JPH0582402B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing an N-vinylformamide polymer according to the following reaction formula.

[Conventional technology]

Conventionally, the manufacturing method for N-vinylformamide, which is a raw material monomer, is as follows: (1) Using acetaldehyde cyanohydrin obtained by the reaction of acetaldehyde and hydrogen cyanide as a raw material, reacting it with formamide to form N-(α- cyanoethyl) formamide, thereby splitting hydrogen cyanide to obtain an N-vinyl compound (2) Electrode reaction of N-formyl-α-alanine or N-ethylformamide with methanol to produce N-(α-methoxyethyl)formamide Methods such as splitting methanol to obtain N-vinyl compounds are known, but method (1) is difficult to produce due to the safety of raw materials and by-products, and also has side effects that inhibit radical polymerization. Polymerization of the monomer obtained by this method is not a satisfactory method for the industrial production of N-vinylformamide polymers because living organisms are generated. Method (2) is difficult to implement industrially because it uses an electrode reaction, and cannot be used as a preliminary step for producing an N-vinylformamide polymer. [Object of the Invention] An object of the present invention is to provide a method for producing an N-vinylformamide polymer that is industrially more advantageous than the conventional method. Therefore, the object of the present invention is to obtain N-(α-hydroxyethyl)formamide by reacting formamide and acetaldehyde in the presence of a basic catalyst as a first step; The obtained N-
A 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. TaN-
(α-alkoxyethyl)formamide in gas phase
Heat to 250-600℃ to cause dealcoholization reaction and N
- Step of obtaining vinylformamide, as a fourth step, the N- obtained in the third step
This is achieved by a method for producing an N-vinylformamide polymer, which includes a step of polymerizing vinylformamide in the presence of a radical initiator to obtain N-vinylformamide polymerization. [Structure of the Invention] (First Step) As the catalyst used in the reaction of formamide and acetaldehyde in the present invention, any general basic compound can be used. Hydroxides of alkali metals, alkaline earth metals, quaternary ammonium, etc., tertiary amines, strong bases, ion exchange resins used for weak bases, weak base salts consisting of strong bases and weak acids, etc. However, the preferred base catalyst is a weakly basic salt consisting of a strong base and a weak acid, particularly a weakly basic salt consisting of a strong base and a weak acid having a PKa value of 4 to 15. Here, the PKa value is
Means the value at 25°C of 0.01 mol/aqueous solution concentration. Such weakly basic salts include various substances, such as strong bases of hydroxides such as lithium, sodium, or potassium, and organic acids, phenols, sulfurous acid, phosphorous acid, hypophosphorous acid, and pyrroline. Examples include salts with weak acids such as phosphoric acid, carbonic acid, boric acid, and metasilicic acid. Particularly preferred weakly basic salts are potassium carbonate, sodium carbonate, potassium phosphate, sodium phosphate, potassium pyrophosphate, and sodium pyrophosphate. The proportion of the weakly basic salt used as a catalyst for the reaction between formamide and acetaldehyde is usually 0.01 to 10 mol%, preferably 0.1% to formamide.
It is appropriately selected from the range of ~5 mol%. The reaction temperature between formamide and acetaldehyde can be selected from a wide range of -10 to 100°C, but from the viewpoint of acetaldehyde selectivity, it is preferably in the range of 0 to 40°C. The ratio of the reaction raw materials, formamide and acetaldehyde, is usually 1:1.0 to 5.0 (molar ratio).
