GB2122191A - A process for preparing N,N%- diacetylethylenediamine - Google Patents

Abstract

N,N%-Diacetylethylenediamine (DAED) is prepared from ethylenediamine and acetic acid by initially using less than 2 moles of acetic acid per mole of diamine, distilling off water of reaction and, if present, of dilution, and then completing the reaction with the addition of excess acetic acid. When the reaction has ended, excess acetic acid and the remaining water is separated in the form of aqueous acetic acid from DAED by distillation.

Description

SPECIFICATION A process for preparing N,N'diacetylethylenediamine The present invention relates to a process for preparing N,N'-diacetylethylenediamine (DAED) by reacting ethylenediamine with acetic acid.

It has already been disclosed (German Offenlegungsschrift 2,828,765) that DAED can be prepared by adding the stoichiometrically necessary amount of acetic acid to ethylenediamine, distilling off at least some of the water contained in the neutralisation mixture, adding excess acetic acid to the remaining neutralisation mixture, then acetylating the ethylenediamine with elimination of water of reaction, and, at the same time, distilling off the resulting aqueous acetic acid. This German Offenlegungsschrift specifically states that the amount of acetic acid "stoichiometrically necessary" for the neutralisation is 2 moles per 1 mole of ethylenediamine.

This method has the disadvantage that in the first step the water distilling off stiil contains sizable amounts of acetic acid. The space-time yield of this process is also unsatisfactory.

There is another known process (European Patent 42,096) for preparing DAED from stoichiometric amounts of ethylenediamine and acetic acid, in which the water distilling off is washed with ethylenediamine. Even after this procedure the distillate still contains 1% by weight of acetic acid and an unspecified amount of ethylenediamine unless more effort is expended on distillation.

It is accordingly the object of the invention to provide a simple process for preparing DAED from ethylenediamine and acetic acid which has a good space-time yield and in which water essentially free of acetic acid can be distilled off.

A process has now been found for preparing DAED from ethylenediamine and acetic acid, which is characterised in that in the steps a) ethylenediamine is initially reacted with less than 2 moles of acetic acid per mole of ethylenediamine and, at the same time, the resulting water of reaction or, subsequently, the water of reaction having been formed and, if present, water of dilution introduced is at least partially distilled off, b) the distillation residue of a) is reacted with excess acetic acid, and c) the reaction mixture of b) is separated by distillation into aqueous acetic acid and essentially pure DAED.

In step a), 50 to 100% by weight strength, preferably 70 to 90% by weight strength, acetic acid is used, the difference to 100% being essentially water. The amount of acetic acid is according to the invention, less than 2 moles per mole of ethylenediamine, for example 1.6-1.99 moles, preferably 1.7-1.9 moles.

The ethylenediamine can likewise be used in the form of an aqueous solution. However, it is preferably used in technically pure form.

The water distilled off in a) is virtually free of acetic acid, so that there is no need to separate water and acetic acid. "Virtually free" is here understood as meaning less than 0.5% by weight of acetic acid in the water. In addition to at least some of the water of dilution which may have been introduced there with the acetic acid and/or the ethylenediamine, 10-70 mol % of the water of reaction, relative to the amount of acetic acid, preferably 20-60 mol %, particularly preferably 30-50 mol %, are distilled off in step a). This water of reaction can be distilled off either at the rate it is formed or after a period of refluxing, if appropriate only after the equilibrium has been established.

The temperature in step a) is in general 140 to 1 800C, preferably 1 50 to 1 700C, and the pressure used can be atmospheric, reduced or superatmospheric, atmospheric pressure being preferred.

In step b), sufficient acetic acid is added for the further reaction so that in total more than 2 moles of acetic acid are used per one mole of ethylenediamine. This molar ratio preferably is 2.1-3:1, particularly preferably 2.2-2.7:1. The concentration of the acetic acid added in step b) is advantageously 80100% by weight. 100% strength acetic acid is preferably used.

The temperature in the steps b) and c) is in general 140 to 2400C, preferably 1 60 to 2300C.

Also in this case it is possible to use atmospheric, superatmospheric or reduced pressure.

