DE1118783B - Process for the preparation of heterocyclic di- and / or tricarboxylic acids of aromatic character - Google Patents

Description

Process for the preparation of heterocyclic di- and or or Tricarboxylic acids of aromatic character As was found earlier, one can use alkali salts of heterocyclic carboxylic acids of aromatic character by heating to higher ones Temperatures in salts of carboxylic acids with at least two carboxyl groups in the molecule convert. In this way, salts of monocarboxylic acids are converted into salts of di- and tricarboxylic acids obtained.

This produces technically valuable reaction products such. B. the Salts of pyridine-2,5-dicarboxylic acid, pyridine-2,4,6-tricarboxylic acid, furan-2,5-dicarboxylic acid. This process was carried out with or without pressure using an inert protective gas, preferably carbon dioxide, carried out so far under a pressure of up to about 250 at was worked (cf. German patent 1095 281).

It has now been found that one can convert the alkali or alkaline earth metal salts from heterocyclic monocarboxylic acids of aromatic character into the corresponding Salts of heterocyclic di- and / or tricarboxylic acids by heating to higher ones Temperatures under carbon dioxide pressure and in the presence of acid-binding agents can thereby be carried out with particularly good yields that one pressure of more than 400 at works. While so far in the production of heterocyclic Di- and tricarboxylic acids of aromatic character by rearrangement of salts accordingly Monocarboxylic acids as by-products include considerable amounts of the carboxyl group-free in question Received heterocyclic compounds, goes according to the process according to the invention practically all of the converted monocarboxylic acid salt into the corresponding salt a di- and / or tricarboxylic acid.

The starting materials used for the process according to the invention are Alkali or alkaline earth salts of such heterocyclic monocarboxylic acids, their carboxyl groups to heterocyclic rings with aromatic character, such as pyridine, a-pyran, furan, Thiophene.

Thiazole, chonoline, isoquinoline, indole, benzotriazole or benzimidazole, are bound. The carboxylic acids mentioned are preferably in the form of the potassium, also the sodium salts are used. The rubidium and cesium salts, which in themselves are also suitable, generally do not come from economic considerations into consideration. When the alkaline earth salts are used, reaction products are obtained many other isomeric di- or tricarboxylic acids than when using the alkali metal salts. It is often advantageous to use mixtures of salts of two different metals, z. B. Mixtures of sodium and potassium salts, as this in many cases the mechanical Properties of the reaction mixtures can be improved.

To achieve good yields, it is necessary to use the inventive To carry out the process in the presence of acid-binding agents, preferably in the presence of carbonates, bicarbonates, formates or oxalates of the alkali metals, in particular Potassium carbonate. The corresponding compounds of the alkaline earth metals are also suitable. The acid-binding agents mentioned do not need to be used in stoichiometric amounts to become.

It is expedient to use such an excess over that for neutralization the amount required in the reaction newly formed carboxyl groups.

The salts or salt mixtures to be reacted are preferably in Processed as dry as possible. If the salts are in the form of aqueous solutions, they can be prepared by methods known per se, preferably by spray drying, Convert into dry powder and, if necessary, to remove small residues dry in moisture.

It has been shown that the inventive method by Presence of catalysts is favored. The metals Zinc, cadmium, mercury, lead and iron as well as compounds of these metals are used, z. B. their oxides or their salts with inorganic or organic acids. the The amount of catalyst can vary within wide limits and up to 15%, preferably 0.5 to 5 percent by weight, based on the reaction mixture. The catalysts can be distributed particularly finely in the reaction mixture by using an aqueous Solution of the salts used as starting material, which dissolve the catalysts or contains suspended, by atomization or otherwise in a dry manner Powder transferred.

In addition to these catalysts, inert, add liquid or solid substances, e.g. B. sand, metal powder, metal shavings, kieselguhr, Activated carbon, finely divided aluminum oxide, finely divided silica or inert Salts, such as sodium sulfate. In many cases, these additives make the mechanical Properties of the reaction mixture improved. Instead of solid inert materials can also be inert liquids, which are under the conditions used do not decompose, find use.

The high pressure required for the reaction, which is more than 400 at, advantageously more than 500 at, can be in a simple manner, for. B. by corresponding pumps or compressors.

But you can, for example, also proceed in such a way that one enters the cooled and evacuated liquid carbon dioxide from a bomb or reactor another storage vessel and then heated. Instead of liquid Carbon dioxide you can also use solid carbon dioxide (dry ice). Through the The temperature required for the reaction depends on the amount of the liquid Carbon dioxide a pressure of z. B. 1500 to 2000 at a. Otherwise the one to be used is Upward pressure is only limited by the equipment available.

