Claims:1. A process for the preparation of compound of formula (I)

comprising the steps of:

i) Reacting compound of formula (V) with 2,6-dichloroquinoxaline in a solvent in the presence of a base to obtain compound of formula (II) at a temperature range from 80 to135°C ;

ii) Reacting compound of formula (II) obtained in step (i) with a compound of formula (III) in a solvent or mixture of a solvents in the presence of a base at a temperature range from 25 to 150°C to obtain a compound of formula (I).

2. The process as claimed in claim 1 wherein the solvent used in step (i) or step (ii) is selected from the group consisting of chlorinated hydrocarbons such as dichloromethane (DCM) and ethylene dichloride (EDC); ketones or substituted ketone such as acetone, ethyl methyl ketone (EMK), methyl isobutyl ketone (MIBK) and isopropyl methyl ketone; esters such as ethyl acetate, butyl acetate and isopropyl acetate; aromatic or substituted aromatic hydrocarbons such as toluene, xylene and chloro benzene; polar protic solvents selected from alcohol such as methanol, ethanol, n-propanol, iso propyl alcohol, butyl alcohol, tert-butanol and n-pentanol; polar aprotic solvents such as dimethyl sulfoxide (DMSO), N,N’-dimethylacetamide (DMAC), N,N’-dimethyl formamide (DMF), 2-methyl pyrolidinone (NMP) and hexamethylphosphoramide (HMPA); ether or cyclic ether such as tetrahydrofuran (THF) and methyl tert butyl ether (MTBE); nitrile such as acetonitrile or mixtures thereof.

3. The process as claimed in claim 1 wherein the base used in step (i) or step (ii) is selected from the group consisting of carbonates, hydrides, bicarbonate and hydroxide of alkali and alkaline earth metals selected from sodium carbonate, sodium bicarbonate, potassium carbonate, potassium hydrogen carbonate, sodium hydroxide and potassium hydroxide; organic bases selected from triethylamine (TEA), pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU) and 1,4-diazabicyclo[2.2.2]octane (DABCO), diisopropylethylamine or mixtures thereof.

4. A process for the preparation of compound of formula (II)

comprising the step of:

i) Reacting compound of formula (V) with 2,6-dichloroquinoxaline in a solvent in presence of a base to obtain compound of formula (II) at a temperature range from 80 to 135°C ;

5. The process as claimed in claim 4 wherein the solvent is selected from the group consisting of chlorinated hydrocarbons such as dichloromethane (DCM) and ethylene dichloride (EDC); ketone or substituted ketone selected from acetone, ethyl methyl ketone (EMK), methyl iso-butyl ketone (MIBK) and isopropyl methyl ketone; esters selected from ethyl acetate, butyl acetate and isopropyl acetate; aromatic hydrocarbons selected from toluene, xylene and chloro benzene; polar protic solvents selected from alcohol such as methanol, ethanol, n-propanol, isopropyl alcohol, butyl alcohol, tert-butanol and n-pentanol; polar aprotic solvents selected from dimethyl sulfoxide (DMSO), N,N’-dimethylacetamide (DMAC), N,N’-dimethyl formamide (DMF), 2-methyl pyrolidinone (NMP) and hexamethylphosphoramide (HMPA); ethers or cyclic ether selected from tetrahydrofuran (THF) and methyl tertiary butyl ether (MTBE); nitrile such as acetonitrile or mixture thereof.

6. The process as claimed in claim 4 wherein the base is selected from the group consisting of carbonates, hydrides, bicarbonates and hydroxides of alkali and alkaline earth metals such as sodium carbonate, sodium bicarbonate, potassium carbonate, potassium hydrogen carbonate, sodium hydroxide, potassium hydroxide or mixture thereof.
, Description:FIELD OF INVENTION

The present invention relates to a novel and improved process for the synthesis of 2-isopropylidenaminoxyethyl (R)-2-[4-(6-chloroquinoxalin-2-yloxy)-phenoxy]propionate (Propaquizafop). The present invention more particularly relates to a novel and improved process for manufacturing of 4-(6-chloroquinoxalin-2-yl) oxyphenol by reacting monoacetyl hydroquinone with 2,6-dichloroquinoxaline.

