This invention relates to a process for prepa¬ ring N, N ' -diacetylethylene diamine by mixing ethylene diamine with the stoichiometric amount of acetic acid, a greater or smaller part of which may be aqueous , and distilling off any water originating from the use of aqueous acetic acid, and then dehydrating the ethylene diamine diacetate salt at a temperature of from 140°C to 150°C while using an auxiliary agent for distilling off water .

This process can be represented by the following reaction scheme :

OyJH _j

Ξthylene Acetic Ethylene diamine Diacetylethylene diamine acid diacetate salt diamine (DAED)

Similar processes are disclosed in the following publications: SU Patent Specification No. 180,605 (confer Chemical Abstracts, Vol. 69 (1968) abstract No. 36131 g), DE Published Specification (DAS) No. 2,118,282, DE Published Specification (DAS) No. 2,133,458, DE Published Specification (DOS) No. 2,828,765 and DE Published Specification (DOS) No. 2,941,023.

The first four of said publications disclose the preparation of DAED from ethylene diamine and acetic acid, a greater or smaller part of which latter may be aqueous, by distilling off any water originating from the use of aqueous acetic acid and dehydrating the "salt" by an excess amount of acetic acid and at an elevated temperature.

Typically, use is made of a molar ratio of acetic acid to ethylene diamine of 2.5:1 and a final temperature in the dehydration process of between 175°C and 240°C. DE Published Speficication (DOS) No. 2,828,765 describes recycling of the major part of the excess amount of acetic acid used, as a 40% aqueous acetic acid to renewed reaction. Thereby the consumption of acetic acid is reduced to about 2.05 moles per mole of ethylene diamine.

The same publication describes in a comparative Example in which a stoichiometric amount of acetic acid in relation to the ethylene diamine is used, that the DAED formed starts melting at about 90°C (as compared to normally 172°C to 174°C for pure DAED) and has an alkaline reaction in an aqueous solution.

Contrary thereto, DE Published Specification (DOS) No. 2,941,023 describes a continuous preparation of DAED from stoichiometric amounts of acetic acid and ethylene diamine and dehydration of the "salt" in a high temperature zone by means of nitrogen.

The temperature in the high temperature zone is described to be between about 140°C and 215°C, pre¬ ferably between 160°C and 180°C. Since the DAED formed is removed in a liquid state from the high temperature zone, the temperature must necessarily lie above the melting point of the DAED of 172°C to 174°C, if the DAED prepared is reason¬ ably pure. Thus, in the above-mentioned publications the dehydration of the "salt" takes place at a temperature which finally is greater than about 170°C, and the reaction mixture has a solidification temperature of about 170°C, if the DAED prepared is reasonably pure. It has now surprisingly been found that if in the dehydration process use is made of an auxiliary

agent for distilling off water which as distinct from the agents mentioned in the cited publications (acetic acid and nitrogen) consists of a water-immiscible organic solvent forming with water an azeotropic 5 mixture having a boiling point preferably lying between 80°C and 200°C, the dehydration process can be accomp¬ lished at a temperature of between 140°C and 150°C.

Accordingly, the process of the invention is characterized by using as the auxiliary agent for

10 distilling off water, an organic solvent forming with water an azeotropic mixture having a boiling point preferably lying between 80°C and 200°C.

The DAED product resulting from such a process is virtually colourless and of a purity greater than 15 98%.

At the same time as the process has the advan¬ tage of being practicable at a temperature lying 20°C to 30°C below that used in previously described proces¬ ses, it is furthermore obtained that the solidification 0 temperature of the reaction mixture is lowered from the described about 170°C to between 80°C and 110°C for the process described herein.

This results in a technically easier handling of the reaction mixture. 5 The process of the invention can be carried out batchwise as well as continuously. The continuous carrying out can take place, e.g., as a cascade reac¬ tion in three steps .

Use can be made of various advantageous embodi- 0 ments of the process of the invention as stated in claims 2 to 6.

The auxiliary agent for distilling off water can expediently be an ester of an organic acid or of carbonic acid, particularly n-butyl acetate, sec-butyl 5 acetate, n-amyl acetate or diethyl carbonate. It can also be a ketone, preferably methyl isobutyl ketone or

2-hexanone. Furthermore, it can be an aliphatic or aromatic hydrocarbon, particularly toluene or xylene.

The process of the invention is further illustrated by the following Examples.

Example 1

Batchwise preparation of DAED while using n-butyl acetate as the auxiliary agent for distilling off water.

3 Moles of ethylene diamine are neutralized with the stoichiometric amount of about 50% acetic acid. Hereafter the mixture is heated while distilling off water containing <0.1% of acetic acid, until a bottom temperature of about 140°C is obtained. 120 g of n-butyl acetate are now added, and the water/n-butyl acetate azeotrope is distilled off and separated, and the n-butyl acetate phase is recycled to the reaction mixture. The temperature is kept at about 140°C. After about 2 hours the dehydration ceases as no more water separates from the n-butyl acetate distilled off. On cooling a crystallization from the reaction mixture takes place at about 90°C. Work-up of the DAED formed from the reaction mixture can take place by further adding 1080 g of n-butyl acetate at the reaction temperature after the dehydration has been completed.

Hereafter the reaction mixture is cooled to about 20°C whereby the DAED formed crystallizes and can be removed from the mother liquor by filtration.

The mother liquor can be used directly for renewed reaction.

