United States Patent Office Patented July 31, 1956
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2,757,214 United States Patent Office Patented July 31, 1956 1 2 - formed according to the following equation, again usin 2,757,214 calcium fluoride: - NEW PROCESS FOR PREPARING CHLORO FLUORO METHANES FROM PHOSGENE 2CaF2-4-3COCI2->2COFC1-COF2--2CaCl2 AND A METAL FLUORIDE 5 It is also possible that part or all of the carbonylfluoride Earl L. Muetterties, Hockessin, Del, assignor to E. I. du results from the carbonyl chlorofluoride initially formed Pont de Nemours and Company, Wilmington, Del, a since it has been found experimentally that carbonyl corporation of Delaware chlorofluoride disproportionates at elevated temperature to give carbonyl fluoride and other products. For exam No Drawing. Application February 18, 1955, 0. ple, when carbonyl chlorofluoride is heated at 500 C. Serial No. 489,295 for one hour under autogenous pressure in a corrosion d resistant bomb, the resulting gaseous product is found by 7 Claims. (CI. 260-653) infrared analysis to contain carbonyl fluoride, carbonyl chlorofluoride, phosgene, carbon dioxide. A similar dis This invention relates to a new process of preparing 5 proportionation of carbonyl chlorofluoride (0.34 mole) fluorine-containing organic compounds. More particu takes place in the presence of finely divided calcium fluo larly, it relates to a process of preparing completely halo ride (0.68 mole) at 500 C. for one hour under autoge genated methanes in which at least one of the halogen nous pressure, and in this case the product contains atoms is fluorine, any other halogen being chlorine. 20% carbonyl fluoride, 35% carbonyl chlorofluoride, These compounds will be referred to hereinafter as fluo 20 10% phosgene, 15% carbon dioxide, 5% chlorotrifluoro rine-containing perhalomethanes. methane and 2% dichlorofluoromethane. The fluorine-containing perhalomethanes, i. e., carbon The reaction between phosgene and the inorganic bi tetrafluoride and the chlorofluoromethanes, and especial nary fluoride to give fluorine-containing perhalomethanes ly dichlorodifluoromethane, are extremely valuable com should be carried out at a temperature of at least 400 C. pounds. They find extensive use as refrigerant liquids as 25 and preferably at least 450° C. At lower temperatures dielectric fluids and as ingredients of insecticidal com the reaction, if it proceeds at all, does not produce per positions, e.g., as propellants in aerosols. halomethanes but solely carbonyl chlorofluoride and/or This invention has as an object a new process for pre carbonyl fluoride. The reaction temperature can be paring fluorine-containing perhalomethanes. Other ob much higher, e.g., up to 1000 C., but there is normally jects will appear hereinafter. 30 no advantage in using temperatures above about 700 C. These objects are accomplished by the present inven The preferred temperature range is from about 500 to tion of the process which comprises reacting phosgene at about 600 C. a temperature of at least 400° C. with a binary inorganic The conversions to perhalomethanes are improved, fluoride of an element having an atomic number from 11 especially in the lower temperature range (400-500 C.) to 83, inclusive, and isolating the fluorine-containing per 35 by the presence of a small amount of a halide (particular halomethanes formed. ly fluoride or chloride) of a metal in a valence state of 3 The phosgene can be used preformed or it can be to 5. Examples of such promoters are aluminum tri formed in situ from carbon monoxide and chlorine which, fluoride, tin tetrachloride, ferric fluoride and antimony as is well known, combine readily at elevated tempera pentachloride. These materials are used in molar ture to give phosgene. When this is done, the two phos 40 amounts between 1 and 5%, based on the binary fluoride gene-forming components, i. e., carbon monoxide and employed. chlorine, can be used in equimolar quantities, or one or The reaction can be carried out at atmospheric pres the other can be used in excess. sure, for example by passing phosgene through a hot tube The inorganic binary fluoride which serves as the source containing the inorganic fluoride and recycling the efflu of fluorine can be the fluoride of any of those elements 45 ent gas, with or without separation of the reaction prod in groups I to VIII, inclusive, of the periodic table, which ducts. This procedure is operable but it entails practical have atomic numbers from 11 to 83, inclusive. Refer difficulties in that, when the inorganic fluoride is solid ence to any accepted periodic table, e.g., that given on at the reaction temperature, intimate contact between it page 27 of F. Ephraim's "Inorganic Chemistry,” fifth and the gaseous reactant is difficult to achieve. If it is English edition (1949), will