KR20060099773A - The preparation method of stable nitroxide free radical compounds - Google Patents

Abstract

The present invention relates to a method for preparing stabilized nitroxide free radicals through oxidation of 2,2,6,6-tetraalkylpiperidine compounds, and more particularly, a) 2,2,6,6 Reacting the tetraalkylpiperidine compound with hydrogen peroxide in an aqueous solution saturated with an unreactive salt in the presence of a catalyst and a basic chelating agent to synthesize an aqueous solution of nitroxide free radicals; b) after the completion of step a), adding an organic solvent to the solution to extract nitroxide free radicals; c) washing the organic solution layer with washing water; It provides a method for producing a high purity nitroxide free radical.

Nitroxide free radicals, 2,2,6,6-tetramethylpiperidine

Description

The preparation method of stable nitroxide free radical compounds

The present invention relates to a method for preparing a stabilized nitroxide free radical compound using a saturated aqueous solution.

Nitroxide free radical compounds are known as very active polymerization inhibitors for pre-radical polymerization of ethylene, unsaturated monomers such as styrene, acrylic acid and methacrylic acid. Due to the polymerization material caused by the polymerization of monomers during the monomer manufacturing process, the monomers are lost and the equipment is contaminated, resulting in the loss of efficiency, as well as the loss of tar treatment and work stoppage for cleaning the equipment. Cause.

Many kinds of compounds are used to suppress such polymerization, and the nitroxide free radical compound also exhibits excellent polymerization inhibitory effect by being used alone or in combination with various nitroaromatic compounds, thus having a low polydispersity. It is used as a polymerization regulator to prepare a stable free radical medium polymerization process for producing homopolymers, random copolymers, block copolymers, multiblock copolymers and graft copolymers at a high conversion rate while maintaining a high polymerization rate. do.

This polymerization regulator is usefully used to prepare a compatibilizer, a reinforcing modifier or a dispersant for coating, to prepare a low molecular weight resin or oligomer for use in coatings and thermoplastic films, or to prepare toner resins and ink additives.

The conventional manufacturing method related to the manufacturing method according to the present invention will be briefly described as follows.

The production methods commonly used up to now include aliphatic alcohols and ethylene using secondary tungsten compounds including 2,2,6,6-tetraalkylpiperidine compounds in tungstate as a catalyst in purified water or organic solvents. After addition of diamine tetraacetic acid salt, peroxides such as aqueous hydrogen peroxide solution are added dropwise to oxidize to form a stable nitroxide compound.After completion of the reaction, the nitroxide free radical compound is removed from the mixed aqueous layer with a solvent of methylene chloride. After separation and extraction, the organic layer was concentrated to dryness to prepare a stable solid nitroxide free radical, and the aqueous layer was washed with salt to further extract the unseparated nitroxide compound, and the rest was treated with wastewater. At this point, a significant amount of wastewater is generated and environmental and economic costs must be paid for this wastewater treatment. In addition, when using a solid product for polymerization control, etc., a separate process of adding a solvent suitable for the purpose to make the liquid.

In addition, the conventional manufacturing method is the oxidation reaction in a simple aqueous solution, such as water, the secondary amine as a raw material is dissolved in some water does not directly participate in the reaction, the reaction time is long, the yield is low, and separated and concentrated using an organic solvent This incurs both time and economic environmental costs, and in the process, significant amounts of air pollution and waste solvents are generated.

According to EJRAUCKMAN et, al. [ Syn . Communications 1975 , 5 (6), 409], the oxidation of secondary amines to nitroxide free radicals was carried out at room temperature using acetonitrile-methanol, sodium tungstate and aqueous hydrogen peroxide solution. Reaction daily yields a yield of 85%. Although a method for obtaining solid nitroxide free radicals using an organic solution of acetonitrile and methanol instead of water has been introduced, there is no mention of treating the generated wastewater and producing liquid, and the yield is very low.

According to U.S. Patent 5,654,434 (1997), 4-hydroxy-2,2,6,6-tetramethylpiperidine is oxidized with hydrogen peroxide solution in purified water to 4-hydroxy-2,2,6,6-tetra. A process for preparing methylpiperidine-N-oxyl free radicals is described, which increases the reaction temperature from 80 ° C. to 99 ° C. without using a catalyst. Again, there is no mention of wastewater treatment and liquid phase produced, and the yield is indicated as more than 99%, but the inventors' experiment shows that the yield does not exceed 90%.

