This invention relates to a process for preparing N-phosphonomethylglycine, known also by its common name glyphosate. Glyphosate is a highly effective and commercially important phytotoxicant useful in controlling a large variety of weeds and crops. It is applied to the foliage of a very broad spectrum of perennial and annual grasses and broad-leafed plants to achieve the desired control. Industrial uses include control of weeds along roadsides, waterways, transmission lines, in storage areas, and in other nonagricultural areas. Usually glyphosate is formulated into herbicidal compositions in the form of its various salts which retain the anionic form of glyphosate in solution, preferably in water.

Glycine phosphonomethylation to produce glyphosate using formaldehyde and trialkylphosphites has been shown in the literature (U. S. Patent No. 5,041,628; Polish Patent Nos. 136,276 and 159,424). However, most approaches using such a combination of starting materials indicate using a ratio of glycine to trialkylphosphite of 1: 1. Other approaches have suggested increasing that ratio, but without regard to the subsequent drop in pH that occurs. Swietoslawski et al. (Polish Patent No. 136,276) suggest that any pH above 7 is sufficient and that increasing the pH of the medium has no significant effect on the reaction. Most of the yields obtained using the aforementioned approaches have been about 60%, and the highest was about 80% (Polish Patent No. 141,981).

Current methods of glycine phosphonomethylation to produce glyphosate begin with a di-or trialkylphosphite which has been purified. However, a process wherein a triarylphosphite is used to produce a reaction mixture containing a trialkylphosphite and using the reaction mixture instead of purifying the trialkylphosphite could be more economical than current methods of glycine phosphonomethylation since a costly purification step has been eliminated.

An improved process for producing glyphosate which is more economical and produces a higher yield than current methods is therefore highly desirable.

SUMMARY OF THE INVENTION In the process for producing glyphosate from glycine formaldehyde and phosphite, it has been found that the selectivity to monophosphonomethylation is sensitive to the amount of excess glycine and equivalents of base. Accordingly, the present invention provides a process for preparing N-phosphonomethylglycine which comprises contacting a glycinate salt, formaldehyde and a trialkylphosphite in an aqueous medium at a pH above about 9 under suitable reaction conditions to produce a reaction mixture comprising N- phosphonomethylglycine dialkylester, wherein the molar ratio of glycine equivalents to trialkylphosphite is about 1.5: 1 to 5: 1, and hydrolyzing the dialkylester under neutral, acidic or basic conditions.

Further according to the invention, a process for preparing N- phosphonomethylglycine dialkylester is provided which comprises contacting a triarylphosphite, an alcohol, sodium ethoxide to produce a first reaction mixture, a glycinate salt and formaldehyde at a pH above about 9 wherein the molar ratio of glycine equivalents to triarylphosphite is about 1.5: 1 to 5: 1.

Still further according to the invention, a process for preparing N- phosphonomethylglycine from the N-phosphonomethylglycine dialkylester is provided which comprises extracting the N-phosphonomethylglycine dialkylester from its reaction mixture using an organic phase, and hydrolyzing the N-phosphonomethylglycine dialkylester under neutral, acidic or basic conditions.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The invention relates to a process for preparing N-phosphonomethylglycine represented by the formula comprising contacting a glycinate salt, formaldehyde and a trialkylphosphite in an aqueous medium at a pH above about 9, wherein the molar ratio of glycine equivalents to trialkylphosphite is about 1.5: 1 to 5: 1 to produce a reaction mixture comprising N- phosphonomethylglycine dialkylester, and hydrolyzing the dialkylester under neutral, acidic or basic conditions.

The invention further relates to a process for preparing N-phosphonomethylglycine dialkylester represented by the formula

wherein R is an alkyl group containing 1 to about 6 carbon atoms, comprising contacting a triarylphosphite, sodium ethoxide, an alcohol wherein the alcohol is represented by the formula R (OH), a glycinate salt and formaldehyde at a pH above about 9 under suitable conditions of time and temperature.