In step b), the reaction mixture of a) is reacted with excess acetic acid and, if appropriate, a period of refluxing is maintained.

It is of course also possible to proceed at once to step c) and to continue the reaction after excess acetic acid has been added while aqueous acetic acid is distilled off.

The aqueous acetic acid distilled off in step c) can be re-used without separation as a whole or in part in step a). In this case, sufficient "fresh" acetic acid is additionally added to establish the desired molar ratio. This "fresh"acetic acid is advantageously a concentrated aqueous or an hydros acetic acid containing, for example, 80-1 00% by weight of acetic acid, preferably technically pure acetic acid.

The distillate in step c) consists of further water of reaction, where relevant water of dilution and of excess acetic acid.

The process according to the invention can be carried out on a batchwise or on a continuous basis. Batchwise the reaction can be carried out, for example, in a heatable stirred vessel. The distillation can be carried out with, for example, a simple distillation attachment. However, to carry out the distillation in step a) (distilling off water) it can be advantageous to insert a distillation column, for example a packed column.

In the continuous process, several, for example 2 to 5, preferably three, reaction zones are connected in series, for example three stirred vessels. For example, ethylenediamine and acetic acid are pumped in a molar ratio of 1:1.6-1.99 into the first stirred vessel. Some of the water of reaction and, if present, water of dilution introduced is distilled out of this vessel. Here it is also advantageous to use a packed column for the distillation.

In a preferred embodiment, the dweil time in the 1 st reactor is chosen to be longer than, particularly preferably almost twice as long as, that in each of the two subsequent reactors.

The temperature in the first stirred vessel is advantageously chosen within the range of 140-1 800C so that the amounts of water of reaction specified above distill off in addition to any amounts of water introduced by the ethylenediamine and/or by the acetic acid.

The water thus distilled off contains less than 0.5% of acetic acid. The overflow of the first reactor is passed into the second. In addition, sufficient acetic acid is pumped into this reactor to establish the specified overall molar ratio of acetic acid to ethylenediamine. Aqueous acetic acid is distilled out of this reactor at 1 4O2400 C, preferably at 1 60-2000C. The overflow of the second reactor is passed into the third, from which further acetic acid is distilled off at 170240 C, preferably at 190--2300C. The DAED can be drawn off as the overflow of the third reactor. The aqueous acetic acids are preferably returned as a whole or in part into the first reactor.

It is not necessary to free the DAED completely from acetic acid, since the latter does not interfere with the processing of DAED into tetraacetylethylenediamine (TAED).

In this process, a space-time yield of about 500 g/liter. h is achieved, while the process described in German Offenlegungsschrift 2,828,765 merely achieves 360 g/liter. h.

Not only the batchwise but also the continuous method is advantageously carried out under an inert'gas, for example nitrogen.

The process according to the invention has the advantage that the reaction of ethylenediamine with acetic acid to give pure DAED merely produces essentially pure water as a by-product. A separate distillative working up of aqueous acetic acid is not required. Compared to existing processes, the process according to the invention has the advantage that water essentially free of acetic acid is distilled off with a comparatively small separation effort.

The DAED obtained is used as the starting material for the bleach activator tetraacetylethylenediamine, the preparation of which is described, for example, in U.S. Patent 3,539,629.

EXAMPLE 1 (batchwise method) A 1 liter stirred apparatus which is equipped with a 40 cm packed column was charged under nitrogen with 577 g of 75% strength aqueous acetic acid (7.2 moles). 245 g (4 moles) of 98% strength ethylenediamine were added dropwise with cooling. The mixture was gradually heated to a bottom temperature of 1 600C, while 218.2 g of water which contained less than 0.2% of acetic acid and less than 0.2% of ethylenediamine were distilled off. 1 68 g (2.8 moles) of technically pure acetic acid were added, and the mixture was refluxedfor 1 hour. 197 of 61 % strength aqueous acetic acid were then distilled off under atmospheric pressure by a simple distillation attachment with a descending condenser until the bottom temperature was 1 800C and then under a pressure of 4 kPa until the bottom temperature was 1 900C. The residue consisted of 567.6 g of colourless DAED which had a melting point of 1 740C and contained 0.53% of acetic acid and 0.02% of water.

