Preparation and use of iminodisuccinic acid salts

A process for the preparation of iminodisuccinic acid alkali metal salts by reaction of maleic acid and ammonia in an aqueous medium in the presence of alkali metal hydroxides and working up thereof.

BACKGROUND OF THE INVENTION 
The invention relates to a process for the preparation of iminodisuccinic 
acid alkali metal salts by reaction of maleic acid and ammonia in an 
aqueous medium in the presence of alkali metal hydroxides and working up 
thereof. The resulting products can be employed as complexing agents for 
alkaline earth metal and heavy metal ions in the fields of detergents and 
cleaning compositions, pharmaceuticals, cosmetics, agriculture, 
electroplating, building materials, textiles and paper. In these fields, 
use as a water softener, bleaching agent stabilizer, trace nutrient 
fertilizer and setting retarder is to be emphasized in particular. The 
invention furthermore relates to the use of iminodisuccinic acid alkali 
metal salts in papermaking. 
Complexing agents have been employed in large amounts for years. Many 
complexing agents customary to date, such as ethylenediaminetetraacetic 
acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic 
acid (NTA) and various phosphonates, are not biodegradable or are 
biodegradable to only a limited degree, remobilize heavy metals in surface 
waters and can even enter drinking water treatment, since they are 
adsorbed neither in sewage sludges nor in soils. Phosphates are complexing 
agents which contribute towards eutrophication of surface waters. 
Summarizing, these are ecotoxicological properties which are found to be a 
disadvantage nowadays. 
It is therefore an important object to develop complexing agents which do 
not have the ecotoxicological disadvantages to date. Iminodisuccinic acid 
is thus a complexing agent which shows a ready biodegradability and 
therefore has an ecotoxicological advantage over the complexing agents to 
date. 
In the future, however, not only will the product properties of chemicals 
which chiefly enter the environment after use be examined critically under 
the aspects described, but also the preparation processes. It was thus 
surprising that an environmentally relevant preparation process could also 
be found for a chemical which is currently not yet available industrially 
and has environmentally relevant properties. 
For iminodisuccinic acid, the following preparation possibilities based on 
maleic anhydride or maleic acid and ammonia are known to date: GB 1 306 
331 describes the preparation of iminodisuccinic acid from maleic acid and 
ammonia in a molar ratio of 2:3 to 2:5 at temperatures of 60 to 
155.degree. C. For working up, either hydrochloric acid or sodium 
hydroxide solution are added. In SU 0 639 863, iminodisuccinic acid is 
prepared from maleic acid and ammonia at a molar ratio of 2:0.8 to 2:1 and 
temperatures of 110 to 130.degree. C. in the presence of alkali metal 
hydroxides. JP 6/329 606 describes a three-stage process for the 
preparation of iminodisuccinic acid. A maleic acid derivative is first 
reacted with ammonia in an aqueous medium. Alkali metal or alkaline earth 
metal hydroxides are then added. In the third process stage, a so-called 
maturation process follows. JP 6/329 607 also describes a three-stage 
process for the preparation of iminodisuccinic acid. In the first stage, a 
maleic acid derivative is again first reacted with ammonia in an aqueous 
medium. Alkali metal or alkaline earth metal hydroxides are then added in 
the second stage. In the third stage, after addition of a further maleic 
acid derivative, the reaction is continued. It is expressly stated in this 
patent application that maleic anhydride, maleic acid or maleic acid 
ammonium salt are employed as maleic acid derivatives. The desired 
reaction is said to take place hardly at all with metal salts of maleic 
acid, so that the aim cannot be achieved. 
It is all the more astonishing that, according to the invention, maleic 
acid and ammonia can be reacted in an advantageous manner to give 
iminodisuccinic acid in high yields precisely in the presence of alkali 
metal hydroxides. 
SUMMARY OF THE INVENTION 
The invention therefore relates to a process for the preparation of 
iminodisuccinic acid alkali metal salts, which is characterized in that 
maleic anhydride (MA), alkali metal hydroxide (MeOH), ammonia (NH.sub.3) 
and water are reacted in a molar ratio of MA:McOH:NH.sub.3 :H .sub.2 
O=2:0.1-4:1.1-6:5-30 at temperatures of 70-170.degree. C., under pressures 
of 1-80 bar over reaction times of 0.1-100 h, ammonia and water are 
distilled off from the reaction mixture at temperatures of 50-170.degree. 
C. under pressures of 0.1-50 bar in the course of 0.1-50 h, with the 
addition of water and 0-4 mol of MeOH per 2 mol of MA originally employed, 
and after the distillation water is added in an amount such that the 
solution formed contains a solids content of 5-60%, based on the total 
weight of the solution. 
DESCRIPTION OF THE INVENTION 
In the process according to the invention, water, alkali metal hydroxide 
(MeOH), maleic anhydride (MA) and ammonia (NH3) are metered into a reactor 
and the maleic acid salt formed is reacted at the reaction temperatures 
(T) and over the reaction times (t) mentioned. Ammonia is then distilled 
off as a mixture with water, with the addition of water and, if 
appropriate, further MeOH. After this distillation, the product is 
adjusted to an expedient concentration by addition of water. If 
appropriate, this product solution can be subjected to a clarifying 
filtration. Me here denotes Li, Na or K, preferably Na or K, particularly 
preferably Na. 