BACKGROUND OF THE INVENTION

Propaquizafop is systemic herbicide used to control annual and perennial grasses. It is applied as a foliar spray. It is quickly absorbed through the leaves and translocated to the meristematic growing regions of the plants, where it inhibits cell growth and division through the inhibition of ACCase inhibition. Propaquizafop can be used on a wide range of broad-leaved crops, including sugarbeet, oilseed rape, soybeans, sunflower, other field crops, vegetables, fruit trees, vineyards and forestry.

US4687849 discloses a process for producing 2-isopropylidene aminoxyethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises reacting 2-isopropylidene aminoxyethyl L(-)-2-(p-toluenesulfonyl)oxypropionate with 4-(6-chloro-2-quinoxalyloxy)phenol, a process for producing 2-isopropylidene aminoxyethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises reacting 2-isopropylidene aminoxyethyl D(+)-2-(4-hydroxyphenoxy)propionate with 2,6-dichloroquinoxaline and a process for producing 2-isopropylideneaminoxyethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises reacting D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionic acid chloride with 2-isopropylidene aminoxyethanol.

The process disclosed in US4687849 makes use of carcinogenic solvents such as benzene and low boiling solvents such as diethyl ether which are not a viable option at industrial scale. Reagents such as diethyl azodicarboxylate and calcium lactate used in the process are not cost effective. The yield is significantly low making the process unviable on an industrial scale.

EP0276741 discloses a process for producing 2-isopropylidene aminoxyethyl D (+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises reacting 2-isopropylidene aminoxyethyl L (-)-2-(p-toluenesulfonyl) oxypropionate with 4-(6-chloro-2-quinoxalyloxy) phenol.

The Process disclosed in EP0276741 involves the use of expensive, commercially unavailable and hazardous reagents. The process involved is not again feasible at higher scale.

Nippon Kagaku Kaishi, The Chemical Society of Japan, p. 253, vol-4 (1991) discloses a process for producing ethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises reacting an alkali metal salt of 4-(6-chloro-2-quinoxalyloxy)phenol with ethyl L-2-chloropropionate.

The process disclosed in Nippon Kagaku Kaishi, The Chemical Society of Japan, p. 253, vol-4 (1991) is not necessarily industrially satisfactory for producing a product of high optical purity on an industrial scale.

JP-A-7-278047 discloses a process for producing D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionic acid, which comprises reacting an alkali metal salt and/or an alkaline earth metal salt of 4-(6-chloro-2-quinozalyloxy)phenol with an alkaline earth metal salt of L-2-chloropropionic acid.

JP-A-7-278047 discloses that in the reaction of an alkali metal salt of 4-(6-chloro-2-quinoxalyloxy) phenol with an alkali metal salt of L-2-chloropropionic acid, the reaction is terminated at a conversion of about 50% due to a side-reaction because of which the yield is very low. The same publication also discloses that a barium salt is particularly preferred as the alkali salt and/or the alkaline earth metal salt. However, use of barium salt results in a large amount of barium-related compounds as typical by-products, making it necessary to develop a more efficient production process.

JP-B-7-25753 discloses a process for producing tetrahydrofurfuryl 2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises reacting tetrahydrofurfuryl 2-bromopropionate with 2-(4-hydroxyphenoxy)-6-chloroquinoxaline.

JP-A-4-295469 discloses a process for producing 2-isopropylidene aminoxyethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises an ester exchange reaction of ethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate obtained by a reaction of 2,6-dichloroquinoxaline with ethyl D(+)-2-(4-hydroxyphenoxy)propionate.

US6136977 discloses a process for producing ethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate, which comprises reacting D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionic acid with diethyl sulfate, a process for producing tetrahydrofurfuryl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate which comprises reacting D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionic acid with tetrahydrofurfuryl alcohol and a process for producing isopropylidene aminoxyethyl D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate which comprises reacting D(+)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionic acid with isopropylidene aminoxyethanol.

