JP7722190B2 - N-vinylacetamide-containing composition and method for producing same - Google Patents

Description

The present invention relates to an N-vinylacetamide-containing composition used in the production of N-vinylacetamide-based polymers used as binders, dispersants, flocculants, liquid absorbents, thickeners, etc., and a method for producing the same.

N-vinylacetamide-based polymers have been found to be useful in a variety of fields, including as binders, dispersants, flocculants, liquid absorbents, and thickeners, and N-vinylacetamide, the monomer used to produce them, is industrially useful.

Many methods have been proposed for producing N-vinylacetamide. For example, one known method involves producing the intermediate N-(1-alkoxyethyl)acetamide from acetamide, acetaldehyde, and an alcohol, and then synthesizing it through thermal or catalytic decomposition. Another known method involves synthesizing ethylidenebisacetamide from acetamide and acetaldehyde, and then decomposing this to N-vinylacetamide and acetamide.

However, N-vinylacetamide has been recognized as a vinyl monomer with low polymerizability, and there has been a demand for improvement in its polymerizability.
The polymerizability of a monomer can vary greatly depending on the amount of polymerization inhibitors contained in the monomer as impurities. For this reason, the monomer may be purified by various methods to reduce the amount of polymerization inhibitors to an acceptable level or below.

From this perspective, attempts have been made to increase the purity of N-vinylacetamide synthesized by the above-mentioned thermal or catalytic cracking by purification methods such as distillation, extraction, and recrystallization to enhance its polymerizability. Examples of purification methods disclosed include an extraction method using water and aromatic hydrocarbons in Patent Document 1, a cooling crystallization method from a mixed organic solvent in Patent Document 2, an extraction method using an aqueous solution of inorganic salts and aromatic hydrocarbons in Patent Document 3, and an extractive distillation method using a polyhydric alcohol in Patent Document 4.

However, with any of the above methods, it was difficult to produce N-vinylacetamide, which has good polymerizability as a monomer for stably producing high molecular weight polymers that can be used as flocculants, liquid absorbents, thickeners, etc.

Patent Document 5 reports that in order to synthesize high-molecular-weight N-vinylcarboxylic acid amide polymers, it is important to reduce the content of N-1,3-butadienylcarboxylic acid amide in the N-vinylcarboxylic acid amide used. Furthermore, it explicitly states that N-vinylcarboxylic acid amides with an N-1,3-butadienylcarboxylic acid amide content of 30 ppm by mass or less are highly polymerizable. It also clearly describes a purification treatment method for reducing this content.

Patent document 6 discloses a method for producing N-vinylcarboxylic acid amide, which is characterized by a step of controlling the content of a monomer in the N-vinylcarboxylic acid amide relative to a conventionally used polymerization monomer composition to 20 ppm by mass or less.

However, even when N-vinylacetamide obtained by these methods is used as a raw material monomer, high polymerizability may not be consistently achieved, especially after long-term storage after production, leaving room for further improvement.

Japanese Unexamined Patent Publication No. 61-289069 Japanese Patent Application Laid-Open No. 63-132868 JP-A-2-188560 U.S. Patent No. 4,401,516 Japanese Patent Application Publication No. 8-81428 International Publication No. 2017/145569

As described above, polymerization monomers for producing N-vinylacetamide polymers may not exhibit high polymerizability even when the content of N-1,3-butadienylacetamide or the content of unsaturated aldehydes is reduced, and it has been predicted that they contain some kind of polymerization inhibitor.
An object of the present invention is to provide a composition for producing an N-vinylacetamide polymer, which has high and stable polymerizability.

The present invention relates to the following:
[1]
1. A composition comprising N-vinylacetamide,
An N-vinylacetamide-containing composition, characterized in that, when measured by high performance liquid chromatography under the following conditions, the total of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 1.1 x ^10-4 or less, when the peak area of N-vinylacetamide is taken as 1.
(Measurement conditions)
Column: Showa Denko K.K. Shodex (registered trademark) SB-802.5HQ x 2 Pump: Showa Denko K.K. Shodex (registered trademark) DS-4
Flow rate: 0.7ml/min
Sample injection volume: 10 μL
Column oven: Sugai U-620
Column oven temperature: 45°C
UV/Vis detector: Shimadzu Corporation SPD-20A, measurement wavelength: 230 nm
Eluent: acetonitrile/water = 1/9 (volume ratio)
Sample: Dilute to 1% by mass with eluent

[2]
The N-vinylacetamide-containing composition according to [1], characterized in that, in the high performance liquid chromatography measurement, when the peak area of N-vinylacetamide is taken as 1, the sum of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 0.05 × 10 ^-5 or more.
[3]
The N-vinylacetamide-containing composition according to [1] or [2], which is purified by crystallization.

