WO1999058574A1

WO1999058574A1 - Chelating agents

Info

Publication number: WO1999058574A1
Application number: PCT/NL1999/000300
Authority: WO
Inventors: Dorine L. Van Brussel-Verraest; Arie C. Besemer; Jeffrey W. Thornton
Original assignee: Sca Hygiene Products Nederland B.V.
Priority date: 1998-05-14
Filing date: 1999-05-17
Publication date: 1999-11-18
Also published as: AU4172099A

Abstract

The invention provides amino-carboxylic acid derivatives of a carbohydrate, wherein at least one -CHOH- or -CH2OH group per 10 monosaccharide units has been converted to a group having the general formula (1): -CH2-A-[NH-(CH2)n-CH(R1)-CO]m-OH, wherein m is an integer from 1 to 10, n is an integer from 0 to 4, A is a direct bond or a (poly)aminoalkylene group, R1 is hydrogen, carboxyl, or C¿1?-C4 alkyl optionally substituted by hydroxy, methoxy, mercapto, methylthio, substituted mercapto or dithio, amino, guanidino, guanyl, ureido, carboxyl, carbamoyl, phenyl, substituted phenyl or a heterocyclic group, or, if n ¸ 0, R?1¿ may also be amino. Other both carboxylated and aminated carbohydrates are equivalent to the derivatives defined above. All these derivatives are useful for binding transition metals, e.g. before bleaching of pulp.

Description

1

CHELATING AGENTS

The invention relates to novel carbohydrate derivatives having chelating properties and to their use as chelating agents e.g. in the paper and pulp industry.

Chelating agents are used in numerous industrial processes, including the paper and pulp industry. Bleaching of pulp is currently performed using non-chlorine oxidants such as hydrogen peroxide and ozone. These oxidants, however, are decomposed by heavy metals such as iron, copper and manganese from the pulp and therefore these metals must be removed prior to bleaching. Common effective chelating agents used for removing the heavy metals are EDTA (ethylenediamine- tetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid), but they have a serious drawback in that they are not biodegradable and are produced from non- renewable raw materials. Replacement of these chelating agents by degradable and renewable materials is therefore desired.

Aspartic acid derivatives such as iminodisuccinic acid and ethylenediamine- disuccinic acid (EDDS) have been proposed recently as chelating agents alone (WO

97/30209) or in combination with a hydroxy acid such as citric acid or gluconic acid (WO 97/30210). EP-A-167502 discloses metal-binding materials obtained by coupling glycine hydroxamate (H₂N-CH₂-CONHOH) to polysaccharides, poly- acrylate or silica through an epoxide, divinyl sulphone, cyanogen bromide, glutar- aldehyde or the like. EP-A-85661 describes metal-absorbing materials wherein a tris(carboxymethyl)ethylenediamine group is attached to a polysaccharide or another polymer. EP-A-637594 proposes the crosslinking of polysaccharides such as carboxymethyl-cellulose with aspartic acid for producing a water-absorbent resin.

US 4,683,298 discloses amino-deoxy derivatives of oxidised poly- saccharides, including glycine and lysine derivatives of xanthan having low degrees of substitution of below 0.19. The derivatives are obtained by oxidation of one of the hydroxymethylene groups of the polysaccharide to keto groups followed by reductive amination. No specific use is given for these derivatives.

The present invention provides novel chelating compounds which are amino-acid derivatives of carbohydrates. The derivatives contain at least one group of formula 1 per 10 monosaccharide units: 2

-CH₂-A-[NH-(CH₂)_n-CH(R¹)-CO]_m-OH 1 wherein m is an integer from 1 to 10, n is an integer from 0 to 4, A is a direct bond or a group -NH-[CH₂]_p- wherein p is an integer from 2 to 6, R¹ is hydrogen, carboxyl, or C_λ-C alkyl optionally substituted by hydroxy, methoxy, mercapto, methylthio, substituted mercapto or dithio, amino, guanidino, guanyl, ureido, carboxyl, carbamoyl, phenyl, substituted phenyl or a heterocyclic group, or, if n ≠ 0, R¹ may be amino. Substituted phenyl may be e.g. hydroxy-, amino-, carbamoyl- or carboxy-substituted. A heterocyclic group may be e.g. pyridyl, pyrimidyl, pyrrolyl, imidazolyl, thienyl, indolyl or the like. The group R¹ can be derived from common natural or non-natural amino acids or peptides. Preferred amino acids are aspartic acid, glutamic acid, histidine, cysteine and cystine. Most preferred is aspartic acid. The derivatives of the invention also include salts and esters of the carboxylic acids. It is preferred that at least part of the monosaccharide units carrying the group with formula 1 is ring-opened, e.g. by C2-C3 cleavage during oxidation.

