FI84818B - Process for preparing an acid amide - Google Patents

Description

1 84818

The present invention relates to a process for the preparation of an acid amide, in which an ester of the corresponding acid is reacted with ammonia and the resulting amide is separated from the liquid reaction mixture by crystallization and the alcohol also formed in the reaction is recovered by transferring it from the liquid phase to the gas phase.

10

Reaction of the ester with ammonia is a well-known process for the preparation of amides. The method has produced, for example, oxamide, which is used as a slow-acting nitrogen fertilizer. The preparation has taken place by reacting dimethyl oxalate with ammonia in methanol solution, separating the resulting oxamide by crystallization and recovering the methanol of the mother liquor and the ammonia remaining in the reaction by distillation.

20 In the above process, if the methanol in the mother liquor is to be recovered in pure form, it must be separated from ammonia. The separation requires the use of an efficient distillation column system. However, such a system is prone to malfunctions, as a result of which ammonia easily remains in the methanol to be separated. The preparation of oxamide with such a small amount of ammonia that no excess ammonia remains in the mother liquor is again out of the question, as the reaction would be halfway to give a large amount of sparingly soluble oxalic acid monomethyl ester monoamide, which would complicate

The object of the present invention is to provide a process which makes it possible in particular to prepare oxamide without the above-mentioned drawbacks of the known process and which, in addition to oxamide, is also suitable for the preparation of other sparingly soluble acid amides. The invention is characterized in that the mother liquor of the amide crystallization step, which contains, in addition to 2,84818 alcohols, excess ammonia from the reaction, is recycled to the process feed, the ammonia in the mother liquor reacts with the ester, and part while reacting the remainder of the solution with the ammonia fed to the process.

Essential to the process according to the invention is that in the mother liquor the excess ammonia returning to the ester feed step reacts completely with the ester to give an ammonia-free solution from which the alcohol can be separated as a pure ammonia-free product.

In contrast to the known process, in which the mother liquor is distilled in its entirety, the invention separates only a part, suitably about 5-15%, of the solution obtained from the ester feed step, from which the alcohol is removed in the same amount as in a continuous reaction. In addition, it is an advantage of the invention that the ammonia is fully utilized, so that it does not have to be fed to the process in excess of the amount of ester fed.

According to a preferred embodiment of the invention, the liquid evaporation residue resulting from the recovery of the alcohol 25 is returned to the mixing tank, where the recycled mother liquor is combined with the ester fed to the process. The liquid evaporation residue may consist mainly of the ester fed to the process, which is either in the molten state or as a concentrated solution. The evaporation residue ester is thus utilized in the subsequent reaction with ammonia.

Alternatively, the liquid evaporation residue from alcohol recovery can be directly reacted with the ammonia fed to the process.

When the ester to be reacted with ammonia is a methyl ester, methanol is obtained from the process in addition to the amide. When the ester is 3,84818 dimethyl oxalate, methanol and oxamide are obtained as end products of the process.

The invention will now be described in more detail by way of examples with reference to the accompanying drawing, which is a diagram of an oxamide preparation process according to the invention, and then to describe the oxamide preparation by way of exemplary embodiments.

The apparatus for producing oxamide according to the drawing comprises a mixing tank 1, two reaction tanks 2,3 and a tank 4 acting as a separator for crystallized oxamide, which tanks are connected in series in said order. The mother liquor containing 15 methanol and ammonia recycled in process 5 and dimethyl oxalate from line 6 are fed to mixing tank 1 and the ammonia in the mother liquor reacts with dimethyl oxalate in mixing tank 1, and the resulting ammonia-free solution is transferred via line 7 to stoichiometrically the amount of dimethyl oxalate fed to the mixing tank 1. The reaction of dimethyl oxalate and ammonia produces oxamide and methanol, and the resulting oxamide begins to separate from the solution in the reaction tank 2 and crystallizes out in the reaction tank 3, into which the reaction mixture has passed up to line 9. From the tank 3, the reaction mixture is further passed down the line 10 to the crystal separator 4, where the oxamide crystals are separated from the mother liquor by filtration. According to the drawing, the separated oxamide passes to line 11, and the mother liquor, which contains, in addition to methanol, 30 excess ammonia in the reaction and any un crystallized oxamide, returns to the mixing tank 1 all the way to the recycle line 5.

