PROCESS FOR PREPARING HYPOFLUORITES AND BIS-HYPOFLUORITES

Abstract: Mono- and bis-hypofluorites respectively of formula: FO₂S-R f -CF₂OF and FOCF₂-R′ f -CF₂OF wherein R f is perfluoroalkylene or perfluorochloroalkylene and R′ f is perfluoroalkylene or perfluorooxyalkylene are prepared by a process which is conducted continuously, at a temperature from 0 to 60°C and comprises starting from the respective acyl fluorides by reaction of fluorine in the gas phase in the presence of a catalyst consisting of K, Rb, Cs or Ba fluorine, preferably supported on a metal material.

Description: The object of the present invention is an improved process for preparing hypofluorites and bis-hypofluorites by reaction of fluorine with starting compounds containing respectively one or two acyl fluoride groups of formula The process is particularly suitable for preparing mono-hypofluorites containing a sulphonyl fluoride group -SO₂F, and represented by the following formula: FO₂S - R f - CF 2 OF (I) wherein R f is a perfluoroalkylene radical or a per fluorochloroalkylene radical having from 1 to 4 carbon atoms and in particular selected from: Starting compounds for preparing the hypofluorites of formula (I) are the corresponding acyl fluorides: which, in turn, are easily preparable according to known methods based on the reaction of SO₃ with fluoroolefins (or fluorochlorolefins) or by electrochemical synthesis with generation of a sultone and subsequent opening of the suitone ring in the presence of basic catalysts, in particular alkaline fluorides or amines, as described in Angew. Chemie Int. Ed. Vol. II (1972) No. 7, 583 and US-A- 4 466 881. The process according to the present invention is also particularly suitable for the preparation of bis-hypofluorites of perfluoroalkanes or perfluoroethers of general formula: FOCF 2 - R' f - CF 2 OF (II) where R' f is a perfluoroalkylene radical, preferably of 1 to 8 carbon atoms such as -CF₂-, -CF₂CF₂-, or it represents a perfluorooxyalkylene radical having from 1 to 10 carbon atoms such as -CF₂OCF₂CF 2 - or (-CF₂O-CF 2 CF 2 -) 2 . Starting products are the corresponding acyl fluorides: The latter are generally prepared by electrochemical fluorination of the corresponding dicarboxylic acids or from corresponding chlorides by reaction with KF in solvents (J.A.C.S. 89, 12 pages 2841-2843) . As starting products, the acid difluorides of malonyl and of succinyl are particularly interesting. In the case of the compounds where R' f is an ether radical, the precursors are obtainable from the perfluoropolyether mixtures obtained in the C₂F₄ photooxidation process, by fractionated distillation. Very few references to the preparation of bis-hypofluorites are contained in the technical literature. In particular, the article by J.H. Prager in J.O.C., Feb. 1966, page 392 "1,3-Bis-(fluoroxy)perfluoropropane and Other Oxygen-Containing Compounds by Direct Fluorination" describes the reaction of gaseous fluorine with fluorinated compounds containing a -OH group, said reaction giving rise also to the compound of fomula however with a yield of 2% beside 2% of mono-hypofluorite. It is clear that this process cannot be of practical interest. The process of the present invention permits to obtain high yields of hypofluorites and bis-hypofluorites of the type indicated hereinbefore by means of a continuous process utilizable on a commercial scale. The process according to the invention consists in reacting, in the gas phase, fluorine with an acyl fluoride of formula optionally with a small excess of fluorine with respect to the stoichiometric amount, at a temperature ranging from 0 to 60°C, and preferably from 20 to 30°C, and in the presence of a solid catalyst composed of a fluoride of an alkaline or alkaline-earth metal, preferably selected from K, Rb, Cs and Ba, in particular CsF, preferably carried on or mixed with a metal selected from Cu, Fe, Ni, and Al. The granulometry of the utilized catalyst preferably is in the range of from 250 to 500 µm and it can be obtained by means of grinding. In any case, the