CN114106217B

CN114106217B - Preparation method of high-substitution-degree 6-O-carboxymethyl chitin

Info

Publication number: CN114106217B
Application number: CN202111576545.3A
Authority: CN
Inventors: 于德君; 彭爽; 李莎莎; 安建华; 刘广景
Original assignee: Micro Energy Life Technology Group Co ltd
Current assignee: Micro Energy Life Technology Group Co ltd
Priority date: 2021-12-22
Filing date: 2021-12-22
Publication date: 2022-09-30
Anticipated expiration: 2041-12-22
Also published as: CN114106217A

Abstract

The invention provides a preparation method of 6-O-carboxymethyl chitin with high degree of substitution, which is different from the existing preparation method and comprises the following steps: firstly, pretreating chitin to prepare chitin gel, then alkalifying under an alkaline condition, and finally reacting with a chloroacetic acid/isopropanol system. The reaction system for preparing the 6-O-carboxymethyl chitin by the gelation of the chitin tends to a homogeneous system, and alkali liquor and an etherification reagent are easy to permeate into chitin molecules in the reaction process, so that the uniformity of the etherification reaction of the chitin is improved, and the problems of low degree of substitution of the heterogeneous reaction and byproduct generation of the homogeneous reaction are solved. The product obtained by the preparation method has high purity and good water solubility, has excellent moisture absorption and retention and gelling property, and can be widely applied to the aspects of medicines, textiles, foods, cosmetics and the like.

Description

Preparation method of high-substitution-degree 6-O-carboxymethyl chitin

Technical Field

The invention belongs to the field of material science, and particularly relates to a preparation method of 6-O-carboxymethyl chitin with high substitution degree.

Background

Chitin is widely distributed in nature, exists in cell walls of certain microorganisms, shells and bones of certain algae, shrimps, crabs, insects and the like, is synthesized in nature only second to cellulose, and is the second largest renewable resource on the earth. Chitin is insoluble in water, dilute acid diluted bases and general organic reagents, but soluble in some special solvents such as: the application of the chitin is greatly limited by the harsh dissolving conditions of sodium hydroxide-urea, dimethylacetamide-lithium chloride, trichloroacetic acid-dichloroethane and the like, so that the development of water-soluble products of the chitin is imperative to expand the application range of the chitin. Chitin can react with chloroacetic acid under alkaline conditions to generate 6-O-carboxymethyl chitin, and the substitution degree is controlled by chemical reaction conditions, so that the chitin can be dissolved in water to form a water-soluble electrolyte.

In the traditional preparation method of 6-O-carboxymethyl chitin, the system is a heterogeneous system, alkali liquor is alkalized, an organic system is dispersed, and then the alkalization reaction and the etherification reaction are carried out layer by layer from the outside to the inside (heterogeneous surface modification), the reaction degree is low, only chitin molecules on the surface are modified, strong cohesive force (hydrogen bonds and Van der Waals force) is still kept among internal molecular structures, the obtained product has low substitution degree and poor solubility. Patent documents at home and abroad always research the chitin homogeneous system modification, a system solvent is an ionic liquid system or a urea low-temperature system, the homogeneous system is not suitable for carboxymethylation modification, a protic solvent in the system can react with chloroacetic acid, the reaction uncertainty is increased, byproducts can be generated, the product purity is influenced, and the industrial application feasibility is low. How to develop an efficient and feasible chitin carboxylation modification method is a breakthrough in solving the application range of chitin.

Disclosure of Invention

Aiming at the problems of the traditional preparation method of 6-O-carboxymethyl chitin, the invention aims to provide the preparation method of the 6-O-carboxymethyl chitin with high substitution degree, and the preparation method aims to prepare chitin gel firstly and then carry out alkalization reaction, thereby overcoming the problems of low heterogeneous substitution degree and byproduct generation in homogeneous phase. The preparation method of the invention accelerates the swelling of the reactant chitin, makes alkali liquor and etherification reagent easier to permeate into molecules of the reactant chitin, and improves the alkalization reaction degree and the uniformity of etherification reaction of the chitin, thereby obtaining the carboxymethylation product of the chitin with higher substitution degree.

