JPS6120539B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an alkali salt of iminodiacetic acid, and more specifically, a method for producing an alkali salt of iminodiacetic acid, in which a glycine alkali metal salt substantially free of free caustic alkali and glycolonitrile are mixed at a temperature of 60° C. or less, and the molar ratio The object of the present invention is to provide an industrially advantageous method for producing an alkali metal salt of iminodiacetic acid and furthermore, iminodiacetic acid, by reacting at a ratio of 1:0.8 to 1.2 and then hydrolyzing it by adding a caustic alkali. .

Iminodiacetic acid, like nitrilotriacetic acid and the like, is a substance that has various uses as a compound with a chelating effect, but the reality is that there is no fully satisfactory industrial method for producing it. In other words, several methods have been known for producing iminodiacetic acid, but most of them are limited to methods that separate by-products during the production of nitrilotriacetic acid, or methods that primarily produce iminodiacetic acid. Even if it is used as a product, it is inevitable that a considerable amount of nitrilotriacetic acid will be produced as a by-product.
Coupled with these difficulties in separation, iminodiacetic acid cannot be obtained with high purity and high yield. By alkaline hydrolysis of iminodiacetonitrile, iminodiacetic acid can be obtained in high yield without producing unnecessary by-products. However, the production of iminodiacetonitrile itself is not necessarily easy, and the industrial production of iminodiacetic acid is difficult. It is hard to say that this is the best manufacturing method.

As a result of various studies on methods for efficiently producing alkali iminodiacetic acid, the present inventors found that, in an aqueous solution containing substantially no free caustic alkali,
After adding approximately equimolar amount of glycolonitrile to glycine alkali salt and reacting sufficiently at a relatively low temperature, add caustic alkali in an amount equal to or slightly in excess of the added glycolonitrile and hydrolyze by heating. It has been found that by carrying out this process, by-products such as nitrilotriacetate can be suppressed and substantially only iminodiacetate can be synthesized in extremely high yield.

To explain the method of the present invention in more detail,
Glycine alkaline salt used in the present invention, for example, sodium glycinate, is obtained by mixing equimolar amounts of glycic acid and caustic soda and is subjected to the reaction as an aqueous solution. An aqueous glycine soda solution obtained by hydrolyzing sinonitrile with caustic soda may also be used. however,
In this case, the presence of excess free caustic soda causes an undesirable reaction with glycolonitrile when it is added, resulting in by-products such as sodium nitrilotriacetate, as well as destabilizing the reaction solution and causing discoloration and abnormal heat generation. Therefore, it is necessary to add glycine in advance to convert it to glycine soda, or to neutralize it by adding mineral acid. The concentration of glycine alkaline salt in an aqueous solution is not necessarily limited, but
Usually, it is preferably about 20 to 50% by weight. Glycolonitrile to be reacted with this alkali glycine salt is usually commercially available as an aqueous solution, but it can also be easily obtained by reaction with hydrocyanic acid and formaldehyde, and as above, it is usually 20 to 55% by weight. It is used at a concentration of about %. If the ratio of glycolonitrile to glycine soda is too large, unreacted residual glycolonitrile will not only become nitrilotriacetate or glycolate during hydrolysis and be wasted, but also these by-products will be lost to the reaction solution. If the amount is too small, it will have no particular effect on the reaction, but it will be uneconomical because glycine, which is relatively expensive as a reaction raw material, will remain unreacted. It is. Therefore, in the method of the present invention, glycolonitrile is used in a ratio of 0.8 to 1.2 mol, preferably approximately equimolar, per mol of glycine alkali salt.

When the alkali glycine salt solution and the glycolonitrile solution are mixed in the above proportions, the reaction proceeds rapidly, and at the same time, considerable heat is generated and the temperature of the solution rises. At this time, if the temperature is too high, the reaction solution will be colored, an abnormal reaction will occur, and the temperature of the solution will further increase due to the reaction heat, which is extremely dangerous and the by-product of nitrilotriacetate will significantly reduce the yield of the target product. I can't even get it right. The reaction temperature should be kept below 60°C, preferably below 40°C, and for this purpose it is necessary to carry out the reaction in a reaction vessel with sufficient cooling capacity.