US6136977 discloses reaction of 2,6-dichloroquinoxaline with hydroquinone in an aromatic hydrocarbon solvent in the presence of an alkali metal hydroxide and aprotic polar solvent to obtain alkali metal salt of 4-(6-chloroquinoxalin-2-yl)oxyphenol, compound of formula II of the present invention. The process involves the use of a mixture of two solvents and reactions are carried out at reduced pressure.

Problem identified
The present inventors have observed that reaction of 2,6-dichloroquinoxaline with hydroquinone in aromatic hydrocarbons solvent in presence of an alkali metal hydroxide led to the formation of dimer impurity (1,4-bis (6-chloro-quinoxalinyl-2-oxy)benzene) at significant levels in compound of formula II. The impurity is carried forward to the final propaquizafop which led to low yield and low purity of propaquizafop. It is observed that on carrying out the reaction by the process disclosed in US6136977, dimer impurity formed in compound of formula II is between 20 to 25% which was then subsequently found in propaquizafop at level of more than 5%.

Solution provided by the present invention

The present inventors have conducted an extensive research to solve the above mentioned problem and as a result, surprisingly have developed a method for producing Propaquizafop (hereinafter referred as compound I) having high purity and good yield which comprises reacting 4-(6-chloroquinoxalin-2-yl)oxyphenol (hereinafter referred as compound II) with 2-isopropylidene aminoxyethyl L(-)-2-(p-toluenesulfonyl)oxypropionate (hereinafter referred as compound III) in the presence of a solvent and a base.

The present inventors have found that using the process of the present invention, compound (II) and compound (III) can be produced in good yield. Compound (II) can be prepared by reacting a compound of formula (V) with 2,6-dichloroquinoxaline using various bases. Because of the use of a compound of formula (V) in place of hydroquinone, the formation of dimer impurity can be controlled unlike as observed in the reaction of hydroquinone with 2,6-dichloroquinoxaline in the literature. The dimer impurity is 1,4-bis (6-chloro-quinoxalinyl-2-oxy)benzene.

Dimer impurity
There is no or very low possibility of formation of dimer impurity in the process of the present invention. The process of the present invention controls the formation of dimer impurity during synthesis of compound (II) which is subsequently used in the preparation of propaquizafop. According to the process of the present invention, level of dimer impurity in compound of formula (II) is not more than 0.30% (by HPLC). Propaquizafop thus prepared by the process of the present invention is either free from dimer impurity or contains a very low level of dimer impurity and having a good yield. According to the process of the present invention, level of dimer impurity is not more than 0.39% (by HPLC) in propaquizafop. The process of the present invention is novel, inventive and suitable for industrial scale production as it involves non-hazardous and commercially available reagents and solvents.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a novel and improved process for the preparation of 2-isopropylidenaminoxyethyl (R)-2-[4-(6-chloroquinoxalin- 2-yloxy)-phenoxy] propionate (Propaquizafop), compound of formula (I) having high purity and good yield.

It is another object of the present invention to provide a novel and improved process for the preparation of 2-isopropylidenaminoxyethyl (R)-2-[4-(6-chloroquinoxalin- 2-yloxy)-phenoxy] propionate (Propaquizafop), compound of formula I either free from dimer impurity or below its threshold value, wherein the dimer impurity is 1,4-bis (6-chloro-quinoxalinyl-2-oxy)benzene.

It is another object of the present invention to provide a novel and improved process for the preparation of 4-(6-chloroquinoxalin-2-yl)oxyphenol, compound of formula II having high purity in good yield.

It is yet another object of the present invention to provide a novel and improved process for the preparation of 4-(6-chloroquinoxalin-2-yl)oxyphenol, compound of formula II either free from dimer impurity or it is below its threshold value, wherein the dimer impurity is 1,4-bis (6-chloro-quinoxalinyl-2-oxy)benzene.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a process for the preparation of compound of formula (I)

comprising the steps of:

i) Reacting compound of formula (V) with 2,6-dichloroquinoxaline in a solvent in the presence of a base to obtain compound of formula (II) at a temperature range from 80 to135°C ;

ii) Reacting compound of formula (II) obtained in step (i) with a compound of formula (III) in a solvent or mixture of solvents in the presence of a base at a temperature range from 25 to 150°C to obtain a compound of formula (I).

