United States Patent Office Faiented Vay 27, 1958 2 Substantially All of the Hydrogen Chioride Is Removed Therefrom

2,336,622 United States Patent Office Faiented Vay 27, 1958 2 substantially all of the hydrogen chioride is removed therefrom. With respect to the reactants usei in this process, the 2,336,622 phosgene car be preformed or it can be formed in situ PREPARATION OF CARBONY, FIUOR);E from carbon monoxide and chlorine which, as is weli Charles W. Tullock, Winnington, Dei., assig or its E. H. known, combine readily at elevated temperature to give iil Pont de Nemours and Conpany, Wii Saiigioia, Bei, phosgene. When this is done, the carbon monoxide is a corporation of Delaware preferably, though not necessarily, used in excess over the amount calculated to react with the chlorine. Simi No Drawing. Appication February 13, 1955 :) larly, the hydrogen fluoride can be used preformed, as the Seria No. 489,294 substantially anhydrous material, or if desired, it can be prepared in situ by employing approximately equivalent 10 Claims. (C. 260-544) amounts of a strong, substantially anhydrous acid such as sulfuric acid or hydrogen chloride and of an alkaline or This invention relates to a new process for preparing alkaline earth metal fluoride, such as Sodium or calcium fluorine-containing organic compounds. in particular, it fuoride. This embodiment is not preferred, however, be relates to a new process for preparing carbonyl fluoride. cause of the additional difficulties encountered in mixing It has recently been discovered that valuable fluorocar the reactants and in separating the reaction product from bons, including tetrafluoroethylene, can be synthesized in solid by-products. Another method of forming both very good yields by reacting carbonyl fluoride with car d phosgene and hydrogen fluoride in situ involves reacting bon at high temperatures, for exampie, by bringing car together formaldehyde, chlorine and a metal fluoride, bonyl fluoride in contact with the carbon electrodes of e.g., calcium fluoride. The reactions taking place are an electric arc. This discovery is disclosed and caimed presumably H2CO--2Cl2-> COCl.--2HCl and in application Ser. No. 420,472, filed on April 1, 1954, by M. W. Farlow and E. L. Muetterties and issued May Regardless of whether the phosgene and hydrogen fluo 24, 1955, as U. S. Patent 2,709,189. ride are used preformed or are formed in situ, it is de Adequate commercial exploitation of this discovery sirable that there be in the reaction mixture at lease one would of course be furthered by economical syntheses of Inole of hydrogen fluoride per mole of phosgene, in order carbonyl fluoride in an acceptable state of purity, and to obtain satisfactory yields of carbonyi fuoride. Since in particular, free from hydrogen chloride. Such a the formation of carbonyl fluoride requires two moles of synthesis has heretofore been lacking. Carbonyl fluoride hydrogen fluoride per mole of phosgene, it is generally has been prepared by reaction of silver II fluoride with preferred to use the reactants in approximately those pro carbon monoxide Rufi et al., Z. anorg. allgem. Chem. poritions, or to use a small to moderate excess of hydro 221, 154 (1934) and, as a mixture with many other gen fluoride, e. g., to use up to three moles hydrogen products, by direct fluorination of acetone Fukuhara et fluoride per mole of phosgene. al., J. Am. Chem. Soc. 63, 788 (1941)). A much more The rate of the reaction between phosgene and hydro practical method involving the reaction of hydrogen fluo gen fluoride is almost negligible below 50° C., and the ride with phosgene has been reported, first by Simons reaction should therefore be carried out above that tem et al., who obtained chiefly carbonyl fluorochloride J. 40 perature. While the reaction rate is already much in Am. Chem. Soc. 68, 1672 (1946), then by Xwasnik creased at temperatures in the neighborhood of 100° C., FIAT Review of German Science 1939-1946, inorganic it is much preferred from a practical standpoint to use Chemistry I, p. 242 (1948)). However, even this atter temperatures of at least 150° C. The temperature can method has little practical utility since the reports indi be as high as the decomposition point of the reactants but cate that these workers were unable to separate the car it is not desirable to exceed 700° C. and preferably about bonyl fluoride from the hydrogen chloride formed in the 500 C. when carbonyl fluoride is the desired main prod reaction. The reason for this is that the two compounds lict because the yields of carbonyl fluoride decrease when have practically the same boiling points, -83.1 and this temperature is approached and other products form -83.7 C., respectively. Moreover, the usual absorbents in increasing amounts, as discussed below. The preferred for hydrogen chloride react with, and destroy, carbonyi temperature range is that between 150 and 400° C., and fiuoride. still more preferably 150-300° C. This invention