[4]
The N-vinylacetamide-containing composition according to any one of [1] to [3], which is produced using as a raw material a composition containing N-alkoxyethylacetamide purified by distillation.
[5]
An N-vinylacetamide polymer obtained by polymerizing the N-vinylacetamide-containing composition according to any one of [1] to [4].
[6]
A method for producing the N-vinylacetamide-containing composition according to [1] or [2], comprising:
A method for producing an N-vinylacetamide-containing composition, comprising a step C' of purifying a crude composition (3') containing N-vinylacetamide by crystallization.

[7]
a step A' of adding an alkali to a crude composition (1') containing N-alkoxyethylacetamide and distilling the mixture to obtain a composition (2') containing N-alkoxyethylacetamide;
and step B' of producing a crude composition (3') containing N-vinylacetamide from a composition (2') containing N-alkoxyethylacetamide through a dealcoholization reaction.

[8]
A method for producing the N-vinylacetamide-containing composition according to [1] or [2], comprising:
A step A of adding an alkali to a crude composition (1) containing N-alkoxyethylacetamide and distilling the mixture to obtain a purified composition (2) containing N-alkoxyethylacetamide;
a step B of producing a crude composition (3) containing N-vinylacetamide from the purified composition (2) containing N-alkoxyethylacetamide through a dealcoholization reaction;
and a step C of purifying the crude composition (3) containing N-vinylacetamide by crystallization.

[9]
A method for selecting an N-vinylacetamide-containing composition, comprising determining whether or not the composition satisfies the following requirement in high performance liquid chromatography measurement under the following conditions: when the peak area of N-vinylacetamide is taken as 1, the sum of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 1.1 x ^10-4 or less; and selecting compositions that satisfy the requirement.
(Measurement conditions)
Column: Showa Denko K.K. Shodex (registered trademark) SB-802.5HQ x 2 Pump: Showa Denko K.K. Shodex (registered trademark) DS-4
Flow rate: 0.7ml/min
Sample injection volume: 10 μL
Column oven: Sugai U-620
Column oven temperature: 45°C
UV/Vis detector: Shimadzu Corporation SPD-20A, measurement wavelength: 230 nm
Eluent: acetonitrile/water = 1/9 (volume ratio)
Sample: Dilute to 1% by mass with eluent

The present invention provides a composition that contains N-vinylacetamide, can be used as a polymerization monomer to produce N-vinylacetamide polymers, and has high and stable polymerizability, as well as a method for producing the composition.

FIG. 1 shows the results of high performance liquid chromatography measurement in Example 4. FIG. 2 shows the results of high performance liquid chromatography measurement in Comparative Example 3. FIG. 3 is a graph showing the relationship between the time to reach the standard temperature peak and the peak area in the polymerization test for the Examples and Comparative Examples.

The present invention will now be described in further detail.
The N-vinylacetamide-containing composition (hereinafter also simply referred to as the composition) according to the present invention is a composition that contains N-vinylacetamide and can be used as a polymerization monomer for producing an N-vinylacetamide-based polymer.

<Composition>
The composition of the present invention is a composition containing N-vinylacetamide monomer as the main component (95% by mass or more), and in high performance liquid chromatography measurement under the following conditions, when the peak area of N-vinylacetamide (hereinafter sometimes referred to as "S-NVA") is taken as 1, the sum (area ratio) of the peak area at retention times of 31.5 minutes to 32.5 minutes (hereinafter sometimes referred to as "S32"), the peak area at 35.5 minutes to 36.5 minutes (hereinafter sometimes referred to as "S36"), and the peak area at 39.5 minutes to 40.5 minutes (hereinafter sometimes referred to as "S40") is 1.1 × 10 ^or less, preferably 1.0 × 10 ^or less, and more preferably 0.9 × 10 ^or less. Compositions satisfying these ranges have good polymerizability and are therefore preferred as monomer compositions for polymerization. The lower limit of this peak area sum is not particularly limited, but from the viewpoint of purification costs, it is preferably 0.05×10 ⁻⁵ or more, more preferably 0.1×10 ⁻⁵ or more, and even more preferably 0.5×10 ⁻⁵ or more.

In this specification, for example, the peak area having a retention time of 31.5 minutes or more and 32.5 minutes or less means the area of a peak having a peak apex at 31.5 minutes or more and 32.5 minutes or less.
When the baselines of peaks overlap, analysis can be performed by vertical splitting, baseline splitting, forced tailing processing, etc., with baseline splitting being preferred.
Attempts were made to identify the structures of the compounds at the peaks S32, S36, and S40, but it was difficult.

