DE3739800A1 - Process for the preparation of partially fluorinated tetracarboxylic acids - Google Patents

Abstract

Process for the preparation of a compound of the formula <IMAGE> in which X denotes the groups <IMAGE> by atmospheric oxidation of a suitable tetramethyl compound in an acidic medium under elevated pressure at elevated temperature in the presence of a catalyst mixture or its anhydride.

Description

The invention relates to a method of manufacture of partially fluorinated tetracarboxylic acids and their dianhydrides with different fluorine contents.

The Production of 1,1-Bis- [4- (1,2-dicarboxyphenyl)] - 1-phenyl-2,2,2-trifluoroethane from the corresponding 1,2-dimethylphenyl compound is known (CA 107: 97 277 j (1987), NASA, Techn. Memory 87 113 [1985]). The oxidation was performed with potassium permanganate and found low Yields and a contaminated very hygroscopic Product (3F-tetracarboxylic acid).

Dixylylhexafluoropropane (DX-F6) and its oxidation with Potassium permanganate in a mixture of pyridine and water to the potassium salt of 2,3-bis (3,4-dicarboxyphenyl) - hexafluoropropane (6F-tetracarboxylic acid) is used in the USP 33 10 573.

The type of oxidation requires a lot of chemicals, the isolation of the tetracarboxylic acid is very good here too cumbersome, and the solvent system used as well the manganese oxide must be worked up.

A process for the production of benzene tetracarboxylic acids and their anhydrides by oxidation of tetraalkyl substituents Benzenes with oxygen or free Gases containing oxygen in the presence of Heavy metal compounds and bromine compounds elevated temperatures is known (DE-OS 21 12 009). The publication shows that the complete Oxidation of two neighboring methyl groups causes considerable problems.  

After the oxidation reaction has ended, Reaction product of non-oxidized methyl groups, CHO and CH₂OH groups. The CH₂OH group forms with the neighboring one Carboxyl group phthalide rings.

Another complicating factor is that neighboring Carboxy groups with heavy metals stable compounds form and can precipitate as metal salts. This puts the catalytic activity of the catalyst is greatly reduced. This metal salt formation is both in the phthalic acid also observed with pyromellitic acid.

To prevent the catalytic activity from sinking of the catalyst and to support the oxidation of one fourth alkyl group, it was necessary for the Reaction large amounts of bromine ions must be present. A transfer of this process to fluorine-containing Connections are not possible because of Bromination reactions among those given Test conditions Products with a high bromine content that are difficult to separate and that End product not in sufficient purity and yield let preserved. It has also been found that the partially fluorinated polycarboxylic acids from the Reaction solution not at all or only incompletely crystallize out and also partially with their Heavy metal salts are mixed, which is a cleaning complicate considerably.

This behavior is all the more surprising because Polycarboxylic acids such as terephthalic acid, phthalic acid or  Pyromellitic acid immediately and in a well crystallized form crystallize from the reaction medium such as acetic acid.

Partially fluorinated tetracarboxylic acids with 12 fluorine atoms (12F-tetracarboxylic acid) are not yet known.

It was therefore the task of a procedure for partially fluorinated tetracarboxylic acids to create the high Yields and high purity of the products obtained enables. The partially fluorinated tetracarboxylic acids and their dianhydrides are building blocks for polyimides that are for technically demanding purposes are used, e.g. B. for thermally highly stressed coatings and adhesives in aircraft construction or in microelectronics. For many in these areas of application, it is therefore desirable high purity of the substances used, for example, 99% or more. The Use of the process according to the invention makes connections in microelectronics it also requires that all metal ions from originate from the catalyst or during the reaction steps be introduced, except for concentrations in ppm range can be removed.

The highly selective oxidation should be as possible complete oxidation of all four methyl groups Tetramethyl compounds and in the prevention of Side reactions such as decarboxylation and condensation consist. To achieve this goal, special needs Oxidation conditions can be found.

The invention relates to a method for manufacturing a compound of the formula

in the X the groups

mean
or their anhydride, by air oxidation in an acidic medium at elevated pressure and temperature in the presence of a catalyst mixture, characterized in that the corresponding tetramethyl compound in an acidic organic medium by introducing atmospheric oxygen at temperatures from 120 to 220 ° C and a pressure between 5 and 40 bar in the presence of at least two heavy metal compounds and bromide ions and oxidized and isolated as such or the reaction product obtained is converted into the dianhydride of the compound of formula (I).

