May 12, 1970 H. M. Fox ETAL 3,511,760 ELECTROCHEMICAL FLUORINATION of ORGANIC Compounds
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May 12, 1970 H. M. Fox ETAL 3,511,760 ELECTROCHEMICAL FLUORINATION OF ORGANIC COMPOUNDs . Filed Nov. 2, 1967 3. Sheets-Sheet l NHSHG NHHG NicHG Silic NH H s 2 1. 727-2777AA I H H HS. it s 727-2 ty ZZZZZYZZZYZZYZZYZZYZIS A/G / INVENTORS H. M. FOX BY F. N. RUEHLEN A 77OAPWAYS May 12, 1970 H. M. FOX ETAL 3,511,760 ELECTROCHEMICAL FLUORINATION OF ORGANIC COMPOUNDS 3. Sheets-Sheet 2 AF/G 2 ------ 76 y - / M M / // M / 2227 74 F/G. 5 6 AF/G, 6 INVENTORS H. M. FOX BY F. N. RUEHEN ATTOARWAYS May 12, 1970 H. M. Fox ETAL 3,511,760 ELECTROCHEMICAL FLUORINATION OF ORGANIC COMPOUNDS Faled Nov. 2, 1967 3. Sheets-Sheet 5 S s INVENTORS : H. M. FOX BY F. N. RUEHLEN %ry /42.47 a 77OARWAYS 3,511,760 United States Patent Office Patented May 12, 1970 1. 2 veniently preparing fluorine-containing compounds. In 3,511,760 ELECTROCHEMICAL FLUORNATION OF our process the extent of fluorination of the fluorinatable ORGANIC COMPOUNDS compound can be readily controlled. Consequently, our Homer M. Fox and Forrest N. Ruehlen, Bartlesville, process is capable of producing a wide variety of fluorine Okla., assignors to Phillips Petroleum Company, a cor containing products with high efficiency and good selec poration of Delaware tivity. Compared with the fluorination processes of the Continuation-in-part of application Ser. No. 435,263, prior art, the reaction conditions utilized in our process Feb. 25, 1965. This application Nov. 2, 1967, Ser. are mild, and the yields of product per kilowatt hour or No. 683,089 per unit of anode area are extraordinarily high. Further Int, C. B.01k 3/00 more, as discussed further hereinafter, we have found that U.S. C. 204-59 20 Claims () we can introduce more fluorine into a fluorinatable com pound per kilowatt hour or per unit of anode area (in the order of at least 100 times as much or more in some ABSTRACT OF THE DISCLOSURE instances) than can be accomplished in processes of the Fluorinatable feedstocks are electrochemically fluori 5 prior art. nated in an electrolysis cell provided with a porous Another surprising result or advantage of our inven anode and using an anhydrous liquid hydrogen fluoride tion is that the primary products obtained in our process electrolyte. The fluorination is carried out under condi are predominantly partially fluorinated materials. It is tions such that it occurs within the pores of the anode. difficult to obtain such materials in the methods of the 20 prior art and, as stated above, even more difficult to pro duce moderately fluorinated hydrocarbons containing This application is a continuation-in-part of our co fluorine atoms in certain specific locations in the mole pending application Ser. No. 435,263, filed Feb. 25, 1965, cule. It is the reactive nature of fluorine to bind itself to now abandoned. a carbon atom to which one or more previous fluorine This invention relates to electrochemical fluorination. atoms have already been bound. Thus, any difluoro com In one aspect this invention relates to a process for pre pounds made by direct fluorination techniques of the paring fluorine-containing compounds by electrochemi prior art almost invariably have both the fluorine atoms cal fluorination of a fluorinatable compound. attached to the same carbon atom. This has made it Fuorine-containing organic compounds are known to necessary to employ indirect methods such as the prep possess value in many fields of industrial chemistry. For 30 aration of appropriate chloro- or hydroxy-analogs foll example, many of the lower molecular weight compounds lowed by replacement of such groups with fluorine. Our are useful as refrigerants, dielectrics, fire extinguishing invention provides a direct fluorination process which un materials, and as aerosol propellants. Many fluorine-con expectedly produces good yields of difluoro compounds taining compounds are also useful as intermediates for in which the two fluorine atoms are not on the same car the production of plastics and synthetic elastomers. A bon atom. As specific examples, 1,2-difluoroethane and numer of techniques are known for producing fluorine 1,4-difluorobutane can be easily and directly produced in containing organic compounds. These include pyrolysis good yields by the process of our invention. Thus, in one techniques in which fluorine-containing materials are pyr aspect, our invention provides a direct process for the olyzed in the presence of carbon or carbon-containing production of such materials directly from a hydrocar materials to obtain a mixture of fluorinated compounds. bon starting material in a one-step process. Another technique is to electrolyze a mixture of an elec Broadly speaking, the process of our invention com trolyzable fluoride having the