The process according to the invention has the advantage that it can be 
carried out both discontinuously and continuously, and a high degree of 
profitability can be achieved here. This state of affairs is of great 
importance, since in spite of all advantages, environmentally friendly 
products are also only competitive if they can be prepared under 
corresponding economic conditions. The process according to the invention 
produces no waste, since after distillation of the ammonia, which can be 
recycled and further processed and, if appropriate, employed again, the 
product which remains is used completely. According to OECD 301 E, this 
product is moreover readily biodegradable. Economy and ecology are 
combined with one another in the process and product in a hitherto unknown 
manner. 
In the process according to the invention, MA, water and alkali metal 
hydroxide are first mixed with one another in a molar ratio of 
MA:MeOH:water=2:0.1-4:5-30, it being possible for different metering 
variants to be carried out. Thus, MA can first be converted into the 
corresponding maleic acid salts with water via the maleic acid stage, or 
alternatively directly with aqueous alkali metal hydroxide solution. The 
second metering variant has proved to be advantageous for technical and 
chemical reasons. With this it is possible to prepare particularly 
concentrated maleic acid salt solutions of low secondary component content 
in a simple manner. These slightly yellowish solutions contain the 
possible secondary components fumaric acid and malic acid in only small 
amounts. The maleic acid salt is thus used in the further process with 
yields of &gt;92%, preferably &gt;95%, particularly preferably &gt;98% of the 
theoretical amount. 
In respect of a continuous process procedure, continuous and simultaneous 
metering of MA and alkali metal hydroxide solutions into an initially 
introduced maleic acid salt solution has proved to be particularly 
advantageous. Even very pure and also colorless solutions can be obtained 
with equally high yields in this manner. 
Preferably, MA and MeOH are employed in a molar ratio of 2:0.5-3.9, 
particularly preferably 2:0.9-3.5, especially preferably 2:1.5-3.1. 
Preferably, MA and NH3 are employed in a molar ratio of 2:1.2-5.5, 
particularly preferably 2:1.5-4.5, especially preferably 2:1.9-3.5. 
Preferably, MA and H.sub.2 O are employed in a molar ratio of 2:5.5-25, 
particularly preferably 2:6-20, especially preferably 2:6.5-15. 
The maleic acid salt is prepared from MA, MeOH and water at temperatures of 
at least 60.degree. C., for example at 60-130.degree. C., preferably at 
70-120.degree. C., particularly preferably at 80-115.degree. C., at which 
rapid and complete reaction of the MA is ensured and at which a 
stirrability and pumpability of the mixture can be maintained. The maleic 
acid salt can thus be present as a suspension or solution, preferably as a 
solution, which furthermore can be stirred for several hours without 
noticeable losses in yield occurring. 
To the maleic acid salt suspensions or solutions formed from MA, MeOH and 
water is added ammonia in a molar ratio of MA:ammonia=2:1.1-6, preferably 
2:1.2-5.5, particularly preferably 2:1.5-4.5. The addition can equally be 
carried out both in a discontinuous and in a continuous process procedure. 
The maleic acid salt solutions formed from MA, MeOH, ammonia and water are 
reacted at temperatures of 70-170.degree. C., preferably at 80-160.degree. 
C., particularly preferably at 85-150.degree. C., especially preferably 
90-145.degree. C., over reaction times of 0.1-100 h, preferably 0.2-50 h, 
particularly preferably 0.3-25 h, especially preferably 0.5-20 h. The 
reaction can be carried out both in discontinuous and in continuous 
reactors. 
The reaction is as a rule carried out under the pressure which is 
established automatically. Pressures of up to 50 bar, preferably up to 30 
bar, particularly preferably up to 20 bar can occur here. The mixture can 
additionally be covered with a layer of inert gases, in particular in 
discontinuous reactors, in which case pressures of up to 80 bar are 
admissible. 
A maleic acid conversion of &gt;93%, preferably &gt;95%, particularly preferably 
&gt;98% of the theoretical conversion is achieved by the reaction conditions. 
After the reaction, ammonia and water are distilled off from the reaction 
mixture, with the addition of water and 0-4 mol, preferably 0.5-3.5 mol, 
particularly preferably 0.7-3.0 mol, especially preferably 0.9-2.5 mol of 
MeOH per 2 mol of MA originally employed. The water and MeOH can be added 
before or during the distillation, both in the discontinuous and in the 
continuous process. The amount of water added is chosen, taking into 
account the water which unavoidably distils off with the NH3, such that a 
solids content of 75% by weight, preferably 70% by weight, particularly 
preferably 65% by weight, based on the total weight of the batch, is not 
exceeded in the work-up mixture which remains. 
The distillation is carried out at temperatures of 50-170.degree. C., 
preferably at 60-150.degree. C., particularly preferably at 70-140.degree. 