According to U.S. Patent 5,629,426 (1997), 4-hydroxy-2,2,6,6-tetramethylpiperidine is added to an alkali metal carbonate salt such as sodium carbonate in distilled water and then oxidized with hydrogen peroxide solution to 4- A method of reacting hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl free radicals is described. Still, the problem of treating many wastewaters generated in this oxidation reaction, the preferred method of reducing the reaction time and increasing the yield have not been discussed, and there is no method for producing liquid products. There is also no specific mention of how nitroxide free radicals are treated in the reaction mixture.

According to US Pat. No. 5,817,824 (1998), triacetoneamine was added to a solution of water and methanol, and sodium tungstate was used as a catalyst in the basic state of ethylenediaminetetraacetic acid salt, and then oxidized with hydrogen peroxide solution and extracted with methylene chloride. A method for producing 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxyfreeradical via concentration and filtration has been described. Also, wastewater and organic solvent methylene chloride are extracted and concentrated to dryness, resulting in process complexity and environmental problems. This method is very basic and is a manufacturing process already commercialized before this patent.

Accordingly, an object of the present invention is to perform a series of processes for preparing stabilized nitroxide free radicals by reacting a 2,2,6,6-tetraalkylpiperidine compound with an aqueous hydrogen peroxide solution in the presence of a catalyst and a basic chelating agent. In

By applying the oxidation reaction by dispersing the reaction raw material in an aqueous solution saturated with a non-reactive substance other than purified water or ordinary water, the 2,2,6,6-tetraalkyl free radical piperidine compound can be reacted with the hydrogen peroxide Reacts to form stable nitroxide free radicals, and participates directly in all reactions where possible as starting materials to shorten reaction time, reduce unreacted substances, and increase production yield to maximize productivity. It is to provide a method for preparing a lockside free radical.

It is another object of the present invention to reduce the waste water by reusing the separated supersaturated solution and to add a suitable solvent to the manufacturing process, thereby making it economical and environmentally friendly to prepare a stable liquid or solid stabilized nitroxide free radical product. To provide a way. According to the present invention, since the oxidation reaction of the 2,2,6,6-tetraalkylpiperidine compound is performed in a saturated aqueous solution and no additional reaction occurs, the wastewater generated in the reaction process can be reused, and the continuous circulation Production processes are also possible.

Furthermore, after the completion of the synthesis reaction, in the step of extracting the prepared nitroxide free radical compound from the mixed solution, by using a separation process using a solubility difference according to the temperature in order to facilitate the removal and separation of impurities, nitroside free radicals The yield and purity of the can be increased.

In addition, the conventional method is separated and extracted using methylene chloride, distilled to produce a solid stabilized nitroxide free radical, and then dissolved in a solvent such as ethylbenzene or styrene depending on the application when used as a polymerization regulator In the extraction step of the present invention, the solid phase nitroxide free radicals can be separated, extracted and concentrated using an extraction solvent such as methylene chloride or ether according to a conventional method. A liquid stabilized nitroxide free radical product can be prepared by separating and extracting nitroxide free radicals using a solvent suitable for use as a polymerization regulator and easy to separate and extract.

That is, the present invention simplifies the conventional process and does not use a separate organic solvent, thereby improving economics and reducing environmental problems. The manufacturing method provided by the present invention provides a yield of 98% or more and a purity of 99% or more. Stabilized nitroxide free radicals can be prepared.

The production method according to the present invention uses a saturated aqueous solution to increase the production yield, synthesize high-purity products, reduce the waste water by its reuse and automate the production line in a continuous circulation, and separate extraction of nitroxide free radicals in the reaction process And a new production method that is economical and environmentally friendly to produce a liquid stabilized nitroxide free radical compound by adding a solvent suitable for use as a polymerization regulator.

In addition, when using the production method according to the invention it is possible to produce a solution or solid nitroxide free radical product in high purity, high yield.

The present invention relates to a method for preparing stabilized nitroxide free radicals through oxidation of a 2,2,6,6-tetraalkylpiperidine compound.

