JP2748170B2 - Process for producing O-methylisourea salt - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a novel process for producing O-methylisourea salt useful as an intermediate for pharmaceuticals, agricultural chemicals and industrial chemicals, and more particularly to a process containing methanol. More specifically, a method for releasing cyanamide from lime nitrogen in an organic liquid and reacting an acid with the cyanamide solution to immediately generate an O-methylisourea salt without isolating the cyanamide from the obtained cyanamide solution. Is to disperse lime nitrogen in an organic liquid containing methanol, to generate a cyanamide solution in the organic liquid by introducing carbon dioxide gas into the obtained dispersion, and then to the cyanamide solution The present invention relates to a method for producing an O-methylisourea salt, which comprises adding an acid.

[Conventional technology]

Conventionally, as a method for producing an O-methylisourea salt, a method is known in which a cyanamide isolate such as a crystal of cyanamide is dissolved in methanol, and the resulting methanol solution of cyanamide is reacted with an acid such as hydrogen chloride or sulfuric acid. Have been.

As a method for producing an isolated form of cyanamide such as a crystal of cyanamide used in the above method, conventionally, industrially, carbon dioxide gas is reacted with lime nitrogen dispersed in a slurry state in water to obtain an aqueous cyanamide solution. Is concentrated to dryness.

In this method, lime nitrogen reacts with water as in the following formula (1), and 2CaCN ₂ + 2H ₂ O → Ca (HNCN) ₂ + Ca (OH) ₂ ... (1) Then, the generated Ca (HNCN) _{It is considered that 2} or Ca (OH) ₂ reacts with carbon dioxide gas as shown in the following equations (2) and (3), respectively.

Ca (OH) ₂ + CO ₂ → H ₂ O + CaCO ₃ (2) Ca (HNCH) ₂ + CO ₂ + H ₂ O → 2H ₂ NCN + CaCO ₃ (3) When these reaction formulas (1) to (3) are combined, It can be considered that the above-mentioned production method eventually follows the following formula (4): CaCN ₂ + CO ₂ + H ₂ O → H ₂ NCN + CaCO ₃ (4)

As is clear from the above reaction formula, in the method for producing cyanamide by dispersing lime nitrogen in water, first, calcium hydroxide is generated as in formula (1). Since the reaction proceeds in an aqueous medium, a part of cyanamide is easily dimerized to easily form dicyandiamide. In the process of isolating cyanamide by concentration and drying from the generated aqueous solution of cyanamide, a small amount of dissolved calcium is also concentrated, and the aqueous solution gradually increases in alkalinity. One part of cyanamide is further dimerized to dicyandiamide. Since this reaction sometimes occurs explosively and is extremely dangerous, it is necessary to reduce the amount of dissolved calcium in the aqueous solution as much as possible, which requires a complicated operation. further,
Since it is generally not easy to separate such by-product dicyandiamide from cyanamide, the cyanamide obtained by the above-mentioned production method is unavoidably contaminated with dicyandiamide, and industrially uses high-purity cyanamide having a purity exceeding 92% by weight. It is extremely difficult to manufacture the same. Furthermore, the stability of the isolated cyanamide powder during storage is not always sufficient, and it dimerizes over time to increase the content of dicyandiamide, and in some cases, this dimerization reaction may explode. There is a danger that it will occur, and it is essential to store it in a refrigerator at low temperatures. As described above, there are many delicate and complicated problems in the method for isolating cyanamide and its storage, and therefore, the method for producing O-methylisourea using the cyanamide isolate has to be costly. Did not.

[Problems to be solved by the invention]

The present inventors have conducted intensive studies on a method for producing O-methylisourea without using a cyanamide isolate which has many problems in production and storage as described above, and as a result, it has been almost studied conventionally. By reacting carbon dioxide gas with lime nitrogen dispersed in methanol, a methanol solution of cyanamide containing a very small amount of impurities such as dicyandiamide is obtained, and then this solution is used without isolating cyanamide. Use
It was found that by adding an acid such as sulfuric acid thereto, a high-purity O-methylisourea salt could be produced safely and easily with high yield, and as a result of further research, the present invention was completed. Reached.

[Means for solving the problem]

In the present invention, lime nitrogen is dispersed in an organic liquid containing methanol, and carbon dioxide gas is introduced into the obtained dispersion to form a cyanamide solution in the organic liquid. It is intended to provide a process for producing an O-methylisourea salt, which comprises adding an acid to a solution.

 Hereinafter, the present invention will be described in detail.

Cyanamide liberation step In the method of the present invention, first, lime nitrogen is dispersed in an organic liquid containing methanol, and carbon dioxide gas is introduced into the obtained dispersion to form a cyanamide solution in the organic liquid. And a cyanamide liberation step.

