JP2000273074A - Synthesis of n-monoalkyl(meth)acrylamide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and stably obtain the subject high-purity compound by using industrially inexpensively available cyclohexylamine as a protective agent for the double bond of a (meth)acrylic ester. SOLUTION: This compound, an N-monoalkyl(meth)acrylamide, is obtained using an amino amide of formula I (R1 is H or CH3; R2 is CnH2n+1; n is a natural number of 1-4) as intermediate. The amide adduct of formula I, in turn, is prepared by synthesizing a Michael adduct of a (meth)acrylic ester of formula II (R3 is CmH2m+1; m is a natural number of 1-4) and cyclohexylamine followed by reaction of the Michael adduct with a monoalkylamine in the presence of a strongly basic catalyst; the amino adduct thus obtained is thermally decomposed to form the objective N-monoalkyl(meth)acrylamide, which can be purified by distillation; thereby the objective compound can be afforded in an industrially advantageous way, such as without substantially producing dimeric adduct.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to the industrial use of the present invention as a resin modifier, an adhesive, a thickener, a dispersant, a paper chemical, a concrete admixture, etc. by copolymerizing with other monomers. To a method for synthesizing N-monoalkylacrylamide and N-monoalkylmethacrylamide (hereinafter referred to as N-monoalkyl (meth) acrylamide).

[0002]

2. Description of the Related Art Conventionally, as an industrial production method of N-substituted (meth) acrylamide, there is a method of reacting a (meth) acrylic ester with an amine compound. For example, USP2,
No. 451,436, methyl or ethyl acrylate is reacted with mono- or dialkylamine to form an aminoamide (hereinafter referred to as amide adduct).
This is thermally decomposed into various N-substituted acrylamides, and as disclosed in JP-A-4-208258,
A method in which an amide adduct is pyrolyzed in a liquid phase to obtain N, N-dialkyl (meth) acrylamide;
No. 683,741 reports a method for producing N-methylacrylamide by reacting ethyl acrylate and methylamine in the presence of water, followed by thermal decomposition.

A method of producing an N-substituted (meth) acrylamide by reacting a (meth) acrylic ester with an amine compound is suitable for producing an N, N-dialkyl (meth) acrylamide. When applied to the production of monoalkyl (meth) acrylamide, since active hydrogen remains in the Michael adduct of (meth) acrylic ester and amine compound, (meth) acrylic ester was further added to this. A double adduct is formed, and a compound obtained by amidating the double adduct is also formed, so that a large amount of impurities having high boiling point and high viscosity coexist.

As a method for suppressing the formation of double adducts, a method of increasing the concentration of monoalkylamine in the reaction solution, for example, in US Pat. No. 2,683,741, a high concentration methylamine is reacted in an aqueous solution, A method for producing N-monoalkylacrylamide while suppressing the formation of a polyadduct is described. However, this method is not industrially satisfactory because the yield is reduced due to hydrolysis of the adduct and a large amount of water needs to be distilled off.

As a method for solving these problems, first, a dialkylamine is added to a (meth) acrylic acid ester by Michael, a monoalkylamine is reacted therewith to form an amide adduct, and then a thermal decomposition is carried out (Japanese Patent Application No. Hei. 3
No. 05860), but since the intermediate amide adduct, which is a major impurity in distillation, has a small difference in boiling point from the target product, N-monoalkyl (meth) acrylamide, it prevents contamination of the product with the amide adduct. In order to obtain a high-purity product, a high reflux ratio is required during distillation. on the other hand,
Since N-monoalkyl (meth) acrylamide has active hydrogen bonded to a nitrogen atom, a cross-linkable popcorn polymer is easily generated during distillation. In particular, popcorn polymerization tends to occur as the residence time becomes longer at a high reflux ratio. When popcorn polymerization occurs, there is a risk that the packed tower and the pipe section will be blocked, and distillation will not be possible.

[0006] When the molecular weight of the amine compound that protects the double bond of the (meth) acrylic acid ester increases, the boiling point of the amide adduct increases, and when it is separated by distillation, separation from N-monoalkyl (meth) acrylamide occurs. It will be easier. However, in the case of a dialkylamine, as the molecular weight increases, the rate of the addition reaction is slow due to steric hindrance during the Michael addition reaction, making it difficult to complete the addition reaction. In addition, the molar price of the amine generally increases, which is disadvantageous in cost. become. Furthermore, in amidation, a monoalkylamine is reacted, so that an amine exchanger is easily generated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and is directed to a method for synthesizing N-monoalkyl (meth) acrylamide using an amide adduct as an intermediate. An object of the present invention is to provide a method for inexpensively and stably synthesizing alkyl (meth) acrylamide.