The progress of the reaction can be easily determined by, for example, analyzing the residual cyanide concentration in the reaction solution, but the reaction generally takes approximately 1 to 1.5 hours at 40°C and approximately 2 to 3 hours at 20°C. When the reaction is completed and a predetermined amount of glycolonitrile is used as a starting material for the reaction, the cyanide concentration in the reaction solution is reduced to a point where it can be virtually ignored.

The reaction solution thus obtained is then mixed with caustic alkali in an amount approximately equal to or slightly in excess of the raw material glycolonitrile, and hydrolyzed. Caustic alkali is usually used as an aqueous solution of 20 to 50% by weight, and although it generates a rapid heat generation upon addition, hydrolysis can proceed without problems by gradual mixing or sufficient stirring. The temperature at this time is not particularly limited, but the dropwise addition is usually carried out in a range from 60°C to the boiling point. Practically speaking, it is desirable to boil the reaction solution at least before the end of the reaction in order to remove ammonia produced by the hydrolysis reaction. The hydrolysis reaction is completed in 1 to 2 hours when carried out at the boiling point of the reaction solution.

Thus, when the reaction is carried out under the most suitable conditions, the obtained solution after the reaction is completed contains iminodiacetic acid alkali salt with a high yield of 95 to 98% based on the raw material glycine alkali salt. The by-product of nitrilotriacetate is about 2 to 5%, but iminodiacetic acid can be easily isolated from this by conventional means such as neutralization and fractional crystallization.

In the method of the present invention, glycine alkaline salt containing substantially no free caustic alkali and glycolonitrile are sufficiently reacted at a predetermined molar ratio at low temperature, and then mixed with caustic alkali and hydrated. It is said that a decomposition reaction is an essential requirement, but if glycolonitrile and caustic soda are added in equal molar amounts to an equimolar mixture of glycine and caustic soda or an aqueous solution of glycine soda at the same time and subjected to a heating reaction, iminodic In addition to sodium acetate, a large amount of sodium nitrilotriacetate is produced, and only a mixture of these is obtained. At this time, as the molar ratio of glycolonitrile and caustic soda to glycine soda increases, the production rate of sodium nitrilotriacetate increases, but even if the ratio is reduced to 1 mole or less, only sodium iminodiacetate can be selectively obtained. cannot,
Rather, the disadvantage is that unreacted glycine soda remains. Also, a known method for producing nitrilotriacetic acid is to add excess caustic soda (2 moles) to 1 mole of glycine soda, heat it, and then add 2 moles of glycolonitrile to hydrolyze it. Using the same concept, if you first add 1 mol of caustic soda to 1 mol of glycine soda and heat it, then add 1 mol of glycolonitrile to this, only sodium iminodiacetate will be selectively synthesized in the same way as above. It is not possible. Furthermore, when equimolar amounts of glycolonitrile and caustic soda are mixed in advance, the reaction sometimes proceeds explosively to obtain sodium nitrilotriacetate as the main product. At this time, it is known that a considerable amount of sodium glycolate is produced as a by-product, but the production of sodium iminodiacetate is extremely small.

Hereinafter, representative examples of the method of the present invention will be shown and explained in more detail. However, these examples are intended to limit the reaction conditions to facilitate understanding of the present invention. It goes without saying that the invention cannot be construed as being limited in any way by these.

Example 1 A 500 ml four-neck flask is equipped with a stirrer, a thermometer, a dropping funnel, and a reflux condenser, and placed in an oil bath.

Add a mixture of 37.5 g (0.5 mol) of glycine, 40.0 g (0.5 mol) of 50% caustic soda solution, and 43.8 g of water and stir. Add to this at room temperature through a dropping funnel.
71.3 g (0.5 mol) of 40% glycolonitrile solution is added dropwise. Stir well and heat at 40°C or less as it generates heat.
It was added dropwise over a period of minutes. After the dropwise addition was completed, the reaction was continued for 1 hour while maintaining the liquid temperature at 40°C. The concentration of cyanide in the solution after 1 hour was determined by silver nitrate titration to be less than 0.01 mmol/g.