C., especially preferably 80-135.degree. C., under pressures of 0.1-50 
bar, preferably 0.5-20 bar, in the course of 0.1-50 h, preferably 0.3-30 
h, particularly preferably 0.5-25 h, especially preferably 0.9-20 h. Very 
substantial removal of unreacted and hydrolyzable ammonia (for example by 
condensation of the amide nitrogen formed RCONH2+MeOH.fwdarw.RCOOMe+NH3 
where R=the hydrocarbon radical of the carboxylic acid on which the 
compound is based) from the reaction mixture is achieved as a result, and 
this can subsequently be worked up and used for a further processing. A 
minimization of the nitrogen content in the product is furthermore 
achieved as a result, and during use an unnecessarily high introduction of 
nitrogen into surface waters is thus avoided. The content of free maleic 
acid which still remains after the reaction is also reduced further. 
After the distillation, water is added in an amount such that the product 
solution formed has a solids content, calculated as the sum of all the 
alkali metal salts, of 5-60% by weight, preferably 10-58% by weight, 
particularly preferably 15-55% by weight. Thereafter, if required, a 
clarifying filtration can be carried out. Such solutions are virtually 
neutral in odor and stable to storage. 
After the reaction and working up, iminodisuccinic acid and its salts 
(formula 1) are obtained in yields of &gt;65%, preferably &gt;70%, particularly 
preferably &gt;74% of the theoretical yield. The sum of all the secondary 
components and their salts are present in amounts of &lt;35%, preferably 
&lt;30%, particularly preferably &lt;26% of the theoretical amounts, where 
maleic acid and its salts (formula 2) are present in &lt;7%, preferably &lt;5%, 
particularly preferably &lt;2% of the theoretical amount, fumaric acid and 
its salts (formula 3) are present in &lt;20%, preferably &lt;15%, particularly 
preferably &lt;10% of the theoretical amount, malic acid and its salts 
(formula 4) are present in &lt;7%, preferably &lt;5%, particularly preferably 
&lt;3% of the theoretical amount and aspartic acid and its salts (formula 5) 
are present in &lt;25%, preferably &lt;20%, particularly preferably &lt;15% of the 
theoretical amount. 
##STR1## 
X=OH, OLi, ONa, OK, ONH4 
Overall, product solutions in which the components of the formulae 1-5 
mentioned are present in total yields of &gt;93%, preferably &gt;96%, 
particularly preferably &gt;98% of the theoretical yield are obtained. 
According to the OECD 301 E test, the biodegradation of the products is 
more than 70%, usually more than 72%, often more than 74%, after 28 days. 
The carboxyl groups of iminodisuccinic acid and its secondary components 
are present in acid or salt form, according to the amount of MeOH employed 
in the reaction and working up and the amount of ammonia distilled off 
during working up. Thus, in the case where Me=Na, iminodisuccinic acid can 
be obtained as the Na.sub.2 to Na.sub.4 salt, preferably as the Na.sub.3 
to Na.sub.4 salt, particularly preferably as the Na.sub.4 salt, the other 
carboxyl groups being present, as appropriate, as the free acid and as the 
ammonium salt. In the case where LiOH or KOH or a mixed MeOH is employed, 
the carboxyl groups are also present as the lithium or potassium salt. 
The products prepared in the process according to the invention are 
distinguished by very low heavy metal contents. The contents of chromium, 
manganese, iron and nickel ions in total is thus less than 80 ppm, 
preferably less then 60 ppm, particularly preferably less than 30 ppm. The 
content of alkaline earth metal ions is less than 500 ppm, preferably less 
than 200 ppm, particularly preferably less than 100 ppm. The products are 
therefore distinguished as effective complexing agents for alkaline earth 
metal and heavy metal ions. 
In the reaction, MA is employed in the form of a melt, flakes or 
briquettes, preferably a melt or flakes, and ammonia is employed in the 
liquid or gaseous form or as a solution in water, preferably in the liquid 
form or as a solution in water. Aqueous ammonia solutions are employed 
with contents of &gt;15% by weight, preferably &gt;20% by weight, particularly 
preferably &gt;25% by weight of NH3. The alkali metal hydroxides MeOH are 
employed in the reaction and working up undiluted or in aqueous solution. 
Aqueous alkali metal hydroxide solutions are metered into the vessel in 
concentrations of 10-60% by weight, preferably 20-55% by weight, 
particularly preferably 25-50% by weight. 
In a particular embodiment, MA melt is metered into aqueous sodium 
hydroxide solution at temperatures of &gt;60.degree. C. and liquid ammonia or 
concentrated aqueous ammonia solution is then added. The 
MA:NaOH:NH3:H.sub.2 O molar ratio here is 2:1.5-3.5:1.5-3.5:6-20. The 
educts are reacted at temperatures of 90-145.degree. C. over reaction 
times of 0.3-25 h. Water and ammonia are distilled off from the reaction 
mixture at temperatures of 80-135.degree. C. in the course of 0.5-25 h, 
with the addition of water and 0.5-2.5 mol of NaOH per 2 mol of MA 
originally employed. After the addition of water, with which solids 
contents of 5-60% by weight are established and a clarifying filtration, 
product solutions which comprise iminodisuccinic acid in yields of &gt;73%, 
maleic acids in amounts of &lt;3%, fumaric acid in amounts of &lt;10%, malic 
acid in amounts of &lt;5% and aspartic acid in amounts of &lt;15% of the 
particular theoretical yields or amounts are obtained. 