The carbohydrate can be any carbohydrate having at least three monosaccharide units and having 1,2-dihydroxyethylene moieties and/or hydroxymethyl groups in at least a part of its monosaccharide units. Suitable carbohydrates include -l,4-glucans, such as starch, amylose, starch hydrolysates and derivatives, dextrins and cyclodextrins; β-l,4-glucans such as cellulose fibres and cellulose derivatives and xanthans; galactans, glucomannans, galactomannans (including guar and locust bean gums), (arabino)xylans, fructans, especially β-2,l-fructans. Most preferred are starch-type carbohydrates, cellulose and inulin.

The derivative can be prepared by oxidation of the carbohydrate in such a manner that 1,2-dihydroxyethylene moieties are converted to dialdehyde groups with ring-opening, e.g. using periodate. The periodate oxidation of starch and other carbohydrates has been known for many years; an improved process is described in WO 95/12619. The dialdehyde can then be reacted with the relevant amine to produce imine functions (Schiff base). The Schiff bases can be reduced in situ to produce an amine having the desired structure. The dialdehyde may also contain carboxyl groups, e.g. obtained by TEMPO oxidation of 6-hydroxy methyl groups in case of gluca s or fructans. Also, part of the aldehyde groups of the dialdehyde 3

carbohydrate may be oxidised to carboxyl groups prior to the amination. An advantage of these products is the presence of carboxyl groups in addition to the amine functions, which adds to the complexing capacity of the product. The derivative can also be prepared by partial oxidation of the carbohydrate in such a manner that hydroxymethyl groups are converted to aldehyde groups. These aldehyde groups are then treated with primary amines and reduced as described above. Again, part of the aldehyde groups may advantageously have been converted to carboxyl groups prior to the amination to improve the complexing capacity. When the oxidised carbohydrate already contains a sufficient level of carboxyl groups, i.e. at least 1 per 10 monosaccharide units, preferably at least 1 per 5 units, the amination of aldehyde groups may be performed with amines not necessarily bearing a carboxyl group, such as ammonia, methyl amine, ethanolamine and ethylenediamine; carboxylated amines such as glycine, aspartic acid and iminodiacetic acid may nevertheless be preferred.

The amination and the reduction can be performed in two steps, but also, and advantageously, in a one-step procedure. Common reducing agents such as sodium borohydride, sodium cyanoborohydride, hydrogen with homogeneous catalysis, dithionite, zinc or iron and hydrochloric acid. For smaller molecules such as inulin and dextrins, heterogeneous catalysis, e.g. hydrogen with palladium or nickel, is preferred, whereas with larger molecules such as starch, homogeneous reduction, e.g. with sodium cyanoborohydride or sodium dithionite is generally preferred. Any residual aldehyde functions may be reduced to alcohol groups, either at the same time as the imine reduction, or afterwards, depending on the actual reducing agent.

The combined amine and carboxyl functions may also be introduced using the Strecker synthesis, by reaction of the carbohydrate-aldehyde with an amine and a cyanide and hydrolysis of the resulting α-aminonitrile, according to the reaction:

R-CHO + NHR⁴R⁵ + HCN → R-CH(NR⁴R⁵)-CN → R-CH(NR⁴R⁵)-COOH

In these formulae, R⁴ and R⁵ are each independently hydrogen, alkyl, aminoalkyl, hydroxyalkyl or carboxy alkyl.

