PROCESS FOR THE PREPARATION OF HYDROFLUOROALKANES

Abstract: A process for the preparation of hydro(halo)fluoroalkanes by direct fluorination of the corresponding hydro(halo)­ alkenes in liquid phase with elemental fluorine at low temperatures (below 0°C).

Description: The present invention relates to a process for the pre­ paration of hydro(halo)fluoroalkanes starting from the respective hydro(halo)alkenes. Hydrofluoroalkanes may be prepared by reduction with LiAlH₄ (Ber. 97(7) 1964), or by U.V. irradiation of halo­ fluoroalkanes in the presence of an alcohol (Czech.136, 735). However, none of these processes can be applied in industrial operations because of the high costs of the reactants or due to the difficulties relating to the equipment required for similar treatments in case of LiAlH₄ or to the use of U.V. light. Moreover, the process of reduction by U.V. is limited, in that only a few spe­ cific compounds mono- or dihydrogenated on the same car­ bon atom can be obtained by it. In fact, in said process, the introduction of the first hy­ drogen atom into the molecule can be relatively simple, even if the reaction time is of the order of twenty hours but the introduction of the second hydrogen atom into the molecule is more difficult than that of the first, and no compounds di-hydrogenated on adjacent carbon atoms are obtained. Such fluorination processes as electrofluorination carried out on hydrocarbons (J.Electrochem. Soc.95, 47, 1949) are also known but these processes are burdensome as regards the equipment and from the energy viewpoint and, above all, fragmentation occurs as a side reaction. Fluorinations of hydrocarbons carried out with elemental fluorine, generally diluted with nitrogen, in the gaseous phase over a Cu/Ag catalyst (Ind.Eng.Chem. 39,290 (1947)) are also known. These processes are, however, also very limited, in that they lead to the formation of side reac­ tion by-products such as high amounts of fragmentation products or dimers and trimers. Fluorinating halogenated olefins with CoF₃ is known as well (J.Org.Chem. 28,494 (1963)), but side reactions as intramolecular H/fluorine, halogen/fluorine substitutions occur. Thus, by this process, the selective preparation of al­ kanes from olefins is not possible. Furthermore, a fluorination process of this type requires particularly sophisticated equipment capable of with­ standing the fluorine used to regenerate CoF₃ at a tem­ perature around 300°C. There was, thus, a need to produce, by a process easily accomplishable on an industrial scale, saturated com­ pounds belonging to the class of hydro(halo)fluoroal­ kanes, both monohydrogenated and containing H atoms on adjacent C atoms. It was also necessary to have available a fluorination process by which the by-product dimers, trimers, and addition polymers could be kept at a minimum and, at the same time, the simultaneous substitution by fluorine of the hydrogen or halogen atoms of the starting product kept at very low percentages. It has now surprisingly been found that, by carrying out the fluorination reaction on hydro(halo)olefins with ele­ mental fluorine at low temperatures of below 0°C, the fluorine addition to the double bond is preferred to sub­ stitution of the hydrogen atoms and/or of the halogen atoms different from fluorine contained in the olefin, the substituion products being contained in very low percentages. The formation of the addition dimer products is, moreover, very low while not even traces of the tri­ mers or polymers are formed. Thus, the object of the present invention is a process for the fluorination in the liquid phase with elemental fluorine at a temperature below 0°C of hydrohaloalkenes or of hydroalkenes having the following general formulae: wherein: X = H, F, Cl, Br R₁, R₂ = H, F, Cl, Br, C₁-C₃-alkyl or -alkoxy, wherein the H atoms can also be completely substituted by such halogens as Cl or F. The fluorination process according to the present inven­ tion is carried out in the liquid phase at temperatures of from 0°C to -100°C, preferably of from -70°C to -85°C, the liquid phase consisting of the reactant and the reac­ tion products. Solvents present in an amount of from 1 to 20 parts, preferably 4 to 10 parts by weight (w/w) per each part of hydro(halo)olefin, can also be used. Suitable solvents are completely fluorinated and completely chlorofluorinated- alkanes which are liquid at the reaction temperature and inert under the fluorination conditions. Preferred solvents are CFCl₃, CF₂Cl₂ and CF₂Cl-CF₂Cl. The elemental fluorine is preferably used diluted with inert gases, such as nitrogen, at an inert gas/F₂ molar ratio of from 5 to 15. The reaction can be carried out under atmospheric pres­ sure or under reduced pressure. The process of the present invention allows the desired product to be obtained with a high selectivity and, at the same time, a high conversion of the starting product is obtained. A further advantage of the process of the invention is that the fluorination of olefins is made possible with a relatively simple process, and with higher yields than