JP2020019888A - Cellulose derivative, heavy metal removal material containing the same, and heavy metal removing method using the same - Google Patents

Abstract

To provide a cellulose derivative that has excellent adsorption of heavy metals and selectively adsorbs heavy metals.SOLUTION: The present invention provides a cellulose derivative having a repeating unit of formula (1), having a molecular weight distribution (Mw/Mn) of 1.2 or more and 4.0 or less, with R being hydrogen or a group represented by formula (a) (where Reach denote a single bond or a C1-10 alkylene group; Reach denote hydrogen or a C1-10 alkyl group; each Rmay be the same or different to denote a C1-10 alkyl group).SELECTED DRAWING: None

Description

  The present invention relates to a novel cellulose derivative, a method for producing the same, a heavy metal removing material containing the cellulose derivative, and a heavy metal removing method using the cellulose derivative.

  Heavy metals such as arsenic, cadmium, and lead are used in various fields. For example, arsenic is used as pharmaceuticals, insecticides, rodenticides, preservatives, high-tech industrial materials, and the like. For this reason, the heavy metals may be dissolved in the stratum, the ocean, rivers, well water, and the like, but it is known that even a trace amount of them may cause environmental pollution. Therefore, a method of efficiently collecting and removing the heavy metal from soil, seawater, industrial wastewater, mine drainage, and the like contaminated with the heavy metal is desired.

  Patent Literature 1 discloses that a cellulose-based adsorbent obtained by introducing a graft chain on the surface of a cellulose-based substrate and binding a chelate-forming group or an ion-exchange group to the introduced graft chain is easily compatible with water, and contains boron and germanium. It is described that it has excellent adsorption power for semimetals or heavy metals such as arsenic. The amount of the chelate-forming group or the ion-exchange group that exerts the metal adsorbing power depends on the rate of graft chain introduction, and the lower the rate of graft chain introduction, the lower the rate of chelate formation that effectively acts on the metal adsorption. It is described that it is not possible to secure a sufficient amount of a group or an ion exchange group. However, since the cellulosic base material has low solubility in an organic solvent, it is very difficult to efficiently introduce the graft chain, and the introduction of the graft chain can be performed only by a method using an expensive apparatus such as a radiation graft method. However, there has been a problem that the rate cannot be improved and the cost increases.

  Patent Document 2 discloses that acylated cellulose has excellent solubility in an organic solvent, a dithiocarbamate group can be efficiently and inexpensively introduced, and a cellulose derivative having a dithiocarbamate group and an acyl group obtained is a metal derivative. It is described as being useful as a metal removing material having excellent adsorption power.

JP 2009-13204 A JP, 2018-83882, A

Acylated cellulose is excellent in solubility in organic solvents, so that dithiocarbamate groups can be efficiently introduced.However, since the degree of substitution of groups containing dithiocarbamate groups is limited, it is necessary to further improve the adsorption amount of heavy metals. There were challenges.
Thus, development of a metal removing material having excellent heavy metal adsorption power is desired.

Therefore, an object of the present invention is to provide a novel cellulose derivative excellent in heavy metal adsorption power, and a method for producing the same.
Another object of the present invention is to provide a heavy metal removing material having excellent heavy metal adsorption power.
It is another object of the present invention to provide a method for selectively adsorbing and recovering heavy metals.

  In addition, metal ions other than heavy metals, such as calcium, often coexist in soil, seawater, industrial effluent, mine drainage, etc., which are contaminated with heavy metals. Therefore, a heavy metal removing material capable of selectively adsorbing heavy metals is desired.

  The present inventors have conducted intensive studies in order to solve the above problems, and as a result, have found a method capable of efficiently and inexpensively introducing a dithiocarbamate group into cellulose. Further, they have found that a cellulose derivative having a dithiocarbamate group having a molecular weight distribution in a specific range is useful as a heavy metal removing material having excellent heavy metal adsorption. The present invention has been completed based on these findings.

