PROCEDURE FOR THE OBTAINING OF N-A QUIL-N-NITRO-GUANIDINAS. Field of the invention. The invention relates to a novel process for the preparation of N-alkyl-N'-nitroguanidine. Description of the prior art. It is known that N-alkyl-N'-nitroguanidines are obtained by first nitrating the 5-ethylisothiouronium sulfate of the formula (A) in the usual manner and then, in a second reaction step, in a conventional manner. substitutes the methylmercapto group for alkylane according to the following reaction scheme:
(see in this regard JACS 76., 1877 (1954)). However this procedure has; the drawback that it is a two-step reaction. When the yields in the two steps are proportionally good, the dissociation of the mercapto group, especially the methylmercapto group, poses problems from the point of view of the process in the case of an industrial-scale embodiment. It is further known that N-alkyl, especially N-methyl-N'-nitroguanidines, can be obtained if an alkaline solution (potassium hydroxide) of ni-troguanidine is reacted with alkyl (especially methyl) amine hydrochloride at 60 °. C according to the following reaction scheme: for example
H2 N .vlHH2_
DO NOT, ,
(see in this respect JACS 69, 3028 (1947), or 49, 2303 (1927)). In this process the yields and especially the purity are very satisfactory. of the final products, which have to be purified in costly procedures. As by-products, large amounts of alkyl (methyl) urea are formed with the evolution of gaseous N20. In addition large amounts of wastewater are produced and the fact that nitroguanidine is a relatively expensive starting product. It is further known that N-alkyl-N'-nitroguanidines can be obtained by nitration of alkylguanidine sulfates (see JACS, 55, 731 (1933)). This process also has the drawback of an unsatisfactory yield as well as a relatively large amount of wastewater. Another known method of obtaining is the dehydration of alkylaniline nitrate by sulfuric acid (see JACS, 55, 739 (1933)). This process certainly proceeds with proportionally good yields, however it is very difficult to obtain the starting products, such as for example methylguanidine nitrate (see in this respect Zeitschrift für angewandte Chemie 42., 380 (1929)). of nitrate, barium nitrate has to be used, the yield being only 40 to 50%. In the same way the reaction of amine nitrates with calcium cyanamide or with dicyandiamide proceeds with unsatisfactory yields (Can. J. Chem. 3_6, 737-743 (1958)). The described processes have several disadvantages: excess of alkylamine, which can only be recovered with difficulty, as well as high process temperatures (with dicyandiamide). Detailed description of the invention. It has now been found that N-alkyl-N'-nitroguanidines of the formula (I) are obtained,
wherein R means alkyl having 1 to 4 carbon atoms, if alkylamines are neutralized, if appropriate in an aqueous solution and, if appropriate, in the presence of an organic solvent, with nitric acid, then concentrated by evaporation and it is reacted with cyanamide in the presence of an organic solvent and, if appropriate, under pressure at temperatures between 80 ° C and 180 ° C and the alkylguanidine nitrate formed is dehydrated. Surprisingly, N-alkyl-N'-nitroguanidines of the formula (I) could be obtained in a simple manner with very good yields and with high purity, even when it was expected, according to the state of the art, that when Equal amounts of amine (or only a very small excess) should be used. Only low yields should be obtained. Finally it was known to obtain guanidine salts substituted by lower alkyl from alkylamine and cyanamide salts at temperatures comprised between 170 to 240 ° C (DOS 2 005 816). Therefore, the person skilled in the art could not foresee that this reaction could also be carried out at significantly lower temperatures. The reaction according to the invention has the advantage that excess amine nitrate has to be used or it only has to be used in a small amount in excess and that the process can be carried out at low temperatures. Therefore it occurs more economically, with saving energy and in a more respectful way for the environment. The compounds obtainable according to the process of the invention are generally defined by means of formula (I). In this formula R is preferably alkyl having 1 to 4 carbon atoms, especially methyl and ethyl. If, for example, methylamine is used as starting material, the development of the reaction of the process according to the invention can be schematized by means of the following formula scheme:
The starting products alkylamine and cyanamide are generally known compounds of organic chemistry. Suitable organic solvents are all inert organic diluents against these reagents. These preferably include alcohols, such as methanol, ethanol or butanol, and also ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether or ethyl tert. -amilster The reaction with cyanamide is preferably carried out with the exclusion of oxygen in a closed vessel so that an overpressure of between 1 and 20 bar is formed, preferably between 5 and 15 bar. The reaction temperatures in the reaction with cyanamide can vary within wide limits. In general, work is carried out at temperatures between 80 ° C and 180 ° C, preferably between 100 ° C and 150 ° C. Suitable dehydrating agents are, in principle, all water-dissociating agents. Preference is given to sulfuric acid and trifluoroacetic acid. In the embodiment of the process according to the invention, preference is given to equimolar amounts. However, it is also possible to work with an excess of alkylamine (from 1 to 1.5 moles). A slight excess of cyanamide (from 1 to 1.2 moles) is also possible. The processing can be carried out in the usual manner. As a step prior to the reaction of the nitric acid salt of the alkylamine with cyanamide, water will preferably be removed, for example, by azeotropic distillation. The N-alkyl-N'-nitroguanidines of the formula (I), to be obtained according to the process of the invention, such as, especially, N-methyl-N'-nitroguanidine can be used as intermediates for obtaining biologically active compounds , for example of insecticides (see, for example, EP-A 0 376 279 and EP-A 0 428 941). Examples of obtaining. Example 1.
.2 g (0.05 mole) of a 30% aqueous solution of methylamine are neutralized with about 4.2 g of 75% nitric acid and then the water is distilled off in vacuo. 15 ml of n-butanol and 2.2 g of cyanamide are added and a 50 ml autoclave is charged in this way. It is then heated for 8 hours at 130 ° C at internal temperature. After decompression, butanol is removed by distillation and the residue is combined, under cooling and stirring, with 8.5 ml of concentrated sulfuric acid at -5 ° C to + 5 ° C. After 30 minutes add 50 g of ice, separate by filtration and finally wash with a little cold water.
.5 g (93% of theory) of N-methyl-N'-nitroguanidine with a melting point of 160 ° C are obtained. Example 2
.2 g (0.05 mole) of a 30% aqueous solution of methylamine are neutralized with about 4.2 g of 75% nitric acid and then the water is distilled off in vacuo. 15 ml of n-butanol and 2.2 g of cyanamide are added and a 50 ml autoclave is charged. Then it is heated for 9 hours at 140 ° C internal temperature. After decompression, it is cooled to 0 ° C to 5 ° C and filtered. The filter cake is dried and combined, under cooling and stirring, carefully with 1.5 ml of concentrated sulfuric acid, at -5 ° C to + 5 ° C. After 20 minutes, add 50 g of ice, separate by filtration and finally wash with a little cold water. 5.3 g (89.6% of theory) of N-methyl-N'-nitroguanidine with a melting point of 160 ° C are obtained. EXAMPLE 3 Add dropwise at 0 ° C, with stirring, to 82.7 g (0.8 mol) of 30% aqueous solution of ethyl-amine, 100.8 g (0.8 mol). of 50% nitric acid, stirred for another 30 minutes at 0 ° C, then allowed to warm to room temperature and the water is distilled off. Then add 400 ml of n-butanol and distill until the rest of the water has been removed. Then 30 g (0.72 mol) of cyanamide are added and heated in an autoclave under stirring for 8 hours at 130 ° C. It is refrigeratedthe precipitated solid product is filtered off and finally washed with a little n-butanol and dried. The solid product is dosed in 250 g of 98% sulfuric acid cooled at 0 ° C (in the course of 10 to 15 minutes). It is then heated to 40 ° C and maintained, under agitation, for 5 to 10 minutes at this temperature. It is then refrigerated again at 0 ° C and combined with 750 g of ice. The precipitated solid product is separated by filtration and dried. 77.3 g (91% of the theory related to the cyanamide used) of methylnitroguanidine- (obtained according to HPLC and 100% capillary electrophoresis) are obtained. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.