[0008]

Means for Solving the Problems The present inventors diligently studied to solve this problem, and found that the boiling point of the amide adduct, which is an impurity in the distillation, is far away from the boiling point of N-monoalkyl (meth) acrylamide. For example, focusing on the point that high purity N-monoalkyl (meth) acrylamide can be easily obtained even if the reflux ratio in the distillation step is low, cyclohexylamine that can be supplied industrially at low cost is considered. By using as a protective agent for the (meth) acrylate double bond, the rate of Michael addition reaction is not affected even though it is an N-monosubstituted amine, and almost no dimer adduct is formed. It is difficult to generate an amine exchanger with a monoalkylamine in the process, and furthermore, the obtained amide adduct has a high boiling point, and even if the reflux ratio in the distillation is low, N-mono Alkyl (meth) that acrylamide is obtained in high purity, and the processing speed of the distillation is fast, thereby completing the findings by the present invention be able to inhibit popcorn polymerization occurs.

That is, the present invention is a method for synthesizing N-monoalkyl (meth) acrylamide using an amide adduct represented by Chemical formula 2 as an intermediate.

Embedded image (N is a natural number from 1 to 4)

Hereinafter, the present invention will be described in more detail. The amide adduct represented by the chemical formula 2 is obtained by synthesizing a Michael adduct of the (meth) acrylate ester represented by the chemical formula 3 with cyclohexylamine, and reacting the adduct with a monoalkylamine under a strong basic catalyst. Can be.

Embedded image (M is a natural number from 1 to 4)

Examples of the (meth) acrylate represented by the chemical formula 3 include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, and butyl methacrylate. Etc. are exemplified.

The Michael addition does not require a special catalyst, and can be easily reacted only by mixing the (meth) acrylate and cyclohexylamine. Also,
For example, the Michael addition reaction can be promoted by adding a protic solvent such as methanol.
Such a Michael addition reaction can be performed at a reaction temperature of 50 to 100 ° C., but is not limited thereto.

Next, an unreacted substance is distilled off under reduced pressure and then subjected to an amidation reaction with a monoalkylamine under a strong basic catalyst to obtain an amide adduct. When the monoalkylamine is gaseous at normal temperature and normal pressure, it may be introduced into the reaction vessel in a state of being pressurized and liquefied, or may be introduced into the reaction solution in a gaseous state or subjected to the reaction as a solution other than water.

Examples of the strong basic catalyst include liquid and highly active alkoxy alkali metals such as sodium methylate, sodium ethylate, potassium methylate, and the like.
An example is potassium ethylate. The amount used is generally 0.5 to 10 mol% based on the Michael adduct, but is not limited thereto. Generally, a strong basic catalyst which is an amidation reaction catalyst is preferably performed in a pressure-resistant closed vessel for the purpose of deactivation by moisture and preventing leakage of monoalkylamine. The reaction is carried out at a temperature of 10 to 100 ° C., but is not limited thereto. After completion of the amidation reaction, the strong base catalyst is neutralized with a mineral such as sulfuric acid, and then the by-product alcohol and unreacted monoalkylamine are distilled off under reduced pressure, whereby the amide adduct of the present invention can be obtained.

The amide adduct is thermally decomposed into N-monoalkyl (meth) acrylamide by a known method, and can be purified by distillation. The main impurity during distillation is undecomposed amide adduct. The distillation step is generally performed at a high vacuum of 0.13 kPa to 0.67 kPa, but the amide adduct of the present invention is almost refluxed because of a large difference in boiling point from N-monoalkyl (meth) acrylamide. And a high-purity product can be obtained. In addition, the fact that there is almost no need for reflux means that the amount of liquid retained in the packed tower section is small and the residence time can be shortened, that is, the processing speed of distillation can be increased. The risk of occurrence of polymerization can be suppressed, and high-purity N-monoalkyl (meth) acrylamide can be obtained industrially stably. As a precautionary measure, a conventional polymerization inhibitor or the like, which has been conventionally used, may be added to the liquid phase or the gaseous phase for the purpose of suppressing popcorn polymerization during thermal decomposition or distillation.