The raw material lime nitrogen is industrially produced by nitriding calcium carbide in a nitriding furnace. Lime nitrogen contains impurities such as graphitic carbon and quick lime that are by-produced during nitriding in addition to calcium cyanamide. Generally, commercially available lime nitrogen has a nitrogen content of 20 to 27% by weight.
And a cyanamide nitrogen content of 19 to 26% by weight. In the production method of the present invention, lime nitrogen is pulverized as necessary, and used so that the particle passing through a 200 mesh Tyler standard sieve becomes 50% by weight or more.

The organic liquid as the dispersion medium used in the production method of the present invention contains methanol. The organic liquid may consist essentially of methanol, but the purity and yield of the resulting cyanamide solution and the subsequent O-
An additional organic solvent may be contained, if necessary, to the extent that the methylisoureation (imidate) reaction is not inhibited.

Examples of the further organic solvent include acetonitrile, dimethylformamide, ethyl acetate, acetone, tetrahydrofuran and the like.

In the present invention, the concentration of lime nitrogen in the lime nitrogen dispersion in the organic liquid as the dispersion medium is preferably 5 to 25% by weight, more preferably 15 to 20% by weight at the time of charging.

In the cyanamide releasing step of the method of the present invention, by introducing carbon dioxide gas into the above-mentioned lime nitrogen dispersion, cyanamide is produced as a cyanamide solution in an organic liquid. Although the reaction mechanism is not necessarily elucidated, the present inventors presume that the reaction proceeds according to the following reaction formula.

Therefore, the amount of carbon dioxide used is preferably at least 2 equivalents to the calcium content in the lime nitrogen.

The carbon dioxide used in the present invention does not necessarily need to be of high purity, and may be appropriately diluted with nitrogen, oxygen, air, or another inert gas for this reaction system. However, if the concentration of carbon dioxide in the gas is too low, problems such as loss of methanol accompanying the gas occur. Therefore, the concentration of carbon dioxide in the gas is generally 20% by weight or more, especially 40% by weight. The above is preferable, and the water content in the gas is also not more than 20% by weight, preferably not more than 2% by weight, especially not more than 0.2% by weight.

The method for introducing carbon dioxide gas is not particularly limited, and a method of directly blowing into an organic liquid, a method of dissolving carbon dioxide gas in methanol or the further organic solvent in advance and adding it as a solution, and the like are employed. However, it is preferable to directly blow carbon dioxide gas for reasons such as ease of operation. Such a reaction caused by blowing carbon dioxide gas is 0.
Under a pressure of 1 to 10 kg / cm ^2, preferably under atmospheric pressure, -10～3
It is carried out at a temperature of 0 ° C, preferably 0-20 ° C. When the reaction temperature is lower than the upper limit, the impurity concentration in the resulting cyanamide solution can be suppressed to a low level, which is preferable. It is preferable because it proceeds.

After the completion of the reaction by the introduction of carbon dioxide, the mud-like reaction dispersion is filtered by a conventional method, so that a cyanamide solution in an organic liquid can be easily obtained.

The water content of the reaction system in the cyanamide releasing step of the method of the present invention (the content of water in the organic liquid as a dispersion medium) is
It is generally at most 20% by weight, preferably at most 5% by weight, more preferably at most 3.5% by weight, even more preferably at most 2.5% by weight, most preferably at most 1% by weight. As the content of water in the reaction system decreases to 20% by weight or less, by-product dicyandiamide due to dimerization of cyanamide is suppressed, and the reaction system does not gel. It is preferable that it is not more than the upper limit.

The water present in the reaction system is, in addition to the water contained in the organic liquid used from the beginning, the water contained in the lime nitrogen as the starting material, and the water contained in the introduced carbon dioxide, etc. Quicklime contained as an impurity in lime nitrogen (Ca
O), calcium hydroxide [Ca (OH) ₂ ], etc. are expected to be water generated by reacting with carbon dioxide gas in an organic liquid as shown below. Increase.

Therefore, the water content of the reaction system in this specification refers to the water content of the reaction system at the end of the carbon dioxide gas introduction reaction.

The water content of the reaction system was measured by the following method. First, the reaction dispersion collected from the reaction system is filtered by centrifugation to remove organic liquid insolubles, and the resulting filtrate (organic liquid solution)
Was subjected to gas chromatographic analysis [hereinafter sometimes abbreviated as GC analysis] (TCD method) to determine the water content in the filtrate, which was taken as the water content of the reaction system.

