Method for decomposing N-oxyl compounds

Abstract

This invention provides a novel method for decomposing N-oxyl compounds in solution. [Solution] A halogen oxo acid or a salt thereof is added to a solution containing an N-oxyl compound, and then a salt of thiosulfate is added.

Description

Technical Field

[0001] The present invention relates to a method for decomposing N-oxyl compounds.

Background Art

[0002] 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) is a water-soluble stable nitroxide radical and is used as a catalyst for oxidation reactions in organic synthesis. For example, when oxidizing the primary hydroxyl groups of cellulose to carboxyl groups and aldehyde groups, TEMPO is used together with an oxidizing agent. After carrying out a reaction using an N-oxyl compound such as TEMPO, waste liquid containing the N-oxyl compound remains. However, since TEMPO corresponds to Class 4 dangerous goods specified by the Fire Service Act, waste liquid containing an N-oxyl compound such as TEMPO needs to be appropriately treated.

[0003] Patent Document 1 discloses a method for decomposing an N-oxyl compound in a solution by adding hydrogen peroxide and an iron salt to a solution containing the N-oxyl compound and allowing the Fenton reaction to proceed. However, in the method described in Patent Document 1, since iron(III) ions (Fe 3+ ) are generated during the reaction, it is considered that insoluble iron hydroxide and iron oxide are generated, and it is considered that time and cost are required to recover and treat these.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a new method capable of decomposing an N-oxyl compound in a solution such as waste liquid after an oxidation reaction. [Means for solving the problem]

[0006] As a result of diligent research, the inventors have found that by adding a halogen oxoacid or a salt thereof to a solution containing an N-oxyl compound, and then adding a salt of thiosulfate, the N-oxyl compound in the solution can be decomposed. The present invention is not limited to the following, but includes the following: (1) A method for decomposing an N-oxyl compound, comprising adding a halogen oxo acid or a salt thereof to a solution containing an N-oxyl compound, followed by the addition of a salt of thiosulfate. (2) A method for decomposing an N-oxyl compound according to claim 1, comprising adding sodium bromide to a solution containing an N-oxyl compound before adding a halogen oxo acid or a salt thereof or before adding a salt of thiosulfate, and / or the solution containing an N-oxyl compound before adding a halogen oxo acid or a salt thereof further contains sodium bromide. (3) A method for decomposing an N-oxyl compound as described in (1) or (2), wherein the halogen oxo acid or its salt is one or more selected from sodium hypochlorite or potassium hypochlorite. (4) The method for decomposing an N-oxyl compound according to any one of (1) to (3), wherein the amount of halogenated oxoic acid or its salt added is 10 to 400 parts by mass per 1 part by mass of the N-oxyl compound. (5) The method for decomposing an N-oxyl compound according to any one of (1) to (4), wherein the amount of thiosulfate salt added is 5 to 100 parts by mass per 1 part by mass of the N-oxyl compound. (6) A method for decomposing an N-oxyl compound according to any one of (1) to (5), comprising adding a salt of thiosulfate three minutes or more after the addition of a halogen oxo acid or a salt thereof. [Effects of the Invention]

[0007] According to the present invention, N-oxyl compounds in a solution can be decomposed. The method of the present invention is useful for treating solutions containing N-oxyl compounds, such as waste liquids after oxidation reactions.

Embodiments for Carrying Out the Invention

[0008] The present invention relates to a method for decomposing N-oxyl compounds, which includes adding a halogen oxoacid or its salt to a solution containing an N-oxyl compound, and then adding a salt of thiosulfuric acid.

[0009] <Solution Containing N-Oxyl Compound> In the present invention, the N-oxyl compound refers to 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its derivatives. Examples of derivatives of TEMPO include 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-acetamino-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, N,N-dimethylamino-2,2,6,6-tetramethylpiperidine-1-oxyl, 1-methyl-2-azaadamantane-N-oxyl, and the like. Among them, N-oxyl compounds having a methyl group as an adjacent group to the nitroxyl radical group are preferred.

[0010] The solution containing an N-oxyl compound may contain only one kind of the above N-oxyl compounds, or may contain two or more kinds. The solvent in the solution containing the N-oxyl compound used in the method of the present invention is not particularly limited, as long as it can dissolve the N-oxyl compound. Examples include water, dimethyl sulfoxide, acetone, ethanol, or mixed solvents combining two or more of these. As one embodiment of the above solution, although not limited thereto, for example, a solution used in the oxidation reaction of cellulose using an N-oxyl compound or waste liquid after the oxidation reaction can be used. Since this oxidation reaction is usually carried out using water as a medium, when the solution used in this oxidation reaction or waste liquid after the oxidation reaction is used as the "solution containing the N-oxyl compound" in the method of the present invention, the solvent in the solution is usually water.

