DE1063593B - Process for the conversion of dialcalite terephthalates, which have been obtained by thermal rearrangement of salts of other benzene carboxylic acids, into terephthalic acid - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

PATENT LETTER 1 063 REGISTRATION DAY:

NOTICE DEK REGISTRATION AND ISSUE OF EDITORIAL:

ISSUE OF PATENT LETTERING:

kl. 12 ο 14

INTERNAT. KL. C 07 C 5TH J ANUAB. 1956

'20. AUGUST 1959 JANUARY 28, 1960

agrees with the exposition

1 063 593 (H 25922IV b / 12 o)

In the production of dialcalite terephthalates by thermal rearrangement of the alkali salts, in particular the potassium salts of other benzenecarboxylic acids, especially o-phthalic acid, isophthalic acid or Benzoic acid, a solid reaction product is obtained, from which the terephthalic acid is obtained after dissolving in water by adding acids that are stronger than terephthalic acid, especially hydrochloric or Sulfuric acid. The alkali is converted into a salt of the stronger acid in question transformed and is in this form for the manufacture of the as starting material for the thermal Rearrangement serving salts of BeTizolcarboxylic acids no longer to be used. For this purpose, you have to go through special procedural steps in an alkaline compound, e.g. B. in the hydroxide or carbonate, convert.

According to an earlier patent not previously published, the crude dialkalite terephthalates are in the manner converted into free terephthalic acid that you can use them as starting materials for the thermal rearrangement serving benzene carboxylic acids or their anhydrides. That’s going to be raw in deni Dialcalite terephthalate present alkali in the alkali salt as a starting material for the thermal conversion benzene carboxylic acid used for storage and can thus be used again immediately for the process can be used. In order to achieve full implementation in this way of working, it is necessary to to use the relevant benzenecarboxylic acid or its anhydride in excess. With a technical However, it is not desirable to use an excess when carrying out the process. The excess of free benzenecarboxylic acid or its anhydride would be in the following thermal treatment at a temperature of around 400 ° C, which is a corresponding reduction the yield would result. One could avoid this loss of yield by after separating off the terephthalic acid, the excess benzenecarboxylic acid by adding additional Alkali neutralized. This would, however, be the one to be used for the thermal rearrangement action Keep increasing the amount of benzenecarboxylic acid salt considerably. This goes without saying not acceptable if the process is carried out technically.

. It has now been found that these disadvantages can be avoided by the implementation of the crude dialkalite terephthalate with the starting materials Serving benzenecarboxylic acids or their anhydrides is carried out in two stages.

In the first stage, the Dialkaliterephthalate in aqueous solution or suspension with equivalents Transfer procedure

of dialcalite terephthalates, which by

thermal rearrangement of salts

other benzenecarboxylic acid obtained

have been in terephthalic acid

Patented for:

Henkel & Cie. GmbH,
Düsseldorf -Holthausen

Dr. Hartwig Schutt, Hagen (Westphalia),

Dr. Werner Stein, Franz Rank, Düsseldorf-Holthausen, and Dr. Hubert Schirp, Düsseldorf,

have been named as inventors

Amounts of the acid salts of the benzene carboxylic acids used as starting materials for the thermal rearrangement converted to monoalkali terephthalate and neutral benzenecarboxylic acid salts. Subsequently the sparingly soluble monoalkali terephthalate is separated from the solution. In the second stage will the monoalkali terephthalate by reaction with equivalent amounts of the free benzene carboxylic acids or their anhydrides converted into free terephthalic acid and acidic benzenecarboxylic acid salts. Latter are returned to the first stage of the process, whereupon the process does not deteriorate the results can be repeated as often as required. ■

In this way, practically all of the alkali is in the form of the benzenecarboxylic acid salt recovered and in this form can be returned directly to the rearrangement reaction will. It is not necessary to use an excess of the benzene carboxylic acid in question. Nevertheless, the terephthalic acid is obtained practically completely and in excellent purity.

The first stage of the process can be represented by the following reaction equation, where Benzolcarboxylic acid o-phthalic acid is used.

COOK

COOH
L- COOK

COOK

COOH

(hardly soluble) COOK -COOK
-COOK

(easily soluble)

The sparingly soluble acid potassium terephthalate can io by centrifugation or filtration. The second verse of the solution, which the easily soluble di- drene stage takes place when using phthalkali metal orthophthalate contains, easily separate, e.g. B. acid anhydride according to the following reaction equation

COOH

COOH

(hardly soluble) -f

, - CO.
L-CO-

;O

H ₂ o

(poorly soluble) -f-

COOH
COOK

(easily soluble)

COOK

COOH

The sparingly soluble terephthalic acid can again easily be separated from the solution, which contains the easily soluble acid o-phthalate.

