HU184459B - Process for producing amino-guanidine or salts - Google Patents

Abstract

The present invention relates to a process for the preparation of aminoguanidine or its salts by the addition of guanidine nitrate, dissolved in concentrated sulfuric acid, to an aqueous suspension of zinc powder over a period of from 2 to 4 hours at a temperature of from 5 to 15 ° C while the pH of the reaction mixture is 5.0 to 5 ° C. After stabilization, the pH of the reaction mixture is adjusted to pH 7.0-7.6 with a 1: 1 mixture of ammonium hydroxide / water, and the resulting zinc hydroxide precipitate is filtered off directly and the resulting clear solution is filtered off. or optionally with an excess of an alkali metal salt, preferably an alkali metal carbonate, preferably sodium hydrogen carbonate, the aminoquanidine salt is precipitated. Amino-guanidine as a feed additive for nitrovine is used. -1-

Description

The present invention relates to a modified process for the preparation of aminoquanidine or its salts by adding guanidine nitrate dissolved in concentrated sulfuric acid to an aqueous suspension of zinc powder with constant stirring for 2 to 4 hours.

At a temperature of 5 to 15 ° C, while the pH of the reaction mixture is stabilized between 5.0 and 5.5, and after completion of the reduction, the reaction mixture is adjusted to pH 7.0-7 with 1: 1 ammonium hydroxide water, The resulting zinc hydroxide precipitate is filtered off, the clear solution obtained is used directly, or the aminoguanidine salt is conveniently precipitated with an excess of an alkali metal salt, preferably an alkali metal hydrogencarbonate.

It is known that aminoguanidine and its salts are widely used heterocyclic compounds (pyrazole, triazole, thiadiazole, tetrazole, pyrimidine and triazine derivatives) and some other derivatives e.g. are the starting material for the preparation of guanyl hydrazines.

(F. KURZER; L. E. A. GODFREY Angew. Chem. 75, 1157-1175 (1963))

BIOGAL Pharmaceuticals uses amino guanidine as a starting material for nitrovin, a feed additive, since aminoquanidine is not produced in Hungary, and therefore economical production allows import savings.

Aminoguanidine and its salts can be prepared in two ways. In one embodiment, the preparation can be accomplished by reaction of cyanamide with hydrazine as described in U.S. Patent Nos. 689,191, 730,331, 753,623, 1,230,777, German Patent 51,029 and French Patent No. 1,241,151.

The other method is based on the reduction of nitroguanidine. The reduction can be accomplished by catalytic hydrogenation according to U.S. Pat. No. 2,033,203 and Hungarian Patent No. 163,928. The disadvantages of these processes are the low yields (55.2%) due to the high temperature (125 ° C) and the special equipment needed for hydrogenation under high pressure.

Japanese Patent Nos. 172,275 / 46 and 3926/55 disclose that nitro-guanidine is electrolytically reduced, although this process is 85% uneconomic due to the high cost of electricity.

Among the methods for reducing nitroguanidine with a chemical reducing agent, the reduction with zinc is carried out either in acetic acid medium (Org. Synth. Coll. Vol.

III. p. 73/1955 / New York; J. Am. Chem. Soc. 55, 2867 (1938), or an aqueous suspension of zinc powder in a neutral or weakly alkaline medium, as disclosed in U.S. Patent Nos. 1,990,511 and 2,123,032, English Patent Nos. 630,296, and 7,161,966; Japanese Patent Nos. 7,116,967.

The reduction can also be carried out with sodium amalgam in Belgian liquid metal 665,233 in U.S. Pat. No. 2,123,032, or with iron shavings in sulfuric acid media according to US Patent No. 862,890.

It is an object of the present invention to provide a process for the preparation of aminoguanidine which provides a more economically feasible form of the finished product in a simpler, more industrially feasible form than known hitherto.

In our experiments for the simple and economical production of aminoguanidine, experiments were initially carried out on a commercial scale for reduction with zinc in acetic acid. Experimental operational experience has shown that the implementation of the reduction with acetic acid has caused equipment problems due to the poor mixing status of the reaction mixture.

The highly basic amino-guanidine formed from nitro-guanidine shifts the pH of the reaction mixture to the alkaline range, thereby promoting the formation of basic zinc acetate and the ammonium salts formed by the decomposition of nitro-guanidine. As a result of these side reactions, the reaction mixture becomes highly concentrated and becomes difficult to stir. Nor can the thickening be prevented by using an excess of acetic acid.

It has been found that overreaction is more pronounced in reductions with zinc in a neutral medium.

In a duplicator with a specially designed sawtooth agitator, acetic acid reduction was feasible at 60-63% yield, but a simpler and more economical solution was sought.

In our attempts to develop the process of the present invention, it has been unexpectedly discovered that the reduction can be carried out simply and in good yields in an acidic medium at pH 5.0-5.5 by adding a solution of guanidine nitrate sulfuric acid in an aqueous suspension of zinc powder. added.

Since the nitro-guanidine formed during the dissolution of guanidine nitrate is soluble only in concentrated sulfuric acid, the concentration of sulfuric acid used for the dissolution is between 85-98% and the amount of guanidine nitrate is chosen so that the resulting solution is 12- 18%.

sulfuric acid The concentration of % Guanidine nitrate dissolved in 100 ml sulfuric acid  g nitroguanidine solution concentration % 85 30 12.3 90 37 14.4 94 44 16.5 98 50 18.2

When the reduction is carried out in this way, the nitroguanidine does not need to be prepared but can be added in the form of a solution so that its degradation is minimized during the reaction.

