JPH06340601A - Production of formamide - Google Patents

Abstract

PURPOSE:To obtain formamide hardly containing any impurities by reacting a formic acid ester with ammonia in the presence of an alcohol under anhydrous and catalyst-free conditions. CONSTITUTION:A formic acid ester is made to react with ammonia in the presence of an alcohol of >=20wt.%, preferably >=30-100wt.% based on the formic acid ester at 10-40 deg.C, preferably 10-30 deg.C under anhydrous and catalyst-free conditions to provide the objective formamide. The formamide obtained by this method contains hardly any formic acid which acts as an acid, ammonium formate and diformamide, thus the method is optimum, especially for synthesizing N-(alpha-hydroxyethyl) formamide using a basic catalyst. Since formic acid produced when polyvinylamine is produced by hydrolyzing a polymer of N- vinylformamide is recovered as a formic acid ester and can be utilized as a raw material in the above reaction, this method has large merit in production fields of n-vinylformamide and polyvinylamine.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing formamide by reacting a formate ester with ammonia.

[0002]

2. Description of the Related Art The reaction for obtaining formamide from a formate ester and ammonia is known. Then, as a method for increasing the yield of formamide in the reaction, a method using a basic catalyst (JP-A-3-68544) and a method in which about 1 to 5% of water is present with respect to the formate ester (JP-B 38-2
857) and the like are known.

[0003]

Formamide can be used for various industrial purposes such as a synthetic raw material and a reaction solvent. For example, N- which is an intermediate for the production of N-vinylformamide.
(Α-Hydroxyethyl) formamide is produced by reacting this formamide with acetaldehyde in the presence of a basic catalyst (JP-A-60-149551).

According to a study by the present inventors, the above N-
When producing (α-hydroxyethyl) formamide, it has been confirmed that diformamide, ammonium formate and formic acid which are main impurities in formamide as a synthetic raw material reduce the activity of the basic catalyst. In addition, impurities in these formamides are the product N-
Not only (α-hydroxyethyl) formamide,
N- (α-alkoxyethyl) formamide produced by reacting this with alcohol, and N-vinylformamide produced by thermally decomposing N- (α-alkoxyethyl) formamide are also trace amounts in the substances of each step. It has also been confirmed that it is a cause of deterioration of the stability of each substance.

Therefore, the formamide used to produce N- (α-hydroxyethyl) formamide is
It is preferable that the concentration of these impurities is as low as possible. For that purpose, it is necessary to establish the conditions for synthesizing formamide in which impurities are by-produced as little as possible, or to use formamide sufficiently distilled and purified as a raw material.

However, in the reaction for obtaining formamide from formic acid ester and ammonia, the method using a basic catalyst increases diformamide, and the method in the presence of water easily produces ammonium formate. There's a problem. On the other hand, polyvinylamine obtained by polymerizing and hydrolyzing N-vinylformamide shown above has recently attracted attention as a water-soluble polymer showing high performance for use as an aggregating agent, a paper chemical, and the like. There is. Then, when the N-vinylformamide polymer is hydrolyzed into polyvinylamine, a large amount of formic acid is produced. Therefore, if this by-product formic acid, which has been conventionally discarded, can be recovered as a formate ester and used as a raw material for the production of formamide, N-
It is also a great advantage in the field of producing vinylformamide or polyvinylamine.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems, and as a result, in the reaction for obtaining formamide from formic acid ester and ammonia, the solubility of ammonia is improved by using alcohol such as methanol as a solvent. That the reaction rate is sufficiently practical even without a catalyst, and that the equilibrium in the reaction is biased toward the production system, the reaction is practically completed even when the reaction is performed in the presence of alcohol. Further, they have found that the amount of impurities by-produced is small, and have reached the present invention.

That is, the gist of the present invention is that, in a method for producing formamide by reacting a formate ester with ammonia, the reaction is carried out in the presence of 20% by weight or more of the alcohol of the formate ester in the absence of water and without catalyst. In the method for producing formamide. Hereinafter, the present invention will be described in detail.

The raw material formic acid ester is formic acid and 1 to 1 carbon atoms.
It is an ester with a lower alcohol of about 3 and is preferably methyl formate. The formic acid ester may contain the alcohol used in the esterification reaction, but it is preferably in a substantially anhydrous state, and the water content is usually 1% by weight or less, preferably 0.
It should remain below 5% by weight. Similarly, it is preferable to use anhydrous ammonia gas as the raw material ammonia.