is selected from the range of, but the preferred usage ratio is
It depends on the mode of supply of acetaldehyde to the reaction system, for example, when acetaldehyde is supplied in gaseous form, it is 1:1.0 to 1.5 (molar ratio), and when it is supplied in liquid form, it is 1:1.5 to 4.0 (molar ratio). is within the range of The reaction between formamide and acetaldehyde can be carried out using any reaction apparatus according to various conventionally known formats, but the supply mode of acetaldehyde, if it is in a gaseous state, is as described above. It is economically advantageous because a high yield can be achieved at a usage rate of acetaldehyde close to the molar amount. A preferred reaction method is a method in which a catalyst and formamide are placed in a stirring tank, and gaseous acetaldehyde is continuously fed into the liquid little by little. Although the reaction can be carried out in the absence of a solvent, the product N-(α-hydroxyethyl)
Formamide is a crystalline substance with a melting point of 52.5 to 53.8°C, and if the reaction is carried out without a solvent at the preferred temperature of 0 to 40°C, the product will precipitate and solidify at the end of the reaction, so a solvent that disperses the crystals should be used. It is preferable. Specific examples include aliphatic hydrocarbons such as hexane and heptane, and aromatic hydrocarbons such as benzene, toluene and xylene. The amount of solvent used is
Usually, the amount is appropriately selected from the range of 0.2 to 2 times the weight of formamide. Incidentally, the solvent may be added to the reaction system immediately before the crystal precipitation described below. N-(α-hydroxyethyl)formamide, the reaction product of formamide and acetaldehyde, is
During the reaction, when crystal precipitation does not occur under normal conditions, specifically, when the conversion rate of formamide is within the range of 50 to 80 mol%, preferably 60 to 80 mol%, crystals are formed by cooling or adding crystal nuclei. Precipitation is preferred because it increases the yield of the product. Therefore, the remaining amount of acetaldehyde determined in advance is fed into the liquid as a gas and dissolved, and then crystals of N-(α-hydroxyethyl)formamide are precipitated according to the method described above.
Next, the reaction is continued, or N-(α-hydroxyethyl)formamide is almost quantitatively precipitated by precipitating crystals, and then the remaining amount of acetaldehyde gas is fed into the liquid to continue the reaction. Obtainable. The cooling is
It is carried out by lowering the reaction temperature to a range of -20 to 25 °C, preferably -5 to 10 °C,
The addition of crystal nuclei is carried out by adding a small amount of N-(α-hydroxyethyl)formamide as crystal nuclei to the reaction system according to methods known in the art of crystallization. (Second step) N-(α-hydroxyethyl)formamide obtained as crystals after the reaction is hygroscopic and unstable to heat, and easily decomposes into the raw material formamide and acetaldehyde, so it is not isolated. By reacting with alcohol, decomposition reactions can be completely avoided and N-(α-alkoxyethyl)formamide can be obtained in extremely high yields. N-(α-hydroxyethyl)formamide obtained in a non-crystallized state can also be converted to N-(α-
alkoxyethyl)formamide, and can be extracted by known means such as distillation. As the alcohol used in the reaction with N-(α-hydroxyethyl)formamide in the method of the present invention, primary or secondary alcohols are used. Alcohols having 1 to 8 carbon atoms are preferred from the viewpoint of solubility with. Polyhydric alcohols are undesirable because they produce two or more types of reactants, resulting in complex products, but they cleave alkoxy groups and produce N.
- No obstacles to obtaining vinylformamide. Particularly preferred alcohols in terms of reactivity are monovalent primary alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, n-propanol, n-butanol, isobutyl alcohol, 2-methoxyethanol, 2-ethoxy It is ethanol. The amount of alcohol to be used relative to N-(α-hydroxyethyl)formamide can be determined arbitrarily, but since N-(α-hydroxyethyl)formamide is a thermally unstable compound and difficult to recover after the reaction. It is preferable to use an equimolar amount or an excess of alcohol, and usually 1.0 to 30 times the molar amount of alcohol is used. Since N-(α-hydroxyethyl)formamide is a crystalline compound, the alcohol used in the reaction is preferably used as a solvent, and the amount of alcohol used in this case is preferably 2.0 to 20 times the mole. Depending on the type of alcohol,
Since acetal is easily produced with unreacted acetaldehyde, in addition to the amount of alcohol used above,
It is preferable to increase the amount of alcohol by twice as much molar amount as the amount of unreacted acetaldehyde. In order to minimize the amount of alcohol used, an inert solvent may be appropriately used in the reaction. Catalysts used for the reaction between N-(α-hydroxyethyl)formamide and alcohol include:
Any of the common acid catalysts can be used. These include mineral acids, organic acids, weak acids, ion exchange resins exhibiting strong acidity, solid acid catalysts, etc. Among these, strongly acidic substances are preferably used. Examples of preferred acid catalysts include sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid, sulfamic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, and crosslinked polystyrenesulfonic acid. The amount of acid catalyst used is 0.001 to 10 mol%, preferably 0.1 to 10 mol%, based on N-(α-hydroxyethyl)formamide.
