A process for preparing 4-amino-1,2,4-triazolin-5-ones

Abstract: The present invention is related to an improved process for the commercial preparation of substituted aminotriazolinones, which are known intermediates in the preparation of herbicidal active compounds. In particular, this invention relates to the preparation of 4-amino-1,2,4-triazolin-5-ones, and more particularly to the preparation of 3-isopropyl-4-aminotriazolinone. The process of the invention includes reacting an oxadiazolinone with hydrazine hydrate in the absence of a solvent. In a preferred embodiment, the hydrazine hydrate is mixed with a basic compound, preferably aqueous sodium hydroxide.

Description: FIELD OF THE INVENTION The present invention relates to an improved process for the commercial preparation of substituted aminotriazolinones, which are known intermediates in the preparation of herbicidal active compounds. In particular, this invention relates to the preparation of 4-amino-1,2,4-triazolin-5-ones, and more particularly to the preparation of 3-isopropyl-4-aminotriazolinone. BACKGROUND OF THE INVENTION It is known that substituted aminotriazolinones are obtained when corresponding oxadiazolinones are reacted with hydrazine hydrate in water. In U.S. Patent 4,952,701, the oxadiazolinone is initially introduced in water and an excess of hydrazine hydrate is added to the reaction mixture at room temperature. The mixture is then heated and cooked. The excess hydrazine is removed by distillation and the desired aminotriazolinones are obtained. Due to the solubility of the aminotriazolinones in water, the resultant product is obtained in low yields and low purity; and therefore, an additional purification step is required. Further, it is also known in the art that substituted aminotriazolinones are obtained when corresponding oxadiazolinones are reacted with hydrazine hydrate in the presence of a basic compound and in the presence of a polar organic solvent. Suitable basic compounds are in general inorganic or organic bases or acid acceptors. Such basic compounds include alkali metal or alkaline earth metal acetates, amides, carbonates, hydrogen carbonates, hydrides, hydroxides or alkoxides. Suitable polar organic solvents include dialkyl ethers, dialkyl ketones, nitriles, amides, esters, alcohols, and sulphoxides. In U.S. Patent Application 08/696,013, the hydrazine hydrate is initially introduced in the basic compound and the polar organic solvent. The mixture is then heated to the required reaction temperature. As the mixture is cooked, the oxadiazolinone is slowly added until the reaction is complete. The desired aminotriazolinones are obtained by adjusting the pH of the mixture to about 7 by adding an aqueous acid and water. For the isolation of the reaction product the solvent and water are removed by distillation and the reaction product remains as a residue which is isolated by filtering. The product is further isolated from this residue in pure form by dissolving the residue in hot water and subsequently cooling the solution to 10 to 20 °C so that the product precipitates from the aqueous solution. However, due to the solubility of the product in water, part of the desired product remains in the water and cannot be recovered. The product is obtained in low yields. In another isolation step described in said patent application the reaction product is isolated from the neutralized solution by phase extraction between water and the organic solvent after water has been added in the neutralization step. The product is recovered from the aqueous phase by distillation. The work-up and isolation of the resultant product is extensive. Therefore, this process is not well suited for a commercial scale preparation of the desired product. In all these known processes, either resultant low yields are observed due to the use of water as a solvent in the reaction mixture/purification step caused by the solubility of the product in water or the isolation of the product requires extensive purification procedures including extraction and distillation steps. Thus, there is a need for an efficient process for preparing substituted aminotriazo-linones, and in particular 4-amino-1,2,4-triazolin-5-ones, that produces a high net yield and high purity. SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved process for the preparation of 4-amino-1,2,4-triazolin-5-ones of the general formula (I): in which R represents alkyl, by reacting an oxadiazolinone of the general formula (II): in which R has the meaning indicated above, with hydrazine hydrate in the absence of a solvent. In a preferred embodiment, R represents an isopropyl group. Further, the reaction is preferably carried out in the presence of a basic compound. The reaction mixture is heated and cooked. The desired product is then isolated and purified using a mixture of a small amount of water in combination with an organic solvent. A preferred organic solvent is toluene. DETAILED DESCRIPTION OF THE INVENTION The process according to the invention relates to the preparation of 4-amino-1,2,4-triazolin-5-ones of the general formula (I): in which R represents alkyl, by reacting an oxadiazolinone of the general formula (II): in which R has the meaning indicated above, with hydrazine hydrate in the absence of a solvent. The alkyl is preferably isopropyl. Further, in a preferred embodiment of the process, the hydrazine hydrate is mixed with a basic compound. Suitable basic compounds are in general inorganic or organic bases or acid acceptors. Such basic compounds include alkali metal or alkaline earth metal acetates, amides, carbonates, hydrogen carbonates, hydrides, hydroxides or alkoxides. A preferred basic compound for the present invention is aqueous sodium hydroxide. The molar ratio of hydrazine hydrate to oxadiazolinone is from 1:1 to 1.5:1, and preferably from 1:1 to 1.1:1. The molar ratio of the basic compound to oxadiazolinone is from 0.05:1 to about 0.5:1, and preferably from 0.075:1 to 0.25:1. The mixture of hydrazine hydrate and basic compound are heated to a temperature of from 100°C to 110°C, and preferably from 102°C to 105°C. The oxadiazolinone of general formula (II) is then slowly added to the hydrazine hydrate and basic compound mixture. The oxadiazolinone is added over a time period of from 20 to 60 minutes, and preferably from about 30 to 40 minutes. This mixture is agitated for 3 to 5 hours at a temperature of from 90°C to 110°C, and preferably from 100°C to 105°C, until the reaction is complete. Following agitation and completion of the reaction, the mixture is cooled to from 80°C to 100°C, and preferably from 85°C to 90°C. Following cooling of the mixture, water and a solvent are added to the mixture. In a preferred embodiment, the water is added prior to the addition of the solvent. Preferably, the solvent is an aprotic, organic solvent. Such solvents are well known in the art. Such suitable solvents include toluene, methyl acetate, t-butyl methyl ether, methyl-isobutyl ketone, and ethyl acetate. Toluene is a preferred solvent for the process of the present invention. The amount of solvent used can vary over a wide range as readily determined by a skilled artisan. The precise amount of solvent will depend on the particular solvent used. Where toluene is the solvent, it is present in a molar ratio of toluene to oxadiazolone of from about 1:1 to about 8:1; and preferably from about 3:1 to about 4:1. The molar ratio of water to oxadiazolone is from 1:1 to 6:1; and preferably from 1:1 to 3:1. The mixture is then cooled to a temperature of from 5°C to 20°C and preferably from 5°C to 10°C. A pH adjusting agent is added to the mixture to adjust the pH from 5.0 to 8.0, and preferably from 6.0 to 7.0. Suitable pH adjusting agents include hydrochloric acid, sulfuric acid, phosphoric acid, and acetic acid. In a preferred embodiment, concentrated hydrochloric acid or aqueous sulfuric acid is used as the pH adjusting agent. The molar ratio of acidic pH adjusting agent to oxadiazolone is from 0.05:1 to 0.5:1. After cooling the reaction mixture (e.g. to 10°C to 20°C) the reaction product precipitates during or after the neutralisation from the reaction mixture. It can be recovered by known separation techniques, e.g. filtering and subsequent washing and drying of the filter cake. The following Examples illustrate preferred embodiments of the present invention and are not limiting of the specification and claims in any way. EXAMPLES Example 1 Preparation of 3-Isopropyl-4-Amino-Triazolinone Using a Mixture of Toluene and 20 ml of Water Approximately 53 g (1.05 mole) of hydrazine hydrate was charged to a flask. The hydrazine hydrate was agitated and then about 15.6 g (0.195 mole) of 50% sodium hydroxide (NaOH) solution was added. This mixture was heated to reflux and then about 132 g (1.0 