has as an object a process for the prep The reaction is most conveniently carried out at atmos aration of carbonyl fluoride, CCF. A further object is pheric pressure, for example, in a tubular reactor which a process providing carbonyl fluoride essentially free from may be packed with contact materials such as active deleterious contaminants. Another object is the provision carbon or calcium fluoride powder or pellets, although of a process for preparing fluorochlorocarbons. A still this is not essential since satisfactory, although lower, further object is a process for preparing fluorochloro conversions to carbonyl fluoride are obtained in the methanes. Still another object is a process for preparing absence of such materials. However, the use of active carbonyl fluoride from carbonyl chlorofluoride. Other ob carbon, which acts as a reaction catalyst, is preferred since jects will appear hereinafter. 60 it leads to high conversions at relatively low temperatures. The present invention is to a process wherein phosgene in atmospheric pressure operation, a gaseous mixture in is reacted with at least a molar equivalent of hydrogen the proper proportions of hydrogen fluoride and phosgene, fluoride, HF, at a temperature of at least 50° C. and the or of hydrogen fluoride, carbon monoxide and chlorine is reaction product with or without a preliminary separation passed through the reactor heated to the desired tempera therefrom of unreacted phosgene and/or hydrogen fluo tre. The contact time is not very critical since appre ride is brought into contact with a stoichiometric amount, ciable conversions are observed even at very short contact based on the hydrogen chloride in the reaction product times, e.g., 5 seconds. Good results are obtained at con and on any hydrogen fluoride there present, of an inor tact times in the range of 15-60 seconds, although much ganic material inert to carbonyl fluoride but reactive wit longer contact times can be used, e.g., 5 minutes or more. hydrogen chloride to form stable products, said inorganic ; ; The effluent gas is treated as described below to remove material being maintained in contact with the reaction the hydrogen chloride formed, and also any unreacted product at a temperature at least as high as 0° C. until hydrogen fluoride. 2,836,622 . es. 4 . Another satisfactory mode of operating consists in car fluoromethane. The carbonyl fluoride is readily separated rying out the reaction in sealed, corrosion-resistant pres from the mixture by fractional distillation as shown be sure vessels, and preferably at the autogenous pressure low. Under the same conditions, but in the presence of developed by the reactants at the operating temperature. a small amount, 1-5%, by weight, of calcium fluoride, a If desired, additional pressure provided by a non-interfer similar disproportionation takes place except that a higher ing gas such as nitrogen or carbon monoxide can be ap amount of chlorofluoromethanes (CCIF, and CFCI) is plied. In particular, carbon monoxide can be introduced found in the product. Thus, it is apparent that the car into the reaction vessel to any desired degree of initial bonyl chlorofluoride can be largely converted into valuable pressure, for example between 10 and 800 atmospheres, products. especially when the phosgene is synthesized in situ from its O if it were not for the presence of hydrogen chloride, components, chlorine and carbon monoxide. However, the separation of carbonyl fluoride from the other com no substantial advantage appears to result from using ponents of the crude. reaction product would offer no carbon monoxide much in excess over the amount re special difficulty. Fractionation in a low temperature quired to form phosgene. Within the preferred tempera still accomplishes this separation. Even carbon dioxide, ture range of 150-400 C., the reaction time in pressure 5 which sublimes at -78° C., can be to a large extent sep vessels can be quite short, Substantial yields are ob arated from carbonyl fluoride (P. B. -83.1° C.) owing tained with a reaction time as short as 10-30 minutes, to the fact that it appears to form a constant boiling mix especially when a catalyst such as active carbon is used. ture with carbonyl fluoride and concentrates in the first It is not necessary to use reaction times exceeding three fraction of this compound distilling over. In any event, hours, and in fact it is undesirable to do so in the higher 20 carbon dioxide is formed only in small amounts and does temperature ranges, e. g., 400-500 C., since the yield not normally interfere with the reactions of carbonyl of carbonyl fluoride appears to decrease as a consequence. fluoride, especially its reaction with carbon at high tem Active carbon, that is, very finely divided, porous peratures, e.g., 1500 C. or higher as in the carbon arc, carbon having a total surface area of at least 20 square to give tetrafluoroethylene.

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