It is in the range of 5 mol%. Furthermore, when a heterogeneous catalyst such as an ion exchange resin is used, the raw material mixture can be passed through a column filled with the catalyst to cause the reaction. The reaction between N-(α-hydroxyethyl)formamide and alcohol is easily accomplished by adding an acid catalyst to a mixture of the two or bringing them into contact. The reaction temperature is -10 to 60℃ from the viewpoint of reactivity and stability of N-(α-hydroxyethyl)formamide.
A range of is preferred. Particularly preferably, the temperature is in the range of 0 to 40°C. The reaction product can also be isolated by a commonly known method such as concentration or distillation after neutralizing or separating the acid catalyst. (Third Step) N-vinylformamide is obtained by heating the N-(α-alkoxyethyl)formamide obtained in the second step in the gas phase and causing a dealcoholization reaction. As a method for vaporizing N-(α-alkoxyethyl)formamide, a method of heating under an inert gas stream, a method of heating under reduced pressure, a method of heating under reduced pressure in the presence of an inert gas, etc. can be used. The temperature for vaporization is usually 100°C to 500°C. The dealcoholization reaction is usually carried out at a temperature of 250°C to 600°C, preferably 350 to 500°C. Examples of methods for heating N-(α-alkoxyethyl)formamide in the gas phase include a method in which it is brought into contact with a heating furnace filled with glass, quartz, metal, etc. through gas, a method in which it is brought into contact with a heated inert gas, etc. . The residence time of the gas is preferably 0.01 to 20 seconds. (Fourth Step) An N-vinylformamide polymer is obtained by polymerizing the N-vinylformamide obtained in the third step in the presence of a radical polymerization initiator. N
- Vinylformamide can be directly polymerized in bulk without using a solvent, or N-vinylformamide polymers can be obtained by solution polymerization using various organic solvents that dissolve N-vinylformamide. Polymerization in an aqueous solution is preferred because a polymer having an extremely high molecular weight can be easily obtained in high yield. N-vinylformamide can be copolymerized with various radically polymerizable vinyl monomers, but when copolymerizing in an aqueous solution, it can be copolymerized with acrylic acid or methacrylic acid and derivatives thereof, acrylamide or acrylamide and derivatives thereof. A high molecular weight polymer can be obtained by this method. When polymerizing in an aqueous solution, the concentration of N-vinylformamide or a mixture of N-vinylformamide and a monomer to be copolymerized is preferably in the range of 5 to 80% by weight, preferably 10 to 60% by weight. It is also possible to mix a sterile organic solvent. The pH of the aqueous solution is preferably adjusted to 5-10, preferably 6-8. Radical polymerization initiators include oil-soluble azo compounds, water-soluble azo compounds, hydrogen peroxide, persulfates, perchlorates, hydroperoxides, dialkyl peroxides, diacyl peroxides, ketone peroxides, and alkyl peresters. , peroxydicarbonate, etc. are used, but azo compounds are preferred in order to obtain a high molecular weight polymer. Particularly preferred are water-soluble azo compounds. An example of a preferred water-soluble azo compound is 2,2'-azobis-(2-amidinopropane)2.
Hydrochloride, azobis-(N,N-dimethyleneisobutyramidine) dihydrochloride, 4,4'-azobis-
(4-dianovaleric acid)-2-sodium is exemplified. The amount of the radical polymerization initiator used is selected in the range of 0.005 to 5% by weight, preferably 0.05 to 0.5% by weight, based on the weight of N-vinylformamide or a mixture of N-vinylformamide and other copolymerizable monomers. The polymerization temperature can be selected in the range of 10°C to 150°C depending on the molecular weight of the desired polymer. When polymerizing in an aqueous solution, the temperature is 20°C to 100°C, preferably 40°C to 80°C.