For producing N-phosphonomethylglycine from the dialkylester produced above, the processes of the invention further comprise extracting the dialkylester in an organic phase and hydrolyzing the dialkylester under neutral, acidic or basic conditions.

In the preparation of N-phosphonomethylglycine dialkylester from triarylphosphite, the components may be added all at once. However, it is preferable that the triarylphosphite, sodium ethoxide and alcohol be contacted to produce a first reaction mixture; the glycinate salt and formaldehyde be contacted at a pH above about 9 to produce a second reaction mixture; and the first and second reaction mixtures be added.

The contacting of glycinate salt and formaldehyde may optionally be conducted in the presence of an alcohol, preferably the same alcohol as that used when contacting the triarylphosphite and sodium ethoxide.

Many trialkylphosphites and triarylphosphites, useful in the processes of the invention, are commercially available. Trialkylphosphites can also be readily prepared by conventional methods such as by reacting PCl3 with an alcohol. See, for example, Ford- Moore et al., Org. Syn., Coll. Vol. IV, p. 955 and Cook et al., J. Chem. Soc., 635 (1949) for methods utilizing PCl3. Trialkylphosphites can be represented by the formula P (OR) 3 wherein R is an alkyl group. The alkyl groups of the trialkylphosphites are linear or branched alkyl groups having 1 to about 6 carbon atoms and are optionally substituted

with-OH groups. Preferred trialkylphosphites are triethylphosphite and triisopropylphosphite. Trialkylphosphites are preferred over dialkylphosphites due to unexpectedly improved yields achievable with the trialkylphosphites. Triarylphosphites can be represented by the formula P (OR') 3 wherein R'is an aryl group, preferably a phenyl group.

Glycinate salt utilized in the processes of the present invention may be made by contacting glycine with an alkali or alkaline earth metal hydroxide or by other processes, such as oxidation of an ethanolamine. The amount of glycinate salt utilized in the processes of the invention can be expressed as a molar ratio of glycine equivalents to phosphite starting material. Broadly, the molar ratio of glycine equivalents to phosphite is about 1.5: 1 to about 5: 1, and preferably about 1.5: 1 to about 2.5: 1. Glycinate salts may also be formed in situ in the processes of the present invention from glycine and an alkali or alkaline earth metal hydroxide. Alkali metal hydroxides are preferred and include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide. Excess glycine may be removed from the reaction mixture through precipitation. Precipitation of excess glycine may be initiated by the addition of strong acid, such as HCI, and cooling.

Formaldehyde can be employed according to the invention as paraformaldehyde or as an aqueous solution of formaldehyde. Aqueous formaldehyde is commercially available as 37-50% by weight aqueous solutions which may contain methanol, ethanol, or n- butanol. The amount of formaldehyde utilized in the processes of the invention can be expressed as a molar ratio of formaldehyde starting material to phosphite starting material.

Broadly, the molar ratio of formaldehyde to phosphite is about 1: 1 to about 5: 1, preferably about 1: 1 to about 2: 1, and most preferably about 1: 1 to about 1.5: 1.

The reactions of glycinate salt and formaldehyde are conducted at a pH above about 9, preferably at a pH in the range of about 9 to 12, and most preferably at a pH of about 10.

The trialkylphosphite and triarylphosphite reactions are conducted at a suitable temperature which can vary over a wide range. The reaction temperature will generally be within the range of about 0 °C to about 120 °C, preferably about 40 °C to about 75 °C. The reactions are also conducted for a suitable time which can vary over a wide range

depending on various parameters, e. g. the reaction temperature. Generally, the reaction time will be within the range of the time necessary for the phosphite to be consumed, between about 0.25 and about 3 hours, preferably between about 0.25 and about 0.75 hours.