(Measurement conditions)
Column: Showa Denko K.K. Shodex (registered trademark) SB-802.5HQ x 2 Pump: Showa Denko K.K. Shodex (registered trademark) DS-4
Flow rate: 0.7ml/min
Sample injection volume: 10 μL
Column oven: Sugai U-620
Column oven temperature: 45°C
UV/Vis detector: Shimadzu Corporation SPD-20A, measurement wavelength: 230 nm
Eluent: acetonitrile/water = 1/9 (volume ratio)
Sample: Dilute to 1% by mass with eluent

The composition of the present invention has a sufficiently low content of components corresponding to peaks with retention times (retention times) of 31.5 minutes or more and 32.5 minutes or less, 35.5 minutes or more and 36.5 minutes or less, and 39.5 minutes or more and 40.5 minutes or less in high-performance liquid chromatography under the above measurement conditions. Because the composition of the present invention has a sufficiently low content of impurity components corresponding to these peaks, it is believed that its polymerizability is not inhibited and that it can retain sufficient polymerizability as a polymerization monomer even after long-term storage.

The composition of this embodiment is not particularly limited, but it is preferable that the content of unsaturated aldehydes is low, typically 10 ppm by mass or less, preferably 5 ppm by mass or less, and more preferably below the detection limit in GC or HPLC. If the content of unsaturated aldehydes in the composition is within the above range, it is preferable because, when used as a polymerizable monomer, it is less susceptible to polymerization inhibition by unsaturated aldehydes.

Examples of unsaturated aldehydes include crotonaldehyde, 2-ethyl-2-butenal, 2-methyl-2-pentenal, 2-hexenal, 2,4-hexadienal, 2,4-octadienal, 2,4,6-octatrienal, and 2-octenal.

Analysis of unsaturated aldehydes is carried out by either GC or HPLC. The content of unsaturated aldehydes is the total content of each unsaturated aldehyde. For example, it is the total amount of crotonaldehyde, 2-ethyl-2-butenal, 2-methyl-2-pentenal, 2-hexenal, 2,4-hexadienal, 2,4-octadienal, 2,4,6-octatrienal, 2-octenal, etc. However, quantitative detection of each unsaturated aldehyde at a concentration of 5 ppm by mass or less is required.
The measurement method used is gas chromatography (GC) or high performance liquid column chromatography (HPLC).

Furthermore, although not particularly limited, the composition of this embodiment preferably has an N-1,3-butadienylacetamide content of 10 ppm by mass or less, more preferably 5 ppm by mass or less, even more preferably 1 ppm by mass or less, and particularly preferably below the detection limit in high-performance liquid column chromatography (HPLC). A low N-1,3-butadienylacetamide content is preferred because it has good polymerizability.

In this embodiment, N-1,3-butadienylacetamide can be identified by mass spectrometry (electron impact method), mass spectrometry (chemical ionization method), infrared absorption spectrometry, and ultraviolet absorption spectrometry.
Mass spectrometry (electron impact method) 111, 69, 54, 43
Mass spectrum (chemical ionization method) 112
Infrared absorption spectrum (cm ⁻¹ ) 3099, 1732, 1654, 1471
Ultraviolet absorption spectrum (nm) 237, 276
The quantitative determination of N-1,3-butadienylcarboxylic acid amide is preferably carried out by high performance liquid column chromatography, but is not limited to this method. For example, the measurement conditions for high performance liquid column chromatography described in the Examples are preferred.

The composition of the present invention may be obtained by any production method as long as it meets the above-mentioned requirements. That is, it may be obtained by a method of synthesizing N-vinylacetamide under conditions that minimize the by-production of components corresponding to the peaks with retention times of 31.5 to 32.5 minutes, 35.5 to 36.5 minutes, and 39.5 to 40.5 minutes, as described above. Alternatively, it may be obtained by synthesizing N-vinylacetamide under conventionally known conditions and then removing the components corresponding to the peaks with retention times of 31.5 to 32.5 minutes, 35.5 to 36.5 minutes, and 39.5 to 40.5 minutes, as described above. Specific examples include a method in which a composition containing N-alkoxyethylacetamide used as a raw material for synthesizing N-vinylacetamide is purified in advance by a method such as distillation, a method in which a composition containing N-vinylacetamide is purified by a method such as crystallization, or a combination of these methods.