［式中、Ｒは、同一又は異なって、水素原子、又は下記式（ａ）で表される基である。セルロース誘導体に含まれる全てのＲのうち、少なくとも１つは下記式（ａ）で表される基である］

（式中、Ｒ¹は単結合又は炭素数１〜１０のアルキレン基を示し、Ｒ²は水素原子又は炭素数１〜１０のアルキル基を示す。Ｒ³は、同一又は異なって、炭素数１〜１０のアルキル基を示す） That is, the present invention provides a cellulose derivative having a repeating unit represented by the following formula (1) and having a molecular weight distribution (Mw / Mn) of 4.0 or less and 1.2 or more.

Wherein R is the same or different and is a hydrogen atom or a group represented by the following formula (a). At least one of all Rs contained in the cellulose derivative is a group represented by the following formula (a)]

(Wherein, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. R ³ is the same or different and has 1 carbon atom Represents an alkyl group of 10 to 10)

（式中、Ｒ³は、同一又は異なって、炭素数１〜１０のアルキル基を示し、Ｒ⁴は同一又は異なって、水素原子又は炭素数１〜３のアルキル基を示す。ｎは１〜３の整数を示す） The present invention also provides the above cellulose derivative, wherein the group represented by the formula (a) is a group represented by the following formula (a-1).

(Wherein, R ³ is the same or different and represents an alkyl group having 1 to 10 carbon atoms, and R ⁴ is the same or different and represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Indicates an integer of 3)

  The present invention also provides the above cellulose derivative, wherein the total average degree of substitution of the group represented by the formula (a) is from 0.1 to 2.95.

The present invention also provides a method for producing a cellulose derivative, wherein the cellulose derivative is obtained through the following steps.
[1] Cellulose hydroxyl group is reacted with an amino group-protected amino acid, and then the amino-protecting group is removed. [2] A quaternary ammonium salt is added to the deprotected amino group in the presence of a sulfur compound. N ⁺ (R ³ ) ₄ X ⁻ ; R ³ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms, and X ⁻ represents a counter anion.

  The present invention also provides a heavy metal adsorbent containing the above-mentioned cellulose derivative.

  The present invention also provides a method for removing heavy metals using the above-mentioned cellulose derivative.

  The cellulose derivative of the present invention has a high adsorption amount of heavy metals (for example, heavy metals such as arsenic, cadmium, and lead), and can adsorb and recover heavy metals efficiently. Further, the cellulose derivative of the present invention is excellent in chemical resistance, heat resistance, and water resistance. Therefore, the cellulose derivative of the present invention is extremely useful as a heavy metal removing material, and is suitably used for purifying soil and seawater contaminated with heavy metals, industrial wastewater containing the above metals, mine wastewater, hot spring water, and the like. can do.

［式中、Ｒは、同一又は異なって、水素原子、又は下記式（ａ）で表される基である。前記式（１）で表される繰り返し単位を有するセルロース誘導体に含まれる全てのＲのうち、少なくとも１つは下記式（ａ）で表される基である］

（式中、Ｒ¹は単結合又は炭素数１〜１０のアルキレン基を示し、Ｒ²は水素原子又は炭素数１〜１０のアルキル基を示す。Ｒ³は、同一又は異なって、炭素数１〜１０のアルキル基を示す） [Cellulose derivative]
The cellulose derivative of the present invention has a repeating unit (glucose unit) represented by the following formula (1).

Wherein R is the same or different and is a hydrogen atom or a group represented by the following formula (a). At least one of all Rs contained in the cellulose derivative having the repeating unit represented by the formula (1) is a group represented by the following formula (a)]

(Wherein, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. R ³ is the same or different and has 1 carbon atom Represents an alkyl group of 10 to 10)

Examples of the alkylene group having 1 to 10 carbon atoms for R ¹ include a methylene group, a methylmethylene group, a dimethylmethylene group, an ethylene group, a 2-methylethylene group, a 1,2-dimethylethylene group, a propylene group, a trimethylene group, Examples thereof include a linear or branched alkylene group such as a 2-methyl-trimethylene group.

In particular, as R ¹ , the longer the carbon chain between the cellulose main chain skeleton and the dithiocarbamate group, the more the metal adsorption power tends to be improved.

Examples of the alkyl group having 1 to 10 carbon atoms in R ² and R ³ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, an s-butyl group, a t-butyl group, a pentyl group, and the like. And a straight-chain or branched-chain alkyl group.