The carbohydrates may be reacted as such, but they may also be crosslinked to obtain a high molecular weight product that can be used in immobilised reactions, e.g. as resins which are useful for absorbing heavy metals from waste waters. The 4

optional crosslinking may be performed before the oxidation, e.g. with epichloro- hydrine or divinyl sulphone, or after oxidation, e.g. with a diamine, or even after the reduction, e.g. with ethylene dibromide or 1,4-diiodobutane. The degree of cross- linking can be varied, e.g. by using from 0.1 to 20 mole% of crosslinking agent with respect to monosaccharide units.

The amino-carboxylic acid carbohydrate derivatives can be used as chelating agents for the removal of heavy metals from paper and pulp prior to or during bleaching e.g. with hydrogen peroxide. The degradation of hydrogen peroxide due to the presence of metal ions is prevented by the addition of the amino-carboxylic carbohydrate derivatives of the invention. The amino-carboxylic acid derivatives can also be used for removal of heavy metals from sludge, waste water and other materials.

Example 1

Reductive amination of dialdehyde polysaccharides with aspartic acid Two grams of 50% oxidised starch (dry matter, 12.4 mmol aldehyde groups) was suspended in 50 ml water and 4 g aspartic acid (24.5 mmol, 2 eq.) was added. The pH of the reaction mixture was adjusted to 6 and then sodium cyanoborohydride (800 mg, 12.7 mmol) was added in small portions. During the reduction of Schiff bases by sodium cyanoborohydride, one proton is consumed, resulting in an increase of the pH. The reaction was performed at room temperature at a constant pH 6

(adding 0.5 M HC1 using a pH-stat equipment). The course of the reductive amination can be monitored by following the HC1 consumption. The reaction time was 48-96 hours. Then, the reaction mixture was adjusted to pH 7 with 0.5 M NaOH and 200 mg of NaBH₄ was added in order to reduce the non-reacted aldehydes. The product was purified by nanofiltration and a white powder was obtained by freeze- drying (yield: 2.1 g). The substitution degree of the products was estimated from the HC1 consumption during the reaction. A more accurate determination of the degree of substitution was carried out by determination of the N-content of the sample. The results of this experiment are given in entry 2 of Table 1. For the other experiments given in Table 1, a similar procedure was followed. Table 1

Reductive amination of DAS and other dialdehyde carbohydrates with amino acids (in situ reduction with NaCNBH₃ at 25°C for 48 h.)

Exp. Starting material Amine DS^e N-cont. DS^f Viscosity (%) of aq. soln.

1 DAS 50% Gly (2 eq.)^d 0.76 4.76 0.74 +++

2 DAS 50% Asp (2 eq.) 0.68 +

3 DAS 100% Asp (2 eq.) 0.84 4.99 1.00 +

4 DAS 80% (?XL°) Asp (2 eq.) 0.54 +++

5 DAI^a 80% Asp (2 eq.) 0.61 -

6 DAC^b 80% Asp (2 eq.) 0.64 +

^a dialdehyde inulin ^b dialdehyde cellulose ^c 0.15% cross-linked with epichlorohydrin equivalents with respect to aldehyde groups ^e degree of substitution estimated from HC1 consumption degree of substitution calculated form nitrogen content (N-cont.)

Determination of the Cu- chelating capacity

The Cu-chelating capacity of the products was determined using a Cu-ion selective electrode. The electrode was calibrated with Cu(NO₃)₂ solutions containing 0.1 M NaNO₃. For the determination of the Cu-chelating capacity, 50 mg of the material was dissolved in 50 ml 0.1 M NaNO₃. This solution was titrated with a 0.1 M Cu(NO₃)₂ solution while measuring the concentration of free Cu(II) ions with the Cu-ion selective electrode. After each addition of Cu solution, the pH was adjusted to 5.5 using a diluted NaOH solution. Additions were made until the concentration of free Cu(II) ions was lower than 10^~5 M. At this point (10^~5 M) the added amount of product was used for the calculation of the Cu-chelating capacity in mmol/g:

CuSC = 0.1 *Λ: ml Cu(NO₃)₂ solution added for Cu(II)_free = 10^~5 M / y g product

The Cu-chelating capacity was compared to the one of DTPA (a commercially available chelating agent) and with free aspartic acid. For some materials, insoluble metal-polysaccharide derivative complexes were formed. The results are given in Table 2. Table 2

Metal-binding properties of the products of reductive amination of DAS and other dialdehyde carbohydrates with amino acids; numbers of experiments correspond to Table 1.

