JP4279110B2 - Production of lignin polymer - Google Patents

Description

This invention relates to beta-O-4 polyether lignin production method and high molecular weight of beta-O-4 polyether lignin.

Lignin is one of the main components of the cell wall of the tree, its structure is a three-dimensional network, and monomers are β-O-4, β-β, β-1, β-5, 5-5, etc. Are combined in various ways, and their proportions and order are also various. Of these, β-O-4 structure accounts for 50 to 60% of the most binding mode, and in the later stage of biosynthesis of lignin in the tree, this β-O-4 structure is often called endwise lignin. What is produced. Synthetic lignin and artificial lignin, in which monomers are oxidatively polymerized with enzymes such as oxidants and peroxidases, are called dehydrogenation polymers (DHP), and are linked by various bonds like natural lignin. .
A β-O-4 polyether having a carbonyl-type lignin having only a β-O-4 structure has already been reported (Non-patent Document 1), and the purified lignin monomer is used in a non-hydrophilic condition such as DMF. A method of polymerizing in the presence of potassium carbonate in a protic solvent is known. However, the obtained polymer as it is is hardly soluble in ordinary organic solvents and derivatization is very difficult, and the subsequent development has not been made.
On the other hand, a method for reducing the carbonyl group of β-O-4 polyether of easily soluble lignin having a low degree of polymerization has also been reported (Non-patent Document 2). However, it is impossible to reduce an insoluble or hardly soluble polymer by this method, and it has been difficult to obtain a polymer having a high molecular weight by this method.

Cellulose Chem. Technol. 12, 713 (1978) Acta Chemica Scandinavica 3, 1358-1374, 1949

The present invention provides a process by which a β-O-4 polyether of high molecular weight lignin having a reduced carbonyl group can be produced.
Conventionally, a β-O-4 polyether synthesized with a carbonyl-type lignin having an α-position is insoluble and hardly soluble, and it was impossible to react the polymer to the inside as an insoluble solid. For example, the resulting lignin β-O-4 polyether dissolves when heated to 90 ° C in m-cresol and 120 ° C in DMF or DMAc, but precipitates when cooled to room temperature. No further development has been made (Non-Patent Document 1).

（式中、Ｒ^１及びＲ^２は、それぞれ同じであっても異なってもよく、水素原子又はメトキシ基を表し、Ｘはハロゲン原子を表す。）で表されるモノマーをアルカリの存在下で無水条件の非プロトン性極性溶媒中で重合させる段階、及び生成したポリマーを極性溶媒であって生成するポリマーを溶解する溶媒中でカルボニル基の還元剤を用いて還元する段階から成るリグニンポリマーの製法である。 In the present invention, it has been found that a β-O-4 polyether of high molecular weight lignin having a reduced carbonyl group can be produced by reducing the produced polymer in a solvent that dissolves the polymer. It came to complete.
That is, the present invention has the following general formula:

(Wherein R ¹ and R ² may be the same or different and each represents a hydrogen atom or a methoxy group, and X represents a halogen atom). A process for polymerizing in an aprotic polar solvent under conditions, and a method for producing a lignin polymer comprising a step of reducing a produced polymer with a reducing agent of a carbonyl group in a solvent that dissolves the produced polymer as a polar solvent. is there.

（式中、Ｒ^１及びＲ^２は、それぞれ同じであっても異なってもよく、水素原子又はメトキシ基を表し、ｎは正の整数を表す。）で表されるポリマーであって分子量が１０００以上であるリグニンポリマーである。 The present invention also includes the following general formula:

(Wherein R ¹ and R ² may be the same or different, each represents a hydrogen atom or a methoxy group, and n represents a positive integer), and has a molecular weight of 1000. That is the lignin polymer.

The polymer obtained by the method of the present invention is a regular polymer having a β-O-4 structure, which is the main binding mode of lignin, and a polymer having a high molecular weight is a novel polymer.
This polymer is considered to be widely applicable in the field where lignin obtained from wood and pulp waste liquid is used. For example, it can be used in fields such as resins, adhesives, carbon fibers, and other biodegradable plastics.
As for the utilization development of lignin, a lot of things related to blend polymers with synthetic polymers have been carried out, and the polymers of the present invention can be used in the same manner. In addition, by introducing various functional groups, it is expected that new functions such as biocompatibility that are not found in natural lignin can be imparted.

