WO2010023679A2

WO2010023679A2 - Preparation of triclopyr, its intermediate and butoxyethyl ester

Info

Publication number: WO2010023679A2
Application number: PCT/IN2008/000830
Authority: WO
Inventors: Dipesh Kantisen Shroff; Ashwin Champraj Shroff; Samir Pradip Dave; Ashok Kundanmal Jain; Rajendra Pralhad Chaudhari; Kaushik Ratilal Joshi; Prashant Nanubhai Shihora; Jaywant Govind Hatim; Bhakti Rajesh Thakkar; Ashit Pradip Dave
Original assignee: Excel Crop Care Limited; C C Shroff Research Institute; Aimco Pesticides Limited
Priority date: 2008-09-01
Filing date: 2008-12-10
Publication date: 2010-03-04
Also published as: WO2010023679A3

Abstract

This invention relates to process for preparation of Triclopyr, Triclopyr- butoxyethyl ester & its intermediate viz. 2-butoxyethyl chloroacetate. Triclopyr is prepared by hydrolysis of its alkyl esters. Triclopyr- butoxyethyl ester is prepared by reaction of triclopyr and 2-butoxyethanol in presence of a catalyst. Triclopyr-butoxyethyl ester is also prepared by transesterification from alkyl esters of Triclopyr. 2-butoxyethyl chloroacetate is prepared by reaction of chloroacetic acid and 2-butoxyethanol in presence of a catalyst.

Description

PREPARATION OF TRICLOPYR, ITS INTERMEDIATE AND BUTOXYETHYL ESTER

FIELD OF INVENTION

This invention relates to process for preparation of herbicidal Triclopyr, its intermediate viz. 2-butoxyethyl ester of chloroacetic acid, and butoxyethyl ester of Triclopyr.

BACKGROUND AND PRIOR ART

Triclopyr is a selective systemic herbicide which is used for control of broadleaf weeds and woody plants in grasslands, parklands, along rights- of- way, forests etc. It is used as ester or salt such as triclopyr butoxyethyl ester, triclopyr ethyl ester and triclopyr triethylammonium salt.

Cava et al. have reported preparation of triclopyr in only 17% yield by hydrolysis of its ethyl ester which was prepared from N2CHCO2C2H5 and halogenated 2-pyridone [Journal of Organic Chemistry (1958), 23, 1614- 16].

Dow Chemical Co. has reported in the patent US3862952 a process for preparation of triclopyr by treating 2,3,5,6-Tetrachloropyridine with paraformaldehyde in Mβ2SO containing KCN followed by hydrolysis to obtain triclopyr. Use of cyanide is a disadvantage of this method.

Oxidation of pyridine and quinoline bases and its use for the production of pyridinecarboxylic acids such as triclopyr has been reported in Chemicke Listy pro Vedu a Prumysl (1961), 55, 1199-209. This method involves an additional step involving oxidation of the pyridine base.

The inventors of present invention have developed a novel process for preparation of Triclopyr by hydrolysis of Triclopyr esters with improved yield and purity compared to the prior art processes.

A process for preparation of butoxyethyl ester of chloroacetic acid, which is an intermediate for synthesis of Triclopyr has been disclosed in US2452350. This method involves catalytic esterification using mineral acid as catalyst. However, impurities are formed in this process.

The inventors of present invention have developed a process for preparation of abovementioned intermediate (butoxyethyl ester of chloroacetic acid) with improved purity.

A method for preparation of triclopyr-butoxyethyl ester has been reported in Indian patent 197707 wherein triclopyr-butoxyethyl ester is obtained in 82% yield and 92% purity by reacting sodium 3,5,6- trichloropyridinate with 2 -butoxyethyl chloroacetate in a solvent medium in presence of a phase transfer catalyst, removing solvent by distillation and distilling triclopyr butoxyethyl ester under vacuum. This method involves carrying out reaction in presence of solvent which consumes more energy and results in greater losses of solvent during reaction than if reaction would have been carried out without- solvent. Moreover, the yield is low and it requires distillation of not only solvent, but also the product to achieve the desired purity of the product.

