A PROCESS FOR PREPARING N,N,N',N'-TETRAACETYLETHYLENE DIAMINE

Abstract: In a process for preparing N,N,N',N'-tetraacetylethylene diamine (TAED) by reacting N,N'-diacetylethylene diamine with acetic anhydride in an inert organic solvent without using a catalyst and while distilling off the acetic acid formed during the reaction, use is made of an inert organic solvent which does not form an azeotropic mixture with either acetic acid or acetic anhydride or both of them and which has a boiling point higher than that of acetic acid and at the same time sufficiently different from the boiling points of acetic acid and acetic anhydride, respectively, to permit separation by distillation, the solvent furthermore dissolving N,N,N',N'-tetraacetylethylene diamine only slightly at temperatures of about 20 DEG C. The solvent may be an ester of acetic acid, preferably n-butyl acetate or amyl acetate, an ester of carbonic acid, preferably diethyl carbonate, or a ketone, preferably 2-hexanone. Thereby, with a virtually stoichiometric amount of acetic anhydride and at a relatively low temperature, about 100 DEG C or above, TAED in a high yield and in a very high purity is obtained.

Description: A process for preparing N,N,N' ,N' -tetraacetylethylene diamine. This invention relates to a process for prepa¬ ring N,N,N' ,N' -tetraacetylethylene diamine (TAED) by reacting N,N' -diacetylethylene diamine (DAED) with acetic anhydride in an inert organic solvent without using a catalyst and while distilling off the acetic acid formed during the reaction. This process can be represented by the following reaction scheme: CHoNHOCCH^ CH 2 N(OCCH 3 ) 2 I + 2 (CH 3 C0) 2 O + 2 CH 3 COOH CH 2 NHOCCH 3 CH 2 N(OCCH 3 ) 2 Diacetyl- Acetic Tetraacetyl- Acetic ethylene anhydride ethylene acid diamine diamine (DAED) ( AED ) Similar processes are disclosed in various publications as stated below: DE Published Specification (DAS) No. 2,052,822 describes a process for preparing TAED from DAED at 40-150°C while using 1 to 50 moles of acetic anhydride and 1 to 3 moles of etene per mole of DAED. By said process which can be carried out both without a cata¬ lyst and a solvent, according to the sole working example, while using a molar ratio of acetic anhydride to DAED of about 3.4 and a temperature of 140-145°C, a yield of 95.5% of the theoretical is obtained. DE Published Specification (DAS) No. 2,118,281 describes a process for continuously preparing TAED from DAED at 120-170°C while using DAED and acetic anhydride in a weight ratio of from 1:3 to 1:30. The - acetic, acid formed is distilled off concurrently with it b ~ eiήg formed. 50-90% by weight of the reaction mixture is recycled for renewed reaction. In said process, according to the sole working example, use is made of a weight ratio of DAED to acetic anhydride of 1:9, corresponding to a molar ratio of about 12.7, and a temperature of about 140°C whereby a yield of about 85.7% of the theoretical is obtained. DE Published Specification (DAS) No. 2,133,458 describes a process for preparing, inter alia, TAED from DAED by reaction with ketene or acetic anhydride. In the sole working example in said publication which deals with the preparation of TAED, viz. Example 2, the procedure is as follows: 1 Mole of DAED is reacted with 13.1 moles of 95% acetic anhydride at 140°C while distilling off the acetic acid formed. On cooling to 5°C 175.5 g of TAED (77% of the theoretical yield) having a melting point of 145-148°C crystallize out. By evaporating the mother liquor a further precipitation of TAED is obtained so as to bring the total yield up to 91%. DE Published Specification (DOS) No. 2,816,174 describes a process for preparing TAED at 120-170°C while using DAED and acetic anhydride in a weight ratio of from 1:1 to 1:10. Unreacted DAED and triacetyl- ethylene diamine (TriAED) formed are recovered and recycled for renewed reaction. The process proceeds to a conversion of 20 to 70 mole% based on DAED used. The direct yield is stated to be about 64%, with a purity of 99.5 to 99.8%. Recycling of residue from evaporation of the mother liquor results in a total yield of 97 to 98%. In all the Examples of said published specifica¬ tion a molar ratio of DAED to acetic anhydride of about 1:6 is stated. DE Published Specification (DOS) No. 2,832,021 describes a process for continuously preparing TAED in a bubble cap column at 120-190°C, preferably 140-190°C and with ethylene diamine and acetic anhydride in a molar