The object of the invention was achieved by compliance special conditions for the oxidation of the Tetramethyl compounds to the corresponding Tetracarboxylic acids, resulting in a turnover rate of over 90% was reached.

The following measures have proven to be beneficial:

• 1) Catalyst:
  • a) Choice of components for the catalyst, in particular Co ²⁺ , Mn ²⁺ , Ce ³⁺ , Br ^-
  • b) optimal ratio of the metal ions to each other
  • c) high total metal concentration in the reaction solution
  • d) high concentration ratio of metal ions: bromide ions
• 2) Reaction conditions:
  • a) high oxygen partial pressure
  • b) controlled water content

The oxidation takes place in an acidic organic medium instead of using the tetramethylphenyl compounds molecular oxygen are oxidized, the acidic Medium at least 40% from a monocarboxylic acid such as Acetic acid or propionic acid or mixtures thereof. Acetic acid is because of its greater resistance to prefer oxidative degradation. The ratio of acidic medium to the starting substance used can be up to a ratio of 40: 60 wt .-%, based on the Total reaction mass can be applied.

The catalyst mixture consists of at least two Heavy metal salts and bromide ions. As heavy metals for example cobalt, manganese or cerium are used, the presence of cobalt always being required is. By mixing the metal salts, the Total metal concentration can be kept lower than if only cobalt is used alone.

Bromide ions are essential for the complete oxidation indispensable. Becomes a mixture as a metal component of cobalt and manganese ions, so are the metals generally in a molar ratio of 3: 1 to 1: 3, preferably used 1: 1. The sum of the Concentrations of the two elements are generally 0.01 to 0.2, preferably 0.02 to 0.12 and in particular 0.04 to 0.08 g / atom / kg total mass. The molar ratio the sum of cobalt and manganese to bromine is general 1: 0.01 to 0.8, preferably 1: 0.05 to 0.4. It is possible, in addition to the two metal ions of the Catalyst also use cerium ions. Catalyze them the oxidation of incompletely oxidized intermediates. Your Presence increased the purity and yield of the partially fluorinated tetracarboxylic acid. The cerions are the Catalyst in the molar ratio of the sum of the cobalt and Manganese ions to cerium ions such as 1: 0.02 to 1.2, preferably 1: 0.05 to 0.6 added. Becomes a mixture of the metal ions  of cobalt and cerium, the molar ratio is of the two metals in general 1: 0.02 to 1.2, where the ratio of metals to bromine is as above described. The molar ratios relate always on the total mass, d. H. from the sum of the to oxidizing compound, solvent and catalyst. The metal ions are preferably in the form of their acetates used.

Bromine can be in the form of bromides, e.g. B. the bromides Alkali metals including ammonium bromide and those the metals cobalt, manganese and cerium or as a solution of Hydrogen bromide can be used in water or glacial acetic acid. In addition, bromine-containing organic compounds can also be used are used, which decay and during the oxidation Release bromine ions e.g. B. Tetrabromomethane. You can do that Bromide ion concentration in the reaction solution very much strong - up to a value of about 20 for the molar ratio ΣMn: Br - lower without causing a noticeable Decrease in the reaction rate comes. Through this Measure that is also the ratio of the Tetramethyl compounds: Br in the reaction solution increased, the unwanted bromination becomes strong decreased.

The oxidation is generally at temperatures of 120 to 220, preferably 140 to 190 and in particular 155 to 180 ° C performed. The pressure in the reactor is generally between 5 and 40, preferably between 10 and 30 and in particular between 14 to 20 bar.

For the procedure, it is favorable that the for Oxidation required air near the bottom of the reactor the liquid phase is introduced and by vigorous stirring or finely distributed through special nozzles in the liquid phase becomes. It is particularly favorable to use an oxidation mixture to retract its oxygen content by adding  pure oxygen in a proportion of over 21% by volume was increased. This measure ensures high oxygen Partial pressures in those entering the liquid phase Gas bubbles reached. It is advantageous if the oxygen Partial pressure at the outlet of the induction device is at least 1 bar, preferably 2 to 15 and is in particular 3 to 10 bar.

