DE1042568B - Process for the production of aromatic di- and polycarboxylic acids - Google Patents

Description

Process for the production of aromatic di- and polycarboxylic acids As already suggested, the alkali salts can be aromatic or heterocyclic-aromatic Monocarboxylic acids by heating to elevated temperatures in salts of aromatic di- or convert polycarboxylic acids, which then in a known manner into the free Acids or their derivatives can be converted. In this procedure will be improved results achieved when, preferably in the presence of acid-binding Medium, working at a carbon dioxide pressure above 400 at.

Based on the yields obtained according to this latter embodiment of di- and polycarboxylic acids, e.g. B. terephthalic acid, it can be assumed that this new carboxyl groups are formed. In addition, a migration of the existing Carboxyl groups take place so that, for. B. those from heterocyclic aromatic monocarboxylic acids The structure of the reaction products obtained does not always correspond to the starting materials.

It has now been found that in the thermal conversion of the Salts of aromatic monocarboxylic acids in salts of di- and polycarboxylic acids too very good yields are obtained at a pressure of less than 400 at if one uses the Heating in the presence of alkali salts of oxalic acid and advantageously in the presence of carbon dioxide or an inert gas, also advantageously with the addition of catalytic more effective metals or metal compounds.

Salts are used as starting materials for the process according to the invention of aromatic monocarboxylic acids such as benzoic acid, α- and ß-naphthoic acid or diphenyl monocarboxylic acids. Also monocarboxylic acids, in which the carboxyl groups are attached to another aromatic Ring system, e.g. B. anthracene, diphenylbenzene, diphenylmethane or benzophenone are, are suitable as starting material for the process according to the invention.

Furthermore, heterocyclic-aromatic salts are used as starting materials Monocarboxylic acids, e.g. from pyridine, quinoline, isoquinoline, a-pyran, furan, Derive thiophene, thiazole, indole, benzotriazole or benzimidazole, in question.

In all of these carboxylic acids, the aromatic ring or the heterocyclic-aromatic ring in addition to the carboxyl group also other substituents wear, e.g. B. halogen atoms or alkyl radicals, unless this does not result in decomposition of the molecule occurs below the reaction temperature.

The carboxylic acids mentioned are used for the process according to the invention used in the form of their salts. The alkali salts are useful here, preferably the potassium and also the sodium salts are used. The rubidium and cesium salts, the are also suitable in themselves, come from economic considerations in general out of consideration.

The process can also be used with salts of other metals, e.g. B. with the alkaline earth salts of the carboxylic acids mentioned. It is often beneficial To use mixtures of salts of two different metals, e.g. B. Mixtures of Sodium and potassium salts, as this in many cases reduces the mechanical properties the reaction mixtures can be improved. The reaction leads to salt formation serving metal affects. For example, a mixture of potassium benzoate is obtained and potash moxalate terephthalic acid in good yield and with practically no formation of By-products. In contrast, it surprisingly arises from a mixture of sodium benzoate and sodium oxalate o-phthalic acid as the main product, along with trimesic acid and isophthalic acid.

Instead of the salts, reaction mixtures can also be used, which provide such salts. Mixtures of carboxylic acid anhydrides are in particular or from carboxylic acid esters and acid-binding metal compounds, e.g. B. alkali carbonates, suitable.

These mixtures do not need to be present in the stoichiometric ratio. One or the other component can be used in excess.

Of the alkali metal oxalates, the oxalates of potassium are preferred or sodium is used. The amount of oxalate can vary within wide limits.

However, it should expediently not be less than half a mole on one Moles of the aromatic carboxylic acid.

The salts or salt mixtures to be processed are preferred used in as dry a condition as possible. If the salts are in the form of aqueous solutions before, they can preferably be used by methods known per se by spray drying, converted into dry powder and, if necessary, for Remove small residual amounts of moisture after drying.

- It has been shown that in order to achieve good yields, the presence of catalysts is required. Metals, in particular, serve as catalysts Cadmium, also zinc, mercury, lead and iron, as well as compounds of these metals, z. B. their oxides or their salts with inorganic or organic acids, as well their complex compounds and organometallic compounds, including theirs Carbonates, bicarbonates, halides, sulfates, phosphates, acetates, formates, oxalates, fatty acid salts or the salts of the metals mentioned with those acids which are used as starting material for the reaction according to the invention or which arise in this reaction, e.g. B. their benzoates or terephthalates. The amount of the catalyst can vary within wide limits and, for example, up to 15 O / o, preferably 0.5 to 5%, based on the reaction mixture. The mentioned Catalysts can also be used in conjunction with known carriers, e.g. B. Kieselguhr, be used.

Particularly good results are achieved if you make sure that the catalyst is present in the finest possible distribution. lThis can e.g. B. thereby shoes that an aqueous solution of the starting material salts, which contain the catalysts dissolved or suspended, by atomization or otherwise converted to a dry powder.

