NL8802907A - Di:carbox poly-saccharide(s) prodn. - by oxidn. of di:aldehyde polysaccharide(s) using alkali(ne earth) chlorite(s) - Google Patents

Abstract

Dicarboxypolysaccharides is prepd by oxidn. of dialdehydepoly-saccharides with an ave. degree of polymerisation of at least 5 in an aq. medium using an alkali(ne earth) metal chlorite in the presence of H2O2.

Description

Process for the production of dicarboxypolysaccharides

The present invention relates to the oxidation of dialdehyde polysaccharides to dicarboxy polysaccharides. The products obtained are suitable, inter alia, as builders in detergents.

The functions of an builder builder in detergents are to increase the washing power and soften the washing water, for example by sequestering calcium and magnesium ions. Certain dicarboxy polysaccharides such as dicarboxy starch have excellent sequestering properties and can replace all or part of the commonly used phosphates in detergents (especially pentasodium triphosphate). This replacement is desired because too high a concentration of phosphates in the wastewater contributes to an uncontrolled growth of algae in the surface water. The use of dicarboxy starch in phosphate-free detergents is described in U.S. Pat. No. 3,629,121. Use as a dissolved co-builder in addition to suspended zeolite NaA is also possible.

A known method of manufacturing dicarboxy starch is described in U.S. Patent 2,894,945. According to this method, starch with periodate is first oxidized to dialdehyde starch and then with a chlorite salt to dicarboxy starch. In Figure 1, these oxidations are illustrated by the oxidation of an anhydroglucose monomer in a starch molecule.

In the oxidation of polysaccharides with periodate, a selective oxidation of the vicinal diol groups present takes place, whereby glycol cleavage occurs to form a dialdehyde. Dialdehyde polysaccharides can be prepared with 0.5 to 100% dialdehyde units. A dialdehyde polysaccharide with, for example, 50% dialdehyde units contains on average 50 dialdehyde units per 100 monomer units.

The dialdehyde polysaccharides thus obtained can be converted into dicarboxy polysaccharides by further oxidation with chlorite salts. Here the aldehyde groups or a part thereof are converted into carboxyl groups. The resulting dicarboxy polysaccharides are also referred to as dicarboxyl polysaccharides, dicarboxylated polysaccharides, polysaccharide dicarboxylic acids or polysaccharide dicarboxylates,

The method described in U.S. Pat. No. 2,894,945 has drawbacks and disadvantages.

Oxidation of the dialdehyde starch requires at least 3 equivalents of chlorite salt per aldehyde group, but only 1 equivalent is effectively used for the oxidation of aldehyde groups to carboxyl groups. The remaining two or more equivalents of chlorite salt are converted into the toxic chlorine dioxide gas. These drawbacks and disadvantages make the process of U.S. Pat. No. 2,894,945 unattractive for practical implementation.

The present method aims to provide a method for oxidizing dialdehyde polysaccharides to dicarboxy polysaccharides without the aforementioned drawbacks and disadvantages.

The present invention relates to processes for the production of dicarboxy polysaccharides by oxidation of dialdehyde polysaccharides with an average degree of polymerization of at least 5 in an aqueous medium using an alkali metal or alkaline earth metal chlorite, characterized in that the oxidation is carried out in the presence of hydrogen peroxide.

The oxidation in the presence of hydrogen peroxide has advantages over the process of U.S. Pat. No. 2,894,945. The process according to the invention makes it possible to reduce the amount of chlorite required from at least 3 moles of chlorite (preferably 4) per mole of aldehyde groups to 1 mole of chlorite per mole of aldehyde groups when using 1 mole of hydrogen peroxide as a co-reagent. The selectivity of the oxidation is thereby retained. All this means significant cost savings. A further advantage of the use of the method according to the invention is the avoidance of the formation of the toxic chlorine dioxide gas during the oxidation. In addition, in the process of the invention chain degradation (depolymerization) is largely prevented, resulting in high molecular weight dicarboxy polysaccharides.