It is still favorable for the conduct of the process that the residual oxygen content of the exhaust gas does not reach certain values falls below. The oxygen partial pressure is defined through the formula

P _O₂ = volume% O₂ · (P _tot - P _{ac - vapor pressure} )

d. that is, it is the mathematical product of the Residual oxygen content and the difference from the total pressure and the acetic acid vapor pressure (ac vapor pressure) at the present reaction temperature. This oxygen Partial pressure in the gas phase above the reaction solution should Do not fall below 0.2 bar and is preferably between 0.35 and 2.8, especially between 0.45 and 1.3 bar.

After the highly exothermic reaction has ended, it is expedient to complete the oxidation of all Methyl groups the reactor for 1 to 3 hours, preferably for 2 hours, at 150 to 190 ° C, preferably 160 to 180 ° C, at an oxygen partial pressure of 0.4 to 2 bar, preferably 0.5 to 1.3 bar.

A significant influence on the implementation of the The method according to the invention has the water concentration of the acidic medium in which the reaction is carried out becomes. The tetramethyl compounds can also in - for example - acetic acid with a Water concentration of 15% and more are oxidized, however, this reduces the yield and above all the  Purity of the products obtained and the oxidation of all four methyl groups are now incomplete. On the other hand, it was found that in anhydrous Acetic acid the metal ions of the catalyst through the Tetracarboxylic acids are precipitated and thus inactivated. The water concentration area in which the Metal ions remain dissolved and in which the oxidation runs completely enough, is between 2 and 12, preferably between 2 and 7 and in particular between 3 and 5% water in the monocarboxylic acid.

It has been found that, surprisingly, the dianhydrides of tetracarboxylic acids in glacial acetic acid or mixtures of Glacial acetic acid and acetic anhydride are sparingly soluble if one the water from the reaction solution by suitable methods removed and the tetracarboxylic acids in their anhydrides transferred. This conversion can be done by distillation and / or by adding acetic anhydride. The Dianhydrides crystallize well and in high yield filterable form and were washed with Glacial acetic acid, preferably a mixture of glacial acetic acid and acetic anhydride, of the metal salts and the soluble ones By-products exempt. Washing with a mixture from glacial acetic acid and acetic anhydride is particularly suitable because this mixture is the caking of the filter cake prevented. The dianhydrides fall with a purity from 94 to 97%.

Surprisingly, the metal salts also dissolve during the anhydride formation, so that after this first Cleaning operation the content of all metal ions at 50 up to 100 ppm.

The conversion of the tetracarboxylic acids is preferably carried out so that a mixture of Distilled off acetic acid and water and then in  over the heat acetic anhydride in a small excess add the calculated amount of acetic anhydride (approx. 3 to 12% Acetic anhydride in the solution)

A special process variant is that at elevated temperature and under pressure from the reaction solution water is distilled off over a column. Under these Conditions also form the dianhydrides of the Tetracarboxylic acids with elimination of water. At the same time the metal salts are also dissolved again. To Completion of the conversion to the dianhydride will take place on So much acetic anhydride added at the end that approx. 3 to 12% Acetic anhydride are in the solution.

The formation of dianhydride by distillation of water is preferably at a temperature above 140 ° C, if necessary under the additional pressure of a Inert gas carried out. The acetic acid can also be whole or in part by another aliphatic carboxylic acid such as propionic acid, hexanoic acid or 2-ethylhexanoic acid be replaced.

Generally the filtered and washed Dianhydrides in the air stream, preferably under reduced pressure Pressure, dried at elevated temperature.

When isolating as tetracarboxylic acid, it is advisable in the presence of an inorganic or organic acid e.g. B. hydrochloric acid to work. The tetracarboxylic acids can advantageous in a well filterable form from water be crystallized out when low concentrations of acetic acid are dissolved therein, preferably 6 to 12% by weight acetic acid. In general, this is how that after oxidation has ended, so much from the reaction solution  Acetic acid is distilled off until the bottom temperature is approx. 130 to 155 ° C and the melt is still stirrable is. Hot water and optionally acid and the solution again, preferably under pressure up to 2 hours at 130 to 150 ° C heated.

The tetracarboxylic acids crystallize out as a hydrate and can be dried by careful drying at room temperature Hexahydrate are isolated. By heating to 50 to 80 ° C in the gas stream they are converted into and through the tetracarboxylic acids Heat to 180 to 190 ° C under reduced pressure in the Dianhydride converted.