To remove the methanol generated in the reaction from process 35, a portion of the ammonia-free solution generated in mixing tank 1 is separated via line 12 to evaporator 13 to give dry, ammonia-free methanol which exits line 14. According to the drawing, the amount of solution fed to evaporator 4 may be about 10%. 1 of the effluent. Evaporation residue, consisting in whole or in part of the dimethyl oxalate fed to the process / returned from the evaporator 13 along line 15 5 to the mixing tank 1 or alternatively via branch line 15 'directly to the reaction tank 2.

In the following embodiments, the apparatus described above was used, with the difference that the reaction vessel used for the crystallization of oxamide at the same time acts as a crystal separator.

Example 1

A 10 wt% methanol solution of dimethyl oxalate was fed to a well-stirred 750 ml reaction vessel at 18 ° C at a rate of 470 g / h. At the same time, the ammonia gas at a rate of 400 ml / min into the reaction tank. The reaction mixture was further passed to a stirred 1,000 ml reaction tank at a constant rate, from which the product crystallized at 25 ° C was collected by filtration. The average oxamide content of the bog was 20% by weight and the ammonia content was 1.7% by weight. The product yielded an average of 34.5 g of 97.2 wt% oxamide, giving an average yield of oxamide from dimethyl oxalate of 98.7%.

25 Example 2

47.2 g / h of dimethyl oxalate and 424.8 g of the filtrate from the previous example experiment were introduced into a stirred 500 ml reaction vessel. From the resulting mixture, which did not contain free ammonia, 10 parts of 30 parts were recovered at a constant rate and 90 parts were further transferred to a well-stirred 750 ml reaction vessel. Ko. at a temperature of 25 ° C, 400 ml / min of ammonia gas were introduced simultaneously into the reaction vessel. The reaction mixture was further passed at a constant rate into a stirred 1,000 ml reaction vessel from which the product crystallized at 35 ° C was collected by filtration. The average oxamide content of the filtrate was 0.01% by weight and the ammonia content was 4.3% by weight. The product yielded an average of 31.4 g / h of 96.1 wt% oxamide, giving an average yield of oxamide from dimethyl oxalate of 96.2%.

Example 3 47.2 g / h of dimethyl oxalate and 407.9 g / h of the filtrate of the experiment of the previous example and 12.7 g / h of the same were added to a stirred 500 ml reaction vessel. the reaction solution removed from the experiment, from which 70% by weight of ammonia-free methanol had been evaporated. Of the resulting mixture, which did not contain free amrao-10 niacia, 10 parts were recovered at a constant rate and 90 parts were further transferred to a well-stirred 750 ml reaction tank. Ko. at the same time, 200 ml / min of ammonia gas was introduced into the reaction vessel at 25 ° C. The reaction mixture was further passed at a constant rate into a stirred 1,000 ml reaction vessel from which the product crystallized at 25 ° C was collected by filtration. The average oxamide content of the filtrate was 0.01 wt% and the ammonia content 2.8 wt%. The product yielded an average of 34.0 g / h of 96.1 wt% oxamide, giving an average yield of oxamide from dimethyl oxalate of 98.4%.

It will be apparent to those skilled in the art that the various embodiments of the invention are not limited to the above examples but may vary within the scope of the appended claims.

Claims (3)

6 84818 A process for preparing an oxamide, which process comprises reacting dimethyl oxalate with ammonia and separating the resulting oxamide from the liquid reaction mixture by crystallization, and recovering the methanol also formed by the reaction by transferring it from the liquid phase to the gas phase, characterized in that the oxamide crystallization ammonia from the reaction is recycled to 10 process feed dimethyl oxalate to react with the amount of ammonia in the mother liquor, and a portion of the the amount of ammonia is stoichiometric compared to the amount of dimethyl oxalate, and that the evaporation residue is returned to the process. Process according to Claim 1, characterized in that the liquid evaporation residue resulting from the recovery of methanol is returned to a mixing tank in which the recycled mother liquor is combined with the dimethyl oxalate fed to the process. 25 Process according to Claim 1, characterized in that the liquid evaporation residue resulting from the recovery of methanol is reacted directly with the ammonia fed to the process. 30 7 84818