184,459

The addition of the sulfuric acid solution is preferably carried out at a temperature of 5 to 15 ° C for 2 to 4 hours.

By slowly adding the sulfuric acid solution to the aqueous suspension of zinc powder, the continuously formed aminoguanidine sulphate and zinc sulphate form a buffer system whose pH is stabilized during the reduction at pH 5.0-5.5. The resulting weak acid medium provides, on the one hand, optimal conditions for amino-guanidine, which is particularly stable in the acid medium, and, on the other hand, neglects the problem of corrosion.

According to Japanese Patent No. 7,116,967, guanidine nitrate is also dissolved in concentrated sulfuric acid. However, the concentrated sulfuric acid nitroguanidine solution thus obtained is first neutralized with ice-water, when the nitroguanidine is precipitated from the solution, and then the resulting suspension is neutralized with ammonium hydroxide solution and the ammonium sulfate formed during the neutralization:

They are performed at values of 8-12.

The process which we have developed is distinguished by the fundamental difference from the process of Japanese Patent No. 7,116,967 in that the reduction is carried out directly in an acidic medium at pH 5.0 to 5.5 using a solution of guanidine nitrate in sulfuric acid. In principle, the acidic medium provides a new pathway for the reduction to occur, since the nitro-guanidine is directly formed from the nitro-guanidine, so that the reduction is not via nitroso-guanidine, as is the case with the neutral or alkaline medium. The shortened reaction path reduces the possibility of decomposition during each reaction step.

In the presence of sulfuric acid, the formation of acetamidoguanidine is also excluded, which should be taken into account as a yield reducing agent for acetic acid.

Upon completion of the reduction, the pH of the reaction mixture was adjusted to pH 7.0-7.6 with 1: 1 ammonium hydroxide / water to remove the zinc salts and filtered. The clear solution obtained after filtration is used either directly for the production of nitrovin or by precipitation of the aminoguanidine bicarbonate in a known manner using excess alkaline hydrogen carbonate.

Not only can this produce a high quality, metal-free product, but starting from commercially available guanidine nitrate, in one step and in better yields, the desired compound is known in the art. In this way, a yield of 75-78% based on guanidine nitrate was obtained, which was approximately 85-90% for nitroguanidine. The technical implementation of our process is very simple and can be carried out using conventional equipment in the chemical industry.

EXAMPLES

Example 1:

g of guanidine nitrate was dissolved in 92 ml of concentrated sulfuric acid with stirring at 5-10 ° C. The temperature of the solution is max. After storage at 25 ° C, it is added dropwise to a suspension of 180 ml of water and 72 g of zinc powder with stirring at 5 to 15 ° C for 2 to 2.5 hours. After completion of the reduction, the pH of the reaction mixture was adjusted to 7.6 with 1: 1 ammonium hydroxide / water, filtered, washed with water, and 25 g of sodium bicarbonate was added to the filtrate. After a few minutes, the precipitated aminoguanidine bicarbonate was filtered off, washed with water and dried.

Yield: 31 g (76.5%)

Mp 150-153 ° C

Content: 99%

Sulphated ash: 0.17%

Example 2:

Dissolve 50.0 kg of guanidine nitrate in 100 l of concentrated sulfuric acid at 5-10 ° C. The solution was added to a suspension of 95 kg of zinc powder and 130 liters of water with constant stirring. The cooling and dosing are controlled so that the temperature is between 5 and 15 ° C. The dosing period is 3.5 to 4 hours. To complete the reduction, the reaction mixture was stirred at 10-15 ° C for another half hour after addition of the sulfuric acid solution. Upon completion of the reduction, the pH of the reaction mixture was adjusted to 7.5-7.6 with stirring with 1: 1 ammonium hydroxide / water. The pH is monitored by an instrument. The precipitated zinc salts are filtered off and the precipitate is washed with 120 liters of water. To the filtrate was added 35 kg of sodium bicarbonate with stirring. After stirring for half an hour, the precipitated aminoguanidine bicarbonate was filtered off, washed with 40 liters of water and dried at 50 ° C.

Yield: 31.6 kg (78%)

Mp 150-153 ° C

Content: 99%

Sulphated ash: 0.16%

Claims (1)

Patent claim A process for the preparation of aminoguanidine or its salts from guanidine nitrate in concentrated sulfuric acid with zinc powder reduction, characterized in that guanidine nitrate dissolved in concentrated sulfuric acid is added to the aqueous suspension of zinc powder at a constant temperature of 5 to 15 ° C over a period of 2 to 4 hours with constant stirring while the reaction mixture is stirred. After stabilization, the pH of the reaction mixture was adjusted to pH 7.0-7.6 with a 1: 1 by volume mixture of ammonium hydroxide / water, and the resulting zinc was removed. the hydroxide precipitate is filtered, the resulting clear solution is used directly, or optionally an excess of an alkali metal salt, preferably an alkali metal bicarbonate, preferably sodium hydrogen carbonate, precipitates the aminoguanidine salt.