in the processes of the prior art as mentioned above. The products which can be obtained by the process of the invention are advantageously used as anaesthetics or, after suitable dehalogenation or dehydrohalogenation by known processes, as comonomers in the preparation of fluorinated polymers. The following examples serve to illustrate the invention. Unless stated otherwise, in the examples parts and percentages are by weight. EXAMPLE 1 100 g of 1,2-dichloroethylene (30/70 by weight cis/trans isomer mixture) and 1000 g of CCl₃F are charged to a cy­ lindrical reactor of Algoflon R having an inner diameter of 85 mm and a volume of 1000 ml and kept at a controlled temperature of -75°C. The elemental fluorine, diluted to a molar ratio of 1 part with 9 parts of nitrogen, is continuously introduced over a period of 8 hours up to a total amount of 1 mol. At the end of the test 1130 g of raw reaction product is collected and washed with an aqueous solution containing 5% by weight of NaOH. It is then thoroughly dried over CaCl₂, and subjected to distillation to separate the pro­ duct from the solvent. The conversion into reaction pro­ ducts is 73 % relative to the CHCl=CHCl supplied and the yield of CHClF-CHClF is 72 % relative to the reacted matter. EXAMPLE 2 Example 1 is repeated by introducing an amount of 1.5 mol of F₂ over a period of 8 hours. The conversion is 80 % and the yield is 74 %. EXAMPLE 3 100 g of 1,2-dichloroethylene (30/70 w/w cis/trans isomer mixture) and 1000 g of CCl₃F are charged to the reactor of Example 1 which is kept at a controlled temperature of -60°C. Elemental fluorine, diluted to a molar ratio of 1 part of F₂ to 9 parts of nitrogen, is continuously fed or in­ troduced over a period of 8 hours up to a total amount of 1 mol of fluorine. At the end of the test, 1110 g of raw reaction product are collected and purified as described in example 1. The conversion is 80 % and the yield of CHClF-CHClF is 63 %. EXAMPLE 4 100 g of 1,2-dichloroethylene (isomeric cis/trans ratio = 30/70 w/w) and 1000 g of CCl₃F are charged to the reac­ tor of example 1 which is kept at a controlled tempera­ ture of -80°C. Elemental fluorine, diluted to a molar ratio of 1 part of F₂ to 9 parts of nitrogen, is continuously introduced over a period of 8 hours up to a total amount of 1 mol of fluorine. At the end of the test, 1130 g of raw reaction product is collected. The conversion is 68 % and the yield of CHClF-CHClF is 74 %. EXAMPLE 5 100 g of 1,2-dichloroethylene (100 % of cis isomer) and 1000 g of CCl₃F are charged to the reactor of Example 1 which is kept at a controlled temperature of -75°C. Ele­ mental fluorine, diluted to a molar ratio of 1 part of F₂ to 15 parts of nitrogen, is continuously introduced over a period of 8 hours up to a total amount of 1 mol of fluorine. At the end of the test, 1120 g of raw reaction product are collected. The conversion is 75 % and the yield of CHClF-CHClF is 70 %. EXAMPLE 6 100 g of 1,2-dichloroethylene (100 % of trans isomer) and 1000 g of CCl₃F are charged to the reactor of example 1 which is kept at a controlled temperature of -75°C Elemental fluorine, diluted to a molar ratio of 1 part of F₂ to 9 parts of nitrogen, is continuously introduced over a period of 8 hours up to a total amount of 1 mol of fluorine. At the end of the test, 1125 g of raw reaction product are collected. The conversion is 70 % and the yield of CHClF-CHClF is 74 %. EXAMPLE 7 100 g of trichloroethylene and 1000 g of CCl₃F are charged to the reactor of Example 1 which is kept at a controlled temperature of -75°C. Elemental fluorine, di­ luted to a molar ratio of 1 part of F₂ to 15 parts of ni­ trogen is continuously introduced over a period of 8 hours up to a total amount of 1 mol of fluorine. At the end of the test, 1135 g of raw reaction product are collected. The conversion is 79 % and the yield of CCl₂F-CHClF is 93 %.

Claims: 1. A fluorination process comprising the addition of fluorine to the double bond of an organic compound of the following general formulae: wherein: X = H, F, Cl, Br R₁, R₂ = H, F, Cl, Br, C₁-C₃-alkyl or -alkoxy, wherein the H atoms can also be completely substituted by such halogens as Cl or F, characterized in that fluorination is carried out in the liquid phase using elemental fluorine at tempera­ tures of from 0°C to -100°C. 2. A process according to claim 1, wherein the reaction temperature is from -70°C to -85°C. 3. A process according to claim 1 or 2, wherein the li­ quid phase is constituted by the reactant and the re­ action products, in the form of a mixture with a per­ halogenated inert solvent. 4. A process according to claim 3, wherein the solvent is used in an amount of from 1 to 20 parts by weight per each part of reactant. 5. A process according to any one of claims 1-4, wherein the elemental fluorine used is diluted with inert gases in a molar ratio of inert gas/F₂ of from 5 to 15.

Inventors: CONTE, LINO, GAMBARETTO, GIAN PAOLO, GERVASUTTI, CLAUDIO
Applicants: AUSIMONT S.R.L.
Application year: 1986
Main classification: C07C17
IPC codes: C07C17, C07C41, C07C19, C07C67