In another particular embodiment, an MA melt and aqueous sodium hydroxide 
solution are metered simultaneously and continuously in a molar ratio of 
MA:NaOH:H.sub.2 O=2:1.5-3.5:6-20 into a maleic acid salt solution or 
pumpable suspension, which has been initially introduced and is of like 
composition, at temperatures of 75-125.degree. C. This solution or 
suspension is pumped, with residence times of 0.1-5 h, into a second 
mixer, into which liquid ammonia or a concentrated aqueous ammonia 
solution is added continuously. The molar ratio of MA:ammonia here is 
2:1.5-3.5. This solution is reacted at temperatures of 90-145.degree. C. 
and residence times of 0.3-25 h in a continuous reactor. Ammonia and water 
are distilled off from the reaction mixture in a continuous distillation 
column at temperatures of 70-140.degree. C. and residence times of 0.1-25 
h, with continuous addition of water and aqueous sodium hydroxide solution 
corresponding to 0.5-2.5 mol of NaOH per 2 mol of MA originally employed. 
After the addition of water, solutions with solids contents of 5-60% by 
weight are obtained, and are subjected to a clarifying filtration, if 
appropriate. The product solutions have yields of &gt;73% of iminodisuccinic 
acid, &lt;3% of maleic acid, &lt;10% of fumaric acid, &lt;5% of malic acid and &lt;15% 
of the particular theoretical yields of aspartic acid. 
In the process according to the invention, product solutions with a high 
iminodisuccinic acid yield and a high complexing capacity are obtained by 
reaction and working up. The secondary components impair neither the 
complexing capacity nor the biodegradation. The products are very 
substantially free from ammonia. They are virtually neutral in odor, 
stable to storage and largely free from troublesome alkaline earth metal 
and heavy metal ions. Secondary components occur by condensation to only a 
very minor extent and are additionally reduced in amount by the working 
up. 
Iminodisuccinic acid alkali metal salts, in particular those prepared 
according to the invention, can be used to increase the degree of 
whiteness and the brightness of plant fibers in papermaking, for example 
in the processing of cellulose or wood pulp (thermomechanical pulp) in the 
pretreatment of fibers or in oxidative or reductive bleaching, for example 
with H.sub.2 O.sub.2 or with sodium dithionite (Na.sub.2 S.sub.2 O.sub.4), 
in particular in the pretreatment of fibers before the bleaching process 
or in reductive bleaching. The invention is further described in the 
following illustrative examples in which all parts and percentages are by 
weight unless otherwise indicated.

EXAMPLES 
The yields and contents stated in the examples relate either to the MA 
employed or to the carbon determined by elemental analysis and have been 
obtained by the following analytical methods: maleic acid, fumaric acid 
and aspartic acid by liquid chromatography (HPLC), malic acid by capillary 
electrophoresis (CE) and iminodisuccinic acid by the calcium carbonate 
dispersing capacity (CCDC). 
The CCDC value is measured at pH 11 in mg of CaCO.sub.3 per g of solid. In 
the example of the iminodisuccinic acid Na.sub.4 salt, the CCDC value 
gives the yield in a good approximation by the following equation: IDA 
Na.sub.4 salt [% of the theoretical yield]=(CCDC-20):2. 
For comparison, for citric acid Na.sub.3 salt and 
ethylenediaminetetraacetic acid Na.sub.4 salt CCDC values of 55 and 280 mg 
of CaCO.sub.3 per g of substance result in this test. The test was carried 
out as follows: 
1.5 g of the substance under investigation (in the case of the comparison 
substances based on 100% Na salt, in the case of the product solutions 
based on the solids content) are dissolved in 90 ml of water, the solution 
is preneutralized, if necessary, and 10 ml of a 10% strength by weight 
Na.sub.2 CO.sub.3 solution are added. The solution is then adjusted to pH 
11 and titrated at 25.degree. C. with a 0.10 molar calcium acetate 
solution until clouding starts, this being generated by calcium carbont 
precipitating out. The titration is monitored with the aid of a light 
conductor photometer. The volume of calcium acetate consumed can be 
determined from the first turning point in the titration curve, and from 
this the amount of calcium ions bonded by the test substance (complexing 
agent) can be calculated. The amount of bonded calcium is stated as 
CaCO.sub.3 /g of test substance. 
The product solutions prepared in the following examples are suitable as 
stabilizers for peroxo compounds in aqueous solution due to the complexing 
action. The stabilization is tested as follows on the example of hydrogen 
peroxide: 
1.5 g of a 33.3% strength H.sub.2 O.sub.2 solution are added to 98 g of 
distilled water. 50 mg of the stabilizer to be tested (based on 100% Na 
salt or solid) are added thereto. The mixture is then adjusted to pH 10.5 
and subsequently heated at 80.degree. C. for 35 minutes. Thereafter, the 
H.sub.2 O.sub.2 content is determined iodometrically. For comparison, the 
residual H.sub.2 0.sub.2 content is determined in a blank sample (without 
stabilizer) treated under identical conditions. The degree of 
stabilization is then determined as follows: 
EQU ((a-b)/(c-b)).times.100=stabilization [%] wherein 
a=H.sub.2 O.sub.2 content in the stabilized sample after heating, b=H.sub.2 
O.sub.2 content in the blank sample after heating and c=initial content of 
H.sub.2 O.sub.2 in the sample. The product prepared in Example 5 showed an 
H.sub.2 O.sub.2 stabilization of 96% in this test. 