The process according to the invention is based on dialdehyde polysaccharides obtained by periodate oxidation of polysaccharides with an average degree of polymerization of at least 5 and with 2 vicinal OH groups in the monomer units. Examples of suitable polysaccharides are starch and physically, enzymatically and / or chemically (dextrinated, oxidized, acid-modified, esterified, etherified and / or cross-linked) modified starch, maltodextrins, cyclodextrins, cellulose and modified cellulose products, dextrans and alginates. The percentage of dialdehyde units in the dialdehyde polysaccharide to be oxidized can vary within wide limits, namely between 0.5 and 100%.

The reaction is preferably carried out in an aqueous medium. The amount of water is not critical. Preferably 1 to 100 parts by weight of water per part by weight of dialdehyde polysaccharide are used. Preferably, the reaction medium is stirred during the oxidation.

As the oxidizing agent, water-soluble inorganic salts of chlorous acid are used, namely alkali metal or alkaline earth metal chlorites. Preferably sodium chlorite or potassium chlorite are used.

In order to achieve a virtually complete conversion of aldehyde groups to carboxyl groups, at least 1 mole of chlorite per mole of aldehyde groups (CHO) is required.

The amount of hydrogen peroxide used is preferably about 1 mole hydrogen peroxide per mole chlorite.

During the reaction, the pH of the reaction medium is preferably between 3 and 8. The desired pH can be adjusted, if necessary, using a weak acid such as acetic acid or propionic acid. The reaction temperature can vary within wide limits, but is preferably between 0 and 100 ° C. The reaction time depends on the reaction conditions. During the reaction, the dialdehyde polysaccharide is gradually converted into the much more soluble dicarboxy polysaccharide. In the case of the polysaccharide starch, it is preferred to start from a suspension of granular dialdehyde starch (heterogeneous system) which gradually changes into an aqueous solution of dicarboxy starch (homogeneous system) during the reaction.

After the oxidation is complete, the dicarboxy polysaccharide can be isolated in various ways. Preferably, the pH of the reaction medium is first adjusted to about 9 by adding a base such as caustic soda. A residual amount of excess oxidant can be reduced by adding, for example, sodium sulfite. Salt-containing (sodium chloride, sodium acetate) end products are obtained by drying the entire reaction mixture by evaporation, lyophilization or spray drying. Salt-free or low-salt end products are obtained by precipitating the dicarboxy polysaccharide as poly sodium salt by adding an organic solvent such as ethanol, propanol, isopropyl alcohol, acetone and the like to the reaction mixture. The gummy precipitate can be dried or redissolved in water and reprecipitated with, for example, ethanol to further remove salts.

The salts can also be removed from the reaction mixture by dialysis (membrane separation). The dicarboxypolysaccharide can then be obtained as a dry product by evaporation, spray drying, precipitation or freeze drying. The product is obtained as sodium salt.

Since the dicarboxypolysaccharides contain carboxyl groups, these products can be converted into the desired salt form before or after isolation from the reaction medium. For example, by treating them with aqueous solutions of potassium hydroxide, potassium salts of dicarboxy polysaccharides can be obtained. Similarly, other organic or inorganic salts can be obtained, for example, from calcium, copper, iron or ammonium. The dicarboxy polysaccharides can be converted into the free acid form by means of ion exchangers. The water-soluble salts of dicarboxy polysaccharides are particularly suitable for use as detergent builder.

The products obtained according to the method of the invention are suitable as a substitute for phosphates in detergents in their function as builder.

Generally speaking, these products can also be used as a sequestrant of metal ions, in particular the polyvalent metal ions calcium, magnesium, barium, copper, iron and manganese, in all cases where the presence of these metal ions can have disturbing effects. Thus, deposits of insoluble salts in cooking equipment, heat exchangers and the like can be prevented. Furthermore, dicarboxypolysaccharides in amounts of, for example, 1 to 5% by weight, can be included in soaps and synthetic detergents to achieve better washing results, by keeping suspended dirt in suspension and preventing it from re-depositing on the washed textile products. The characterization of the end products is as follows.

The degree of oxidation of the dicarboxy polysaccharides is determined by an acid-base titration.