The reactions of glycinate salt and formaldehyde can optionally be conducted in the presence of an alcohol wherein the alcohol is represented by the formula R" (OH) and R"is an alkyl group having 1 to about 6 carbon atoms. The alkyl group, R", can be linear or branched and preferably is the same alkyl group as that utilized in the trialkylphosphite starting material. Examples of suitable alcohols include, but are not limited to, methanol, ethanol, isopropanol, n-butanol and mixtures thereof.

The hydrolysis reaction can be conducted under neutral, acidic or basic conditions using any one of several conventional methods known to those skilled in the art. When the hydrolysis reaction is conducted under neutral conditions, a preferred method is to contact the reaction mixture with water. The concentration of the reactant to be hydrolyzed, i. e. the intermediate esters of N-phosphonomethylglycine, in water is broadly within the range of about 40 weight percent to about 5 weight percent, preferably about 30 weight percent to about 15 weight percent. The temperature for the neutral hydrolysis reaction is generally in the range of about 100°C to about 260°C, preferably about 120°C to about 180°C. Generally, the reaction time will be within the range of the time necessary for hydrolysis to occur to about 24 hours, preferably about 3 hours to about 8 hours. After the hydrolysis reaction is completed, the N-phosphonomethylglycine can be recovered by any conventional method known to those skilled in the art such as the method utilized in Example 18.

When the hydrolysis reaction is conducted under acidic conditions, a preferred method is to remove the excess glycine from the reaction mixture together with any alcohol solvent optionally present followed by hydrolyzing the reaction mixture in hydrochloric acid. The concentration of the hydrochloric acid is preferably in the range of 6N HCl to 12N HCl (concentrated HCl). The temperature for the acid hydrolysis reaction is generally in the range of the boiling point of the HCl to about 180 °C, preferably about 80 °C to 120 °C. Generally, the reaction time will be within the range of the time necessary for hydrolysis to occur to about 24 hours, preferably about 2 hours to about 16 hours. After

the hydrolysis reaction is completed, the N-phosphonomethylglycine can be recovered by any conventional method known to those skilled in the art, such as the method utilized in Example 18.

When the hydrolysis reaction is conducted under basic conditions, a preferred method is to contact the reaction mixture with an alkali metal hydroxide or alkaline earth metal hydroxide, preferably an alkali metal hydroxide. The concentration of the alkali metal hydroxide or alkaline earth metal hydroxide is broadly within the range of about 15% to about 90% by weight, preferably about 40% to about 60% by weight, and most preferably about 50% by weight. The amount of alkali metal hydroxide or alkaline earth metal hydroxide utilized in the hydrolysis reaction can be expressed as the ratio of equivalents of hydroxide to moles of phosphite starting material. Broadly, the ratio is about 2: 1 to about 5: 1, preferably about 2.5: 1 to about 4: 1, and most preferably about 3: 1.

The temperature for the base hydrolysis reaction is generally in the range of about 80°C to about 250°C, preferably about 80°C to about 180°C, most preferably about 120°C to about 150°C. Generally, the reaction time will be within the range of the time necessary for hydrolysis to occur to about 48 hours, preferably 2 hours to about 24 hours and most preferably about 2 hours to about 16 hours. After the hydrolysis reaction is completed, the N-phosphonomethylglycine can be recovered by any conventional method known to those skilled in the art such as the method utilized in Example 18.

Prior to hydrolysis, the dialkylester may be extracted from the reaction mixture using an organic phase. Preferably, aromatic compounds are used to extract the dialkylester from the reaction mixture. More preferably, a mixture of toluene and water is used to extract the dialkylester.

The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

In the phosphonomethylation of glycine with trialkylphosphites, the product spectrum was found to be quite sensitive to the number of equivalents of base (pH) and to excess glycine. Examples 1-7 display the pH dependency for achieving a selective mono- phosphonomethylation. Examples 8-16 show the impact of maintaining the pH profile while incorporating excess glycine.