In order to achieve the purpose of the invention, the invention is realized by adopting the following technical scheme:

the invention provides a preparation method of 6-O-carboxymethyl chitin with high degree of substitution, which comprises the following steps:

(1) cleaning chitin block with distilled water, removing surface impurities, oven drying, grinding, and sieving to obtain chitin powder;

(2) adding the chitin powder into DMAc/LiCl ionic liquid, stirring and dissolving to obtain chitin solution;

(3) adding a non-solvent into the chitin solution to enable chitin to form gel, performing suction filtration, recovering filtrate, and cleaning a filtrate with a large amount of water until the filtrate does not contain lithium chloride and DMAc (N, N-dimethylacetamide) to obtain chitin gel;

(4) soaking chitin gel in alkaline solution, vacuum filtering, and drying the residual alkali solution on the surface of the gel with filter paper to obtain chitin jelly;

(5) adding isopropanol and monochloroacetic acid into the chitin jelly, stirring, and reacting in a constant-temperature water bath;

(6) and after the reaction is finished, performing suction filtration on a product, cleaning with absolute ethyl alcohol, dissolving in water, adding an acidic solution to adjust the pH value to be neutral, stirring and dissolving, repeatedly washing and extracting with absolute ethyl alcohol, centrifuging, and freeze-drying to obtain the 6-O-carboxymethyl chitin.

Further, the dosage in the step (2) is chitin powder: DMAc/LiCl ionic liquid as 1: (100-500), wherein the mass ratio of the chitin powder to the LiCl is 1: (1-5).

Further, the non-solvent in the step (3) is at least one of water, alcohols, ketones and ethers, wherein the non-solvent: DMAc in a volume ratio of (50-300): (30-200).

Further, the alcohol is ethanol, the ketone is acetone, and the ether is diethyl ether.

Further, the alkaline solution in the step (4) is a 50% NaOH solution, and the alkalization soaking time is 5-8 h.

Further, in the step (5), monochloroacetic acid: the chitin is prepared from the following components in percentage by weight: (2-5): 1.

further, the volume mass ratio of the isopropanol to the chitin in the step (5) is as follows: (50-100): 1, the mol ratio of chloroacetic acid to chitin is as follows: (4-10); 1. in the volume-to-mass ratio and the mass-to-volume ratio in the present invention, the unit of volume is ml and the unit of mass is g.

Further, in the step (5), the reaction is carried out for 2-6h in a constant-temperature water bath at 25 ℃.

Compared with the prior art, the invention has the advantages and the technical effects that:

1. the reaction system of the 6-O-carboxymethyl chitin prepared by the gelation of the chitin is more similar to a homogeneous system, and is different from the traditional heterogeneous reaction system (layer-by-layer reaction), and the alkali liquor and the etherification reagent in the system are completely permeated into the structure of each layer of the chitin, so that the uniformity of the etherification reaction of the chitin is improved, and the problems of nonuniform substitution and low substitution degree of the heterogeneous reaction are solved. The preparation method is convenient and controllable, and the obtained product has uniform carboxymethylation, good water solubility, excellent moisture absorption and retention and good gelatinizing property, and can be widely applied to the aspects of medicines, textiles, foods, cosmetics and the like.

2. The dissolution system of the lithium chloride and the N, N-dimethylacetamide is an aprotic dissolution system which can be dissolved at room temperature, wherein the N, N-dimethylacetamide has low toxicity and good stability and is not easy to decompose, and the N, N-dimethylacetamide is prevented from participating in side reactions and influencing subsequent reaction products.

3. The chitin powder is alkalized after being prepared into chitin gel, so that the penetration and diffusion of alkali liquor can be promoted, the alkalization reaction is easier and more sufficient, the alkali removal is convenient, the squeezing procedure of a water medium method is omitted, and the harsh reaction conditions are simplified.

4. Compared with the traditional heterogeneous reaction, the time of alkalization treatment is shorter, and the deacetylation reaction of acetyl at C2 caused by the long-time immersion of chitin in alkali liquor is effectively avoided.

Drawings

FIG. 1 is a thermogravimetric plot of samples a, b and c from example 5.

Detailed Description

The following examples are provided to further illustrate embodiments of the present invention.