ratio of from 1:2.1 to 1:10, preferably from 1:2.5 to 1:4. The purity of the crude product is stated to be about 95%. Purification of said crude product takes place by distillation at 165°C and 2.5 mbar. The yield of distillation is stated to be about 95%. There is no description of the purity of the distilled pro¬ duct. DE Published Specification (DOS) No. 2,906,606 describes a process which is a further development of the process described in DE Published Specification (DOS) No. 2,816,174. The former specification does not deviate substantially from DE Published Specification (DOS) No. 2,816,174 as regards process description, but elaborate the latter specification by also using, in addition to acetic anhydride, 0.01-0.3 part by weight of ketene per part by weight of DAED. The direct yield is stated to be 61 mole%, based on DAED used. The mother liquor therefrom is recycled to renewed reaction. DE Published Specification (DOS) No. 3,024,694 describes a process which does not differ substantially from the processes described in the above-mentioned publications. However, a molar ratio of DAED to acetic anhydride of at least 1:6 should be used. The direct yield, at a molar ratio of DAED to acetic anhydride of 1:7.05, is stated to be 56%. On recycling of the mother liquor for renewed reaction the total yield is stated to be about 86%. There is no description of the purity of the product. DE Published Specification (DOS) No. 3,042,148 describes a process for preparing TAED from DAED and excess acetic anhydride at 190°C, where the acetic acid formed is removed under vacuum (3 mbar). The molar ra¬ tio of DAED to acetic anhydride as led to a cascade reactor is stated to be 1:2.08. Internally in the cascade, reactor the molar ratio of DAED to acetic anhydride is stated to be 1:15. The yield is stated to be 96 to 97%, and the purity of the product is stated to be 99.2 to 99.5%. By the prior art processes it is only possible to prepare TAED in a very high purity (>99.5%) from DAED and acetic anhydride when using a large excess of acetic anhydride and possibly catalysts, as well as high temperatures. By way of example, at the lowest stated molar ratios of DAED to acetic anhydride in the reaction zone (1:3.4 and 1:8) it is necessary a) to use 1.2 mole of ketene per mole of DAED (DE Published Specification (DAS) No. 2,052,822) or b) to recycle 30-80 mole% of the DAED used, for renewed reaction (DE Published Specification (DOS) No. 2,906,606) in order to obtain a yield of between 96% and 98% and a purity of >99.5%. The temperature range for the processes described in the above-mentioned Published Specifica¬ tions is from 140°C to 190°C. It has now been found that in a process of the type stated by way of introduction, TAED in a very high purity (>99.5%) can be obtained while using acetic an¬ hydride in a virtually stoichiometric amount and at a relatively low temperature, when use is made of an inert organic solvent which is specific in respect of certain properties. Thus, contrary to what appears from the above-mentioned Published Specifications, it is possible at a molar ratio of DAED to acetic anhydride in the reaction zone of between 1:2 and 1:2.1 to di¬ rectly obtain a yield of TAED of >98%, based on DAED used, and a purity of >99.5% without using ketene or recycling the reaction mixture for renewed reaction. Moreover it is possible to carry out the reaction in the temperature range from 100°C to 140 β C. The process of the invention is characterized by using an inert organic solvent which does not form an azeotropic mixture with either acetic acid or acetic anhydride or both of them and which has a boiling point higher than that of acetic acid and at the same time sufficiently different from the boiling points of ace¬ tic acid and acetic anhydride, respectively, to permit separation by distillation, the solvent furthermore dissolving N,N,N' ,N'-tetraacetylethylene diamine only slightly at temperatures of about 20°C. The process of the invention which proceeds, as will appear, in a solvent without use of a catalyst, can be carried out with acetic anhydride in an amount of or below 2.1 moles per mole of DAED and at a tempe¬ rature of about 100°C and above. At reaction tempera¬ tures lower than the boiling point of acetic acid at atmospheric pressure, the reaction is carried out under a slight vacuum. The process of the invention can be carried out batchwise as well as continuously. Use can be made of various advantageous embodi¬ ments of the process of the invention as stated in claims 2 to 6. Thus, as the solvent use can expediently be made of an ester of acetic acid, preferably n-butyl acetate or amyl acetate or the like. As the solvent use can al¬ so expediently be made of an esteϊr of carbonic acid, preferably diethyl carbonate or the like, or a ketone, preferably 2-hexanone or the like. The boiling points at atmospheric pressure of acetic acid, acetic anhydride and the above-mentioned preferred solvents are as follows: Acetic acid 118.1°C piethyl carbonate 126 °C 2-Hexanone 126 °C n-Butyl acetate 126.5°C Acetic anhydride 136. °C Amyl acetate 148.8°C In the process of the invention the solvent is generally used in an amount corresponding to all of the TAED formed being dissolved in the solvent at the reaction temperature. After the reaction has been completed the TAED formed is precipitated by cooling of the reaction mixture, generally to room temperature. Since the TAED is only slightly soluble in the solvent at room temperature, a high yield is obtained which is generally >98%, based on the amount of DAED used. The precipitated TAED is slightly light yellow to light brow . . An expedient embodiment of the process of the invention consists in distilling off acetic acid from the solution during the reaction so that the residual content of acetic acid in the solution is less than 2% by weight. This contributes to obtaining the TAED pro¬ duct in a high purity. According to the invention, in order to obtain the TAED product in a high purity, it is furthermore expedient to perform directly on the reaction mixture a purification by activated carbon. To this end the reac¬ tion mixture can be treated, before the cooling, with 0.1 to 3% by weight (based on the theoretical content of TAED) of activated carbon and 0.03 to 1% by weight of filter aid for % to 1 hour, whereupon the activated carbon and filter aid are filtered off. Thereafter a quite white TAED product will precipitate on cooling. The process of the invention is further illu¬ strated by the following Examples. . . . Example 1 Batchwise preparation of TAED. In a 2-litre flask mounted with a stirrer, a dosing vessel and equipment for distilling-off through a column provided with a reflux distributor, 288 g (2 moles) of DAED and 900 ml of n-butyl acetate are heated to beginning reflux (126°C). From the vessel 428 g (4.2 moles) of acetic anhydride are now dosed over about l hour. When half of the acetic anhydride has been dosed, the distilling-off of the acetic acid formed is started. The distilling-off of the acetic acid is con- tinued after the addition of acetic anhydride has been completed, until the top temperature in the column begins to raise from the boiling point of acetic acid (118°C) to the boiling point of n-butyl acetate (126°C). Here the distillation is discontinued and the reaction mixture is cooled to room temperature while stirring whereby TAED formed crystallizes out. when the reaction mixture has been cooled to room tem¬ perature the crystallized TAED is filtered off and dried. The yield of the process is 452 g of light yellow TAED product containing: >99.5% of TAED <0.2% of TriAED (triacetylethylene diamine) and <0.1% of DAED The melting point of the product is 150°C. - - • Example 2 Batchwise preparation of TAED. In a 2-litre flask mounted with a stirrer, a dosing vessel and equipment for distilling-off through a column provided with a reflux distributor, 288 g (2 moles) of DAED and 900 ml of n-butyl acetate are heated to beginning reflux (126°C) . From the vessel 428 g (4.2 moles) of acetic anhydride are now dosed over about 1 hour. When about half of the acetic anhydride has been dosed, distilling-off of the acetic acid formed is started. The distilling-off of the acetic acid is continued after the addition of acetic anhy- dride has been completed, until the top temperature in the column begins to raise from the boiling point of acetic acid (118°C) to the boiling point of n-butyl acetate (126°C). Here the distillation is discontinued, and 2 g of powdered activated carbon and 1 g of filter aid are added to the reaction mix¬ ture while stirring. After stirring at about 110°C for ή hour the reaction mixture is filtered through a pre-coated pressure filter whereby the activated carbon and filter aid added are removed. Hereupon ' the reaction mixture is cooled to room temperature and crystallized TAED is filtered off and dried. The fil¬ trate which is * limpid can be