DE2556206C3 - Process for the production of terephthalaldehyde - Google Patents

Description

The present invention is an improvement of the process for the production of Terephthalaldehyde by reducing terephthaloyl chloride with hydrogen in the presence of noble metal catalysts and sulphurous regulators.

The reduction of acid chlorides to the corresponding aldehydes and of terephthaloyl chloride to Terephthalaldehyde in the presence of precious metal analyzers by hydrogen is under the name Rosenmund reduction in the literature for a long time known. The use of a catalyst and its activity is particularly characteristic of the process by adding low-volatility sulfur compounds, also called regulators, is reduced to such an extent that the Rate of reaction of the reduction of the aldehydes formed to alcohols and hydrocarbons compared to the hydrogenolysis of the acid chlorides is very much reduced.

Frequent reuse of the noble metal catalyst used is essential for the technical usability of the reduction process. In the case of the reduction of trephthaloyl chloride, it has been shown that, when working discontinuously, the activity of the catalyst decreases sharply after a few batches. By increasing the temperature to 120 ^° C., it is then possible to carry out a few more batches with the catalyst, but at these high temperatures the yield of terephthalaldehyde falls sharply.

It is also already known to carry out the reduction of the terephthaloyl chloride in such a way that the acid chloride and the sulfur-containing regulator dissolved in a high-boiling organic solvent are present and hydrogen is passed through this solution in the presence of catalysts. at However, this procedure according to DE-OS 16 43 639 decreases the Aktivi'ät d <; s catalyst quickly, so that only a few approaches can be carried out with the same catalyst.

It has now been found that the activity of the catalyst can be maintained over a significantly longer period of time can, if one considers the process for the preparation of terephthalaldehyde, in which a solution of terephthaloyl chloride and sulfur-containing additives in high-boiling organic solvents from hydrogenolysis are subjected to hydrogen in the presence of lidelmetall catalysts, that the solution for 1 to 6 hours at temperatures between 90 ° C and the boiling point of Solution heated.

The duration of the heating in the solvent used should, if possible, not be less than one hour. Heating for more than 6 hours is possible in principle, but does not bring any additional Effect. Heating is preferably carried out for about 3 hours

Using this procedure, the noble metal catalyst lasts at least three times as long start as without this additional treatment, without its activity noticeably decreasing

In principle, all organic solvents in which terephthaloyl chloride are suitable as solvents

ίο is soluble and which are not attacked by hydrogen in the presence of the catalysts. The boiling point of the solvent should be above 80 ^0C. Suitable solvents are e.g. B. aromatic hydrocarbons such as toluene, the xylenes or ethylbenzene. However, other solvents can also be used, provided these do not change under the reaction conditions and the boiling temperature is sufficiently high. Dioxane is an example

The solvents can be of technical quality

2 (be i; additional purification methods as recommended by F. Zymalkowski (in the book "Katalytische Hydrierungen", F. Enke Verlag, Stuttgart, 1965, page 171) are not required.
The catalyst used is a porous carrier material known per se, such as carbon, γ-AhOj or BaSO +, on which the noble metal (preferably palladium) is deposited in finely divided form as metal. The metal content of the catalysts is between 2.5 and 10% by weight, but preferably between 4.5 and 5.5

«Ι% by weight. The amount of the catalysts, based on the terephthaloyl chloride used, is 0.5 to 10% by weight, preferably 4 to 5% by weight.

Known regulators are those used in the catalytic reduction of acid chlorides to aldehydes

π sulfur-containing substances used, such as. B. Quinoline sulfur, thiourea, mercaptobenzothiazole or thioquinanthrene. The preferred regulator is Quinoline-sulfur, a regulator known to the person skilled in the art from technical thioquinanthrene, which is described in in the above-mentioned book by Zymalkowski on page 172. The amount of regulators can between 0.1 and 2% by weight, based on the catalyst used, vary. To be favoured 0.8 to 1.5 wt .-% used.

■ π The procedure is carried out in general in such a way that a solution of terephthaloyl chloride in the solvent is prepared, their Concentration shouldn't be too high. The preferred concentration range is between 15 and 25

in% by weight; however, there are also concentrations up to about 40% by weight can be used. In the solvent is then the regulator is still dissolved and the mixture, optionally under reflux, to temperatures heated between 90 ° C and the boiling point of the solution.

Ti The catalyst is then added and the terephthaloyl chloride is reduced to the aldehyde by passing hydrogen through the solution in a manner known per se. The reduction is preferably carried out at temperatures between 80 and 110 ⁰ C.

wi The resulting gaseous hydrochloric acid is converted into a template. The end of the reaction can easily be seen from the decrease or cessation of the HCl development recognize.

example

There are 900 parts by weight of xylene and 203 parts by weight of terephthaloyl chloride with 0.1 parts by weight of quinoline

Sulfur for 3 hours at 100 ⁰ C heats the solution is then added to 10 parts by weight of a catalyst consisting of AI2O3 is at the 5 wt .-% of metallic palladium is deposited Subsequently, with vigorous stirring at 90 to 100 "C a An amount of hydrogen of 125 liters per hour is introduced The evaporating xylene is condensed in a reflux condenser and returned to the reaction vessel The hydrogen-HCl mixture is passed through an absorption unit where the hydrogen chloride is determined by titration with NaOH. After 2.5 hours 95% of the split off theoretically possible amount of hydrogen chloride.

The catalyst is then filtered off while hot and 700 parts by weight of xylene are evaporated Hydrogen chloride and unreacted acid chloride are extracted with an excess NaHCOj solution eliminated. When the remaining xylene solution cools, the terephthalaldehyde crystallizes with a purity of over 99%.

Another fraction of terephthalaldehyde can be obtained from the mother liquor and the bicarbonate solution with a purity of less than 96%; when calculating the yield (see table) this Post-precipitation not taken into account

The filtered and washed out catalyst is used in further approaches that are completely analogous Way to be carried out, further used. The following table shows the yields as a function from the number of returns of the catalyst jo.

In a comparative series, xylene, acid chloride and regulator were not heated to 100 ° C, but immediately added to the catalyst and reduced with hydrogen. The rest of the process was carried out completely y, analogously to the experiments according to the invention described above.

Ver running time yield Comparative series search up to 95%
sales Lauizeit yield
(up to 95% Sales) (Hours.) (Wt .-%) (Hrs.) (Wt .-%)

2.5 3.5 4.0 4.1 4.3 4.7 5.1 5.3 5.4 5.8 5.8 6.8 6.4 6.8 6.6 7.5 6.8 6.8 6.8 6.8 6.3 7.5 7.2 7.0 7.5 7.8

62 62 66 66 68 68 69 68 69 67 67 68 68 70 70 69 67 68 68 69 70 69 71 68 68 69

3.0

4.5

5.0

6.5

8.0

9.0 10.3 12.4

Conversion remained at 75%

64 67 68 69 69 70 68 66 35

Series canceled although the catalytic converter was still partially intact

Claims (1)

Claim: Process for the production of terephthalaldehyde, in which a solution of terephthaloyl chloride and sulfur-containing additives in high-boiling organic solvents of hydrogenolysis using hydrogen in the presence of noble metal catalysts is subjected, characterized in that the solution before the Hydrogenolysis for 1 to 6 hours to temperatures between 90 ° C and the boiling point the solution heated