EXAMPLES 1-7 The dependence of achieving selective mono-phosphonomethylation on pH is exemplified by the following tests in which glycine (1.87 g, 25 mmol) was dissolved in 10% (w/v) NaOH. The molar ratio of NaOH to glycine added was adjusted to vary the pH of the solution from about 9 to about 12. Formaldehyde (37%) (2.0 g, 25 mmol) was added dropwise at <30 °C and stirred for 30 min. Isopropyl alcohol (3 mL) was added and the reaction mixture was heated to 60 °C. At this temperature triisopropylphosphite (5.21 g, 25 mmol) was added over 1 hour. The initially two-phase reaction mixture became homogeneous during the addition period. Fifteen minutes after the addition was complete the reaction mixture was examined by 31p NMR. The major products were identified as the diphosphonate ester of glyphosate (Glyphosate Diester), the tetraphosphonate ester of bisphosphonmethylated glycine (Glyphosine Tetraester), and the diphosphonate ester of hydroxymethyl phosphonic acid (HMPA Diester). The results are reported in Table 1 below and are expressed in % of the total phosphorous integration of the 31P NMR spectrum of the reaction mass. The amount of NaOH added is expressed as the molar ratio of NaOH to glycine added.

TABLE 1. pH Dependency for Achieving Mono-Phosphonomethylation at 60 °C Example NaOH/pH Glyphosate Glyphosine HMPA Diester Glycine Diester Tetraester 1 1. 10 12 24 1 60 1. OS 11. 5 37 50 3 1. 00 11 61 5 31 4 0. 96* 10 76 11 11 5 0.96 10 69 16 11 6 0.91 10 68 1 7 ** 9 71 2 3 "zoom temperature ** 1 equivalent of Et3N

EXAMPLES 8-16 The dependence of achieving selective mono-phosphonomethylation on the amount of excess glycine in the reaction mixture is exemplified by the following tests in which glycine was dissolved in 10% (w/v) NaOH. The amount of glycine added varied from about 1.87 g (25 mmol) to about 9.35 g (125 mmol). The ratio of glycine to NaOH was kept similar to maintain a pH of the solution of about 10. Formaldehyde (37%) (2.0 g, 25 mmol) was added dropwise at <30 °C and stirred for 30 min. Ethyl alcohol (6 mL) was added followed by triethylphosphite (4.15 g, 25 mmol) and the reaction mixture was heated to 75 °C. Within a few minutes of reaching this temperature, the initially two-phase reaction mixture became homogeneous. Ten minutes after reaching 75 °C the reaction mixture was examined by 31 P NMR. The major products were identified as the diphosphonate ester of glyphosate (Glyphosate Diester), the tetraphosphonate ester of bisphosphonmethylated glycine (Glyphosine Tetraester), and the diphosphonate ester of hydroxymethyl phosphonic acid (HMPA Diester). The results are reported in Table 2 below and are expressed in % of the total phosphorous integration in the 31P NMR spectrum of the reaction mass. The amount of glycine added is expressed in equivalents, with 1 equivalent equal to about 1.87 g (25 mmol). The amount of NaOH added is similarly expressed in equivalents, with 1 equivalent equal to about 10.9 g (25 mmol).

TABLE 2. Impact of Excess Glycine on Phosphonomethylation at 75 °C Example Trialkyl Equiv. Equiv. Glyphosate Glyphosine HMPA Phosphite Glycine aOH Diester Tetraester Diester 8'sopropyl 1. 0 0. 9 68 1 9 sopropyl 1. 5 1. 2 78 11 3 10 ethyl*. 0 1. 5 82 1 11'sopropyl. 0 1. 5 83 12 thyl 2. 0 1. 5 93 3 2 13 ethyl 2. 5. 0 94 3 14 isopropyl 2. 5 2. 0 86 5 2 15 isopropyl 3. 0 2. 5 86 4 3 16 isopropyl 5. 0 t. 0 89 2 2 * C

EXAMPLE 17 This example illustrates the removal of excess glycine from the crude reaction mixture.