It is ℃. The present invention is not limited to the polymerization method or the order of addition, but examples of aqueous solution polymerization include a method of polymerizing with stirring, a method of polymerizing adiabatically in a static container, a method of polymerizing while removing heat in a sheet form, and a method of polymerizing while removing heat in a sheet form. Examples include a method of polymerizing in a type emulsion, a method of polymerizing in a water-in-oil emulsion, or a dispersion state. An example of a method for polymerizing under stirring is to remove oxygen by passing nitrogen gas into an aqueous solution of N-vinylformamide, then bring the solution to a predetermined temperature, add a radical polymerization initiator, and maintain the temperature at a predetermined temperature under a nitrogen gas stream. [Examples] The present invention will be explained in more detail by Examples below, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded. Example 1 (1) Synthesis of N-(α-methoxyethyl)formamide 5-4 equipped with a stainless steel stirrer, a gas inlet tube, a thermometer and an ice-cooled condenser with an exhaust tube
A trap containing a small amount of liquid paraffin was connected to the exhaust pipe of the two-necked flask. Approximately 750 ml of acetaldehyde was placed in a pressure-resistant glass reactor equipped with a magnetic stirrer, a heat insulator, and a needle valve, and the needle valve and the gas inlet pipe of a four-necked flask were connected with a fluororesin tube. Formamide 450 in a 4-necked flask
(10 moles), 6.9 g of potassium carbonate, and 450 g of n-hexane were added and stirred vigorously while maintaining the temperature at 25°C. The pressure-resistant glass reactor was maintained at 40°C, and the needle valve was gradually opened while acetaldehyde was stirred to introduce acetaldehyde in gaseous form into the reaction solution. Observing the trap containing liquid paraffin, adjusting the needle valve so that the maximum amount of acetaldehyde was supplied without leaking from the trap in gaseous form, and reacting at a bath temperature of 25°C.
530 g (12 moles) of acetaldehyde were absorbed in 3.5 hours. After the supply of acetaldehyde was stopped and the mixture was stirred for an additional 30 minutes, the mixture was cooled to 5°C, and the reaction product crystallized into a slurry. Since heat is generated due to crystallization, cool it down to 5℃ again.
Add 900g of methanol and raise the temperature to 20℃ while stirring.
A mixture of 9.8g sulfuric acid and 61g methanol was added to obtain a clear solution. After reacting at 25° C. for 4 hours, 12.5 g of aqueous ammonia was added to neutralize the mixture, and the resulting inorganic substances were filtered through a Nutssie filter. The upper n-hexane layer of the liquid was separated, concentrated using an evaporator, and then distilled under reduced pressure to obtain 961 g of N-(α-methoxyethyl)formamide (boiling point 70-73°C/0.2 mmHg) containing 2.5% by weight of formamide. . The yield based on formamide was 95.5%. (2) Synthesis example of N-vinylformamide A stainless steel electric furnace with an inner diameter of 27 mm and a length of 300 mm was installed vertically and filled with glass beads of 1.5 mm in diameter. Keep column temperature at 400℃, 145mm
The reaction product is pumped from the top under reduced pressure of Hg at 80% per minute.
ml of nitrogen gas was introduced by means of a metering pump at a rate of 1.0 g/min. The distillate was cooled with a Dimroth and then collected into a trap cooled with dry ice. After removing methanol with an evaporator, it was distilled under reduced pressure using a 10 cm Vicrow column. N-vinylformamide containing 4% formamide (boiling point 41-40℃/0.1mmHg)
Obtained 651g. This yield corresponds to 89% of the raw material formamide. (3) Synthesis example of N-vinylformamide polymer Dissolve 10.4 g of the above product in 39.3 g of demineralized water in a 100 ml four-necked flask equipped with a stirrer, cooling tube, nitrogen gas introduction tube, and initiator inlet. and introduced it. After heating to 50℃ while passing nitrogen gas,
0.3 g of an aqueous solution of N,N'-azobis-(2-amidinopropane) dihydrochloride (wt%) was added thereto, and the mixture was maintained at 50 DEG C. for 8 hours with stirring under a nitrogen gas stream.
