benzoyl chloride, benzene sulfonyl chloride and p-iso 1. The initial charge of 450 grams of p-isoheptyl benzoyl heptyl benzoyl chloride. Preferred starting materials in 70 chloride in anhydrous hydrogen fluoride was electrofluori clude benzoyl fluoride, butyryl fluoride, octanoyl fluoride nated at between 6.2 and 8.0 volts for a period of 259.9 and octane sulfonyl fluoride. The starting compound can Faradays at a current density of 7.9 amperes per square be added to the liquid hydrogen fluoride either before or foot. The electrical yield was 48.7% and the organic yield after the liquid hydrogen fluoride is introduced into the was 41.3% for liquid perfluorinated product obtained. cell. 75 This product was analyzed by ethanol esterification and 3,692,643 5 6 distillation and was found to be 62% esterifiable. The sludge formation was observed. Liquid fluorinated product weight loss from the electrodes was at a rate of 31 (18.8 kilograms) was obtained; an 85.3% organic effi grams/1,000 ampere hours. ciency and 88.9% electrical efficiency. The rate of loss (B) The above experiment is repeated with additions of nickel from the electrode pack was less than 2.2 grams/ of thio ethyl butyrate so that concentrations of at least 1,000 ampere hours. 0.09 percent of this thioester is maintained in the elec Similar results were obtained when the following cell trolyte, as determined by vapor phase chromatography charges and thioester additives were substituted for the of the electrolyte solution. The resulting organic yield is cell charge and thioester additive of Example 6. raised to above 60% while the weight loss of the electrode pack is less than 2 grams/1,000 ampere hours. O Cell charge: EXAMPLE 3 CHCOCl As a comparative example to that of the invention as CH(CH)COCl described in Example 4, forty-six moles of para (n-butyl) CHCOF benzoyl chloride was electrofluorinated in the apparatus 5 CHSOF described in Example 1 at 8.0 to 8.8 volts for a period CHCOF of 1085 Faradays, at a current density of 3.5 amperes per CHSOC square foot. An initial 10% charge was used and subse: (CH) CHCOCl quent additions were made at 24 hour intervals. Liquid CHSOF perfluorinated product was obtained at an electrical effi 20 ciency of 78.3% and an organic efficiency of 57.0%. The Thioester additive: run was continually hampered by inability to remove CHCHCOSCHCH product from the bottom of the cell due to viscous sludge CHCOS (CH ) 5CH3 formation. At the termination of the run, 751 grams of CHCOSCCH2)3CH3 partially fluorinated nickel containing Solids were scraped 25 CHCOS (CH2)3CH from the electrode plates. CH(CH2)COSCH EXAMPLE 4 3-CH (CH-COS(CH2)2CH The electrofluorination of 3.6 moles of para (n-butyl) 4-CH3(CH2)6(CH-COSCH3 benzoyl chloride is conducted in Cell II at 4 inch plate 30 CH2COS (CH2)3CH3 spacing and a total anode area of 1.967 square feet. Three weight percent of thio(n-butyl)benzoate is added along where, {CH) is phenylene, and C6H5 is phenyl. with the organic charge. The resultant electrofluorination From the foregoing, it will be seen that this invention is conducted at 7.0 to 7.5 volts while maintaining a cur is generally well adapted to obtain all of the ends and rent density of 20 amperes per square foot. The loss of 35 objects hereinabove set forth, together with other ad weight from the electrode pack is less than 2 grams/1,000 vantages which are obvious and which are inherent there ampere hours. Moreover, no sludge is formed during the in. The addition of thioester additive not only decreases run and no film is found on the electrode plates at the the rate of electrode decomposition, increases the elec termination of the run. trolyte conductivity, and increases the yield of perfluori EXAMPLE 5 40 nated products, but also effectively reduces or eliminates (A) Benzoyl chloride (14.6 moles) is electrofluorinated operating difficulties due to the formation of viscous ma in Cell I at 4 inch electrode spacing, 1.967 square foot terials during the electrofluorination of alkyl substituted or anode area. An initial charge of 10% benzoyl chloride unsubstituted, aromatic or aliphatic, sulfonic or carbox is employed. A current density of only 4.7 amperes per ylic, acid halides. Prior to the adoption of the present square foot is drawn at 7.0 to 7.5 volts. The draining of 45 invention, the formation of tarry materials polluted the liquid product from the cell bottom is severely hampered electrolyte solution, formed a dense tarry deposit on elec by the appearance of viscous sludge in the product drain trode plates and also contaminated the fluorinated prod line. A nitrogen pressure of 20 p.s. i. is needed in order uct, thereby complicating recovery and purification of the to extrude the product and sludge mixture from the bot desired product. tom of the unit. The system becomes inoperative at the 50 As seen by the above examples, the improvement re 159 Faraday point. At this time the electrical