According to another aspect of the present invention there is provided a process for process for the preparation of compound of formula (II)

comprising the step of:

i) Reacting compound of formula (V) with 2,6-dichloroquinoxaline in a solvent in presence of a base to obtain compound of formula (II) at a temperature range from 80 to135°C.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a novel and improved process for the synthesis of 2-isopropylidenaminoxyethyl (R)-2-[4-(6-chloroquinoxalin-2-yloxy)-phenoxy] propionate (Propaquizafop). The present invention further relates to a novel and improved process for manufacturing of 4-(6-chloroquinoxalin-2-yl) oxyphenol by reacting monoacetyl hydroquinone with 2,6-dichloroquinoxaline.

In an embodiment of the present invention, there is provided a process for preparation of propaquizafop, compound of the formula (I)

comprising the steps of:

a. Oxidation of compound of formula (IV) in a suitable solvent selected from chlorinated hydrocarbons such as dichloromethane(DCM), ethylene dichloride (EDC), chloroform and carbon tetrachloride; esters selected from ethyl acetate, isopropyl acetate and butyl acetate; one or more oxidizing agent selected from hydrogen peroxide, m-chloro perbenzoic acid (m-CPBA), oxone and tert-butyl hydrogen peroxide (TBHP) with acid such as acetic acid, benzoic acid, substituted benzoic acid, trifluoroacetic acid, formic acid or with its peracids to obtain compound of formula (V); The reaction is carried out at a temperature between -10 to 60°C, preferably at 35-45°C.

wherein R is selected from hydrogen, alkyl, aryl or substituted alkyl or aryl group having straight or branch C1-C4 carbon chain.

b. Reacting compound of formula (V) with 2,6-dichloro quinoxaline in a suitable solvent selected from chlorinated hydrocarbons such as dichloromethane (DCM) and ethylene dichloride (EDC); ketone or substituted ketones selected from acetone, ethyl methyl ketone (EMK), methyl iso-butyl ketone (MIBK) and isopropyl methyl ketone (PMK); esters selected from ethyl acetate, butyl acetate and isopropyl acetate; aromatic hydrocarbons selected from toluene, xylene and chloro benzene; polar protic solvents selected from alcohol such as methanol, ethanol, n-propanol, isopropyl alcohol, butyl alcohol, tert-butanol and n-pentanol; polar aprotic solvents selected from dimethyl sulfoxide (DMSO), N,N’-dimethylacetamide (DMAC), N,N’-dimethyl formamide (DMF), 2-methyl pyrolidinone (NMP) and hexamethylphosphoramide (HMPA); ethers or cyclic ether selected from tetrahydrofuran (THF) and methyl tert. butyl ether (MTBE); nitrile such as acetonitrile or mixtures thereof and one or more bases selected from carbonates, hydrides, bicarbonates and hydroxides of alkali and alkaline earth metals such as sodium carbonate, sodium bicarbonate, potassium carbonate, potassium hydrogen carbonate, sodium hydroxide and potassium hydroxide to obtain compound of formula (II); The reaction is carried out at a temperature between 80 to 135°C, preferably at 110-125 °C;