R ² is preferably a hydrogen atom. R ³ is preferably an alkyl group having 1 to 3 carbon atoms.

As the group represented by the formula (a), a group represented by the following formula (a-1) (in the formula, n represents an integer of 1 to 3, and R ⁴ is the same or different and represents hydrogen Represents an atom or an alkyl group having 1 to 3 carbon atoms. R ³ is the same as defined above), and particularly preferably a group represented by the following formula (a-1) wherein n in the formula is 2 is there.

The group represented by the formula (a) is more preferably a group represented by the following formula (a-1 ′) (in the formula, n represents an integer of 1 to 3, R ⁴ is the same or different, A hydrogen atom or an alkyl group having 1 to 3 carbon atoms), and particularly preferably a group represented by the following formula (a-1 '), wherein n is 2 in the formula.

The group represented by the formula (a) is particularly preferably a group represented by the following formula (a-1-1) or (a-1-2), and particularly preferably a group represented by the following formula (a-1- It is a group represented by 2). Note that R ³ in the following formula is the same as described above.

The group represented by the formula (a) is most preferably a group represented by the following formula (a-1′-1) or (a-1′-2), and particularly preferably a group represented by the following formula (a- It is a group represented by 1'-2).

  A group represented by the formula (a) (preferably a group represented by the formula (a-1), more preferably a group represented by the formula (a-1 ′), and still more preferably a group represented by the formula (a-1-1) ) And a group represented by (a-1-2), most preferably a group represented by the formula (a-1′-1) and a group represented by (a-1′-2) The total average degree of substitution of the group (group) is, for example, 0.1 to 2.95, and preferably 0.2 to 2.95. It is 2.90, particularly preferably 0.3 to 2.90. It is preferable that the cellulose derivative contains the group represented by the formula (a) in the above range, since excellent metal adsorption power can be exhibited.

  As described above, the molecular weight distribution (the molecular weight distribution Mw / Mn obtained by dividing the weight average molecular weight Mw by the number average molecular weight Mn) of the cellulose derivative of the present invention is 4.0 or less, 1.2 or more, and 3.5 or less. It is preferably 5 or more, more preferably 3.0 or less and 2.0 or more. When the molecular weight distribution exceeds 4.0 or is less than 1.2, the molecular weight distribution becomes broad or sharp, which may affect the heavy metal adsorptivity such as a lack of a target heavy metal adsorption force. For example, when the molecular weight distribution of the cellulose derivative of the present invention is 4.0 or less and 1.2 or more, the balance between the heavy metal adsorption power and the adsorption selectivity (the heavy metal adsorption performance in the presence of coexisting ions other than heavy metals such as calcium). They tend to be compatible at a very high level.

The molecular weight distribution (Mw / Mn) of the cellulose derivative of the present invention is such that at least one part of a hydroxyl group (OH group) in cellulose, which is an intermediate of [Production method of cellulose derivative] described below, is -OOC-R ^1-. It can be determined by measuring the molecular weight distribution (Mw / Mn) of the compound (1-3) substituted with an NH ₂ group. Details will be described later.

  The cellulose derivative of the present invention has excellent heavy metal (particularly, As (III), Cd (II), Pb (II), etc.) adsorption power. The amount of heavy metal adsorbed is, for example, 0.01 mmol / g or more, preferably 0.02 mmol / g or more, and particularly preferably 0.03 mmol / g or more. The adsorption amount of As (III) is, for example, 0.01 mmol / g or more, preferably 0.02 mmol / g or more, and particularly preferably 0.03 mmol / g or more. The upper limit of the adsorption amount of As (III) is, for example, about 2.0 mmol / g, preferably 1.0 mmol / g, and particularly preferably 0.20 mmol / g.

  The shape of the cellulose derivative of the present invention is not particularly limited as long as the effects of the present invention are not impaired, and examples thereof include a sheet shape, a spherical shape (a true spherical shape, a substantially true spherical shape, an oval spherical shape, etc.), a polyhedral shape, a rod shape ( Columnar, prismatic, etc.), scaly, irregular, and the like.