The inventors of this invention have developed a process for preparation of triclopyr-butoxyethyl ester wherein the reaction between sodium salt of 3,5,6-trichloro~2-pyridinol and 2-butoxyethyl ester of chloroacetic acid is carried out in presence of catalyst without solvent, thereby avoiding extra consumption of energy and solvent losses during reactio'n. The process of present invention though requires solvent for separation of the product after reaction, the quantity required thereof is very less compared to the process of prior art.

A novel process for preparation of triclopyr-butoxyethyl ester in more than 96% yield by trans-esterification from lower alkyl esters of triclopyr has also been developed in the present invention.

OBJECTS OF INVENTION

It is an object of this invention to provide an efficient process for preparation of Triclopyr by hydrolysis of Triclopyr-alkyl esters.

Another object of invention is to provide an efficient process for preparation of Triclopyr-butoxyethyl ester from Triclopyr and 2- butoxyethanol.

Another object of invention is to provide an efficient process for preparation of Triclopyr-butoxyethyl ester by transesterification from Triclopyr-alkyl ester.

Another object of invention is to provide an efficient process for preparation of Triclopyr-butoxyethyl ester by reaction of 2-butoxyethyl ester of chloroacetic acid with sodium salt of 3,5,6-trichloro-2-pyridinol in presence of a catalyst, which obviates the need to carry out reaction in presence of any solvent, and thereby avoiding solvent losses during the reaction and reducing energy consumption. Another object of invention is to provide a process for preparation of Triclopyr-butoxyethyl ester in good yield compared to the process of prior art, without need for distillation of the product.

Another object of invention is to provide an efficient process for preparation of an intermediate for triclopyr viz. 2-butoxyethyl chloroacetate, from chloroacetic acid and 2-butoxyethanol.

SUMMARY OF INVENTION

This invention relates to novel processes for preparation of herbicidal Triclopyr, its intermediate viz. butoxyethyl ester of chloroacetic acid, and butoxyethyl ester of Triclopyr. Triclopyr is prepared by hydrolysis of its lower alkyl esters. Butoxyethyl ester of Triclopyr is prepared by reaction of 2-butoxyethyl chloroacetate with sodium salt of 3,5,6-trichloro-2- pyridinol. Butoxyethyl ester of Triclopyr is also prepared by transesterification from ethyl- or methyl-ester of triclopyr. A novel process for preparation of butoxyethyl ester of Triclopyr by reaction of Triclopyr with 2-butoxyethanol has also been disclosed.

DETAILED DESCRIPTION OF INVENTION

Preparation of Triclopyr By Hydrolysis of its alkyl esters:

As per an embodiment of the present invention, Triclopyr can be prepared by hydrolysis of its alkyl ester by heating the slurry of alkyl ester of Triclopyr with an alkali.

Though hydrolysis can be carried out in presence of any alkali, the preferred alkali is NaOH for convenience and economic reasons. Since it is inherent property of NaOH to absorb water and it has tendency to partially convert into bicarbonate and carbonate when exposed to atmospheric CO2, excess weight may be considered to compensate for the same.

The colour of the product is improved by adding an oxidizing agent such as NaOCl or H2O2. The oxidizing agent should be added after cooling the reaction mass to room temperature.

Details of process for preparation of Triclopyr by hydrolysis of its alkyl esters is given hereunder.

Preparation of Triclopyr By Hydrolysis of Methyl Ester of Triclopyr:

Methyl ester of triclopyr was prepared by process disclosed in US3969360. Methyl ester was then hydrolyzed to Triclopyr by heating a slurry of said ester in water with an alkali, cooling the reaction mass to room temperature, adding NaOCl or H2O2 for oxidation of impurities and colour improvement, acidifying the mass with a mineral acid, e.g., sulfuric acid or an organic acid, e.g., acetic acid to pH 1-2 to obtain precipitate of the product, and filtration thereof.

