DRY ALKALI METAL GLYPHOSATE PROCESS

Abstract: A particulate mono-alkali metal salt of N-phosphonomethylglycine can be prepared by adding a solid alkali metal base with agitation to N-phosphonomethylglycine containing up to 25% water.

Description: Title: "DRY ALKALI METAL GLYPHOSATE PROCESS" This invention relates to a process for preparing a particulate, alkali metal salt of N-phosphonomethylglycine, and especially the sodium salt of N-phosphonomethylglycine. The compound, N-phosphonomethylglycine, commonly known in the agricultural chemical art as glyphosate, is a well-known and widely used broad-spectrum herbicide. It is usually formulated with other adjuvants in the form of its water-soluble salts, especially the mono-isopropylamine salt. Certain of the alkali metal salts, especially the sodium salt, have also been prepared and used. U.S. Patent 3,977,860 to John E. Franz discloses phytotoxic compositions, including concentrates which require dilution prior to application to the foliage of plants. Such compositions are prepared by mixing the active ingredient with an adjuvant, including diluents, extenders, carriers and conditioning agents, to provide compositions- in the form of finely-divided particulate solids, pellets, solutions, dis¬ persions, or emulsions. Thus, the active ingredient can be used with an adjuvant such as a finely-divided solid, a liquid or organic solvent, water, a wetting agent, a dispers¬ ing agent, an emulsifying agent, or any suitable combination of these. Although finely-divided particulate solids of N- phosphonomethylglycine have been disclosed in the prior art, it has been found in practice to be particularly difficult to prepare the alkali metal salts- of N-phosphonomethylglycine in a particulate form. Typically, when an aqueous solution of the alkali metal salt of N-phosphonomethylglycine is spray- dried, or even freeze-dried, it is difficult to remove sufficient water to form the solid material, and a paste is often obtained. Clearly it would be advantageous to provide a particulate, alkali metal N-phosphonomethylglycinate, not only for economy in shipping the product, but also for ease of use by the "farmer. Merely adding such a product to water, along with any necessary adjuvants, would provide a herbici- dal composition that could be more economically packaged and handled. Now it has been found that such a dry, particulate, alkali metal N-phosphonomethylglycinate can be prepared by the process of the present invention. Summary of The Invention These and other advantages are achieved by a method of preparing a particulate, alkali metal salt of N-phosphono- - methylglycine, which comprises adding a solid alkali metal base with agitation to of N-phosphonomethylglycine containing up to 25% water. Detailed Description of The Invention The N-phosphonomethylglycine for use in the method of the present invention can be prepared by any number of methods known to those skilled in the art. For example U.S. Patent 3 / 977,860 discloses that N-phosphonomethylglycines can be prepared by the phosphonomethylation. of a glycine, prefer¬ ably with chloromethylphosphonic acids. An alternate procedure disclosed in U.S. Patent 4,486,358 comprises reacting amino- ethanephosphonic acid with glyoxal in an aqueous solution in the presence of sulfur dioxide. .Many other processes have been disclosed in the prior art for the preparation of N-phos¬ phonomethylglycine. Typically, in commercial operations, the ' N-phosphonomethylglycine is obtained as a solid or paste con¬ taining up to 25% water, and more typically containing from about 15% to about 9% solids. This, intermediate product is then reacted with a suitable base to provide a water soluble salt which can then be formulated into a herbicidal composition. _ The alkali metal base for use in the method of the present invention include those bases of lithium, sodium, potassium and the like, such as the corresponding hydroxides, carbonates, and bicarbonates. Examples of such bases include lithium hydroxide, lithium bicarbonate, lithium carbonate, sodium hydroxide, sodijm bicarbonate, sodium Carbonate, potas¬ sium, hydroxide, pottasium carbonate, and the like. Sodium hydroxide and sodium carbonate are preferred, and sodium hydr¬ oxide is especially preferred. The quantity and the conditions under which the alkali metal base is added to the N-phosphonomethylglycine slurry depends upon the alkali metal base used and the concen¬ tration of solids in the aqueous slurry. For example, if the aqueous slurry of N-phosphonomethylglycine contains at least 75% solids, but less than about 85% solids, the material should be heated to a temperature above about 509C, and prefer¬ ably higher, before a stoichiometric quantity of the solid alkali metal base is added with agitation to the. N-phosphono¬ methylglycine. Under these conditions when using N-phosphono- methylglycine containing less than 85% solids, the use of sodium carbonate and sodium hydroxide is especially preferred, since the heat of reaction and heat of solubility of the potassium bases is not as high as ' that of sodium bases. The use of sodium hydroxide and sodium carbonate is especially preferred. On the other hand, when the aqueous slurry of N- phosphonomethylglycine contains at least about 85% solids, it is desirable that some of the alkali metal base is added as an aqueous solution, say a 50% aqueous solution of the base, to provide sufficient water in the mixture to insure that the solid alkali, metal base reacts with the N-phosphonomethylgly¬ cine to form the mono-alkali metal salt. Up to 70% of the alkali metal base can be adeed to the mixture as a 50% so¬ lution, but it is important in the process of the present in- vention that the remainder of the stoichiometric quantity of alkali metal base be added as the solid. The use of solid sodium hydroxide or sodium carbonate is preferred since the heat of solution and heat of reaction is sufficient to form the particulate alkali metal salt without the necessity of heating the slurry prior to the addition of the alkali metal base. However, when potassium hydroxide or potassium carbo¬ nate is used, it may be necessary to heat the N-phosphono- methylglycine to 509C or above prior to the addition of the potassium base to insure that a paste does not form. It is important in the method of the present invention that the slurry of N-phosphonomethylglycine is agitated, not only, during the addition of the alkali metal base, but also during the cooling period, to insure that there is reaction between the alkali metal base and the N-phosphonomethylgly¬ cine, and to insure that the resulting product is particulate. As will occur to these skilled in the art, when the alkali metal base is a carbonate or bicarbonate, part of the agita- tion will be achieved by the evolution of carbon dioxide. However, other forms of agitation, such as stirring, blending, and the like, can be used, as will occur to those skilled in the art, and the means of agitation is not particularly im¬ portant i the method of .the present invention. This invention is further illustrated by, but not limited to, the following examples: Example 1 To a laboratory-scale planetary mixer equipped with a stirrer, is placed 380 grams of N-phosphonomethylglycine (1.784 moles) . While stirring at a rate of 120 revolutions per minute, 30 grams of a 49+ aqueous solution of sodium hydr¬ oxide is added to the mixer. After about one minute, 22 • grams of flake sodium hydroxide (0.535 moles) is added to the mixer. After the addition .of the solid sodium hydroxide, the remainder of the stoichiometric amount of sodium hydroxide (71.95 grams) as a 50 percent solution is added as rapidly as possible. The material in the mixer turns to a liquid and remains in the liquid state for approximately 15 seconds. Then it gradually turns to a paste, and finally, to a finely- divided solid of mono-sodium N-phosphonomethylglycinate. Example 2 The procedure of Example 1 is repeated except that 50 grams of 50% sodium hydroxide solution is added to the mixer, then the flake sodium hydroxide, and thereafter the 5 remainder of the 50% solution of sodium hydroxide to form the stoichiometric quantity of sodium hydroxide to form the mono- sodium salt of N-phosphonomethylglycine. After the material in the mixer turns to the liquid state, it remains in the liquid state for approximately 90 seconds. The overall reaction time 10 is between about 13 and about 15 minutes. The temperature rises to approximately 1109C. Upon cooling while stirring, finely-divided mono-sodium N-phosphonomethylglycinate is ob¬ tained. Example 3 15 To the planetary mixer of Example 1 is added an 85% slurry of N-phosphonomethylglycine • (380 grams) . This slurry is heated to 659C, and thereafter, 35 grams of 50% potassium hydroxide solution is added. Then, 69.9 grams of potassium hydroxide pellets are added cautiously to the heated and stir- 20 red slurry. While stirring until the material cools to a solid, a particulate mono-potassium N-phosphonomethylglycinate is ob¬ tained. * * * Although the invention has been described in terms of specified embodiments which are set forth in considerable 25 detail, it should be understood that this is by illustration only, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. For example, other alkali metal salt of N- T phosphonomethylglycine can be obtained by changing the stoi- 30 chiometry between the alkali metal base and the N-phosphpno- methylglycine have been found to have herbicidal properties, and such derivatives can also be prepared as a particulate material by slight changes to the method, of the present inven¬ tion. In addition, certain adjuvants such as a particular sur- 35 face active agent and the like, could be added to either the slurry of N-phosphonomethylglycine before the solid base is added, or thereafter, to provide a particulate mono-alkali salt of N-phosphonomethylglycine with the desired adjuvant, and further formulation may not be required. Accordingly, modi¬ fications can be made without departing from the spirit of the described invention.