EXAMPLE 2 (comparative example) The same apparatus as in Example 1 was charged under nitrogen with 635 g (8 moles) of 75% strength aqueous acetic acid. 245 g (4 moles) of ethylenediamine (98% strength) were added within 20 minutes. On heating up gradually as in Example 1, but only up to a bottom temperature of 1400 C, 157 g of water containing 4.5% of acetic acid distilled over.100 g of technically pure acetic acid (1.67 moles) were then added. The temperature was then slowly raised to 1 750C in the course of 2 hours, during which, at the same time, acetic acid was distilled off. The remaining acetic acid was then distilled off under 5 kPa in the course of 1 5 minutes. A total of 233 g of 39% strength acetic acid were distilled off.The residue consisted of 586 g of colourless DAED having a melting point of 1 730C.

The product also contained 1.3% of acetic acid and 0.2% of water.

EXAMPLE 3 (continuous preparation) 426 g/h of ethylenediamine (98% strength) and 879 g/h of 88% strength aqueous acetic acid were pumped into the first reactor of a stirred vessel cascade comprising 3 reactors having 950 ml, 470 ml and 570 ml capacities. 252 g/h of water which contained 0.4% of acetic acid distilled at a bottom temperature of 1 600C from the first reactor via a 30 cm packed column.

The overflow of the 1 st reactor was passed into the second reactor. 370 g/h of technically pure acetic acid were also pumped into this reactor.

The bottom temperature in the second reactor was 1800C.

The overflow of reactor 2 was passed into reactor 3, in which a temperature of 2200C was established. A total of 344.5 g/h of a 67% strength aqueous acetic acid distilled from the reactors 2 and 3, and were mixed with 541 g/h of technically pure acetic acid and returned into the first reactor.

The overflow of the third reactor consisted of 1078.5 g/h of colourless DAED having a melting point of 1 73-1 740 C. The DAED contained 0.3% of water, 7% of acetic acid and 0.3% of monoacetylethylenediamine. This corresponds to a yield of 99.5%. The space-time yield thus was 500.8 g/l . h of DAED.

Claims (12)

1. Process for preparing N,N'-diacetylethylenediamine (DAED) from ethylenediamine and acetic acid, characterized in that in the steps a) ethylenediamine is initially reacted with less than 2 moles of acetic acid per mole of ethylenediamine and, at the same time, the resulting water of reaction or, subsequently, the water of reaction having been formed and, if present, water of dilution introduced is.at least partially distilled off, b) the distillation residue of a) is reacted with excess acetic acid, and c) the reaction mixture of b) is separated by distillation into aqueous acetic acid and essentially pure DAED.

2. Process according to Claim 1, characterized in that the acetic acid in the first process step is used in the form of aqueous acetic acid.

3. Process according to Claim 1 and 2, characterized in that at least some of the aqueous acetic acid distilled off is returned into the first process step.

4. Process according to Claim 1 to 3, characterized in that 1.6 to 1.99 moles of acetic acid are used per mole of ethylenediamine in the first process step.

5. Process according to Claim 1 to 4, characterized in that 1 0-70 mole-% of the water of reaction are distilled off in step a).

6. Process according to Claim 1 to 4, characterized in that 20-60 mole-% of the water of reaction are distilled off in step a).

7. Process according to Claim 1 to 4, characterized in that 30-50 mole-% of the water of reaction are distilled off in step a).

8. Process according to Claim 1 to 7, characterized in that it is carried out in 3 reaction zones connected in series.

9. Process according to Claim 8, characterized in that the dwell time in the first reaction is:chosen to be longer than in the subsequent zones.

10. Process according to Claim 9, characterized in that the dwell time in the first reaction zone is chosen to be about twice as large as in the subsequent zones.

11. Process according to Claim 1, substantially as described in Example 1 or 3.

12. N,N'-diacetylethylenediamine whenever produced by the process of any of Claims 1 to 1- 1..

1 3. Tetraacetylethylenediamine whenever produced from N,N'-diacetylethylenediamine as claimed in Claim 12.