[0016]

The present invention will be described more specifically with reference to the following examples. 86.1 parts by weight of methyl acrylate (1.0 mole ratio), 104.1 parts by weight of cyclohexylamine (1.0 mole ratio)
5 mol ratio) and 32.04 parts by weight (1.0 mol ratio) of methanol were mixed under water cooling and reacted at 50 ° C. for 3 hours to obtain a Michael adduct. As a result of analysis by gas chromatography, the conversion was 100.0% and the double adduct was 0.43%. The methanol and excess cyclohexylamine were distilled off under reduced pressure to obtain a Michael adduct having a purity of 99.33%.

176.01 parts by weight of the obtained Michael adduct (0.95 mol ratio) and 81.15 parts by weight of a 40% methanol solution of monomethylamine (1.04 mol of monomethylamine)
Mol ratio) and 3.67 parts by weight of a 28% methanol solution of sodium methylate (0.04% sodium methylate).
(19 mol ratio) and reacted at 50 ° C. for 22 hours to obtain an amide adduct. As a result of analysis by gas chromatography, the conversion was 99.8%, and the amine exchanger was 0.3%.
%Met. After sodium methylate was neutralized with 0.93 parts by weight of sulfuric acid (0.0095 molar ratio), monomethylamine and by-produced methanol were distilled off under reduced pressure.

To 167.21 parts by weight (0.91 mole ratio) of the obtained amide adduct, 0.17 parts by weight of a polymerization inhibitor phenothiazine, 0.17 parts by weight of p-methoxyphenol, and 2.68 sulfuric acid as a thermal decomposition catalyst. Parts by weight (0.027
(Molar ratio), and in a pyrolysis apparatus equipped with a McMahon packed tower, in the presence of NO gas, a kettle temperature of 150 to 163 ° C and a degree of vacuum of 2.
The liquid phase was pyrolyzed at 66 kPa for 2 hours, and crude N-monomethylacrylamide 5 having a purity of 92.5% at a decompression temperature of 90 ° C.
7.0 parts by weight were obtained. During this period, no popcorn polymer was formed in the packed tower and the condenser section.

To 50 parts by weight of the obtained crude N-monomethylacrylamide, 0.15 parts by weight of phenothiazine was added.
In the presence of O gas, simple distillation was performed at a degree of vacuum of 0.133 to 0.266 kPa for 1 hour. Although it was simple distillation, the purity was 99.
40 parts by weight of 7% N-monomethylacrylamide were obtained. No popcorn polymer was found in the pot or condenser after distillation.

Comparative Example An amide adduct was obtained in the same procedure as in the example using diethylamine for Michael addition. The amine exchanger in the amide adduct was 3.5 mol%. Amide adduct 14
To 4.00 parts by weight (0.91 mole ratio) were added 0.14 parts by weight of a polymerization inhibitor phenothiazine and 0.1 part by weight of p-methoxyphenol.
14 parts by weight, 2.68 parts by weight of sulfuric acid (0.027 mol ratio) as a thermal decomposition catalyst were added, and in the same thermal decomposition apparatus as in the example, in the presence of NO gas, the vessel temperature was 145 to 155 ° C., and the degree of vacuum was 2.
Liquid phase pyrolysis was performed at 66 kPa for 2 hours. The obtained crude N-
Monomethylacrylamide was 30 parts by weight and had a purity of 86%.

0.38 parts by weight of phenothiazine was added to 127 parts by weight of crude N-monomethylacrylamide, and a distillation apparatus equipped with a distributor equipped with a packed column filled with a McMahon packing was used. 0.333kP
Vacuum distillation was carried out at a. In order to obtain a purity of 99.0%, the reflux ratio had to be 2 or more. Thirty minutes after the start of distillation, the packed tower was blocked by popcorn polymerization, and almost no product could be obtained.

[0022]

According to the present invention, in a method for synthesizing N-monoalkyl (meth) acrylamide using an amide adduct as an intermediate, high-purity N-monoalkyl (meth) acrylamide can be synthesized inexpensively and stably. I was able to do it.

Claims (1)

[Claims] 1. A method for synthesizing N-monoalkylacrylamide and N-monoalkylmethacrylamide using an aminoamide represented by Chemical Formula 1 as an intermediate. Embedded image (N is a natural number from 1 to 4)