mole) of isopropyl-oxadiazolinone was added via a funnel. The total time for addition of the isopropyl-oxadiazolinone was about 40 minutes. The reaction mixture was cooked at a temperature of about 105°C for about 5 hours. Following completion of the reaction, the mixture was cooled to about 85°C. About 300 g (3.26 mole) of toluene and about 20ml of fresh water was added to the mixture. The mixture was then cooled to about 10°C. The pH of the mixture was adjusted to about 7.0 by the addition of about 15 g (0.076 mole) of 50% sulfuric acid. The solids were recovered via filtering. The solids were then washed with about 100 ml of toluene and then with 2 x 20 ml ice-cold water. The solids were dried at a temperature of about 60°C under vacuum. The toluene phase was then separated from the mother liquor and the toluene was recovered via distillation. The active ingredient (A.I.) of the product and net yield are shown in Table I. Example 2 Preparation of 3-Isopropyl-4-Amino-Triazolinone Using a Mixture of Toluene and 40 ml of Water The process as described in Example 1 was repeated, with the exception that following completion of the reaction and it being cooled to about 85°C, about 40 ml (instead of 20 ml) of fresh water was added with about 300 g (3.26 mole) of toluene to the reaction mixture. The results are shown in Table I. Example 3 Preparation of 3-Isopropyl-4-Amino-Triazolinone Using a Mixture of Toluene and 60 ml of Water The process as described in Example 1 was repeated, with the exception that following completion of the reaction and it being cooled to about 85°C, about 60 ml (instead of 20 ml) of fresh water was added with about 300 g (3.26 mole) of toluene to the reaction mixture. The results are shown in Table I. Example 4 Preparation of 3-Isopropyl-4-Amino-Triazolinone Using a Mixture of Toluene and 50 ml of Water The process as described in Example 1 was repeated, with the exception that following completion of the reaction and it being cooled to about 85°C, about 50 ml (instead of 20 ml) of fresh water was added with about 280 ml (instead of 300 g) of toluene to the reaction mixture. The results are shown in Table I. Run No. Reaction Temp. (C) Reaction Time (Hrs.) A.I. (%) Net Yield (%) 1 103 4 96 93 2 103 3.5 97 91 3 103 4 98.3 89 4 103 4 98 90

Claims: A process for preparing 4-amino-1,2,4-triazolin-5-ones of the formula: wherein R represents alkyl, comprising: a) reacting an oxadiazolinone of the formula: wherein R has the meaning indicated above, with hydrazine hydrate in the absence of a solvent; b) adding water and a solvent to the reaction product of step a), following completion of the reaction in step a); c) adjusting the pH of the mixture of step b) to from about 5.0 to about 8.0 by the addition of an acidic material to allow the 4-amino-1,2,4-triazolin-5-ones to precipitate; and d) recovering the precipitate. The process of Claim 1 wherein R represents isopropyl. The process of Claim 1 wherein step a) is carried out in the presence of a basic compound selected from the group consisting of aqueous sodium hydroxide, alkali metal and alkaline earth metal acetates, amides, carbonates, hydrogen carbonates, hydrides, hydroxides, and alkoxides. The process of Claim 1 wherein the solvent used in step b) is an aprotic organic solvent selected from the group consisting of toluene, methyl acetate, t-butyl methyl ether, methyl-isobutyl ketone, and ethyl acetate. The process of Claim 1 wherein the acidic material used in step c) is selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid and acetic acid. The process of Claim 1 wherein the temperature in step a) is from 90°C to 110°C, in step b) from 80°C to 100°C, and in step c) from 5°C to 20°C. The process of Claim 1 wherein in step a) the molar ratio of hydrazine hydrate to oxadiazolinone is from 1:1 to 1.5:1. The process of Claim 3 wherein the molar ratio of basic compound to oxadiazolinone is from 0.05:1 to 0.5:1. The process of Claim 4 wherein the molar ratio of toluene to oxadiazolinone is from 1:1 to 8:1. The process of Claim 1 step b) wherein the molar ratio of water to oxadiazolinone is from 1:1 to 6:1.

Inventors: DESAI VIJAY C, DIEHR HANS-JOACHIM DR, JELICH KLAUS DR, LANTZSCH REINHARD DR, DESAI, VIJAY C., DIEHR, HANS-JOACHIM, DR., JELICH, KLAUS, DR., LANTZSCH, REINHARD, DR.
Applicants: BAYER AG, BAYER CORPORATION
Application year: 1999
Main classification: C07D249
IPC codes: C07D249