JP5428941B2 - Method for producing N-tert-butylacrylamide with reduced coloring - Google Patents

Description

The present invention relates to a method for producing N-tert-butylacrylamide (general formula 1) with reduced coloring. More specifically, acrylonitrile, sulfuric acid and isobutylene are reacted to give 2-acrylamido-2-methylpropanesulfonic acid. The present invention relates to a production method capable of reducing coloring during storage of N-tert-butylacrylamide produced at the same time when producing (hereinafter referred to as ATBS).
That is, N-tert-butylacrylamide is recovered as a crude crystal after removing ATBS from a reaction solution in which ATBS crystals are dispersed, contacted with an alkaline aqueous solution, and recrystallized with alcohol. This invention relates to a method for producing tert-butylacrylamide.

Conventionally, N-tert-butylacrylamide has been used as a raw material for rubber chemicals, paint products and the like by copolymerizing with monomers such as acrylonitrile and acrylate esters. Furthermore, in recent years, its usefulness has been recognized as a raw material for cosmetics and high-grade inks, and its uses are expanding.
In the use of cosmetics and high-grade ink, if the hue of a product changes due to coloring of raw material components, the commercial value will be significantly reduced. For this reason, raw materials not colored during the storage period as well as the initial stage have been demanded.

N-tert-butylacrylamide is generally obtained by reaction and purification of acrylonitrile and tert-butyl alcohol.
As a specific method for producing N-tert-butylacrylamide, a method is known in which acrylonitrile and tert-butyl alcohol are reacted under a strong acid such as sulfuric acid.
In this method, various impurities are contained in the obtained reaction liquid, and the purification process after the reaction is the main point. It is not easy to distill N-tert-butylacrylamide, and a method used for purification of solids such as crystallization is used as the purification method.
For example, when water or an aqueous solution of a lower alcohol is added to the reaction solution obtained by the above reaction to precipitate N-tert-butylacrylamide crystals, the water or aqueous solution adjusted to pH 0.1 to 3 is used. A method of adding to a reaction solution (Patent Document 1) or a reaction solution similar to the above is neutralized with an aqueous alkaline solution in the presence of aminopolyphosphoric acid or aminopolycarboxylic acid to precipitate N-tert-butylacrylamide. A method (Patent Document 2) is known.

On the other hand, it is known that N-tert-butylacrylamide is produced as a by-product when ATBS is produced by a three-way addition reaction of acrylonitrile, sulfuric acid and isobutylene. N-tert-butylacrylamide produced as a by-product is an impurity for ATBS, and conventionally, the waste liquid containing it has been disposed of as industrial waste.
As an effective use of such waste liquid, a method of recovering crude crystals of N-tert-butylacrylamide from the waste liquid and purifying the crude crystals with a solvent such as acrylonitrile (Patent Document 3) has been proposed.

Japanese Patent Laid-Open No. 10-87587 JP-A-9-124568 JP 2005-29476 A

N-tert-butylacrylamide obtained by reacting acrylonitrile and tert-butyl alcohol tended to be colored during storage even though the coloration was reduced after production.
In addition, even when N-tert-butylacrylamide obtained from ATBS waste liquid is purified with acrylonitrile or the like, the crystals after the trial production are colored blue to green and brown during storage. Thus, there is a problem that the field of use is limited.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a reaction liquid obtained by addition reaction of acrylonitrile, sulfuric acid and isobutylene (a dispersion liquid in which ATBS crystals are dispersed in acrylonitrile as will be described later) is converted into ATBS. After the N-tert-butylacrylamide crude crystals taken out from the reaction solution or the one purified with an organic solvent such as acrylonitrile (hereinafter referred to as the crude crystals together) are recrystallized with alcohol. It was found that N-tert-butylacrylamide having no color such as blue to green or brown can be produced during storage by contacting with an aqueous alkaline solution.
In addition, when producing N-tert-butylacrylamide, a specific polymerization inhibitor is used, and a specific amount of the polymerization inhibitor in the final product is contained to obtain N-tert-butylacrylamide without further coloring. As a result, the present invention has been completed.

That is, according to the first aspect of the present invention, 2-acrylamido-2-methylpropanesulfonic acid obtained by reacting acrylonitrile, sulfuric acid and isobutylene is separated from the reaction solution, and N-tert-butylacrylamide is obtained from the subsequent reaction solution. in the case of recovering, after neutralization with 2-acrylamido-2-methylpropane sulfonic acid alkali the separated reaction solution, to recover the N-tert-butylacrylamide as crude crystals, alkali and the crude crystals It is a method for producing N-tert-butylacrylamide, characterized in that after contacting with a mixed aqueous solution of a metal compound and ammonium hydroxide, recrystallization is further performed using alcohol as a solvent.

