PROCESS FOR THE PREPARATION OF BROMOFLUOROETHYLHYPOFLUORITE

Abstract: The new compound bromofluoroethylhypofluorite, having the formula CF₂BrCF₂OF is obtained by starting from by the reaction in gaseous phase with fluorine, in the presence of a catalyst constituted by CsF on a support constituted by copper (or by another metal) in the form of a porous material having a surface area of at least 0.1m²/g.

Description: The present invention relates to a process for the synthesis of a compound having the hypofluorite structure, of formula CF₂BrCF₂OF. This compound is particularly important as a starting product for the synthesis of bromofluorovinylethers. The bromofluorovinylether compounds are particularly interesting comonomers in the preparation of fluoroelastomers vulcanizable with peroxides. The preparation of fluoro-oxy-compounds by starting from acyl fluorides by means of the reaction in gaseous phase with fluorine, by a continuous process, is disclosed in EP-A-194 862. The preparation process disclosed in the above patent application is also indicated as being suitable for the preparation of bromofluoroalkyl hypofluorites by starting from bromofluorinated acyl compounds. It was observed, however, that the operating conditions indicated in that patent application, and, in particular, the catalyst based on cesium fluoride therein disclosed and exemplified, are not suitable for obtaining the compound CF₂Br-CF₂-OF in an appreciable amount by a continuous process. The catalyst according to the above patent application can be a metal fluoride as such (e.g., Cs fluoride), or it can be prepared by mixing cesium fluoride with a metal material (copper) in the form of chips, or of other compact shapes. In general, the optimum granulometry of CsF is obtained by grinding. The catalyst, when used for the preparation of the compound according to the above patent application, is deactivated within very short times, of the order of minutes, such as not to allow it to be prepared on an industrial scale. We unexpectedly found that bromofluoroethylhypofluorite can be synthetized by means of the fluorination of the corresponding bromofluoroacetyl fluoride in an industrial process, if a specific catalyst is used and, furthermore, if the reaction temperature is strictly controlled so to be kept within a very narrow range. Object of the present invention is a continuous process for obtaining the compound CF₂Br-CF₂OF, consisting in reacting, in the gaseous phase, bromofluoroacetyl fluoride: with fluorine, preferably in excess with respect to the stoichiometric amount, in the presence of a catalyst based on cesium or potassium fluoride, supported on a metal selected from Cu, Fe, Ni, preferably Cu, in the form of a porous material, with a large surface area, higher than 0.1m²/g and preferably higher than 0.4m²/g, and with a bulk specific weight generally lower than 5 g/cm³, preferably, in case of copper, of the order of 3.5-4 g/cm³. The catalyst should have a granulometry suitable for accomplishing a stationary bed, and, in general, it should have a minimum size not lower than 0.05 mm. The fluorination reaction is carried out at a temperature of from 10 to 45°C and preferably of from 20 to 30°C, and the two reactants are suitably diluted with an inert gas, such as nitrogen or helium, to allow the reaction temperature to be strictly controlled, such a temperature control being made difficult by the exothermic character and the high rate of the same reaction. The reaction takes place within very short times; for example, at 25°C the contact time is shorter than 1 minute. A suitable method for preparing a catalyst having the desired requisites consists in subjecting a copper oxide (CuO or Cu₂O, or a mixture of them), in the form of small pieces or granules (small beads, cylinders, etc.) to a reduction with hydrogen diluted with nitrogen, at a temperature of from 200 to 500°C, preferably of from 250 to 350°C, a copper metal support being thus obtained, in porous form and with the specific surface area indicated above. This support is then impregnated with a solution of cesium or potassium fluoride, and the solvent used is evaporated under vacuum. In general, the amount of CsF or KF which can be fixed on the support is a rather large amount, up to approximately 10% by weight. Even amounts of 3% yield a good catalyst. The so prepared catalyst shows a high activity, which remains good also after a very long continuous operation: in fact, even after a use of some days, its activity does not show a noticeable decay. Furthermore, should a reactivation become necessary, this can be very simple accomplished inside the same reactor, by means of a hydrogen stream at a temperature of, e.g., 200 -300°C. In order to strictly control the reaction temperature it is also possible to use said catalyst (cesium or potassium fluoride) in the form of powder,not supported but in suspension in a fluorinated oil such as, for example a perfluoropolyether oil (Fomblin ® YO4). In this case the fluorination reaction is carried out under the same conditions as described above but the starting compound can be injected into the reactor also in liquid form. The conversion of the compound in the process of the present invention is practically total. The yield of CF₂BrCF₂OF is very high. The product obtained in the reaction, in the gaseous form, generally diluted with the inert gas and with the possibly used excess of fluorine, can be separated from the gaseous mixture by a low-temperature condensation, at about -80°C, or it can be recovered by dissolution in a fluorocarbon-type solvent, in particular, Delifrene (R) . The following examples are supplied for illustrative purposes, and are not limitative of possible practical embodiments of the present invention. EXAMPLE 1 CATALYST PREPARATION 84 g of Carlo Erba's CuO needles "RS for microanalysis" grade, are placed in a cylindrical glass reactor and heated under a nitrogen stream (50 Nl/h) up to the temperature of 300°C. A mixture of nitrogen containing 10% of hydrogen is then introduced. The reduction is continued for 3.5 hours. In this way, 67 g of needles (0.5 mm of diameter, and average length of 5 mm) of spongy metallic copper having a surface area of 0.5 m²/g are obtained. The so obtained copper metal is placed in a rotary evaporator and is degassed under vacuum for 30 minutes. A solution of 6 g of CsF dissolved in 10 ml of methanol is then sucked up, and the vacuum-drying is continued for 2 hours. The so-prepared catalyst is fed to the actual reactor, and, before being used, is dried under an inert gas stream at 120°C for two hours. SYNTHESIS OF CF₂Br-CF₂OF A cylindrical reactor of AISI 316, 30 mm of diameter and 350 mm long, is charged with 610 g of catalyst CsF on copper prepared as disclosed above. The amount of cesium fluoride deposited on the metal is 8% by weight. The reactor is maintained at the controlled temperature of 25°C, and in to it a gaseous mixture of 1 Nl/h of fluorine and 0.5 Nl/h of CF₂Br-COF is introduced. Furthermore, diluent helium is fed at the flow rate of 30 Nl/h. With these gas flow rates, the resulting contact time is about 30 seconds. The reaction mixture leaving the reactor is analysed by I.R. spectrophotometry and gas-chromatography. By GLC, the disappearance is observed of the starting product CF₂BrCOF,and the presence is observed, together with the unreacted excess of fluorine supplied, of only one product corresponding to CF₂Br-CF₂OF. A similar result is obtained from IR analysis, with the disappearance of the carbonyl band of the initial pr oduct, and the presence of an absorption band at 1,300 cm⁻¹, to be attributed to the hypofluorite. The ¹⁹F-NMR spectrum recorded at -35°C shows signals (δ ,ppm relative to CCl₃F) at: -95 attributed to -C F ₂-Br -65.5 attributed to -C F ₂-OF +139.7 attributed to -O F . EXAMPLE 2 (Comparative Example) The cylindrical reactor of AISI 316 of the preceding example is charged with 500 g of catalyst CsF on copper prepared by evaporating a methanol solution of CsF in a rotary evaporator in the presence of copper turning chips and sieving the residue. The resulting amount of CsF stably deposited on the copper in this prepartion is equal to 1.5% by weight. The reaction is carried out by operating as in the preceding example. The reaction mixture leaving the reactor is analysed after 30 minutes by gas-chromatography: a partial conversion (10%) of the initial product, as well as the presence of small amounts (5%) of BrCF₂-CF₂OF identified as in the preceding example are observed. Afer a 2-hour run, the resulting catalytic activity is at a minimum, and by GLC the presence of the practically unaltered initial product is demonstrated. EXAMPLE 3 A reactor of AISI 316 having 0.8 liters of capacity is charged with 200 g of commercial CsF in the form of powder in the presence of 500 ml of a fluorinated oil (Fomblin YO4 (R) of Montedison). Said reactor is externally cooled by water. To this reactor 2.5 g/h of liquid CF₂Br-COF and a gaseous mixture of 3.4 l/h of helium containing 12% vol. of fluorine are fed. The gaseous stream leaving the reactor contains an amount of 2% of unreacted excess of fluorine and some unidentified products having low boiling points in a quantity less than 1% vol. besides the reaction product CF₂BrCF₂OF. It is observed that the starting product CF₂BrCOF is almost completely reacted (more than 95%) and converted into CF₂BrCF₂OF. Said product is detected by gas-chromatography as already stated in the previous examples.

