DEV0006122MA - - Google Patents

Description

IDESREPUBLIC OF GERMANY

Registration date: August 3, 1953 Advertised on October 6, 1955

GERMAN PATENT OFFICE

PATENT APPLICATION

CLASS 12 ο GROUP 14

V 6122 IVd / 12o

Dr. Rudolf Lotz, Klingenberg / Main

has been named as the inventor

United Glanzstoff-Fabriken AG _r Wuppertal-Elberfeld

Process for the preparation of dimethyl terephthalate

The invention relates to a process for the preparation of dimethyl terephthalate from p-xylylene chloride.

. It has already been proposed to use dimethyl terephthalate by oxidation of p-xylene. Following this procedure is p-xylene with ! oxygen or gases containing oxygen up to the formation of p-Toluic acid treated this intermediate separated, esterified and in a further reaction again oxidized with oxygen and then esterified with holes, so that the diester of terephthalic acid arises. This process has the disadvantage of leaving it only with the deposition of occurring Intermediate products and can be carried out in several stages is. In addition, the method may be tied to the application of pressure. Continue it is known, especially p-xylylene dichloride in several stages with the aid of aqueous alkali hydroxide using pressure and temperatures to convert from 300 to 400 ° into terephthalic acid, so that it can optionally be in one an esterification to the corresponding dimethyl ester can follow in another operation. Also it has already been proposed that the oxidation of p-xylylene dichloride to terephthalic acid without application of pressure at temperatures above 100 ° with nitric acid of medium and also higher concentration perform. The terephthalic acid formed can in turn be converted into a known esterification reaction convert into the corresponding dimethyl ester.

It has been found that dimethyl terephthalate can be obtained directly in one operation with good yield can reach if one p-xylylene-

509 565/33

Claims (3)

V 6122 IVd / 12 ο dichloride oxidized with nitric acid of medium concentration at the same time in the presence of methyl alcohol. A major advantage of this type of reaction is that the reaction can be carried out in one operation without the use of pressure. According to the previous information on the known prior art, one also receives di-ethyl terephthalate if one z. R. treated p-xylylene dichloride with alkali metal hydroxide under pressure and at temperatures above 300 "and esterified the terephthalic acid formed after several intermediate stages by customary processes. However, this process has the disadvantage that a solid salt, for example NaCl, is deposited during the reaction which interferes with the course of the reaction and does not allow the process to be carried out continuously According to the process according to the invention, it is also possible to use vertical containers as reaction vessels. These are particularly corrosion-resistant to nitric acid and the nitrous acids that occur (40 to (> 5 "/, |, preferably 50'V0) and the neactioiisgcniiseh aiii temperatures which are above the melting point of p-xylylene dichloride, that is to over 100, preferably to 105 to 110, heated. The oxidation takes place in (nowadays of methyl alcohol, that is, methyl alcohol can be added dropwise during the heating process. It is also possible to pass the methyl alcohol in vapor form through the reaction mixture. It is also useful to set the temperature after the main reaction, as "after 5 to (> hours. To increase the yield, it has been found to be advantageous to add phosphoric acid, calcium oxide or even sodium, potassium or calcium biphosphere to the reaction mixture and expediently to pass hydrogen chloride gas through during the reaction. The amount of the above-mentioned compounds to be added should be approximately equivalent to the amount of nitric acid used. The passage of hydrogen chloride should be carried out in a moderately gentle stream. If all measures are observed, a dimethyl terephthalate is obtained which contains only very small amounts of terephthalaldehyde or p-chloromethyl benzoate and has no nitration products whatsoever. The di-ethyl terephthalate obtained is used as a starting product for the production of stringy aromatic polyesters. Example 1 350 g (.iMol) p-xylylene dichloride, 800 g HXO3 ((> 5 "/" ig) and 300 g water are heated for about 6 hours with turbines to temperatures of 105 in the sleinzeug vessel and at the same time in the same reaction mixture with the introduction of HCl -Ga 2000 g of methanol added dropwise and then heated to temperatures of around 100 ° for a further 7 hours. After cooling, the main part of the dimethyl terephthalate precipitates within half an hour (in addition to small amounts of terephthalic acid ester). The residue consists of unreacted terephthalic acid, which is again esterified in the same way. Some p-chloromethylbenzoic acid ester can also be obtained from the mother liquor. Yield of dimethyl terephthalate: 80%. Example 2 350 g (2 mol) p-xylylene dichloride, 800 g HNO (650,000 g ) and 300g of water are about 5 to 6 hours] with turbines to temperatures around 100 ° and at the same time to the same reaction mixture under phosphoric acid simultaneous introduction of HCl gas added. 2000 g of methanol are allowed to act on the reaction mixture drop by drop at the same time. After a further 8 to 10 hours of heating to temperatures around 100 °, the dimethyl ester of terephthalic acid precipitated after cooling, in addition to z. B. from some Terephthalaldehydsänreeste in solid form. By recrystallizing from ζ. Β Methanol gives the dimethyl ester in pure form, which has a melting point of 1410. Example 3 After about 3 - Up to 5 hours of heating to temperatures around 100 "another 6 to 8 hours of HCl gas are introduced. At the same time, 400 liters of methanol in vapor form are passed through the reaction mixture Melting point: 1410 P Λ T F. NT Λ NS II R CC II E: 1. Process for the preparation of dimethyl terephthalate by oxidation of p-xylylene dichloride with medium concentration nitric acid and esterification with methyl alcohol, there characterized in that the oxidation and di (esterification of p-xylylene dichloride simultaneously be performed. 2. The method according to claim 1, characterized in that the reaction while initiating voi HCl gas and, in the presence of phosphoric acid, calcium oxide, sodium, potassium or calcium biphosphate is carried out. 3. The method according to claim 1 and 2, dadurcl characterized in that gaseous methyl alcohol is brought to: action. Referred publications:
U.S. Patent No. 2,563,820. © 509 565/33 9. 55