In addition to these catalysts, the reaction according to the invention can be carried out in The presence of inert liquid or solid additives can be carried out, e.g. B. in the presence of sand, metal powder, metal shavings, kieselguhr, activated carbon, finely divided material Aluminum oxide, finely divided silica or inert salts such as sodium sulfate. In many cases, these additives reduce the mechanical properties of the reaction mixture improved. Instead of solid, inert substances, inert liquids, which do not decompose under the conditions used are used.

It is advantageous to carry out the reaction in the presence of carbon dioxide. Instead of carbon dioxide, gas mixtures can be used, which in addition to carbon dioxide other gases, e.g. B. nitrogen, alethane or argon contain. The presence of Oxygen should be avoided if possible. It has been shown that too in the absence of carbon dioxide, e.g. B. in a nitrogen atmosphere, a carboxylation takes place. For example those obtained in this way from potassium benzoate Yields of terephthalic acid are higher than disproportionation of potassium benzoate would correspond to potassium terephthalate and benzene. The presence of carbon dioxide However, you see a further increase in the yield.

The particular advantage of the method according to the invention is that that no high pressures are needed. The reaction is already at one pressure below 100 at can be carried out with good yields.

The reaction usually starts at a temperature above 3000 Zein. The optimal reaction temperature depends on the starting materials used different. She is z. B. in the production of terephthalic acid from potassium benzoate and potash moxalate at 400 lis 4100 C. The upper temperature limit for the -travel is generally only due to the decomposition temperature of the organic matter given.

When carrying out the method according to the invention, it can be used for Avoidance of local overheating and the resulting decomposition as well as to prevent the reaction mixture from caking together, this can be useful keep moving. This can e.g. B. by working in stirred vessels, shaking or roller autoclaves. The uniform heating can also be brought about by this be that one works in a thin layer, the reaction material being mobile or can be immovable. However, good yields are obtained even without this Measures if one takes care that strong local overheating is avoided will.

The reaction mixtures are worked up in a known manner. First you dissolve the raw product in water or dilute acids and clean it optionally by filtration or by treatment with activated charcoal or with others Decolorizing agents.

The salts formed can then be acidified, for example with organic or inorganic acids or by introducing CO with or convert into the free acids without pressure. The oxalic acid present can, for. Am be separated in a known manner by crystallization or destroyed by oxidation. The carboxylic acids formed can be due to their different solubility or Volatility separated and isolated in pure form and optionally into their derivatives be convicted. The salt mixtures obtained can also be converted directly into derivatives of the Carboxylic acids, e.g. B. in their esters or halides, and these optionally Purify by fractional distillation.

Example 1 A mixture of 20.0 g of potassium benzoate, 20.0 g of anhydrous Dipotassium oxalate and 5.0 g of cadmium fluoride were prepared by grinding in a ball mill intimately mixed and filled into a roller autoclave with a capacity of 200 cm3. Of the Autoclave was flushed with carbon dioxide. Then 50 atm were carbon dioxide pressed and the autoclave heated to 4050 C for 1 hour. The maximum pressure during the heating was 180 at. After cooling and releasing the pressure, the autoclave was the crude reaction product dissolved in 5 times the amount of hot water and insoluble Fractions filtered off. The clear filtrate was heated to boiling and treated with hydrochloric acid acidified. The precipitated terephthalic acid was sucked off in the heat and with washed in hot water. The yield was 17.3 g of terephthalic acid.

Example 2 In the same manner as in Example 1, a mixture was prepared from 10.0 g of potassium benzoate, 30.0 g of anhydrous dipotassium oxalate and 3.0 g of cadmium fluoride heated to 4000 C for 9.5 hours under an initial pressure of 50 at CO2. During the The reaction reached a maximum pressure of 150 atm. The work-up, which carried out in the manner described above gave a yield of 7.6 g of terephthalic acid.

Example 3 A mixture of 10.0 g sodium benzoate, 25.0 g sodium moxalate and 2.0 g of cadmium fluoride was intimately mixed by grinding in a ball mill and in the same way as described in Example 1, under a carbon dioxide pressure of 10 at (at 4200 C) Heated to 4200 C for 5 hours. The crude reaction product, which weighed 31.0 g, was suspended in 500 cm3 of water and filtered hot. Of the The sodium oxalate content of the filtrate was determined analytically; it was 22.7 g. The oxalate was diluted by adding solid potassium permanganate to that previously used Sulfuric acid acidified solution at 700 C destroyed. The brownstone formed was removed with the help of hydrogen peroxide. Then the solution was in the perforator extracted with ether. Evaporation of the ether extract gave 5.8 g of a mixture obtained from organic carboxylic acids.

This mixture was digested with 75 cm3 of chloroform, with a Part solved. The portion insoluble in chloroform weighed 1.5 g. By ultrared analysis it was found to be composed of o-phthalic acid with an impurity of about 3 o / o benzoic acid.

The portion soluble in chloroform (4.3 g) consisted of benzoic acid.