Particularly pure products are obtained if they are still water-moist tetracarboxylic acid in a solvent suspended and the water is distilled off. Thereby forms first the hydrate-free tetracarboxylic acid, from which at further increase in temperature the dianhydride is formed.

Aromatic solvents such as toluene are particularly suitable. o-xylene, tetralin, acetophenone or diphenyl ether.

Anhydride formation in aromatic solvents can by adding catalytic amounts of carboxylic acids, e.g. B. aliphatic carboxylic acids such as acetic acid, 2-ethylhexanoic acid, or other acids such as toluenesulfonic acid significantly be accelerated.

In the examples below,% is always percent by weight.

Examples 1) 1,1-bis (3,4-dicarboxyphenyl) -1-phenyl-2,2,2- trifluoroethane (3F-tetracarboxylic acid)

A mixture of 148.3 g 1,1-bis (3,4-dimethylphenyl) - 1-phenyl-2,2,2-trifluoroethane, 2.49 g Co (OAc) ₂ · 4 H₂O,  2.45 g Mn (OAc) ₂ · 4 H₂O, 0.41 g HBr corresponding to 4.1 g a 10% HBr solution in glacial acetic acid and 550 g glacial acetic acid was under 7.5 bar oxygen pressure at 180 to 185 ° C. heated. The exothermic reaction started at approx. 100 ° C, which lasted about 85 minutes. Then the Temperature maintained at 176 ° C for 1 hour. It resulted in 784 g of solution. Over a descending cooler about 530 g were added to the reaction solution with stirring Acetic acid water distilled off, the bottom temperature rose to 145 ° C. 150 g of water became the hot melt of 80 ° C added, the mixture with 50 ml more concentrated Hydrochloric acid added and heated to boiling for one hour. The mixture was cooled with vigorous stirring and the mixture was mixed with Crystals of 3F-tetracarboxylic acid inoculated. The Crystal suspension was suctioned off and four times with 50 ml of 2N Hydrochloric acid and washed twice with 25 ml of water. The moist crystals were at 50 ° C / 64 mbar in an air stream dried. Yield: 190.4 g (96.8% of theory) of 3F-tetracarboxylic acid Mp 210-213 ° C, water elimination; Carboxyl group content: 8.08 mVal COOH / g (calc. 8.20).

2) 1,1-bis (3,4-dicarboxyphenyl) -1-phenyl-2,2,2- trifluoroethane dianhydride (3F dianhydride)

From a reaction solution with the same oxidation mixture as in Example 1, with stirring over a descending cooler 400 g acetic acid-water mixture distilled off. Then was at boiling temperature a mixture of 122.4 g acetic anhydride and 120 g glacial acetic acid dropped over half an hour and an hour on Reflux cooked. When cooling with stirring, the Crystallization below 85 ° C. After 4 hours aspirated and three times with 25 ml of a mixture of 95% Glacial acetic acid and 5% acetic anhydride. The Crystals were at 80 ° C / 65 mbar in a light air stream dried.  Yield: 119.0 g (65.3% of theory) of 3F-dianhydride, yellowish Crystals; Fixed point: 204 to 205.5 ° C.

A further 36.6 g (20.1% d. Th.) 3F-dianhydride with an mp of 201 to 204 ° C. won.

3) 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane (6F-tetracarboxylic acid)

In a 1 liter glass autoclave equipped with a metering pump, Thermometer, stirrer and reflux condenser solution of 2.5 g cobalt acetate tetrahydrate, 2.45 g manganese acetate tetrahydrate and 0.44 g hydrogen bromide submitted in 311 g of glacial acetic acid. At the same time, a Solution of 180.2 g of dixylylhexafluoropropane in a mixture of 102 g acetic anhydride and 60 g glacial acetic acid in one Dosing device provided. The autoclave was by introducing oxygen under a total pressure of 7.5 bar, an exhaust gas value of 30 Nl / h and the content heats up. At about 160 ° C with the Dixylylhexafluoropropane metering started and the total amount added within 100 minutes. The temperature of the exothermic reaction was 170 to Kept 175 ° C and the batch after the end of the dosage held for another hour at 175 ° C by heating. The reaction mixture (approx. 790 to 800 g) was added to Normal pressure approx. 500 g acetic acid-water mixture distilled off. Once the temperature of the residue had risen to 145 ° C, the autoclave was discharged of nitrogen at a pressure of 4 bar, 500 g distilled water added and the mixture for one Kept at 145 ° C for one hour. Then was up on Cooled to room temperature and the formed Aspirated crystal leaves. The mother liquor contained 6 to 10% acetic acid. The filter cake was used 8 times  Washed 50 ml ice water. The damp product that from 6F-tetracarboxylic acid hexahydrate and adhering water existed, was for 8 hours at 40 to 50 ° C / 50 mbar dried in an air stream. Then the temperature increased to 80 ° C and the solid for a further 12 hours dried. Yield 212.3 g (88.4% of theory), 6F-tetracarboxylic acid, m.p .: 231 to 234 ° C (elimination of water), Carboxyl group content: 8.45 mVal COH-g (calc. 8.33), Bulk density 0.30 g / cm², metal ion content (microgram / g): Cobalt 1, manganese 1, bromine 189.