As mentioned earlier, the color of the product is improved by adding a decolorising agent such as NaOCl or H2O2 (30%). The decolorising agent should be added after cooling the reaction mass to room temperature.

The product is finally precipitated by acidifying the reaction mass to pH 1-2 with a mineral acid like H2SO4 or an organic acid like acetic acid. The yield obtained is found to be better when a mineral acid is used.

The purity of the product obtained by this process is >98%. EXAMPLE-I

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.351 moles of triclopyr-methyl ester was taken. Water was added to make 10% aqueous slurry. 16.85 g (0.421 moles) of NaOH was added. The slurry was heated to 80-85⁰C for four hours. The reaction mass was then cooled to room temperature. 85 ml 4% NaOCl solution was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with sulfuric acid to get white precipitate which was filtered and dried to obtain product in 94% yield.

EXAMPLES 2 & 3

The process as described in Example- 1 above was repeated except the molar ratio of triclopyr-methyl to NaOH was changed. The results are tabulated in the following Table.

EXAMPLE-4

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.351 moles of triclopyr-methyl ester was taken. Water was added to make 10% aqueous slurry. 16.85 g (0.421 moles) of NaOH was added. The slurry was heated to 80-85⁰C for four hours. The reaction mass was then cooled to room temperature. 70 ml H2O2 was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with sulfuric acid to get white precipitate which was filtered and dried to obtain product in 94.2% yield.

EXAMPLES 5 & 6

The process as described in Example-4 above was repeated except the molar ratio of triclopyr to NaOH was changed. The results are tabulated in the following Table.

EXAMPLE-7

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.351 moles of triclopyr-methyl ester was taken. Water was added to make 10% aqueous slurry. 16.85 g (0.421 moles) of NaOH was added. The slurry was heated to 80-85⁰C for four hours. The reaction mass was then cooled to room temperature. 85 ml 4% NaOCl solution was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with acetic acid to get white precipitate which was filtered and dried to obtain product in 83% yield. EXAMPLES 8 & 9

The process as described in Example-7 above was repeated except the molar ratio of triclopyr to NaOH was changed. The results are tabulated in the following Table.

EXAMPLE-10

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.351 moles of triclopyr-methyl ester was taken. Water was added to make 10% aqueous slurry. 16.85 g (0.421 moles) of NaOH was added. The slurry was heated to 80-85⁰C for four hours. The reaction mass was then cooled to room temperature. 70 ml H2O2 was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with acetic acid to get white precipitate which was filtered and dried to obtain product in 82.8% yield.

EXAMPLES 11 & 12

The process as described in Example- 10 above was repeated except the molar ratio of triclopyr to NaOH was changed. The results are tabulated in the following Table.

Preparation of Triclopyr By Hydrolysis of Ethyl Ester of Triclopyr:

Ethyl ester of triclopyr was prepared by process disclosed in US4701531. Ethyl ester was then hydrolyzed to Triclopyr by . heating a slurry of said ester in water with an alkali, cooling the reaction mass to room temperature, adding NaOCl or H2O2 for oxidation of impurities and colour improvement, acidifying the mass with a mineral acid e.g., sulfuric acid or an organic acid e.g., acetic acid to pH 1-2 to obtain precipitate of the product, and filtration thereof. The purity of the product obtained by this process is >98%.

EXAMPLE- 13

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.404 moles of triclopyr- ethyl ester was taken. Water was added to make 10% aqueous slurry. 19.42 g (0.485 moles) of NaOH was added. The slurry was heated to 80⁰C for 3.5 hours. The reaction mass was then cooled to room temperature. 115 ml 4% NaOCl solution was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with sulfuric acid to get white precipitate which was filtered and dried to obtain product in 93% yield. EXAMPLES 14 85 15

The process as described in Example- 13 above was repeated except the molar ratio of triclopyr-ethyl to NaOH was changed. The results are tabulated in the following Table.