で表されるものを用いる。
この式中、Ｒ^１及びＲ^２は、それぞれ同じであっても異なってもよく、水素原子又はメトキシ基を表す。
Ｘはハロゲン原子、好ましくは臭素原子又は塩素原子、より好ましくは臭素原子を表す。 The method of the present invention consists of two stages. This will be described in order below.
First, the following general formula as a monomer

Is used.
In this formula, R ¹ and R ² may be the same or different and each represents a hydrogen atom or a methoxy group.
X represents a halogen atom, preferably a bromine atom or a chlorine atom, more preferably a bromine atom.

This monomer is polymerized in an aprotic polar solvent under anhydrous conditions in the presence of alkali.
The anhydrous conditions refer to those having a water content of 50 ppm or less, and the water content is preferably lowered as much as possible after repeated dehydration.
Examples of the alkali include K ₂ CO ₃ and Na ₂ CO ₃ . The amount of alkali is usually about 1.5 equivalents (1.5 eq) (150 mol%) based on the monomers.
As the solvent, an aprotic polar solvent is used. Examples of the solvent include DMF (N, N-dimethylformamide), DMAc (N, N-dimethylacetamide), HMPA (hexamethyl phosphate triamide), and the like.
The monomer concentration is preferably 0.4 to 1.0M.
A catalyst need not be used, but when used, potassium iodide (KI), crown ether (18-Crown-6), tetrabutylammonium iodide (n-Bu ₄ NI), etc. may be used, and the amount of the catalyst. Is usually about 0.1 equivalent (eq) (10 mol%) relative to the monomer.
It is preferable to appropriately select the polymerization conditions such as the purity of the monomer and anhydrous conditions so that the molecular weight of the polymer is 1000 or more.

Next, the polymer obtained above is reduced.
As the solvent, a solvent that dissolves the polymer produced by the reduction is selected. This point is important, and when the reduction was performed in a solvent that does not dissolve the high molecular weight polymer as in the past, it was not possible to reduce the interior of the polymer. Since the polymer to be dissolved gradually dissolves in the solvent, the reduction reaction proceeds completely. As a result, all high molecular weight polymers can be reduced.
Examples of such solvents include dimethyl sulfoxide (DMSO), 1,4-dioxane, methyl cellosolve (2-methoxyethanol, CH ₃ CH ₂ CH ₂ OH), dimethylacetamide (DMAc), pyridine, sulfolane, diethylene glycol monomethyl ether Hexamethylphosphoric triamide (HMPA, [(CH ₃ ) ₂ N] ₃ PO), preferably DMSO can be used.

Examples of the reducing agent include borohydride compounds such as sodium borohydride (NaBH ₄ ), sodium cyanoborohydride (NaBH ₃ CN), potassium borohydride (KBH ₄ ), and lithium aluminum hydride (LiAlH ₄ ). An aluminum hydride compound such as diisobutylaluminum hydride (iC ₄ H ₉ ) ₂ AlH can be used. Of these, sodium borohydride and lithium aluminum hydride, particularly sodium borohydride are preferred. The amount of the reducing agent is usually about 5 equivalents (eq) (500 mol%) with respect to the monomer.
When sodium borohydride is used as the reducing agent, dimethyl sulfoxide is preferably used as the solvent. When lithium aluminum hydride is used, 1,4-dioxane is preferably used.
The polymer thus obtained is a β-O-4 polyether of high molecular weight lignin in which the carbonyl group is reduced. In the present invention, the molecular weight is 1000 or more, preferably 1000 to 30000, more preferably 3000. ~ 10000.

The terminal of the β-O-4 polyether of high molecular weight lignin with the carbonyl group reduced and / or the α-position hydroxyl group may be esterified or etherified. Such introduction of substituents can be appropriately performed by applying known methods. Such derivatives of lignin polymers into which various functional groups are introduced can have new functions not found in natural lignin.

The following examples illustrate the invention but are not intended to limit the invention.