Since the obtained cyanamide solution may cause gelation during storage due to the action of slightly dissolved calcium ions or the like, if necessary, a small amount of acid can be added to the solution to stabilize the solution. . Examples of such an acid include inorganic acids such as phosphoric acid, sulfuric acid, nitric acid, and hydrochloric acid; organic acids such as acetic acid and oxalic acid; and cation exchange resins such as a sulfonic acid type cation exchange resin. Among them, phosphoric acid is preferably used. The addition amount of these acids is preferably about 1 equivalent to the dissolved calcium in the cyanamide solution.

The cyanamide solution thus obtained is concentrated as necessary or diluted with methanol or the above-mentioned organic solvent to obtain a solution having a desired cyanamide concentration, and used in the next imidation reaction step.

The black residue after the cyanamide solution was filtered off generates carbon dioxide gas by the addition of water, and separates and generates methanol. Therefore, it is possible to recover and reuse these methanol and carbon dioxide gas by a conventional method. is there.

Imidate-forming step The method of the present invention comprises an imidate-forming step in which an acid is added to a cyanamide solution in an organic liquid containing methanol obtained in the cyanamide liberating step to cause an acid to react to form an O-methylisourea salt. .

The cyanamide concentration in the cyanamide solution is generally 40% by weight or less, preferably 30% by weight or less, more preferably 20 to 30% by weight, and a methanol solution of 20 to 30% by weight of cyanamide. Is particularly preferred. If the cyanamide concentration is less than or equal to the upper limit, the resulting O-
Since the slurry viscosity of methylisourea salt does not become too high, there is no hindrance to stirring, and if it is 20% by weight or more, the production yield of O-methylisourea can be kept at a high level. It is preferred.

Acids that can be used in this step include, for example,
Hydrohalic acid such as hydrogen chloride, concentrated sulfuric acid, concentrated nitric acid, concentrated phosphoric acid (85% by weight or more, preferably substantially 100% by weight
), And organic acids such as methanesulfonic acid and paratoluenesulfonic acid. The water content of these acids is preferably as low as possible. If the water content is small, by-products such as urea are suppressed and O
This is preferred because the yield of -methylisourea increases.

It is assumed that the reaction mechanism of this imidation reaction step usually proceeds as follows.

(However, HA represents an acid.) Thus, the amount of the acid used in this reaction step is generally 1 equivalent or more, preferably 1 to 3 equivalents, per 1 mol of cyanamide.

However, when concentrated sulfuric acid is used as the acid, the following 2
It is thought to be a step reaction.

Generally, the reaction of the above (9) is extremely fast, and the reaction of the above (10) is slow. For this reason, when trying to obtain a sulfate of O-methylisourea, first, all the cyanamide is converted into a hydrogen sulfate of O-methylisourea using an equimolar amount of sulfuric acid with respect to cyanamide, and then, as shown in the following formula, In this reaction system, a method of obtaining a target O-methylisourea sulfate by adding and reacting a compound acting as an alkali (hereinafter, may be simply referred to as an alkaline compound) may be suitably employed. In this case, the sulfuric acid is preferably used in an amount of 2 equivalents or more per 1 mol of cyanamide,
It is more preferable to use an equivalent amount.

(However, BOH represents an alkali.) The amount of the alkaline compound used is generally an amount required to neutralize an excess of sulfuric acid added in excess of 1 equivalent which is a necessary amount of an acid to 1 mol of cyanamide. I just need.

Prior to adding the alkaline compound,
An appropriate amount of water is added to dissolve the hydrogensulfate to form a homogeneous solution. Such a uniform solution allows the reaction (11) to proceed smoothly.

Examples of the alkaline compound include carbonates or hydroxides of alkaline earth metals such as calcium carbonate and calcium hydroxide; and alkali metal salts such as sodium carbonate, sodium hydrogen carbonate, sodium hydroxide and potassium hydroxide. Carbonates, bicarbonates or hydroxides;
Anion exchange resin; and the like. Of these, use of calcium carbonate is preferred for reasons such as availability, ease of handling, and low cost.

〔effect〕

According to the production method of the present invention, carbon dioxide gas is reacted with lime nitrogen in a methanol-containing organic liquid without using a cyanamide isolate such as a cyanamide crystal having many problems in production and storage as a starting material. Thus, cyanamide is released as a solution, and only an acid such as sulfuric acid is added and reacted to the solution as it is, so that a high-yield, high-purity O-methylisourea salt is produced industrially, safely and easily in a high yield. It becomes possible.

