RU2156756C2 - Method of preparing hexafluoroacetone - Google Patents

Abstract

FIELD: preparation of organofluorine products. SUBSTANCE: hexafluoroacetone is prepared by reacting 2- hydroheptafluoropropane with molecular oxygen at 150-300 C in the presence of catalyst which is activated carbon promoted by alkali metal fluorides up to 60 wt %. Hydroheptafluoropropane to molecular oxygen molar ratio ranges from 1: 0.1 to 10. Yield of hexafluroacetone in terms of coolant 227 being converted is 77-83%. EFFECT: simplified preparation method, cheaper and accessible catalysts and wider range of raw materials used in said process. 2 cl, 1 ex, 1 tbl

Description

 The invention relates to a method for producing perfluorinated ketones, and in particular to a method for producing hexafluoroacetone (HFA), which is used as an intermediate in the synthesis of crosslinking agents, drugs, and pesticidal preparations.

 A known method of producing hexafluoroacetone by the interaction of hexachloroacetone with hydrogen fluoride or antimony pentafluoride [1]. The disadvantage of this method is the large amount of chlorine-containing waste.

Known methods for producing hexafluoroacetone by isomerization of hexafluoropropylene oxide in the presence of catalysts — partially fluorinated metal oxides (Al ₂ O ₃ , Cr ₂ O ₃ ) [2], Lewis acids from the group of aluminum chlorofluorides of the formula AlF _n Cl _3-n (n = 0.05 - 2.95) [3], antimony pentafluoride [4] and hydrogen fluoride [5]. The disadvantage of these methods is the use of scarce and expensive oxide of hexafluoropropylene.

 Known methods for producing hexafluoroacetone by the catalytic oxidation of hexafluoropropylene (HFP), for example, get hexafluoroacetone by the reaction of HFP with oxygen in the presence of iron, tin or indium oxides. The yield of HFA on the initial HFP is 38%, the conversion of HFP is 71% [6]. The disadvantage of this method is the low yield of the target product.

The closest technical solution is a method for producing hexafluoroacetone by the interaction of HFP with oxygen at a temperature of 130 - 250 ^o C in the presence of a catalyst.

Rare metals, including ruthenium, rhodium, palladium, platinum and iridium supported on activated carbon in an amount of 0.3-5.0 wt.%, Are used as a catalyst. Activated carbon is used as a catalyst carrier. So for the preparation of a palladium catalyst, activated carbon was impregnated with 1N. a solution of PdCl ₂ • HCl, washed with water and dried at 120 ^o C. After reduction with hydrogen at 450 ^o C received a catalyst containing 5 wt.% palladium. The process was carried out in a circulating reaction apparatus with a capacity of 0.32 dm ³ at an initial pressure of 258 torr (0.35 kgf / cm ² ), a molar ratio of HFP: O ₂ 1: 1 and a temperature of 130 or 250 ^o C. The reaction lasted from 45 to 180 min, during this time the pressure decreased to a constant value. According to this method, the yield of hexafluoroacetone reached 57% with the conversion of HFP to 65% [7].

 The disadvantages of the prototype are the use of an expensive catalyst, the complexity in their preparation, as well as the use of the circulation method with a significant duration to achieve the desired effect on the conversion of HFP and the release of HFA. In addition, HFP, which is used as a feedstock, is not always available.

 The objective of the invention is to simplify the process of producing hexafluoroacetone and expanding the raw material base.

The problem is achieved by the interaction of 2-hydroheptafluoropropane (HFC 227) with molecular oxygen at a temperature of 150 - 300 ^o C in the presence of a catalyst, which is activated carbon, promoted by alkali metal fluorides, such as NaF, KF or C ₃ F.

 The process is carried out continuously in the flow system. A tubular metal reactor is used, equipped with an electric furnace, nozzles for supplying source gases and outputting reaction products, a sleeve for a thermocouple. The reactor is 80% filled with catalyst.

To prepare the catalyst, activated carbon BAU brand is mixed with an aqueous solution of alkali metal fluoride, the mixture is kept for up to 24 hours, then filtered and dried at a temperature of no higher than 150 ^o C to achieve a constant weight.

