DE1032261B - Process for separating secondary amines from a mixture containing primary and secondary amines - Google Patents

Description

GERMAN

The isolation of secondary amines, especially secondary aromatic amines, is organic chemical industry, especially in the dye and pharmaceutical industries, of great importance. The primary amines are generally just as reactive as the secondary amines and for this reason usually have to be completely removed before the secondary amines are industrialized be used. The tertiary amines, on the other hand, are relatively inert, and it is not always strictly necessary to remove.

Many chemical methods have been described in the literature to convert primary amines from secondary to separate; but in practice such methods are either only portable or only for laboratory experiments too expensive or not efficient.

The present invention relates to secondary amines, especially secondary aromatic amines from mixtures of secondary and primary amines through a simple, cheap and particularly powerful one Separate process.

It is known that a mixture of primary and secondary amines with phthalic anhydride at room temperature to the phthalamic acids corresponding to the primary and secondary amines implements. Tertiary amines do not enter into this reaction. It has now been found that when using an amount of phthalic anhydride not less than the amount required to react with the primary amine is required, d. H. 1 mole of phthalic anhydride for each mole of primary amine, all of the phthalic anhydride, preferably with the primary Amine the corresponding phthalic acid process for separation

secondary amines from a primary

and containing secondary amine

mixture

Applicant:
Leda Chemicals Limited, London

Representative: Dipl.-Ing. K.-A. Brose, patent attorney,
Pullach near Munich, Wiener Str. 1/2

Claimed priority:
Great Britain 8 March 1955

Dr. Zvi Enrico Jolles, London
has been named as the inventor

amide forms, while the secondary amine does not enter into this reaction. If the mixture is after the The reaction is heated or when the reaction is carried out at a moderately elevated temperature, around 100 to 180 ° C the phthalamic acid corresponding to the primary amine loses water and goes into the Imid over. The response can be expressed by the following equation:

-CO

-CO

> 0 + H ₂ NR '

y_COOH

: - CO-NHR '

_; 'VCO

NO'

The phthalate corresponding to the secondary amine is 40 when treated with a primary amine

amic acid can not react in this way and moderately elevated temperature, e.g. B. around 100 to 180 ° C,

also cannot form an imide. the imide of the primary amine is formed and the secondary

It has also been found that amine is released from phthalates. This reaction

amic acid produced by reaction between phthalic acid- can be expressed by the following equation:

anhydride and a secondary amine were obtained

- COOH

-CO- NR "R '"

+ H ₂ NR '

-CO

CO

NO'

HNR "R '"

In a preferred embodiment of the invention, which is based on this reaction, an excess used by anhydride and the reaction carried out at a moderately elevated temperature; the unchanged secondary amine is then distilled off. The secondary amine, which is

809 557/479

shot entered the reaction, can then be recovered by adding primary amine, which forms the imide with regression of the secondary amine according to the second equation. It has also been shown that hexahydrophthalic anhydride reacts in the same way.

The present invention therefore relates to a method for separating secondary amines from a Mixture of primary and secondary amines, in which the mixture with phthalic anhydride or Hexahydrophthalic anhydride in the proportion of not less than 1 mole for each mole present primary amine is treated and the unchanged secondary amine from the reaction product is separated off by distillation.

The reaction can be carried out at room temperature. Here the mixture becomes several Keep moving for hours until all of the phthalic anhydride has reacted, it just gets a little Anhydride excess over the required amount, which reacts with the primary amine present, is used and then the unchanged secondary amine is distilled off.

However, it is preferable to carry out the reaction at a moderately elevated temperature, up to about 180 ° C and using an excess of anhydride and then distilling off the unchanged secondary amine. Since some secondary amine is retained by the excess anhydride, it can do a lot simply and easily can be recovered by using just another amount of primary amine or is heated with the starting mixture of primary and secondary amine. This method works fast and effective and can be carried out so that the separation of the secondary amine from the primary Amine is complete.

Instead of the anhydride, that formed by reacting it with a secondary amine can also be used Acid amide can be added as this is in accordance with the above when heated with primary amine cited second equation responds. It is particularly easy to use the anhydride or acid amide in to be added to the secondary amine or in the mixture to be treated, as in this way any difficulties that might arise when placing the solid in the reaction vessel will be avoided. The addition of the anhydride in solid form can, for. B. therefore be difficult because it tends to stick to the inlet port of the reaction vessel. Since the anhydride in the secondary Amine or in the mixture of primary and secondary amine to be treated can, solutions are obtained which contain up to 30 percent by weight of anhydride, and this can be Operation carried out in this way very quickly and smoothly and without any mechanical difficulty will.

The new method provides a simple and effective way of separating secondary from primary Amines, even if the primary amine is present in very small amounts, since the formation of the Imide from the primary acid amide is not declining and therefore runs completely. The way of working according to the invention is particularly valuable for purifying the lower alkyl substituted secondary aromatic Amines that contain no more than S carbon atoms in the alkyl group. So z. B.

4 ■,;,

0.1% aniline from a lower alkyl aniline completely can be removed by using a small excess of phthalic anhydride, which ■ either solid or in solution in crude lower alkyl aniline is added and the mixture Maintained for 1 hour at a temperature of 120 to 160 ° C and then the alkylaniline by distillation is removed at atmospheric pressure or reduced pressure. * For example

453.6 kg of a mixture of aniline, monoethylaniline and diethylaniline containing 1% aniline are added contains, with 6.804 kg of phthalic anhydride. The mixture is heated to 160 ° C for approximately 1 hour. As soon as the primary amine can no longer be determined, the secondary and tertiary amines are removed; Amines from the reaction mixture by distillation over a two- to three-stage column. In the distillate " primary aromatic amine is not detectable.

Example 2

27.206 kg of a solution obtained by dissolving 6.804 kg of phthalic anhydride in 20.412 kg of monoethylaniline, which contains some diethylaniline, is obtained to 453.6 kg of a mixture of aniline, N-monoethylaniline and N-diethylaniline given, wherein the primary amine is 1% of the total mixture. The mixture is about 1 hour Heated to 160 ° C and distilled over a two- to three-stage column. The distillate does not contain a primary aromatic amine,

Example 3

6.804 kg of hexahydrophthalic anhydride are added to 453.600 kg of a mixture of aniline, monoethylaniline and diethylaniline which contains 1% aniline. The mixture was cooked for about 1 hour at 170 ' heated to 180 ° C. After the presence of traces of the primary amines was determined, the secondary and tertiary amines were removed from the reaction mixture removed by distillation over a three to four stage column. The distillate gave a negative test for primary aromatic amine.

Claims (4)

Patent claims: 1. A method for separating secondary amines from a primary and secondary amine-containing mixture, characterized in that one the mixture is heated with phthalic anhydride or hexahydrophthalic anhydride, in proportion of not less than 1 mole for each mole of primary amine present, and the secondary Amine distilled off from the reaction mixture. 2. The method according to claim 1, characterized in that the phthalic anhydride is in dissolves the secondary amine or in the amine mixture. 3. The method according to claim 1 or 2, characterized by the application to secondary aromatic Amines, especially N-alkylanilines, the contain no more than 5 carbon atoms in the alkyl group. 4. Embodiment of the method according to claim 1 to 3, characterized in that one instead of phthalic anhydride, the corresponding acid amides of the secondary amines admits. " © 809 557/479 6.