More specifically, a) the nitroxide of formula 2 is reacted by reacting the 2,2,6,6-tetraalkylpiperidine compound of formula 1 with hydrogen peroxide in an aqueous solution saturated with an unreactive salt in the presence of a catalyst and a basic chelating agent. A synthetic step of preparing a free radical (mixed) aqueous solution; b) an extraction step of extracting nitroxide free radicals by adding an organic solvent to the solution after step a) is completed; c) a washing step of washing the organic solution layer with washing water; and characterized in that the nitrosite free radical is produced in high purity.

[Formula 1]

[Formula 2]

In Formula 1 and Formula 2, R ₁ , R ₂ , R ₃ , and R ₄ may be the same or different as alkyl groups having 1 to 15 carbon atoms, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl , Octyl, nonyl and the like. Preferably, lower alkyl is methyl, ethyl, propyl, butyl and the like, and R ₁ , R ₂ , R ₃ , and R ₄ are all methyl. T is a hydrogen group, an oxygen group, an amine group, an acetamine group, an ethoxy group, a phthalate group, a sebacic acid group, a succinate group, etc., and n is an integer of 1 or more.

Exemplary examples of the 2,2,6,6-tetraalkylpiperidine compound represented by Chemical Formula 1 used in the present invention include 2,2,6,6-tetramethyl-piperidine and 4-amino-2. , 2,6,6-tetramethyl-piperidine, 4-oxo-2,2,6,6-tetramethyl-piperidine, 4-dimethylamino-2,2,6,6-tetramethyl-pipe Ferridine, 4-methanoyloxy-2,2,6,6-tetramethyl-piperidine and the like and the compounds exemplified above do not limit the scope of the invention.

Specific examples of the stabilized nitroxide free radical represented by the formula (2) include 2,2,6,6-tetramethyl-piperidinyloxy, 4-amino-2,2,6,6-tetramethyl-piperidi Nyloxy, 4-oxo-2,2,6,6-tetramethyl-piperidinyloxy, 4-dimethylamino-2,2,6,6-tetramethyl-piperidinyloxy, 4-methanoyloxy -2,2,6,6-tetramethyl-piperidinyloxy, bis (1-oxyl-2,2,6,6-tetramethyl-piperidin-4-yl) succinate, bis (1-oxyl -2,2,6,6-tetramethyl-piperidin-4-yl) sebacate, bis (1-oxyl-2,2,6,6-tetramethyl-piperidin-4-yl) phthalate, etc. These and the compounds exemplified above do not limit the scope of the invention.

Hereinafter, the present invention will be described in detail.

The method for producing a stabilized nitroxide free radical according to the present invention comprises the following steps.

a) The aqueous solution of nitroxide free radicals of formula 2 is reacted by reacting the 2,2,6,6-tetraalkylpiperidine compound of formula 1 with hydrogen peroxide in an aqueous solution saturated with an unreactive salt in the presence of a catalyst and a basic chelating agent. Preparing a synthetic step;

b) an extraction step of extracting nitroxide free radicals by adding an organic solvent to the solution after step a) is completed;

c) a washing step of washing the organic solution layer using washing water.

Detailed description of the synthesis step a) is as follows.

Water, such as purified water, is maintained at a temperature of 20 ° C. to 60 ° C., preferably 40 ° C., and stirred to form a saturated aqueous solution by adding an unreacted substance.

The unreacted material for producing a saturated aqueous solution uses salt (salt) or 98% or more refined salt (purified salt) which is not reactive in the process of the present invention, and the amount of water is 2,2,6,6-tetra to participate in the reaction. 0.5 to 4 times the weight of the alkyl piperidine compound is used, but 1.5 to 2.5 times is appropriate for the process, and the amount of unreacted substance is good enough to saturate purified water.

The non-reactive substance is preferably about 10-50 g of salt with respect to 100 g of water, 25 g to 45 g is better, and 30 g to 40 g is most appropriate. If the amount of non-reactant is too small, the effect of using the saturated solution is small, so that the yield decreases, and if too much, the effect of improvement is no longer obtained.