  Since the cellulose derivative of the present invention has an excellent heavy metal adsorption power as described above, it can be suitably used, for example, as a heavy metal adsorbent.

  The heavy metal adsorbent containing the cellulose derivative of the present invention (or the heavy metal adsorbent composed of the cellulose derivative of the present invention) includes, for example, heavy metals (particularly, heavy metals such as As (III), Cd (II), and Pb (II)). It can be suitably used for purifying soil and seawater contaminated with, and other industrial wastewater, mine wastewater, and hot spring water containing the metal.

  The method for removing heavy metals of the present invention, that is, soil or seawater contaminated with heavy metals (particularly heavy metals such as As (III), Cd (II) and Pb (II)) using the cellulose derivative of the present invention as a heavy metal adsorbent. The method for adsorbing and removing metals from industrial wastewater containing the heavy metals, mine wastewater, hot spring water and the like is not particularly limited.For example, a cellulose derivative of the present invention is filled in a column or the like, and the column is filled therein. Examples of the method include a method of flowing industrial wastewater and the like, and a method of adding the cellulose derivative of the present invention to industrial wastewater and stirring the mixture. In particular, when the cellulose derivative of the present invention exhibits solubility in an organic solvent, it can be used as a homogeneous heavy metal adsorbent (that is, a substance exhibiting an action of adsorbing and removing metals in a state of being dissolved in industrial wastewater or the like). .

  In the heavy metal removal method of the present invention, adjusting the pH of the cellulose derivative to, for example, 1 to 9 (especially 1 to 7) can further improve the metal adsorption power and efficiently remove the metal. It is preferable in that it can be performed. The pH of the cellulose derivative can be adjusted using a commonly used pH adjuster (acid such as nitric acid or alkali such as sodium hydroxide).

  Further, the heavy metal can be easily recovered by firing the cellulose derivative having the heavy metal adsorbed thereon, and the recovered heavy metal can be reused as a useful resource.

[Method for producing cellulose derivative]
The cellulose derivative of the present invention can be produced, for example, through the following steps.
[1] Cellulose hydroxyl group is reacted with an amino group-protected amino acid, and then the amino-protecting group is removed. [2] A quaternary ammonium salt is added to the deprotected amino group in the presence of a sulfur compound. N ⁺ (R ³ ) ₄ X ⁻ ; R ³ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms, and X ⁻ represents a counter anion.

[Raw material cellulose]
The cellulose used in the above step [1] is a polysaccharide in which glucose has a β-glucoside bond. These polysaccharides may include hemicellulose components such as mannan and xylan or complex sugars such as glucomannan. Further, cellulose composed of glucose alone may be used. Examples of cellulose containing a hemicellulose component include pulp of wood linter.
For example, wood pulp (softwood pulp, hardwood pulp), cellulose derived from cotton linter pulp, and the like can be suitably used. These can be used alone or in combination of two or more.

In order to obtain the cellulose derivative having a specific molecular weight distribution of the present invention, it is important to select the molecular weight distribution of the raw material cellulose. By derivatizing the cellulose of the present invention, the molecular weight distribution transitions to a smaller (narrower) one. Although the degree of the transition varies depending on the derivatization conditions, it is generally in a proportional relationship with the molecular weight distribution of the raw material cellulose. Therefore, in order to obtain a cellulose derivative having a narrow molecular weight distribution according to the present invention, it is important to select cellulose having a desired molecular weight distribution.
In the present invention, the molecular weight distribution of the starting material cellulose is not specified. It is determined by measuring according to the description in 235-242, Apr, 2013.
Generally, biocellulose and the like tend to have a large molecular weight distribution, and cotton cellulose has a smaller molecular weight distribution. Wood pulp tends to have a narrow (small) molecular weight distribution depending on the pulp treatment.
The raw cellulose is preferably used in a finely pulverized state, for example, by subjecting it to a crushing treatment.

The amino acid whose amino group is protected is represented, for example, by the following formula (3).
HOOC-R ¹ -NHY (3)
R ¹ in the formula (3) corresponds to R ¹ in the formula (a). Y is a protecting group for protecting an amino group, and examples thereof include a t-butoxycarbonyl group (Boc) and a 9-fluorenylmethyloxycarbonyl group (Fmoc). As the amino-protecting group, Fmoc is particularly preferred because it can be deprotected under mild conditions.

