JPH1129601A - Method for producing tricarboxypolysaccharide by nitrogen dioxide - Google Patents

Abstract

(57) [Summary] [Problem] A scale adhesion inhibitor, a pigment dispersant, a sizing agent,
In addition to a concrete admixture, a method for producing a tricarboxypolysaccharide polymer which can be suitably used particularly as a detergent builder is provided. A polysaccharide is oxidized with nitrogen dioxide / dinitrogen tetroxide at least 4 times the number of moles of pyranose units constituting the polysaccharide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a highly carboxylated tricarboxypolysaccharide or a salt thereof by oxidation of the polysaccharide. The tricarboxypolysaccharide or a salt thereof obtained by the present invention can be suitably used as a scale builder, a pigment dispersant, a sizing agent, a concrete admixture, and especially as a detergent builder.

[0002]

2. Description of the Related Art Various attempts have been made to industrially utilize polysaccharides as renewable resources ubiquitous on the earth. Japanese Patent Publication No. 49-1281 discloses a method of oxidizing a polysaccharide using a combination of periodic acid and chlorite or a hypochlorite, wherein the second and third positions of the polysaccharide are oxidized. It is described that dicarboxystarch obtained by oxidation has a detergent builder function.

Further, as a method for producing a tricarboxy polysaccharide by oxidizing a polysaccharide, Japanese Patent Publication No. 47-40552 and Czechoslovakia Patent No. 235576 disclose a method in which starch is aldehyde-modified with periodate and then aldehyde-modified. A method for oxidative carboxylation with nitrous oxide is disclosed. However, the methods described in JP-B-49-1281, JP-B-47-40552 and Czechoslovakia Patent 235576 have disadvantages for industrialization because expensive periodate must be used. Accompany.

[0004] Further, EP 542496 discloses a method of oxidizing and carboxylating starch by adding a vanadium salt and a nitrite in a nitric acid / sulfuric acid solvent. However, the method described in EP 542496 is a method of nitric acid oxidation of candy-like starch using a high-concentration sulfuric acid as a solvent, so that the treatment of the reaction solution is not easy, and the method is industrial. It is not suitable as a manufacturing method. JP-A-9-71601 discloses a method for tricarboxylating starch using hypochlorite in the presence of a ruthenium catalyst.

[0005] JP-A-7-500853, JP-A-7-503495 and JP-A-8-510494 disclose that starch is oxidized with dinitrogen tetroxide / nitrogen dioxide to form a 6-position of a pyranose unit. -C
A series of techniques for producing monocarboxy starch by oxidizing H2OH groups to carboxyl groups have been disclosed. But,
In the method described, the amount of nitrogen dioxide used is about 1 to 2 times the molar amount of pyranose units constituting starch, and as a result, monocarboxystarch in which the 6-position of the pyranose units has been converted to a -COOH group is mainly produced. . For use as a detergent builder having higher functional activity per weight, a polycarboxylic acid structure having a higher content of carboxyl groups is required.

Generally, in order to obtain a detergent builder having a high functional activity, a high Ca ion sequestering ability is required. For that purpose, a polycarboxylic acid structure containing a carboxyl group in a molecule at a high density is important. The polymer structure is important. However, it has been extremely difficult to highly oxidize and carboxylate using a polysaccharide as a raw material without excessively decomposing the polymer structure inherent to the polysaccharide.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to oxidize a polysaccharide as a raw material without causing a drastic decrease in the molecular weight derived from the polysaccharide, so that a -CH2OH group and a -CHOH- group become -COOH. It is an object of the present invention to provide a method for producing a polycarboxylic acid polymer having a very high carboxyl group content.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for producing a polycarboxylic acid polymer having an extremely high carboxyl group content by using a polysaccharide as a raw material. Reached. That is, the present invention
A process for producing a tricarboxypolysaccharide, comprising oxidizing a polysaccharide with nitrogen dioxide / dinitrogen tetroxide at least four times the number of moles of pyranose constituent units.

The tricarboxy polysaccharide of the present invention comprises: (1) an average of 80% or more of the -CH2OH group at the 6-position of the pyranose unit is oxidized to be converted to a -COOH group or a salt thereof; On average, 20% or more of the -CHOH- groups at the 2- and 3-positions are polymers having a molecular weight of 1,000 or more and 100,000 or less, comprising a polycarboxylic acid structure which has been oxidatively cleaved and converted to a -COOH group or a salt thereof.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polysaccharide used as a raw material in the present invention includes:
Examples include starch and cellulose, which are polymers composed of pyranose (anhydroglucose) units. Starch is preferred because of the ease of reaction. Starch includes corn starch, potato starch, tapioca starch, wheat starch, sweet potato starch, rice starch, and the like.
Water-soluble starch reduced in molecular weight using these as raw materials can also be used. Particularly preferred for industrial implementation are corn starch and tapioca starch. The lower the water content of the polysaccharide, the better, and preferably 20% or less.