The reaction product is carefully weighed, dissolved in water and brought into the COOH with the aid of a strongly acidic ion exchanger. An excess of sodium hydroxide solution is then added and the solution is titrated back with a hydrochloric acid solution to pH 7, after which the carboxyl content of the product can be calculated. Since the aldehyde content of the starting material is known, the total composition of the product can be calculated from this.

The calcium sequestering capacity of the products is determined by titration using a calcium ion selective electrode.

To a solution of 100 mg of dicarboxypolysaccharide (Na salt) in 100 ml of distilled water at pH 11 (adjusted with ammonia) and ionic strength 0.02 (adjusted with sodium chloride), in steps of 0.200 ml with an interval of 2 minutes, a 0.1 M calcium chloride solution added. After each addition, the concentration of uncomplexed calcium ions is measured using a calcium ion selective electrode.

The sequestering capacity of a complexant is defined as the number of mmol of calcium ions that can be added to a solution of 1 gram of the complexant (under the above conditions) until the concentration of non-complexed calcium ions exceeds -5 M (this value applies as the maximum permissible calcium concentration during the washing process).

The sequestering capacity is expressed as mmol Ca 2 + / gram complexant. For comparison: The sequestering capacity of two commonly used builders in detergents is: - sodium tripolyphosphate: 2.00 mmol / g - copolymer acrylic acid-maleic acid (70:30): 2.78 mmol / g

The invention is illustrated by the following examples.

Example 1

To a suspension of 4.0 grams of dialdehyde starch (aldehyde content 99%, 50 mmol aldehyde groups) in 200 ml of water in a thermostated reaction vessel (20 ° C) with a mechanical stirrer, 5.0 grams of 35% hydrogen peroxide solution (50 mmol) were added. Then, a solution of 5.66 grams of sodium chlorite (80% pure; 50 mmol) and 1.0 gram of acetic acid (17 mmol) in 15 ml of water (pH 5) was added dropwise over 30 minutes. During the reaction, a solution of 2.5 M sodium hydroxide was added to keep the pH constant at 5. The reaction was completed after 8 hours. The pH of the reaction mixture was adjusted to 9 with 2.5 M sodium hydroxide solution. By adding two volumes of 96% ethanol, the dicarboxy starch was obtained as a gummy precipitate. The precipitate was dissolved in 50 ml of water and freeze-dried. 5.59 grams of dicarboxy starch were obtained in the form of the sodium salt, yield 98%. The carboxyl content was 7.21 mmol / g, which corresponds to 80% oxidation of aldehyde to carboxylic acid groups. The product thus still contains 1% vicinal diol groups, 20% aldehyde groups and 79% carboxyl groups. The calcium sequestering capacity is 2.67 mmol / g.

Example 2

The oxidation of dialdehyde starches with different aldehyde contents was carried out according to the procedure of Example 1 with the proviso that the amounts of sodium chlorite, acetic acid and hydrogen peroxide were reduced in proportion to the aldehyde content of the starting material, so that the molar ratio of the reagents was the same as in Example 1 The results of these oxidations are as follows: No. aldehyde carboxyl conversion yield sequestering groups groups of aide capacity output product hyd- to 0 carboxyl groups%%%% mmol / g 1 20 13 65 82 0.16 2 46 26 57 76 0.39 53 66 41 62 80 0.99 4 87 61 70 84 2.27 5 99 79 80 98 2.67

These examples indicate that in all cases 1 oxidation of aldehyde to carboxylic acid groups takes place.

However, for excellent calcium sequestering capacity (higher than that of sodium tripolyphosphate), the products should contain more than 60% carboxyl groups.

Thus, the oxidation is preferably conducted so that the percentage of carboxyl groups is greater than 60%.

