EP0000930A1 - N-Carboxyalkane-aminoalkane-diphosphonic acids, N-carboxyalkane-azacycloalkane-diphosphonic acids and N-carboxyalkane-aminoarylkane diphosphonic acids, process for their preparation and their use as sequestering agents - Google Patents

Abstract

1. Process for the production of N-carboxyalkane-aminoalkane diphosphonic acids, N-carboxy-alkane-azacycloalkane-diphosphonic acids and N-carboxyalkane-aminoaryl-diphosphonic acids of the general Formula I see diagramm : EP0000930,P8,F1 wherein R**1 is a hydrogen atom, or an alkyl radical of formula -(CH2 )xCH3 with x = 0 to 10, or a hydroxy ethyl radical, or a carboxy methyl radical, or a phenyl radical, or an N,N-bis-(carboxyalkyl)-aminoalkyl radical, or a methyl- or ethyl-phosphonic acid radical, or R**1 together with R**2 is an alkylene group with 3 to 5 C-atoms and forms an azacycloalkane ring with the grouping see diagramm : EP0000930,P8,F2 R**2 is a hydrogen atom, or a methyl radical, or the same radical as R**3 , or R**2 together with R**1 is an alkylene group with 3 to 5 C-atoms and forms an azacycloalkane ring with the grouping see diagramm : EP0000930,P8,F3 R**3 is a carboxy-substituted unbranched alkyl radical with the formula (CH2 )m COOH in which m = 1 to 12, or a 2-carboxy-2,2-dimethyl ethyl radical, or a 1,2-dicarboxy-ethyl radical, characterised in that an amino alkane, azacyclo alkane or aminoaryl alkane diphosphonic acid of the general Formula II see diagramm : EP0000930,P8,F4 wherein R**1 is defined as stated in Formula I and R**4 is a hydrogen atom, or a methyl radical, or R**4 together with R**1 is an alkylene group with 3 to 5 C-atoms and forms an azacyclo alkane ring with the grouping see diagramm : EP0000930,P8,F5 is heated with a corresponding unbranched or branched halogen alkane carboxylic acid or halogen succinic acid, its alkali salts, earth alkali salts or alkali-heavy metal salts or its esters in a molar ratio of 1:1 to 1:3 in aqueous medium at a temperature between 50 and 160 degrees C and at a pH value between 4.0 and 12.0 until the reaction is concluded.

Description

The present invention relates to N-carboxyalkane-aminoalkane-diphosphonic acids, N-carboxyalkane-azacycloalkane-diphosphonic acids and N-carboxyalkane-aminoarylalkane-diphosphonic acids, and a process for their preparation.

From DT-PS 23 18 416 N-carboxymethylaminoalkane diphosphonic acids and N-carboxymethylaminoarylalkane diphosphonic acids are known, which can be obtained by reacting aminoalkane or aminoarylalkane diphosphonic acids in an alkaline medium with formaldehyde and alkali metal cyanide while heating to 70-150 ° C receives.

This process has the disadvantage that very great caution is required when working with alkali metal cyanides, especially on an industrial scale, and therefore extensive safety precautions are essential.

Surprisingly, it has now been found that both the compounds known from German Patent 23 18 416 and new N-carboxyalkane-aminoalkane-diphosphonic acids, N-carboxyalkane-azacycloalkane-diphosphonic acids and N-carboxyalkane-aminoarylalkane-diphosphonic acids are used can produce more favorable working conditions if you use aminoalkane, azacycloalkane or aminoarylalkane diphosphonic acids of the general formula II