A basic chelating agent such as ethylenediaminetetraacetic acid or tetrasodium salt or ethylenediaminetetraacetic acid or disodium salt is added so that the reaction proceeds in a basic state, and sodium tungsten is used as a reaction catalyst. A 2,2,6,6-tetraalkyl piperidine compound is added while stirring with the addition of a state or an alkali metal carbonate salt.

The basic chelating agent is used in about 0.1 to 4 mol% based on the piperidine compound. The basic chelating agent also serves as a hydrogen peroxide stabilizer to prevent metal ions from causing decomposition of hydrogen peroxide by acting as a metal ion blocking agent. If it exceeds the above range, it does not help the reaction and there is no economic feasibility.

As a catalyst, sodium tungstate is more effective and 0.02 to 3 mol% is added to the piperidine compound, but 1 to 2.5 mol% is preferable, and more preferably 2 mol%. If it is less than the above range, the yield of reaction decreases and the reaction time is long, and if it exceeds the above range, it is economically disadvantageous.

In addition, the reaction can be carried out smoothly by adding about 10% -50% of the saturated aqueous solution of methanol, ethanol or isopropanol, which is an aliphatic alcohol, but does not significantly affect the result of the reaction.

While adding 2,2,6,6-tetraalkyl piperidine compound and stirring thoroughly to completely disperse and disperse it in a saturated aqueous solution, 30 to 50% by weight of hydrogen peroxide solution is added to 1.5 mol times to 4 mol times of the piperidine compound. Add 30 minutes to 3 hours. Hydrogen peroxide is most preferably 2.5 to 3.5 mole times with respect to the 2,2,6,6-tetraalkylpiperidine compound. Yield drops below 1.5 mole times and economic effects cannot be expected above 4 mole times and side reactions occur. At this time, since the temperature rises rapidly due to the exothermic reaction, the dropping rate is controlled or the temperature is not exceeded 100 ° C by external cooling.

After completion of the dropping, be careful not to exceed the temperature of 100 ℃ and the reaction is enough for 30 minutes to 5 hours in the temperature range of 40 ℃ to 50 ℃ and then confirmed by gas chromatography to terminate the reaction.

The extraction step of b) is described in detail as follows.

As the aqueous solution becomes unsaturated solution due to the water produced after the step a), the non-reactive solute is added to the amount of water to be saturated to maintain the saturated aqueous solution. The amount of solute is added to 10 to 100% by weight of the amount of hydrogen peroxide solution added, but 30 to 60% by weight is appropriate for the process. This prevents the resulting stable nitroxide free radicals from dissolving even a small amount of water and reducing the yield.

Stabilized nitroxide free radicals from the mixed solution can be easily separated and extracted, and are stable even after long-term maintenance, and a solvent suitable for use as a polymerization regulator is selected to be 0.5 to 1.5 times the amount of nitroxide free radicals. A weight amount is added to dissolve the stabilized nitroxide free radicals in the mixed solution. In this case, ethylbenzene or styrene is used as a solvent for extraction and liquid preparation, and the preferred amount is preferably the same as the weight of nitroxide free radical.

After the organic solvent was added and stirred, the mixture was left still for about 30 minutes to 2 hours. The mixed solution was separated into two phases into an organic layer containing an upper stabilized nitroxide free radical and a saturated aqueous layer below. All. At this time, by adjusting the temperature in the range of -10 ℃ to 20 ℃ to prevent the dissolution of impurities other than the stabilized nitroxide free radicals in the organic layer by using the solubility of each material according to the solution, the stabilized nitroxide free radicals Dissolve in traces of saturated aqueous layer to avoid yield loss during layer separation.

At this time, impurities are absorbed into the saturated aqueous layer and liquid stabilized nitroxide free radicals are separated into the organic solution layer with high purity. This process is called primary separation. The saturated aqueous layer obtained by the primary separation is sent to the first step of the reaction for reuse. Sodium sulfite or sodium carbonate is added to the separated organic layer to remove residual hydrogen peroxide and confirmed by potassium iodine (KI) test paper.

Next will be described in detail the washing step of c).

After washing with water, the organic layer is sufficiently washed and then left to stand again so that the mixed solution is separated into two phases. The organic layer and the lower aqueous layer are separated by temperature control in the same manner as the primary separation. This process is called secondary separation, and the wash water obtained after the secondary separation process is recycled to the washing water of this process step in the next reaction. The organic layer cleaning process may be repeated one or more times.