Example 1

The preparation method of the 6-O-carboxymethyl chitin in the embodiment comprises the following steps:

(1) cleaning chitin block with distilled water for three times, removing surface impurities, oven drying, grinding, and sieving with 60 mesh sieve to obtain powder with uniform size;

(2) weighing 50ml of N, N-dimethylacetamide (DMAc), adding the N, N-dimethylacetamide (DMAc) into a 100ml conical flask, adding 2.5g of anhydrous lithium chloride (LiCl), and stirring to dissolve;

(3) weighing 1.0g dried chitin powder, dissolving in dimethylacetamide-lithium chloride solution, filtering off insoluble substances, adding 30ml water to generate jelly, performing suction filtration (recovering filtrate), and cleaning the filtrate with a large amount of water until lithium chloride and N, N-dimethylacetamide are not contained;

(4) soaking chitin jelly in 50ml of 50% NaOH solution for 5 hr, filtering the solution, and sucking residual alkali solution on the surface of the jelly with filter paper;

(5) adding 100ml of isopropanol and 3g of monochloroacetic acid into the alkalized chitin jelly, mechanically stirring, and reacting for 2 hours in a thermostatic water bath at 25 ℃;

(6) and after the reaction is finished, performing suction filtration on a product, cleaning with absolute ethyl alcohol, dissolving in 200ml of water, adding HCl to adjust the pH value to be neutral, stirring and dissolving for 1h, repeatedly washing and extracting with absolute ethyl alcohol, centrifuging, and freeze-drying to obtain the carboxymethyl chitin required.

Example 2

(3) weighing 1.0g of dried chitin powder, dissolving in a dimethylacetamide-lithium chloride solution, filtering insoluble substances, adding 30ml of absolute ethyl alcohol to generate a jelly, performing suction filtration (filtrate recovery), and cleaning the filtrate with a large amount of water until the filtrate does not contain lithium chloride and N, N-dimethylacetamide;

(4) soaking chitin jelly in 50ml of 50% NaOH solution for 5 hours, filtering the solution, and sucking residual alkali liquor on the surface of the jelly with filter paper;

(5) adding 100ml of isopropanol and 3g of monochloroacetic acid into the alkalized chitin jelly, mechanically stirring, and reacting for 3 hours in a thermostatic water bath at 25 ℃;

Example 3

(2) 50ml of N, N-dimethylacetamide (DMAc) is weighed and added into a 100ml conical flask, 2.5g of anhydrous lithium chloride (LiCl) is added, and stirring is carried out to dissolve the mixture;

(4) soaking chitin jelly in 50ml of 50% NaOH solution for 6 hours, filtering the solution, and sucking residual alkali liquor on the surface of the jelly with filter paper;

(5) adding 100ml of isopropanol and 4.2g of monochloroacetic acid into the alkalified chitin jelly, mechanically stirring, and reacting for 3 hours in a thermostatic water bath at 25 ℃;

Example 4

(5) adding 100ml of isopropanol and 4.2g of monochloroacetic acid into the alkalized chitin jelly, mechanically stirring, and reacting for 4 hours in a thermostatic water bath at 25 ℃;

Example 5

Taking 1.0g of chitin, and drying in vacuum to obtain a sample a; taking the chitin jelly obtained in the step (3) in the embodiment 4, dispersing in 50ml of 50% NaOH solution, taking out after soaking at room temperature for 6h, and placing in a vacuum drying oven for drying to obtain a sample b; and (3) dispersing 1.0g of dried chitin in 50ml of 50% NaOH solution, soaking for 1h at 4 ℃, freezing at-20 ℃ overnight, taking out, and drying in a vacuum drying oven to obtain a sample c. The samples were thermally analyzed using a thermogravimetric analyzer. The thermogravimetric plots of samples a, b and c were recorded separately using a non-isothermal thermogravimetric method with a heating rate of 10 ℃/min from room temperature to 800 ℃ and a flow of 100 mL/min of high purity nitrogen as a shielding gas (fig. 1).

As shown in figure 1, the pyrolysis temperature of chitin is greatly changed after the chitin is subjected to alkalization treatment, compared with a sample a, samples b and c have weight loss peaks at 100 ℃, 150 ℃ and 250 ℃, the weight loss temperature of the sample b is most obviously reduced, and the reaction degree of chitin which is subjected to gelatinization and then alkalization is higher than that of chitin which is subjected to direct alkalization.