Example 3

In order to determine the influence of the amounts of sodium chlorite and hydrogen peroxide used on the conversion of aldehyde to carboxylic acid groups, the oxidation was carried out with a number of different reagent ratios. The starting material was dialdehyde starch with an aldehyde content of 99%, the experiments were carried out as in Example 1, the molar ratio of aldehyde groups: sodium chlorite: hydrogen peroxide being varied according to the table below. The results were as follows.

no. reagent dicarboxy conversion of rec. sekwestr.

attitude units aldehyde to capac.

aldehyde: in product carboxyl

NaCl02: H202 groups%%% mmol / g 1 1: 0.8: 0.8 69 70 91 2.24 2 1: 1: 1 79 80 98 2.67 3 1: 1.5: 1.5 80 81 91 2.39

These results clearly show that a 1: 1: 1 ratio gives the best results. r, and lower oxidant gives a lower conversion of aldhyd to carboxyl groups. An excess of oxidant does not give a higher conversion than with the 1: 1: 1 ratio. Although complete conversion of aldehyde to carboxyl groups is not obtained, all products have excellent sequestering capacity, especially the product of the oxidation with a reagent ratio of 1: 1: 1.

Example 4

Dialdehyde starch having an aldehyde content of 99% was oxidized by the method of Example 1. The same starting material was also oxidized by the hitherto known process of U.S. Patent 2,894,945 requiring three (or more) equivalents of sodium chlorite to convert to dicarboxy starch. This section was performed as follows:

To a suspension of 4 grams of dialdehyde starch (aldehyde content 99%; 50 mmol aldehyde groups) in 200 ml water in a thermostated reaction vessel (20 ° C) with a mechanical stirrer, a solution of 17.6 grams sodium chlorite (80%; 156 mmol) was added over 30 minutes and Drop 5.9 grams of acetic acid (98 mmol) in 25 ml of water. The pH is 4.0, which rose to 4.5 during the reaction. After 8 hours, nitrogen gas was passed through the solution to remove the chlorine dioxide gas until the solution was colorless.

The solution was adjusted to pH 9 with a 2.5 M solution of sodium hydroxide. By adding 2 volumes of 96% ethanol, the dicarboxy starch was obtained as a gummy precipitate. The precipitate was dissolved in 50 ml of water and freeze-dried (yield 6.54 grams; 93%; carboxyl content 7.68 mmol / g). This corresponds to 88% oxidation of aldehyde to carboxylic acid groups.

Thus, the dicarboxy starch contains 1% vicinal diol groups, 12% aldehyde groups and 87% carboxyl groups. The calcium-sequestering capacity is 2.20 mmol / g. The oxidation according to the new method (example 1) yields a product with a slightly lower percentage of carboxylic acid groups (79%), however the sequestering capacity of this product (2.67 mmol / g) is better than that of the dicarboxy starch prepared according to the known procedure.

Obviously, the slightly lower conversion of aldehyde to carboxylic acid groups in the improved method does not adversely affect the sequestering properties of the oxidation product.

Example 5

Dialdehyde cellulose (98% aldehyde content) was oxidized according to the method of Example 1. The dicarboxy cellulose obtained (5.18 grams, 93% yield; carboxyl content 7.40 mmol / g) contains 2% vicinal diol groups, 16% aldehyde groups and 82% carboxyl groups. The sequestering capacity is 2.30 mmol / g. Dicarboxy cellulose is therefore also an excellent sequestrant. It appears that the nature of the glycosidic bond (ct-1.4 for the starches, 8-1.4 for cellulose) has little influence on the sequestering properties of the dicarboxy polysaccharides.

Claims (5)

A process for the production of dicarboxy polysaccharides by oxidation of dialdehyde polysaccharides with an average degree of polymerization of at least 5 in an aqueous medium using an alkali or alkaline earth metal chlorite, characterized in that the oxidation is carried out in the presence of hydrogen peroxide. 2. Process according to claim 1, characterized in that dialdehyde polysaccharide is used as dialdehyde polysaccharide. 3. Process according to claim 1, characterized in that dialdehyde cellulose is used as dialdehyde polysaccharide. 4. Process according to claims 1-3, characterized in that the oxidation is carried out at a pH of 3 to 8. 5. Process according to claims 1-4, characterized in that the chlorite salt used is sodium chlorite or potassium chlorite.