The amino acid before protecting the amino group is represented by the following formula (3 ′).
HOOC-R ¹ -NH ₂ (3 ′)
R ¹ in the formula (3 ') in correspond to R ¹ in the formula (a). Examples of the amino acid before protecting the amino group (= the compound represented by the formula (3 ′)) include, for example, L-alanine, β-alanine, 4-aminobutyric acid, 5-aminopentanoic acid, and 7-aminoheptanoic acid And the like.

  The reaction between the cellulose and the amino acid whose amino group is protected is preferably performed in the presence of a catalyst. Examples of the catalyst include triethylamine, pyridine, N, N-dimethyl-4-aminopyridine (DMAP) and the like. These can be used alone or in combination of two or more.

  The amount of the catalyst to be used is, for example, about 0.01 to 1.0 mol per 1 mol of the amino acid in which the amino group is protected.

  The reaction is preferably performed in the presence of a condensing agent. Examples of the condensing agent include 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC-HCl), N, N′-dicyclohexylcarbodiimide, N, N′-diisopropylcarbodiimide and the like. it can. These can be used alone or in combination of two or more.

  The amount of the condensing agent to be used is, for example, about 0.01 to 1.0 mol per 1 mol of the amino acid in which the amino group is protected.

  The reaction is preferably performed in the presence of a solvent. Examples of the solvent include aliphatic hydrocarbons such as hexane, heptane and octane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene; chloroform, dichloromethane, 1,2- Halogenated hydrocarbons such as dichloroethane; ethers such as diethyl ether, dimethoxyethane, tetrahydrofuran and dioxane; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as methyl acetate, ethyl acetate, isopropyl acetate and butyl acetate; Amides such as dimethylformamide and N, N-dimethylacetamide; nitriles such as acetonitrile, propionitrile and benzonitrile; alcohols such as methanol, ethanol, isopropyl alcohol and butanol; Sulfoxide, and the like. These can be used alone or in combination of two or more.

  In particular, it is preferable to use a mixture of dimethylacetamide and lithium chloride as a solvent. However, this reaction does not require the raw material cellulose to be dissolved to form a uniform solution, and the reaction can proceed as a slurry in which the solvent and the cellulose are suspended. Therefore, it is not necessary to use a large amount of expensive lithium chloride necessary for dissolving ordinary cellulose. The concentration of lithium chloride in the organic solvent is not particularly limited as long as cellulose is dissolved, but is, for example, about 0.5 to 30% by weight.

  The amount of the solvent used is, for example, about 0.5 to 30 times the total amount of the reaction substrates. When the amount of the solvent used exceeds the above range, the concentration of the reaction component tends to decrease, and the reaction rate tends to decrease.

Through the above reaction, from the acylated cellulose (1-1), at least a part of the hydroxyl group (OH group) in the acylated cellulose is converted to an —OOC—R ¹ —NHY group (Y is a protecting group for an amino group, Compound (1-2) substituted with the same as Y in formula (3) is obtained.

In the reaction for removing the amino-protecting group, the amino-protecting group (Y) in the compound (1-2) obtained through the reaction is removed, and at least a part of the hydroxyl group (OH group) in the acylated cellulose is removed. , -OOC-R ¹ -NH ₂ -substituted compound (1-3). The reaction for removing the protecting group is preferably appropriately selected according to the type of the protecting group. For example, when Y is Fmoc, the protecting group can be quickly removed by reacting a secondary amine such as pyridine. When Y is Boc, the protecting group can be promptly removed by reacting with a strong acid such as trifluoroacetic acid.

In the step [2], the deprotected amino group, that is, the —OOC—R ¹ —NH ₂ group in the compound (1-3) obtained through the step [1] is added to the fourth group in the presence of a sulfur compound. grade ammonium _{^{(N + (R 3) 4}} X -; R 3 are the same or different and each represents an alkyl group having 1 to 10 carbon atoms, X ^- represents a counter anion) were reacted to cellulose of the present invention This is a step of obtaining a derivative.

