FORM 2
THE PATENTS ACT, 1970 (39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
SYNTHESIS OF DISUBSTITUTED AROMATIC CARBOXYLIC ACID
AND THEIR SALTS
Applicant: GHARDA CHEMICALS LIMITED
An Indian company of
B-27/29, MIDC Dombivli (East)
Thane-421203, Maharashtra, India
Inventors:
1. MATHUR SUCHET S.
2. DAMANIA RAJESWARI P.
3. BOOKWALAHUSENIF.
4. KULKARNI KETAN S.
5. VISHENARENDRAN.
6. BERKAL BAJIRAO D.
7. KAPSERAJUH.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

FIELD
The present disclosure relates to a process for the preparation of di-substituted aromatic carboxylic acid and their salts. Particularly, the present disclosure relates to a process for the preparation of Bispyribac-metal salts.
BACKGROUND
Bispyribac-sodium
IUPAC Name: sodium 2, 6-bis (4, 6-dimethoxypyrimidin-2-yloxy) benzoate
Structure:

Chemical formula: C19H17N4NaO8
Molecular Weight: 452.4
Physical State: white powder
Melting point: 223-224°C
Solubility in water: 73.3g/l at 25°C
Mode of action: selective, systemic action post-emergence herbicide, absorbed by
foliage and roots.
Bispyribac sodium is a systemic herbicide that moves throughout the plant tissue and works by interfering with production of a plant enzyme necessary for growth, acetolactate synthase (ALS). It is used to control grasses, sedges and broad-leaved weeds, especially Echinochloa spp., in direct seeded rice. It is also used to stunt growth of weeds in non-crop situations.

Bispyribac sodium is broken down by microbes and has a half-life (the time it takes for half of the active ingredient to degrade) of 42-115 days. The primary degradation product of bispyribac sodium is sodium 2-(4,6 dimethoxypyrimidin-2-yl)oxy-6-(4-hydroxy-6-methoxypyrimidin-2-yl) benzoate. Bispyribac sodium does not bind to soil, is moderately persistent and somewhat mobile through the soil. Testing indicates that the aquatic formulation of bispyribac sodium is nontoxic to fish and invertebrates. Bispyribac sodium is also non-toxic to both birds and mammals.
The various processes for the preparation of Bispyribac sodium have been disclosed in the prior art documents. These processes utilize strong acids such as sulphuric acid and hydrochloric acid and the time required for the reaction is very high. Furthermore, the known processes are low yielding. Accordingly, it is desirable to develop a simple, economic and high yielding process for the preparation of Bispyribac sodium.
OBJECTS
It is an object of the present disclosure to provide a simple and high yielding process for the preparation of Bispyribac-metal salt.
It is another object of the present disclosure to provide a time saving process for the preparation of Bispyribac- metal salt.
It is another object of the present disclosure to provide a process for the preparation of Bispyribac- metal salt which employs mild base rendering the process economic.

Brief description of accompanying drawing:
Figure 1 illustrates a reaction scheme for the preparation of Bispyribac- metal salt in accordance with the present disclosure.
Summary
A process for the preparation of Bispyribac-metal salt; said process comprising the following steps: i. reacting 2,6-dihydroxy benzoic acid with dialkyl sulphate using a base in a solvent to form 2,6-dihydroxy alkyl benzoate;
ii. condensing 2-(methylsulfonyl)-4,6-dimethoxy pyrimidine with 2,6-dihydroxyalkyl benzoate to obtain alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate; and
iii. subjecting said alkyl-2,6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate to hydrolysis with at least one alkali metal or alkaline earth metal to obtain Bispyribac- metal salt.
Typically, the dialkyl sulphate is selected from the group consisting of dimethyl sulphate, diethyl sulphate, dipropyl sulphate, dibutyl sulphate and dipentyl sulphate. In one embodiment, the dialkyl sulphate is dimethyl sulphate.
Typically, the base is selected from the group consisting of hydroxides and carbonates of alkali and alkaline earth metals.
Typically, the base is alkali metal hydroxide selected from the group consisting of lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH) and combinations
thereof.