Exp. CuSC (mmol/g) Solubility of Cu(II) complex

1 1.2 —

2 1.4 +

3 1.9 +

4 0.8 -

5 1.5 +

6 1.0 ±

DTPA 2.0 +

Asp 2.8 +

The strength of the Cu-complexes can be expressed by the stability constant. Conditional stability constants (K=[CuL]/[Cu]^*[L])) were measured at pH 5.5 for the carbohydrate derivatives and they were compared with the value for aspartic acid. Although accurate measurement of conditional stability constants was not possible due to the insensitivity of the Cu-ion selective electrode at pCu<5, it is clear that the Cu-complexes of the carbohydrate derivatives are much more stable than the Cu-complex of free aspartic acid (log K' = 5.5-6 for the former, vs. log K' = 4.7 for aspartic acid).

During application in pulp bleaching, a variety of metal ions is present. A requirement for the chelating agent is that it is selective for heavy metals, such as Fe, Cu and Mn, but not for Ca, Mg (the latter are beneficial for the bleaching process). For this reason, the Ca-sequestering capacity of the products was measured. The values were low as compared to the Cu-chelation. The results are shown in Table 3.

Table 3

Ca-sequestering capacity

Exp. CaSC

1 0.24

2 0.33

3 0.60

7

Example 2

Reductive amination of 6-carboxy dialdehyde starch with glycine

Starch was converted into 6-carboxy dialdehyde starch by a two step oxidation method. First the 6-hydroxy groups were oxidised using the TEMPO/Br^" catalysed oxidation (80% oxidation), and then the product was oxidised using periodate to obtain dialdehyde functions (80% oxidation). 6-Carboxy dialdehyde starch (2 g, 17 mmol aldehyde groups on the 2- and 3-positions, 8.5 mmol carboxylate groups on the 6-positions) was dissolved in 50 mL water and 2.6 g glycine (34 mmol, 2 eq.) was added. The pH of the reaction mixture was adjusted to 6 and then sodium cyanoborohydride (1.1 g, 17.5 mmol) was added in small portions. The reaction was performed at room temperature at a constant pH 6 (adding 0.5 M HC1 using a pH-stat. equipment). The reaction time was 48 hours. The reaction mixture was adjusted to pH 7 with 0.5 M NaOH and 200 mg of NaBH₄ was added in order to reduce the non-reacted aldehydes. The product was purified by nanofiltration and a white powder was obtained by freeze-drying (yield: 1.8 g). The substitution degree (glycine moieties) of the product was 0.50 (as determined from the N-content of the product (3.01%)).

The Cu-chelating capacity of the products was determined as described in example 1 (1.77 mmol/g). The conditional stability constant (log K') was estimated to be about 6. The Ca-sequestering capacity was low as compared to the Cu-chelation:

1.0 mmol/g.

Example 3

Reductive amination of 6-carboxy dialdehyde starch with ammonium acetate

Starch was converted into 6-carboxy dialdehyde starch by a two step oxidation method as described in example 3. 6-Carboxy dialdehyde starch (1 g,

8.5 mmol aldehyde groups on the 2- and 3-positions, 4.3 mmol carboxylate groups on the 6-positions) was dissolved in 50 mL water and 2.7 g ammonium acetate (34 mmol, 4 eq.) was added. The pH of the reaction mixture was adjusted to 6 and then sodium cyanoborohydride (0.53 g, 8.5 mmol) was added in small portions. The reaction was performed at room temperature at a constant pH 6 (adding 0.5 M HC1 using a pH-stat. equipment). The reaction time was 48 hours. Then, the reaction mixture was adjusted to pH 7 with 0.5 M NaOH and 100 mg of NaBH₄ was added in order to reduce the non-reacted aldehydes. The product was purified by nano- filtration and a white powder was obtained by freeze-drying (yield: 1.8 g). The substitution degree (amine moieties) of the product was 0.74 (as calculated from the N-content (5.42%)).

