DE1114801B - Process for the preparation of benzene polycarboxylic acids - Google Patents

Description

Process for the preparation of benzene polycarboxylic acids It is known Tetrachlorophthalic acid (anhydride) or tetrachloroterephthalic acid with potassium cyanide and copper cyanide in an aqueous alkaline solution by heating in an autoclave to 180 to convert up to 2000 C to mellitic acid (see F. Feist, reports of the German chemical Gesellschaft, Vol. 68, 1935, p. 1942). When reworking this reaction, see more precisely Compliance with the conditions specified by Fis t was able to achieve the 600% yield to be achieved; but this is a raw ash-containing product. The yield of pure mellitic acid is only 370/0.

It has now been found that you can use this method with respect to his Significantly improve yield and, moreover, generally apply to the production of Benzene carboxylic acids can apply by using ring-chlorinated benzene carboxylic acids or their anhydrides with alkali cyanide, copper cyanide and alkali in the presence of Metal oxides or salts, e.g. B. the elements Cr, Cu, Fe, or mixtures thereof heated. Even small amounts of these compounds are sufficient, e.g. B. 0.5 to 5 e / 0, based on the nucleus chlorinated starting acids, to the implementation significantly to improve. Additions of 30 to 60% or more generally result in the best results. To favor the initiation of the reaction is recommended prior thorough mixing of these substances with all solid starting materials.

As was also found, surprisingly, in addition to the Metal oxides and salts mentioned are the complex salts of heavy metals, especially the cyan complex salts of divalent and trivalent iron and copper, still opposite the usual oxides and salts increased yields, but especially in a mixture with small amounts of metal compounds. If the commercially available cyan colors, like Berlin blue, Parisian blue or steel blue, such impurities are insufficient Amount, it is advisable to add small amounts of oxides to these complex salts, in particular to add iron oxides or hydroxides.

The method according to the invention does not only lead to an increased Yield of benzenecarboxylic acids, but also allows the proportions of Reduce alkali cyanide and / or copper cyanide. It still allows that Shorten the reaction time, which depends on the amount used, and the temperature lower than before. Temperatures of around 1700 C are completely sufficient, to complete the reaction in a sufficiently short time. Also the addition to Water can be lower are maintained, which means the throughput per autoclave unit increased accordingly.

As was also found, surprisingly, the insoluble Share of the fully reacted reaction mixture as a fully effective catalyst for new ones Use approaches, d. H. the catalyst can be circulated. This Circulation processes can be made particularly economical by additionally the hydrogen cyanide which develops during the isolation of the free benzenecarboxylic acids brings to action on this insoluble part. For this purpose one separates the insoluble fraction is first removed from the alkaline reaction mixture and then added him again with alkali or a new approach of alkali and nuclear chlorinated Acid. The hydrogen cyanide is then passed into this slurry. It lies It is obvious that one can by recovering the hydrogen cyanide in the form of cyanides hardly any free cyanide needed for further sales.

The reaction solution freed from insolubles is worked up by acidification (during which hydrogen cyanide is evolved) and furthermore according to the usual Methods of organic chemistry, e.g. B. by extraction or evaporation and sublimation.

With these measures, too, there is a backlog that accounts for part of the represents the catalyst used and therefore expediently before or after Recovery of the hydrogen cyanide with the insoluble residue of the reaction mixture is united.

In these embodiments of the method, you only need at the first approach copper cyanide and metal salts or cyan complex salts in larger ones Amounts. In all subsequent conversions, only more is essentially used up To replace hydrogen cyanide with alkali metal cyanide. It can do that for this cheap Potassium-sodium cyan double salt can be used.

In particular, the process leads to almost theoretical yields in those cases in which the halogen on the benzene nucleus has an ortho position negative Group is relaxed or is relaxed in the course of the reaction. This applies e.g. B. on the conversion of trichlorotrimesic acid and trichlorotrimellitic acid to mellitic acid to, as well as to the conversion of 2,6- or 2,3-dichlorobenzoic acid to hemimellitic acid or from o-chlorobenzoic acid to phthalic acid.

Example 1 30 g of tetrachlorophthalic anhydride, 50 g of KCN, 15 g of Cu C N, 20 g Parisian blue R 931 (commercial product from G. Siegle & Co.) and 2 g Fe2O3 are intimately mixed with one another and placed in a 0.6 liter iron autoclave filled. To this 100 g of H2O are added with 15 g of KOH. The autoclave is then Heated to 1700 C for 7 hours, the pressure rising to 37 atm. After cooling down the reddish colored autoclave contents are flushed over into a flask and after addition of 250 cm3 of 500 / o sulfuric acid and with moderate air flow (for Expelling the hydrogen cyanide) heated to boiling for 1 hour. The insoluble residue is filtered off and the filtrate extracted with butanone. The extract that is free Contains mellitic acid is freed from butanone by distillation under a water seal and the aqueous mellitic acid is concentrated to 150 cm3. Then 300 cm3 of nitric acid are added (D. = 1.5) was added and, after cooling, the precipitated mellitic acid was filtered off. Yield: 31 g 87 / o of theory. Acid number: 980, ash 0.05%.

The insoluble residue separated off before the butanone extraction exists predominantly made of copper oxides and is set free using the Hydrogen cyanide reprocessed on CuCN.