bildet, mit gerad- oder verzweigt-kettigen Halogenalkanmonocarbonsäuren mit 2 bis 12 Kohlenstoff-Atomen oder mit Halogenalkandicarbonsäuren bzw. deren Alkalisalzen oder Estern bei Temperaturen von 50 - 160° C im Molverhältnis von 1 : 1 bis 1 : 3 in wäßrigem Medium umsetzt.In which R _{1 is} a hydrogen atom, or an alkyl radical of the formula - (CH ₂ ) _x CH ₃ with x = 0 to 10, or a lower hydroxyalkyl radical, or a lower carboxyalkyl radical, or an aryl radical, or an N, N-bis- ( carboxyalkyl) aminoalkyl radical, or a lower alkylphosphonic acid radical, or R ₁ together with the substituent R _{2 is} an alkylene group having 3 to 5 carbon atoms and an azacycloalkane ring
forms and R _{4 is} a hydrogen atom, or a lower alkyl radical or R ₄ together with the substituent R _{1 is} an alkylene group having 3 to 5 carbon atoms and an azacycloalkane ring with the grouping

forms, with straight-chain or branched-chain haloalkane monocarboxylic acids having 2 to 12 carbon atoms or with haloalkanedicarboxylic acids or their alkali metal salts or esters at temperatures of 50-160 ° C. in a molar ratio of 1: 1 to 1: 3 in an aqueous medium.

in der R₁ wie vorstehend bei Formel II definiert ist, während R₂ ein Wasserstoffatom, oder ein niedriger Alkylrest, oder der gleiche Rest wie R₃, oder R₂ zusammen mit dem Substituenten R₁ eine Alkylengruppe mit 3 bis 5 C-Atomen ist und einen Azacycloalkanring mit der Gruppierung

bildet, und R₃ ein carboxylsubstituierter unverzweigter oder verzweigter Alkylrest, oder ein dicarboxylsubstituierter Alkylrest ist.In this way, compounds of general formula I are obtained

in which R _{1 is} as defined above for formula II, while R _{2 is} a hydrogen atom, or a lower alkyl radical, or the same radical as R ₃ , or R ₂ together with the substituent R _{1 is} an alkylene group having 3 to 5 C atoms and an azacycloalkane ring with the moiety

forms, and R _{3 is} a carboxyl-substituted unbranched or branched alkyl radical, or a dicarboxyl-substituted alkyl radical.

New compounds of this type are N-carboxymethane-azacycloheptane-2,2-diphosphonic acid, N-carboxypentane-1-aminoethane-1,1-diphosphonic acid, N-carboxyethane-1-aminoethane-1,1-diphosphonic acid, N-carboxy -2,2-dimethylpropane-aminomethane-diphosphonic acid, N-10-carboxydecane-aminomethane-diphosphonic acid, N, N-bis-10-carboxydecane-aminomethane-diphosphonic acid and N- (1,1-diphosphonoprop-1-yl) -DL -aminosuccinic acid.

Suitable compounds for the carboxylation of the aminoalkane, aminoarylalkane or azacycloalkane diphosphonic acids are, for example, monochloro- or bromoacetic acid, 6-bromohexanoic acid, 3-chloropropionic acid, 3-chloro 2,2-dimethylpropionic acid (ß-chloro-pivalic acid), 11-bromundecanoic acid, and as dicarboxylic acid bromosuccinic acid.

To produce the substances according to the invention, it is possible to dissolve the aminodiphosphonic acid in excess alkali metal hydroxide solution and then to enter the halocarboxylic acid in such a way that the pH does not fall below 4. The process can be carried out much more elegantly if only as much alkali metal hydroxide solution is introduced as is required for the desired pH between 4 and 12, preferably 7 and 9. The further metering of alkali and halocarboxylic acid is then controlled depending on the pH.

In some cases, the diphosphonic acid and halocarboxylic acid are advantageously suspended in water and completely or partially neutralized with alkali metal hydroxide. Using the heat of neutralization, the reaction time and temperature are 0.5 to 3 hours and 50 - 160 ° C, advantageously 60 to 110 ° C.

In this way, completely or partially neutralized salts are obtained as reaction products, which can be converted into the free acids by means of cation exchangers.

