DD298643A5 - PROCESS FOR PREPARING WATER-SOLUBLE SULFUR ACIDS HALF-PRESENT OF CELLULOSE AND RELATED POLYSACCHARIDES - Google Patents

Abstract

The invention relates to a process for the preparation of water-soluble sulfuric acid semi-esters of cellulose and related polysaccharides with the aim and the task to carry out a homogeneous sulfation by varying the reaction conditions without isolation of the intermediates. According to the invention, the starting materials are activated in the presence of aprotic solvents by an amine or ammonia treatment, silylated with trimethylchlorosilane, sulfated and subsequently converted into the stable salt form. The sulfuric acid semi-esters are water-soluble and can be used in the food industry, biotechnology, pharmacy and medicine. {Cellulose; Strength; Sulfuric acid; silylation; sulfation; Activation; homogeneous derivatization}

Description

Field of application of the invention

The invention relates to a process for the preparation of water-soluble sulfates of cellulose and other polysaccharides, which are used as viscosity enhancers, thickeners, gel-forming additives and as components for the production of membranes and microencapsulation or as biologically active polymers in a variety of applications in the food industry, biotechnology, Pharmacy and medicine can be used.

Characteristic of the known state of the art

For the preparation of sulfates of cellulose and other polysaccharides nind numerous processes are known in which the polymer is usually reacted under heterogeneous reaction conditions or under transition from heterogeneous to homogeneous reaction system with sulfuric acid, its anhydride or ^ol r.dm acid chloride of sulfuric acid in a nonaqueous medium. Here, in most cases, products are obtained which are either not or only at a high degree of substitution of> 1.5 completely soluble in water and in their preparation undergo a significant chain length degradation, so that they are unsuitable for a number of the aforementioned applications. Comprehensive sets of preparation methods, including the patent literature on cellulose sulfates are described in "Methods of Organic Chemistry" (Houben-Weyl) G. Thieme Verlag Stuttgart 1987, Vol. E 20/3, p.2119-2121 and B. Philipp u. W Wagenknecht, Cell Chem., Technol 17 (1983), 443-459 Corresponding reviews for sulfates of starch can be found in "Methods of Organic Chemistry" (Houben-Weyl) G. Thieme-Varlag Stuttgart 1987, Vol 20/3, pp. 2161-2163 and for various other polysaccharides in KB Guiseley "Sulfation of Polysaccharides", ACS Symp. Ser 77 (1978), 148-162 .Thus, from a technical-economical point of view, the technical relevance of synthesis method is especially important Cellulose or starch base too.

To achieve less degraded and already at low level of substitution (0.3) completely water-soluble sulfates of cellulose, it is according to current knowledge (RG Schweiger, Carbohydrate Sulfates, ACS Symp. Ser. 77 (1978), 163-172) rather necessary, the cellulose first in a homogeneous system in a suitable medium to dissolve and to sulfate under homogeneous reaction conditions. A dissolution of the cellulose in various non-derivatizing solvent systems, such. As N-methylmorpholine-N-oxide, dimethylacetamide / LiCl or SO ₂ / aliphatic amine / polar organic liquid, proved to be unsuitable for the intended purpose, since the systems partially coagulate in the subsequent sulfation or greatly degraded due to exothermic side reactions and or strongly contaminated products (W. Wagenknecht, B. Philipp, H. Schleicher, Acta Polymerica 30 [1979], 108; W. Wagenknecht, B. Philip, M. Keck, Acta Polymerica 36 [1985], 697).

The sulphation of starch can also be carried out in the aqueous alkaline system using correspondingly stable trialkylamine / SO ₃ complexes, US Pat. No. 2,784,833 and US Pat. No. 2,967,178. However, in this way exclusively low-substituted products are accessible. In addition, the method for producing water-soluble polysaccharide sulfates without serious hydrolytic polymer degradation remains limited to already largely water-soluble polysaccharides. Even at a low degree of substitution, water-soluble cellulose sulfates having a high solution viscosity have hitherto been obtained only after dissolution of the cellulose in the NjCV dimethylformamide system, the sulfation of the DMF-soluble nitrite ester of cellulose (RG Schweiger, Tappi 57 (1974), 86) formed during or after the sulfation Dissolution with sulfur trioxide (US Pat. No. 4,035,569, DE-OS 2120964, DE-OS 2530541), with sulfur dioxide (DD-WP 152565, DD-WP 211688), with nitrosyl hydrogen sulfate (Cellulose Chem. Techn. 17 (1983), 443-459 , with acetylsulfuric acid (US Pat. No. 4,480,091) or with sulfamic acid salts (SU-PS 1150253) All of the aforementioned process variants give products whose property pattern is suitable for the fields of application mentioned at the outset Problems that are a synthesis in the technical