Example 1 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:3:2:12.6, 100.degree. C., 48 h. 
A maleic acid Na salt solution which had been formed in sequence from 908 
g=50.44 mol of water, 784 g=8 mol of MA and 480 g=12 mol of NaOH was 
initially introduced into a 3 liter autoclave, 136 g=8 mol of ammonia 
(liquid) were added at 90-100.degree. C. and the mixture was stirred at 
100.degree. C. for 48 h. After dilution with water to 4000 g and after 
addition of 160 g=4 mol of NaOH, 2000 g of aqueous ammonia were distilled 
off from the reaction mixture at 70.degree. C. under 240 mbar. The product 
solution was diluted with water to 4000 g and filtered. The solids 
content, which was taken as the basis for the CCDC value measurement, was 
33.7% by weight. The following yields (% of theory) were obtained: 0.1% of 
maleic acid, 5.6% of fumaric acid, 77.5% of iminodisuccinic acid and 14.6% 
of aspartic acid. 
Example 2 
MA:NAOH:NH.sub.3 :H.sub.2 O molar ratio=2:3:2:12.6, 110.degree. C., 12 h. 
A maleic acid Na salt solution which had been formed in sequence from 227 
g=12.61 mol of water, 196 g=2 mol of MA flakes and 120 g=3 mol of NaOH was 
initialy introduced into a 0.7 liter autoclave, 34 g=2 mol of ammonia 
(liquid) were added at 90-100.degree. C. and the mixture was stirred at 
110.degree. C. for 12 h. After dilution with water at 70.degree. C. and 
after addition of 40 g=1 mol of NaOH, 500 g of ammonia and water were 
distilled off from the reaction mixture at 70.degree. C. under 240 mbar. 
The product solution was diluted with water to 1500 g and filtered. The 
solids content was 22.5% by weight. The following yields (% of theory) 
were obtained: 1.7% of maleic acid, 7.7% of fumaric acid, 78.5% of 
iminodisuccinic acid and 11.7% of aspartic acid. 
Example 3 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:3:2:12.6, 120.degree. C., 6 h. 
The metering sequence, the metered amounts and the working up corresponded 
to Example 2. The reaction mixture was stirred at 120.degree. C. for 6 h. 
The product solution was diluted with water to 1500 g and filtered. The 
solids content was 22.5% by weight. The following yields (% of theory) 
were obtained: 2.0% of maleic acid, 8.5% of fumaric acid, 74.5% of 
iminodisuccinic acid and 11.4% of aspartic acid. 
Example 4 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:3:2:12, 120.degree. C., 6 h 
196 g=2 mol of MA melt and 210 g=2.625 mol of 50% strength sodium hydroxide 
solution were metered simultaneously at 60-70.degree. C. into an initial 
amount of 30 g=0.375 mol of 50% strength sodium hydroxide solution. After 
a clear solution had been obtained at 100.degree. C., 130 g=2 mol of 26.2% 
strength aqueous ammonia solution were added thereto, cooling to 
65.degree. C. taking place. The solution was then stirred in a 0.7 liter 
autoclave at 120.degree. C. for 6 h. After addition of 250 g of water and 
80 g=1 mol of 50% strength sodium hydroxide solution, ammonia and water 
were distilled off at temperatures of 94-111.degree. C. The product was 
diluted with water to 850 g and filtered. The solids content was 39.6% by 
weight. The following yields (% of theory) were obtained: 2.1% of maleic 
acid, 9.0% of fumaric acid, 79.5% of iminodisuccinic acid and 10.1% of 
aspartic acid. 
Example 5 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:3:2:12, 120.degree. C., 6 h. 
240 g=3 mol of 50% strength sodium hydroxide solution were initially 
introduced into the reaction vessel and heated to 60.degree. C. 196 g=2 
mol of MA melt were metered in at 70.degree. C. After a solution had been 
obtained at 100.degree. C., 130 g=2 mol of 26.2% strength aqueous ammonia 
solution were added at 60-70.degree. C. The resulting solution was stirred 
in a 0.7 liter autoclave at 120.degree. C. for 6 h. After addition of 200 
g of water and 80 g=1 mol of 50% strength sodium hydroxide solution, 220 g 
of ammonia and water were distilled off at 75.degree. C. under 240 mbar. 
The product was diluted with water to 750 g and filtered. The solids 
content was 44.9% by weight. The following yields (% of theory) were 
obtained: 2.1% of maleic acid, 8.3% of fumaric acid, 76.0% of 
iminodisuccinic acid and 11.0% of aspartic acid. 
Example 6 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:3:2:12.6, 120.degree. C., 6 h. 
250 kg=2.55 kmol of MA flakes were metered into a initial mixture of 19 kg 
of water and 306 kg=3.825 kmol of 50% strength sodium hydroxide solution. 
