DE3104530A1 - METHOD FOR PRODUCING O-TRIMETHYLSILYL CELLULOSES - Google Patents

Description

Man-made fiber Lenzing Aktiengesellschaft Lenzing, Austria

Process for the production of O-trimethylsilyl celluloses

The invention relates to a process for the production of O-trimethylsilyl celluloses by treating cotton or Wood cellulose with cellulose swelling agents, in particular nitrogenous bases, reaction with trimethylchlorosilane and dissolving the product obtained in an organic solvent and using the process in Production of new O-trimethylsilyl celluloses with a degree of substitution (DS) below 2.

Various attempts have been made to remove the free hydroxyl groups of cellulose in the positions 2, 3 and 6 of the anhydroglucose units to be silylated.

The processes known up to now were aimed at obtaining trimethylsilyl or other di- and triorganosilyl derivatives of cellulose, which are soluble in non-polar solvents. This goal can only be achieved through generation of products with the highest possible average DS, i.e. by silylating all three hydroxyl groups per Anhydroglucose unit.

G. Keilich et al. (Makromol. Chem. 120: 87-95 (1968))

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produced 2,3,6-Tris-O-trimethylsilyl cellulose for the first time Made from native cotton cellulose with a weight average degree of polymerisation (DP)

from about 5800 ago. The cellulose was reacted under nitrogen with 0.5% aqueous NaOH solution with excess trimethylchlorosilane in pyridine. The resulting tris-O-trimethylsilyl cellulose (O-TMS cellulose, I) was only soluble in non-polar solvents, such as η-hexane and cyclohexane, and could be precipitated from these solutions with ethanol. Tetrahydrofuran (THF), dioxane, benzene, toluene and chloroform only caused (I) to swell. Keilich et al. have also already established that this O-TMS cellulose is significantly less sensitive to hydrolysis than, for example, the O-TMS glucoses. The hydrolysis of one TMS group per building block in the O-TMS cellulose by K ₃ CO ₃ in methanol does not take place until after 75 minutes at 50 ° C. Complete desilylation takes place under these conditions only after three hours of refluxing.

O-TMS celluloses also soluble in aliphatic and aromatic, optionally chlorinated hydrocarbons, which contain 2 to 3 0-TMS groups per anhydroglucose unit are products of the process according to FIG U.S. Patent 3,418,312, according to which cellulose is a mixture of trimethylchlorosilane, a mono- or disaccharide, a Solvent and a tertiary amine is added.

U.S. Patent 3,418,313 relates to the manufacture of O-TMS celluloses with the same solubility properties by adding pure trimethylchlorosilane - produced by reaction of hexamethyldisilazane with anhydrous hydrogen chloride - to a mixture of cellulose, a tertiary amine and a solvent.

J. Nagy et al. (Period. Polytechn. Chem. Eng. V8, 91-98,

(1972)) chose to silylate as a model substance used cellophane hexamethyldisilazane in pyridine in the presence of catalytic amounts of trimethylchlorosilane. The product obtained was soluble in toluene. The inconsistency of literature references with regard to the solubility behavior of cellulose derivatives silylated with trialkylchlorosilanes in organic solvents shown in this publication.

In the course of our own investigations it has now been recognized that O-trimethylsilyl celluloses are still due to production existing small amounts of acidic salts rapidly hydrolyzed in the presence of atmospheric moisture and thus insoluble will. Such products cannot be stored and are therefore unsuitable for operational use. Solutions of the silylated celluloses, which are used for the production of shaped products from regenerated cellulose can be used are too volatile and subject to change.

The object of the invention is to avoid the deficiencies described and to make them easy to handle O-trimethylsilyl celluloses · to create reproducible solubility properties.

To solve this problem, a method of the type defined at the outset is proceeded in such a way that the organic Solvent dissolved crude reaction product, a basic reagent, preferably sodium carbonate, added is used to neutralize small amounts of acidic salts present, whereupon solids are removed from the solution and, if necessary Trimethylsilyl cellulose is precipitated from the solution and processed into a solid preparation.