To allow scale only with a disproportionate effort when reproducible product parameters should be guaranteed and the manufacturing process should meet the requirements of health and environmental protection. Among these technological disadvantages and difficulty-causing problems, the following are particularly noteworthy:

- Working with N ₂ O ₄ implies complicated redox processes in the formation and decomposition of cellulose nitrite ester in a strongly acidic medium, whereby this redox process and associated hydrolytic cellulose degradation can be performed on an industrial scale only with great difficulty and reproducibility ,

- The taking place with elimination of the nitrite ester groups isolation of cellulose sulfate is difficult in so far as either a contamination of the final product Na cellulose sulfate by large amounts of inorganic salts must be taken into account, which can be completely removed only with great effort, or in the case of isolation the acidic half-ester form (H ⁺ form) of cellulose sulfate uncontrolled chain length degradation is difficult to avoid.

- In the production of cellulose sulfate by the nitrite process in the course of the process highly toxic by-products, of which especially dimethylnitrosamine may be mentioned, which always arises from the dimethylamine present in the DMF by reaction with N ₂ O ₄ and its safe handling and disposal an open one. It requires a great deal of effort and is in no case completely risk-free.

In summary, the current state of the art can be outlined in that although methods are known which lead to cellulose sulfates with the required application properties, but that these previously known methods for a technical realization require a very high effort and at the same time involve environmental risks, so that the search for alternatives without use of N ₂ O _{4 represents} a technically and economically meaningful task.

Object of the invention

The aim of the invention is the development of a technically simple process for preparing water-soluble sulfuric acid half-ester of cellulose and related polysaccharides, which works without isolation of intermediates, as far as possible avoid a Kettenlä ngenabbaus the setting of a purpose adapted substitution Grados allowed and avoids the formation of toxic by-products.

Explanation of the essence of the invention

The invention is therefore based on the object to develop a technically advantageous process that allows to carry out a homogeneous sulfation of cellulose and related polysaccharides in aprotic media without formation of toxic by-products without isolation of intermediates and the variation of the reaction conditions, the degree of substitution in a wide Targeted range. In this case, complete water solubility of the products should be achieved even at low degrees of sulfation and these products are obtained in comparatively simple workup in high purity.

According to the invention the object is achieved by etherifying cellulose or related polysaccharides in the presence of a primary aliphatic amine having 1 to 4 carbon atoms or ammonia with chlorotrimethylsilane to Trimethylsilylderivat, the amine or ammonia removed and without intermediate isolation of the polymer in the presence of aprotic organic solvents with a suitable sulfating agent, such as sulfur trioxide, chlorosulfonic acid or sulfuryl chloride, to the desired degree of substitution, the products obtained optionally precipitates, ungagged gesulfatierungsagens and transferred after or during the removal of the existing trialkylsilyl groups in a stable salt form of the sulfuric acid half.