c. Reacting ethylene carbonate with acetone oxime in presence of a base selected from pyridine, N-methyl morpholine, triethylamine (TEA), diisopropylethylamine, 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) and 1,4-diazabicyclo[2.2.2]octane (DABCO) in aromatic hydrocarbons such as toluene and xylene. The reaction is carried out at a temperature between 75°C and 125°C preferably between 100 and 125°C. Product purifies by fractional distillation at reduced pressure. Alternatively, reacting acetone oxime with 2-chloro ethanol in a suitable solvent selected from alcohols such as methanol, ethanol and isopropyl alcohol; polar aprotic solvents such as dimethyl sulfoxide (DMSO), N,N’-dimethylformamide (DMF) and N,N’-dimethylacetamide (DMAC), water and one or more base selected from carbonate, hydrides, bicarbonate and hydroxide of various alkali and alkaline earth metals such as sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium hydrogen carbonate and potassium hydroxide; organic bases selected from pyridine, N-methyl morpholine, triethylamine (TEA) and diisopropylethylamine to obtain oximeglycol; The reaction is carried out at a temperature between -5 and 100°C, preferably at 25-30°C.
d. Reacting the oximeglycol obtained in step (c) above with (S)-lactic acid in a suitable solvent selected from toluene, xylene and chloro benzene; mineral acids selected from HCl, HBr and H2SO4; organic acids selected from p-toluene sulfonic acid, methane sulphonic acid, acetic acid and formic acid to obtain lactate ester of formula (IIIa); The reaction is carried out at a temperature between 25 and 150°C. Preferably at 120-140°C.

e. Protecting the lactate ester of formula (IIIa) obtained in step (d) above in a suitable solvent selected from chlorinated solvents such as dichloromethane (DCM) and ethylene dichloride (EDC); ketones selected from acetone, ethyl methyl ketone and methyl isobutyl ketone (MIBK); esters selected from ethyl acetate, isopropyl acetate and butyl acetate; polar aprotic solvent selected from dimethyl sulfoxide (DMSO), N,N’-dimethylformamide (DMF) and N,N’-dimethylacetamide (DMAC) to obtain compound of formula (III); organic bases selected from triethylamine (TEA), pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,4-diazabicyclo[2.2.2]octane (DABCO) to accelerate the protection to obtain protected (IIIa). The reaction is carried out at a temperature between -5 and 25°C preferentially at 20-25°C.

f. Reacting compound of formula (II) obtained in step (b) above with a compound of formula (III) obtained in step (e) above in a suitable solvent selected from chlorinated solvents such as dichloromethane (DCM) and ethylene dichloride (EDC); ketones or substituted ketones such as acetone, ethyl methyl ketone(EMK) and methyl isobutyl ketone (MIBK); esters such as ethyl acetate, butyl acetate and isopropyl acetate; aromatic hydrocarbons such as toluene, xylene and chloro benzene; polar protic solvents selected from alcohols such as methanol, ethanol, n-propanol isopropyl alcohol, tert-butanol, butyl alcohol and n-pentanol; polar aprotic solvents such as dimethyl sulfoxide (DMSO), N,N’-dimethylacetamide (DMAC), N,N’-dimethylformamide (DMF), 2-methyl pyrolidinone (NMP) and hexamethylphosphoramide (HMPA); ether or cyclic ether such as tetrahydrofuran (THF) and methyl tert butyl ether (MTBE); nitrile such as acetonitrile or mixtures thereof, with the addition of one or more bases selected from carbonates, hydrides, bicarbonate and hydroxide of various alkali and alkaline earth metals selected from sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium hydrogen carbonate and potassium hydroxide; organic bases selected from triethylamine (TEA), pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,4-diazabicyclo[2.2.2]octane (DABCO), diisopropylethylamine to obtain compound of formula (I); The reaction is carried out at a temperature between 25 and 150°C, preferably at 80-100°C.

In an embodiment of the present invention, acid used in step a. for oxidation is formic acid and the oxidizing agent is hydrogen peroxide.

In another embodiment of the present invention, step b. is carried out in DMF as a solvent and potassium carbonate as a base and wherein the optimum temperature for the reaction is 110-125°C.

The compound of formula (II) obtained in step b. is either free from dimer impurity or it is below its threshold value, wherein the dimer impurity is 1,4-bis (6-chloro-quinoxalinyl-2-oxy)benzene. The formation of dimer impurity is controlled during the preparation of a compound of formula (II).

In another embodiment of the present invention, step f. is carried out in acetonitrile as a solvent and potassium carbonate as a base and wherein optimum temperature required for conducting the reaction is 80 to 85°C.