  In the second invention of the present invention, the purified N-tert-butylacrylamide crystal contains 0.5 to 10 mass ppm of hydroquinone compound and 10 to 50 mass ppm of phenothiazine. The method for producing N-tert-butylacrylamide as described in 1. above.

  The third invention of the present invention is the method for producing N-tert-butylacrylamide according to the second invention, wherein the hydroquinone compound is hydroquinone monomethyl ether.

  A fourth invention of the present invention is the method for producing N-tert-butylacrylamide according to any one of the first to third inventions, wherein the solvent used for recrystallization is methyl alcohol.

Furthermore, the fifth aspect of the present invention is that, when N-tert-butylacrylamide is stored at 25 ° C. for 1 week, a hue of 10% by mass methyl alcohol solution is a * of −0.20 to +0.10, The method for producing N-tert-butylacrylamide according to any one of the first to fourth inventions, wherein b * is 0 to +6.00 and APHA is 70 or less.

  According to the production method of the present invention, N-tert-butylacrylamide having no color and good purity can be produced from ATBS waste liquor. The crystals are not colored during storage and can be used in fields where hue is important, such as cosmetics and high-grade inks.

Hereinafter, the present invention will be described in more detail.
In the addition reaction of acrylonitrile, sulfuric acid and isobutylene in the present invention, ATBS is a product obtained by reacting the above three components in equimolar amounts. Acrylonitrile in the reaction is used in a large excess relative to the other two components in order to use it as a reaction solvent. It is preferable to use approximately equimolar amounts of sulfuric acid and isobutylene. The specific amount of acrylonitrile used with respect to sulfuric acid and isobutylene is preferably 10 to 20 moles. In the reaction of the three components, sulfuric acid is mixed in acrylonitrile cooled to −20 ° C. to −10 ° C., and then isobutylene gas is blown into the resultant mixed liquid with stirring. The reaction is started by blowing isobutylene gas. The reaction is preferably performed at a temperature of 30 to 70 ° C. for 30 minutes or more under normal pressure.
Since ATBS produced by the reaction is insoluble in acrylonitrile as a solvent, the reaction solution is obtained as a slurry in which ATBS crystals are precipitated in acrylonitrile. The solid content concentration in the slurry is usually 10 to 25% by mass.

The ATBS crystals are obtained by solid-liquid separation of the slurry by an operation such as filtration or centrifugation.
The filtrate obtained by the above solid-liquid separation, that is, the acrylonitrile solution usually contains N-tert-butylacrylamide at a concentration of 1% by mass or more. Therefore, for the purpose of separating N-tert-butylacrylamide from the filtrate. It is necessary to evaporate acrylonitrile from the filtrate and concentrate it.
However, since some of the sulfuric acid used in the above reaction remains unreacted in the filtrate, in order to obtain a product that is not colored immediately after production and during storage, the sulfuric acid is applied by alkali washing before concentration of the filtrate. Need to be removed.

As a method for removing sulfuric acid in acrylonitrile, the filtrate may be brought into contact with a solid base such as calcium oxide, but more preferably, the filtrate and an aqueous alkali solution are mixed together in a liquid-liquid mixture. -A liquid separation method is adopted.
Furthermore, the filtrate from which the acidic substance has been removed is heated to evaporate acrylonitrile to obtain an acrylonitrile solution having a solid content of 50 to 70% by mass. This operation is usually performed by simple distillation or the like, and the acrylonitrile distilled thereby is further purified as necessary and then used again as a raw material for producing ATBS.
N-tert-butylacrylamide, which is the object of the present invention, is concentrated in the can after distillation (generally referred to as the kettle residue).

During distillation, in order to prevent polymerization of acrylonitrile and N-tert-butylacrylamide having radical polymerizability, a mixed gas of oxygen gas and inert gas is blown into the distillation can, or the top of the condenser tower is It is preferable to employ means for spraying a polymerization inhibitor.
In the present invention, in order to obtain a product with reduced coloring and very little coloring during storage, it is preferable to use a hydroquinone compound and phenothiazine in combination as a polymerization inhibitor.
Examples of hydroquinone compounds include hydroquinone, hydroquinone monomethyl ether, hydroquinone dimethyl ether, and di-tert-butyl hydroquinone. Of these, hydroquinone monomethyl ether is preferred because it can reduce discoloration.