 The fluoride content in the catalyst is from 5 to 60 wt.%. Within this interval, a change in the concentration of fluoride does not affect the conversion of 2-hydroheptafluoropropane and the yield of hexafluoroacetone. A decrease in the fluoride content of less than 5% leads to a decrease in the yield of HFA on converted 2-hydroheptafluoropropane. An increase in the concentration of fluoride above 60% significantly impairs the physicochemical properties of the catalyst (sintering ability) and has no practical significance.

The process is carried out at a temperature of 150 - 300 ^° C. At a temperature below 150 ^° C., the reaction does not proceed, and when the temperature rises above 300 ^° C., 2-hydroheptaphthopropane is deeply oxidized to carbonyl fluoride and the catalyst decomposes.

The molar ratio of HFC 227: O ₂ is in the range of 1.0: 1-10. When oxygen is supplied in a smaller amount, the oxidation reaction does not occur, and an increase in the amount of oxygen over a 1:10 molar ratio is impractical and gives many by-products.

The reaction products containing HFA, carbonyl fluoride (COF ₂ ), as well as unreacted 2-hydroheptafluoropropane, are condensed at low temperature, analyzed by gas-liquid chromatography and separated by low-temperature distillation.

 According to the developed method, the yield of hexafluoroacetone based on convertible 2-hydroheptafluoropropane is 77 - 78%.

 This method allows to simplify the process of producing HFA by conducting it in a flow system, as well as using cheaper and more affordable catalysts that do not require special treatment. In addition, the use of 2-hydroheptafluoropropane as a feedstock allows expanding the raw material base for the process of producing hexafluoroacetone.

 Distinctive features of the proposed method are the use of activated carbon promoted with alkali metal fluorides as a catalyst, as well as the use of 2-hydroheptafluoropropane as a feedstock. These signs that distinguish the claimed method from the prototype are not identified in other technical solutions.

 The following examples illustrate the invention.

 Example 1

0.25 dm ^{3 of} catalyst, which is activated carbon promoted with potassium fluoride in an amount of 60.0 wt.%, Is loaded into a tubular reactor equipped with electric heating and a thermocouple with a capacity of 0.3 dm ³ . The catalyst is heated in a stream of dry nitrogen at a temperature of 180 - 200 ^o C for four hours, after which serves Freon 227 and O ₂ with a speed of 1 DM ³ / hour (7.6 g / hour) and 5 DM ³ / hour, respectively, at a temperature 280 ^o C and a molar ratio of refrigerant 227 and O ₂ equal to 1: 5.

The oxidation products leaving the reactor are condensed in a trap cooled to -90 ^° C and analyzed by gas-liquid chromatography. For 6 hours, 46 g of a gas mixture containing, according to GLC, vol.%: 42.5 HFA, 10.1 COF ₂ and 47.4 HFC 227 were condensed. 18.9 g of HFA were isolated by low-temperature distillation. The yield of hexafluoroacetone to converted HFC 227 is 80.8%.

 Subsequent syntheses (examples 2 to 5) were carried out analogously to example 1. The oxidation conditions of HFC 227 and the results are shown in the table.

Literature
1. Krespan CG Hexafluoracetone. Fluor Chem. Rew., 1967, 1 (1), p. 145.

 2. Japanese Application N 58-62131, C 07 C 49/167, publ. 04/13/83. RCL 1984, 12 H 30.

 3. US patent N 5457238, C 07 C 45/70, publ. 10/10/95. Fig. countries of the world, 1996, c. 41, N 17, p. 42.

 4. US patent N 4302608, C 07 C 45/58, publ. 11.24.81. Fig. for rub., 1982, c. 57, N 16, p. 115.

 5. Application of Germany N 3046604, C 07 C 49/167, publ. 07/22/82. Fig. for rub., 1983, century 57, N 8, p. 45.

 6. US patent N 4284822, C 07 C 45/32, publ. 08/18/81. Fig. for rub., 1982, c. 57, N 9, p. 100.

 7. Japanese application N 4-55415, C 07 C 49/167, publ. 09/03/92. Fig. countries of the world. 1994, c. 41, N 11, p. 85 (prototype).

Claims (2)

 1. A method of producing hexafluoroacetone by reacting a fluorinated hydrocarbon with molecular oxygen at an elevated temperature in the presence of a catalyst, characterized in that 2-hydroheptafluoropropane is taken as a fluorinated hydrocarbon, and activated carbon promoted with alkali metal fluorides is used as a catalyst.  2. The method according to claim 1, characterized in that the potassium or sodium or cesium fluoride is used as alkali metal fluorides.

Images