Since the solubility of ammonia in formic acid ester is small, ammonia is usually less soluble in formic acid ester.
It is used in an amount of 1.0 to 3.0 times, preferably 1.1 to 2.0 times. In the present invention, the presence of alcohol in this reaction system, by increasing the solubility of ammonia in the liquid phase in which the reaction is carried out, under reaction conditions near atmospheric pressure, and
It enables a reaction at a practical rate even under anhydrous and non-catalytic conditions.

As the alcohol, one corresponding to the ester portion of the formic acid ester is usually used, and in the reaction system,
20% by weight or more, preferably 30% with respect to the formate ester
Add more than weight%. The upper limit of the amount added is not particularly limited, but is usually 200% by weight or less, preferably 100% by weight or less with respect to the formate ester. The reaction conditions are:
The reaction temperature is usually 10 to 40 ° C, preferably 10 to 30
Ammonia gas is blown in at normal pressure at ℃. After completion of blowing, aging is carried out for 5 minutes to 10 hours, preferably 1 to 10 hours. After the reaction is completed, the alcohol is distilled off, and then formamide is purified by distillation by a conventional method.

The formamide thus obtained is
The content of formic acid, ammonium formate and diformamide, which act as an acid, is small and is maintained at a constant amount, so it is most suitable for use in the synthesis of N- (α-hydroxyethyl) formamide using a basic catalyst. . The above-described method for producing formamide of the present invention is particularly effective when combined with the step for producing N-vinylformamide or polyvinylamine. N- (α-hydroxyethyl) formamide synthesized from formamide is further converted into N-vinylformamide through alkoxylation and thermal decomposition steps. This N-vinylformamide can be produced alone or by polymerizing with vinyl monomers such as ethylene, acrylonitrile, vinyl acetate, and acrylic acid ester, and further hydrolyzed to produce polyvinylamine. At this time, formic acid derived from the formyl group of the N-vinylformamide unit is by-produced.

As a method for recovering formic acid from the polymerization and hydrolysis reaction solution, formic acid may be distilled off, but an efficient method is to add alcohol to the reaction solution and distill off as formic acid ester having a low boiling point. is there. The alcohol is preferably a low-boiling lower alcohol, particularly methanol, and is usually added in an amount of 1.1 to 5 times the molar amount of formic acid. Distilled formic acid or formic acid ester can be obtained by cooling or by absorbing with water. It is preferable to make water basic in order to increase the recovery rate of formic acid and prevent corrosion by acid. In particular, methyl formate has a low boiling point, but is preferable because it can be recovered as sodium formate by absorption with basic water, for example, caustic soda aqueous solution, so that vaporization can be prevented.

As described above, when formic acid is recovered from the reaction solution as sodium formate in an alkaline aqueous solution, a strong acid such as sulfuric acid is added to the recovered solution in excess of the neutralized amount, and if necessary, an alcohol is added. Can be added and heated to carry out reactive distillation to distill and recover a higher-purity formic acid ester.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded. Example 1 (Production of Polyvinylamine, Recovery of Formic Acid) 400 g of cyclohexane and 400 g of polyoxyethylene oleyl ether were placed in a 21-necked 4-necked flask equipped with a stirrer, a condenser, a dropping funnel, a jacket condenser, and a nitrogen gas inlet tube. (Daiichi Kogyo Seiyaku Co., Ltd., trade name "Neugen ET140E") 2
g, ammonium chloride 7 g, and water 83 g are put under stirring 50
The temperature was raised to ° C.

Next, 2.7 g of a 10% by weight aqueous solution of 2,2'-azobis-2-amidinopropane dihydrochloride was added under a nitrogen gas stream, and then N-vinylformamide (purity 90
%) 79 g, acrylonitrile (purity 99.5%) 65
The mixed solution of g was added dropwise over 3 hours. After that, 55 more
The reaction was continued for 3 hours at ° C. The above reaction liquid was directly charged into an autoclave equipped with a stirrer, a heater, and a cooling pipe equipped with an oil / water separator, and 4 g of polyethylene glycol (average molecular weight 20000) was further charged.

The inside of the autoclave was sealed, 40.2 g of hydrogen chloride gas was blown into the autoclave with stirring, and the mixture was heated until the internal temperature reached 100 ° C. The reaction was carried out for 4 hours while maintaining the temperature. Subsequently, the pressure was released to atmospheric pressure. The released gas was introduced into a 25% caustic soda aqueous solution and collected.