Although it does not specifically limit as a method of obtaining the crude crystal | crystallization of N-tert- butylacrylamide from the said concentrate, There exist the following three methods. The first method is a method of gradually cooling the concentrated solution to 10 ° C. or less, and the second method is pouring into a large amount of solvent having low solubility of N-tert-butylacrylamide, such as water. In the third method, a crude crystal is obtained by precipitating crystals of N-tert-butylacrylamide, and the third method is to pour the concentrated solution into an alkaline aqueous solution instead of a large amount of water, and add N-tert-butylacrylamide. This is a method for precipitating crude crystals.
Further, the crude crystals are added to acrylonitrile and dissolved again by heating, and the resulting solution is cooled again to 10 ° C. or lower or poured into a large amount of water to precipitate crystals, which are purified by filtration and purified by N-tert- There is also a method for obtaining crystals of butylacrylamide.

The crude crystal of N-tert-butylacrylamide obtained by the above operation is washed with a mixed aqueous solution of an alkali metal compound and ammonium hydroxide (hereinafter referred to as an alkaline aqueous solution) , and then recrystallized with alcohol.
Although there is no particular limitation on the alkali metal compound used in alkaline aqueous solution, operating on the water solutions, preferably sodium hydroxide having a high aqueous potassium hydroxide, etc. carbonate sodium.
The concentration of the aqueous alkaline solution is not particularly limited, but it is 0.2% by mass or more as the concentration that can obtain the effect of preventing coloring during storage. If it becomes too economical and too dark, it becomes difficult to remove the brown color in recrystallization. 5 mass% or less is preferable. Furthermore, in consideration of both coloring prevention during storage and prevention of initial coloring during recrystallization, a mixed aqueous solution of an alkali metal compound such as sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide is used. The ratio of the alkali metal compound and ammonium hydroxide is preferably 5/1 to 1/5 (mass ratio).
The amount of the alkaline aqueous solution used is not particularly limited, but it is preferably 1 to 5 times by mass with respect to the crude crystal cake to be washed in consideration of the amount sufficient for washing and economy.

The solvent used for recrystallization is an alcohol such as methyl alcohol, ethyl alcohol, or isopropyl alcohol having high solubility of N-tert-butylacrylamide.
If the alcohol is contained in an amount of 50% by mass or more, it may be used by mixing with an organic solvent such as acrylonitrile, acetone, ethyl acetate, or may be diluted with water.
Preferably, methyl alcohol, which has a particularly high solubility of N-tert-butylacrylamide and is highly miscible with water, is used in an amount of alcohol heated to 50 to 80 ° C. (but below the boiling point). -Tert-butylacrylamide can be completely dissolved, and there is no limitation as long as recrystallization precipitates at 20 ° C, but usually 3/1 to 1/3 (mass to the crude crystals of N-tert-butylacrylamide Ratio).
In addition, you may recrystallize what was recrystallized further by the same method.

  By drying the crystals obtained by recrystallization, N-tert-butylacrylamide that can be used for various industrial applications is obtained. Since N-tert-butylacrylamide has sublimation properties, it is preferable to dry under reduced pressure at 70 ° C. or lower.

In the present invention, in order to obtain N-tert-butylacrylamide with little coloring of the product and very little discoloration during storage, 0.5% of the hydroquinone compound is added to the crystal of N-tert-butylacrylamide after recrystallization. It is preferable to contain 10-50 mass ppm of -10 mass ppm and phenothiazine.
Such a compound functions as a polymerization inhibitor, but surprisingly also has a function of suppressing discoloration.
If the hydroquinone compound and phenothiazine exceed the upper limit, discoloration of the polymer after storage and polymerization with other monomers increases, and if it is less than the lower limit, stability during storage (prevention of side reactions and polymerization) is insufficient. It is not preferable.
Hydroquinone monomethyl ether is preferred as the hydroquinone compound because the polymerization rate is not excessively suppressed when N-tert-butylacrylamide and other monomers are polymerized, and the effect of preventing coloring is great.
More preferably, it contains 1 to 4 ppm by mass of hydroquinone compound and 20 to 30 ppm by mass of phenothiazine.