It is also readily possible to use alkali hydroxide, e.g. Alkali carbonate or, for special purposes, alkali and alkaline earth hydroxides together, e.g. Sodium or calcium hydroxide or alkali heavy metal hydroxides, e.g. Use sodium aluminate, sodium zincate or sodium stannate.

Products manufactured in this way are particularly suitable for corrosion protection agents and for products in the treatment of service water.

Depending on the properties or the desired application, the solutions are used directly, the salts crystallize or, after ion exchange, the acid is obtained by methods known per se, such as evaporation concentration or precipitation or extraction with organic solvents.

The carboxylation gives, depending on the molar ratios used and the aminodiphosphonic acid used, single or multiple carboxyalkylated products. With a molar ratio of the reactants of 1: 1, N-carboxyalkane-aminoalkane-diphosphonic acids are preferably obtained. A molar ratio of the reactants of aminodiphosphonic acid: halocarboxylic acid of 1: 2 to 1: 3 preferably gives N, N-bis-carboxyalkane-aminoalkane-diphosphonic acids.

The substances obtained according to the present invention can be used wherever a good complex binding capacity with respect to di- and polyvalent metal ions is required. They are particularly characterized by their resistance to hydrolysis at high temperatures. They can be used in all media in which the hardness constituents of the water interfere or in which all influences of polyvalent metal ions are to be eliminated. The treatment of hard water, textile treatment baths, paper production, photographic processing baths, electroplating baths and tanning are to be mentioned here in detail. These diphosphonic acids are also suitable for stabilizing the water hardness in substoichiometric amounts. They can also serve as stabilizers for dispersions and suspensions.

Since the products according to the invention have the properties of phosphonic acids and aminocarboxylic acids, they offer application-related advantages over the phosphonic acids or aminocarboxylic acids alone, which are greater than the sum of their own of the individual components.

Example 1:

6.72 kg of 50% strength potassium hydroxide solution are placed in a stirred vessel with a thermometer and reflux condenser, and 2.05 kg of 1-aminoethane-1,1-diphosphonic acid are added so that the bottom temperature does not exceed 60.degree. A solution of 1.89 kg of monochloroacetic acid in 2.2 kg of water is then added dropwise in the course of an hour and the mixture is then heated to 100 ° C. for three hours.

After desalting an aliquot of the reaction product using a strongly acidic cation exchanger and concentrating the solution, the N, N-bis-carboxymethane-1-aminoethane-1,1-diphosphonic acid could be crystallized with methanol / ethanol in a yield of 91.3% Theory can be gained.

• ber.: C: 22,40 %, N: 4,36 %, P: 19,29 %
• gef.: C: 22,6 %, N: 4,4 %, P: 19,3 %.
• Molverh.: C : P : N = 5,99 : 1,98 : 1.

The product shows the following analysis:

• calculated: C: 22.40%, N: 4.36%, P: 19.29%
• Found: C: 22.6%, N: 4.4%, P: 19.3%.
• Molverh .: C: P: N = 5.99: 1.98: 1.

Example 2:

28 g of potassium hydroxide are dissolved in 100 ml of water and 20.5 g of 1-aminoethane-'1,1-diphosphonic acid are added. Then 13.9 g of bromoacetic acid are added and the mixture is refluxed for three hours.

The reaction product is treated with an acid exchanger (Lewatit S 100) and the solution is concentrated. The result is a light yellow, viscous oil which is crystallized with methanol / ethanol. After drying in a water jet vacuum at 80 ° C., 25.4 g of N-carboxy are obtained methane-1-aminoethane-1,1-diphosphonic acid, which corresponds to a yield of 96.6% of theory.

Analysis: calc .: C: 18.26%, N: 5.32%, P: 23.55% found: C: 17.6%, N: 5.2%, P: 23.3%. Molverh .: C: P: N = 3.95: 2.02: 1.

Example 3:

47.8 g of aminomethane diphosphonic acid are dissolved in 148 g of 50% potassium hydroxide solution at 60 ° C. and a solution of 99.4 g of the potassium salt of monochloroacetic acid in 250 ml of water is added. The mixture is then heated to 80-90 ° C for three hours.