The organic layer in which the stabilized nitroxide free radicals are dissolved is further added with ethylbenzene or styrene to adjust the concentration and filtered to prepare a liquid stabilized nitroxide free radical.

When preparing a solid nitroxide free radical in the present invention, a conventional method of separating and extracting using methylene chloride or ether as an extraction solvent, followed by filtration and concentration can be used.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1

72 g of purified water was added to 200 g of purified water to form a saturated solution. Then, 8.7 g of ethylenediaminetetraacetate tetrasodium salt and 4.2 g of sodium tungstate dihydrate were dissolved, and the temperature was raised to 40 ° C., followed by 2,2,6, 100 g of 6-tetramethyl-piperidine was added thereto. To this solution, 188 g of 35% aqueous hydrogen peroxide solution was slowly added dropwise for 2 hours and reacted for 3 hours.

107 g of ethylbenzene and 54 g of sodium chloride were further added to make a saturated solution. After stirring, the temperature was lowered to 5 ° C., and after standing for 30 minutes, the organic layer was separated by layer separation. The separated organic layer was washed with 100 g of purified water and separated again to obtain 4-oxo-2,2,6,6-tetramethyl-piperidinyloxyfreeradical dissolved in ethylbenzene.

A 50% concentration of liquid stable 4-oxo-2,2,6,6-tetramethyl-piperidinyloxyfreeradical was obtained with a yield of 98.6% and a purity of 99.2%.

Example 2

In Example 1 except that 107g of styrene monomer instead of 107g of ethylbenzene was carried out in the same manner as in Example 1. As a result, a stable 4-oxo-2,2,6,6-tetramethyl-piperidinyloxy free radical was obtained with a liquid yield of 98.4% and a purity of 99.1%.

Example 3

In Example 2, instead of using purified water, the initial reaction water and wash water were carried out in the same manner as in Example 2, except that the reaction water and wash water obtained in Example 2 were reused. As a result, a stable 4-oxo-2,2,6,6-tetramethyl-piperidinyloxy free radical was obtained with a yield of 99.0% and a purity of 99.5%.

[Comparative Example]

It was prepared by a conventional method.

First, 8.7 g of ethylenediamine tetraacetic acid tetrasodium salt and 4.2 g of sodium tungstate dihydrate were dissolved in 200 g of purified water, and the temperature was raised to 40 ° C., followed by 100 g of 2,2,6,6-tetramethyl-piperidine. It was. 188 g of 35% aqueous hydrogen peroxide solution was slowly added dropwise to the solution for 3 hours, and reacted for 4 hours with stirring. 300 ml of methylene dichloride and 100 g of sodium chloride were added thereto, stirred for 2 hours, and allowed to stand at room temperature for 3 hours to separate layers, and then separated an organic layer. The separated organic layer was washed with 100 g of purified water, and the obtained organic layer was concentrated and solidified. The yield was 78.1% and the purity was 93.6% to obtain 4-oxo-2,2,6,6-tetramethyl-piperidinyloxy free radicals.

The method for producing nitroxide free radicals according to the present invention increases the production yield using a saturated aqueous solution and synthesizes a high purity product, and can produce a target product with an equivalent yield even when the saturated aqueous solution is reused, thereby reducing wastewater by reuse in the process. In addition, it is possible to automate the production line in a continuous circulation, and to prepare a liquid stabilized nitroxide free radical compound by adding a solvent suitable for use as a separation extraction and polymerization control agent of nitroxide free radical in the reaction process. It is an economical and environmentally friendly new manufacturing method.

According to the preparation method according to the present invention, 2,2,6,6-tetramethylpiperidine compound is dissolved in a saturated aqueous solution to induce dissolution and react in a dispersed state so that 2,2,6,6-tetramethylpiperi is reacted. The dean compound reacts directly with the hydrogen peroxide solution in a fast time to prepare stable nitroxide free radicals with high yield.