Typically, the base is an alkaline earth metal hydroxide selected from the group consisting of beryllium hydroxide (Be(OH)2), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2) and combinations thereof.
Typically, the base is a carbonate selected from the group consisting of potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, lithium carbonate, cesium carbonate, barium carbonate, calcium carbonate and combinations thereof.
Typically, the solvent is selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and combinations thereof.
Typically, the alkali metal/ alkaline earth metal is in the form of hydroxide.
Typically, the alkali metal is in the form of carbonates.
In one embodiment the step (i) includes heating 2,6-dihydroxy benzoic acid, a base and a solvent at a temperature of 30 to 100°C to obtain a mixture, adding dialkyl sulphate to said mixture over 0.5 to 3 hours and refluxing at 40 to l00°C for 1 to 10 hours to obtain 2,6-dihydroxy alkyl benzoate.
In another embodiment the step (i) further includes distilling off the solvent and concentrating 2,6-dihydroxy alkyl benzoate followed by cooling, quenching in ice water, filtering, washing and drying.
In one embodiment the step (ii) includes mixing 2,6-dihydroxy alkyl benzoate and a solvent to obtain a solution, heating said solution to 30 to 80°C, adding a base to said solution to obtain a mixture, stirring said mixture for 0.5 to 3 hrs,

incorporating 4,6-dimethoxy-2-(methyl sulfonyl) pyrimidine to said mixture to obtain a mass and heating said mass to 40 to 90°C to obtain alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate.
In another embodiment the step (ii) further includes distilling off the solvent under vacuum below 70°C, concentrating alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate followed by cooling, quenching in water, filtration, washing, slurring and drying.
In one embodiment the step (iii) includes mixing alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate and a solvent, adding at least one alkali metal or alkaline earth metal at 25-50°C to obtain a mass, stirring said mass for 2-60 minutes to obtain a stirred mass and heating said mass under reflux to obtain Bispyribac- metal salt.
In another embodiment the process step (iii) further comprises cooling of Bispyribac- metal salt, equilibrating, filtering, washing and drying.
In one embodiment the 2,6-dihydroxy alkyl benzoate is 2,6-dihydroxy methyl benzoate.
In one embodiment the Bispyribac-metal salt is Bispyribac sodium; said process comprises the following steps:
- heating 2,6-dihydroxy benzoic acid, sodium bicarbonate and a solvent selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and combinations, thereof at a temperature of 30 to 100°C to obtain a mixture,

- adding dimethyl sulphate over 0.5 to 3 hours to said mixture and refluxing at 40 tol00°C for a time period of 1 to 10 hours to obtain a reaction mass, distilling off the solvent and concentrating the reaction mass to obtain 2,6-dihydroxy methyl benzoate;
- mixing 2,6-dihydroxy methyl benzoate and at least one solvent is selected from the group consisting of dimethyl formamide and acetonitrile to obtain a solution, heating said solution to 30 to 80°C, adding potassium carbonate to said solution to obtain a mixture, stirring said mixture for 0.5 to 3 hrs., incorporating 2,6-dimethoxy-2-(methyl sulfonyl) pyrimidine to said mixture to obtain a mass, heating said mass to 40 to 90°C to obtain a heated mass, maintaining said mass at 50-90°C for 5-15 hrs, distilling off the solvent under vacuum below 70°C, concentrating the mass and cooling the mass followed by quenching, cooling, filtration, washing, slurring and drying to obtain 2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] methyl benzoate; and
- admixing methyl-2,6-bis[(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate (bis ether) and at least one solvent is selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone and methyl isobutyl ketone to obtain a dispersion, adding sodium hydroxide to said dispersion at 25 to 50°C, to obtain a mass, stirring the mass for 2 to 60 minutes to obtain a stirred mass, heating said mass under reflux followed by cooling, equilibrating, filtering, washing and drying to obtain bispyribac sodium.
Description:
In accordance with the present disclosure there is provided a process for the preparation of Bispyribac-metal salt. The process is described herein below:

In the first step, 2,6-dihydroxy benzoic acid is reacted with dialkyl sulphate using a base in a solvent to form 2,6-dihydroxy alkyl benzoate.
In accordance with the present disclosure, the dialkyl sulphate employed in the reaction includes but is not limited to dimethyl sulphate, diethyl sulphate, dipropyl sulphate, dibutyl sulphate and dipentyl sulphate. In one embodiment, the dialkyl sulphate is dimethyl sulphate. In one embodiment the 2,6-dihydroxy alkyl benzoate is 2,6-dihydroxy methyl benzoate.
The base is selected from the group consisting of hydroxides and carbonates of alkali and alkaline earth metals. In one embodiment the base is alkali metal hydroxide selected from the group consisting of lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH) and combinations thereof. In another embodiment, the base is an alkaline earth metal hydroxide selected from the group consisting of beryllium hydroxide (Be(OH)2), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2) and combinations thereof. Alternatively, the base is a carbonate selected from the group consisting of potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, lithium carbonate, cesium carbonate, barium carbonate, calcium carbonate and combinations thereof.
The solvent employed in the reaction includes but is not limited to acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and combinations thereof.
In one embodiment 2,6-dihydroxy alkyl benzoate is obtained by the following
procedure:
Initially, 2,6-dihydroxy benzoic acid, a base and a solvent are heated at a
temperature of 30 to 100°C to obtain a mixture. To this mixture, dialkyl sulphate is

added over 0.5 to 3 hours which is then refluxed at 40 tol00°C for 1 to 10 hours to obtain 2,6-dihydroxy alkyl benzoate. The process further includes distilling off the solvent and concentrating 2,6-dihydroxy alkyl benzoate followed by cooling, quenching in ice water, filtering, washing and drying.
In the second step, 2-(methylsulfonyl)-4,6-dimethoxy pyrimidine is condensed
with 2,6-dihydroxyalkyl benzoate to obtain alkyl-2, 6-bis [(4,6-dimethoxy-2-
pyrimidinyl) oxy] benzoate.
In one embodiment alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate is
obtained by the following procedure:
Initially, 2,6-dihydroxy alkyl benzoate and a solvent are mixed to obtain a solution
which is then heated to 30 to 80°C. To this solution a base is added to obtain a
mixture which is then stirred for 0.5 to 3 hrs. To this mixture, 4,6-dimethoxy-2-
(methyl sulfonyl) pyrimidine is incorporated to obtain a mass which is heated to
40 to 90°C to obtain alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate.
The process further includes distilling off the solvent under vacuum below 70°C, concentrating alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate followed by cooling, quenching in water, filtration, washing, slurring and drying.
Finally, the obtained alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate is subjected to hydrolysis with at least one alkali metal or alkaline earth metal to obtain Bispyribac- metal salt. In accordance with the present disclosure the alkali metal/ alkaline earth metal is in the form of hydroxide, whereas the alkali metal is in the form of carbonates.
In one embodiment Bispyribac- metal salt is obtained by the following procedure: Initially, alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate and a solvent are mixed. To this at least one alkali metal or alkaline earth metal is added