Next, 48 g of methanol was added to the above reaction solution and heated under reflux for 1 hour. 25% of reflux line
The solution was introduced into a caustic soda aqueous solution, and the cyclohexane layer phase-separated in the mixed liquid of the reflux liquid and caustic soda aqueous solution was separated and circulated in the reaction liquid. After heating and refluxing until the temperature of the reaction liquid reached 81 ° C., the reaction liquid was taken out, filtered, and dried by ventilation to obtain a powdery cationic water-soluble polymer. On the other hand, the composition of the aqueous phase alkali solution recovered by being guided to the caustic soda aqueous solution is sodium formate 21.
The content was 4% by weight, methanol 8.8% by weight, water 68.1% by weight, caustic soda 1% by weight, and sodium chloride 0.7% by weight.

(Production of Methyl Formate) 1 kg of an alkaline solution (containing 214 g of sodium formate: 3.15 mol, 10 g of caustic soda: 0.25 mol, 7 g of sodium chloride and 88 g of methanol) recovered by the above method was mixed with 17% sulfuric acid 17%.
7.4 g (1.76 mol) were added to neutralize sodium formate and caustic soda and acidify the solution. Further, 62.8 g of methanol was added (methanol is 1.5 times the molar amount of formic acid). This solution was put into a flask equipped with a theoretical 9.6-column tower and totally refluxed. After stabilizing the tower, the mixture was distilled at a reflux ratio of 3 to obtain 219 g of a distillate. The composition of the distillate was methyl formate 80.2% by weight, methanol 19.6% by weight, and water 0.2% by weight.

(Production of formamide) The above methyl formate solution was placed in a flask equipped with a coolable jacket, stirrer, reflux condenser and blowing tube, and 9.7 g of methanol (total 30% by weight of methyl formate) was added. added. Next, 54.6 g of anhydrous ammonia gas (1.1 times mol of methyl formate) was blown in over 3 hours. Reaction is 2
It was carried out at 5 ° C. and atmospheric pressure. After the completion of blowing, it was further aged for 1 hour. The results of analysis of the reaction liquid by liquid chromatography are shown in Table 1.

Subsequently, the reaction solution was separated by light boiling and then simple distillation (3
Torr vacuum distillation) to obtain formamide with a distillation yield of 95%. This formamide is ammonium formate 1.
Although it contained 3% by weight, both formic acid and diformamide were below the detection limit (about 10 ppm).

Example 2 The results are shown in Table 1 which was the same as Example 1 except that methanol was not added to the methyl formate solution (total 24% by weight of methyl formate) recovered in Example 1. .

Comparative Example 1 The same reaction as in Example 1 was carried out except that 25% aqueous ammonia solution was used instead of anhydrous ammonia. As shown in Table 1, the conversion rate of methyl formate was 100% and the formamide selectivity was 100%. The rate was 86%, and the rest was ammonium formate.

COMPARATIVE EXAMPLE 2 Methyl formate (purity: 99.9%) cooled to 5 ° C. was blown with anhydrous ammonia gas in the same manner as in Example 1 to produce formamide. Methyl formate was only diffused out of the system.

Comparative Examples 3 to 55 Table 1 shows methyl formate (purity 99.9%) cooled to 55 ° C.
After adding the amount of methanol described in 1 above, the result of carrying out the reaction by blowing in anhydrous ammonia in the same manner as in Example 1 is shown in Table 1.

[0026]

According to the method of the present invention, formamide containing few impurities can be obtained. The formamide is
N- (α-, which is an intermediate for the production of N-vinylformamide
It is suitable as a raw material for producing hydroxyethyl) formamide. Further, since formic acid produced during the production of polyvinylamine by hydrolyzing a polymer of N-vinylformamide can be recovered as a formic acid ester and used as a raw material in the method of the present invention, N-vinylformamide or It is also a great advantage in the field of producing polyvinylamine.

[0027]

[Table 1]

Claims (2)

[Claims] 1. A method for producing formamide by the reaction of a formate ester and ammonia, which comprises reacting in the presence of 20% by weight or more of the alcohol of the formate ester in an anhydrous and non-catalytic manner. 2. The method for producing formamide according to claim 1, wherein the formic acid ester is an ester of formic acid produced by hydrolysis of the N-vinylformamide polymer.