Examples of the counter anion (X ⁻ ) in the quaternary ammonium salt include OH ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , F ⁻ , SO ₄ ²⁻ , BH ₄ ⁻ , BF ₄ ⁻ , PF ₆ ^{− and the} like. Is mentioned.

  Examples of the quaternary ammonium salt include tetramethylammonium hydroxide and tetraethylammonium hydroxide.

  The amount of the quaternary ammonium salt to be used is, for example, about 20 to 500 parts by weight based on 100 parts by weight of the compound (1-3).

  Examples of the sulfur compound include carbon disulfide. The amount of the sulfur compound to be used is, for example, 100 parts by weight or more based on 100 parts by weight of the compound (1-3).

  The reaction in step [2] is preferably performed in the presence of a solvent. Examples of the solvent include aromatic hydrocarbons such as toluene, xylene and ethylbenzene; alcohols such as methanol, ethanol, 2-propanol, isopropyl alcohol and butanol; N-methylpyrrolidone, dimethyl sulfoxide, N, N-dimethylformamide and the like. Is mentioned. These can be used alone or in combination of two or more. The amount of the solvent used is, for example, about 0.5 to 30 times the total amount of the reaction substrates.

  The reaction temperature in step [2] is, for example, about 10 to 100 ° C. The reaction time is, for example, about 1 to 24 hours. After completion of the reaction, the obtained reaction product can be separated and purified by a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography or a combination thereof.

  The molecular weight distribution (Mw / Mn) of the cellulose derivative of the present invention can be determined by measuring the molecular weight distribution (Mw / Mn) of the compound (1-3). Since the cellulose derivative of the present invention is in the form of a dithiocarbamate and is hardly soluble in an organic solvent, it is difficult to directly measure the molecular weight distribution. However, since the conversion of the compound (1-3) into the cellulose derivative of the present invention in the above step [2] proceeds under relatively mild conditions, almost all reactions that affect the molecular weight distribution, such as cleavage of cellulose chains, have progressed. It is thought that there is not. Therefore, the molecular weight distribution of the cellulose derivative of the present invention can be indirectly determined by measuring the molecular weight distribution at the stage of compound (1-3), which is an intermediate for producing the cellulose derivative of the present invention. .

Alternatively, when only the cellulose derivative (final product) of the present invention is available, dithiocarbamate is converted to an amino group, and the compound (1-3) is converted back to the intermediate compound (1-3). By measuring the molecular weight distribution of the cellulose derivative, the molecular weight distribution of the cellulose derivative of the present invention can be determined.
The conditions for returning the cellulose derivative (final product) of the present invention to the compound (1-3) are not particularly limited, but a method of treating with a reducing agent (for example, Journal of environmental quality 1994 v.23 no.2 pp.279) -286) can be used.
Specifically, elimination of the dithiocarbamate group occurs by treating the cellulose derivative (final product) of the present invention with an acid such as hydrochloric acid or subjecting the cellulose derivative to a reducing condition using a reducing agent such as sodium borohydride. Can be reconverted to compound (1-3).

The molecular weight distribution (Mw / Mn) of the compound (1-3) can be measured by gel permeation chromatography (Gel Permeation Chromatography: GCP).
In GCP, a high performance liquid chromatography system in which a gel filtration column is connected to a detector for detecting refractive index and light scattering can be used. For example, Shodex GPC SYSTEM-21H can be used as the high performance liquid chromatography system. As the detector, for example, a differential refractive index detector (RI) can be used. The measurement conditions of such a GCP are as follows.
Solvent: dichloromethane Column: two TSKgel GMHXL (7.8 × 300 mm) Guard column: TSKgel guardcolumn HXL-H
Sample concentration: 2000 ppm
Flow rate: 0.8 mL / min
Sample injection volume: 100 μL
Standard sample: PMMA (molecular weight 1850, 7360, 29960, 79500, 201800, 509000, 625500)
Column temperature: 28 ° C

Both the weight average molecular weight (Mw) and the number average molecular weight (Mn) can be measured under the same measurement conditions as described above. The molecular weight distribution can be calculated from the weight average molecular weight and the number average molecular weight obtained from the measurement results according to the following formula.
Molecular weight distribution = Mw / Mn
Mw: weight average molecular weight, Mn: number average molecular weight