The reaction sequence required for preparing the cellulose sulfate thus consists of the steps "activation of cellulose", "silylation", "sulfation of the silylcellulose in solution", "splitting off remaining silyl ether groups", "neutralization of the acid cellulose sulfate half ester", "workup of the Na cellulose sulfate ", which are all carried out one after the other in a heatable Reaktionsgofäß at different temperature without isolation of intermediates and without the formation of toxic, environmentally questionable hub products. As Ausgangsmatertal serve cellulose in fiber form or in powder form of eg cotton Unters, wood pulp, cellulose powder or Celluioseregeneratfäden or chemically related polysaccharides such as starch or xylan. To ensure the most uniform possible silylation in order to obtain a silylcellulose which is completely soluble in a DS of about 0.5, the cellulose is first subjected to an activation process. The activating agent and at the same time medium for the subsequent silylation are ammonia or primary aliphatic amines having one to four C atoms -Atomen in admixture with a suitable aprotic organic liquid, preferably dimethylformamide, dimethyl sulfoxide or tetrahydrofuran. According to the invention, 1-50 parts, preferably 2-20 parts of NH ₃ or amine and 1-200 parts, preferably 10-100 parts of DMF or another suitable liquid per part by weight of polysaccharide are used. The activation takes place during 0.5-3 h, preferably 1-2 h at temperatures in the range of -78 ⁰ C to +25 ⁰ C, preferably -5O ⁰ C to + 1O ⁰ C. The silylation of the polysaccharide is carried out by metered addition of chlorotrimethylsilane , which can be dissolved in a suitable aprotic organic medium, preferably the component used in the activation. The amount of TMS chloride used is 0.2-3 mol, preferably 0.3-1.5 mol per mole of OH group of the polysaccharide, wherein Silylierungsgrade of 10-100%, preferably 30-90%, based on the OH Groups of polysaccharide, can be achieved. The metered addition of the silylating agent is expediently carried out over a period of 0.1 to 3 h. The reaction temperature during the silylation is in the range between -78 ⁰ C and + 8O ⁰ C, preferably -50 ° C to + 60 ⁰ C, the reaction time is 0.2-1Oh, preferably 0.5-5h. During or after silylation, the NH ₃ or amine is removed from the reaction system by vacuum and / or temperature elevation which then contains the TMS ether of the polysaccharide in dissolved form and finely divided ammonium chloride or amine hydrochloride as co-precipitated products. The sulfating agents used are sulfur trioxide, chlorosulfonic acid or sulfuryl chloride, preferably in the form of a dissolved complex in a dipolar aprotic solvent such as DMF or DMSO or THF. The sulfating agent is used in an amount of 0.1-3 mol, preferably 0.2-1.5 mol per mol of OH group of the starting polysaccharide. The dosing of the Sulfatierungsnvttels done under constant mixing of

Systems within 5 to 120min, preferably 15 to 60 min. The reaction time Leträgt 0.25 to 5 h, preferably 0.5 to 2 h at -15 ° C to + 40 ⁰ C, preferably 0 to 25 ⁰ C. To adjust over the metered amount of sulfating agent dun aspired content of sulfate half ester groups in the final product and to avoid losses of sulfating agent, the aforementioned removal of NH 3 or amine from the system prior to addition of the sulfating agent is of considerable importance. The polysaccharide derivative obtained after the sulfation contains both silyl ether and sulfate half ester groups and is preferably present in dissolved form in the reaction system. It has been found in terms of cleaning and purity of the final product useful to split off already at this stage without precipitation of the polymer, the essential part of the silyl ether groups by addition of water or other suitable protic liquid to the liberated trimethylsilanol or hexamethyldisiloxane formed in to get dissolved and thus easily removable form. For this purpose, the reaction mixture 1 to 50 parts, preferably 3 to 10 parts of water, glacial acetic acid or mixtures thereof with stirring at the present after the expiration of the sulfation temperature and allowed the mixture for 5 min to 24 h, preferably 15min to 3 h, react , The polymeric reaction product is still present in dissolved form when using DMF or DMSO as medium and is now precipitated by addition of an aliphatic alcohol, preferably ethanol, or by addition of acetone or another suitable protic or aprotic liquid. In the case of the use of THF as the medium, a phase separation takes place without further addition of precipitant, with precipitation of the polymer product. This is now separated in each case by filtration or by centrifugation of the liquid phase. The precipitate is washed with ethanol or hydrous acetone and then neutralized by neutralization with a base, preferably NaOH, in the presence of a suitable protic medium, preferably ethanol, optionally with the elimination of the remaining silylotherms the stable salt form of Polysaccharidsulfates, preferably the Na SaIz is obtained. This can then be further purified by washing with ethanol, an ethanol-H ₂ O or an acetone-HjO mixture and then dried. As end products, sodium salt-free sodium polysaccharide sulfates with very low chain length degradation are obtained as far as possible, for example when using wood pulp (Cuoxsm-DP 600) as starting cellulose water-soluble cellulose sulfates with a DS of 0.25 or 0.33 and a viscosity _tt = 120 mPa χ s or 80 mPa χ s in 1% aqueous solution at 20 ° C are obtained.