<Method for selecting compositions>
The method for selecting a composition of the present invention is a method for determining whether an N-vinylacetamide-containing composition satisfies the above-mentioned requirements and selecting a composition that satisfies the requirements. That is, the method determines whether the N-vinylacetamide-containing composition has, in the above-mentioned high-performance liquid chromatography measurement, a total of the peak areas (area ratio) of the peaks at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes, where the peak area of N-vinylacetamide is defined as 1, of 1.1 × 10 ^or less, preferably 1.0 × ¹⁰ or less, more preferably 0.9 × ¹⁰ or less, and selects a composition that satisfies these requirements. In this case, the lower limit of the total peak area of the composition to be selected at the retention times of 31.5 minutes or more and 32.5 minutes or less, 35.5 minutes or more and 36.5 minutes or less, and 39.5 minutes or more and 40.5 minutes or less is not particularly limited, but from the viewpoint of purification costs, it is preferably 0.05 × 10 ^-5 or more, more preferably 0.1 × 10 ^-5 or more, and even more preferably 0.5 × 10 ^-5 or more.

<Method of producing the composition>
The method for producing a composition of the present invention is a method for producing a composition containing N-vinylacetamide, which is used for producing an N-vinylacetamide-based polymer.
N-vinylacetamide can be produced, for example, by the reaction steps shown in the following reaction formula:

(wherein _R1 represents an alkyl group having 1 to 5 carbon atoms, _R2 represents a hydrogen atom, and _R3 represents a methyl group.)

The lower part of the above formula shows a step in which N-(1-alkoxyethyl)acetamide is subjected to a dealcoholization reaction to produce N-vinylacetamide.
The method for producing a composition containing N-vinylacetamide of the present invention may include this step, that is, a step of obtaining N-vinylacetamide from N-(1-alkoxyethyl)acetamide by dealcoholization reaction.

In the dealcoholization reaction process, N-(1-alkoxyethyl)acetamide is used as a raw material. However, the N-(1-alkoxyethyl)acetamide obtained by the method described in the upper part of the above formula generally contains impurities, and this has traditionally been used as is in the dealcoholization reaction process.

The method for producing the first composition of the present invention includes the steps of:
A step A of adding an alkali to a crude composition (1) containing N-alkoxyethylacetamide and distilling the mixture to obtain a purified composition (2) containing N-alkoxyethylacetamide;
a step B of producing a crude composition (3) containing N-vinylacetamide from the purified composition (2) containing N-alkoxyethylacetamide through a dealcoholization reaction;
and step C of purifying the crude composition (3) containing N-vinylacetamide by crystallization.

In step A, an alkali is added to a crude composition (1) containing N-alkoxyethylacetamide and a solvent to adjust the pH to preferably 8.0 to 8.5, and the resulting mixture is then distilled to purify the N-(1-alkoxyethyl)acetamide and obtain a purified composition (2) containing N-alkoxyethylacetamide. Examples of alkali that can be used include sodium hydroxide and potassium hydroxide. The purified composition (2) containing N-alkoxyethylacetamide preferably has an N-alkoxyethylacetamide content of 80% by mass or more, more preferably 85% by mass or more.

The above-mentioned step B is a step of producing a crude composition (3) containing N-vinylacetamide from the purified composition (2) containing the N-alkoxyethylacetamide via a dealcoholization reaction. The conditions for the dealcoholization reaction are not particularly limited, but it is desirable to carry out thermal decomposition at a temperature of 300°C or higher, preferably 350 to 450°C, under reduced pressure.

The crude composition (3) may be the composition itself after the dealcoholization reaction, but it is preferable that at least a portion of the by-product alcohol has been removed. That is, step B may include a step of removing at least a portion of the by-product alcohol from the composition after the dealcoholization reaction. Removal of the by-product alcohol can be carried out, for example, by distillation to remove the alcohol.

It is also preferable that the crude composition (3) is one from which at least a portion of the N-1,3-butadienylacetamide has been removed. That is, step B may include a step of removing at least a portion of the by-product N-1,3-butadienylacetamide from the composition after the dealcoholization reaction. N-1,3-butadienylacetamide can be removed, for example, by converting it into harmless N-butylacetamide or N-buteneacetamide by hydrogenation. N-1,3-butadienylacetamide can be removed by hydrogenation, for example, by contacting it with hydrogen gas using a column packed with a hydrogenation catalyst such as a Pd—Al ₂ O ₃ catalyst.

Step C above is a step in which the crude composition (3) containing N-vinylacetamide is purified by crystallization. Crude composition (3) containing N-vinylacetamide often contains impurities such as unreacted N-alkoxyethylacetamide in addition to N-vinylacetamide. In Step C, crystallization can be performed to reduce the content of these impurities. In Step C, crystallization may be performed once or may be repeated two or more times. In the present invention, it is preferable to perform crystallization two or three times in Step C. Crystallization can be performed by known methods, such as dissolving the N-vinylacetamide in a solvent such as methylcyclohexane or ethyl acetate, cooling from approximately 35-45°C to approximately 5-10°C, precipitating N-vinylacetamide crystals, and then separating the crystals by filtration or the like and washing them as necessary.