After addition of 162 kg=2.57 kmol of 27% strength aqueous ammonia 
solution, the mixture was stirred at 120.degree. C. for 6 h. 450 kg of 
ammonia and water were distilled off at 70-80.degree. C. under 300 mbar, 
with the addition of 102.5 kg=1.28 kmol of 50% strength sodium hydroxide 
solution and 755 kg of water. After the filtration, 1144.5 kg of product 
solution with a solids conent of 37.5% by weight and yields (% of theory) 
of 2.5% of maleic acid, 9.2% of fumaric acid, 4.1% of malic acid, 77.0% of 
iminodisuccinic acid and 10.0% of aspartic acid were obtained. In OECD 301 
E, the product showed a biodegradation of 80% after 28 d. 
Example 7 
MA:NaOH:NH.sub.3 H.sub.2 O molar ratio=2:3:2:6.7, 120.degree. C., 3 h. 
196 g=2 mol of MA melt were metered at temperatures of &gt;75.degree. C. into 
an initial amount of 240 g=3 mol of 50% strength sodium hydroxide 
solution. After addition of 34 g=2 mol of ammonia (liquid), the reaction 
mixture was stirred at 120.degree. C. for 3 h. After addition of 730 g of 
water and 40 g=1 mol of NaOH, 500 g of water and ammonia were distilled 
off at 70.degree. C. under 240 mbar. The product was diluted with water to 
1000 g and filtered. The solids content was 33.7% by weight. The following 
yields (% of theory) were obtained: 5,9% of maleic acid, 7.5% of fumaric 
acid, 78.5% of iminodisuccinic acid and 8.4% of aspartic acid. 
Example 8 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:3:2:6.7, 120.degree. C., 3 h. 
196 g=2 mol of MA were dissolved in 120 g=6.7 mol of water. After addition 
of 120 g=3 mol of NaOH and 34 g=2 mol of ammonia, the mixture was stirred 
at 120.degree. C. for 3 h. After dilution with water to 1200 g and 
addition of 40 g=[lacuna] NaOH, 500 g of ammonia and water were distilled 
off at 70.degree. C. under 240 mbar. The product was diluted with water to 
1000 g and filtered. The solids content was 33.7% by weight. The following 
yields (% of theory) were obtained: 4.7% of maleic acid. 8.8% of flumaric 
acid, 77.5% of iminodisuccinic acid and 8.6% of aspartic acid. 
Example 9 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:4:2:12.6, 100.degree. C., 96 h. 
196 g=2 mol of MA were dissolved in 227 g=12.6 mol of water. After addition 
of 160 g=4 mol of NaOH and 34 g=2 mol of ammonia, the mixture was stirred 
at 100.degree. C. for 96 h. After dilution with water to 1200 g, 500 g of 
ammonia and water were distilled off at 70.degree. C. under 240 mbar. The 
product was diluted with water to 1500 g and filtered. The solids content 
was 22.5% by weight. The following yields (% of theory) were obtained: 
2.7% of maleic acid, 5.6% of fumaric acid, 80.5% of iminodisuccinic acid 
and 7.3% of aspartic acid. 
Example 10 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:2:2:12.6, 110.degree. C., 12 h. 
196 g=2 mol of MA were dissolved in 227 g=12.6 mol of water. After addition 
of 80 g=2 mol of NaOH and 34 g=2 mol of ammonia, the mixture was stirred 
at 10.degree. C. for 12 h. After dilution with water to 1200 g and 
addition of 80 g=2 mol of NaOH, 500 g of ammonia and water were distilled 
off at 70.degree. C. under 240 mbar. The product was diluted with water to 
1000 g and filtered. The solids content was 33.7% by weight. The following 
yields (% of theory) were obtained: 0.5% of maleic acid, 6.7% of fumaric 
acid, 77.0% of iminodisuccinic acid and 11.8% of aspartic acid. 
Example 11 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:2:2:12.6, 120.degree. C., 3 h. 
196 g=2 mol of MA were dissolved in 227 g=12.6 mol of water. After addition 
of 80 g=2 mol of NaOH and 34 g=2 mol of ammonia, the mixture was stirred 
at 120.degree. C. for 3 h. After dilution with water to 1200 g and 
addition of 80 g=2 mol of NaOH, 500 g of ammonia and water were distilled 
off at 70.degree. C. under 240 mbar. The product was diluted with water to 
1000 g and filtered. The solids content was 33.7% by weight. The following 
yields (% of theory) were obtained: 2.7% of maleic acid, 7.2% of fumaric 
acid, 75.0% of iminodisuccinic acid and 11.9% of aspartic acid. 
Example 12 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:2:3:12.6, 100.degree. C., 24 h. 
196 g=2 mol of MA were dissolved in 227 g=12.6 mol of water. After addition 
of 80 g=2 mol of NaOH and 51 g=3 mol of ammonia, the mixture was stirred 
at 100.degree. C. for 24 h. After dilution with water to 1200 g and 
addition of 80 g=2 mol of NaOH, 500 g of ammonia and water were distilled 
off at 70.degree. C. under 240 mbar. The product was diluted with water to 
1500 g and filtered. The solids content was 22.5% by weight. The following 
yields (% of theory) were obtained: 0.6% of maleic acid, 4.5% of fumaric 
acid, 79.5% of iminodisuccinic acid and 15.4% of aspartic acid. 