show what these elements 50 liquid and/or volatile, it is at least partly entrained by are. the gas stream and must be recovered and recycled. The respective proportions of phosgene (or its com Thus, conversions are low when operating at atmospheric ponents) and inorganic fluoride are not critical. How pressure. It is therefore preferred to carry out the re ever, it is desirable to use the two reactants in such ratio action in a pressure vessel. Also, the use of pressure that there is present in the reaction mixture at least one 55 favors the presence of phosgene in the equilibrium reac fourth, preferably at least one-half, gram atom of fluorine tion between it and its components, carbon monoxide per gram atom of chlorine. Normally, the reactants are and chlorine. The reaction is normally conducted under used in approximately the ratio of one atom of fluorine the autogenous pressure developed by the reactants and per atom of chlorine. reaction products at the operating temperature but if de The reaction produces a mixture of products. The 60 sired additional pressure furnished by a non-interfering three possible chlorofluoromethanes are formed, prin gas, such as carbon monoxide or nitrogen, can be applied, cipally chlorotrifluoromethane and dichlorofluorometh e.g., an additional pressure of 100-1000 atmospheres or ane, which may be formed according to the following even higher. equation, using calcium fluoride as the illustrative re When operating under pressure, appreciable conver actant: 65 sions are obtained at reaction times as low as thirty minutes at the reaction temperature. Normally, the re Carbon dioxide is always found in the reaction products. action is allowed to proceed for at least one hour, and Carbon tetrafluoride is normally formed in small preferably for three to eight hours. Longer reaction amounts, and traces of carbon tetrachloride are some 70 times can be used, e. g., up to twelve hours, but they times present. Two other products, carbonyl fluoride and offer no special advantages since the conversions are not carbonyl chlorofluoride are also formed. These may be materially increased. It has been found that the catalysts 2,757,214 3 4 or promoters already mentioned improve the conversions a corrosion-resistant bomb. The gaseous reaction prod obtainable in short reaction times. uct, which weighed 53.3 g. after removal of any carbon A convenient procedure for working up the crude re monoxide present, was scrubbed with aqueous 40% potas action product consists in transferring the gaseous re sium hydroxide. The residual gas weighed 12.2 g. (47% action mixture to an evacuated cylinder, leaving in the conversion based on the phosgene, with chlorotrifluoro reaction vessel the non-volatile materials (unreacted in methane considered to be the entire product) and had organic fluoride and inorganic chlorides). The cylinder the following composition in moles percent: carbon is then externally cooled to a low temperature, for ex tetrafluoride, 1%; chlorotrifluoromethane, 60%; dichloro ample by means of liquid nitrogen, and pumped off to difluoromethane, 35%; trichlorofluoromethane, 10%. a low pressure, e. g., 0.1-1 mm. of mercury. This re O Iodometric titration of the scrubbing solution showed moves from the reaction mixture any air present in it, and that 76% of the initial amount of chlorine had been it also removes the residual carbon monoxide, whose recovered unchanged. presence results either from its addition as a reactant or Example III additional pressure gas or from its formation by partial dissociation of the phosgene used. After removal of the 5 The process of this example is similar to that of Ex carbon monoxide, the cylinder is closed and allowed to ample I except that an excess of calcium fluoride was warm to room temperature or to a temperature sufficient used. to permit vaporization of the volatile mixture, which A mixture of 78.0 g. (1.0 mole) of commercial cal is then fractionated in a suitable low temperature still cium fluoride and 49.5 g. (0.5 mole) of phosgene was to separate the various constituents. If the perhalo 20 heated at 500 C. under autogenous pressure for 6 hours. methanes are the only components it is desired to isolate, The gaseous product, after removal of any carbon mo it is convenient to remove all the acidic gases (carbon noxide present and scrubbing with aqueous 40% potas dioxide, chlorine, unchanged phosgene, carbonyl chloro sium hydroxide, weighed 10.6 g. (41% conversion based fluoride and carbonyl fluoride) prior to fractional distill on phosgene with chlorotrifluoromethane considered to lation. This can be done by bringing the crude gaseous 25 be the only product). This gas contained, on a molar reaction product in contact with an aqueous alkaline basis, 1-2% carbon tetrafluoride, 65% chlorotrifluoro solution,