Example 4 A mixture of 10.0 g sodium benzoate, 25.0 g sodium oxalate and 2.0 g of cadmium fluoride was intimately mixed by grinding in a ball mill and in a rolling autoclave of 200 cm3 capacity under an initial carbon dioxide pressure heated from 50 at 3 hours to 3620 C. A maximum pressure was established during the heating from 132 at a. The crude reaction product, which weighed 34.8 g, was in 11 hot Dissolved water, filtered off from the undissolved catalyst and treated with dilute sulfuric acid acidified. On cooling, a precipitate precipitated out, which was filtered off with suction and isolated became. It weighed 5.0 g and consisted of 3.15 g of sodium acid moxalate and 1.85 g of p-enzoic acid. Extracanion with ether gave the filtrate 4.0 g of a mixture of carboxylic acids obtain. 1.8 g of benzoic acid were separated therefrom by digestion with chloroform. The remainder of 2.2 g consisted of o-phthalic acid.

Example 5 A mixture of 20.0 g of potassium benzoate, 10.0 g of anhydrous Dipotassium oxalate, 10.0 g calcium oxalate and 3.0 g cadmium fluoride were prepared by grinding intimately mixed in a ball mill and placed in a roller autoclave of 200 cm3 capacity filled. The autoclave was flushed with carbon dioxide. Then 50 at Pressed carbon dioxide and the autoclave heated to 4050 C for 1 hour. After this Cooling and releasing the pressure in the autoclave was the reaction mixture in the same Way as described in Example 1, worked up. There were 12.1 g of terephthalic acid obtain.

Example 6 A mixture of 20.0 g of potassium benzoate, 20.0 g of dipaline moxalate and 10.0 g of anhydrous zinc oxalate was prepared under the same conditions as in Example 5 described, heated to 4050 C for 1 hour. The work-up of the reaction mixture, which was made in the same manner as in Embodiment 1 resulted a yield of 10.8 g of terephthalic acid.

Example 7 A mixture of 20.0 g of the potassium salt of nicotinic acid, 30.0 g of potassium moxalate and 3.0 g of anhydrous cadmium chloride were placed in a rolling autoclave of 0.2 l capacity at an initial pressure of 50 at carbon dioxide 10 hours Heated to 3500. After this The reaction mixture was cooled and let down in the autoclave dissolved in 250 cm3 of water. The solution was filtered and the filtrate treated cleaned with activated charcoal in the usual way. The solution was then treated with hydrochloric acid acidified. After standing in the cold for some time, the precipitated crystals became sucked off. The mother liquor was extracted with ether. A total of 11.4 g of pyridine-2,5-dicarboxylic acid was obtained obtain.

Example 8 A mixture of 20.0 g rubidium benzoate, 20.0 g anhydrous Dicaline moxalate and 5.0 g of cadmium fluoride were made by grinding in a ball mill intimately mixed and filled into a roller autoclave with a capacity of 200 cm3. Of the Autoclave was flushed with carbon dioxide. Then 50 atm were carbon dioxide pressed and heated to 4000 C for 1 hour. The crude reaction product was in Dissolved water and worked up in the same way as in Example 1. There were 13.1 g of terephthalic acid were obtained.

Example 9 A mixture of 50.0 g sodium benzoate, 5.0 g sodium oxalate and 2.5 g of cadmium fluoride was placed in a rolling autoclave of 200 cm3 capacity at a carbon dioxide pressure of 155 at (at reaction temperature) 5 hours to 4400 Heated. After cooling and releasing the pressure in the autoclave, the crude reaction product became dissolved in 400 cm3 of water. The solution was filtered and acidified with sulfuric acid.

This resulted in a precipitation, which, however, required further work-up didn't bother. The unreacted oxalate was now by adding solid Potassium permanganate destroyed. The excess of permanganate and the excreted Manganese dioxide was reduced by means of hydrogen peroxide and brought into solution. Afterward became the solution together with the precipitated with acidification with ice chilled. 4.9 g of a mixture of the monopotassium salt of trimesic acid separated out and free trimesic acid which has been separated.

The mother liquor was exhaustively extracted with ether in a perforator. The ether solution was evaporated. The residue was treated with chloroform. Here were in the same way as described in embodiment 3, 7.2 g of o-phthalic acid and 8.6 g of benzoic acid were obtained.

PATENT APPROACH 1. Process for the production of aromatic or aromatic-heterocyclic Di- and polycarboxylic acids or their salts or derivatives by heating the salts of aromatic or aromatic heterocyclic monocarboxylic ren if necessary in the presence of catalytically active metals or metal compounds under pressure, where appropriate, the salts obtained by methods known per se in the free acids or their derivatives are converted, characterized in that heating in the presence of alkali salts of oxalic acid at a pressure of performs less than 400 at.

Claims (1)

2. The method according to claim 1, characterized in that the Heating carried out in the presence of carbon dioxide or an inert gas. Documents considered: German Patent No. 966 335; German interpretation document 1 036 841.