reused for renewed TAED reaction without regeneration. The yield of the process is 455 g of white TAED product containing: >99.5% of TAED *■ <0.2% of TriAED (triacetylethylene diamine) and <0.1% Of DAED The melting point of the product is 152°C. _ , Example 3 Batchwise preparation of TAED. In a 2-litre flask mounted with a stirrer, a dosing vessel and equipment for vacuum distillation through a column provided with a reflux distributor, 288 g (2 moles) of DAED and 900 ml of amyl acetate are heated to beginning reflux (100°C) at about 250 mbar. From the vessel 428 g (4.2 moles) of acetic an¬ hydride are now dosed over about 1 hour. When about half of the acetic anhydride has been dosed, the di¬ stilling-off of acetic acid formed is started under continuous vacuum (250 mbar). The distilling-off of acetic acid is continued after the addition of acetic anhydride has been completed, until the top temperature in the column begins to raise from the boiling point of acetic acid (80°C at 250 mbar) to the boiling point of amyl acetate (100°C at 250 mbar). Here the vacuum distillation is discontinued and the reaction mixture is cooled to room temperature while stirring whereby TAED formed crystallizes out. When the reaction mixure has been cooled to room temperature, the crystallized TAED is filtered off and dried. The yield of the process is 450 g of light yellow TAED product containing: n>99.5% of TAED <0.2% of TriAED (triacetylethylene diamine) and <0.1% of DAED The melting point of the product is 150°C. - - • Example 4 Continuous preparation of TAED. Into a bubble cap column provided with a reflux distributor and a reboiler DAED suspended in diethyl carbonate (300 kg of DAED per 1000 litres of diethyl carbonate) and acetic anhydride (2.05 moles per mole of DAED) are concurrently pumped through a heat exchanger to about the middle of the column. The temperature of the mixture supplied to the column is kept at about 120°C. The reaction proceeds in the lower part of the column where acetic acid formed is driven off by di¬ ethyl carbonate vapour which is distilled off from the reboiler. In the upper part of the column an enrich¬ ment of the acetic acid driven-off takes place so that an almost pure acetid acid is removed from the reflux distributor. The level in the reboiler is kept constant by continuously pumping away formed TAED dissolved in diethyl carbonate. The work-up of the TAED formed is also effected continuously via a treatment with activated carbon, filtering-off of the carbon and filter aid, cooling to crystallize out TAED, filtering-off the crystallized TAED and drying of the latter. The dried product is white and has a TAED content >99.5%. The melting point of the product is 152-154°C. The yield of the process based on DAED pumped into the column is >98%.

Claims: P A T E N T C .A I M S 1. A process for preparing N,N,N' ^'-tetraace¬ tylethylene diamine by reacting N,N'-diacetylethylene diamine with acetic anhydride in an inert organic solvent without using a catalyst and while distilling off the acetic acid formed during the reaction, characterized by using an inert organic solvent which does not form an azeotropic mixture with either acetic acid or acetic anhydride or both of them and which has a boiling point higher than that of acetic acid and at the same time sufficiently different from the boiling points of acetic acid and acetic anhydride, respective¬ ly, to permit separation by distillation, the solvent furthermore dissolving N,N,N' ,N'-tetraacetylethylene diamine only slightly at temperatures of about 20°C. 2. A process according to claim l, characterized by using as the solvent an ester of acetic acid, preferably n-butyl acetate or amyl acetate. 3. A process according to claim 1, characterized by using as the solvent an ester of carbonic acid, preferably diethyl carbonate. 4. A process according to claim 1, characterized by using as the solvent a ketone, preferably 2-hexa- none. 5. A process according to any one of the prece¬ ding claims, characterised by distilling off acetic acid from the solution during the reaction so that the residual content of acetic acid in the solution is less than 2% by weight. 6. A process according to any one of the pre¬ ceding claims, characterized by performing directly on the reaction mixture a purification by activated carbon.

Inventors: FRIIS NIELS, FRIIS, NIELS
Applicants: CHEMINOVA AS, A/S CHEMINOVA
Application year: 1988
Main classification: C07C102
IPC codes: C07C233