[0011] The content of the N-oxyl compound in a solution containing the N-oxyl compound is not particularly limited. For example, the content of the N-oxyl compound in the solution is preferably 1 to 200 ppm, more preferably 3 to 100 ppm, and even more preferably 5 to 80 ppm.

[0012] As described above, the solution containing the N-oxyl compound may be the liquid used in the oxidation reaction of cellulose using the N-oxyl compound or the waste liquid after the oxidation reaction. In this case, the solution may contain substances other than the N-oxyl compound that are used in the oxidation reaction or products of the oxidation reaction. Examples of such substances include by-products of the oxidation reaction such as NaCl, NaClO3, NaBrO, NaBrO3, halide salts, and perhalates, as well as alkalis used for pH adjustment such as NaOH. In particular, N-oxyl In the case of wastewater after the oxidation reaction of pulp using a compound, it may contain unreacted cellulose, oxidized cellulose, glucose, etc. It may also contain hydrogen peroxide used for the short-fiber treatment of oxidized cellulose. Furthermore, the above wastewater may be the filtrate produced when the oxidized cellulose is removed by filtration after the completion of the cellulose oxidation reaction. Furthermore, the above wastewater may further contain wastewater from washing the oxidized cellulose after filtration.

[0013] <Addition of halogen oxoacids or their salts> A halogen oxoacid or a salt thereof is added to a solution containing an N-oxyl compound. Examples of halogen oxoacids or salts thereof include sodium hypochlorite, potassium hypochlorite, sodium chlorite, perchloric acid, sodium perchlorate, sodium hypobromite, sodium bromate, potassium bromate, sodium periodate, sodium iodate, etc., and one or more of these can be added in combination. Among these, sodium hypochlorite (NaOCl) and / or potassium hypochlorite are preferred, and sodium hypochlorite is the most preferred.

[0014] The amount of halogen oxoacid or its salt added to the solution is preferably 10 to 400 parts by mass, and more preferably 40 to 200 parts by mass, per 1 part by mass of the N-oxyl compound. The temperature at which the addition is made is not particularly limited and can be carried out, for example, at room temperature (e.g., around 15 to 40°C).

[0015] After adding a halogen oxoacid or its salt, it is preferable to hold the mixture for a certain period of time before adding a thiosulfate salt. The holding time is not limited, but is preferably 3 minutes or more, and more preferably 5 minutes or more. The upper limit of the holding time is not particularly limited, but is preferably 120 minutes or less, more preferably 90 minutes or less, and even more preferably 60 minutes or less. During holding, it is preferable to stir continuously or intermittently. The temperature during holding is not particularly limited, and can be, for example, at room temperature (e.g., around 15-40°C).

[0016] The radical form of the N-oxyl compound (NO·) reversibly changes its form through oxidation and reduction. When reduced, it becomes a hydroxyamine (N-OH), and when oxidized, it becomes an oxoammonium (N·) compound. +It becomes =O). The oxoammonium form is unstable and easily changes to a radical form or a hydroxyamine form. When a halogen oxoacid or its salt is added to an N-oxyl compound, it is considered that the N-oxyl compound is oxidized to become an oxoammonium form. Thereby, it is considered that the decomposition reaction of the N-oxyl compound by the salt of thiosulfuric acid added later is promoted.

[0017] <Addition of salt of thiosulfuric acid> In the present invention, after adding a halogen oxoacid or its salt, a salt of thiosulfuric acid is added. In order to proceed with the reaction uniformly, it is preferable to add the salt of thiosulfuric acid in a state dissolved in water. The concentration of the aqueous solution is not particularly limited. For example, it can be added as an aqueous solution having a concentration of about 0.35% by mass. As described above, after adding a halogen oxoacid or its salt, it is preferable to hold for a certain period of time before adding the salt of thiosulfuric acid. That is, the addition of the salt of thiosulfuric acid is preferably carried out after a certain period of time, for example, 3 minutes or more, more preferably 5 minutes or more, has elapsed since the addition of the halogen oxoacid or its salt.

[0018] Examples of the salt of thiosulfuric acid include sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, etc., and one or a combination of two or more of these can be added. Among them, it is preferable to use sodium thiosulfate (Na2S3O3).

