JPS5843406B2 - Funny news - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses partially deacetylated chitin (hereinafter referred to as modified chitin).

This invention relates to a method for obtaining chitin having a completely homogeneous structure, that is, po'J (N-acetyl-D-glucosamine), by acetylating the amino groups present in (N-acetyl-D-glucosamine).

To be more specific, the present inventors have clarified the method for producing a film or fiber of modified chitin (a part of the method for producing a modified chitin film is described in Seitsu Canine Science Faculty of Engineering Engineering Report, No. 18, P. 1373 (November 1973) and Makromol, Chem 0.176 (in press).

) has one acetamido group or an amino group generated by its deacetylation and two hydroxyl groups per glucose unit.

In order to obtain chitin with the same structure as naturally occurring chitin, only the amino groups must be acetylated.

However, at present it is difficult to obtain this complete selectivity.

Therefore, in the method of the present invention, an acetylating reagent is first applied to the modified chitin to completely acetylate the amino group and form an acetamide bond.

At this time, some of the hydroxyl groups are also necessarily acetylated, and chitin having various degrees of acetylation is produced, so the next step is to selectively remove only the acetyl groups bonded to these hydroxyl groups.

These are shown by the chemical formulas below.

Chitin is contained in large amounts in the shells of shrimp, crabs, and insects, and is the second most abundant polysaccharide compound in nature after cellulose.

However, chitin itself is insoluble and infusible in all solvents, so even though it is available in large quantities and at low cost, little research has been done on its use.

There have been previous attempts to regenerate chitin films using solid-phase acetylation methods from chitosan films in which chitin has been completely deacetylated. Many problems remain, such as the acetylation reaction.

However, as described herein, by using a modified chitin film, fiber, or powder obtained by a method newly developed by the present inventors, a chitin film with a completely uniform structure, which has been difficult until now, can be obtained. fiber,
Alternatively, the powder can be obtained easily and at low cost.

Acetylation carried out in the present invention is carried out using common acetylation reagents such as acetic anhydride, acetyl chloride, or isopropenyl acetate.

At this time, the reaction does not proceed easily because modified chitin does not dissolve or swell in these acetylation reagents.

Therefore, when trying to obtain chitin with a high degree of acetylation, it is necessary to use a swelling solvent.

When water-soluble modified chitin is used as a starting material, it is dissolved in water and treated with a basic solvent such as pyridine, N-methylmorpholine, triethylamine, dimethylformamide, dimethylacetamide, dimethylsulfoxide, etc.
N-Methylpyrrolidone is poured into a polar solvent such as hexamethylphosphoramide or acetic acid, allowed to precipitate in a swollen state, filtered, and treated with an acetylation reagent without drying.

As the acetylation reagent, acetic anhydride, acetyl chloride, a mixed system of these with pyridine, a polar solvent, or acetic acid, or a three-component system thereof are easy to handle and effective.

When using modified chitin that is insoluble in water, a chitin film, fiber, or powder is immersed in water or a common polar solvent such as dimethylformamide or m-cresol to swell it, and then acetylation is performed in the same manner.

Regardless of the solubility of modified chitin in water, acetylation proceeds well with acetic acid alone when heated.

In general, it is well known that amino groups are much more easily acetylated than hydroxyl groups, so if the reaction is carried out sufficiently in a swollen state as in this method, at least the amino groups will be completely acetylated. Ru.

The above acetylation conditions will be explained in detail in the examples, but the temperature range is from ~20 to ioo°C, preferably from 40 to 70°C.
Perform at a temperature between 0°C.

This acetylation reaction proceeds well with the acetylation reagent alone or with a mixture of the acetylation reagent and pyridine or acetic acid, but it is best to use a solvent that will swell both the modified chitin, which is the starting material, and the acetylated chitin, which is the product. Even better results can be obtained.

Examples of solvents that can be used include dimethylformamide,
Examples include dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, hexamethylphosphoramide, tetramethylenesulfone, m-cresol, or a mixed solvent system thereof.

Among these systems, acetic anhydride-pyridine and acetic anhydride-
It was confirmed from the infrared absorption spectrum that the pyridine-dimethylformamide system gave a particularly high degree of acetylation.

The acetylated chitin obtained by this method has an infrared absorption spectrum of 1630 to 1655 (1'ii' and 1550cf/L'), in addition to the characteristic strong absorption of acetamide groups, absorption due to ester groups is observed at 1730CTL'. The structure can be confirmed from the fact that it is

In addition, in modified chitin, the amide I absorption band is 1650
It was found near -1655CrfL', but it was found that a shift in the absorption position was observed by acetylating this.

That is, in samples with a low degree of acetylation in the hydroxyl group, absorption was observed at 1630 to 1635c/rL-1, suggesting that the amino group was completely acetylated and became structurally uniform, resulting in a strong association state. are doing.