Claims: WHAT IS CLAIMED IS: 1. A method of. preparing a particulate alkali.metal salt of. N-phosphonomethylglycine, which comprises adding. a solid alkali metal base with agitation to N-phosphonomethylglyc ' ine containing up to 25% water. 2. A method of Claim- 1 wherein the N-phosphonomethylglycine contains up to 25%' water, and is heated to a temperature above about 50°C. 3. A method of Claim 2 wherein the alkali metal base is selected from the group consisting of sodium hydroxide and sodium carbonate. 4. A method of Claim 1 wherein the N-phos¬ phonomethylglycine contains up to about 15% water, and up to 70 percent of the alkali metal base is added to the slurry as a 50 percent solution, the remainder of the alkali metal base being added as the solid. 5. A method of Claim 4 wherein the alkali . metal base is selected from the group consisting of sodium hydroxide and sodium carbonate. 6. -A method of Claim 4 wherein the alkali metal base is selected from the group consisting of potassium hydroxide and potassium carbonate and the of N-phosphonomethylglycine is heated to at least about 50°C. 7. A method of Claim 5 wherein up to 50 percent of the alkali metal base is added as a 50 percent solution, the remainder being added as a solid. 8. A method of Claim 7 wherein the alkali ' metal base is sodium hydroxide. 9. A particulate mono-sodium N-phosphono¬ methylglycinate prepared by the method of Claim 1.

Inventors: BERGSON FERNANDES BARRETO HENR, TEIXEIRA COSTA FILHO GERALDO, VON ZUBEN FERNANDO JOSE, BERGSON FERNANDES BARRETO, HENRI, TEIXEIRA COSTA FILHO, GERALDO, VON ZUBEN, FERNANDO, JOSE
Applicants: MONSANTO BRASIL, MONSANTO DO BRASIL S.A.
Application year: 1987
Main classification: C07F9
IPC codes: A01N57, C07F9