The present invention uses nitrogen dioxide / dinitrogen tetroxide as the active species for the oxidation reaction. The expression nitrogen dioxide / nitrogen tetroxide means the equilibrium mixture of nitrogen dioxide and its dimer, nitrous oxide, under the reaction conditions.

In the present invention, the amount of nitrogen dioxide / nitrogen tetroxide used is at least four times the number of moles of pyranose units constituting the polysaccharide when the equilibrium is theoretically completely shifted to the nitrogen dioxide side. Quantity. The preferred amount of nitrogen dioxide used is at least 6 times the molar amount of pyranose units constituting the polysaccharide.
The amount is 0 mol or less, more preferably 7 mol or more and 15 mol or less.

If the amount of nitrogen dioxide / dinitrogen tetroxide is less than the above range, the oxidation reaction of the polysaccharide is insufficient in the carboxylation of the -CHOH- groups at the 2- and 3-positions of the pyranose unit, and No tricarboxypolysaccharide of the invention is produced. When the use amount of nitrogen dioxide is more than the above range, not only is it economically useless, but also the molecular weight is reduced due to excessive decomposition of the tricarboxypolysaccharide.

The nitrogen dioxide / nitrogen tetroxide at the time of supply may be in a liquid state or a gas state. Alternatively, nitrogen dioxide / nitrogen tetroxide can be supplied as a solution dissolved in a solvent such as carbon tetrachloride. When supplying in gaseous state,
It can also be supplied as a mixed gas with a gas other than nitrogen dioxide / nitrogen tetroxide, such as nitrogen or nitric oxide. It is also preferred to use a mixture of nitrogen dioxide / nitrogen tetroxide and oxygen.

In the present invention, the oxidation reaction of the polysaccharide is
It is performed under high temperature conditions of 50 ° C or higher. The upper limit of the oxidation reaction temperature is usually 120 ° C. in consideration of the stability of the resulting tricarboxypolysaccharide. A more preferred oxidation reaction temperature range is 60-100 ° C, most preferably 70-90 ° C. When the oxidation reaction temperature is low, the reaction stops at the monocarboxylation stage, and the reaction rate for tricarboxylation is too low to be practical. If the oxidation reaction temperature is too high,
The molecular weight is reduced due to excessive decomposition of the tricarboxypolysaccharide.

The reaction is usually carried out at normal pressure or under pressure.
The reaction pressure is preferably from 0.01 to 20 MPa, more preferably from 0.1 to 5 MPa. After the reaction, the recovered gas is oxidized if necessary, and can be used again as nitrogen dioxide / nitrogen tetroxide.

The oxidation reaction is usually carried out in a gas-solid two-phase system, but can also be carried out in a gas-liquid two-phase system or a gas-liquid-solid three-phase system. When using a liquid phase, a solvent that is stable to the oxidation reaction can be used. As the solvent, an aprotic organic solvent such as a halogenated hydrocarbon exemplified by carbon tetrachloride is preferable.

The oxidation reaction of the present invention can be carried out in the presence of a catalyst. The catalyst is preferably 4A of the periodic table,
It is selected from transition metal compounds containing at least one element selected from the group consisting of groups 5A, 6A, 7A, 8, 1B and 2B. Among them, compounds containing a group 5A or 6A element are preferable, and compounds containing vanadium, such as ammonium vanadate, sodium vanadate, vanadium pentoxide, and vanadium oxide acetylacetonate, are preferred because of their small side reaction. Particularly preferred. The amount of the catalyst used is 0.001 to 20% by weight, preferably 0.01 to 5% by weight of the polysaccharide raw material.

By performing a purification operation on the oxidation reaction mixture obtained in the present invention, a tricarboxypolysaccharide suitable for use can be separated. Examples of the purification operation include solvent extraction, chelate extraction, ion exchange resin treatment, ultra-membrane treatment, dialysis membrane treatment, RO membrane treatment, ion selective membrane treatment, microfiltration, concentration, and lyophilization. Further, if necessary, the product can be dissolved in water, and then precipitated by adding a lower alcohol or a lower ketone to purify the product.