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 (Preparation of cellulose derivative (MI3001))
Under a nitrogen atmosphere, cellulose (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight distribution (Mw / Mn) = 2.2) (3.02 g, 18.74 mmol) and N, N -Dimethylacetamide solution (65.0 mL) was charged. After Boc-β-alanine (7.09 g, 37.48 mmol) and DMAP (4.58 g, 37.48 mmol) were added to the reaction vessel, the reaction system was cooled to 0 ° C. After further adding EDC-HCl (7.19 g, 37.48 mmol), the reaction system was returned to room temperature and stirred overnight. The solid precipitated by reprecipitation in a mixed solvent of MeOH / H ₂ O (70/30, v / v) was collected by centrifugation. The mixture was heated at 60 ° C. and dried under vacuum to obtain a compound represented by the following formula (I) as a white solid (8.01 g, 73.0%). ^From the result of ¹ H-NMR, the degree of substitution of Boc-β-alanine was calculated to be 2.48.
¹ H-NMR (500MHz, DMSO-d ₆ ) δ 7.23-6.59 (NH), 5.56-3.35 (glucose ring, CH), 1.47-1.35 (Boc), 1.35-1.04 (CH ₃ )

Under a nitrogen atmosphere, a compound represented by the above formula (I) (1.98 g, 3.38 mmol), dichloromethane (43.56 mL), and trifluoroacetic acid (1.67 mL, 21.82 mmol) were added to a two-necked eggplant flask. And stirred at room temperature overnight. After removing the supernatant of the gelled reaction system, the gel was dissolved in MeOH and reprecipitated in a saturated aqueous sodium hydrogen carbonate solution. The precipitated solid was collected by centrifugation and dried under vacuum to obtain a compound represented by the following formula (II) as a white solid (1.11 g, 53.0%).
¹ H-NMR (500MHz, DMSO-d ₆ ) δ 7.22-6.53 (NH ₂ ), 5.73-3.28 (glucose ring, CH), 1.35-1.01 (CH ₃ )

The molecular weight distribution (Mw / Mn) of the obtained compound represented by the above formula (II) was measured by GCP under the following conditions and found to be 2.1.
Solvent: dichloromethane Column: two TSKgel GMHXL (7.8 × 300 mm) Guard column: TSKgel guardcolumn HXL-H
Sample concentration: 2000 ppm
Flow rate: 0.8 mL / min
Sample injection volume: 100 μL
Standard sample: PMMA (molecular weight 1850, 7360, 29960, 79500, 201800, 509000, 625500)
Column temperature: 28 ° C

In a mixed solution of dimethyl sulfoxide (86.0 mL), CS ₂ (15.58 mL), and 10% tetramethylammonium hydroxide (1.95 mL), the compound represented by the above formula (II) finely crushed with a mortar was used. .46 g, 0.74 mmol) and stirred at room temperature for 2 hours under light shielding. The progress of the reaction was confirmed by the appearance of C = S absorption at 1489 cm ^-1 by IR measurement. The solid in the reaction system was washed by adding methanol, and collected by centrifugation. Vacuum drying provided MI3001 (0.36 g, 69.0%) as a white solid. From the results of the elemental analysis (S), the total average degree of substitution of the dithiocarbamate group (—CS ₂ ⁻ ) of MI3001 was calculated to be 2.48. The molecular weight distribution (2.1) of the compound (intermediate) represented by the above formula (II) was defined as the molecular weight distribution of MI3001.

Example 2 (Preparation of cellulose derivative (MI2001))
MI2001 was obtained in the same manner as in Example 1, except that cellulose having a molecular weight distribution of 2.5 (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a raw material. The total average degree of substitution of the dithiocarbamate group (—CS ₂ ⁻ ) of MI2001 was 2.51, and the molecular weight distribution of the intermediate was 2.4.

Comparative Example 1
Dithiocarbamate group (DTC group) in the same manner as in Example 1 except that raw material cellulose (Mw / Mn = 4.5) obtained by mixing 50% by weight of hardwood kraft pulp and 50% by weight of linter pulp was used as a raw material. Was obtained. The total degree of substitution of the DTC group was 2.48, and the molecular weight distribution of the intermediate was 4.2.