〔Example〕

 Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 In a four-necked flask equipped with the stirring device of 1 and a reflux condenser, 600 ml (475 g) of methanol (purity of 99.5% by weight or more,
Water content 0.1% by weight or less) and lime nitrogen 100g [nitrogen content 2
3.6% by weight (nitrogen content as calcium cyanamide 2
3.6% by weight); 65% by weight passing through a particle size of 200 mesh] and dispersed in a slurry by stirring. Subsequently, 88 g of carbon dioxide (purity: 99.99% by weight) was introduced in about 5 hours while maintaining the temperature at about 10 ° C. with stirring, and the mixture was reacted at the same temperature with stirring for 1 hour. After completion of the reaction, methanol-insoluble matter was separated by filtration. The water content in the obtained filtrate (methanol solution) was 1.8% by weight according to GC analysis (TCD method). The methanol insoluble content is the same as the methanol used in the reaction, 150m
1 (119 g) and the washings were combined with the filtrate. In order to remove dissolved carbon dioxide, the filtrate was concentrated under reduced pressure at a temperature of 30 ° C. or less until the volume became about half, thereby obtaining 250 g of a concentrated filtrate, that is, a methanol solution of cyanamide. The contents of cyanamide and by-product dicyandiamide in the methanol solution were determined to be 13.9% by weight and 0.3%, respectively, by liquid chromatography (hereinafter sometimes abbreviated as LC) analysis.
The yield of cyanamide relative to calcium cyanamide in the raw coal nitrogen was 98.2%, and the yield of dicyandiamide was 0.38%.

A small amount of 85% by weight phosphoric acid was added to the methanol solution, and the mixture was stirred. The resulting insolubles were separated by filtration. :
(2.2 equivalents per 1 mol of cyanamide) was added over 3 hours, and the temperature was maintained at that temperature for 2.5 hours. Then, 200 ml of deionized water was added to dissolve the precipitated hydrogen sulfate sulfate of O-methylisourea to obtain 541 g of a methanol-water homogeneous solution of hydrogen sulfate of O-methylisourea. When this homogeneous solution was analyzed by LC, the content of hydrogen sulfate of O-methylisourea was 24.5% by weight, and the by-product urea was 0.36% by weight.
It was 5% by weight, and the production yield of O-methylisourea based on cyanamide in the raw lime nitrogen was 91.4%.

Next, calcium carbonate powder (purity: 98% by weight) was added to the obtained homogeneous solution of hydrogen sulfate of O-methylisourea in methanol-water until the pH became 3 to 5 with stirring, and the mixture was further stirred for 1 hour. Continued. The precipitated calcium sulfate was filtered off and washed with 150 ml of deionized water, and the washing solution was combined with the filtrate.

The solution of O-methylisourea sulfate thus obtained was concentrated to dryness under reduced pressure at a temperature of 50 ° C. or lower, 100 ml of methanol was added, and the mixture was cooled to room temperature. Separately, then dried under reduced pressure at a temperature of 60 ° C. The resulting O-methylisourea sulfate crystals were 85.0
g (production yield of O-methylisourea sulfate relative to cyanamide in raw lime nitrogen: 82.4%).

 The analysis was as follows.

Purity 99.2% by weight Urea 0.5% by weight Water 0.05% by weight Example 2 A small amount of 85% by weight phosphoric acid was similarly added to 250 g of a methanol solution of cyanamide obtained in the same manner as in Example 1 and stirred. After filtering off the insolubles generated, 72 g of hydrogen chloride gas (purity 99.9% by weight: 2 equivalents per mol of cyanamide) was added to 4 parts of the solution while maintaining the temperature of the solution at 5 to 10 ° C.
Over time and kept at that temperature for 24 hours. The resulting crystals of O-methylisourea hydrochloride are filtered off and then
It dried under reduced pressure at the temperature of 60 degreeC. The obtained O-methylisourea hydrochloride crystals were 66.0 g (64.5% yield of O-methylisourea hydrochloride based on cyanamide in the raw lime nitrogen). Further, the filtrate was concentrated to dryness under reduced pressure at a temperature of 30 ° C. or lower, then cooled to room temperature by adding 30 ml of methanol, and the generated crystals were separated by filtration to obtain a further 20.0 g.
O-methylisourea hydrochloride having a yield of 19.5% of O-methylisourea hydrochloride with respect to cyanamide in the raw material lime nitrogen could be obtained. The total production yield of O-methylisourea hydrochloride relative to cyanamide in the raw lime nitrogen is
84%.

 The analysis was as follows.

 Purity 99.9% by weight Urea 0% by weight Water 0.1% by weight

Continuation of the front page Examiner Zenichi Wakimura (56) References JP-A-61-180760 (JP, A) JP-A-62-22751 (JP, A) JP-B-52-24007 (JP, B1) US Patent 3931316 (US, A) US Patent 3670022 (US, A) West German Patent 2,358,904 (DE, A)

Claims (1)

(57) [Claims] (1) Lime nitrogen is dispersed in an organic liquid containing methanol, and carbon dioxide gas is introduced into the obtained dispersion to form a cyanamide solution in the organic liquid. A method for producing an O-methylisourea salt, comprising adding an acid to a cyanamide solution.