The Cu-chelating capacity of the products was determined as described in example 1 (0.44 mmol/g).

Example 4

Reductive amination of dialdehyde starch with aspartic acid and ethylene diamine Two grams of 50% oxidised starch (dry mater, 12.4 mmol aldehyde groups) was suspended in 50 mL water and 4 g aspartic acid (24.5 mmol, 2 eq.) was added. The pH of the reaction mixture was adjusted to 6 and then sodium cyanoborohydride (800 mg, 12.7 mmol) was added in small portions. The reaction was performed at room temperature at a constant pH of 6 (adding 0.5 M HC1 using a pH-stat. equipment). After 24 h reaction, 2.9 g (12 mmol) ethylene diamine was added and the reaction was proceeded for another 48 h. Then, the reaction mixture was adjusted to pH 7 with 0.5 M NaOH and 200 mg of NaBH4 was added in order to reduce the non- reacted aldehydes. The product was purified by nanofiltration and a white powder was obtained by freeze-drying (yield: 2.3 g). The substitution degree of the product was calculated from the N-content after the reaction with aspartic acid and after reaction with ethylene diamine. The reaction product had a substitution degree of 0.83 of aspartic acid units and 0.46 of ethylene diamine moieties. The Cu-chelating capacity was determined as described in example 1 (2.26 mmol/g).

Example 5 Peroxide stability tests with conditions close to those in the bleaching process were carried out. Solutions were prepared containing hydrogen peroxide (10 mM), Mn ions (0.5 mM) and chelating agent. The amount of chelating agent applied was dependent on the binding capacity (1.2 mM CuBC): DTPA 0.3 g/L; DAS-asp (example 1, exp. 3) 0.7 g/L; DAC-asp (example 1, exp. 6) 1.2 g/L; DAI-asp (example 1, exp. 5) 0.8 g/L; CDAS-gly (example 2) 0.7 g/L, DAS-asp-EN (example 4) 0.7 g/L and aspartic acid 0.9 g/L.

The solutions were adjusted to pH 9 and heated at 60°C. After 1 hour and after 2 hours, the residual hydrogen peroxide in the solutions was measured by iodometric titration. The results are shown in Table 4.

The main conclusion from this experiment is that the new derivatives are able to form complexes with Mn ions at pH 9 which are strong enough to prevent the Mn-catalysed peroxide degradation under bleaching conditions. Also, the chelating agents are stable under bleaching conditions (oxidative, pH 9, 60°C, 2 hours). The products DAS-asp, CDAS-gly and DAS-asp-EN perform about as well as DTPA, whereas aspartic acid itself forms only weak complexes with Mn, or, alternatively decomposes (no peroxide stability seen). The adducts from dialdehyde cellulose and inulin and aspartic acid (DAC-asp and DAI-asp) perform less effectively than DTPA, probably due to the lower degree of substitution of the material.

Table 4

Stability of 10 mM Hydrogen Peroxide at pH 9; 60°C; 0.5 mM Mn(II)

chelating agent remaining H O₂ after 1 h remaining H₂O₂ after 2 h (mM) (mM)

DTPA (comp.) 9.4 9.4

DAS-asp 9.4 9.4

DAI-asp 8.2 7.2

DAC-asp 5.3 2.7

CDAS-gly 9.9 9.4

DAS-asp-EN 9.2 8.5

Asp 0 0

Claims

10Claims

1. An amino-carboxylic acid derivative of a carbohydrate, wherein at least one -CHOH- or -CH₂OH group per 10 monosaccharide units has been converted to a group having general formula 1:

-CH₂-A-[NH-(CH₂)_n-CH(R¹)-CO]_m-OH 1 wherein m is an integer from 1 to 10, n is an integer from 0 to 4, A is a direct bond or a group -NH-[CH₂]_p- wherein p is an integer from 2 to 6, R is hydrogen, carboxyl, or C_j- ^ alkyl optionally substituted by hydroxy, methoxy, mercapto, methylthio, substituted mercapto or dithio, amino, guanidino, guanyl, ureido, carboxyl, carbamoyl, phenyl, substituted phenyl or a heterocyclic group, or, if n Γëá 0, R¹ may also be amino.

2. An amino-carboxylic acid derivative according to claim 1, wherein n = 0 and R¹ is carboxymethyl, carbamoylmethyl, carboxyethyl, imidazolylmethyl, mercaptomethyl or ╧ë-aminoalkyl.

3. An amino-carboxylic acid derivative according to claim 1 or 2, containing 2 to 12 groups of formula 1 per 10 monosaccharide units.

4. An amino-carboxylic acid derivative according to any one of claims 1-3, wherein m = 1.

5. An amino-carboxylic acid derivative of a carbohydrate, wherein at least one -CHOH- or -CH₂OH groups per 10 monosaccharide units has been converted to a group having general formula 2:

-CH(NR⁴R⁵)-COOH 2 wherein R⁴ and R⁵ are each independently hydrogen or C_j-C₄ alkyl optionally substituted by hydroxy, amino or carboxyl. 11

6. An amino-carboxylic acid derivative of a carbohydrate, wherein at least one -CHOH- or -CH₂OH groups per 10 monosaccharide units has been converted to a carboxyl group and at least one -CHOH- or -CH₂OH groups per 10 monosaccharide units has been converted to a group having the general formula 3:

-CH₂-A-NR²R³ 3 wherein A is as defined in claim 1, R is hydrogen, C_j- _j alkyl, hydroxy(C₁-C₃ alkyl), carboxy(C₁-C₂ alkyl) or dicarboxy(C₁-C₃ alkyl), and R³ is hydrogen, amino- (C₂-C₃ alkyl), hydroxy(C₁-C₃ alkyl) or carboxy(C₁-C₂ alkyl).

7. An amino-carboxylic acid derivative according to any one of claims 1-6, wherein said carbohydrate is an ╬▒-l,4-glucan, a ╬▓-l,4-glucan or a ╬▓-2,l-fructan.

8. An amino-carboxylic acid derivative according to any one of claims 1-7, wherein said carbohydrate derivative has an average degree of polymerisation of at least 3, preferably at least 8.

9. An amino-carboxylic acid derivative according to any one of claims 1-8, which is crosslinked.

10. A process for producing an amino-carboxylic acid derivative according to any one of claims 1-7, comprising oxidising a carbohydrate to produce a carbohydrate aldehyde, reacting said carbohydrate aldehyde with an amine having the general formula 4:

H-A-tNH CH^-C^R^-COj^OH 4 or an ester or salt thereof, wherein A, m, n and R¹ are as defined in claim 1 or 2, to produce an imine, and reacting the imine with a reducing agent.

11. A process for producing an amino-carboxylic acid derivative according to claim 5, comprising oxidising a carbohydrate to produce a carbohydrate aldehyde, reacting said carbohydrate aldehyde with an amine having the formula HNR⁴R⁵ and cyanide, to produce an aminonitrile group having the formula -CH(NR⁴R⁵)-CN, and 12

hydrolysing said aminonitrile group.

12. A process for producing an amino-carboxylic acid derivative according to claim 6, comprising oxidising a carbohydrate to produce a carbohydrate having aldehyde groups and carboxyl groups, reacting said aldehyde groups with an amine having the general formula HNR R³ wherein R² and R³ are as defined in claim 6, to produce an imine, and reacting the imine with a reducing agent.

13. A process according to any one of claims 10-12, wherein a carbohydrate containing 1,2-dihydroxyethylene groups in its monosaccharide units is oxidised to produce a dialdehyde, which is then reacted with the amine.

14. A process according to any one of claims 10-12, wherein a carbohydrate containing hydroxymethyl groups in its monosaccharide units is oxidised to produce an aldehyde, which is then reacted with the amine.

15. A process according to any one of claims 10-14, wherein the reaction with amine and the reaction with a reducing agent are performed in a single step.

16. A process according to any one of claims 10-15, wherein the carbohydrate is crosslinked prior to or after the oxidation or after the reduction.

17. Use of an amino-carboxylic acid derivative of a carbohydrate according to any one of claims 1-9 as a chelating compound, especially in the paper and pulp industry, as a polarity-inducing compound, especially in films or coatings, and or as a water-absorbing compound, especially in hygiene products.