Instead of o-phthalic acid or its anhydride, other benzenecarboxylic acids can also be used, whereby one has to consider their value. In the case of benzoic acid, the second is used Process stage, instead of 1 mole of phthalic acid, 2 moles of benzoic acid. One gets in this way instead of 1 mole of acid o-phthalate, a mixture of 1 mole of benzoic acid and 1 mole of benzoate, which in can be used in the same way in the first process stage as 1 mol of acidic o-phthalate.

The preferred solvent for the reactions described is water. It can also Mixtures of water and organic solvents can be used. In some cases it is useful to the dialcalite terephthalates used as starting materials for the process according to the invention to be subjected to a pre-cleaning, e.g. B. by recrystallization. In general, however, it is sufficient when the aqueous solution obtained by dissolving the crude dialkali terephthalate is filtered freed from impurities.

The reactions in the first and second stage are advantageously carried out in such concentrations that the terephthalic acid and the monoalkali terephthalate are practically completely undissolved. Saturated aqueous solutions of Monoalkaliterephthalat contain from 0.05 to 0.06% of the salt at about 2O ⁰ C. As a rule, solutions of dialcalite terephthalate containing, for example, 1 to 10% of the salt are processed. However, it is also possible to process even more concentrated solutions, it being possible for the saturation concentration to be reached or exceeded at the temperature in question. In the case of dipotassium terephthalate, the saturation concentration at 20 ° C. is about 15 percent by weight. Any undissolved starting material present in the approach dissolves in the course of the implementation. As the amount of undissolved starting material increases, a point is reached at which the solubility of the alkali metal salt of the benzene carboxylic acid formed in the first reaction stage is exceeded, so that it is precipitated in solid form. Although this salt is more soluble than the monoalkali terephthalate formed and can therefore be separated from it by washing, it is advisable to choose the concentration of the dialkalite terephthalate to be processed so that all of the benzenecarboxylic acid salt formed remains in solution at the reaction temperature used.

In the second stage of the process, you generally go think of at least 10% solutions or slurries of the reaction mixture. It 40% aqueous slurries can also be processed, and at higher temperatures one can go up to 45 to 60%.

The reaction according to the invention can be carried out at room temperature. You prefer to work at elevated temperatures, especially in the second process stage. When using Temperatures above 80 ° C. must be taken into account that this will result in a disproportionation of the monoalkali terephthalate can take place in terephthalic acid and dialkali terephthalate.

example 1

960 g of dipotassium terephthalate, obtained by thermal rearrangement of dipotassium o-phthalate, 600 g of phthalic anhydride and 720 cm ^{3 of} water were heated to 190 ° C. for 1 hour in a stirred autoclave. After cooling, 781 g = 96.8% of the calculated amounts of monopotassium terephthalate had separated out, while the filtrate (= filtrate 1) contained the same amount of monopotassium o-phthalate. 510 g of the monopotassium terephthalate obtained in this way were stirred with 370 g of phthalic anhydride and 5 l of water at 90 ° C. for 30 minutes. After cooling to room temperature, 410 g of terephthalic acid (AN = 675) were isolated. The filtrate was admixed with 605 g of dipotassium terephthalate and stirred for 30 minutes while cold. The reaction mixture was separated by filtration in 490 g of acid potassium terephthalate (AN = 275) and a solution of dipotassium o-phthalate. These substances were returned to work-up or to the rearrangement.

Example 2

242 g dipotassium terephthalate, produced by thermal rearrangement of dipotassium o-phthalate and Purification of the crude reaction product by recrystallization was dissolved in 1.5 l of water. then 240 g of acid potassium o-phthalate in the form of the solution prepared as filtrate 1 in Example 1 were added

25 ° C added. The mixture was stirred for a further 15 minutes at this temperature and filtered off with suction. 194.0 g of acid potassium terephthalate (AN = 275) were obtained. The mother liquor was then concentrated ^{to 300 cm 3 by boiling.} After cooling, a further 9.6 g of acid potassium terephthalate crystallized from it. The mother liquor was free of terephthalic acid. Spraying gave 240.0 g of dipotassium o-phthalate from it in a form which could be reused in the thermal treatment of the rearrangement. The monopotassium terephthalate was processed as in Example 1.

When this experiment was repeated, the first stage was carried out at a higher concentration. There were 242 g of the purified dipotassium terephthalate in a solution of 204 g of monopotassium phthalate given in 1.5 l of water. The results were essentially the same.

