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United States Patent Office Patented Sept 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.
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