Glycine (7.51 g, 100 mmol, 2 equivalents), 50% sodium hydroxide (6.0 g, 75 mmol, 1.5 equiv.), and 6.0 g of water were mixed to form a solution. 37% Formaldehyde (4.26 g, 52.5 mmol, 1.05 equiv.) and 5 mL ethanol were added. The temperature was adjusted to 45 °C. The pH of the solution at this time was about 10. The alcohol formed a small second phase. Triethylphosphite (8.31 g, 50 mmol, 1.0 equiv.) was added over 30-45 minutes with the temperature being maintained at 45 °C. The phosphite produced a second phase during the addition, but slowly reacted. After the addition, the reaction was maintained at 45 °C for an additional 45 minutes during which time the mixture became a clear homogeneous solution.

The addition of 3.1 mL of concentrated HCl (37.5 mmol) and cooling caused excess glycine to precipitate. This was filtered, washed with ethanol, and dried to recover about 2.4 g of glycine (64% of the excess). To the filtrate was added 20.7 mL of concentrated HCl (5 equiv.) and the mixture was heated to distill ethanol. Stripping continued until the reaction temperature reached 108 °C. These conditions were maintained for 4 h until the hydrolysis reaction was complete. The mixture was diluted with water to maintain solubility of all components and analyzed by HPLC to indicate the presence of 7.77 g (92% yield) of glyphosate based on the starting phosphite.

EXAMPLE 18 This example illustrates the isolation of N-phosphonomethylglycine after hydrolysis.

A post-hydrolysis mixture was prepared according to Example 17 and was stripped of excess HCl solution to leave a viscous mass. Water was added (13 mL) and the mixture heated to give a slurry of product. The pH of the mixture was adjusted to about 1.5. At room temperature the mixture was filtered, washed with water, and dried to give 7.44 g of material which contained 7.05 g of glyphosate (83.4% yield). The filtrate was concentrated to precipitate salt and filtered. The filtrate was found to contain an additional 0.58 g of glyphosate (6.8% yield). The filtrate was recycled into the next batch. Overall yield of glyphosate from this procedure was 90.2% based on the starting phosphite.

EXAMPLE 19 In the phosphonomethylation of glycine to produce glyphosate using trialkylphosphites, the trialkylphosphites are often used in a pure form. Production of trialkylphosphites from triarylphosphites produces a reaction mixture that can be used directly in the phosphonomethylation without the need for purification, yet produce a glyphosate diethylester yield in excess of 80%. This example illustrates the preparation of glyphosate diethylester from triphenylphosphite, ethanol, glycine and formaldehyde.

Triphenylphosphite (98%, 50 mmol), ethanol (500 mmol) and NaOEt (0.5 mmol) were heated under reflux for 6 hours. 31P NMR showed 95% triethylphosphite, 3% diethylphenylphosphite, and 2% diethylphosphite. This mixture was added dropwise over a period of 45 min. at 45 °C to a solution containing glycine (100 mmol), 50% NaOH (75 mmol), water (5 mL), ethanol (5 mL) and 37% formaldehyde (52.5 mmol). The mixture was held at 45 °C for an additional 45 min. 31 P NMR of the reaction mixture showed 88.5% glyphosate diethylester. HCl (37.5 mmol) was added to the reaction mixture and ethanol was removed (rotovap). A total of 3.74 g of a white solid was filtered from the reaction mixture. Analysis showed that the solid contained 2.87 g of glycine, or 76% of the excess glycine in the reaction mixture.

EXAMPLE 20 This example illustrates the separation of glyphosate diethylester from the salt and excess glycine in the reaction mixture produced in Example 19 by extraction in an organic phase.

An unfiltered concentrate was produced according to Example 19. One mL of the concentrate was added to a mixture containing about 0.5 mL water and about 0.5 mL toluene. Substantially all of the phosphorous compounds separated from the mixture into the organic phase as determined by 31P NMR spectroscopy.

All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it

will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.