Comparative Example 2
A cellulose derivative having a dithiocarbamate group (DTC group) was obtained in the same manner as in Example 1, except that biocellulose (Mw / Mn = 5.7) produced from acetic acid bacteria was used as a raw material. The total average degree of substitution of the DTC group was 2.51, and the molecular weight distribution of the intermediate was 5.1.

[Evaluation]
The arsenic adsorption power of the cellulose derivative was evaluated by the following method.
1. Preparation of sample solution and buffer solution Sample containing 10 μM As (III) by dissolving arsenic trioxide (As (III)) (special grade; manufactured by Wako Pure Chemical Industries, Ltd.) in 0.01 M NaOH solution A solution was prepared. As for the buffer solution, a 0.1 M MES buffer solution was prepared and adjusted to pH 3 by adding a small amount of 1 M nitric acid or 1 M NaOH solution.

2. Preparation of Solid Phase Column and Solid Phase Extraction About 1 g of each cellulose derivative obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was transferred to a mortar and ground with a pestle until the particle size became about 2 mm or less. Hard and pestle-free parts were cut with scissors.
0.050 g of each crushed cellulose derivative was weighed out, filled in a Teflon (registered trademark) tube having an inner diameter of 2 mm and a length of 3 cm, and filled with Teflon (registered trademark) wool at both ends to prepare solid phase columns.
A silicon tube having an inner diameter of 2 mm was connected to each of the obtained solid phase columns, and a sample solution containing 10 μM As (III) prepared as described above was sent using a tube pump (Peristalpump, manufactured by As One Corporation). First, 10 mL of a 0.1 M MES buffer solution (pH = 3) is sent to each solid phase column to adjust the pH in the column, and then 5 mL of a 10 μM sample solution is passed at a flow rate of 5 mL / min, and the arsenic solid phase is passed. An extraction was performed. 1 mL of 1 M HCl was added to 5 mL of the eluate and stored. The metal concentration in the eluate was quantified by ICP-OES (iCAP6300DUO, manufactured by Thermo Fisher Scientific KK), and the amount of adsorption by the solid phase was determined. Table 1 shows the results. From Table 1, it was found that the cellulose derivatives of Examples 1 and 2 having a molecular weight distribution within the specified range of the present invention can exhibit excellent heavy metal adsorption power. On the other hand, the heavy metal-adsorbing power of the cellulose derivatives of Comparative Examples 1 and 2 having a molecular weight distribution exceeding the specified range of the present invention was inferior to that of the cellulose derivatives of the present invention.

Claims (6)

A cellulose derivative having a repeating unit represented by the following formula (1) and having a molecular weight distribution (Mw / Mn) of 4.0 or less and 1.2 or more.

Wherein R is the same or different and is a hydrogen atom or a group represented by the following formula (a). At least one of all Rs contained in the cellulose derivative is a group represented by the following formula (a)]

(Wherein, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. R ³ is the same or different and has 1 carbon atom Represents an alkyl group of 10 to 10) The cellulose derivative according to claim 1, wherein the group represented by the formula (a) is a group represented by the following formula (a-1).

(Wherein, R ³ is the same or different and represents an alkyl group having 1 to 10 carbon atoms, and R ⁴ is the same or different and represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Indicates an integer of 3)   The cellulose derivative according to claim 1 or 2, wherein the total degree of substitution of the group represented by the formula (a) is from 0.1 to 2.95. A method for producing a cellulose derivative, wherein the cellulose derivative according to any one of claims 1 to 3 is obtained through the following steps.
[1] Cellulose hydroxyl group is reacted with an amino group-protected amino acid, and then the amino-protecting group is removed. [2] A quaternary ammonium salt is added to the deprotected amino group in the presence of a sulfur compound. N ⁺ (R ³ ) ₄ X ⁻ ; R ³ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms, and X ⁻ represents a counter anion.   A heavy metal adsorbent comprising the cellulose derivative according to claim 1.   A method for removing heavy metals using the cellulose derivative according to claim 1.