granulometry is chosen so as to obtain a fixed bed. Preferably, the catalyst is mixed with metal particles having dimensions of the order of a few mm; the metal can be selected from Cu, Ni, Fe and Al, in order to facilitate the heat exchange of the reactor. The catalyst may also preferably be carried on the indicated metal material, as described in EP-A- 263309. In particular, a method of preparing the catalyst consists in subjecting a copper oxide (CuO or Cu₂O or a mixture thereof) having the shape of small pieces or granules (beads, small cylinders and the like), to reduction with nitrogen-diluted hydrogen, at a temperature from 200 to 500°C, preferably from 250 to 350°C, so obtaining a copper metal carrier of porous nature and of specific surface, as described in the above patent application. This carrier is then impregnated with an alkaline fluoride solution, in particular a cesium fluoride solution. Generally, the amount of CsF that can be fixed on the carrier is rather high, up to about 10% by weight. Also amounts of 3% provide a good catalyst. At last, the solvent utilized is removed by evaporation under vacuum. The catalyst so prepared affords a high yield, which is satisfactory even after a very long continuous run: in fact, after having been utilized for a few days, it does not exhibit a sensible decay. Furthermore, in the case that a regeneration should become necessary, it could be obtained in a very simple manner in the same reactor by means of a hydrogen stream at a temperature, for example, of 200°-300°C. Due to the high exothermicity and the high reaction rate it is generally advisable, for an easier temperature control, to dilute the reagents with a suitable inert gas, such as nitrogen or helium, or also with a chlorofluorohydrocarbon in the vapour state and inert under the reaction conditions, in particular C₂F₄Cl₂ or C₂F₅Cl. The reaction can be conducted at a pressure equal to or higher than atmospheric pressure. The reaction occurs with very short contact times, generally below 1 minute. The conversion is practically complete and the hypofluorite yield is very high, generally higher than 95%. As is known, the hypofluorites are capable of reacting with fluorinated olefins to form ethers which, by consecutive reactions, provide fluorinated vinylethers. The latter, when obtained from the compounds of formula (I), i.e. when they contain the sulphonyl group, are utilizable as monomers in the preparation of polymeric substances (resins), which are useful as acid catalyst of soluble nature or as material for the production of ion-exchange membranes or diaphragms. The bis-hypofluorites of general formula (II) can be utilized in the preparation of the corresponding bis-vinylethers (diglycidyl ethers) by reaction of both hypofluorite groups with fluorinated olefins, as mentioned hereinbefore. In the reaction with fluoroolefins for the preparation of vinylethers it is possible to directly use the reaction mixture containing the inert diluent, if any, because the conversion of the starting product is generally total and the hypofluorite yield is very high. Some of the compounds obtainable according to the process of the invention are new, in particular those of formula (I) wherein R f is -CFCl- or and those of formula (II) wherein R' f is -CF₂O-CF₂CF₂-, or (-CF₂O-CF₂CF₂-)₂. The following examples are given merely to illustrate possible embodiments of the process according to the invention. EXAMPLE 1 Preparation of 1-fluoroxy-2-(fluorosulphonyl)-tetrafluoroethane. To an AISI 316 steel reactor having a diameter of 50 mm and a capacity of 500 ml, filled with a catalyst prepared by mixing copper chips with 350 g of CsF, dried at 350°C in a nitrogen stream for 4 hours, ground and subjected to screening in an anhydrous environment, a gaseous mixture consisting of N₂/F₂/FO₂S-CF₂-C(O)F in a molar ratio of 1/1/1 was continuously fed at a total flow rate of 12 Nl/h (5.10⁻⁴ moles/h per gram of catalyst for each reagent) and at a pressure of 0.11 MPa (1.1 atm). The reagent mixture had previously been purified from HF, H₂O