4) 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride

Following the procedure in Example 3, 2.24 g Cobalt acetate tetrahydrate, 2.21 g manganese acetate tetrahydrate and 0.365 g of hydrogen bromide in 302 g of glacial acetic acid with a Solution of 142.6 g dixylyl hexafluoropropane in 125 g Glacial acetic acid reacted. The oxygen pressure was 8 bar and the reaction temperature during the oxidation was kept in the range of 165 to 175 ° C. From the obtained reaction solution was while stirring Acetic acid and water distilled off to a bottom temperature of 130 ° C was reached. Then at that temperature a mixture of 92 g acetic anhydride within 20 minutes and added 200 g of glacial acetic acid. The approx. 5% by weight Liquid containing acetic anhydride was one hour boiled at reflux, cooled to 20 ° C and at this Temperature stirred for 2½ hours. After suction was the filter cake eight times with 50 g of a mixture washed from glacial acetic acid and acetic anhydride (95: 5) and the obtained crystals at 100 ° C and 60 mbar in the weak Airflow dried. Yield 165.5 g (94.7%) colorless Crystals, start of sintering 237 ° C, mp .: 242 to 243 ° C, Purity 95.8% 6F-dianhydride, contamination by Traces of catalyst: 10 ppm cobalt, 6 ppm manganese, 215 ppm Bromine.  

5) 6F-Dianhydride from 6F-tetracarboxylic acid

212.3 g of 6F-tetracarboxylic acid were placed in a flask Rotary evaporator in an oil bath at 190 ° C. The Water vapor was formed by a gentle stream of air displaced from the piston. In a cold trap, 15.1 g Water caught. Yield 198.5 g 6F-dianhydride, mp 242 up to 243.5 ° C, anhydride groups 4.51 mbar (calculated 4.50).

6) 6F-Dianhydride from water-moist 6F-tetracarboxylic acid

342.2 g of water-moist 6F-tetracarboxylic acid, obtained in accordance with Example 3 were in a flask equipped with a stirrer and Water separator was equipped in 700 g Tetrahydronaphthalene suspended. The approach was under heated vigorous stirring and distilled off about 125 g of water. Then the temperature was raised to the boiling point and slowly tetrahydronaphthalene, the rest removed water, distilled off. The Anhydride formation ceased when there was no more water was deposited. The deposited crystals were washed at 20 ° C with tetrahydronaphthalene and at 100 ° C dried under reduced pressure. Yield 206.4 g (85.9% of theory), purity 99.9%, mp .: 243 to 245 ° C.

In the following Examples 7 to 31, which under the Conditions and procedure of Example 4 the superiority of the The inventive method clearly demonstrated. So is the influence in Examples 7 to 13 (Table 1) the catalyst composition clearly. Among the Conditions according to the invention are products with high Purity obtained in good yield.

In Examples 14 to 20 (Table 2) the influence the ion concentration and the ratio of cobalt demonstrated to manganese. It can be seen that at  low total metal ion concentration an increase the bromine ion concentration increases the yield causes, but these are not brought up to date can, as obtained by the measures of the invention becomes. Examples 21 to 25 (Table 3) also reflect again the influence of the bromide ion concentration again. The higher this is, the greater the proportion of organically bound bromine in the end products. Is this Very high ratio of the sum of the metal ions to the bromine ions large, the yield drops considerably. In the examples 26 to 31 (Table 4) it is clear that the Water concentration already at 15% water content causes a significant drop in yield.