efficiency sulting from the use of the present invention has very for production of liquid product is 13.3% and the organic materially increased the electrical and organic yield effi efficiency is 9.7%. ciency of electrofluorination processes while decreasing (B) Using identical apparatus, and an initial 10 weight the rate of decomposition of the electrodes and materially percent of benzoyl chloride charge, to which had been 55 reducing or virtually eliminating the formation of viscous added 6 weight percent of thio(n-butyl)benzoate, a sludge sludge or tarry material. free run averaging 6.5 to 7.5 volts and a current density Obviously, many other modifications and variations of of 20 amperes per square foot was easily maintained for the invention as hereinbefore set forth may be made with a period of 1013 Faradays. No sludge appearance in the out departing from the spirit and scope thereof. liquid product and 17.3 kilograms of liquid perfluorinated 60 What is claimed is: product was obtained from the 8.9 kilograms of benzoyl 1. An electrochemical process of making fluorocarbon chloride and 0.5 kilogram of thio (n-butyl)benzoate em acid fluorides by electrolyzing, in a cell containing an ployed as the cell charge. This yield represents a greater electrode pack, an electrolyte solution comprising anhy than 80% organic and electrical efficiency for the pro drous liquid hydrogen fluoride mixed with a hydrocarbon duction of perfluorinated liquid product. 65 acid halide starting compound having the formula: EXAMPLE 6 Benzoyl fluoride (69.2 moles), to which had been added 3 weight percent of thio (n-butyl)benzoate, was electro fluorinated in Cell I at 4 inch electrode spacing, 1.967 70 square foot anode area. An initial charge of 9.7% benzoyl where n is an integer between 0 and 10 when b is 1 and fluoride, containing 0.3% thio (n-butyl)benzoate, was em n is an integer between 1 and 10 when b is 0; b is either ployed. The electrofluorination was conducted for a period 0 or 1; and Y is CO or SO and Z is Cl or F, which proc of 1,032 Faradays, at an average current density of 18.3 ess is characterized by the feature that the electrolyte amperes per square foot at 6.0 to 7.5 volts. No viscous 75 solution contains a small proportion, relative to the hy 3,692,643 7 8 drocarbon acid halide starting compound, of an additive liquid hydrogen fluoride, wherein about 0.5 to about 6 having the following formula: percent by weight of an additive, based on the weight of the acid halide charge, is present in the electrolyte; said Olso additive having the formula: where n is an integer from 0 to 10 when b is equal to 1 and n is an integer from 1 to 10 when b is 0; b is an ca. OSR integer of 0 or 1; and R is a C to Cs alkyl group. 2. A process according to claim in which the addi O where n is an integer from 0 to 10 when b is equal to 1 tive is thio (n-butyl) benzoate. and n is an integer from 1 to 10 when b is 0; b is an 3. A process according to claim wherein the additive integer of 0 or 1; and R is a C to Cs alkyl group. is thio (n-butyl) octanoate. 11. A process according to claim 10 in which the addi 4. A process according to claim 1 wherein the addi tive is thio (n-butyl) benzoate. tive is thio (n-butyl) butyrate. 5 12. A process according to claim 10 wherein the addi 5. A process according to claim 1 in which the addi is thio (n-butyl) octanoate, tive is thioethyl butyrate. 13. A process according to claim 10 wherein the addi 6. A process according to claim 1 wherein the start tive is thio (n-butyl) butyrate. ing compound is benzoyl fluoride. 14. A process according to claim 0 wherein the addi 7. A process according to claim 1 wherein the starting 20 tive is thioethyl butyrate. compound is para (n-butyl benzoyl chloride. 15. A process according to claim 10 wherein the start 8. The process according to claim 1 wherein the start ing compound is benzoyl fluoride. ing compound is octane sulfonyl fluoride. 16. A process according to claim 10 wherein the start 9. A process according to claim 1 wherein the starting ing compound is para (n-butyl) benzoyl chloride. compound is octanoyl fluoride. 2 5 17. The process according to claim 10 wherein the 10. The process for the electrofluorination of a start starting compound is octane sulfonyl fluoride. ing compound having the formula: 18. The process according to claim 10 wherein the starting compound is octanoyl fluoride. 30 References Cited where n is an integer between 0 and 10 when b is 1 and UNITED STATES PATENTS n is an integer between 1 and 10 when b is 0; b is either 2,717,871 9/1955 Scholberg et al. --- 204-59 R 0 or 1; and Y is CO or SO2 and Z is C1 or F, which process 2,732,398 1/1956 Brice et al. 204-59 RX comprises electrolyzing the acid halide charge starting 3,028,321 4/1962 Danielson et al. ----. 204-59 R compound in a cell containing nickel anodes and a cur rent conducting electrolyte solution comprising anhydrous F. C. EDMUNDSON, Primary Examiner