FI62542B - FOER REFRIGERATION FOR CELLULOSANITRITESTER - Google Patents

Abstract

1521125 Cellulose nitrites, sulphates and nitrates R G SCHWEIGER 8 July 1975 [10 July 1974] 28676/75 Heading C3A Nitrite esters of cellulose which may be converted to sulphates or nitrates are prepared by reacting water-containing, cellulose having not more than 12% water content with dinitrogen tetroxide or nitrosyl chloride at less than 50‹ C. with stirring in the presence of at least three parts by weight of a swelling or solubilizing solvent for the nitrite ester per part by weight of cellulose in the presence of proton acceptor. The cellulose preferably contains 4-12% water by treatment with a highly polar aprotic solvent. The solvent used is N,N-dimethylformamide and the highly polar aprotic solvent may be N,N-dimethylformamide, N,N-dimethylacetamide or pyridine. The sulphate ester may be prepared by reacting the nitrile ester with SO3 or a complex thereof and neutralizing with a base to give the alkali salt form.

Description

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The invention relates to a process for the preparation of a nitrite ester of cellulose.

Ester derivatives of polyhydroxypolymers are known and have been extensively described in the prior literature. The chemical and physical properties of such ester derivatives depend greatly on the nature of the polymer in question, its molecular weight, the type of ester substituent and the degree of substitution of the polymer (hereinafter abbreviated as SA). Due to the way in which the ester derivatives of the polyhydroxypolymers have been prepared in the past, the SA of the obtained ester derivatives has not been very uniform. In this way, ester derivatives have been obtained whose properties, for example water solubility and compatibility with various metal ions, have not been generally satisfactory but have limited the fields of application of the ester derivatives.

The starting cellulose is suspended in a suitable solvent containing a swelling or solubilizing agent of the polymeric reaction product and a proton acceptor. Solvents that have been found to be suitable as both a proton acceptor and a swelling or solubilizing agent include, for example, a tertiary amine base such as pyridine, quinoline and isoquinoline, and sekä, dial-dialkylacylamides such as Ν, Ν-dimethylformamide and Ν, Ν-dimethylamide hereinafter abbreviated as DMF and DMAC, respectively) and mixtures thereof. Suitable swelling or dissolving agents are generally solvents that can dissolve polymeric esters. Typical examples of such swelling or solubilizing agents include ethyl acetate, ethyl formate, benzene, acetone, methyl ethyl ketones and the like, and mixtures thereof.

The amount of solvent used to suspend the cellulose is not critical and can vary within relatively wide limits. However, the solvent should be used sufficiently to avoid difficulties in handling the resulting viscous mixture. In general, it has been found that the minimum weight ratio of solvent to polymer is 3: 1, i. 3 parts by weight of solvent for each polymer part.

In general, it is recommended that the solvent be able to both swell or dissolve the resulting cellulose nitrite ester and also act as a proton acceptor. The use of a single solvent compared to using a mixture of a proton acceptor with a swelling or solubilizing agent is advantageous from the point of view of the economics of the method because it simplifies the recovery and reuse of the solvent. However, if a mixture of a proton acceptor with a swelling or solubilizing agent is used, it is necessary that the mixture contain at least one mole of proton acceptor for each mole of nitrosating agent, for example nitrous oxide.

The invention relates to an improved process for the preparation of nitrite esters of cellulose. The use of a cellulose nitrite ester intermediate allows the preparation of new cellulose esters, such as cellulose sulfate or cellulose nitrate, in which the properties of the finished product can be considered to be due to the fact that the ester groups are substantially evenly distributed along the cellulose polymer units. The nitrosation of cellulose is described in U.S. Patent 3,702,843. The nitrosation of cellulose with nitrous oxide or nitrosyl chloride and subsequent sulfation has been found to be further enhanced if the reacting cellulose is in an activated state or suitably activated.

The process of the invention for preparing a cellulose nitrite ester having a degree of substitution of 0.1 to 3 by reacting substantially unsubstituted cellulose with nitrous oxide or nitrosyl chloride in the presence of a cellulose nitrite ester solubilizer or swelling agent and a proton acceptor at a temperature below about 50 ° C. wherein the combination of solubilizing or swelling agent and proton acceptor is present at least 3 parts by weight for each anhydroglucose unit, which proton acceptor is a highly polar aprotic solvent or a weak tertiary amine in which the amine nitrogen atom is in an aromatic structure with at least 1 mole of proton acceptor per mole of nitrosyl chloride, and if the proton acceptor is also a solubilizing or swelling agent, the proton acceptor is present in an amount of at least 3 parts by weight for each anhydroglucose unit. The process is characterized in that, prior to the reaction, the cellulose is activated and hydrated with water so that it contains a substantially uniform distribution of 4-1? % by weight of water, or the cellulose is activated and its water content is reduced to less than 4% by weight, which is obtained by treating hydrated cellulose containing 4% by weight or more of water evenly distributed as a solvent which is also suitable as a proton acceptor.

When hydrated cellulose is used as the reactant, the nitrosation reaction can be performed in a shorter time and using a substantially stoichiometric amount of nitrosating agent. This results in a more homogeneous reaction mixture, a clearer product and thus makes it easier to separate the product from the reaction mixture and reduces the need for filtration.

In a variation of the invention, hydrated cellulose, which may contain greater than about 4% by weight of water distributed substantially evenly through the cellulose, is washed as a highly polar aprotic solvent to reduce the water content of the cellulose to less than about 4% by weight. Surprisingly, it has been found that the cellulose remains in the activated state after washing as an aprotic solvent, although the water content of the washed cellulose is less than about 4% by weight. The washed cellulose can then be used as described above for nitrosation with nitrous oxide or nitrosyl chloride.

It has been found that the nitrite substituent groups present in nitrite esters of cellulose are surprisingly stable. Thus, unlike other nitrites, nitrite substituents in cellulose (or other polyhydroxy polymer) can be easily removed.

In the process of this invention, cellulose suspended in a suitable solvent is nitrosated with nitrous oxide, nitrosyl chloride, or a mixture thereof to give the corresponding nitrite ester of cellulose.

The nitrosating agent is used in the reaction mixture so that the molar ratio of anhydroxlucose or polymer unit in general to ditvopitetroxide or nitrosyl chloride is about 1: 0.1 to 1: 3, giving a degree of conversion of 0.1 to 3. Since the reaction is quantitative, SA roughly corresponds to the molar amount of nitrosating agent used. If nitrosyl chloride is used in combination with DMF and DMAC, a 2.5 to 3.0-fold excess of nitrosating agent is required to achieve these SA values. Ts. one mole of nitrous hydroxide or nitrosyl chloride is required to replace one mole of the cellulose hydroxyl radical, and if nitrosyl chloride is used in combination with N, N-dialkylacylamide as a proton acceptor, 2.5 to 3.0 moles of nitrosyl chloride are required.

The maximum degree of substitution of cellulose is about 3 »for hemicellulose it is about 2} The molar amount of nitrous oxide required to achieve complete esterification of cellulose is thus about 3 moles per mole of anhydrohexose unit and for hemicellulose about 2 moles per mole of anhydropentose unit. The same molar ratio of nitrosyl chloride is required for complete esterification of each of the polyhydroxy polymer classes described above unless DMF or DMAC is used as the solvent, in which case the amounts must be substantially tripled. A greater amount of nitrosating agent can be added than is required for complete esterification, with the only effect being a higher esterification rate.

The nitrosation reaction is best carried out by stirring the reaction mixture all the time. It is necessary that the nitrosating agent be added to the polymer suspension to prevent the ingress of moisture. It is recommended to cool the reaction vessel in an ice bath or the like because the reaction is moderately exothermic. The temperature of the reaction mixture is kept below 50 ° C.

If maximum esterification is desired, completion of the reaction is indicated by the formation of a clear solution or paste, while partial esterification is indicated by swelling and / or partial dissolution of the product in the reaction mixture.

5,62542

Cellulose nitrite esters are relatively sensitive products and decompose immediately upon addition of a protic solvent such as water, methanol, ethanol, isopropanol or the like in the presence of a mineral acid catalyst. This results in the regeneration of the starting cellulose.

Since the main use of the cellulose nitrite esters of this process is as an intermediate in the preparation of other ester derivatives such as polymeric nitrate and sulfate esters and the like, the nitrite esters need not be isolated because the reaction mixture can be used in these other processes as described above. However, nitrite esters of cellulose can be isolated by neutralizing the reaction mixture by adding a base such as mono-, di- and trialkylamines, pyridine, alkali or alkaline earth metal hydroxides, carbonates, bicarbonates or the like. The addition of such a base is necessary only if N, N-dialkylacylamide is used as the proton acceptor, since an equimolar amount of nitric acid or hydrochloric acid is formed during nitrosation with nitrous oxide or nitrosyl chloride. If a weak tertiary amine base such as pyridine or quinoline has been used as the proton acceptor, the addition of a base is not necessary because the tertiary amine base neutralizes the acid formed, which cannot act as a decomposition catalyst for the polymer nitrite. The neutralized or preferably slightly alkaline solution is then added to cold water while stirring to separate the polymeric nitrite ester as a fibrous material that can be easily separated. Products with a degree of substitution significantly lower than the maximum may swell or even dissolve in water, in which case alcohol is used instead of water.

The isolated product is relatively unstable, and for storage, it is recommended that it be solvated in a suitable solvent such as benzene, ethyl acetate, ethylene dichloride, DMFA, DAMC or the like, and preferably stored at a low temperature below 10 ° C.

The following examples illustrate preferred embodiments of this invention. All ratios in the following examples, both in the specification and in the claims, are weight ratios unless otherwise indicated, and temperatures are expressed in degrees Celsius.

Example I (comparative example)

The cotton pulp was dried at 100-110 ° C under vacuum for 5 hours over phosphorus pentoxide. 20 g of the dried mass was placed in a round-bottomed three-necked flask equipped with a calcium chloride tube, a vigorous stirrer and a dropping funnel, and 1 liter of dimethylformamide was added. 30 g of N2O4 were then added over a period of about 30 minutes while stirring and keeping the temperature of the mixture below 30 ° C by cooling in a cold water bath. The mixture thickened, but the reaction did not proceed to completion even after stirring for several hours, as evidenced by the turbidity and apparently unreacted fibers. No significant improvement was obtained by adding an additional 3 g of N2O4.

Upon isolation and analysis of the resulting cellulose nitrite ester, an excess of pyridine was added to a small amount of the mixture. The slightly alkaline mixture was added to ice water, the precipitate was collected, washed with ice water and compressed while maintaining the temperature at about 0 ° C.

The material was redispersed in distilled water in a sealed Erlenmeyer flask and acidified with sulfuric acid. After stirring with a magnetic stirrer for about 1 hour, the mixture was neutralized and the regenerated cellulose was removed, washed, dried and weighed. The filtrate was collected quantitatively and the nitrite was determined by oxidation with permanganate to nitric acid. The presence of nitric acid after oxidation was determined by determining it as nitron nitrate by the Hick method. Analyst. Butter. 59, pp. 18 - 25 (1934). The degree of nitrosoin was found to be about 2.7 to 2.8.

The cellulose nitrite reaction mixture prepared from 20 g of cellulose and 30 g of N 2 O 4 was sulfated by the slow addition (about 30 minutes) of a solution of DMF-SO 3 complex (about 5 g of RO 3) in dimethylformamide. The reaction was carried out with vigorous stirring and preventing the ingress of moisture and the temperature was kept below about 20 ° C. The mixture remained cloudy and still contained fibers even after stirring for about 1-2 hours.

In the second experiment, 20 g of anhydrous cotton pulp was treated in the same manner as above, but only 15 g of N2O4 was used for nitrosation to give a degree of substitution of about 1.5, and in the subsequent sulfation, the DMF-SO3 complex contained about 12 g of SO3. The results were similar to the above. The degree of substitution of the cellulose sulfate was about 1.5, and the viscosity of the 1% aqueous solution was about 500 cPs, but the solution was turbid and contained fibers, indicating that the nitrite groups are not evenly distributed in the cellulose.