[0019] The addition amount of the salt of thiosulfuric acid to the solution is preferably 5 to 100 parts by mass, more preferably 6 to 70 parts by mass, relative to 1 part by mass of the N-oxyl compound. The temperature at the time of addition is not particularly limited, and for example, it can be carried out at room temperature (for example, about 15 to 40 °C).

[0020] When a thiosulfate is added after adding a halogen oxo acid or its salt, these redox reactions proceed, sulfuric acid is generated in the system, and the solution gradually becomes acidic. For example, when sodium hypochlorite is used as the halogen oxo acid or its salt and sodium thiosulfate is used as the thiosulfate, sulfuric acid is generated by the reaction of formula 1 below and the solution gradually becomes acidic. 4NaOCl + Na2S3O3 + H2O → Na2SO4 + H2SO4 + 4NaCl (Formula 1) Since sodium hypochlorite decomposes under acidic conditions to generate chlorine gas, for safety, when adding the thiosulfate, it is preferable to add an aqueous alkali solution (for example, an aqueous sodium hydroxide solution) in parallel to keep the pH of the solution at 7 or higher. It is more preferable to keep the pH at a value greater than 7, and even more preferable to keep the pH at 7.5 or higher.

[0021] Also, in order to enable pH adjustment of the solution, the method of adding the thiosulfate is preferably a sequential addition method in which the total amount is not added at once, but is added in multiple portions little by little or is gradually added little by little over a certain period of time. The addition rate may be any rate at which pH adjustment is possible and is not particularly limited. For example, 0.005 to 0.020 g of the thiosulfate in solid content can be added per minute to 1 L of the reaction system, and more preferably 0.007 to 0.015 g can be added.

[0022] In the present invention, it is necessary to add the thiosulfate after adding the halogen oxo acid or its salt. If the order of these additions is reversed, that is, if the halogen oxo acid or its salt is added after adding the thiosulfate, the decomposition of the N-oxyl compound hardly proceeds.

[0023] The reason why the N-oxyl compound can be decomposed by the method of the present invention is not clear, but the present inventors speculate as follows: By adding a halogen oxo acid or its salt, followed by the addition of a thiosulfate salt, the intermediate product of the reaction between the halogen oxo acid or its salt and the thiosulfate salt, polythionate ion ((S4O6)) is produced. 2- and / or (S3O6) 2- (It is presumed that) the oxoammonium form of the N-oxyl compound reacts with the oxyl compound, destroying the methyl group structure that stabilizes the radical form of the N-oxyl compound, and thus the N-oxyl compound decomposes.

[0024] <Sodium bromide> The solution containing the N-oxyl compound used in the method of the present invention may further contain sodium bromide. As described above, in the method of the present invention, in order to prevent the generation of chlorine gas derived from sodium hypochlorite as much as possible, it is preferable to maintain the pH of the solution at 7 or higher by adding an alkaline aqueous solution (e.g., an aqueous sodium hydroxide solution) in parallel with the addition of the thiosulfate salt. In this case, if sodium bromide is included in the solution containing the N-oxyl compound beforehand, the pH fluctuations during the reaction will be gentler, which has the advantage of making it easier to control and adjust the pH.

[0025] Sodium bromide may be added to the solution containing the N-oxyl compound before the addition of the halogen oxo acid or its salt, or to the solution after the addition of the halogen oxo acid or its salt but before the addition of the thiosulfate salt. Alternatively, a solution further containing sodium bromide may be used as the solution containing the N-oxyl compound before the addition of the halogen oxo acid or its salt. Or, both of these (i.e., a solution containing sodium bromide) Further addition of sodium bromide may be performed. Of these, it is more preferable that the solution containing the N-oxyl compound before the addition of the halogen oxoic acid or its salt already contains sodium bromide, either by adding sodium bromide to the solution containing the N-oxyl compound before the addition of the halogen oxoic acid or its salt, or by using a solution containing sodium bromide as the solution containing the N-oxyl compound before the addition of the halogen oxoic acid or its salt, or by doing both. The pH of the reaction system may increase with the addition of the halogen oxoic acid or its salt. If the solution before the addition of the halogen oxoic acid or its salt contains sodium bromide, in addition to the advantages mentioned above, it is possible to reduce the increase in pH due to the addition of the halogen oxoic acid or its salt, and thus reduce the risk of damage to the equipment due to high pH. The amount of sodium bromide when the solution contains sodium bromide is not particularly limited, but it is preferably 1 to 200 parts by mass, and more preferably 5 to 150 parts by mass, per 1 part by mass of the N-oxyl compound. [Examples]

[0026] The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to these. Unless otherwise specified, % and ppm refer to mass-based % and ppm (ppmw).