The composition obtained by this method for producing a composition of the present invention has excellent polymerizability and maintains sufficient polymerizability even after long-term storage. This is thought to be because the method for producing a composition of the present invention produces a composition with a low content of components that inhibit polymerization.

In the method for producing a composition of the present invention, preferably, when the resulting polymerization monomer composition is measured by high performance liquid chromatography under the above-described conditions, the sum of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 1.1 × 10 or less, more preferably 1.0 × 10 ^{or less} , and even more preferably 0.9 × 10 ^or less, where the peak area of N-vinylacetamide is taken as 1. A polymerization monomer composition satisfying such ranges is preferred because it has good polymerizability. Furthermore, the lower limit of this peak area sum is not particularly limited, but from the viewpoint of purification costs, it is preferably 0.05 × 10 ^or more, more preferably 0.1 × 10 ^or more, and even more preferably 0.5 × ¹⁰ or more.

The second composition production method of the present invention is a method for producing a composition containing the N-vinylacetamide of the present invention described above. That is, the second composition production method of the present invention is a method for producing a composition in which, when measured by high performance liquid chromatography under the above-mentioned conditions, the sum of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 1.1 × 10 ^or less, when the peak area of N-vinylacetamide is defined as 1.

The second method for producing a composition of the present invention includes a step C' of purifying the crude composition (3') containing N-vinylacetamide by crystallization.
The method for producing the second composition of the present invention preferably includes the steps of:
a step A' of adding an alkali to a crude composition (1') containing N-alkoxyethylacetamide and distilling the mixture to obtain a composition (2') containing N-alkoxyethylacetamide;
and step B' of producing a crude composition (3') containing N-vinylacetamide from composition (2') containing N-alkoxyethylacetamide through a dealcoholization reaction.

The specific operations of steps A', B', and C' in the method for producing the second composition of the present invention are the same as steps A, B, and C described above in the method for producing the first composition of the present invention, respectively.

In this second method for producing a composition of the present invention, the resulting composition contains N-vinylacetamide, has a low content of components that inhibit polymerization, has excellent polymerizability, and retains sufficient polymerizability even after long-term storage.

The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[Example 1]
Preparation of N-vinylacetamide
<Synthesis of N-(1-methoxyethyl)acetamide>
298 g of acetaldehyde (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 651 g of methanol (manufactured by Junsei Chemical Co., Ltd.), and 100 g of acetamide (manufactured by Tokyo Chemical Industry Co., Ltd.) were reacted in the presence of sulfuric acid (manufactured by Junsei Chemical Co., Ltd.) as a catalyst to obtain a crude composition (1) containing N-(1-methoxyethyl)acetamide and having a pH of 1.6.

<pH Adjustment of Crude Composition (1) Containing N-(1-Methoxyethyl)acetamide>
A 48% by mass aqueous solution of sodium hydroxide (manufactured by Junsei Chemical Co., Ltd.) was added to the obtained crude composition (1) containing N-(1-methoxyethyl)acetamide, and the pH was adjusted to 8.0.

<Distillation purification of N-(1-methoxyethyl)acetamide>
Next, the composition containing N-(1-methoxyethyl)acetamide whose pH was adjusted was distilled using a simple distillation apparatus under conditions of a degree of vacuum of 0.27 to 33 kPa (absolute pressure) and a bottom temperature of 90°C or higher and 100°C or lower, thereby obtaining composition (2) containing N-(1-methoxyethyl)acetamide with a purity of 92% by mass.

<Synthesis of N-vinylacetamide (thermolysis and dealcoholization reaction)>
The purified N-(1-methoxyethyl)acetamide-containing composition (2) obtained above was fed at a rate of 1.5 g/min to a reactor (a tubular reactor with an inner diameter of 20 mm and a length of 240 mm) maintained at 400°C and a pressure of 20 kPa (absolute pressure). A mixture of N-vinylacetamide and methanol produced by the thermal decomposition reaction was condensed using a cooling tube installed at the reactor outlet, and crude N-vinylacetamide was recovered. The conversion of N-(1-methoxyethyl)acetamide was 90%.