There are two types of changes in the hue of N-tert-butylacrylamide in the present invention: a cold-colored color such as bluishness and greenishness, and a change from yellow to brown.
Any hue is not preferable in the field of cosmetics and high-grade ink, which greatly affects the commercial value even if the hue changes minutely.
The N-tert-butylacrylamide of the present invention is difficult to have such a color even after storage. Specifically, after N-tert-butylacrylamide is stored at 25 ° C. for 1 week, it is 10% by mass. As for the hue when it is set as a methyl alcohol solution, it is preferable that a * is −0.20 to +0.10, b * is 0 to +6.00, and APHA is 70 or less.
a * and b * are called chromatic index and are obtained from the CIELAB chromaticity diagram. a * is colored in the red direction when + is large, and in the green direction when-is large. b * changes in the yellow direction when + is large, and in the blue direction when-is large.
It is in the range where a * is −0.20 to +0.10 and b * is 0 to +6.00 that the blueness or greenness is not conspicuous and the brownness is not felt by visual sensory evaluation.
APHA, also called Hazen number, measures the degree of coloring by comparing a colorimetric tube (Hazen standard solution) graded from yellow to brown with a measured object. The higher the value, the more yellow, light brown, and dark brown.
It is APHA of 70 or less that yellow to brown is not conspicuous in visual sensory evaluation and is almost colorless to light yellow.
Preferably, a * is −0.15 to 0, b * is 0 to +3.50, and APHA is 30 or less.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
○ Reference Example 1 Production of ATBS Two reactors equipped with a mixing stirrer were connected, and acrylonitrile and fuming sulfuric acid were introduced into the first-stage reactor under the following reaction conditions, and acrylonitrile and sulfuric acid were introduced. The mixture in the first stage reactor was introduced into the second stage reactor, and isobutylene gas was introduced into the second stage reactor to carry out the reaction continuously. The raw material charge ratio was 11 mol of acrylonitrile and 0.9 mol of isobutylene with respect to 1 mol of fuming sulfuric acid. The concentration of fuming sulfuric acid (concentration of sulfur trioxide in sulfuric acid) is 9%. The first stage reactor is maintained at -5 to -15 ° C, the residence time of the reaction solution is 10 minutes, the second stage reactor is maintained at 40 to 60 ° C, and the reaction solution is retained. The time was 40 minutes.
The dispersion of ATBS that flowed out from the second-stage reactor was filtered through a glass filter, and separated into a crystal cake and a filtrate. The cake on the glass filter was washed by flowing down 2 times its mass of acrylonitrile, and the washing filtrate was separated. ATBS was obtained by drying the cake after washing.

Reference Example 2 Production of N-tert-butylacrylamide Crude Crystals After neutralizing 110 kg of the acrylonitrile solution, which is a combination of the filtrate obtained in Reference Example 1 and the washing filtrate, with a 25% by mass ammonium hydroxide aqueous solution, By separating and removing, 115 kg of an acrylonitrile solution containing about 4% by mass of N-tert-butylacrylamide was obtained. Hydroquinone monomethyl ether (hereinafter referred to as MQ) is added to this solution at 500 ppm by mass and phenothiazine (hereinafter referred to as Pz) at 500 ppm by mass, and the solution is concentrated under reduced pressure while blowing nitrogen gas containing 5% oxygen into the solution. , 7.6 kg of a solution containing about 60% by mass of N-tert-butylacrylamide was obtained. About 100 kg of acrylonitrile was separated in this distillation. The obtained concentrated solution (7.6 kg) was gradually cooled in an ice bath to precipitate crystals. The obtained dispersion was filtered to obtain 2.5 kg of N-tert-butylacrylamide crude crystal cake.

○ Example 1
A crude crystal cake of N-tert-butylacrylamide obtained in Reference Example 2 in a mixed aqueous solution of 8.1 g of 0.5% by mass aqueous sodium hydroxide and 8.0 g of 0.5% by mass aqueous ammonium hydroxide. After adding 1 g and stirring for 10 minutes, an alkali washing cake was obtained by filtration under reduced pressure.
32.5 g of methyl alcohol and 27.9 g of water were heated to 60 ° C., while stirring, the stirring was continued until the alkali-washed cake was almost completely dissolved. Then, heating and stirring were stopped, and the mixture was allowed to cool to 15 ° C. It was cooled slowly to obtain a crystal slurry.
A recrystallized cake was obtained by filtration under reduced pressure, and 27.9 g of methyl alcohol cooled to 10 ° C. was poured therein, and the purified cake obtained by filtration under reduced pressure was again dried under reduced pressure, and 9.2 g of purified N-tert. -Crystals of butylacrylamide were obtained. The obtained purified crystal was a white powder having a faint yellow color.
The obtained N-tert-butylacrylamide was analyzed under the following HPLC conditions. Confirmation of the retention time of N-tert-butylacrylamide was performed by comparison with the peak position by a reagent manufactured by Tokyo Chemical Industry Co., Ltd. As a result, the purity was 99.9%, and MQ and Pz were almost removed by alkali washing when purifying the crystals, so that MQ was added to 3 ppm by mass and Pz to 21 ppm by mass.
HPLC (manufactured by Shimadzu Corporation)
Column: ODS column Eluent: Acetonitrile: Water = 30: 70
Detection: 213 nm
The purified crystal was spread on a petri dish, stored at 25 ° C. for one week, and then dissolved so as to be a 10% by mass methyl alcohol solution, and the hue was measured with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd. A * was -0.04, b * was +2.26, and APHA was measured to be 24. Visually, it was slightly blue-green.
The results are shown in Table 1.