embodiments example 1

20g (0.125 mL) dry linters cellulose (Cuoxam DP = 1400) is pre-activated with stirring suspended in 600 ml of dry dimethylformamide and h by the addition of 300 ml of liquid ammonia at -5o C ^0. 2 To the suspension are dissolved at -50 ° C 27.1 g (0.25 mol) of chlorotrimethylsilane, added dropwise in 100ml of dry dimethylformamide (DMF) within 1 h and stirred for 0.5 h. After addition of 300 ml of dry DMF is heated to remove ammonia to about 20 ⁰ C with stirring and dissolution of trimethylsilyl cellulose and then removed at about 45 ⁰ C within 1 h. After tempering to 20 ⁰ C, a freshly prepared solution of 10 g (0.125 mol) of sulfur trioxide in 200 ml of dry DMF is added dropwise with stirring and exclusion of moisture within 30 min and stirred for 1 h. The acid form of Celluloseschwefelsäurehalbesters is precipitated by the addition of 500 ml of 96% ethanol, filtered off with suction, washed with precipitating agent 3 times within 1 h until sulfate ions can no longer be detected in the washing solution, neutralized with ethanolic sodium hydroxide solution (1% NaOH in 90% aqueous ethanol) , washed with ethanol nachgcwaschön and dried in vacuo at 13.3Pa and 6O ⁰ C. The completely water-soluble sodium cellulose sulfate has a DS of 0.88 and a solution viscosity at 20 ° C of 490OmPa in s in 1% aqueous solution. It is free ν -in inorganic salts.

Example 2 The procedure is as in Example 1, but 40 g (0.5 mol) of sulfur trioxide dissolved in 400 ml of dimethylformamide to Sulfation used. The resulting completely water-soluble sodium cellulose sulfate has a DS of 1.63. Example 3

15g (0.09 mol) dry linters cellulose (Cuoxam DP = 800) are added to the activation with 700 ml of a saturated at -15 ⁰ C NH ₃ / DMF solution and stirred at -15 ° C for 3 h. Subsequently, 20 g (0.18 mol) of chlorotrimethylsilane are added dropwise within 30 min and stirred at -15 ° C for 2 h. To remove the ammonia is heated to 4O ⁰ C and degassed the viscous trimethylsilyl cellulose solution in a water jet vacuum (1600 Pa). For homogeneous sulfation of the polymer, 10.5 g (0.09 mol) of chlorosulfonic acid in 150 ml of DMF are added dropwise within 30 min without intermediate isolation of the polymer and separation of the ammonium chloride with stirring at 2O ⁰ C, after 1 h 50 ml of distilled water was added and stirred for 2 h. Subsequently, the sulfuric acid half-ester of cellulose is precipitated with acetone, washed 3 times 15 min with 4% water-containing acetone until no more sulfate can be detected in the washing medium. The product is neutralized according to Beispiol 1, washed and dried. The sodium cellulose sulfate obtained is completely soluble in water, has a solution viscosity at 2O ⁰ C in 1% aqueous solution of ι = 84 mPa χ s and a DS = 0.48. The chlorine content is 0.14%.

Example 4

The procedure is as in Example 3, but 12.2 g (0.09 mol) of sulfuryl chloride dissolved in 150 ml of DMF are used for sulfation of 15g (0.09 mol) of cellulose instead of chlorosulfonic acid. The sodium cellulose sulfate obtained after drying is completely water-soluble, has a DS _m = 0.37 and a chlorine content of 0.10%.

Example 5

15 g (0.09 mol) of dry cellulose powder (DPc = 150) are activated with exclusion of moisture with a mixture of 30 g of ammonia and 170 ml of DMF at -15 ° C with stirring for 1 h. Subsequently, a mixture of 20 g (0.1 mmol) of chlorotrimethylsilane and 100 ml of DMF is added dropwise within 0.5 h and stirring is continued for 0.5 h. To remove the ammonia is heated to 40 ° C and then degassed at 1600Pa in a water jet vacuum.

After cooling the polymer solution to ⁰ ° C., 6.3 g (0.045 mol) of chlorosulfonic acid in a mixture with 100 ml of DMF are added dropwise over a period of 15 minutes and the mixture is stirred for a further 15 minutes. A mixture of 1 part of acetic acid and vacuum vacuum 1 part of water are added subsequently at 0 ° C 80ml, and stirred for 2 h at ^{0 °} C.

The acid form of cellulose sulfate is precipitated with acetone, washed with acetone until sulfate ions can no longer be detected in the washing solution, neutralized with ethanolic sodium hydroxide solution (1% NaOH in 90% aqueous ethanol), 2% with 70% aqueous ethanol and 2 × with washed with dry ethanol and dried in vacuo at 1600Pa and 6O ⁰ C. The water-soluble sodium cellulose sulfate has a DS of 0.25 and a solution viscosity in 1% aqueous solution at 2O ⁰ C of "ι = 6mPa x s.