After working up the reaction solution as described in the previous example, 75.2 g of the N, N-bis-carboxymethane-aminomethane-diphosphonic acid are obtained.

Analysis: calculated: C: 19.56%, N: 4.56%, P: 20.17% found: C: 20.3%, N: 4.7%, P: 20.3%. Molverh .: C: P: N = 5.04: 1.95: 1.

Example 4:

95.5 g of aminomethane diphosphonic acid are dissolved in 224 g of 50% potassium hydroxide solution at 60 ° C., 300 ml of water and 54.3 g of methyl chloroacetate are added. After refluxing for 3 hours, the mixture is allowed to cool.

After working up the solution with an acid exchanger, concentrating, crystallizing and drying, 115 g of N-carboxymethane-aminomethane-diphosphonic acid are obtained, which corresponds to a yield of 92.3% of theory.

Analysis: calculated: C: 14.47%, N: 5.62%, P: 24.87% found: C: 15.1%, N: 5.7%, P: 25.0%. Molverh .: C: P: N = 3.09: 1.98: 1.

Example 5:

13.4 g of phenylaminomethane diphosphonic acid are dissolved in a solution of 8 g of NaOH in 100 ml of water so that the temperature does not exceed 60 ° C., and 4.8 g of monochloroacetic acid are then added. The reaction solution is then kept at 110 ° C. for three hours, allowed to cool and treated with a strongly acidic exchanger.

15 g of crystalline N-carboxymethane-phenylaminomethane-diphosphonic acid are obtained from the concentrated solution with methanol.

Analysis: calculated: C: 33.23%, N: 4.31%, P: 19.05% found: C: 32.8%, N: 4.3%, P: 18.6%. Molverh .: C: P: N = 8.9: 1.95: 1.

Example 6:

54.8 g of 1-aminopropane-1,1-diphosphonic acid are stirred into 200 ml of water and 14.6 g of basic zinc carbonate are slowly added. After the evolution of gas has ceased, 140 g of 50% potassium hydroxide solution are added and, after cooling to 50 ° C., 47.3 g of monochloroacetic acid are added in portions.

After refluxing for two hours, a clear, pale yellow solution of the potassium zinc salt of N, N-bis-carboxymethane-1-aminopropane-1,1-diphosphonic acid is obtained. Thin-layer chromatographic studies show a minimum conversion of 90% of theory. Part of the solution is worked up as described in the previous examples.

Analysis: calculated: C: 25.09%, N: 4.18%, P: 18.48% found: C: 24.5%, N: 4.2%, P: 18.2%. Molverh .: C: P: N = 6.81: 1.96: 1.

Example 7:

90 g of potassium hydroxide are dissolved in 250 ml of distilled water and 103.6 g of aza-cycloheptane-2,2-diphosphonic acid are introduced into this solution in such a way that the temperature does not exceed 60.degree. After adding 38 g of monochloroacetic acid, the mixture is heated to 110 ° C. for 2 1/2 hours. The mixture is allowed to cool and then 102.5 g of N-carboxymethane-aza-cycloheptane-2,2-diphosphonic acid are obtained from the solution by the method described in Example 1.

Analysis: calculated: C: 30.49%, N: 4.44%, P: 19.66% found: C: 30.0%, N: 4.5%, P: 20.0%. Molverh .: C: N: P = 7.8: 1: 2.

Example 8:

41 g of 1-aminoethane-1,1-diphosphonic acid are dissolved in 187 g of 30% strength potassium hydroxide solution with stirring and 39 g of 6-bromohexanoic acid are added at 60.degree. To complete the reaction, the mixture is slowly heated to 100 ° C. and left at this temperature for three hours. After working up according to Example 1, N-carboxypentane-1-aminoethane-1,1-diphosphonic acid is obtained.