The Scheme of the present invention is as follow:

The compound of the formula (I) can be purified further by standard methods, for example by recrystallization using a suitable solvent. A suitable solvent is non-polar hydrocarbon and/or mixture of non-polar hydrocarbon such as pentane, hexanes, heptane and octane, polar protic solvents such as methanol, ethanol, isopropyl alcohol, n-butyl alcohol, tert-butyl alcohol, pentanol or mixture of non-polar hydrocarbons with polar protic solvents such as mixture of heptane and isopropyl alcohol, heptane and ethanol etc.

In an embodiment of the present invention, compound of formula (I) is recrystallized using various aliphatic non-polar solvents such as pentane, hexanes, heptane and octane and its mixture; polar protic solvents such as methanol, ethanol, n-propanol, isopropyl alcohol, propanol and Butanol; mixture of non-polar solvent with polar solvent such as mixture of heptane and isopropyl alcohol; mixture of alcohols and ethers such as mixture of isopropyl alcohol and diisopropyl ether at temperature ranges from -5°C to 82°C.
In another embodiment of the present invention, the solvent used for recrystallization of propaquizafop is isopropyl alcohol and the temperature ranges from -5 to 82 °C.

Propaquizafop prepared by the process of the present invention is either free from dimer impurity or is below its threshold value, wherein the dimer impurity is 1,4-bis (6-chloro-quinoxalinyl-2-oxy)benzene.

The examples below serve to illustrate the invention and are not to be understood as limiting it.

Examples:

EXAMPLE 1: Preparation of compound of formula (II): 4-(6-chloroquinoxalin-2-yl) oxyphenol

Step 1: Preparation of Monoacetyl hydroquinone

To a mixture of 4’-hydroxy acetophenone (125 g, 0.918 mol) and formic acid (85%) (375 ml, 3T/v) was dropwise added hydrogen peroxide (30% w/v) (125 ml, 1.102 mol) at 25-35°C. The reaction mass was stirred for 3-5 h at 35-40°C. Progress of the reaction was monitored by HPLC. On completion of the reaction, ethyl acetate (1250 ml) and water (1250 ml) were added to the reaction mass, stirred for 10-15min and layers were separated. Ethyl acetate layer was washed with water (1250 ml) followed by 10% aq. sodium bicarbonate solution (1250ml, 10T/v), 2.5% Aq. sodium thiosulphate solution (1250ml, 10T/v), 10% brine solution (1250ml, 10T/v). Ethyl acetate was distilled off under reduced pressure at 35-45°Cto get monoacetyl hydroquinone 106 g (76% yield).

Step 2: 4-(6-Chloroquinoxalin-2-yl)oxyphenol,

To a mixture of 2,6-dichloroquinoxaline (50g, 0.251mol) and monoacetyl hydroquinone obtained in step-1 (53.4 g, 0.351 mol) in DMF (250ml) was charged powdered potassium carbonate (69.41g, 0.502 mol) at 25-35°C. The reaction mass was stirred for 10-12 h at 120-125°C. Progress of the reaction was monitored by HPLC. On completion of the reaction, the reaction mass was added to water (2500ml) and stirred for 2h at 20-25°C. The reaction product was filtered and washed with water (1200ml). The said product was air dried till constant weight is achieved. The said product was dissolved in DMF (620 ml) and treated with activated charcoal. The filtrate was added to water (6200 ml) and stirred for 2-3h at 20-25°C. Product was filtered and washed with water (3100 ml). The product was air dried for 14-16h at 50-55°C to get pure 4-(6-chloroquinoxalin-2-yl)oxyphenol, compound of formula (II) (54.8 g, 88% yield, Purity: 98.73% by HPLC).