In addition, since the chemical reaction proceeds in the saturated aqueous phase, the wastewater generated during separation can be reused to drastically reduce the wastewater, and the liquid is directly stabilized in the process by selecting a solvent suitable for use as a polymerization regulator as an extraction solvent. It is possible to manufacture the nitroxide free radicals, thereby increasing the convenience of the work, and is environmentally friendly because it does not use a separate extraction solvent for the recrystallization process, it can bring a simplification of the manufacturing process.

Claims (13)

a) adding 2,2,6,6-tetraalkylpiperidine compound of Formula 1 to an aqueous solution saturated with an unreactive salt; b) slowly adding hydrogen peroxide to the solution in the presence of a catalyst to synthesize nitroxide free radicals of formula (2); c) after completing step b), extracting nitroxide free radicals by adding an organic solvent; d) washing the organic solution layer with washing water; Method of producing a stabilized nitroxide free radical compound comprising a. [Formula 1]

[Formula 2]

(In Formula 1 and Formula 2, R ₁ , R ₂ , R ₃ , R ₄ may be the same or different as an alkyl group having 1 to 15 carbon atoms, and T is a hydrogen group, an oxygen group, an amine group, an acetamine group, or an ethoxy group. It is a time period, a phthalate group, a sebacyl acid group, or a succinate group, n is an integer of 1 or more.) The method of claim 1, The organic solvent is a method for producing a nitroxide free radical solution, characterized in that using ethylbenzene or styrene. The method of claim 1, A solid phase nitroxide free radical production method characterized by extracting and concentrating the organic solvent using methylene chloride or ether. The method of claim 1, The extraction step is a method for producing nitroxide free radicals, characterized in that the extraction by maintaining the supersaturated aqueous solution by adding a non-reactive salt. The method of claim 1, In step b), 0.1 to 4 mol% of ethylenediaminetetraacetic acid tetrasodium salt or ethylenediaminetetraacetic acid disodium salt is added to 2,2,6,6-tetraalkylpiperidine compound in a basic state. Process for producing nitroxide free radicals that react. The method of claim 1, Recycling the saturated aqueous layer in step c) to reuse the non-reactive salt in step a) as a saturated aqueous solution. The method according to any one of claims 1 to 6, The extraction step is a method for producing nitroxide free radicals, characterized in that at -10 ℃ to 20 ℃. The method of claim 7, wherein The catalyst is a method for producing nitroxide free radicals, characterized in that selected from sodium tungstate or alkali metal carbonate salt. The method of claim 7, wherein The non-reactive substance is selected from saline or purified salt. The method of claim 9, The non-reactive material is a method for producing nitroxide free radicals, characterized in that 10 to 100% by weight of the amount of hydrogen peroxide solution. a) adding 2,2,6,6-tetraalkylpiperidine compound of Formula 1 to an aqueous solution of saturated salts and purified salts; b) To the solution, a catalyst selected from 0.02 to 3 mol% of sodium tungstate or an alkali metal carbonate salt with respect to the piperidine compound and 1.5 to 4 mol times hydrogen peroxide with respect to the piperidine compound are slowly added thereto. Synthesizing nitroxide free radicals; c) After completion of step b), nitroxide free radicals are added at -10 ° C to 20 ° C by the difference in solubility by adding additional salts and purified salts to organically select the organic solvent and the saturated aqueous solution selected from ethylbenzene or sterene. Extracting; d) washing the separated organic solution phase with washing water; Method of producing a stabilized nitroxide free radical compound solution comprising a. [Formula 1]

[Formula 2]

(In Formula 1 and Formula 2, R ₁ , R ₂ , R ₃ , R ₄ may be the same or different as an alkyl group having 1 to 15 carbon atoms, and T is a hydrogen group, an oxygen group, an amine group, an acetamine group, or an ethoxy group. It is a time period, a phthalate group, a sebacyl acid group, or a succinate group, n is an integer of 1 or more.) The method of claim 11, Method for producing a stabilized nitroxide free radical compound solution, characterized in that to reuse the saturated aqueous layer separated in step c) as the aqueous solution of step a). The method of claim 11 or 12, In step b), 0.1 to 4 mol% of ethylenediaminetetraacetic acid tetrasodium salt or ethylenediaminetetraacetic acid disodium salt is added to 2,2,6,6-tetraalkylpiperidine compound in a basic state. Method for producing a nitroxide free radical solution to react.