○ Examples 2 to 4, Reference Examples 1 to 3
Except that the crude crystal cake was washed under the conditions shown in Table 1, the same operation as in Example 1 was performed to obtain purified N-tert-butylacrylamide. Next, the color after one week of storage was observed and measured. The results are shown in Table 1.

○ Comparative Example 1
16.1 g of the crude crystal cake of N-tert-butylacrylamide obtained in Reference Example 2 was added to 16.1 g of water, and after stirring for 10 minutes, a water-washed cake was obtained by vacuum filtration.
While stirring 9 g of methyl alcohol to 60 ° C., stirring was continued until the water-washed cake was almost completely dissolved, then heating and stirring were stopped, and after cooling, the mixture was slowly cooled to 15 ° C. to obtain a crystal slurry. It was.
After obtaining a recrystallized cake by vacuum filtration, 11 g of methyl alcohol cooled to 10 ° C. was poured therein, and the purified cake obtained by vacuum filtration was dried again under reduced pressure, and 7 g of N-tert-butylacrylamide was added. Crystals were obtained. The obtained crystal was a slightly light brownish white powder.
When stored at 25 ° C. for one week, it turned pale brown with a blue-green color, and the hue was measured with a 10% by weight methyl alcohol solution. As a result, a * was −2.20 and b * was +5.56. As a result, APHA reached 200.

○ Comparative Example 2
The crude crystal cake obtained in Reference Example 2 was used, washed with twice the amount of acrylonitrile at 5 ° C., and then dried under reduced pressure at room temperature. The obtained crystal was a slightly light brownish white powder. The a * was +1.80, b * was +2.16, and APHA was 50 in a 10% by mass methyl alcohol solution immediately after drying.
When the crystal was spread on a petri dish and allowed to stand at 25 ° C. for 1 week, it turned green brown and the hue of a 10% by mass methyl alcohol solution was measured. As a result, a * was −9.91 and b * was +8.12. APHA was 250, showing a greenish brown color.

According to the production method of the present invention, N-tert-butylacrylamide is recovered from the waste liquid during the production of ATBS, and purified by an industrially easy method to obtain high-purity crystals without coloring.
The N-tert-butylacrylamide thus obtained has no change in hue even during storage, and is particularly suitable for applications that care about color, such as cosmetics and high-grade inks.

Claims (5)

Acrylonitrile, in a case where the 2-acrylamido-2-methylpropane sulfonic acid obtained by reacting sulfuric acid and isobutylene is separated from the reaction solution, to recover the N-tert-butylacrylamide from further reaction solution, 2- After neutralizing the reaction solution from which acrylamide-2-methylpropanesulfonic acid has been separated with alkali , N-tert-butylacrylamide is recovered as crude crystals, and the crude crystals are mixed with an aqueous solution of an alkali metal compound and ammonium hydroxide. A method for producing N-tert-butylacrylamide, characterized in that , after the contact, alcohol is further recrystallized using a solvent. The N-tert-butylacrylamide according to claim 1, wherein the purified N-tert-butylacrylamide crystal contains 0.5-10 mass ppm of hydroquinone compound and 10-50 mass ppm of phenothiazine. A method for producing acrylamide.   The method for producing N-tert-butylacrylamide according to claim 2, wherein the hydroquinone compound is hydroquinone monomethyl ether.   The method for producing N-tert-butylacrylamide according to any one of claims 1 to 3, wherein the solvent used for recrystallization is methyl alcohol. After storing N-tert-butylacrylamide at 25 ° C. for 1 week, the hue when a 10% by mass methyl alcohol solution is obtained is −0.20 to +0.10, b * is 0 to +6.00, And APHA is 70 or less, The manufacturing method of N-tert- butylacrylamide in any one of Claims 1-4 characterized by the above-mentioned.