On the other hand, in the case where most of the hydroxyl groups were acetylated, absorption appeared at 1650 to 1655C1rL-1, indicating that the introduction of many ester groups deteriorated the association state and appeared on the higher wavenumber side.

Furthermore, by examining these infrared absorption spectra, it was found that by appropriately selecting the acetylation reagent, solvent, and reaction conditions including temperature and time, amino groups can be changed from partially acetylated to completely acetylated. It is possible to freely obtain chitin with various degrees of acetylation, including those in which the hydroxyl group has various degrees of acetylation.

Amino groups are acetylated, and in order to keep the degree of acetylation of hydroxyl groups low, it is necessary to use an acetylating reagent alone, use an acidic solvent such as acetic acid or m-cresol as a cosolvent, or heat with acetic acid alone. There is a better way to do that.

Acetylated chitin is reacted at a predetermined temperature for a predetermined time, filtered, and isolated by washing with a low boiling point solvent such as methanol.

To selectively remove only the acetyl groups bonded to hydroxyl groups in acetylated chitin and return it to chitin, a water splitting reaction using a weak basic substance or a transesterification reaction using a large excess of methanol can be used.

In the hydrolysis reaction, weakly basic substances such as sodium carbonate, sodium bicarbonate, sodium acetate, or their potassium derivatives can be used, but sodium carbonate gives particularly good results.

The reaction conditions at this time are in the temperature range of 0 to 100°C, preferably in the range of 30 to 70°C.

The chitin film, fiber or powder obtained by this method has an infrared absorption spectrum of 1730 crrL.
The characteristic absorption due to the ester group of ' completely disappeared, and 1
625.1550cfrL' shows strong absorption due to the acetamide group, so its structure can be confirmed.

These chitins exhibited different properties from the starting material, modified chitin, in the following points.

That is, the amide I absorption band due to the acetamide group in the infrared absorption spectrum of chitin obtained by the method of the present invention has a larger absorption than that of modified chitin, and the absorption position is also about 25 to 30 crrL-1 lower than that of modified chitin. 16
25crrL-1, and this indicates that natural chitin exhibits an amide ■ absorption band for 1626CrrL-1, as reported by Falk et al. (M, Falk, D, G, S
m1th J.

McLachlan 1 and A, GoMe In
nes, Can, J.

Chem., 44.2269 (1966)) and supports the structure.

Differences were also observed in solubility and swelling properties, and when chitin was reverted to a uniform structure, the solubility and swelling properties were lower than that of modified chitin.

When carrying out the transesterification reaction in methanol, since acetylated chitin does not swell in methanol, it is necessary to use another solvent to bring it into a swollen state before carrying out the reaction.

In this reaction, the acetylated chitin is pulverized,
Alternatively, it has been found that if the swelling treatment with a polar solvent is insufficient, a slight absorption of ester groups remains in the infrared absorption spectrum even if the reaction is carried out for a long time, so it is necessary to perform these operations completely. .

It is effective to swell the acetylated chitin in a general polar solvent such as dimethylformamide, dimethylacetamide, m-cresol, etc. at a temperature ranging from room temperature to 100°C.

After sufficient swelling, anhydrous methanol and a catalyst are added to carry out the reaction.The catalysts used are metallic sodium, p
-) Substances used in general transesterification reactions such as luenesulfonic acid and pyridine can be mentioned.

Among these catalysts, metallic sodium is particularly effective.

The reaction conditions at this time can be carried out in the temperature range from room temperature to heating to reflux, but since the reaction rate is slow due to the heterogeneous reaction, the reaction is completed more quickly by heating to reflux.

Example 1 21 parts of acetic anhydride is added to 0.1' of modified chitin, and the mixture is heated under reflux with the legs opened at 7 o'clock.

After cooling to room temperature, the acetylated chitin product was filtered, thoroughly washed with methanol, and dried.

The infrared absorption spectrum of this product shows 1635CIr.
Strong absorption of acetamide group is seen in L,', but 173
The absorption caused by the ester of 0CrrL-1 is very weak, indicating that the amino groups in the polymer are completely acetylated, while the degree of acetylation of the hydroxyl groups in the polymer is very low.

Example 2 0.11 g of water-soluble modified chitin was dissolved in 15 g of water and poured into excess pyridine.

The swollen and precipitated modified chitin was filtered, thoroughly washed with pyridine, and then pyridine was added to make the total weight 21, and 4 tons of acetic anhydride was added thereto.

After reacting at 40° C. for 72 hours, the product was isolated as in Example 1.

The yield was 0.073P.

The infrared absorption spectrum of the produced polymer is 1730CI.
Strong absorption due to ester group and 1650,
Strong absorption due to acetamide group was observed at 1550 crrL-1.

This fact indicates that the acetylation reaction proceeded sufficiently and not only the amino groups but also most of the hydroxyl groups were acetylated.

The highly acetylated chitin obtained here was insoluble in water and organic solvents, but swelled well in water and polar solvents such as dimethylformamide and m-cresol.

