DE881647C - Process for the preparation of dicarboxylic acids, especially adipic acid - Google Patents

Description

Process for the production of dicarboxylic acids, especially adipic acid In, the technical production of nitrogen-containing organic compounds with a saturated open or cyclic chain of 6 carbon atoms, such as Cyclöh @ 2xylamin, Dicyclohexylamine, hexamethylenediamine, caprolactam, or aminocapronitrile or adipic dinitrile, there are always more or less large amounts of higher-boiling by-products that remain behind as distillation residues and so far could not be used.

It has now been found that these distillation residues can be converted into valuable Can convert products when; it is expedient to use hydrous nitric acid in the presence of oxidation catalysts, oxidized at moderately elevated temperature. In this way, adipic acid is obtained in good yield in addition to smaller amounts of glutaric, Succinic and oxalic acid, which can be separated off using methods known per se.

It is known that, by oxidation. of pure cyclohexylamine or from hydrogenation products of aniline with nitric acid adipic acid. It is also known to produce adipic acid by oxidation of nitrogen-free cyclic acids Compounds such as cyclchexanol and cyclohexanone can be produced. ! that the above-mentioned have hitherto been seen as annoying by-products respected Distillation residues in the described simple way into valuable products, especially adipic acid.

The parts mentioned in the following examples are parts by weight.

EXAMPLE i To 2ioa parts of 50% nitric acid to which 2 parts of ammonium vanadate and 20 parts of sodium nitrite are added as oxidation catalysts, 55o parts of adipic dinitrile decomposition residues are allowed to flow in at 50 ° in the course of 1 to 2 hours Heating has liquefied. It is ensured by cooling that the temperature of the oxidate ion mixture does not exceed 6a0; increases. After the end of the introduction of the adipic dinitrile residue, the mixture is stirred for a further 2 hours at 60.degree. And then air is blown through the mixture until the nitrogen oxides have been removed. The solution, which has turned pale yellow, is concentrated to about half to a quarter of its original volume under reduced pressure and at a maximum of 70 °. On cooling, 350 to 370 parts of crude adipic acid with a mp = 148 ° crystallize out. They can be cleaned in the usual way. The filtrate, which still contains about 30 to 50 parts of adipic acid, is expediently added to the next batch.

Example 2 In 42oo parts of 65% nitric acid with 4 parts. Ammonium vanadate and 30 parts of sodium nitrite were added, the mixture is stirred as in the example i, but at 40 to 45 °, gradually i2oo parts of Gaprol.actam still bottoms a. About 800 parts of crude adipic acid with a melting point of 147 ° are obtained.

In a corresponding way, the distillation residues of Convert hexamethylenediamine, co-aminocapronitrile or dicyclohexylamine into adipic acid.

Claims (1)

PATENT CLAIM: Process for the production of dicarboxylic acids, in particular Adipic acid,. Characterized in that one, distillation residues from the extraction nitrogen-containing compounds with a saturated open or cyclic chain 6 carbon atoms with aqueous nitric acid, expediently in the presence of oxidation catalysts, oxidized at moderately elevated temperature.