Next, when 40.0 g (0.5 mol) of caustic soda solution was added at once, heat was generated, the liquid temperature reached approximately 80°C, and ammonia began to be generated. The temperature was raised without worrying, and the mixture was heated at the boiling point for 2 hours while being refluxed. There is 210.1g of liquid after the reaction, 482mmol of sodium iminodiacetate, 8mm of sodium nitrilotriacetate.
It contained ol. The reaction yield is 96.4% based on glycine soda. The reaction solution was adjusted to pH2.4 with 50% sulfuric acid.
After the mixture was neutralized to a maximum temperature, it was concentrated by heating, and as precipitates of Glauber's salt began to crystallize, concentration was stopped and a small amount of warm water was added to redissolve the precipitates of Glauber's salt, followed by cooling while stirring. Since iminodiacetic acid crystallized, it was filtered at 33°C to separate iminodiacetic acid. The weight after washing with water and drying is 50.5g, and the purity of iminodiacetic acid is
It was 98.2% and contained 1.5% nitrilotriacetic acid. The liquid and washings were reheated and concentrated. Although Glauber's salt crystals were crystallized, the mixture was further concentrated to crystallize as much Glauber's salt as possible without crystallizing iminodiacetic acid, and then subjected to heat aging to separate the Glauber's salt.
The weight after washing with water and drying is 53.2g, and the purity of Glauber's salt is
It was 99.1%. The water washing solution and the liquid were combined and cooled. Since iminodiacetic acid crystallized, it was separated at 30°C. The weight after washing with water and drying was 11.8 g, and the purity of iminodiacetic acid was 97.4%. The iminodiacetic acid obtained in the two operations was combined and dissolved in hot water.
After treatment by adding 0.5 g of powdered activated carbon, it was recrystallized. 56.4 g of iminodiacetic acid (purity 99.0%) was obtained. The yield from the raw material glycine soda was 84.0%.

Example 2 The reaction between sodium glycinate and glycolonitrile was carried out in the same manner as in Example 1, except that the reaction was carried out at 20°C. After 1 hour of reaction, the concentration of cyanide in the solution was as follows.
0.12 mmol/g, and the liquid after the completion of the hydrolysis reaction contained 467 mmol of sodium iminodiacetate and 21 mmol of sodium nitrilotriacetate.

Comparative example 1 The reaction between glycine soda and glycolonitrile
The reaction was carried out in the same manner as in Example 1 except that the reaction was carried out at 65° C. for 30 minutes, and the solution after the hydrolysis reaction contained only 277 mmol of sodium iminodiacetate and 147 mmol of sodium nitrilotriacetate. Also,
The reaction solution at this time was colored reddish brown.

Comparative Example 2 92.7g (0.65 mol) of 40% glycolonitrile solution was used, and 50% caustic soda solution was added during hydrolysis.
The reaction was carried out in the same manner as in Example 1 except that 52.0 g (0.65 mol) was used, and the solution after the hydrolysis reaction contained 460 mmol of sodium iminodiacetate, 68 mmol of sodium nitrilotriacetate, and 14 mmol of sodium glycolate.
was included.

Comparative Example 3 The reaction between glycine soda and glycolonitrile was carried out in the same manner as in Example 1, except that 0.05 mol of free caustic soda was allowed to coexist in the reaction solution from the beginning, resulting in a hydrolysis reaction. After completion, the solution contained only 391 mmol of sodium iminodiacetate.
Sodium nitrilotriacetate contained 73 mmol.

Claims (1)

[Claims] 1. After reacting a glycine alkali metal salt substantially free of free caustic alkali and glycolonitrile at a temperature of 60°C or lower at a molar ratio of 1 in the range of 0.8 to 1.2, a caustic alkali is added to cause hydrolysis. A method for producing an alkali salt of iminodiacetic acid, characterized by the following.