DE1051841B - Process for the preparation of terephthalic acid or mixtures thereof with p-sulfobenzoic acid - Google Patents

Description

Process for the production of terephthalic acid or mixtures thereof with p-sulfobenzoic acid It has been found that terephthalic acid or mixtures from terephthalic acid and p-sulfohenzoic acid can be produced by the Potassium salt of benzenesulfonic acid in the presence of carbon dioxide. which possibly can also be in bound form. as well as in the presence of acid-binding substances heated to a temperature above 2000 C.

The potassium salts obtained in this way can be used in a known manner into the free acids or their derivatives, e.g. B. their chlorides or esters, transferred turn around. Depending on the conditions used, this initially contains the reaction product obtained potassium salt of terephthalic acid larger or smaller amounts of p-sulfobenzoic acid Potassium as a by-product.

The potassium benzenesulfonate is heated in the presence of carbon dioxide, which is also in bound form, e.g. B. as a carbonate can. For example, the henzolsulfonsaure potassium in the presence of alkali metal be heated. Particularly good yields are achieved when using potassium carbonate obtain. It is advantageous to use the heating in the presence of gaseous carbon dioxide under pressure, whereby in many cases by increasing the pressure a Improvement in the yield is achieved. The carbon dioxide can also be inert Gases, e.g. B. be diluted by nitrogen.

Acid-binding substances are used for the process according to the invention advantageously the carbonates of the alkali metals, especially potassium carbonate.

Also for the carbonates of magnesium, calcium, aluminum and others Metals are suitable. Instead of the carbonates of these metals, you can also use theirs Use oxides, hydroxides, bicarbonates or oxalates. The starting materials mentioned should be as free of water as possible. It is also useful to use the inventive Carry out reaction in the absence of oxygen.

The inventive method is carried out at elevated temperature, in general above 2000 C. the upper limit only being determined by the decomposition temperature the organic matter is given. which is mostly above 5000 C. The optimal one The reaction temperature is different for the individual starting materials and is mostly between 300 and 4500 C.

In many cases, the reaction temperature increases when a lower reaction temperature is maintained the yields of p-sulfobenzoic acid. while larger at a higher temperature Amounts of terephthalic acid can be obtained.

It has shown. that reaction by the presence of a number is favored by catalysts. Heavy metals and are particularly beneficial their connections, e.g. B. zinc, cadmium, lead, mercury, iron, bismuth or thallium. The metals can e.g. B. in the form of their oxides or their salts with inorganic ones or organic acids can be used.

In addition to the catalysts, the reaction mixture can also be inert Fillers, e.g. B. Sanrd, finely divided carbon, kieselguhr, bentonite, metal powder or chips, also inert salts, e.g. B. sodium sulfate, potassium sulfate and the like., Add. Use is made of this measure in particular. when the reaction mixture tends to cake. It is advantageous to use the starting materials for the according to the invention Process crude 5 ulfonierungsgemi cal, which with an excess of carbonate added and dried in a known manner, for. B. I by atomization. Even organic solvents or diluents such as benzene, toluene, xylene. high-boiling Gasoline, etc., can be added to the reaction mixture.

To work up the reaction mixture you can use this z. Am Dissolve water and by filtration, optionally with the addition of activated carbon or free from other decolorizing agents and unwanted constituents. By The carboxylic acids formed can be acidified from any aqueous solution and filtered off or extracted with a solvent. The acidification can z. B. with hydrochloric acid, sulfuric acid or other strong acids. Often is it is also expedient to acidify to be carried out with carbon dioxide. Through this it is possible to separate the terephthalic acid as the acidic potassium salt. The entire The remaining mixture can be evaporated and fed back into the reaction.

The p-sulfobenzoic acid which is more soluble in water than terephthalic acid can be extracted from the mother liquor of terephthalic acid precipitation after acidification with a strong acid, for example by extraction with an organic solvent, be won. You can also use their salts, if appropriate after concentrating the aqueous Solution, thereby isolating salting out, or the acid in the form of its calcium or barium salt fail.