at 25-50°C to obtain a mass which is then stirred for 2-60 minutes to obtain a stirred mass. Finally, the mass is heated under reflux to obtain Bispyribac- metal salt.
The process further involves cooling of Bispyribac- metal salt, equilibrating, filtering, washing and drying.
In one exemplary embodiment the Bispyribac-metal salt is Bispyribac sodium which is prepared by the following process.
Initially, 2,6-dihydroxy benzoic acid, sodium bicarbonate and a solvent selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and combinations thereof are heated at a temperature of 30 to 100°C to obtain a mixture.
To this mixture, dimethyl sulphate is added over 0.5 to 3 hours and refluxed at 40 tol00°C for a time period of 1 to 10 hours to obtain a reaction mass. The solvent is then distilled off and the reaction mass is concentrated to obtain 2,6-dihydroxy methyl benzoate. The obtained 2,6-dihydroxy methyl benzoate and at least one solvent is selected from the group consisting of dimethyl formamide and acetonitrile are mixed to obtain a solution which is then heated to 30 to 80°C. To this, potassium carbonate is added to obtain a mixture which is stirred for 0.5 to 3 hrs. To this stirred mixture 2,6-dimethoxy-2-(methyl sulfonyl) pyrimidine is incorporated to obtain a mass which is then heated to 40 to 90°C to obtain a heated mass followed by maintaining said mass at 50-90°C for 5-15 hrs. The solvent is then distilled off under vacuum below 70°C and the mass is concentrated. The concentrated mass is then cooled followed by quenching, cooling, filtration, washing, slurring and drying to obtain 2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] methyl benzoate.

The obtained methyl-2,6-bis[(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate (bis ether) and at least one solvent is selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone and methyl isobutyl ketone are mixed to obtain a dispersion. To this dispersion, sodium hydroxide is added at 25 to 50°C to obtain a mass which is then stirred for 2 to 60 minutes to obtain a stirred mass. In the next step, the obtained mass is heated under reflux followed by cooling, equilibrating, filtering, washing and drying to obtain bispyribac sodium.
The disclosure is further illustrated by way of the following non limiting
examples.
Example-1: preparation of 2,6-dihydroxy methylbenzoate
154g of 2,6-dihydroxy benzoic acid was added in 1.5-litre acetone. To this 107.5g of sodium bicarbonate was added and then heated to 40°C. To this, 13 lg dimethyl sulphate was slowly added at 40°C over 2hrs followed by heating to reflux at 55°C. The reaction mass was maintained at reflux for 6hrs. Acetone was then distilled off. The concentrated mass was then cooled, quenched in ice water and further cooled to 10°C. The product thus obtained was filtered and washed with water. The wet product was then dried in an oven below 60°C under vacuum. Yield = 90% (white colored solids) Purity = 98%
Example-2: preparation of 2,6-dihydroxymethylbenzoate
154g of 2,6-dihydroxy benzoic acid was added in 1.5-litre methyl ethyl ketone. To this 107.5g of sodium bicarbonate was added and then heated to 40°C. To this, 13lg dimethyl sulphate was slowly added at 40°C over 2hrs followed by heating to reflux at 55°C. The reaction mass was maintained at reflux for 6hrs. Methyl

ethyl ketone was then distilled off. The concentrated mass was then cooled, quenched in ice water and further cooled to 10°C. The product thus obtained was filtered and washed with water. The wet product was then dried in an oven below 60°C under vacuum.
Yield = 92% (white colored solids) Purity = 98%
Example 3: preparation of 2,6-bis-l(4,6-dimethoxy-2-pyrimidyl)oxy] methyl benzoate:
168g of 2,6-dihydroxy methyl benzoate was taken in 1300ml of N,N'-dimethyl formamide along with 317.4g of potassium carbonate. To this, 436g of 2,6-di-methoxy 2-methyl sulfonyl pyrimidine was added. The obtained mass was heated to 40°C and maintained at 40°C for 7hours. N,N'-dimethyl formamide was then distilled off and 2000ml of water was added to the concentrated mass. The product thus obtained was filtered, washed with water and finally with methanol. The wet product was then dried under vacuum. Yield = 94.7% (Light brown shiny solids) Purity = 98.9%
Example 4: preparation of 2,6-bis-[(4,6-dimethoxv-2-pyrimidyl)oxyl methyl benzoate:
168g of 2,6-dihydroxy methyl benzoate was taken in 1300ml of acetonitrile along with 317.4g of potassium carbonate. To this, 436g of 2,6-di-methoxy 2-methyl sulfonyl pyrimidine was added. The obtained mass was heated to 40°C and maintained at 40°C for 7hours. Acetonitrile was then distilled off and 2000ml of water was added to the concentrated mass. The product thus obtained was filtered,

washed with water and finally with methanol. The wet product was then dried under vacuum.
Yield = 77.5% (Light brown shiny solids) Purity = 96.5%
Example 5: preparation of Bispyribac Sodium
444g of 2,6-bis-[(4,6-dimethoxy-2-pyrimidyI) oxy] methyl benzoate was taken in 2000ml of methyl ethyl ketone along with 500g of 40% sodium hydroxide. The reaction mass was then heated to reflux and maintained at reflux for lOhours. The reaction mass was cooled to 30°C and filtered. The cake was then taken in 2.0 litre MeOH and the pH was adjusted to 2.5 below 10°C using concentrated hydrochloric acid. The product thus obtained was washed with 200ml MeOH twice. The wet product was then dried under vacuum. Yield = 68.0% Purity = 97.0%
Example 6: preparation of Bispyribac sodium
444g of 2,6-bis-[(4,6-dimethoxy-2-pyrimidyl) oxy] methyl benzoate was taken in 2000ml of methyl isobutyl ketone along with 500g of 40% sodium hydroxide. The reaction mass was then heated to reflux and maintained at reflux for lOhours. The reaction mass was cooled to 30°C and filtered. The cake was then taken in 2.0 litre MeOH and the pH was adjusted to 2.5 below 10°C using concentrated hydrochloric acid. The product thus obtained was washed with 200ml MeOH twice. The wet product was then dried under vacuum.
Yield = 55.0%

Purity = 99.0%
"Whenever a range of values is specified, a value up to 10 % below and above the lowest and highest numerical value respectively, of the specified range, is included in the scope of the disclosure".
While considerable emphasis has been placed herein on the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiments as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the forgoing descriptive matter to be implemented merely as illustrative of the disclosure and not as limitation.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these

matters form part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

WE CLAIM;
1. A process for the preparation of Bispyribac-metal salt; said process comprising
the following steps:
i. reacting 2,6-dihydroxy benzoic acid with dialkyl sulphate using a base in a solvent to form 2,6-dihydroxy alkyl benzoate;
ii. condensing 2-(methylsulfonyl)-4,6-dimethoxy pyrimidine with 2,6-dihydroxyalkyl benzoate to obtain alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate; and
iii. subjecting said alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrirnidinyl) oxy] benzoate to hydrolysis with at least one alkali metal or alkaline earth metal to obtain Bispyribac- metal salt.
2. The process as claimed in claim 1, wherein the dialkyl sulphate is selected from the group consisting of dimethyl sulphate, diethyl sulphate, dipropyl sulphate, dibutyl sulphate and dipentyl sulphate, preferably dimethyl sulphate.
3. The process as claimed in claim 1, wherein the base is selected from the group consisting of hydroxides and carbonates of alkali and alkaline earth metals.
4. The process as claimed in claim 1, wherein the base is alkali metal hydroxide selected from the group consisting of lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH) and combinations thereof.
5. The process as claimed in claim 1, wherein the base is an alkaline earth metal hydroxide selected from the group consisting of beryllium hydroxide (66(011)2), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2) and combinations thereof.
6. The process as claimed in claim 1, wherein the base is a carbonate selected from the group consisting of potassium carbonate, sodium carbonate,

potassium bicarbonate, sodium bicarbonate, lithium carbonate, cesium carbonate, barium carbonate, calcium carbonate and combinations thereof.
7. The process as claimed in claim 1, wherein the solvent is selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and combinations thereof.
8. The process as claimed in claim 1, wherein the alkali metal/ alkaline earth metal is in the form of hydroxide.
9. The process as claimed in claim 1, wherein the alkali metal is in the form of carbonates.
10. The process as claimed in claim 1, wherein the step (i) includes heating 2,6-dihydroxy benzoic acid, a base and a solvent at a temperature of 30 to 100°C to obtain a mixture, adding dialkyl sulphate to said mixture over 0.5 to 3 hours and refluxing at 40 tol00°C for 1 to 10 hours to obtain 2,6-dihydroxy alkyl benzoate.
11. The process as claimed in claim 1, wherein the step (i) further includes distilling off the solvent and concentrating 2,6-dihydroxy alkyl benzoate followed by cooling, quenching in ice water, filtering, washing and drying.
12. The process as claimed in claim 1, wherein the 2,6-dihydroxy alkyl benzoate is 2,6-dihydroxy methyl benzoate.
13.The process as claimed in claim 1, wherein the step (ii) includes mixing 2,6-dihydroxy alkyl benzoate and a solvent to obtain a solution, heating said solution to 30 to 80°C, adding a base to said solution to obtain a mixture, stirring said mixture for 0.5 to 3 hrs, incorporating 4,6-dimethoxy-2-(methyl sulfonyl) pyrimidine to said mixture to obtain a mass and heating said mass to 40 to 90°C to obtain alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate.
14. The process as claimed in claim 1, wherein the step (ii) further includes distilling off the solvent under vacuum below 70°C, concentrating alkyl-2, 6-

bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate followed by cooling, quenching in water, filtration, washing, slurring and drying.
15. The process as claimed in claim 1, wherein the step (iii) includes mixing alkyl-2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate and a solvent, adding at least one alkali metal or alkaline earth metal at 25-50°C to obtain a mass, stirring said mass for 2-60 minutes to obtain a stirred mass and heating said mass under reflux to obtain Bispyribac- metal salt.
16. The process as claimed in claim 1, wherein the process step (iii) further comprises cooling of Bispyribac- metal salt, equilibrating, filtering, washing and drying.
17. The process as claimed in claim 1, wherein the Bispyribac-metal salt is Bispyribac sodium; said process comprises the following steps:

- heating 2,6-dihydroxy benzoic acid, sodium bicarbonate and a solvent selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and combinations thereof at a temperature of 30 to 100°C to obtain a mixture,
- adding dimethyl sulphate over 0.5 to 3 hours to said mixture and refluxing at 40 to l00°C for a time period of 1 to 10 hours to obtain a reaction mass, distilling off the solvent and concentrating the reaction mass to obtain 2,6-dihydroxy methyl benzoate;
- mixing 2,6-dihydroxy methyl benzoate and at least one solvent is selected from the group consisting of dimethyl formamide and acetonitrile to obtain a solution, heating said solution to 30 to 80°C, adding potassium carbonate to said solution to obtain a mixture, stirring said mixture for 0.5 to 3 hrs., incorporating 2,6-dimethoxy-2-(methy] sulfonyl) pyrimidine to said mixture to obtain a mass, heating said mass to 40 to 90°C to obtain a heated mass, maintaining said mass at 50-90°C for 5-15 hrs, distilling off the

solvent under vacuum below 70°C, concentrating the mass and cooling the mass followed by quenching, cooling, filtration, washing, slurring and drying to obtain 2, 6-bis [(4,6-dimethoxy-2-pyrimidinyl) oxy] methyl benzoate; and - admixing methyl-2,6-bis[(4,6-dimethoxy-2-pyrimidinyl) oxy] benzoate (bis ether) and at least one solvent is selected from the group consisting of acetone, methyl ethyl ketone, methyl isopropyl ketone and methyl isobutyl ketone to obtain a dispersion, adding sodium hydroxide to said dispersion at 25 to 50°C, to obtain a mass, stirring the mass for 2 to 60 minutes to obtain a stirred mass, heating said mass under reflux followed by cooling, equilibrating, filtering, washing and drying to obtain bispyribac sodium.