EXAMPLE 2: Preparation of 2-[(isopropylideneamino)oxy]ethanol; compound of formula (III):

Step 1: Preparation of oximeglycol

To a solution of ethylene carbonate (276g, 3.13mol) and DBU (25g, 0.164 mol) in toluene (500 ml) was added solution of acetone oxime (200g, 2.73 mol) at 80-110°C. Reaction mixture was stirred for 3-4h at reflux temperature. The progress of the reaction was monitored by GC analysis. Upon completion of the reaction, toluene was distilled off at reduced pressure at 50-60°C. Crude compound was subjected to fractional distillation at reduced pressure to obtain oximeglycol (251g, 78% yield).

An alternate process for the synthesis of an oximeglycol:

To an aqueous solution of sodium hydroxide [(32.87 g, 0.821 mol) in water (100 ml (2T/v)] was charged acetone oxime (50 g, 0.684 mol) and 2-chloroethanol (80.5 g, 0.821 mol) at 0-15°C. Reaction mass was stirred for 10-15 h at 25-35°C. Progress of reaction was monitored by TLC. On completion of the reaction, to the reaction mass was added toluene (250 ml) and water in reaction mass was removed by azeotropic distillation. Inorganic salts in reaction mass were filtered off and washed with toluene (100 ml). The filtrate was concentrated under reduced pressure to obtain oximeglycol (67 g, 83% yield).

Step 2: Preparation of 2-[(isopropylideneamine) oxy]-ethyl-L-(-)-lactate; Compound of formula (IIIa)

To a solution of oximeglycol obtained in step-1 of example-2 (200 g, 1.70 mol) and (S)-lactic acid (176 g, 1.95 mol) in toluene (2000 ml, 10T/v) was added conc. sulphuric acid (33.4 g, 0.341 mol) at 25-35°C. In the course of the reaction, water was azeotropically removed for 4-6h. The progress of the reaction was monitored by GC. On completion of reaction, Toluene was distilled off at reduced pressure at 50-60°C to get crude 2-[(isopropylideneamine)oxy]-ethyl-L-(-)-lactate which was further subjected to fractional distillation at reduced pressure to get pure 2-[(isopropylideneamine)oxy]-ethyl-L-(-)-lactate (102g, 32% yield).

Step 3: Preparation of 2-isopropylidene aminoxyethyl L(-)-2-(p-toluenesulfonyl)oxypropionate; Compound of formula (III):

To a solution of compound of formula (IIIa) obtained from step 2 of example-2 (50 g, 0.264 mol), triethyl amine (40 g, 0.396 mol), DMAP (6.45g, 0.0528 mol) in dichloromethane (500 ml) was added p-toluene sulphonyl chloride (60.4g, , 0.316 mol) in small portions at 0-5°C. Reaction mass was stirred for 3-5 h at 20-30°C. Progress of reaction was monitored by HPLC. On completion of the reaction, the reaction mass was cooled and its pH was adjusted to 1-2 using 2N HCl (50 ml) after adding water (300ml). Dichloromethane layer was washed with aq. 10% sodium bicarbonate solution (300 ml), water (300 ml) and 10% brine solution (300 ml). Dichloromethane was distilled off under reduced pressure to obtain compound of formula (III) (87g, 80% yield).

EXAMPLE 3: Preparation of compound of formula (I): Propaquizafop

To a solution of compound of formula (II) obtained in example 1 (50 g, 0.183 mol) and compound of formula (III) obtained in step-3 of example 2 (68 g, 0.198 mol) in acetonitrile (1000 ml) was added powdered potassium carbonate (75 g, 0.54 mol) at 25-35°C. Reaction mass was stirred for 8-10 h at 75-85°C. Progress of reaction was monitored by HPLC. On completion of the reaction, inorganic salts were filtered off and washed with acetonitrile (2*200 ml). Acetonitrile in the filtrate was distilled off under reduced pressure at 40-45°C. Compound of formula (I) was obtained by extractive work up using ethyl acetate. Activated charcoal treatment was given to ethyl acetate layer. Ethyl acetate was distilled off at reduced pressure at 40-45°C to get the crude compound of formula (I) (89g). Crude compound of formula (I) was recrystallized using isopropyl alcohol (300ml) to obtain a pure compound of formula (I) (51g, 62% yield, Purity: 98.30% by HPLC)