The reaction usually takes place at temperatures 200 and 3000 C. The optimal reaction temperature depends on the one used Starting materials different. It is often between 330 and 4500 C. The upper one Temperature limit for the process is only due to the decomposition temperature of the organic Substance given, but temperatures of 5000 C should not be exceeded as a rule will.

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, the To keep the reaction product moving. This can e.g. B. by working in stirred vessels take place. However, good yields are obtained even without such measures if one ensures that strong local overheating is avoided.

The reaction mixtures are worked up in a known manner. The reaction product is expediently dissolved in water and freed by filtration or by treatment with activated charcoal or other decolorizing agents of undesired Components. The heterocyclic ones formed in the reaction according to the invention Di- or tricarboxylic acids are usually less soluble in water than the starting materials. Therefore, after acidification of the aqueous solution, they often crystallize out and can easily from the other constituents of the reaction mixture, especially not converted starting materials are separated. The acids obtained can be used in known way into their derivatives, especially their chlorides or esters will. For the preparation of the esters or chlorides, however, you can also use the raw or purified reaction product without prior isolation of the acid according to known methods Use procedure directly.

The process according to the invention makes it possible to produce heterocyclic To produce di- and tricarboxylic acids in a simple way and with very good yields, z. B. the pyridine-2,5-dicarboxylic acid (isocinchomeronic acid), the pyridine-2,4,6-tricarboxylic acid (Trimesitic acid), furan-2,5-dicarboxylic acid (dehydro-mucic acid), thiophene-2,5-dicarboxylic acid.

Example 1 In an autoclave of 0.21 capacity, a Mixture of 16.1kg of the potassium salt of nicotinic acid (pyridine-ß-carboxylic acid), 13.8 g potassium carbonate and 1.0 g cadmium fluoride heated to 3500 C for 8 hours. Before start of the experiment, 180 g of carbon dioxide were placed in the autoclave. Put at 3500 C. a pressure of 1800 at. After cooling and releasing the pressure, the autoclave was the crude reaction product, weighing 32 g, was dissolved in 400 cm2 of hot water. The solution was filtered, acidified with hydrochloric acid and evaporated to half its volume. After cooling to 0 ° C., 16.1 g of the monopotassium salt of isocinchomeronic acid crystallized (Pyridine-2,5-dicarboxylic acid).

Example 2 A mixture of 22.0 g of the potassium salt of thiophene-a-carboxylic acid, 27.6 g of potassium carbonate and 2.0 g of cadmium fluoride were stored in an autoclave for 3 t / 2 hours heated to 3400 C. Before the start of the experiment, after displacement of the air, it was like this a lot of carbon dioxide pressed that at the reaction temperature a pressure of 800 at originated. The crude reaction product, weighing 54.2 g, was dissolved in 600 cm9 of hot water solved. The solution was filtered and the filtrate acidified with hydrochloric acid. the precipitated thiophene-2,5-dicarboxylic acid was filtered off, washed with water and dried. The yield was 17.0 g. From the mother liquor and from the wash water were extracted with ether another 2.2 g of a mixture of thiophene mono- and dicarboxylic acid with an acid number of 595.

Example 3 A mixture of 32.2 g of the potassium salt of isonicotinic acid, 27.6 g of potassium carbonate and 3.0 g of cadmium fluoride were placed in a 600 cm3 autoclave Capacity heated to 3900 C for 16 hours.

At the beginning of the experiment, after the air had been displaced, there was so much carbon dioxide pressed that a pressure of 1500 at was created at the reaction temperature.

The crude reaction product weighing 64.5 g was dissolved in hot water. The solution was filtered and the clear filtrate with that of the potassium present calculated amount - acidified by hydrochloric acid.

On cooling, 26.2 g of the monopotassium salt of trimesitic acid crystallized (Pyridine-2,4,6-tricarboxylic acid). Extraction of the mother liquor made more 2.75 g of pyridine tricarboxylic acid were obtained.

Claims (1)

PATENT CLAIM: Process for the production of heterocyclic di- and / or aromatic tricarboxylic acids Character or their Salts or derivatives by heating the alkali or alkaline earth salts of heterocyclic Monocarboxylic acids of aromatic character in the presence of carbon dioxide under pressure and in the presence of acid-binding agents and optionally catalytically effective seeds metals or metal compounds and optionally by transfer the salts obtained into the free acids or their derivatives, characterized in that that the heating is carried out under a carbon dioxide pressure of more than 400 atm.