[0020]

The present invention will be described below in more detail with reference to examples. In Examples, the carboxyl group content of the product was determined by precisely weighing a sample, dissolving in water, and titrating with an N / 20 aqueous sodium hydroxide solution. The structure of the product was analyzed by ¹³ C-NMR. The molecular weight is 0.3M NaCl, 0.1M NaH2PO4, 0.33M
GPC (column: Shodex O) using KH2P04 aqueous solution as eluent
Hpack SB-G / Shodex OHpack SB-803HQ 8mmID × 300mmL 、
The weight average molecular weight was measured using a polysaccharide as a sample with a RI detector).

Example 1 SUS316 equipped with a stirrer, pressure gauge, thermometer and gas vent tube
3.60 g of corn starch in an autoclave reactor made of
(Dry amount 3.15 g, pyranose unit 19.4 mmol) and 80 ml of carbon tetrachloride were put into a container cooled with an ice bath and weighed 8.95 g (liquefied mixture of nitrogen dioxide / nitrogen tetroxide 8.95 g (194 mmol as nitrogen dioxide, raw material) (Starch pyranose unit 10 times mol), and after sealing, immerse in a hot water bath.
The mixture was heated with stirring and maintained at a reactor internal temperature of 70 ° C. for 6 hours. The pressure in the autoclave was increased to 20 MPa. After cooling,
The gas in the reactor was released, and the air was replaced. Discard the carbon tetrachloride phase, dissolve and collect the paste remaining in the reactor by dissolving in water, concentrate and freeze-dry to obtain 2.98 g of the product.
I got

The carboxyl group content of the product was 9.2 meq / g. The product had a structure having a weight average molecular weight of 3,300, in which almost 100% of the 6-CH2OH group and about 35% of the 2- and 3-position -CHOH- groups of the pyranose unit constituting the raw starch were oxidatively cleaved to a carboxyl group. Of tricarboxy starch.

Example 2 A reaction was carried out in the same manner as in Example 1 except that 5.96 g of a liquefied mixture of nitrogen dioxide and dinitrogen tetroxide was added (130 mmol of nitrogen dioxide, 6.7 times the molar amount of starch pyranose units). Done. As a result of maintaining the temperature at 70 ° C. for 6 hours, the pressure in the autoclave was increased to 2.4 MPa. The product was obtained in the same manner as in Example 1.

The carboxyl group content of the product is 8.2
It was meq / g. The structure of the product was as follows. Almost 100% of the 6-CH2OH group and almost 25% of the 2- and 3-position -CHOH- groups of the pyranose unit constituting the raw starch were oxidatively cleaved to a carboxyl group, and the weight average molecular weight was 3,400. Of tricarboxy starch.

COMPARATIVE EXAMPLE 1 1.78 g of a liquefied mixture of nitrogen dioxide and nitrous oxide (38.7 mmol as nitrogen dioxide, twice as much as the starting starch pyranose unit) was added, and the internal temperature of the reactor was changed to 50 ° C. The reaction was carried out in the same manner as in Example 1. At 50 ° C
As a result of holding for 6 hours, the pressure in the autoclave was increased to 0.08 MPa. The product was obtained in the same manner as in Example 1.

The carboxyl group content of the product was 3.3 meq / g. The structure of the product is a monocarboxystarch in which almost 60% of the 6-CH2OH group of the pyranose unit constituting the raw starch is oxidatively cleaved to a carboxyl group and the -CHOH- groups at the 2-position and 3-position are unchanged. Met.

[0027]

According to the present invention, a polysaccharide is used as a raw material,
Both the -CH2OH group and the -CHOH- group of the pyranose unit that oxidize while maintaining the molecular weight to some extent and constitute the raw polysaccharide are -COOH
There is provided a method for industrially producing a tricarboxypolysaccharide, which is a polymer having a high carboxyl group content, which has been converted into a group.

Claims (3)

[Claims] 1. A method for producing a tricarboxypolysaccharide, comprising oxidizing a polysaccharide with nitrogen dioxide / dinitrogen tetroxide at least four times the number of moles of pyranose units constituting the polysaccharide. 2. The tricarboxy polysaccharide is formed by oxidative cleavage of a —CH 2 OH group at the 6-position of the pyranose unit and a —CHOH— group at the 2- and 3-positions of the pyranose unit constituting the raw material polysaccharide, resulting in a —COOH group or Converted to its salt, molecular weight 1,000 or more10
2. The method of claim 1, wherein the method comprises less than 10,000 polycarboxylic acid structures. 3. The method according to claim 1, wherein the polysaccharide is starch.