Example 6

Determination of degree of substitution of 6-O-carboxymethyl chitin obtained in examples 1 to 4

A certain amount of the product is taken, accurately weighed and marked as W, placed in a 250ml volumetric flask, and added with 100ml of deionized water and 25.00ml of 0.1mol/L NaOH standard solution while stirring, and slightly heated. Titration was carried out with 0.1mol/L HCl standard solution using phenolphthalein as an indicator, the volume V consumed by the HCl standard solution was recorded, and the Degree of Substitution (DS) was calculated according to the following formula

A=（25C1-VC2）/W

DS=0.203A/(1-0.058A)

In the formula: 25-volume ml of NaOH Standard solution used

C1-concentration mol/L of NaOH Standard solution used

V-volume ml of HCl Standard solution used

C2-concentration mol/L of HCl Standard solution used

W is the mass g of 6-O-carboxymethyl chitin.

The degree of substitution of the 6-O-carboxymethyl chitin obtained in example 1 was determined to be 0.316 according to the above method; the degree of substitution of the 6-O-carboxymethyl chitin obtained in example 2 was 0.386; the degree of substitution of 6-O-carboxymethyl chitin obtained in example 3 is 0.423; the degree of substitution of 6-O-carboxymethyl chitin obtained in example 4 was 0.538.

Example 7

Determination of transparency of 6-O-carboxymethyl chitin obtained in examples 1 to 4

The transparency is an index for indirectly representing the substitution uniformity, and in the traditional preparation of carboxymethyl chitin by heterogeneous reaction, because the reaction reagent infiltrates into the chitin layer by layer to react, the obtained product has uneven substitution distribution and poor solubility, so that a plurality of insoluble swelling particles exist in the solution after dissolution, and the transparency is poor.

The product of the example was prepared as a 1% (g/ml) aqueous solution of 6-O-carboxymethyl chitin, and slowly poured into a transparent glass tube until the black cross on the bottom plate of the glass tube was not visible, at which time the scale was read as transparent. The transparency is related to the degree of substitution shown in Table 1.

TABLE 1 degree of substitution vs. clarity

As can be seen from Table 1, the transparency of the solution increases with the degree of substitution, and the degree of substitution and the transparency have certain regularity, indicating that the etherification reaction in the method is relatively uniform.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions.

Claims

1. A preparation method of 6-O-carboxymethyl chitin with high degree of substitution is characterized by comprising the following steps:

(2) adding the chitin powder into DMAc/LiCl ionic liquid, stirring and dissolving to obtain chitin solution; the chitin powder is prepared by the following steps: DMAc/LiCl ionic liquid as 1: (100-500), wherein the mass ratio of the chitin powder to the LiCl is 1: (1-5);

(3) adding a non-solvent into the chitin solution to enable chitin to form gel, performing suction filtration, recovering filtrate, and cleaning a filtrate with a large amount of water until the filtrate does not contain lithium chloride and DMAc to obtain chitin gel; the non-solvent is at least one of water, alcohols, ketones and ethers, wherein the non-solvent: DMAc in a volume ratio of (50-300): (30-200); the alcohol is ethanol, the ketone is acetone, and the ether is diethyl ether;

2. The method for preparing 6-O-carboxymethyl chitin according to claim 1, wherein the alkaline solution in step (4) is 50% NaOH solution, and the alkalization soaking time is 5-8 h.

3. The method for preparing 6-O-carboxymethyl chitin according to claim 1, wherein in the step (5), monochloroacetic acid: the weight ratio of the chitin is as follows: (2-5): 1.

4. the method for preparing 6-O-carboxymethyl chitin according to claim 1, wherein the volume-to-mass ratio of isopropanol to chitin in step (5) is: (50-100): 1, the mol ratio of monochloroacetic acid to chitin is as follows: (4-10): 1.

5. the method for preparing 6-O-carboxymethyl chitin according to claim 1, wherein the step (5) is performed in thermostatic waterbath at 25 ℃ for 2-6 h.