Claims: Process for preparing 2-bromo-perfluoroethyl-hypofluorite, which comprises reacting, in the gaseous phase and in a continuous manner, the compound of formula : with fluorine, at a temperature of from 10 to 45°C, in the presence or absence of an inert gaseous diluent and in the presence of a catalyst comprising cesium or potassium fluoride, supported on a metal selected from Cu, Fe, Ni, in the form of a porous material having a specific surface area of at least 0.1 m²/g, and a minimum particle size not lower than 0.05 mm. Process according to claim 1, wherein the catalyst is prepared according to the following steps: a) reduction with H₂ diluted with N₂, at 200-500°C, of copper oxide in the form of pieces of small dimensions (e.g. granules, small beads, small cylinders); b) impregnation of the so-obtained porous support with a CsF solution; c) removal of the solvent under vacuum. Process according to claim 1, wherein the reaction is carried out in the presence of an excess of fluorine relative to the stoichiometric amount. Process for preparing 2-bromo-perfluoroethyl-hypofluorite, which comprises reacting, in a continuous manner, the compound of formula : with fluorine, at a temperature of from 10 to 45°C, in the presence or absence of an inert gaseous diluent and in the presence of a catalyst comprising cesium or potassium fluoride, in the form of powder and suspended in an inert fluorinated oil, the reactant being fed in liquid or vapor state. Process according to claim 4 wherein said inert fluorinated oil is a perfluoroalkylpolyether.

Inventors: CALINI, PIERANGELO, GREGORIO, GUGLIELMO, DR., GUGLIELMO, GIORGIO, DR.
Applicants: AUSIMONT S.P.A.
Application year: 1987
Main classification: C07C71
IPC codes: C07C71, B01J27, C07B61, B01J23, C07C201, C07C67