The reaction of this example is shown in FIG.
First, monomers 1, 2, and 3 were synthesized. This method can be synthesized according to a report (Non-Patent Document 1).
Acetobanilone (26 g) was dissolved in a mixed solvent of 400 ml of anhydrous ether (dehydrated using molecular sieves 4A) and 300 ml of anhydrous 1,4-dioxane (distilled using metal Na), and 0 times using an ice bath. After cooling to 0 ° C., bromine (25 g) was slowly added dropwise over 2 hours under a nitrogen stream. After the completion of the addition, another 1 hour was added, and 500 ml of ether was added and washed with 200 ml of ice-cold water three times using a separatory funnel, and the organic layer was further washed with saturated brine. The organic layer was taken, dehydrated with anhydrous sodium sulfate, and concentrated at 30 ° C. or lower with an evaporator. Although it crystallized when cooled, after decolorization with activated carbon, recrystallization from a mixed solvent of ether and hexane gave monomer 1 in a yield of 76%. For the polymerization, one that was recrystallized once again with the same solvent was used.
The melting point of the obtained crystal is 82.3 to 82.8 ° C., which is higher than the melting point of 81 ° C. in the literature (Non-patent Document 1) and high in purity.
Monomer 2 was synthesized in the same manner starting from acetosyringone. The melting point of the obtained crystal was 127.0 to 127.5 ° C. Similarly, monomer 3 was obtained from acetophenol. The melting point of the obtained crystal is 130.3 to 130.9 ° C., which is higher than that of 129 to 130 ° C. in the literature (Non-patent Document 1), and it can be said that the purity is high.

Next, monomers 1, 2, and 3 were polymerized to synthesize polymers 4, 5, and 6.
For the polymerization, purified N, N-dimethylformamide (DMF) (for example, manufactured by Aldrich) having a water content of 50 ppm or less was used. The glassware used was thoroughly dried in an oven. As the monomer, P ₂ O ₅ was used, which was sufficiently dried using a vacuum pump in a desiccator.
500 mg of monomer 1 was dissolved in 2.5 ml of DMF, 422 mg of K ₂ CO ₃ finely refined in a mortar was added, and the mixture was reacted at 50 ° C. with stirring for 3 hours. Gradually precipitation occurs. After completion of the reaction, the reaction solution was added dropwise to 100 ml of ice water, and the precipitate was separated by filtration. Further, the precipitate was washed with methanol and dried to obtain a polymer 4 in a yield of 94%.
A similar method was used to obtain polymer 5 from monomer 2 and polymer 6 from monomer 3.

Next, the polymers 4, 5, and 6 were subjected to reduction treatment to synthesize polymers 7, 8, and 9.
200 mg of polymer 4 was suspended in 10 ml of dimethyl sulfoxide (DMSO), 230 mg of NaBH ₄ was added, and the mixture was stirred at 50 ° C. for 24 hours. The polymer gradually dissolved and became a clear liquid. After 24 hours, the solution was added dropwise to 200 ml of ice-cold water. Further, 2N HCl was added to decompose excess NaBH _4, and HCl was added until pH 3 to obtain a precipitate. The precipitate was filtered off and washed thoroughly with water. The obtained polymer was dried, dissolved in 2 ml of 1,4-dioxane, and purified by dropwise addition to 50 ml of diethyl ether for reprecipitation.
By the same method, Polymer 5 to Polymer 8 and Polymer 6 to Polymer 9 were obtained. ¹³ C-NMR was used to confirm the chemical structure. The results are shown in FIGS. In these NMR spectra, there is no ketone-derived signal, indicating that all the ketones in the polymer chain have been reduced.
¹³ C-NMR (DMSO-d ₆ ): polymer 7: δ: 55.5 (OCH ₃ ), 70.7 (α), 74.1 (β), 110.7 (2), 113.1 (5), 118.3 (6), 135.2 (1 ), 147.1 (3), 148.5 (4); polymer 8: δ: 55.9 (OCH ₃ ), 71.6 (α), 78.2 (β), 103.7 (2,6), 135.6 (1), 137.5 (4), 152.1 (3,5); polymer 9: δ: 70.4 (α), 73.1 (β), 113.9 (3,5), 127.4 (2,6), 134.3 (1), 157.7 (4).