<Purification of N-vinylacetamide>
Next, a column was packed with 0.3 mass% Pd—Al ₂ O ₃ catalyst (the amount packed was such that 1 ml of catalyst was used for 20 g of crude N-vinylacetamide). The crude N-vinylacetamide was then circulated together with hydrogen gas at a reaction temperature of 40°C, a hydrogen gas pressure of 0.03 MPa (gauge pressure), and a space velocity (SV value) in the catalyst-packed column of 100/hr. This reaction was carried out for 4 hours to hydrogenate and reduce the N-1,3-butadienylacetamide by-product of the thermal decomposition reaction. The crude N-vinylacetamide with reduced N-1,3-butadienylacetamide was distilled using a simple distillation apparatus at a vacuum of 0.27 kPa (absolute pressure) or less and a bottom temperature of 50°C to 60°C to remove methanol, yielding a crude N-vinylacetamide-containing composition (3).

The resulting crude composition (3) containing N-vinylacetamide was cooled from 40°C to 10°C in a crystallizer to precipitate N-vinylacetamide crystals, which were then separated using a centrifugal filter. The separated crystals were washed with a methylcyclohexane:ethyl acetate solution (95:5 by mass), yielding 40 g of N-vinylacetamide. This N-vinylacetamide was then added to 44 g of methylcyclohexane and 8 g of ethyl acetate in a crystallizer, heated to 40°C, and completely dissolved. The mixture was then cooled to 5°C and crystallized again to precipitate crystals, which were then separated using a centrifugal filter. The crystals were washed with a methylcyclohexane:ethyl acetate solution (95:5 by mass), and dried at 25°C and 3-5 kPa (absolute pressure), yielding 33.6 g of purified N-vinylacetamide.

This was analyzed by high-performance liquid chromatography (HPLC) under the following measurement conditions. The area ratio was calculated using the peak area values (S32) at retention times of 31.5 to 32.5 minutes, the peak area value (S36) at retention times of 35.5 to 36.5 minutes, and the peak area value (S40) at retention times of 39.5 to 40.5 minutes, together with the peak area value of N-vinylacetamide (S-NVA) according to the following formula, and was found to be 0.34 × 10 ^-4 . The N-vinylacetamide peak appears in the retention time range of 43.5 to 44.5 minutes. The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were also measured under the following conditions, and both were below the detection limit (N.D.).

(HPLC measurement conditions)
a) Pump: Shodex (registered trademark) DS-4 manufactured by Showa Denko K.K. Flow rate: 0.7 ml/min
b) Autosampler: Jasco AS-2055plus Sample injection volume: 10 μL
c) Column oven: Sugai U-620 manufactured by Sugai Corporation Column oven temperature: 45°C
d) UV/Vis detector: Shimadzu Corporation SPD-20A Measurement wavelength: 230 nm
e) Column: Showa Denko Co., Ltd. Shodex (registered trademark) SB-802.5HQ x 2
f) Eluent: Acetonitrile (Kanto Chemical Co., Ltd., for high performance liquid chromatography)/water (ion-exchanged water) = 1/9 (volume ratio)
g) Sample: Dilute to 1% by mass with eluent.
(Formula for calculating area ratio)
Area ratio = (S32+S36+S40)/(S-NVA)

<Measurement of unsaturated aldehyde content>
The total content of each unsaturated aldehyde is measured by gas chromatography (GC) and high performance liquid column chromatography (HPLC). The detection limit for each unsaturated aldehyde is 5 ppm by mass in both GC and HPLC methods.
The GC method is performed under the following measurement conditions.
Apparatus: Shimadzu Corporation GC-2014
Column: HP-WAX φ0.25mm x 30m
Flow rate: He 1cm ³ /min
Spirit ratio: 40
Column temperature: 40°C (7 min) → temperature increase (25°C/min) → 130°C (15 min) → temperature increase (30°C/min) → 220°C (2 min)
Injection temperature: 200°C
Detector: Flame ionization detector (FID)
Detector temperature: 230°C

The HPLC method is performed under the following measurement conditions.
Column: Showa Denko K.K.: Shodex (registered trademark) SIL-5B
Flow rate: 1.0mL/min
Column temperature: 40°C
Eluent: isopropyl alcohol (IPA)/n-hexane=1/9 (mass ratio)
Detector: ultraviolet photodetector, 254 nm

<Analysis of N-1,3-butadienylcarboxylic acid amide>
The N-1,3-butadienylcarboxylic acid amide was quantitatively determined by high performance liquid column chromatography (HPLC) and confirmed and identified by ultraviolet-visible light absorption spectrum. The measurement conditions were as follows:
Column: Showa Denko K.K.: Shodex (registered trademark) SIL-5B
Eluent: isopropyl alcohol (IPA)/n-hexane=1/9 (mass ratio)
Column temperature: 40°C
Flow rate: 1.0mL/min
Detector: UV/Vis detector, 254 nm

Polymerization Test The polymerization test of the N-vinylacetamide-containing composition was carried out as follows: The standard time to reach the peak temperature in the polymerization test of this example was 88 minutes.
Here, the standard temperature peak arrival time is the time from the injection of the polymerization initiator until the temperature reaches its maximum. A product having a standard temperature peak arrival time of less than 130 minutes can be determined to be a non-defective polymer.

[1] Prepare a 100 ml glass vessel equipped with a catalyst injection tube, a nitrogen gas inlet tube, a nitrogen gas exhaust tube, and a thermometer.
[2] 20 g of N-vinylacetamide and 58 g of ion-exchanged water are weighed into the glass container [1].
[3] Heat to 30°C in a water bath while bubbling nitrogen gas at 50 ml/min. Continue passing nitrogen gas through until the end of polymerization.
[4] 1.6 g of VA-044 (2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 48.4 g of ion-exchanged water.
[5] 4.0 g of V-50 (2,2'-azobis(2-methylpropionamidine) dihydrochloride, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 46.0 g of ion-exchanged water.
[6] After one hour of nitrogen gas aeration, 1 g of the aqueous polymerization initiator solution [4] and then 1 g of the aqueous polymerization initiator solution [5] are added using syringes.
[7] The glass container is removed from the water bath, and the moisture on the surface of the glass is removed with paper. The glass container is then transferred to an insulated container to continue polymerization.
[8] The polymerization temperature was monitored, and the time from the addition of the polymerization initiator in [6] until the temperature of the N-vinylacetamide solution reached its maximum (standard temperature peak time) was used as an index of polymerization.

[Example 2]
35.6 g of purified N-vinylacetamide was obtained in the same manner as in Example 1. The area ratio was 0.86 × 10 ^-4 . The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The time to reach the standard temperature peak in the polymerization test was 108 minutes.

[Example 3]
36.4 g of purified N-vinylacetamide was obtained in the same manner as in Example 1. The area ratio was 0.95 × 10 ^-4 . The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The time to reach the standard temperature peak in the polymerization test was 115 minutes.

[Example 4]
34.8 g of purified N-vinylacetamide was obtained in the same manner as in Example 1. The area ratio was 0.74 × 10 ^-4 . The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The time to reach the standard temperature peak in the polymerization test was 105 minutes.

[Example 5]
36 g of purified N-vinylacetamide was obtained in the same manner as in Example 1. The area ratio was 0.88 × 10 ^-4 . The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The time to reach the standard temperature peak in the polymerization test was 113 minutes.

[Example 6]
30 g of N-vinylacetamide prepared in the same manner as in Example 1 (except for the five-fold increase in the amount charged) was stored in a constant-temperature bath at 20°C for one year. 33 g of methylcyclohexane and 6 g of ethyl acetate were added to a crystallizer and heated to 40°C until completely dissolved. The mixture was then cooled to 5°C and crystallized again to precipitate crystals, which were then separated using a centrifugal filter. The crystals were washed with a 95:5 (mass ratio) solution of methylcyclohexane and ethyl acetate and dried at 25°C and 3 to 5 kPa (absolute pressure) to obtain 24.8 g of purified N-vinylacetamide. The area ratio was 0.45 × ^10-4 . The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The standard temperature peak time in the polymerization test was 96 minutes.

[Example 7]
The same procedure as in Example 6 was repeated, except that the storage period was changed from one year to three years, to obtain 22.2 g of purified N-vinylacetamide. The area ratio was 0.98 × 10 ^-4 . The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The time to reach the standard temperature peak in the polymerization test was 113 minutes.

[Comparative Example 1]
N-vinylacetamide prepared by the same method as in Example 1 (except that the amount charged was five times larger) was stored in a thermostatic chamber at 20°C for one year, and when analyzed by the same method as in Example 1, the area ratio was 4.39 × ^10-4 . In addition, the contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The standard temperature peak arrival time in the polymerization test was 250 minutes.

[Comparative Example 2]
N-vinylacetamide prepared by the same method as in Example 1 (except that the amount charged was five times larger) was stored in a thermostatic chamber at 20°C for three years, and when analyzed by the same method as in Example 1, the area ratio was 16.02 × 10 ^-4 . The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The time to reach the standard temperature peak in the polymerization test was 360 minutes.

[Comparative Example 3]
N-vinylacetamide prepared by the same method as in Example 1 (except that the amount charged was five times larger) was stored in a thermostatic chamber at 40°C for three months, and when analyzed by the same method as in Example 1, the area ratio was 58.30 × 10 ^-4 . Furthermore, the contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. A polymerization test was conducted, but the standard temperature peak was not reached even after 24 hours.

[Comparative Examples 4 and 5]
Two lots of N-vinylacetamide produced by the same method as in Example 1 (except that the amount charged was five times larger) were stored in a refrigerated warehouse at 10°C for three years, and when analyzed by the same method as in Example 1, the area ratios were 1.26 x ^10-4 and 1.17 x ^10-4 , respectively. The contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit. The standard temperature peak arrival times in the polymerization test were 128 minutes and 124 minutes.
The results of the above examples and comparative examples are shown in Table 1.

From the above examples and comparative examples, it was found that an N-vinylacetamide-containing composition in which the sum of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes relative to the peak area of N-vinylacetamide (hereinafter also referred to as the "area ratio") satisfies 1.1 x ^10-4 or less, and the amount of impurities appearing at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is sufficiently small, relative to the peak area of N-vinylacetamide, exhibits excellent polymerizability. On the other hand, in the comparative N-vinylacetamide-containing composition, which did not satisfy the area ratio of 1.1 x ^10-4 or less and had a large amount of impurities appearing at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes, the polymerizability was insufficient, even though the contents of unsaturated aldehydes and N-1,3-butadienylcarboxylic acid amide were both below the detection limit.

The composition of the present invention can be suitably used as a polymerization monomer for producing N-vinylacetamide-based polymers.

Claims (9)

1. A composition comprising N-vinylacetamide,
An N-vinylacetamide-containing composition, characterized in that, when measured by high performance liquid chromatography under the following conditions, the total of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 0.45 × 10 ^-4 or less, when the peak area of N-vinylacetamide is taken as 1.
(Measurement conditions)
Column: Showa Denko Co., Ltd. Shodex (registered trademark) SB-802.5HQ x 2
Flow rate: 0.7ml/min
Sample injection volume: 10 μL
Column oven: Sugai U-620
Column oven temperature: 45°C
UV/Vis detector: Shimadzu Corporation SPD-20A, measurement wavelength: 230 nm
Eluent: acetonitrile/water = 1/9 (volume ratio)
Sample: Dilute to 1% by mass with eluent 2. The N-vinylacetamide-containing composition according to claim 1, wherein, in the high performance liquid chromatography measurement, when the peak area of N-vinylacetamide is taken as 1, the sum of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 0.05 × 10 ^-5 or more. The N-vinylacetamide-containing composition according to claim 1 or 2, which has been purified by crystallization. The N-vinylacetamide-containing composition according to any one of claims 1 to 3, which is produced using as a raw material a composition containing N-alkoxyethylacetamide purified by distillation. An N-vinylacetamide polymer obtained by polymerizing the N-vinylacetamide-containing composition according to any one of claims 1 to 4. A method for producing the N-vinylacetamide-containing composition of claim 1 or 2, comprising:
A method for producing an N-vinylacetamide-containing composition, comprising a step C' of purifying a crude composition (3') containing N-vinylacetamide by crystallization. a step A' of adding an alkali to a crude composition (1') containing N-alkoxyethylacetamide and distilling the mixture to obtain a composition (2') containing N-alkoxyethylacetamide;
and step B' of producing a crude composition (3') containing N-vinylacetamide from a composition (2') containing N-alkoxyethylacetamide through a dealcoholization reaction. The method for producing an N-vinylacetamide-containing composition according to claim 6, A method for producing the N-vinylacetamide-containing composition of claim 1 or 2, comprising:
A step A of adding an alkali to a crude composition (1) containing N-alkoxyethylacetamide and distilling the mixture to obtain a purified composition (2) containing N-alkoxyethylacetamide;
a step B of producing a crude composition (3) containing N-vinylacetamide from the purified composition (2) containing N-alkoxyethylacetamide through a dealcoholization reaction;
and a step C of purifying the crude composition (3) containing N-vinylacetamide by crystallization. A method for selecting an N-vinylacetamide-containing composition, comprising determining whether or not the composition satisfies the following requirement in high performance liquid chromatography measurement under the following conditions: when the peak area of N-vinylacetamide is taken as 1, the sum of the peak areas at retention times of 31.5 minutes to 32.5 minutes, 35.5 minutes to 36.5 minutes, and 39.5 minutes to 40.5 minutes is 1.1 x ^10-4 or less; and selecting compositions that satisfy the requirement.
(Measurement conditions)
Column: Showa Denko Co., Ltd. Shodex (registered trademark) SB-802.5HQ x 2
Flow rate: 0.7ml/min
Sample injection volume: 10 μL
Column oven: Sugai U-620
Column oven temperature: 45°C
UV/Vis detector: Shimadzu Corporation SPD-20A, measurement wavelength: 230 nm
Eluent: acetonitrile/water = 1/9 (volume ratio)
Sample: Dilute to 1% by mass with eluent