Example 2 A mixture of 30 g of tetrachloroterephthalic acid, 80 g of sodium cyanide, 20 g CuCN, 10 g Fe2O3, 20 g Na OH and 90 g H2 ° are put in a 0.6 liter Iron autoclave heated to 1800 C for 8 hours.

This results in a pressure of 40 atmospheres. After it has cooled down the contents of the autoclave worked up according to Example 1. The precipitated mellitic acid possesses an acid number of 978. The yield is 90% of theory.

Example 3 A mixture of 250 g of tetrachlorophthalic anhydride, 520 g KCN, 216 g CuCN, 160 g chemically pure Berlin blue (Siegle & Co.), 8 g each 203, 120 g KOH and 800 g 11.30 am for 14 hours in a 2.5 liter iron autoclave heated to 1700 C.

The pressure rises to 86 atmospheres. The processing of the contents of the autoclave takes place according to example 1.

The mellitic acid obtained has an acid number of 979 and contains 0.09 ° / o ashes. The yield is 262 g = 88% of theory.

Example 4 250 g of tetrachlorophthalic anhydride, 520 g of K C N, 216 g CuCN, 160 g Berlin blue, 8 g Fe2 03, 120 g KOH and 800 g 1120 are 14 hours in one 2.5 liter iron autoclave heated to 1700 C.

The pressure rises to 86 atm. After the completion of the reaction, the pressure is reduced drained, the contents of the autoclave made up to 2.5 liters, and the insoluble residue filtered off. This still moist residue is stirred with 600 cm3 of H, O. To be 300 g of K O H and a further 400 g of alkali metal cyanide are added (marked with template).

The filtrate separated from the residue is transferred to a container with Reflux condenser and inlet port for air (or nitrogen) and outlet port for given the hydrogen cyanide; this leads to the template. Become the filtrate while air was passed through, 650 cm3 of concentrated 112.504 were gradually given. Simultaneously is heated to boiling.

The released hydrogen cyanide passes the template, with under Heating copper and iron are converted to cyan complex salts.

After cooling, the acidified filtrate is extracted with butanone and the extract worked up to mellitic acid as in Example 1. Yield 262g = 880lo the Theone.

The nitric acid filtrate of the mellitic acid filling is evaporated and the evaporation residue (40 to 60 g) after combining with the template in the Given to the autoclave. It is rinsed with 200 cm3 of H, O and 250 g of tetrachlorophthalic acid admitted. The mixture is then heated (60 atmospheres) at 1850 C for 20 hours. After that it will be again the residue separated and again with 300 g of KOH + 400 g of KCN + 600 g of H, O as Template used for hydrogen cyanide recovery. Separation of the mellitic acid takes place, as already described in Example 1, by acidifying the filtrate, extraction with butanone and precipitation with nitric acid.

The average yield from eight batches is 223 g = 75% the theory. Ash 0.050 / 0, acid number 970.

Example 5 30 g of o-chlorobenzoic acid, 20 g of KCN, 10 g of CuCN, 6 g of Fe2 O3 are intimately mixed with one another and placed in a 0.6 liter iron autoclave filled.

After adding 120 g of H2O and 10 g of KOH, the mixture is heated to 1700 ° C. for 7 hours (Pressure about 20 atmospheres).

After cooling, the autoclave contents are filled to 500 cm3, the The insoluble residue is filtered off and stirred with 90 cm3 H2O while it is still moist. To be 18 g of KOH and 20 g of KCN are given (template for the next batch). The filtrate will as in Example 4 placed in a flask with inlet and outlet ports and below Passing air with 100 cm3 of concentrated H2 504 added. The one that has become free Hydrogen cyanide is passed through the template (see above), with copper and iron are converted to the corresponding cyan complex salts. After it has cooled down the now acidic filtrate is extracted with butanone, the solvent is distilled off and the phthalic acid formed from water, mixed with a trace of nitric acid, crystallized out. Yield: 30 g = 94/0 of theory.

The filtrate from the crystallization is evaporated and the evaporation residue given to the above-mentioned template. This template is filled with 30 cm3 of water and 30 g of o-chlorobenzoic acid were flushed into the autoclave and heated to 1700 ° C. for 7 hours.

The residue is then separated off again, as already described above and with 18 g KOH + 20 g KCN + 90 g H2O as a template for collection the hydrogen cyanide used from the next experiment. The average yield from five runs is 28.7 g of phthalic acid = 90%.

Example 6 A mixture of 30 g of tetrachlorophthalic acid, 80 g of potassium cyanide, 16 g Cu C N, 12 g Cu-Cr oxide, 20 g Na OH and 90 g H2O are in a 0.6 liter Iron autoclave heated to 1950 C for 8 hours at a pressure of 75 atm. After cooling down the contents of the autoclave are worked up according to Example 1.

The yield is 81 81% of theory. Acid number of the mellitic acid: 976.

Claims (2)

PATENT CLAIMS: 1. Process for the preparation of benzene polycarboxylic acids by heating nuclear chlorinated Benzene carboxylic acids or their anhydrides with alkali metal cyanides and copper cyanide in the presence of alkali at 2000 C, characterized in that that the heating either in the presence of oxides of the metals of VI. and or or VIII. main group of the periodic system or in the presence of cyan complex compounds of iron and copper, which may contain small amounts of oxides or salts the metals of the VI. or VIII. main group of the periodic system are added, performs. 2. The method according to claim 1, characterized in that the oxides and salts which can be separated off during work-up of the reaction mixture and, if appropriate, the liberated hydrogen cyanide is used for further reactions.