The reduced viscosity of the product is η _sp /C = 6.3, and the polymerization rate is
It was 99.1%. The consistent yield from the raw formamide corresponds to 84%. The consistent yield from the raw material acetaldehyde is equivalent to 70%. Example 2 In place of methanol in Example 1, 2280 g of 2-
N-[α-(2-methyloxy)ethyloxy]formamide was synthesized under the same conditions as in Example 1 except that methoxyethanol was used. 1250 g of formamide-free product (boiling point 94-95°C/0.65
mmHg) was obtained. Yield based on formamide is 85
It was %. Thermal decomposition was carried out under the same conditions as in Example 1, and N-vinylformamide substantially free of formamide was synthesized in a yield of 87%. Polymerization was carried out under the same conditions as in Example 1 to obtain an N-vinylformamide polymer. The reduced viscosity of the product was η _sp /C=6.1, and the polymerization rate was 99.5%. The consistent yield from raw formamide corresponds to 73%. The consistent yield from the raw material acetaldehyde is equivalent to 60%. Comparative Example 1 Lactonitrile and formamide
37406 80% yield from lactonitrile (literature value 82%), yield from formamide according to Example 1
36% N-formylalanine nitrile, which was heated at 5 mmHg according to Example 1 of Japanese Patent Publication No. 43-928.
Dehydrocyanation at 600℃, yield 38%
(Yield 46% from N-formylalanine determined from literature values) N-vinylformamide was obtained. Example 1, (1)N after distillation under the same conditions as Example 1
- Polymerization was carried out under the same conditions as in the synthesis example of vinylformamide polymer. The reduced viscosity of the product is η _sp /C
= 3.2, and the polymerization rate was 87.2%. The consistent yield from raw formamide corresponds to 12%. The consistent yield from the raw material lactonitrile corresponds to 26.5%. (Measurement of reduced viscosity) The polymer was dissolved in 1N saline solution to a concentration of 0.1 g/dl, and measured using an Ostwald viscometer (t _p = 30.2 seconds).
It was determined from the value (t seconds) measured at 25°C. Reduced viscosity η _sp /C = (t-t _p /t _p )/0.1 (dl/g) (Measurement of polymerization rate) Approximately 2 g of aqueous solution of polymer in a 500 ml Erlenmeyer flask
was accurately weighed and dissolved in 200 ml of demineralized water. Sodium acetate 5
After adding and dissolving 1/10N iodine aqueous solution 25g
ml and stored for 30 minutes. This solution was titrated with a 1/10 normal sodium thiosulfate aqueous solution using starch as an indicator. A blank test was conducted under the same conditions, and the polymerization rate was calculated from the difference in titer. [Effects of the Invention] According to the method for producing N-vinylformamide polymers of the present invention, high yields can be easily produced using acetaldehyde, formamide, and alcohol as raw materials without using highly toxic nitrile compounds as starting materials. Since it is possible to produce high quality N-vinylformamide polymers, it will greatly contribute to the field of application of water-soluble and hydrophilic polymers.

Claims (1)

[Claims] 1. In the first step, formamide and acetaldehyde are reacted in the presence of a basic catalyst to form N-
Step of obtaining (α-hydroxyethyl)formamide, as the second step, the N-
A 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. TaN-
(α-alkoxyethyl)formamide in gas phase
Heat to 250-600℃ to cause dealcoholization reaction and N
- Step of obtaining vinylformamide, as a fourth step, the N- obtained in the third step
1. A method for producing an N-vinylformamide polymer, comprising the step of polymerizing vinylformamide in the presence of a radical initiator to obtain an N-vinylformamide polymer.