Example 13 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:2:4:12.6, 100.degree. C., 12 h. 
196 g=2 mol of MA were dissolved in 227 g=12.6 mol of water. After addition 
of 80 g=2 mol of NaOH and 68 g=3 mol of ammonia, the mixture was stirred 
at 100.degree. C. for 12 h. After dilution with water to 1200 g and 
addition of 80 g=2 mol of NaOH, 500 g of ammonia and water were distilled 
off at 70.degree. C. under 240 mbar. The product was diluted with water to 
1500 g and filtered. The solids content was 22.5% by weight. The following 
yields (% of theory) were obtained: 3.4% of maleic acid, 4.5% of fumaric 
acid, 76.5% of iminodisuccinic acid and 14.5% of aspartic acid. 
Example 14 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:2:2:10, 120.degree. C., 3.5 h. 
196 g=2 mol of MA melt were pumped at temperatures of &gt;75.degree. C. into 
an initial mixture of 180 g=10 mol of water and 80 g=2 mol of NaOH in an 
autoclave. After addition of 34 g=2 mol of ammonia, the mixture was 
stirred at 120.degree. C. for 3.5 h. 200 g of water and 80 g=2 mol of NaOH 
were added to the reaction mixture and about 130 g of ammonia and water 
were distilled off. During this operation, the temperature rose. 100 g of 
water were added thereto at 110.degree. C. under normal pressure in the 
course of 1 h and distillation off was repeated. The virtually odour-free 
product was diluted with water to 800 g and filtered. The solids content 
was 42.1% by weight. The following yields (% of theory) were obtained: 
0.6% of maleic acid, 6.7% of fumaric acid, 75.5% of iminodisuccinic acid 
and 13.3% of aspartic acid. 
Example 15 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:2:2:10, 110.degree. C., 7 h. 
196 g=2 mol of MA melt were pumped at temperatures of &gt;75.degree. C. into 
an initial mixture of 180 g=10 mol of water and 80 g=2 mol of NaOH in an 
autoclave. After addition of 34 g=2 mol of ammonia, the mixture was 
stirred at I 110.degree. C. for 7 h. 200 g of water and 80 g=2 mol of NaOH 
were added to the reaction mixture, and about 130 g of ammonia and water 
were distilled off. During this operation, the temperature rose. 100 g of 
water were added thereto at 110.degree. C. under normal pressure in the 
course of 1 h and distillation off was repeated. The virtually odour-free 
product was diluted with water to 800g and filtered. The solids content 
was 42.1% by weight. The following yields (% of theory) were obtained: 
1.3% of maleic acid, 5.9% of fumaric acid, 80.0% of iminodisuccinic acid 
and 11.2% of aspartic acid. 
Example 16 
MA:NaOH:NH.sub.3 :H.sub.2 O molar ratio=2:2:2:10, 130.degree. C., 1.5 h. 
196 g=2 mol of MA melt were pumped at temperatures of &gt;75.degree. C. into 
an initial mixture of 180 g=10 mol of water and 80 g=2 mol of NaOH in an 
autoclave. After addition of 34 g=2 mol of ammonia, the mixture was 
stirred at 130.degree. C. for 1.5 h. 200 g of water and 80 g=2 mol of NaOH 
were added to the reaction mixture, and about 130 g of ammonia and water 
were distilled off. During this operation, the temperature rose. 100 g of 
water were added at 110.degree. C. under normal pressure in the course of 
1 h and distillation off was repeated. The virtually odour-free product 
was diluted with water to 800 g and filtered. The solids content was 42.1% 
by weight. The following yields (% of theory) were obtained: 0.6% of 
maleic acid, 6.5% of fumaric acid, 75.0% of iminodisuccinic acid and 15.6% 
of aspartic acid. 
Example 17 
355 g/h=3.62 mol/h of MA and 501 g/h=3.86 mol/h of 30.8% strength by weight 
sodium hydroxide solution were metered simultaneously and continuously 
into an initial maleic acid Na salt solution of the composition to be 
prepared in a 1 liter stirred tank reactor, while cooling at a temperature 
of 118.degree. C. The solution formed was pumped continuously into a 
cascade of stirred tanks comprising three reactors with a total volume of 
7.4 liters. 68 g/h=4 mol/h of gaseous ammonia were admixed in the first 
reactor of the cascade. The temperature of the reaction solution was kept 
at 109-114.degree. C. The reaction product was then mixed continuously 
with 991 g/h=3.92 mol/h of 15.8% strength by weight sodium hydroxide 
solution in a static mixer. Thereafter, the solution was passed to the top 
of a bubble tray column comprising ten trays and operated with about 520 
g/h of stripping steam. 1037 g/h of ammonia and water were distilled off 
at a bottom temperature of 112.degree. C., an overhead temperature of 
101.degree. C. and a liquid volume of about 1.3 liters, and 1398 g/h of 
product solution were obtained. The solids content was 43.8% by weight. 