With the help of the method according to the invention, the technically important Terephthalic acid and p-sulfobenzoic acid from the easily accessible benzenesulfonic acid can be obtained. So a new one emerges on the way via the benzenesulfonic acid Possibility of obtaining terephthalic acid or p-sulfobenzoic acid from benzene.

Example 1 A mixture of 24.5 g of dry benzene sulfone, acidic Potassium, 5.5 g Ides double salt K2 Cd Cl2 F2 and 70 g anhydrous potassium carbonate was filled into a roller autoclave with a capacity of 250 cm3.

Then 50 atmospheres of carbon dioxide were injected and Ender's autoclave Heated to 4000 C for 5 hours. A pressure of 170 atm was established here. To the reaction product was also dissolved in 500 cm3 of water for cooling and letting down and filtered. The filtrate was acidified with hydrochloric acid and after standing for some time vacuumed hot. This gave 1.1 g of terephthalic acid. By extraction 2.5 g of p-sulfobenzoic acid were isolated from the filtrate with ether.

Example 2 A mixture of 24.5 g of potassium benzenesulfonate, 70 g anhydrous potassium carbonate and 5 g of cadmium fluoride were placed in an autoclave of 200 cm3 capacity filled. The autoclave was then evacuated and about Filled with 50 g of liquid carbon dioxide. The contents of the autoclave were 9 hours heated to 3600 ° C., a pressure of about 300 atm. After cooling down and releasing the pressure, the reaction product was dissolved in water. The solution was filtered and acidified in the heat with hydrochloric acid. 3.1 g of terephthalic acid crystallized in the process from which was filtered off hot. The mother liquor became by shaking obtained with ether a mixture of 3.5 g of p-sulfobenzoic acid and 1.3 g of terephthalic acid.

Example 3 A mixture of 24.5 g dry potassium benzenesulfonate, 5 g of cadmium fluoride and 70 g of anhydrous potassium carbonate were placed in a roller autoclave from 250 cm3 capacity filled. 70 g of liquid carbon dioxide were added to this and the autoclave is heated to 3600 ° C. for 16 hours. A pressure of 300 at a. The processing of the reaction product was carried out in the same way as described in example 1. There were 9.2 g of terephthalic acid and 1.2 g of p-sulfobenzoic acid obtain.

Example 4 23.7 g of potassium benzenesulfonate were mixed with 95.0 g of anhydrous Potassium carbonate finely ground in a ball mill and transferred to a roller autoclave from 250 cm3 capacity filled. To this 70 g of carbon dioxide were added and the Autoclave heated to 3600 C for 16 hours. This resulted in a pressure of 300 at a. Working up was carried out in the manner described above and yielded 0.6 g Terephthalic acid and 1.2 g p-sulfobenzoic acid.

Example 5 A mixture of 12.3 g of dry potassium benzenesulfonate, 2.5 g of cadmium fluoride and 30.0 g of anhydrous potassium carbonate were placed in a roller autoclave with a capacity of 250 cm3. Then 50 g of carbon dioxide were added and the contents of the autoclave are heated to 4000 C for 30 hours. Here it turned out a pressure of 260 at.

After cooling and releasing the pressure in the autoclave, S became the reaction product dissolved in 250cm3 water and filtered. The filtrate was acidified with hydrochloric acid. After a short boil, the precipitated terephthalic acid was filtered off with suction while hot. There were 4.2 g of terephthalic acid were obtained. The filtrate was extracted with ether. It could no p-sulfobenzoic acid can be isolated in this way.

PATENT CLAIM 1. Process for making terephthalic acid or mixtures thereof with p-sulfobenzoic acid, characterized in that the Potassium salt Ider benzenesulfonic acid in the presence of carbon dioxide, which optionally can exist in bound form, as well as in the presence of acid-binding substances heated to a temperature above 2000 C and optionally the salts obtained converted in a known manner into the free acids or their derivatives.

Claims (1)

2. The method according to claim 1, characterized in that one Idas Heating under elevated pressure I is carried out. 3. The method according to claim 1 and 2, characterized in that Idaß the acid-binding substances used are alkali metal carbonates, preferably potassium carbonate. 4. The method according to claim 1 to 3, characterized in that one heating in the presence of inorganic salts of cadmium.