モノマー濃度、触媒の種類（３種）、反応温度をかえて検討した。反応収率はモノマー１，２，３の重合とその後の還元処理まで含めた合計収率である。数平均分子量、重量平均分子量はポリマー７，８、９をさらにアセテート１０，１１，１２に変換した後、テトラヒドロフランに溶解し、GPCにより解析した。２本のカラム（Shodex
KF803L, KF802）を直列につないで測定し、ポリスチレン換算で求めた。重量平均重合度（ＤＰｗ）は平均分子量から計算によって求めた。
Exp. No.２，３，４に示すように触媒の使用により、若干重合度を上げることができるが、反応温度を室温にし、反応時間を２４時間にしたExp. No.5のほうがより効果的に重合度を上げることができる。また、モノマー濃度を半分にしたExp. No.7によっても、重合度をある程度あげることが可能であった。
In this example, polymerization conditions were examined.
Table 1 shows the results of the investigation of the polymerization conditions.

The monomer concentration, the type of catalyst (3 types), and the reaction temperature were examined. The reaction yield is the total yield including polymerization of monomers 1, 2, and 3 and subsequent reduction treatment. The number average molecular weight and the weight average molecular weight were obtained by further converting the polymers 7 , 8 , and 9 to acetates 10 , 11, and 12 , then dissolving them in tetrahydrofuran and analyzing them by GPC. Two columns (Shodex
KF803L, KF802) were connected in series and measured in terms of polystyrene. The weight average degree of polymerization (DPw) was calculated from the average molecular weight.
As shown in Exp. No. 2, 3, and 4, the degree of polymerization can be slightly increased by using a catalyst, but Exp. No. 5 is more effective when the reaction temperature is set to room temperature and the reaction time is 24 hours. In particular, the degree of polymerization can be increased. In addition, the degree of polymerization could be increased to some extent by Exp. No. 7 in which the monomer concentration was halved.

３０ｍｇのポリマー７を無水酢酸２ｍｌ、ピリジン２ｍｌに溶解し、室温で１２時間反応させた。反応後、エタノール５ｍｌを加え、エバポレーターで約２ｍｌまで濃縮した。これを水５０ｍｌに滴下すると沈殿が生じた。これを濾別し乾燥させるとポリマー１０が得られた。同様の方法により、ポリマー８からポリマー１１、ポリマー９からポリマー１２を得た。 In this example, polymers 10, 11, and 12 (Chemical Formula 3) were prepared.

30 mg of the polymer 7 was dissolved in 2 ml of acetic anhydride and 2 ml of pyridine, and reacted at room temperature for 12 hours. After the reaction, 5 ml of ethanol was added and concentrated to about 2 ml with an evaporator. When this was added dropwise to 50 ml of water, precipitation occurred. This was filtered off and dried to obtain polymer 10. Polymer 8 to polymer 11 and polymer 9 to polymer 12 were obtained in the same manner.

1 is a diagram showing a reaction mechanism of Example 1. FIG. 2 is a diagram showing an NMR spectrum of the lignin polymer obtained in Example 1. FIG. 2 is a diagram showing an NMR spectrum of the lignin polymer obtained in Example 1. FIG. 2 is a diagram showing an NMR spectrum of the lignin polymer obtained in Example 1. FIG.

Claims (4)

The following general formula

(Wherein R ¹ and R ² may be the same or different and each represents a hydrogen atom or a methoxy group, and X represents a halogen atom). A process for producing a lignin polymer comprising: polymerizing in an aprotic polar solvent under conditions, and reducing the produced polymer with a reducing agent for a carbonyl group in a solvent that dissolves the produced polymer in a polar solvent. The aprotic polar solvent is DMF, DMAc, or HMPA, and the solvent that dissolves the polymer that is the polar solvent is DMSO, 1,4-dioxane, methyl cellosolve, dimethylacetamide, pyridine, sulfolane, diethylene glycol monomethyl ether or hexamethyl phosphoric acid triamide a process according to claim 1 wherein the reducing agent is NaBH ₄ or LiAlH _4. The following general formula

(Wherein R ¹ and R ² may be the same or different, each represents a hydrogen atom or a methoxy group, and n represents a positive integer), and has a molecular weight of 1000. This is the lignin polymer. The lignin polymer according to claim 3, wherein the polymer is produced by the production method according to claim 1 or 2.

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