compound to be fluorinated prises electrolyzing a current-conducting essentially an dissolved therein. In many instances, a wider commercial hydrous liquid hydrogen fluoride electrolyte in an electro application of fluorine-containing organic compounds has lysis cell provided with a cathode and a porous anode, in been limited due to difficulties in their preparation. Many 45 troducing a fluorinatable organic compound into the pores of the prior art processes for preparing such compounds of said anode and therein at least partially fluorinating involve several chemical and mechanical steps and re at least a portion of said organic compound within said quire the utilization of costly starting materials. Further pores of said anode, and recovering fluorinated compound more, when employing the methods of the prior art it products from said cell. is difficult to produce moderately or only partially fluori 50 An object of this invention is to provide an improved nated products in satisfactory yields. It is even more dif electrochemical process for the production of fluorine ficult to produce moderately or partially fluorinated prod containing compounds. Another object of this invention ucts, e.g., fluorinated hydracarbons, containing fluorine is to provide an electrochemical process for the produc atoms in certain specific locations in the molecule. It is tion of fluorine-containing organic compounds in good also difficult to produce fluorinated products electrochem 55 yields and with good selectivity. Another object of this ically at high rates of conversion and avoid the formation invention is to provide an improved electrochemical proc of Substantial amounts of cleavage products. ess for the production of fluorine-containing compounds The present invention provides a solution for the which is economical, commercially feasible, provides for above-described difficulties. We have now discovered an the maximum utilization of the starting fluorinatable ma improved electrochemical process for efficiently and con 60 terial, and is accompanied by the minimum formation of 3,511,760 3. 4. undesirable by-products. Another object of this invention Since fluorine is so reactive, no list of practical length is to provide an improved electrochemical process for the could include all starting materials which can be used production of fluorine-containing organic compounds in the practice of our invention. However, representative which process can be readily controlled to yield products examples of the above-described starting materials in having a desired fluorine content. Still another object of clude, among others, the following: methane; ethane; this invention is to provide an improved electrochemical 5 propane; butane; isobutane; pentane; n-hexane; n-octane: . fluorination process for the production of partially fluori cyclopropane; cyclopentane; cyclohexane; cyclooctane; nated fluorine-containing compounds, such as difluoro 1,2-dichloroethane; 1-fluoro-2-chloro-3-methylheptane; compounds, wherein the two fluorine atoms are attached ethylene; propylene; cyclobutene; cyclohexene; 2-meth to different carbon atoms. Other aspects, objects, and ad ylpentene-1; 2,3-dimethylhexene-2; butadiene; vinyl chlo vantages of the invention will be apparent to those skilled 10 ride; 3-fluoropropylene; acetylene; methylacetylene; vinyl in the art in view of this disclosure. acetylene; 3,3-dimethylpentyne-1; allyl chloride; methyl Thus, according to the invention, there is provided a amine; ethylamine; diethylamine; 2-amino-3-ethylpentane; process for the electrochemical fluorination of a fluorina 3-bromopropylamine; triethylamine; dimethyl ether; di table organic compound, which process comprises: Pass 5 ethyl ether; methyl ethyl ether; methyl vinyl ether; 2-iodo ing an electric current through a current-conducting es ethyl methyl ether; di-n-propyl ether; methyl formate; sentially anhydrous liquid hydrogen fluoride electrolyte methyl acetate; ethyl butyrate; ethyl formate; n-amyl contained in an electrolysis cell provided with a cathode acetate; methyl 2-chloroacetate; methyl mercaptan; ethyl and a porous anode; passing said organic compounds into mercaptan; n - propyl mercaptan; 2 - mercaptohexane; the pores of said anode and therein into contact with 20 2-methyl-3-mercaptoheptane; acetonitrile; propionitrile; the fluorinating species produced by said electrolyzing; n-butyronitrile; acrylonitrile; n-hexanonitrile; methanol; and recovering fluorinated organic compound as product ethanol; isopropanol; n-hexanol; 2,2-dimethylhexanol-3; of the process. n-butanol; ethylenebromohydrin; benzene; toluene, cu Very few organic compounds are resistant to fluorina mene; o-xylene; p-xylene; and monochlorobenzene. tion. Consequently, a wide variety of feed materials, both The electrochemical process of the invention is carried