A conversion of 73.4% of theory was determined by determining the free amino groups using the Van Slyke method.

Example 9:

140 g of 50% potash are added to a mixture of 51 g of 1-aminoethane-1,1-diphosphonic acid, 27.2 g of 3-chloropropionic acid and 150 ml of water with stirring at 70 ° C. in the course of one hour lye was added dropwise and the clear solution was then refluxed for two hours.

After working up the solution, 57.5 g of N-carboxyethane-1-aminoethane-1,1-diphosphonic acid are obtained.

Analysis: calculated: C: 21.67%, N: 5.05%, P: 22.35% found: C: 20.5%, N: 4.8%, P: 21.3%. Molverh .: C: N: P = 4.98: 1: 2.

Example 10:

34.6 g of 3-chloro-2,2-dimethylpropionic acid (β-chloropivalic acid) are added to a solution of 47.8 g of aminomethane diphosphonic acid in 288 g of 30% strength potassium hydroxide solution with stirring. The solution is heated to boiling within one hour and kept at this temperature for two hours. After working up, N-2-carboxy-2,2-dimethylethane-aminomethane-diphosphonic acid was obtained.

A conversion of 73.5% of theory could be determined by determining the primary amino groups in the solution.

Example 11:

54.7 g of 1-aminopropane-1,1-diphosphonic acid are dissolved in 150 g of 40% sodium hydroxide solution and 49.5 DL-bromosuccinic acid are introduced at 60 ° C. To complete the reaction, the mixture is boiled under reflux for a further two hours.

In the solution, 21 g of 1-aminopropane-1,1-diphosphonic acid and 51.4 g of N- (1,1-diphosphonoprop-1-yl) -DL-aminosuccinic acid were detected by quantitative thin-layer chromatography.

Example 12:

47.8 g of aminomethane-diphosphonic acid are dissolved in 150 g of 50% potassium hydroxide solution, and 88.8 g of 11-bromundecanoic acid are introduced into this solution at 80.degree. After refluxing for 2 hours and cooling the solution, thin-layer chromatographic studies were able to give approximately 30% aminomethane diphosphonic acid, approximately 60% N-10-carboxydecane aminomethane diphosphonic acid and approximately 10% N, N-bis-10-carboxy - Decane-aminomethane-diphosphonic acid can be detected.

Example 13:

127.7 kg of 1-amino-ethane-1,1-diphosphonic acid are placed in 292.2 kg of water and 69.8 kg of 50% potassium hydroxide solution in 292.2 kg of water and 69.8 kg of 50% potassium hydroxide solution in a 1 m ³ stirred tank with reflux condenser, heating, built-in pH combination electrode and two dropping funnels solved. Using the heat of neutralization, the solution is heated to 80 ° C. and 147.7 kg of 80% monochloroacetic acid solution and about 362 kg of 50% potassium hydroxide solution are metered in from the two templates. The addition is controlled so that the pH in the reaction medium is between 8.0 and 8.5. The reaction mixture can be kept at 80 to 90 ° C by the heat of reaction. After the end of the feed, the pH is adjusted to 8.5 with potassium hydroxide solution and the solution is stirred at 90-100 ° C. for one hour.

The resulting solution has a content of about 20% N, N-bis-carboxymethylene-1-aminoethane-1,1-diphosphonic acid.

Example 14:

58.7 g of 3-hydroxy-1-aminopropane-1,1-diphosphonic acid are introduced into a solution of 84 g of KOH in 300 ml of water. The solution is heated to 60 ° C. and 56 g of 3-chloropropionic acid are introduced with vigorous stirring so that the temperature slowly rises to 80 ° C. After refluxing for 3 hours, a pale yellow solution results. After working up the solution using a strongly acidic ion exchanger, concentrating, crystallizing and drying, 81 g of slightly yellowish hygroscopic crystals are obtained. The thin-layer chromatographic analysis shows a content of about 20% N-carboxyethane-3-hydroxy-1-aminopropane-1,1-diphosphonic acid and about 80% N, N-bis-carboxyethane-3-hydroxy-1-aminopropane-1 , 1-diphosphonic acid.