and possible impurities (alcohols). The temperature in the reactor was maintained at +20°C by means of a thermostatic bath. The outflowing gaseous mixture, analyzed by IR spectrophotometry, 19 F NMR and iodometry, showed the presence of FO₂S-CF₂-CF₂OF. Conversion and yields were of about 100%. The NMR analysis exhibited a typical signal of hypofluorites (δ, with respect to CFCl₃ : + 150 ppm); the IR band at 895 cm⁻¹ is typical of a hypofluorite. Conversion of the reagents and yields remained unchanged also after a 10-hour run. EXAMPLE 2 Into the reactor of example 1 there was continuously introduced a gaseous mixture consisting of N₂/F₂/FO₂S-CF₂-C(O)F in a molar ratio of 1/2/1, at a total flow rate of 8 N1/h (5.10⁻⁴ moles/h of F₂ per gram of catalyst and 2.5.10⁻⁴ moles/h of FO₂S-CF₂-C(O)F per gram of catalyst) and at a pressure of 0.11MPa (1.1 atm). The temperature in the reactor was maintained at +30°C by means of a thermostatic bath. The outflowing mixture, subjected to IR spectrophotometric analysis and to iodometric analysis, showed a complete conversion of FO₂S-CF₂-C(O)F to FO₂S-CF₂-CF₂OF; in fact, the IR band between 6.8 and 7 µm was present and its intensity remained unchanged (typical band of -SO₂F); while the band between 5.3 and 5.5 µm (typical band of COF) was fully absent and a new band typical of the group -CF₂OF appeared; ν (OF) = 895 cm⁻¹. EXAMPLE 3 Into the reactor of example 1 there was continuously introduced a gaseous mixture consisting of in a molar ratio of reagents of 1/2/1, at a total flowrate of 8 N1/h and at a pressure of 0.11 MPa (1.1 atm). The temperature in the reactor was maintained at +20°C by means of a thermostatic bath. The outflowing mixture, subjected to IR spectrophotometric analysis and to iodometric analysis, showed a complete conversion of in fact, the IR band between 6.8 and 7 µm was present and its intensity remained unchanged (typical band of -SO₂F); while the band between 5.3 and 5.5 µm (typical band of COF) was fully absent and a new band centered at about 887 cm⁻¹ attributed to -CF₂OF appeared. The NMR analysis exhibited a typical signal of hypofluorites (δ , with respect to CFCl₃: + 157.7 ppm). EXAMPLE 4 Into the reactor of example 1 there was continuously introduced a gaseous mixture consisting of N₂/F₂/FOC-CF₂-CF₂-COF in a molar ratio of reagents of 2/5/1, at a total flow rate of 8 N1/h and at a pressure of 0.11 MPa (1.1 atm). The temperature in the reactor was maintained at +20°C by means of a thermostatic bath. The outflowing mixture, subjected to IR spectrophotometric analysis and to iodometric analysis, showed a satisfactory conversion FOC-CF₂-CF₂-COF to FOCF₂-CF₂-CF₂-CF₂OF; in fact, the IR band between 5.3 and 5.5 µm (typical band of COF) was nearly absent and a new band typical of the group -CF₂OF appeared.

Claims: Process for preparing hypofluorites and bis-hypofluorites, respectively of formula: (I) FSO₂-R f -CF₂OF and (II) FOCF 2 -R' f -CF₂OF wherein R f is perfluoroalkylene or perfluorochloroalkylene having from 1 to 4 carbon atoms and R' f is perfluoroalkylene or perfluorooxyalkylene having from 1 to 10 carbon atoms, by reaction of the respective acid fluorides of formulae with fluorine, in the gas phase at 0 to 60°C and in the presence of a catalyst composed of a K, Rb, Cs or Ba fluoride, preferably supported on a material composed of particles of a metal selected from Cu, Fe, Ni and Al and arranged in the reactor in the form of a fixed catalytic bed, the process being conducted continuously. Process according to claim 1, wherein hypofluorites of formula (I) in which R f is are prepared. Process according to claim 1 or 2, wherein the reagents are diluted with an inert gas such as nitrogen or helium or with the vapour of a chlorofluorohydrocarbon which is inert under the reaction conditions.

Inventors: GUGLIELMO, GIORGIO, DR., MALACRIDA, ALESSANDRO, DR., MARRACCINI, ANTONIO, DR., ROBERTI, LAMBERTO
Applicants: AUSIMONT S.P.A.
Application year: 1987
Main classification: C07C71
IPC codes: B01J27, C07C303, C07C71, C07C309, C07C301, C07B61, C07C201, C07C67