Example 3 _ao

a) 605 g of the dipotassium terephthalate processed in Example 2 and 370 g of phthalic anhydride were suspended in 5 l of water. The mixture was refluxed with stirring for 30 minutes. By suction 468 g of a mixture of terephthalic acid and acid potassium terephthalate were obtained from it obtained an acid number of 353.5. The terephthalic acid-free mother liquor contained 552 g of a mixture of dipicalite-o-phthalate and acid potassium ophthalate. with an SZ = 220. The further processing of this mother liquor is described under c).

b) 271 g of phthalic anhydride and 3 l of water were added to the filter cake, and the suspension Cooked for 1 hour. After cooling, 370 g of terephthalic acid (AN = 675) receive. The mother liquor contained 373 g of acid potassium o-phthalate. She was brought back to the trial and reacted with the equivalent amount of dipotassium terephthalate.

c) From the mother liquor mentioned under a), the 552 g of a mixture of dipotassium o-phthalate and Contained monopotassium o-phthalate, a part was which contained 449 g of this mixture, mixed with 426 g of dipotassium terephthalate; the mixture became stirred cold. Then 349 g of acid potassium terephthalate (AN = 277) were isolated from it by suction. The terephthalic acid-free mother liquor provided 514 g of dipotassium o-phthalate by evaporation of the water a water content of 1%>, which is then dried and returned to the thermal rearrangement would. The acid potassium terephthalate obtained was in the work-up process with phthalic anhydride reacted again to terephthalic acid and acid potassium phthalate.

Example 4 ^ 5

51.0 g of acid potassium terephthalate (AN = 275) and 64.0 g of benzoic acid were introduced into a mixture of 570.0 g of water and 30.0 g of dimethylformamide and the resulting suspension was refluxed for 1 hour with stirring. After cooling, the solid fractions were filtered off with suction and the moist filter cake was ^{digested with 250 cm 3 of} methanol to separate off the benzoic acid present. After renewed suction, 40.5 g of terephthalic acid remained. (AN = 674; 0.28% sulfated ash) = 97% of theory. The mother liquor from the first filtration contained 1.2 g of terephthalic acid.

Example 5

51.0 g of acid potassium terephthalate and 64.0 g of benzoic acid were mixed with 600.0 g of water and refluxed with stirring for 1 hour. Immediately thereafter, the solids of the suspension Sucked off boiling hot and washed out with a little methanol. This left 39.0 g of terephthalic acid (AN = 670, 1.24% sulfated ash) = 94% of theory. The mother liquor gave 1.0 g Terephthalic acid isolated.

Example 6

102.0 g of acid potassium terephthalate and 128.0 g of benzoic acid were combined with 1160.0 g of water in one Stirrer autoclave stirred at 100 ° C. for 1 hour. Then the 100 ° C hot autoclave contents with nitrogen through a built-in frit filter into a second, heated to the same temperature Autoclave filtered and the filter residue washed once with 200.0 g 100 ° C hot water. After the filter residue had been dried at 110 ° C., it weighed 74.8 g and consisted of terephthalic acid with a 'SZ = 669.

Claims (3)

Patent claims: 1. Process for the conversion of dialcalite terephthalates by thermal rearrangement obtained from salts of other benzenecarboxylic acids into free terephthalic acid by reaction with the benzene carboxylic acids or their anhydrides serving as starting materials for the thermal rearrangement, characterized in that that the reaction is carried out in two stages in such a way that in the first stage the dialcalite terephthalates in solution or suspension with equivalent amounts of acidic salts which converts benzene carboxylic acids to monoalkali terephthalate and neutral benzene carboxylic acid salts and in the second stage the monoalkali terephthalate by reaction with equivalents Amounts of the free benzenecarboxylic acids or their anhydrides in terephthalic acid and acidic benzenecarboxylic acid Salts transferred, whereupon the latter returned to the first stage of the process will. 2. The method according to claim 1, characterized in that in place of the acidic salts Dibasic or polybasic benzene carboxylic acid mixtures of equivalent amounts of benzoic acid and alkali benzoate are used. 3. The method according to claim 1 and 2, characterized in that instead of 1 mol of a dicarboxylic acid, 2 moles of benzoic acid are used. Considered publications: "Chemisches Zentralblatt", 1915, L, p. 1017; B ei Istein, "Handbuch derorganischen Chemie", 4th edition, H. W., Vol. 9, p. 107; Hollemann-Wiberg, "Textbook of Chemistry", Part I, 22nd and 23rd editions (1943), p. 447; U.S. Patent No. 2,697,723; "Journal of the American Chemical Society", Vol. 39 (1917), pp. 762/63. " Older patents considered: German Patent No. 960 986. © 909 608/428 8. (909 703/344 1.60)