Example 15:

24.9 g of 2-carboxy-1-aminoethane-1,1-diphosphonic acid are dissolved in 119 ml of 30% strength potassium hydroxide solution at 50 ° C. while stirring, and 19 g of 5-bromovaleric acid are introduced at this temperature. The mixture is boiled under reflux for 3 1/2 hours, cooled, the solution is treated with a cation exchanger, the acid solution is evaporated almost to dryness and fractionated with mixtures of methanol, ethanol and acetone. The yield of 2-carboxy-1,1-diphosphono-ethane-1-aminopentanoic acid is 24.5 g.

Analysis: calculated: C: 27.52%, N: 4.01%, P: 17.74% found: C: 27.5%, N: 3.9%, P: 17.8%. Molverh .: C: P: N = 8.23: 2.06: 1.

Example 16:

6.9 g of 1-aminododecane-1,1-diphosphonic acid are dissolved in 56 g of 10% strength potassium hydroxide solution, 2.8 g of 3-chloro-2,2-dimethylpropionic acid are added at 60 ° C. and the mixture is refluxed for three hours. After working up the reaction solution using an acidic cation exchanger, filtering and concentrating the acid solution, 6 g of N-2-carboxy-2,2-dimethylethane-1-aminododecane-1,1-diphosphonic acid are obtained by crystallization with methanol / water.

Analysis: Calculated: C: 45.84%, N: 3.14%, P: 13.91% Found: C: 47.8%, N: 3.2%, P: 14.4%. Molverh .: C: P: N = 17.43: 2.03: 1.

Claims (14)

1. Process for the preparation of N-carboxyalkane-aminoalkane diphosphonic acids, N-carboxyalkane-azacycloalkane-diphosphonic acids and N-carboxyalkane-aminoarylalkane diphosphonic acids of the general formula 1, or their salts,

in the R _{1 is} a hydrogen atom, or an alkyl radical of the formula - (CH ₂ ) _x CH ₃ with x = 0 to 10, a lower hydroxyalkyl radical, or a lower carboxyalkyl radical, or an aryl residue, or an N, N-bis (carboxyalkyl) aminoalkyl, or a lower alkylphosphonic acid residue, or R ₁ together with the substituent R _{2 is} an alkylene group with 3 to 5 C atoms and an azacycloalkane ring with the grouping

educates R _{2 is} a hydrogen atom, or a lower alkyl radical, or the same residue as R ₃ , or R ₂ together with the substituent R _{1 is} an alkylene group with 3 to 5 carbon atoms and an aza cycloalkane ring with the grouping

forms, and R _{3 is} a carboxyl-substituted unbranched or branched alkyl radical, or is a dicarboxyl-substituted alkyl radical,
characterized,
that an aminoalkane, azacycloalkane or aminoarylalkane diphosphonic acid of the general formula II

in the
R ₁ is defined as indicated in formula I, and
R _{4 is} a hydrogen atom, or a lower alkyl radical, or R ₄ together with the substituent R _{1 is} an alkylene group with 3 to 5 carbon atoms and an azacycloalkane ring with the grouping

educates
with a straight or branched haloalkane acid, a haloalkane dicarboxylic acid, its alkali metal salts or its esters in a molar ratio of 1: 1 to about 1: 3 in an aqueous medium at a temperature between 50 ° C and 160 ° C and at a pH between about 4.0 and about 12.0 as long be heated until the reaction is complete. 2. The method according to claim 1,
characterized,
that the pH is maintained between pH 7.0 and 9.0 during the reaction. 3. The method according to claim 1,
characterized,
that the reaction is carried out in a temperature range from about 60 ° C to 110 ° C. 4. The method according to claim 1,
characterized,
that the aminoalkane, azacycloalkane or aminoarylalkane diphosphonic acid react / and a compound of formula II