Example β

16.2 g (0.10 mol) of dry cellulose powder (DP _n , = 150) are activated with exclusion of moisture at -40 ° C. with 35 g of liquid, dry ammonia and 100 ml of anhydrous tetrahydrofuran for 2 h. With constant stirring, 43.5 g (0.40 mol) of chlorotrimethylsilane dissolved in 100 ml of dry tetrahydrofuran are added dropwise within 30 min. The mixture is then heated within 3 hours to 60 ⁰ C and ammonia is completely removed (A sample has a Si content of 20.9% according to a DSD of 2.6).

After conditioning at 20 ⁰ C for * for the exclusion of moisture is added dropwise a solution of 24g (0.3mol) SO ₃ in 200 ml of DMF and 40g (0.5mol) SO ₃ in 400 ml DMF within 30 minutes, further stirred for 30 minutes, the resultant precipitate is filtered off with suction and wash with 96% acetone until no more sulfate is detectable in the washing liquid. The neutralization of the resulting acid form of the sulfuric monoester is carried out according to Example 1 with ethanolic NaOH. After subsequent washing with ethanol and drying, the product has a DS _n , of 1.11 and 2.0 respectively sulfate groups and dissolves completely in water.

Example 7

5 g of dry starch (0.03 mol) are pre-swollen with 100 ml of distilled water for 3 h at 50 ° C with stirring, mixed with 500 ml of DMF and distilled from the suspension, the water and 200 ml of DMF in vacuo. After tempering to -55 ° C., 150 ml of liquid ammonia are added and stirring is continued for 1 h, 7.8 ml of chlorotrimethylsilane dissolved in 100 ml of DMF are added dropwise over 1 h, stirring is continued for 1 h, the mixture is heated to 20 ° C. within 1.5 h and concentrated in vacuo (1600 Pa). at 4O ⁰ C NH ₃ completely removed. For sulfation, 4.9 g (0.06 mol) of sulfur trioxide dissolved in 50 ml of DMF are added dropwise within 30 min, after 1 h reaction time at 2O ⁰ C added 50 ml of a mixture of 1 part by volume of acetic acid and 2 parts by volume of water. After stirring for 30 min, the sulfuric acid half ester of the starch is precipitated in acetone and washed, neutralized and dried as in Example 3. The water-soluble product has a DS of 0.91.

Bfllsplel 8

The procedure is as in Example 7, but are used as the starting polysaccharide instead of 5g starch 4.1 g (0.03 mol) of dry Beech xylan used. The resulting water-soluble Na xylansulfate has a degree of substitution of sulfate ester groups of 0.53. Example 9

30 g (0.18 mol) of dry spruce sulphite pulp (DP _n , = 600) are activated under exclusion of moisture with a mixture of 62 g (2 mol) monomethylamine and 500 g dimethyl sulphoxide with stirring at +5 ° C. for 3 h.

Chlortrimeihylsilan added dropwise within 1.5 h at +5 ⁰ C and stirred for 4h. To remove the amine is heated to 40 ° C and then degassed for 1 h at 1600Pa in a water jet vacuum. For sulfation of the trimethylsilyl cellulose formed at +5 ⁰ C, a solution of 14g (0.18 mol) of sulfur trioxide in 200 g DMSO added dropwise within 1 h and stirred for 1 h. Then 200 ml of distilled water are added. After 2 h Stirring at ⁰ +5 C, the Schwefelsäurehalbester of the cellulose is precipitated with ethanol and washed with ethanol until no Sulfate ions are more detectable in the filtrate, neutralized with 2% Etiianolischer NaOH and finally in a vacuum at

13.3 Pa and 6O ⁰ C dried. The resulting sodium cellulose sulfate is water-soluble and has a DS of 0.42.

Claims (21)