The amounts of substance required for the reaction result from the total mass of the batch and the concentrations given in the table. These concentrations of the substances are in [mol / kg] based on the total mass of all reaction components used (except O₂). The acetic acid is the residual amount to the total mass, e.g. B. corresponds to the value C _DX-F6 = 0.66 mol / kg in the table with a total mass of 0.6 kg, the amount of dixylylhexafluoropropane (DX-F6) of 0.396 mol or 142.7 g. As in Example 4, the DX-F6 is metered in during the reaction. For the preparation of this solution ¹ / ₃ the total amount of acetic acid is used.

Examples 7) to 13) Influence of the catalyst composition

The product quality relates to the sintered and the Melting point of a compound. The higher these values the purer the connection.

Table 1

Examples 14) to 20) Dependence of the yield and the Product quality from total ion concentration and from Ratio [Co]: [Mn]

Table 2

Examples 21) to 25) Influence of the bromide concentration on yield and product quality

Table 3

Examples 26) to 31) Influence of water concentration in of acetic acid on the yield and purity of the product

Table 4

32) 4,4'-bis [2- (3,4-dicarboxyphenyl) hexafluoroisopropyl] - diphenyl ether (12F-tetracarboxylic acid)

a) 200.3 g of 4,4′-bis [2- (3,4-dimethylphenyl) hexafluoroisopropyl] - diphenyl ether, 2.49 g Co (OAc) ₂ · 4 H₂O, 2.45 g Mn (OAc) ₂ · 4 H₂O, 0.41 g HBr corresponding to 4.1 g 10% HBr solution in glacial acetic acid and 550 g glacial acetic acid were l glass autoclave, the one with stirrer, gas inlet tube, thermometer and was equipped with a reflux condenser. Under 7.5 bar Oxygen pressure was heated to a maximum of 188 ° C. The exothermic reaction intervened with oxygen uptake 90 and 100 ° C and lasted 65 minutes. The final temperature of 177 ° C was held for 1¼ hours. There were 816 g Solution isolated.

b) The reaction solution cooled to 90 ° C. was filtered and transferred to a 2-liter four-necked flask with stirrer, from which as long as acetic acid was distilled off until the Bottom temperature was 140 ° C. The violet melt became Given 1 liter of water at 95 ° C, creating an emulsion formed. With rapid stirring, 200 ml of conc. Hydrochloric acid added. The emulsion was at 75 ° C Crystals of the 12F-tetracarboxylic acid inoculated, which causes formed a crystal suspension on cooling.

The crystal suspension was at 22 ° C on a suction filter aspirated and twice with 200 ml of 2N hydrochloric acid and once washed with 200 ml of water. The water-moist substance will dried at 60 ° C / 65 mbar in a light air stream. Yield: 227.2 g (96.4%) 12F-tetracarboxylic acid, colorless Crystals, mp. 163 to 165 ° C with elimination of water, Carboxyl group content: 5.06 mVal COOH / g (calc. 5.01).

Analysis for C₃₄H₁₈F₁₂O₉:
calc .:
C 51.13%, H 2.26%, F 28.57%;
found:
C 51.00%, H 2.20%, F 28.35%.

33) 12F-tetracarboxylic acid dianhydride

The solution of 3.02 g of oxalic acid dihydrate in 30 ml of acetic acid was added dropwise to the reaction solution from Example 1a) at 95 ° C. with stirring. After two hours at reflux, the 100 ° C solution was filtered and the filtrate was washed with 200 ml of hot acetic acid. 590 g of acetic acid + water were distilled off from the filtrate. 72.3 g of acetic anhydride were added dropwise to the residue with rapid stirring above 80 ° C. in the course of 30 minutes. The temperature rose to 120 ° C and was held at this value for one hour. (12% acetic anhydride in acetic acid). When cooling, the crystallization started below 60 ° C. The temperature was further lowered to 20 ° C over 6 hours. The crystal suspension obtained was suction filtered through a suction filter, washed three times with 25 ml of a mixture of 90% acetic acid and 10% acetic anhydride, and the filter cake was dried at 60 ° C./65 mbar in a gentle stream of air. Yield: 179.2 g (79.6% of theory) of 12F-dianhydride, melting behavior: phase transition: 115-120 ° C with melting and solidification again, melting point: 168-170 ° C, anhydride group content after titration with ⁿ / 10 Sodium hydroxide solution / ⁿ / 10 hydrochloric acid: 2.625 meq COOH / g (calc. 2.625).