Example 3 In the same manner as in Example 2, 0.1z water-soluble modified chitin was dissolved in water.
It was reprecipitated with pyridine and the precipitate was filtered.

41 acetic anhydride, 6z dimethylformamide, and 2t pyridine were added to this swollen polymer, and the mixture was heated at 45°C for 2 hours.
The reaction was allowed to proceed for 0 hours.

The product was isolated in the same manner as in Example 1 and the yield was 0.0
It was 95S'.

When examined by infrared absorption spectrum, it completely matched the spectrum of acetylated chitin obtained in Example 2,
This indicated that acetylation had progressed sufficiently.

In this reaction, highly acetylated chitin was similarly obtained even when excess acetyl chloride was used in place of acetic anhydride.

Example 4 A solution of 0.1i of water-soluble modified chitin dissolved in 15S' of water was poured into excess acetic acid to precipitate it.

The swollen precipitate was filtered and thoroughly washed with acetic acid, and then acetic acid was added to make the total weight 2.91. To this was added 2 da acetic anhydride and 3 g pyridine, and the mixture was reacted at 45°C for 40 hours.

The product was isolated according to Example 1 with a yield of 0.
When the infrared absorption spectrum of 054P was measured, it matched that of the acetylated chitin obtained in Example 2, indicating that it was highly acetylated.

Example 5 Modified chitin film 0.11 m-cresol 2.5i
was added and left at room temperature for 72 hours to swell.

This was mixed with 2.5 g of acetic anhydride and 0.05 g of concentrated sulfuric acid, and reacted at 40°C for 20 hours.

The film was washed with methanol and acetone and dried.

In the infrared absorption spectrum, 1730CvrL'
Although the absorption by the ester group of 1635.1 is very weak,
Since strong absorption by acetamide groups was observed in 550crfL', only amino groups can be acetylated quite selectively using this reaction system.

Example 6 Modified chitin film 0.11 was soaked in excess water at room temperature.
After swelling for 2 hours, without filtering and drying, the mixture was reacted with 41 acetic anhydride, 61 dimethylformamide, and 42 pyridine at 45° C. for 40 hours.

The film was isolated as in Example 5.

The infrared absorption spectrum of this film almost matched the spectrum of the film obtained in Example 5, confirming that only the amino groups were highly selectively acetylated.

Example 7 A modified chitin film 0.11 was heated under reflux in excess glacial acetic acid for 10 hours.

Reaction Wave An acetylated chitin film was isolated according to Example 1.

In the infrared absorption spectrum, strong absorption by the acetamide group was observed at 1635.1550 cm', but the absorption at 1730crfL' by the ester group was very weak, and as in Examples 5 and 6, only the amino group was selectively absorbed by the acetyl group. I confirmed that it has been changed.

Example 8 Highly acetylated chitin obtained in Example 2 0.11
Add 2 rul of a 10% concentration sodium carbonate aqueous solution to
Heated at 50°C for 4 hours.

The reaction mixture was filtered, and the product was thoroughly washed with methanol and acetone and dried.

1625.1550CrrL in infrared absorption spectrum
Strong absorption due to the acetamide group was observed in ', but the absorption of 1730cIrL'' due to the ester group completely disappeared.

Other absorption bands also matched the spectrum reported by Falk et al., indicating that chitin with a uniform structure was obtained.

The chitin obtained here was insoluble in water and organic solvents.

Example 9 40 mg of highly acetylated chitin obtained in Example 2
was swollen in m-cresol 11 for 20 hours at room temperature, followed by 1 g of anhydrous methanol and a catalytic amount of metal (IJ).
The mixture was heated under reflux for 48 hours.

The reaction solid was filtered, washed with methanol and dried.

According to the infrared absorption spectrum, the transesterification reaction progressed, and the absorption by ester groups decreased to a moderate level.

Example 10 40 μm of acetylated chitin obtained in Example 2 was finely powdered, 11 dimethylformamide was added thereto, and the mixture was heated at 60°C for 20
After swelling for an hour, anhydrous methanol 11 and a small amount of sodium metal were added, and the mixture was heated under reflux for 48 hours.

In the infrared absorption spectrum of the product isolated according to Example 9, no absorption by the ester of 1730 crrL-1 was observed, confirming that chitin with a uniform structure was regenerated as in Example 8.

Claims (1)

[Claims] 1. An acetylation reagent selected from the group consisting of acetic anhydride, acetyl chloride, and isopropenyl acetate, or the like, in a swollen state of a partially deacetylated modified chitin film, fiber, or powder obtained from naturally occurring chitin. Acetylation using a mixed system of and a solvent,
Chitin films, fibers, or powders with various degrees of acetylation are produced, and then subjected to hydrolysis treatment with a weak basic substance or transesterification reaction in a swollen state to remove only acetyl groups bonded to hydroxyl groups. A method for regenerating chitin having a uniform structure, characterized by: