JP3365430B2 - Method for producing N-vinylformamide polymer - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method of making high molecular weight N-vinylformamide polymers.

[0002]

2. Description of the Related Art N-vinylformamide polymers can be used for various purposes such as flocculants and raw materials for paper chemicals. In order to obtain this N-vinylformamide polymer, it is premised that N-vinylformamide, which is a monomer raw material, can be efficiently produced. As the most preferred method for producing N-vinylformamide, acetaldehyde and formamide are reacted to form N- (α-hydroxyethyl) formamide, which is alkoxylated to N- (α-alkoxyethyl) formamide,
Further, there is a method of dealcoholation by thermal decomposition to obtain N-vinylformamide. And N-obtained by the method
A method for producing a polymer using vinylformamide is known (JP-A-61-97309).

[0003]

Conventionally, in the case of polymerizing N-vinylformamide, there is a problem that it is difficult to stably obtain a high molecular weight polymer due to the influence of impurities and decomposed products in N-vinylformamide. there were. Therefore, a method of distilling and purifying N-vinylformamide by a specific method (JP-A-62-19352, JP-A-63-190).
862) has been proposed, but there were problems such as loss of thermal decomposition during distillation and purification of N-vinylformamide and complication of the process.

[0004]

In view of the above problems, the present inventors have made various studies on rational processes for obtaining a high molecular weight N-vinylformamide polymer, and as a result,
If specific impurities contained in N- (α-alkoxyethyl) formamide, which is an intermediate of N-vinylformamide, can be reduced, a high molecular weight N-in the subsequent polymerization step can be used.
The present inventors have found that a vinylformamide polymer can be stably produced, and arrived at the present invention.

That is, according to the present invention, the first step of reacting acetaldehyde and formamide in the presence of a basic catalyst to obtain N- (α-hydroxyethyl) formamide, and the N- (α obtained in the first step A second step of reacting -hydroxyethyl) formamide with a primary or secondary alcohol in the presence of an acidic catalyst to obtain N- (α-alkoxyethyl) formamide, N- (α obtained in the second step -Alkoxyethyl) formamide is heated in the gas phase to carry out dealcoholization reaction to obtain N-vinylformamide, and the N-vinylformamide obtained in the third step is polymerized in the presence of a radical initiator. A fourth step of obtaining an N-vinylformamide polymer, the method comprising the step of: The method for producing an N-vinylformamide polymer is characterized in that the content of acetaldehyde and its derivative in N- (α-alkoxyethyl) formamide is adjusted to 3.0% by weight or less.

The present invention will be described in detail below. The method for producing the N-vinylformamide polymer of the present invention comprises four steps as shown below. The first step of the present invention is a step of reacting acetaldehyde and formamide in the presence of a basic catalyst to obtain N- (α-hydroxyethyl) formamide. The basic catalyst is not particularly limited as long as it is a general basic compound, but is preferably a weak basic salt composed of a strong base and a weak acid having a pKa value of 4 to 15, and specifically, carbonic acid. Examples include sodium, sodium bicarbonate, potassium phosphate, hydrogen-potassium phosphate, sodium pyrophosphate and the like.

The ratio of the weakly basic salt used as a catalyst for the reaction between formamide and acetaldehyde is usually appropriately selected from the range of 0.01 to 10 mol% with respect to formamide. The reaction temperature of formamide and acetaldehyde can be selected from a wide range of -10 to 100 ° C, but it is preferably 0 to 40 ° C from the viewpoint of the selectivity of acetaldehyde. The use ratio of the reaction raw materials formamide and acetaldehyde is usually 1: 1.0.
To 5.0 (molar ratio). As the formamide and acetaldehyde, commercially available products can be used as they are, but the acetic acid content in the acetaldehyde is 300 ppm by weight by being purified by distillation in advance.
In the following, 100% of diformamide in formamide is also used.
It is preferable to use those having 0 wt ppm or less and formic acid of 100 wt ppm or less from the viewpoint of maintaining a high reaction yield.

Although the reaction can be carried out in the absence of a solvent, usually, a solvent is used, and the product N- (α-hydroxyethyl) is used after the reaction or at a stage in the middle of the reaction. The method of precipitating formamide crystals is generally used. Specific examples of the solvent include aliphatic hydrocarbons such as hexane and heptane, and aromatic hydrocarbons such as benzene, toluene and xylene. The amount of the solvent used is usually appropriately selected from the range of 0.2 to 2 times the weight of formamide.

In the second step of the present invention, N- (α-hydroxyethyl) formamide obtained in the first step is reacted with a primary or secondary alcohol in the presence of an acid catalyst to form N- ( In this step, α-alkoxyethyl) formamide is obtained. N- (α-obtained as crystals in the first step
Since hydroxyethyl) formamide generally has high hygroscopicity and lacks thermal stability, it is preferable to react with alcohol in the second step without isolation after the first step. The solvent in the first step may be separated or may be used as it is as a part of the solvent in the second step.

As the alcohol used for the reaction with N- (α-hydroxyethyl) formamide, a primary or secondary alcohol is used.
Particularly preferable alcohols from the viewpoint of solubility with (α-hydroxyethyl) formamide include C 1 -C 1
4 monohydric primary alcohols such as methanol,
Examples include ethanol, n-propanol, n-butanol and isobutyl alcohol.

The amount of alcohol to be used with respect to N- (α-hydroxyethyl) formamide can be arbitrarily determined. However, N- (α-hydroxyethyl) formamide is a thermally unstable compound and is recovered after the reaction. It is difficult to use alcohol in an equimolar amount or more, and usually 1.0 to 30 times mol of alcohol is used. N-
As the catalyst used for the reaction of (α-hydroxyethyl) formamide and alcohol, any of the general acid catalysts can be used. Examples include mineral acids, organic acids, ion exchange resins exhibiting weak and strong acids, and solid acid catalysts. Preferably, examples of the acid catalyst include sulfuric acid, hydrochloric acid, nitric acid,
Examples thereof include sulfamic acid, methanesulfonic acid, and crosslinked polystyrenesulfonic acid. The amount of acid catalyst used is N-
0.00 with respect to (α-hydroxyethyl) formamide
It is in the range of 1 to 10 mol%.

The reaction between N- (α-hydroxyethyl) formamide and alcohol is easily accomplished by adding or contacting an acid catalyst to the mixture of the two. The reaction temperature is usually in the range of -10 to 60 ° C, preferably 0 to 40 ° C from the viewpoint of reactivity and stability of N- (α-hydroxyethyl) formamide. The reaction product N- (α-
The alkoxyethyl) formamide can be isolated by a method such as concentration or distillation after neutralizing or separating the acid catalyst.

In the method of the present invention, the above-mentioned first step, second step, and third step and fourth step described later can be integrated, but the most important point in the present invention is N- obtained in the second step and used as a reaction raw material in the third step
The content of acetaldehyde and its derivatives in (α-alkoxyethyl) formamide is adjusted to 3.0% by weight or less, preferably 2.0% by weight or less, and more preferably 1.0% by weight or less.

Here, the acetaldehyde derivative is an impurity passing through an aldol produced by the aldol condensation of acetaldehyde, and is 3-hydroxybutanal, crotonaldehyde, 2,4-hexadecane by an analysis method by gas chromatography. Dienal, octatrienal, 1,1-dimethoxyethane, 1,1-dimethoxy-3-hydroxybutane (dimethyl acetal of acetaldehyde), 3-methoxybutanal can be quantified, and acetaldehyde and its derivatives can be quantified. The total amount can be easily analyzed.

N-vinyl produced when a compound of these groups was subjected to a thermal decomposition reaction in the third step described later using N- (α-alkoxyethyl) formamide in a content higher than the above range. Even if formamide is polymerized,
It becomes very difficult to obtain a polymer having a high molecular weight. As the cause, acetaldehyde and its derivatives are
It is considered that this is because it has a relatively high reactivity with free radicals, and thus acts as a factor inhibiting polymerization during the polymerization of N-vinylformamide.

Of the above acetaldehyde derivatives, N- (α-alkoxyethyl) formamide is
Usually, examples of compounds containing a relatively large amount include 3-hydroxybutanal, crotonaldehyde, and 1,1-dimethoxy-3-hydroxybutane, each containing 0.5
It is preferable to adjust the amount to be less than or equal to wt%, and since hexadienal has a particularly large polymerization deteriorating effect,
It is preferably adjusted to 0.05% by weight or less.

As a method for reducing acetaldehyde and its derivatives in N- (α-alkoxyethyl) formamide, firstly, a condition in which the production of N- (α-alkoxyethyl) formamide is small is selected during the production of N- (α-alkoxyethyl) formamide. There are two possible methods, secondly, a method for efficiently purifying N- (α-alkoxyethyl) formamide. The first method is to set the reaction conditions in the first step and the second step to optimal conditions as appropriate and is not uniquely determined. For example, in the first step, weak conditions such as sodium carbonate are used. When a basic salt is used as a catalyst, the catalytic amount is preferably 0.1 to 0.4 mol% with respect to formamide. If acetaldehyde or formamide, which is a reaction raw material, contains some amount of acetic acid, formic acid, diformamide (presumably diformamide also works as a weak acid), etc. as acid components, these acids are used. It is preferable that the amount of the catalyst be slightly larger than the above amount in consideration of the neutralized component. If the amount of the catalyst is less than the above range, the reaction rate is lowered, which is not preferable. On the contrary, if the amount is too large, a side reaction between acetaldehyde proceeds and the amount of the acetaldehyde derivative increases, which is not preferable.

In the second method, since N- (α-alkoxyethyl) formamide is a relatively stable compound, the light boiling components such as alcohol and water in the reaction solution after the alkoxylation are first It is a method of removing acetaldehyde and its derivative as much as possible by removing the acetaldehyde and then performing precision distillation. As conditions for precision distillation, for example, a distillation column having theoretical plates of about 2 to 30 is used, and the column top pressure is usually set to 2 to 30 mmHg and the column top temperature is set to about 60 to 100 ° C.

Further, in practice, it is preferable that the first and second methods are not limited to one of them, but that both methods are appropriately combined to assemble the process. Next, in the third step of the present invention, N- (α-alkoxyethyl) formamide having a reduced content of acetaldehyde and its derivative by the above-mentioned method is heated in a gas phase to carry out dealcoholization reaction to give N- (α-alkoxyethyl) formamide. This is a step of obtaining vinylformamide.

As a method of vaporizing N- (α-alkoxyethyl) formamide, a method of heating in a stream of an inert gas, a method of heating while reducing the pressure to about 50 to 250 mmHg, and a method of heating in the presence of an inert gas under a reduced pressure are used. A method etc. can be used. The temperature for vaporization is usually 100 to 50.
Performed at 0 ° C. The dealcoholization reaction is usually 250 to
600 ° C., preferably 350 to 500 ° C. N- (α
Examples of the method for heating the -alkoxyethyl) formamide in the gas phase include a method in which a gas is brought into contact with a heating furnace filled with glass, quartz, metal, etc., and a method in which it is brought into contact with a heated inert gas. The residence time of the gas is preferably 0.01 to 20 seconds.

In the present invention, the mixed solution containing N-vinylformamide obtained by the thermal decomposition reaction of N- (α-alkoxyethyl) formamide is an acetaldehyde-derived impurity which causes the most decrease in polymerization activity as described above. Since the amount is adjusted, it may be used as it is for the polymerization in the fourth step. For example, a simple distillation without a column may be used to distill a light boiling alcohol and a high boiling N 2
It is more preferable to remove polymerization and condensation products of vinylformamide. As a method for distilling this N-vinylformamide, specifically, an evaporator is preferably used, and the once evaporated fraction is directly introduced into a condenser and condensed. That is,
In this type, since there is no reflux step, the heat history in the distillation apparatus is small, and the loss of decomposition of N-vinylformamide is very small. The distillation may be carried out batchwise or continuously, and it is preferable that the high boiling point is separated after the light boiling point is separated. Examples of evaporator types include vertical tube falling film type, vertical or horizontal scraping type forced thin film type, centrifugal thin film type, forced circulation type, rising thin film type, natural circulation type, rotary evaporator, etc., but in this range It is not limited.

Among the N-vinylformamide recovered by the above method, formamide, N- (α-hydroxyethyl) formamide, N-, which are impurities having relatively close boiling points,
Although (α-alkoxyethyl) formamide and acetaldehyde derivative are mixed, the acetaldehyde derivative is limited to an amount that does not affect the polymerization. Specifically, the content of acetaldehyde and its derivative in N-vinylformamide is limited. Is usually an equivalent amount to about 1/2 of the content in N- (α-alkoxyethyl) formamide. Further, formamide in N-vinylformamide, N- (α-hydroxyethyl)
Since formamide and N- (α-alkoxyethyl) formamide have a smaller effect on the polymerization reaction than aldehyde derivatives, this N-vinylformamide can be used for the polymerization reaction without further purification treatment such as precision distillation. Can be used.

Next, the N-vinylformamide obtained in the third step is subjected to the fourth step, a polymerization step, according to a conventional method. The polymerization raw material may be N-vinylformamide alone or a copolymer with another radically polymerizable monomer. Other radically polymerizable monomers are (meth)
Acrylonitrile, (meth) acrylamide, vinyl acetate, N, N'-dimethylaminoethyl (meth) acrylate, and quaternary products thereof are used.

Polymerization can be carried out by known methods such as bulk polymerization, solution polymerization using a solvent of a kind, suspension polymerization, emulsion polymerization and the like. The polymerization reaction is generally carried out under an inert gas flow,
Usually, it is performed under a temperature condition of 30 to 100 ° C. Water is used as a solvent for solution polymerization, and the monomer concentration is usually 5 to 30%.
As the suspension polymerization, the aqueous solution having a monomer concentration of 20 to 80% by weight is usually polymerized in a dispersion state of water in oil using a hydrophobic solvent and a dispersion stabilizer. As the emulsion polymerization, usually, an aqueous solution having a monomer concentration of 20 to 80% by weight is polymerized in an oil-in-water type or water-in-oil type emulsion state using a hydrophobic solvent and an emulsifier.

As the polymerization initiator, an ordinary radical polymerization initiator is used, but an azo initiator is preferable. Particularly preferable initiators are 2,2'-azobis-4-amidinopropane hydrochloride and acetate, 4,4'-azobis-4-cyanovaleric acid sodium salt, and azobis-N, N'-dimethylenyliso. Butyl amidine hydrochloride and sulfate. The amount of these polymerization initiators used is usually 0.01 to 1% by weight based on the weight of the monomers.

[0026]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the present invention as long as the gist thereof is not exceeded. '(Quantitative method for each component) Formamide, N- (α-hydroxyethyl) formamide, N- (α-alkoxyethyl) formamide, N-vinylformamide, formic acid,
Acetic acid and diformamide were quantified using liquid chromatography. Methanol, acetaldehyde and acetaldehyde derivatives were quantified using gas chromatography.

Example 1 (1) Synthesis of N- (α-hydroxyethyl) formamide (first step) 600 g of toluene was charged into a 2 liter glass reactor equipped with a stirrer and a temperature controller, and degassed with nitrogen gas. After that, 235 g of acetaldehyde having an acetic acid content of 50 ppm by weight was added, and the temperature was maintained at 20 ° C. with stirring. Next, formamide 200 having a diformamide content of 500 ppm by weight and a formic acid content of 10 ppm by weight or less.
0.98 g of potassium carbonate (to 0.16 of formamide)
A formamide solution in which (mol%) was dissolved was prepared, and 20% of the solution was added over 30 minutes. Then, after aging for 30 minutes, 0.5 g of crystals of N- (α-hydroxyethyl) formamide was added to precipitate N- (α-hydroxyethyl) formamide. After performing this operation, 30 more
Aged. Then, add the remaining formamide solution to 2.5
After adding over time, aging was carried out for 1 hour. Most of the toluene phase was separated from this reaction slurry by filtration, and N- (α
Crystals of -hydroxyethyl) formamide were obtained.

(2) Synthesis of N- (α-methoxyethyl) formamide (second step) Next, 430 g of methanol containing 3.5 g of sulfuric acid was added,
The alkoxylation reaction was performed at 20 ° C. for 1 hour with stirring. After the reaction, 25% sodium hydroxide was added for neutralization, and the precipitated salt was separated by filtration, and then a light-boiling fraction mainly containing methanol was separated using a rotary evaporator under reduced pressure of 60 ° C. and 50 mmHg. Subsequently, a distillation column was used to obtain a distillate of N- (α-methoxyethyl) formamide under operating conditions of a column top pressure of 3 mmHg and a column top temperature of 60 to 90 ° C. Table 1 shows the analysis results of the amounts of acetaldehyde and its derivatives at this time.

(3) Synthesis of N-vinylformamide (3rd step) The above N- (α-methoxyethyl) formamide was added to 45
N at the temperature of 0 ° C with a residence time of 0.5 seconds on average
A mixed solution containing vinylformamide was obtained. The obtained mixed liquid was 50 mmHg using a rotary evaporator,
At 60 ° C., the light boiling components mainly composed of methanol were removed. Then, it was made to evaporate at 3 mmHg and a jacket temperature of 110 ° C. by a vertical scraping type thin film evaporator, and the evaporating liquid was completely condensed to obtain N-vinylformamide. The obtained N-vinylformamide had a purity of 90% by weight, impurities were 7.0% by weight of formamide, 1.5% by weight of N- (α-methoxyethyl) formamide; acetaldehyde and its derivative were 0.40% by weight. .

(4) Synthesis of N-vinylformamide polymer (4th step) 2,2'azobisamidinopropane hydrochloride as a polymerization initiator was added to the monomer in a 60% aqueous solution of N-vinylformamide as described above. 3000 ppm was added, and suspension polymerization was carried out at a temperature of 70 ° C. in a cyclohexane medium in which 0.5% ethyl cellulose was dissolved as a dispersion stabilizer. The obtained polymer was azeotropically dehydrated, filtered, and then dried under reduced pressure. The obtained N-vinylformamide polymer was prepared into a 0.1% concentration solution using 1N saline, and the reduced viscosity of the solution was measured by an Ostwald viscometer.
The results are shown in Table-1.

Comparative Example 1 Using the same formamide and acetaldehyde as in Example 1, 0.5 mol% of potassium carbonate catalyst to N-formamide was used.
(Α-Methoxyethyl) formamide was synthesized, and the same operation as in Example 1 was performed using it. Table of experimental results
Shown in 1. Example 2 The N- (α-alkoxyethyl) formamide produced in Comparative Example 1 was placed in a distillation apparatus (column top pressure 3 mmHg, column top temperature 82 ° C., reflux ratio 3) equipped with an Oldershaw 10-stage rectification column. The first distillate 10% was removed, and the rest was distilled to produce N- (α-
A purified product of alkoxyethylformamide was obtained, which was thermally decomposed and polymerized in the same manner as in Example 1. The experimental results are shown in Table-1.

[0032]

[Table 1]

[0033]

INDUSTRIAL APPLICABILITY According to the method of the present invention, a high yield and high molecular weight N-vinylformamide polymer can be produced using acetaldehyde, formamide and alcohol as raw materials.

Claims (8)

(57) [Claims] 1. A (1) the presence of acetaldehyde and formamide basic catalyst, the first step of obtaining a by N- (alpha-hydroxyethyl) formamide is reacted, obtained in (2) the first step N- A second step of reacting (α-hydroxyethyl) formamide with a primary or secondary alcohol in the presence of an acidic catalyst to obtain N- (α-alkoxyethyl) formamide, (3) obtained in the second step Third step of heating N- (α-alkoxyethyl) formamide in the gas phase to dealcoholize to obtain N-vinylformamide, (4) Radical initiation of N-vinylformamide obtained in the third step A fourth step of polymerizing in the presence of an agent to obtain an N-vinylformamide polymer, the method comprising the step of: A method for producing an N-vinylformamide polymer, which comprises adjusting the content of acetaldehyde and its derivative in N- (α-alkoxyethyl) formamide, which is a reaction raw material, to 3.0% by weight or less. 2. N- (α-alkoxyethyl) formia
The content of acetaldehyde and its derivatives in amide
The amount is adjusted to 1.0% by weight or less.
The manufacturing method described. 3. A N-(alpha-alkoxyethyl) The method according to claim 1 or 2 wherein the 3-hydroxy content of butanal in formamide and adjusting to 0.5% by weight or less. 4. A N-(alpha-alkoxyethyl) any of claims 1 to 3 content of crotonaldehyde in formamide and adjusting to 0.5 wt% or less
The production method described in Crab . 5. The content of 1,1-dimethoxy-3-hydroxybutane in N- (α-alkoxyethyl) formamide is adjusted to 0.5% by weight or less . The manufacturing method according to any one . 6. The content of 2,4- hexadienal in N- (α-alkoxyethyl) formamide is 0.05.
Claim and adjusting the wt% or less 1 to 5
The manufacturing method according to any one of 1 . 7. The amount of basic catalyst present in the first step is
It is 0.1-0.4 mol% with respect to formamide, The manufacturing method in any one of Claim 1 thru | or 6 characterized by the above-mentioned. 8. The content of acetaldehyde and its derivative in N- (α-alkoxyethyl) formamide is adjusted to 3.0% by weight or less by distillation by a distillation column . The manufacturing method according to any one .