[0027] (Example 1) 49.66 g of an aqueous solution containing 5 ppm TEMPO and 659 ppm NaBr was to which 12% NaClO (manufactured by Takasugi Pharmaceutical Co., Ltd.) was added to bring the total NaClO concentration to 1000 ppm, and the pH of the solution was adjusted to 10 with 3 M NaOH.

[0028] Sixty minutes after adding NaClO, a 0.35% by mass aqueous solution of sodium thiosulfate (Na2S3O3) was added at a rate of 0.1 mL / min (amount of sodium thiosulfate added per 1 L of reaction system: 0.007 g / min). During the addition of the sodium thiosulfate aqueous solution, the pH of the solution was maintained above 7 by adding NaOH aqueous solution as needed. The reaction was carried out at room temperature. The addition of sodium thiosulfate solution was stopped when it was assumed that all NaClO had disappeared when the pH fluctuation stopped. The time from the start to the end of the addition of the sodium thiosulfate aqueous solution (referred to as the reaction time) was approximately 36 minutes.

[0029] After the addition of the sodium thiosulfate aqueous solution, 5 mL of the solution was allowed to stand overnight. This solution was then filtered through a membrane filter (GL Chromatodisk 25A, pore size 0.45 μm, GL Sciences Inc.) to obtain a sample. The amount of TEMPO (radical and hydroxyamine forms) contained in the sample was measured using high-performance liquid chromatography (HPLC) equipped with an electrochemical detector under the following conditions. • Electrochemical detector (COULOCHEM III, manufactured by Thermo Fisher Scientific) • Analytical cell: Model 5010 • Pump: LC-20AD (manufactured by Shimadzu Corporation) • Column oven: CTO-20AC (manufactured by Shimadzu Corporation) • Degasser: DGU-20A (manufactured by Shimadzu Corporation) • System controller: CBM-20A (manufactured by Shimadzu Corporation) • Sample injection volume: 10 μL ·Flow rate: 1.0mL / min • Column oven setting temperature: 40°C Eluent: 10mM lithium perchlorate aqueous solution:methanol = 70:30 Using the peak area values ​​of the radical form of TEMPO and the hydroxyamine form (OH form) of TEMPO obtained under the above conditions, the T in the sample was determined based on the peak area values ​​of these standards. The concentrations of the radical form of EMPO and the hydroxyamine form of TEMPO were calculated. Note that the oxoammonium form of TEMPO is highly reactive and quickly converted to either the radical or hydroxyamine form; therefore, TEMPO is not detected as an oxoammonium form.

[0030] (Example 2) The procedure was the same as in Example 1, except that the concentration of TEMPO in the initial aqueous solution was changed from 25 ppm to 5 ppm.

[0031] (Example 3) The procedure was the same as in Example 2, except that sodium thiosulfate aqueous solution was added 5 minutes after the addition of NaClO.

[0032] (Example 4) The procedure was the same as in Example 2, except that the concentration of TEMPO in the initial aqueous solution was set to 50 ppm.

[0033] (Example 5) The procedure was the same as in Example 2, except that the concentration of NaBr in the initial aqueous solution was set to 0 ppm. (Example 6) 500g (absolutely dry) bleached, unbeaten kraft pulp (whiteness 85%) derived from coniferous trees as the cellulose raw material was mixed with TEMPO (Sigma Aldrich) (0.025 mmol / g relative to the cellulose raw material), sodium bromide (1.0 mmol / g relative to the cellulose raw material), and water to make 20L, and stirred until the pulp was uniformly dispersed. A commercially available low-sodium sodium hypochlorite aqueous solution (effective chlorine concentration 12% by mass, sodium chloride content 4% by mass or less) was added to the reaction system to an effective chlorine concentration of 3.2 mmol / g relative to the cellulose raw material. The mixture was added as described, and the oxidation reaction was initiated. As the reaction progressed, the pH in the system decreased, so 3M sodium hydroxide aqueous solution was added sequentially to adjust the pH to 10. The reaction was terminated after 80 minutes from the start. Hydrochloric acid was added to the mixture after the reaction to lower the pH to 2.4 or below, and the pulp was separated by filtration with a glass filter. The pulp was dispersed again in deionized water, hydrochloric acid was added to lower the pH to 2.5 or below, and the pulp was separated by filtration with a glass filter. This process was repeated to remove excess salt and impurities, yielding oxidized pulp (TEMPO-oxidized cellulose). The carboxyl group content of this TEMPO-oxidized cellulose was 0.99 mmol / g That was the case.