is in the R _{1 is} a hydrogen atom, or an alkyl radical having 1 to 11 carbon atoms, or a hydroxyethyl radical, or a carboxymethyl radical, or a phenyl radical, or an N, N-bis (carboxymethyl) aminomethyl or ethyl radical, or a methyl or ethylphosphonic acid residue, or R ₁ together with R _{4 is} an alkylene group with 3 to 5 carbon atoms and
R _{4 is} a hydrogen atom, or a methyl radical, or R ₄ together with R _{1 is} an alkylene group with 3 to 5 carbon atoms. 5. An N-carboxyalkane-aminoalkane-diphosphonic acid of the general formula I

in the R _{1 is} a hydrogen atom, or an alkyl radical having 1 to 11 carbon atoms, or an aryl residue, or a lower hydroxyalkyl radical, or a lower carboxyalkyl radical, or R ₁ together with the substituent R _{2 is} an alkylene group with 3 to 5 carbon atoms and an azacycloalkane ring with the grouping

educates R _{2 is} a hydrogen atom, or
the substituent R ₃ , or R ₂ together with the substituent R _{1 is} an alkylene group with 3 to 5 carbon atoms and an azacycloalkane ring with the grouping

forms, and R _{3 is} a carboxyl-substituted unbranched alkyl radical having the formula (CH ₂ ) _m COOH, in which m = 2 to 12, is a carboxyl-substituted branched alkyl radical, or a dicarboxyl-substituted alkyl radical. 6. A compound according to claim 6, in which R1 together with R _{2 is} an alkylene group with 5 C atoms and an azacycloheptane ring with the grouping

educates R _{3 is} a carboxymethyl group and the compound is thus N-carboxymethane-azacycloheptane-2,2-diphosphonic acid. 7. A compound according to claim 6, in which R _{1 is} a methyl radical, R _{2 is} a carboxypentyl radical, R _{3 is} a hydrogen atom and the compound is thus N-carboxypentane-1-aminoethane-1,1-diphosphonic acid. 8. A compound according to claim 6, in which R _{1 is} a hydrogen atom, R _{2 is} a 2-carboxy-2,2-dimethylethyl radical, R _{3 is} a hydrogen atom and the compound is thus N- (2-carboxy-2,2-dimethyl-ethane) aminomethane diphosphonic acid. 9. A compound according to claim 6, in which R _{1 is} an ethyl radical, R _{2 is} a group with the formula -CH-COOH CH ₂ -COOH, R _{3 is} a hydrogen atom and the compound is thus N- (1,1-diphosphonoprop-1-yl) - D, L-aminosuccinic acid. 10. A compound according to claim 6, in which R _{1 is} a hydrogen atom, R ₂ and R _{3 are} 10-carboxydecyl groups and the compound is thus N, N-bis (10-carboxydecane) aminomethane diphosphonic acid. 11. The compound of claim 6, in which R _{1 is} a carboxymethyl group, R _{2 is} a pentanecarboxylic acid residue, R _{3 is} a hydrogen atom and the compound is thus 2-carboxy-1,1-diphosphonoethane - 1-aminopentane carboxylic acid. 12. A compound according to claim 6, in which R _{1 is} an undecyl radical, R _{2 is} a 2-carboxy-2,2-dimethylethyl group, R _{3 is} a hydrogen atom and the compound is thus N- (2-carboxy-2,2-dimethylethane) - 1-aminododecane-1,1-diphosphonic acid. 13. A compound according to claim 6, in which R _{1 is} a hydroxyethyl radical, R _{2 is} a carboxyethyl group, R _{3 is} also a carboxyethyl group and the compound is thus N, N-bis (carboxyethane) -3-hydroxy - 1-aminopropane-1,1-diphosphonic acid. 14. Use of the compounds according to claim 6 in processes for the treatment of aqueous systems with the purpose of eliminating the adverse effects of polyvalent metal ions.