Analysis for C₃₄H₁₄F₁₂O₇:
calc .:
C 53.54%, H 1.84%, F 29.92%;
found:
C 53.40%, H 2.00%, F 29.30%.

Claims (20)

1. Process for the preparation of a compound of formula in the X the groups mean
or their anhydride, by air oxidation in an acidic medium at elevated pressure and temperature in the presence of a catalyst mixture, characterized in that the corresponding tetramethyl compound in an acidic organic medium by introducing atmospheric oxygen at temperatures from 120 to 220 ° C and a pressure between 5 and 40 bar in the presence of at least two heavy metal compounds and bromide ions and oxidized and isolated as such or the reaction product obtained is converted into the dianhydride of the compound of formula (I). 2. The method according to claim 1, characterized in that the acidic organic medium to at least 40 wt .-% at least one monocarboxylic acid, based on the Total weight. 3. The method according to claim 1 or 2, characterized characterized in that the reaction temperature 140 to 190, is in particular 155 to 180 ° C. 4. The method according to one or more of claims 1 to 3, characterized in that at a pressure between 10 and 30, in particular between 14 and 20 bar. 5. The method according to one or more of claims 1 to 4, characterized in that the one used for the oxidation  Atmospheric oxygen an oxygen content of over 21 vol .-% has and that at the point of introduction of oxygen Oxygen partial pressure at least 1 bar, preferably 2 to 15, in particular 3 to 10 bar. 6. The method according to one or more of claims 1 to 5, characterized in that the oxygen partial pressure in the gas phase over the reaction medium, which results from the formula P _O₂ = volume% O₂ (P _total - P _{acetic acid} vapor _pressure ), at least 0, 2 bar, preferably 0.35 to 2.8, in particular 0.45 to 1.3 bar. 7. The method according to one or more of claims 1 to 6, characterized in that as heavy metal ions Cobalt, manganese and / or cerium used and this in shape of acetate compounds are added. 8. The method according to one or more of claims 1 to 7, characterized in that bromine in the form of bromides or as a solution of hydrogen bromide in water or glacial acetic acid is used. 9. The method according to one or more of claims 1 to 8, characterized in that the molar ratio of cobalt to manganese is 3: 1 to 1: 3, the sum of the Concentrations of the two elements cobalt and manganese equal to 0.01 to 0.20 g-atom / kg total reaction mass, preferably 0.02 to 0.12, in particular 0.04 to 0.08 g Atom / kg. 10. The method according to one or more of claims 1 to 9, characterized in that the molar ratio of the sum from cobalt and manganese to bromine 1: 0.01 to 0.8, preferably 1: 0.05 to 0.4.   11. The method according to one or more of claims 1 to 10, characterized in that as an additional metal ion Cerium is contained in the catalyst in a molar ratio of Sum of cobalt and manganese to cerium like 1: 0.02 to 1.2, preferably 1: 0.05 to 0.6. 12. The method according to one or more of claims 1 to 11, characterized in that the molar ratio of cobalt to cerium 1: 0.02 to 1.2. 13. The method according to one or more of claims 1 to 12, characterized in that the reaction mixture after The exothermic reaction ceases for 1 to 3 hours 150 to 190 ° C at an oxygen partial pressure of 0.4 to 2 bar is kept. 14. The method according to one or more of claims 1 to 13, characterized in that the reaction at a Water concentration of monocarboxylic acid from 2 to 12, preferably 2 to 7 and in particular 3 to 5% is carried out. 15. The method according to one or more of claims 1 to 14, characterized in that the dianhydride under Use of acetic anhydride formed in a slight excess becomes. 16. The method according to one or more of claims 1 to 15, characterized in that the anhydride by Removal of water from the reaction solution by distillation at a temperature above 140 ° C, if necessary under pressure. 17. The method according to claim 16, characterized in that that to complete the implementation acetic anhydride is added up to a content of 3 to 12% in the Solution.   18. The method according to one or more of claims 1 to 14, characterized in that the dianhydride by Heating the tetracarboxylic acid to 180 to 190 ° C below is produced under reduced pressure. 19. The method according to one or more of claims 1 to 14, characterized in that the dianhydride by Distillative removal of the water from the water-moist Tetracarboxylic acid, which is immiscible with water Solvent is suspended, is formed. 20. The method according to claim 19, characterized in that toluene, o-xylene, tetralin, Acetophenone or diphenyl ether is used.