O-TMS celluloses with a DS below 2 are new. These new O-TMS celluloses are made using the inventive Process produced by swollen cellulose with less than 2.0 moles of trimethyl

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chlorosilane per mole of anhydroglucose unit of the cellulose.

Suitable cellulose swelling agents are known as nitrogenous ones Base is advantageously used pyridine.

As a solvent for the raw silylated celluloses come polar solvents such as dimethylformamide (DMF), dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethyl sulf oxide (DMSO), tetrahydrofuran (THP), but also non-polar, such as aliphatic and aromatic, optionally halogenated hydrocarbons, in embossing. The higher the DS is the O-TMS cellulose, the better it becomes Solubility in non-polar or weakly polar solvents; Products with a DS around 2 are just loosening even in weakly polar solvents such as THP, while silylated celluloses, which have a DS of about 1.5 and below, only dissolve in strongly polar solvents.

In addition to sodium carbonate, other basic reagents, such as the carbonates of the rest, can also be used for neutralization Alkali metals, alkali and alkaline earth hydrogen carbonates and alkaline earth carbonates or oxides can be used.

Alcohols, preferably alkanols such as methanol, ethanol, n- and i-propanol, are expediently used as precipitants and butanols, are used. Acetone, for example, is also suitable for precipitating highly silylated products.

The method according to the invention is used in the following examples explained in more detail.

Example 1: Production of 0-trimethylsilyl cellulose with DS 2.65

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In a three-necked flask with a capacity of 100 ml, equipped with a stirrer and reflux condenser, which is in contact with the surrounding atmosphere via a drying tube, 2 g (12.34 mmol) of cellulose and Submitted 50 ml of anhydrous pyridine and the mixture heated to boiling under reflux for four hours. Thereafter 6 g (55.6 mmol) of trimethylchlorosilane are added dropwise at room temperature and the contents of the flask for three hours touched. The swelling of the silyl cellulose is reduced by adding methanol and the silylated substance is reduced washed with suction with methanol. The crude product thus obtained is dissolved in petroleum ether and about 0.1 g Sodium carbonate is added to neutralize any small amounts of pyridinium hydrochloride that are still present otherwise it would be sufficient to hydrolyze the silylated cellulose. The solution is centrifuged or pressure filtered and the O-TMS cellulose from the resulting clear Solution precipitated with ethanol. After drying in a high vacuum, a white, in non-polar solvents, is obtained like the hydrocarbons, or in ethers like tetrahydrofuran, soluble product.

Yield: 3.75 g (85% of theory), analysis: Si: 21%, DS: 2.65

Example 2: Become 2 g (12.34 mmol) of cellulose in pyridine heated to boiling for 4 hours under reflux for the purpose of swelling. Then 2.2 g (20.37 mmol) of trimethylchlorosilane are added added dropwise and allowed to react at room temperature for 3 hours. By adding methanol, the The swelling is suppressed, the product is filtered off with suction and washed with methanol. For purification, the product is in DMF solved. Small amounts of pyridinium hydrochloride still present are neutralized by adding potassium carbonate and the solution centrifuged or pressure filtered. The silyl cellulose is precipitated from the clear solution with water and dried.

Yield: 2.9 g (88% of theory), Si: 14.7%, DS: 1.37

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Claims (2)

310A530 Patent claims: ί 1. Process for the production of O-trimethylsilyl celluloses by treating cotton or wood cellulose with cellulose swelling agents, especially nitrogenous ones Bases, reacting with trimethylchlorosilane and dissolving the product obtained in an organic one Solvent, characterized in that the crude reaction product dissolved in the organic solvent a basic reagent, preferably sodium carbonate, is added to reduce the presence of small amounts acidic salts, whereupon solids are removed from the solution and, if necessary, trimethylsilyl cellulose from the solution precipitated and processed into a solid preparation. 2. Use of the method according to claim 1 hot cfer production of new trimethylsilyl celluloses with a degree of substitution (DS) below 2.0, characterized in that that one swollen cellulose with less than 2.0 moles of trimethylchlorosilane per mole of anhydroglucose unit the cellulose converts. 130049/0636