DE966335C - Process for the production of terephthalic acid or its salts and derivatives - Google Patents

Description

ISSUED JULY 25, 1957

H 26638 IVb 112 ο

The subject of patent 965 399 is a process for the production of terephthalic acid or its salts or derivatives from potassium benzoate by heating to temperatures above 340 ⁰ in the presence of inert gases, metals or their as catalysts. Connections are used. Here, cadmium and cadmium oxide are particularly effective catalysts.

It has now been found that this process gives particularly good yields of terephthalic acid obtained when the catalysts used are salts of cadmium with organic or inorganic Acids used. Such salts are z. B. the halides, especially the fluoride, also the Carbonate, bicarbonate, sulfate, phosphate, acetate, formate, oxalate, the fatty acid salts 11. a., Or also the salts of cadmium with those acids which are used as the starting material for the Processes according to the invention are used or the main or in this reaction By-products are formed, as well as salts with such acids, which are also produced by heating their alkali salts can be converted into terephthalic acid, e.g. benzoate, phthalate, isophthalate, Terephthalate or trimesinate of cadmium. Also mixtures of such salts with one another or with metallic cadmium or

709 601/20

Cadmium oxide can be used. In In some cases it is also advantageous to use mixtures of the cadmium compounds mentioned with others catalytically active metals such as zinc, iron, lead, mercury or their compounds, as Use catalysts.

The amount of catalyst can vary within wide limits and ο to 15, preferably 0.5 to 5 percent by weight, based on the reaction mixtures. The catalysts can be distributed particularly finely in the reaction mixture by using an aqueous solution the salts used as starting material in which the catalyst is dissolved or suspended is converted to a dry powder by atomization or otherwise. The mentioned Catalysts can also be used in conjunction with known carriers, e.g. B. kieselguhr used will.

The effect of the catalysts manifests itself in an acceleration of the conversion reaction compared to certain side reactions proceeding with decomposition and thus an increase in yield.

Furthermore, the use of the catalysts mentioned enables the reaction temperature to be reduced and to work at lower temperatures Printing, even at normal pressure.

In addition to the catalysts, the Reaction can be carried out in the presence of inert, liquid or solid additives, z. B. in the presence of sand, metal powder, metal shavings, kieselguhr, activated carbon or even of inert salts such as potassium or sodium carbonate or sodium sulfate. By, such additives In many cases, the mechanical properties of the reaction mixture are improved.

During the reaction, in which as a by-product If benzene is formed, it is advisable to keep oxygen away. It is advantageous to work in Presence of inert gases, preferably carbon dioxide, also e.g. nitrogen, Methane or carbon dioxide. The reaction can be carried out at normal, elevated or reduced pressure take place. In many cases, particularly good yields are obtained when in the presence of Carbon dioxide works under pressure.

The work-up of the reaction mixtures is due to the different solubility of benzoic acid and terephthalic acid in water simply. You can z. B. proceed so that the reaction mixture dissolves in water, filtered off impurities and removed from the solution by adding acids such as hydrochloric acid or Sulfuric acid, which precipitates organic acids. From the separated acid mixture one can Dissolve the unchanged benzoic acid and the terephthalic acid by extraction with water win as an insoluble residue. You can also use the raw terephthalate that you get obtained through the reaction, directly to the production of derivatives of terephthalic acid use. It can be converted into dichloride or into ester by known methods.

example 1

In a Eisenautoklav, which was surrounded on all sides with an electric heater winding, 100 g of potassium benzoate, mixed with 3 g of cadmium fluoride, heated for 2 hours to an internal temperature of 440 ^0th A constant CO ₂ pressure of 10 atm was maintained and the benzene formed during the reaction, about 25 g, was blown off and condensed. .

After cooling, the dark gray crude product, which smelled strongly of benzene, was in 300 ecm Dissolved water, heated to boiling and filtered. The filter residue was repeated with dilute Washed hot sodium hydroxide solution. The combined filtrates were treated with hydrochloric acid up to strongly acidic reaction added; the acids which separated out were filtered off and repeated extracted with boiling water. 42.6 g of pure terephthalic acids remained as white, residue insoluble in water.

The yield was 41% of theory, based on the potassium benzoate used. One assumes that the reaction is based on a disproportionation of the benzoate to terephthalate and benzene, so this number as well as the percentages given in the following examples are to be doubled.

Example 2 ",

As described in Example 1 in the same way, a mixture of 100 g of potassium benzoate and 5.5 g Cadmiumphthalat was heated for 2 hours at 440 ^0th 42.7 g of terephthalic acid = 41.1%, based on the potassium benzoate used, were obtained from the crude product weighing 79.8 g.

Example 3

In the same manner as in Example 1 Working X05 written, a mixture of 100 g of potassium benzoate and 7 g Cadmiumbenzoat was heated for 2 hours at 440 ^0th From the crude product weighing 77.9 g, 43.6 g of terephthalic acid = 42%, based on the benzoate used, were obtained.

Example 4

As described in Example 1, 100 g of Kaliumbenzoa.t, mixed with 2 g of cadmium fluoride, were _{heated for 4 hours at 440 to 445 ° under a constant CO 2} pressure of 10 at. When the crude product, which weighs 77 g, was worked up, 45.7 g of terephthalic acid = 44%, based on the benzoate used, were obtained. 3.3 g of benzoic acid were recovered from the mother liquor by extraction with ether.

Example p

In an electrically heated furnace equipped with gas inlet and outlet valves,

were in small tubs made of sheet iron each loo g of potassium benzoate, mixed with first 0.5 g, second ι g, third 2 g and fourth 3 g of cadmium fluoride as a catalyst, heated to an internal temperature of ^{440 to 450 0 for 6 hours.} Before the experiment, the air was displaced _{by CO 2;} A valve remained open during the heating so that no excess pressure could arise and at the same time the benzene formed during the reaction could escape and condense. 91 g = 46.5% of theory were obtained in this way.

The solid reaction products were worked up in the known manner and resulted in the above order

1. 14.15 g terephthalic acid

2. i3.75g

3. 13.40 g
4 x i4.95g

Example 6

In the experimental setup described above, four small pans made of sheet iron with 100 g of potassium benzoate each, mixed with first 0.5 g, second 1 g, third 1.5 g, fourth 2 g of cadmium fluoride as a catalyst, were heated to 440 to 45 ° for 6 hours heated. In contrast to Experiment 5, however, the apparatus was flushed _{through with CO 2} ^{at intervals of 1} Iz up to 1 hour.

The solid reaction products were obtained on working up in the manner described earlier

1. 14.88 grams of terephthalic acid

2. I5.95g
3 x i5.55g
4. 14.10 g

Claims (1)

Claim: Process for the production of terephthalic acid or its salts and derivatives from potassium benzoate by heating to temperatures above 340 ⁰ in the presence of inert gases and metal compounds, the salts obtained being optionally converted into terephthalic acid or its derivatives, according to Patent 965 399, characterized in that that the Kalrambenzoat heated in the presence of salts of cadmium with inorganic or organic acids. © 609 709/405 11.56 (709 601/20 7.57)