The following yields (% of theory) were obtained. 2.3% of maleic acid, 
9.2% of fumaric acid, 77.0% of iminodisuccinic acid and 11.5% of aspartic 
acid. 
Use Example 1 
Increasing the degree of whiteness and brightness in the oxidative 
bleaching of wood pulp (thermo-mechanical pulp) by using the product from 
Example 6 in the pretreatment. 
The wood pulp was beaten at a pulp density of 4% in a disintegrator at 3000 
rpm for 10 min. The product from Example 6 was added as a 1.3% strength by 
weight solution, based on the solids, to the stirred suspension. The 
amount of solids (=total of all the Na salts) here corresponded to 
0.13-0.52%, based on the oven-dried (odr) fibrous material. The action 
time was 30 min at a temperature of 80.degree. C. Dewatering to the pulp 
density of 25% required for the bleaching operation was carried out by 
means of a laboratory filter press. A portion of the complexed heavy metal 
ions was separated off from the fibrous material via the filtrate as a 
result. 0.7% of NaOH as a 1% strength by weight solution and 2% of 
hydrogen peroxide as a 20% strength by weight solution, based on the odr 
fibrous material, were added to the resulting fibrous material. Intensive 
thorough mixing and uniform distribution were achieved by means of a 
laboratory mixer. The bleaching time was 2.5 h at 60.degree. C. After the 
bleaching, specimen sheets were produced with a Rapid-Kothen sheet former 
and the degree of whiteness and brightness were determined in accordance 
with DIN 53.145 and 53.140 respectively. For comparison, an experiment was 
carried out without the 5 addition of a complexing agent in the 
pretreatment. The following results were obtained. 
______________________________________ 
Addition of product from Example 6; 
solids [%], based on the 
Degree of whiteness 
Brightness 
odr fibrous material 
[%] [%] 
______________________________________ 
0.00 57.4 71.2 
0.13 57.7 72.3 
0.26 58.8 73.6 
0.39 60.5 75.3 
0.52 61.9 76.6 
______________________________________ 
In the presence of the product from Example 6, a significant increase in 
the degree of whiteness and brightness is to be found. 
Use Example 2 
Increasing the degree of whiteness and brightness in the oxidative 
bleaching of wood pulp (thermo-mechanical pulp) by using the product from 
Example 6: 
The wood pulp was beaten as in Use Example 1 at a pulp density of 4% in a 
disintegrator at 3000 rpm. After an action time of 30 min at 80.degree. 
C., the suspension was concentrated to a pulp density of 25% by means of a 
laboratory filter press. 0.7% of NaOH as a 1% strength solution, 2% of 
hydrogen peroxide as a 20% strength solution and 0.13-0.52% of product 
(corresponds to the solids) from Example 6 as a 1.3% strength solution 
were added to the resulting fibrous material. The amount employed in each 
case is based on the odr fibrous material. Intensive thorough mixing and 
uniform distribution was achieved by means of a laboratory mixer. The 
bleaching time was 2.5 h at 60.degree. C. After the bleaching, specimen 
sheets were produced with a Rapid-Kothen sheet former and the degree of 
whiteness and brightness were determined in accordance with DIN 53.145 and 
53.140 respectively. For comparison, a bleaching experiment was carried 
out without complexing agent. The following results were obtained: 
______________________________________ 
Addition of product from Example 6; 
solids [%], based on the 
Degree of whiteness 
Brightness 
odr fibrous material 
[%] [%] 
______________________________________ 
0.00 57.4 71.2 
0.13 58.7 72.2 
0.26 59.5 73.2 
0.39 60.4 74.3 
0.52 61.0 75.0 
______________________________________ 
In the presence of the product from Example 6, a significant increase in 
the degree of whiteness and brightness is to be found. 
Use Example 3 
Increasing the degree of whiteness in the reductive bleaching of wood pulp 
(thermo-mechanical pulp) by using the product from Example 6: 
0.26-0.52% of product (corresponds to the solids) from Example 6 and, with 
exclusion of air, 1.0-1.5% of technical-grade sodium dithionite (approx. 
85% strength) were added to the wood pulp at a pulp density of 4% at 
60.degree. C. The amount employed in each case is based on the odr fibrous 
material. After a bleaching time of 1 h at 60.degree. C. (bag bleaching) 
and a pH of 6.0, the degree of whiteness of the TMP was determined. For 
comparison, a bleaching experiment was carried out without complexing 
agent. The following results were obtained: 
______________________________________ 
Addition of product from 
Degree of whiteness 
Degree of whiteness 
Example 6; solids [%], based 
[%] [%] 
on the odr fibrous material 
at 1.0% of Na.sub.2 S.sub.2 O.sub.4 
at 1.5% of Na.sub.2 S.sub.2 O.sub.4 
______________________________________ 
0.00 52.3 53.1 
0.26 53.6 54.3 
0.39 54.0 54.1 
0.52 53.8 53.9 
______________________________________ 
In the presence of the product from example 6, an increase in the degree of 
whiteness is to be found. 
Although the present invention has been described in detail with reference 
to certain preferred versions thereof, other variations are possible. 
Therefore, the spirit and scope of the appended claims should not be 
limited to the description of the versions contained therein.