Example II

The cotton pulp described in Example I was suspended in water, mixed for 2 minutes in a Waring Blender, pressed, washed with dimethylformamide and re-pressed. The water content of the cellulose was then about 8-10%. 20 g of this cellulose was nitrosated as described above with 30 g of N2O4. The resulting solution was clear and free of fibers after a reaction time of 20-30 minutes, and no excess of nitrous oxide was required to obtain a quantitative reaction. Sulfation was performed as described in Example I to give products that formed completely clear solutions and did not contain fibers, indicating that the nitrite ester groups are evenly distributed in the cellulose backbone.

Similar results were obtained when the residual water content was 5% and 2%, or when cotton cellulose was replaced with wood cellulose or cellulose obtained from bagasse or chemically treated cellulose.

Example III

The cotton pulp was hydrated by treating with water as described above in a Waring Blender but not treated as a solvent. The cellulose was then compressed and divided into four parts. One portion was dried in vacuo at 30-40 ° C with constant stirring to a water content of about 20%. The other three portions were dried under the same conditions to water contents of 8-10%, 4-5% and 1-2%, respectively. In the last sample, the temperature was raised somewhat. 20 g of each part was nitrosated as described above with 30 g of N2O4. For samples containing 8-10% and 4-5% moisture, the reactions proceeded easily and were complete after about 8,62542 after 20-30 minutes to give clear, viscous solutions. Cellulose containing 20% moisture required about 35 g of N2O4 and formed a clear solution as soon as said excess of 5 g was added. The cellulose portion, which contained 1 to 2% moisture, had to be stirred for a long time, and the solution remained somewhat cloudy and still contained fibers even after the addition of a moderate excess of N2O4.

Subsequent sulfations using a DMF-SO 2 complex containing about 6 g of sulfur trioxide yielded cellulose sulfates in each case with a degree of substitution of about 0.6. These resulted in sparkling clear aqueous solutions using cellulose with initial moisture contents of 20%, 8-10% and 4-5%.

However, solutions of the reaction product prepared from lower moisture cellulose are somewhat turbid and appeared to contain fibers.

Similar results were obtained when the cotton pulp was replaced with wood cellulose or cellulose obtained from the bark or bagasse of plants, or when dimethylformamide was replaced with DMAC, or when a complex with dioxane, DMAC, DMSO or the like was used instead of DMF-SO3.

In another identical series of experiments in which amounts of 20 g of cellulose were nitrosated with about 20 g of N2O4 (for cellulose containing about 20% moisture, about 25 g of N2O4 was required) and sulfated with DMF-SO3 complex containing about 10-12 g of sulfur trioxide , products with SA values of 1.1 to 1.2 were obtained, but otherwise the results were similar.

Nitrosation and subsequent sulfation were similarly easy to obtain, and resulted in sulfated products that formed clear aqueous solutions when directly used commercial cotton pulp or wood pulp with moisture contents ranging from about 4 to 12%. If 5%, 10% or 20% water was added to the anhydrous cellulose at once just before the reaction, the results were similar to those used in Example I using anhydrous cellulose.

Claims (4)

A process for preparing a cellulose nitrite ester having a degree of substitution of 0.1 to 3 by reacting substantially unsubstituted cellulose with nitrous oxide or nitrosyl chloride in the presence of a cellulose nitrite ester solvent or swelling agent and a proton acceptor at a temperature below about 50 ° C, and the proton acceptor combination is present in at least 3 parts by weight for each anhydroglucose unit, which proton acceptor is a highly polar aprotic solvent or a weak tertiary amine in which the nitrogen atom of the amine is in an aromatic structure, the proton acceptor being present at least 1 mole of if the proton acceptor is also a solubilizing or swelling agent, the proton acceptor is present in an amount of at least 3 parts by weight for each anhydroglucose unit, characterized in that the cellulose is activated and hydrated with water before the reaction so that it contains substantially evenly distributed 4-12% by weight of water, or the cellulose is activated and its water content is reduced to less than 4% by weight, obtained by treating hydrated cellulose containing 4% by weight or more of water evenly distributed as a solvent which is also suitable as a proton acceptor . Process according to claim 1, characterized in that said solvent is a proton acceptor and a weak tertiary amine base, N, N-dialkylacylamide or a mixture thereof. Process according to Claim 2, characterized in that the solvent is also a proton acceptor and is N, N-dimethylformamide. Process according to Claim 1, characterized in that the reaction temperature is below about 30 ° C.