The product yield after vacuum drying is quan- titative with a purity >99%, and the colour of the product is only slightly light yellow. Melting point: 170-171°C

i However, the reaction mixture will typically be directly further processed to TAED, confer the specification of Danish patent application No. 688/87 5

Example 2

Batchwise preparation of DAED while using n-butyl acetate as the auxiliary agent for distilling off 10 water.

3 Moles of ethylene diamine are mixed with 120 g of n-butyl acetate and neutralized with the stoichiome¬ tric amount of about 50% acetic acid. Hereafter the

15 mixture is heated while distilling off the water/n-bu- tyl acetate azeotrope which is separated, and the n-butyl acetate phase is recycled to the reaction mixture. The temperature is increased concurrently with water being removed from the reaction mixture.

20 With the amount of n-butyl acetate added in relation to the starting amount of ethylene diamine it is possible to obtain a reaction temperature of about 140°C.

The reaction temperature can be increased, if

25 it is not possible to reach the desired about 140°C, by removal of some of the n-butyl acetate added, as it is possible to lower the reaction temperature by further addition of n-butyl acetate in relation to the starting amount.

30 Work-up of the product after the dehydration has been completed, is carried out as described in Example 1.

The product yield is quantitative with a purity >99%, and the colour of the product is only slightly

35 light yellow, v Melting point: 170-171°C.

Example 3

Batchwise preparation of DAED while using n-butyl acetate as the auxiliary agent for distilling off water.

The process takes place as described in Example 2, but instead of an about 50% aqueous acetic acid glacial acetic acid is used.

Work-up of the product after the dehydration has been completed, is carried out as described in Example 1.

The product yield is quantitative with a purity >99%, and the colour of the product is only slightly light yellow. Melting point: 170-171°C.

Example 4 (Comparative Example)

Batchwise preparation of DAED without using an auxili¬ ary agent for distilling off water.

To 3 moles of ethylene diamine 7.5 moles of acetid acid is led, whereby the temperature rises to about 120°C The temperature is further increased while distilling off water and acetic acid. When the temperature reaches about 140°C, it is kept constant. After 5 hours the distilling off from the reaction mixture ceases .

The product is cooled while crystallizing, ground and analysed.

The resulting product is hygroskopic and easily deliquesces . The product yield, calculated as DAED, is about 82%, and the purity of the product is about 80% with

about 20% as "salt". The colour of the product is light yellow to light brown. Beginning of melting at 120°C

Example 5

Batchwise preparation of DAED while using diethyl carbonate as the auxiliary agent for distilling off water.

3 Moles of ethylene diamine are mixed with 120 g of diethyl carbonate and neutralized with the stoichio¬ metric amount of about 50% acetic acid. Hereafter the mixture is heated while distilling off the water/di- ethyl carbonate azeotrope which is separated, and the diethyl carbonate phase is recycled to the reac¬ tion mixture. The temperature is increased concurrently with water being removed from the reaction mixture. The reaction temperature is finally kept at about 140°C, until the dehydration ceases.

The solidification temperature of this reaction mixture is about 90°C.

The product yield is quantitative with a purity >99%, and the colour of the product is quite white. Melting point: 172-173°C

Example 6

Batchwise preparation of DAED while using xylene as the auxiliary agent for distilling off water.

3 Moles of ethylene diamine are mixed with 120 g of technical xylene and neutralized with the stoichio¬ metric amount of acetic acid. Hereafter the mixture is heated while distilling off the water/xylene azeotrope which is separated, and the xylene phase is recycled to

the reaction mixture. The temperature is increased con¬ currently with water being removed from the reaction mixture. The reaction mixture is finally kept at about 150°C, until the dehydration ceases. When using aliphatic and aromatic hydrocarbons the reaction mixture consists of 2-phase systems, as the DAED formed is not fully miscible with these types of solvents.

Therefore, when cooling the reaction mixture with xylene, a separation of a phase rich in DAED takes place which begins to solidify around 110°C.

Work-up of the reaction mixture takes place by adding a further 1080 g of technical xylene and cooling the reaction mixture to about 20°C while stirring. Hereby the DAED formed is precipitated as crystals which can be filtered off and dried.

The product yield is quantitative with a purity >99%, and the colour of the product is slightly light yellow. Melting point: 170-171°C.

Example 7

Continuous preparation of DAED from acetic acid and ethylene diamine while dehydrating with methyl iso- butyl ketone (MIBK) as the auxiliary agent for distil¬ ling off water.

To the 1st step in a cascade reaction stoichio- metric amounts of ethylene diamine and acetic acid are led together with MIBK. The acetic acid is added in the form of a 30-50% aqueous acetic acid. 60 kg of MIBK is added per kmol of ethylene diamine added. The reac¬ tion heat from the mixing of the two components raises the temperature to the point where the water/MIBK azeo¬ trope begins to distil.

In the 2nd step in the cascade reaction the aqueous salt solution is heated to 140°C while distil¬ ling off the water/MIBK azeotrope which is separated, and the MIBK phase is recycled to the 2nd step in the cascade reaction.

In the 3rd step in the cascade reaction the temperature is kept at about 140°C while continuously distilling off the water/MIBK azeotrope which is separated, and the MIBK phase is recycled to the 3rd step in the cascade reaction.

From the 3rd step in the cascade reaction the reaction mixture is removed for being further processed to TAED.

Analysis of the product from the 3rd step in the cascade reaction shows a purity >98%. The melting point of a worked-up DAED product is 168-170°C