1. A process for the preparation of water-soluble Schwefelsäurehalbestern the cellulose and related polysaccharides by reaction with sulfating agents such as sulfur trioxide, chlorosulfonic acid or sulfuryl chloride in the presence of aprotic solvent, characterized in that the cellulose or related polysaccharides in the presence of 1-50 parts by weight of a primary aliphatic amine with 1 -4 C atoms or ammonia, based on 1 part by weight polysaccharide, in 1-200 parts by weight of an aprotic organic solvent per part by weight polysaccharide, in a time of 0.5 to 3 hours and at a temperature between -78 ° C and +25 ⁰ C, with 0.2 to 3 mol of trimethylchlorosilanes per hydroxyl group of the monomer unit of Polysaccarids in an aprotic solvent at temperatures between -78 ⁰ C and + 6O ⁰ C and over a period of 0.1 to 3 hours and dosed at temperatures between -78 ⁰ C and + 8O ⁰ C implemented in a period of 0.2 to 10 hours, d As excess amine or ammonia in the usual manner by increasing the temperature and / or reduced pressure, the remaining reaction mixture 0.1 to 3mol sulfur trioxide, chlorosulfonic acid or sulfuryl chloride per hydroxyl group of the monomer unit of Aubüoigs polysaccharide in the form of a dissolved complex in 1 to 20 parts by weight of aprotic organic Solvents with continuous mixing within 5 minutes to 2 hours at temperatures between -15 ° C and +40 ⁰ C added the reaction 0.25 to 5 h is carried out by adding 2 to 200 parts by weight of a precipitating acting protic solvent, based on 1 Part of the polymer before, during or after this step a non-precipitating, Trimethylestergruppen cleaving protic medium in concentrations of 1 to 50 parts by weight, based on 1 mass of polysaccharide, for a period of 5 minutes to 24 hours and temperatures from -15 ° C to +40 ⁰ C act, the present acidic sulfuric acid half ester of polysaccharide in the usual form, worked up with one or a mixture of said precipitating agent in a known manner to the stable salt form, washed, transferred with appropriate alkali or alkaline earth metal compounds in the salt form, washed and dried. Process according to claim 1, characterized in that 3 to 1.5 mol of chlorotrimethylsilane per hydroxyl group of the monomer unit of the polysaccharide are used for the silylation. 3. The method according to claim 1 and 2, characterized in that the amount used for activating and silylating the polysaccharide ammonia or amine is 2 to 20 parts by mass per part by mass of polysaccharide. 4. The method according to claim 1 and 3, characterized in that is used as the primary aliphatic amine monomethylamine. 5. The method according to claim 1 to 4, characterized in that added during the activation and silylation in addition to the ammonia or amine 10 to 100 parts by mass of aprotic organic solvent per part by mass of polysaccharide. 6. The method according to claim 1 to 5, characterized in that the activation within 1 to 2 hours, at temperatures between -50 ⁰ C to + 1O ⁰ C is made. 7. The method according to claim 1 to 6, characterized in that the metered addition of chlorotrimethylsilane as a solution in an aprotic organic solvent at temperatures between -5O ⁰ C and +25 ⁰ C, over a period of 0.2 to 2 hours. 8. The method according to claim 1 to 7, characterized in that the silylation over a period of 0.5 to 5 hours, at a temperature between -50 ⁰ C and +60 ⁰ C is performed. 9. The method according to claim 1 to 8, characterized in that are used as aprotic solvents Ν, Ν-dimethylformamide, dimethyl sulfoxide or tetrahydrofuran. 10. The method according to claim 1, characterized in that the sulfating agent is used in an amount of 0.2 to 1.5 mol per hydroxyl group of the monomer unit of the starting polysaccharide. 11. The method according to claim 1 and 10, characterized in that the metered addition of the sulfating agent is carried out with continuous mixing within 15 minutes to 1 hour. 12. The method according to claim 1, 10 and 11, characterized in that the sulfation reaction is carried out in a time of 30 minutes to 2 hours. 13. The method according to claim 1 and 10 to 12, characterized in that the metered addition of the sulfating agent takes place at temperatures between 0 and 25 ⁰ C. 14. The method according to claim 1 and 10 to 12, characterized in that the sulfation is carried out at temperatures of 0 to 25 ⁰ C. 15. The method according to claim 1, characterized in that are used to carry out the desilylation as protic medium water, glacial acetic acid or mixtures thereof. 16. The method according to claim 1 and 15, characterized in that the protic medium for the desilylation in concentrations of 3 to 10 parts by weight, based on 1 part by weight of polysaccharide, is applied. 17. The method of claim 1.15 and 16, characterized in that the desilylation is carried out in a period of 15 minutes η to 2 hours. 18. The method according to claim 1 and 15 to 17, characterized in that the desilylation is carried out at temperatures between 0 and 25 ⁰ C. 19. The method according to claim 1 to 18, characterized in that the raw material used as a starting material ν polysaccharide is starch. 20. The method according to claim 1 to 18, characterized in that the polysaccharide used as starting material is xylan. 21. The method according to claim 1 to 6 to 8, characterized in that the protic precipitant after silylation is ethanol or hydrous acetone.