[0034] After the oxidation reaction of cellulose with TEMPO, the entire filtrate from the aforementioned filtration wash was collected. The combined concentration of TEMPO radicals and hydroxyamines in the filtrate was 12 ppm. This combined concentration was calculated by determining the concentration of TEMPO radicals and TEMPO hydroxyamines in the filtrate separately using HPLC and then adding them together. The concentration of NaBr in the filtrate was 659 ppm.

[0035] The procedure was the same as in Example 1, except that 50 g of the filtrate was used instead of the 49.66 g of aqueous solution with a TEMPO concentration of 5 ppm and a NaBr concentration of 659 ppm used in Example 1.

[0036] (Reference example 1) The procedure was the same as in Example 2, except that an aqueous sodium thiosulfate solution was not added. (Comparative Example 1) The procedure was the same as in Example 2, except that NaClO was not added, and the same amount of sodium thiosulfate aqueous solution as in Example 5 was added.

[0037] (Comparative Example 2) The procedure was the same as in Example 2, except that the order of adding NaClO and sodium thiosulfate aqueous solution was reversed (i.e., NaClO was added 60 minutes after the sodium thiosulfate aqueous solution was added).

[0038] (Comparative Example 3) The procedure was the same as in Example 2, except that NaBH4, a common reducing agent, was used instead of an aqueous solution of sodium thiosulfate.

[0039] The results are shown in Table 1.

[0040] [Table 1]

[0041] As shown in Table 1, the decomposition of the N-oxyl compound could be promoted by adding a fixed amount of NaClO and sodium thiosulfate in this order (Examples 1-5). The same result was obtained when using wastewater from the oxidation reaction of cellulose using the N-oxyl compound. In this case, the decomposition of the N-oxyl compound was successfully promoted (Example 6). On the other hand, when only sodium thiosulfate was added without the addition of NaClO, the decomposition did not proceed (Comparative Example 1).

[0042] Even with the addition of NaClO alone, without the addition of sodium thiosulfate, approximately 40% of the N-oxyl compound could be decomposed (Reference Example 1). It is possible that the N-oxyl compound was decomposed because NaClO acted as an oxidizing agent. In contrast, it was found that the decomposition of the N-oxyl compound could be further accelerated by adding sodium thiosulfate in addition to NaClO (Examples 1-5).

[0043] When the order of adding NaClO and sodium thiosulfate was reversed, the decomposition hardly proceeded (Comparative Example 2). This is thought to be because the neutralization reaction between sodium thiosulfate and NaClO took precedence.

[0044] When sodium borohydride, a common reducing agent, was used instead of sodium thiosulfate, the decomposition did not proceed (Comparative Example 3). It is thought that the salt of thiosulfate plays a major role in the decomposition of the N-oxyl compound.

Claims

1. A method for decomposing an N-oxyl compound, comprising adding a halogen oxo acid or a salt thereof to a solution containing an N-oxyl compound, followed by the addition of a salt of thiosulfate.

2. A method for decomposing an N-oxyl compound according to claim 1, comprising adding sodium bromide to a solution containing an N-oxyl compound before adding a halogen oxoacid or a salt thereof or before adding a salt of thiosulfate, and / or the solution containing the N-oxyl compound before adding a halogen oxoacid or a salt thereof further contains sodium bromide.

3. The method for decomposing an N-oxyl compound according to claim 1 or 2, wherein the halogen oxoacid or its salt is one or more selected from sodium hypochlorite or potassium hypochlorite.

4. The method for decomposing an N-oxyl compound according to claim 1 or 2, wherein the amount of halogen oxo acid or its salt added is 10 to 400 parts by mass per 1 part by mass of the N-oxyl compound.

5. The method for decomposing an N-oxyl compound according to claim 1 or 2, wherein the amount of thiosulfate salt added is 5 to 100 parts by mass per 1 part by mass of the N-oxyl compound.

6. A method for decomposing an N-oxyl compound according to claim 1 or 2, comprising adding a salt of thiosulfate three minutes or more after the addition of a halogen oxo acid or a salt thereof.

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