EXAMPLE- 16

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.404 moles of triclopyr-ethyl ester was taken. Water was added to make 10% aqueous slurry. 19:42 g (0.485 moles) of NaOH was added. The slurry was heated to 80⁰C for 3.5 hours. The reaction mass was then cooled to room temperature. 95 ml H2O2 was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with sulfuric acid to get white precipitate which was filtered and dried to obtain product in 92.5% yield.

EXAMPLES 17 85 18

The process as described in Example- 16 above was repeated except the molar ratio of triclopyr-ethyl to NaOH was changed. The results are tabulated in the following Table.

EXAMPLE- 19

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.404 moles of triclopyr-ethyl ester was taken. Water was added to make 10% aqueous slurry. 19.42 g (0.485 moles) of NaOH was added. The slurry was heated to 80⁰C for 3.5 hours. The reaction mass was then cooled to room temperature. 115 ml 4% NaOCl solution was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with acetic acid to get white precipitate which was filtered and dried to obtain product in 75% yield.

EXAMPLES 20 & 21

The process as described in Example- 19 above was repeated except the molar ratio of triclopyr-ethyl to NaOH was changed. The results are tabulated in the following Table.

EXAMPLE-22

In a reactor equipped with a mechanical stirrer, thermometer pocket and reflux condenser, 0.404 moles of triclopyr-ethyl ester was taken. Water was added to make 10% aqueous slurry. 19.42 g (0.485 moles) of NaOH was added. The slurry was heated to 80⁰C for 3.5 hours. The reaction mass was then cooled to room temperature. 95 ml H2O2 was added and mixture was stirred for 30 min. The reaction mass was then acidified to pH 1-2 with acetic acid to get white precipitate which was filtered and dried to obtain product in 74.45% yield.

EXAMPLES 23 & 24

The process as described in Example-22 above was repeated except the molar ratio of triclopyr-ethyl to NaOH was changed. The results are tabulated in the following Table.

Preparation of Triclopyr-Butoxyethyl ester from triclopyr and 2-butoxyethanol

Triclopyr-butoxyethyl ester is prepared by reaction of triclopyr and 2- butoxyethanol in toluene in presence of a catalyst. During the reaction, water is removed with the help of dean & stark arrangement. Catalyst is removed by washing the reaction mass with cold water. Water washings are extracted with toluene in order to recover fraction of product dissolved therein. The organic layers are combined and dried over anhydrous sodium sulfate. The solution of product thus obtained can be optionally decolorized with silica gel. The solvent is then removed by distillation under vacuum to obtain triclopyr-butoxyethyl ester with >99% purity.

EXAMPLE-25

In a reactor equipped with a mechanical stirrer, thermometer pocket, dean & stark and reflux condenser, 0.384 moles of triclopyr in 240 ml toluene were taken. 0.41 1 moles of 2-butoxyethanol was added. 2.0 g. of p-toluene sulfonic acid catalyst was added. The mixture was heated in an oil bath to reflux temperature i.e., 110-112⁰C for three hrs. Water during the reaction was removed by dean 85 stark arrangement. The reaction mass was cooled to room temperature and was washed with 150 ml cold water. The washings were extracted with 75 ml toluene. Two organic layers were combined, dried over anhydrous sodium sulfate and decolorized with silica gel. Solvent was removed by vacuum distillation to get triclopyr-butoxyethyl ester in 93.13% yield.

EXAMPLE-25-A

The process as described in Example-25 above was repeated except the catalyst used was 2.0 g methane sulfonic acid. The product Triclopyr- butoxyethyl ester was obtained with 90.89% yield and 99.5% purity. EXAMPLE-25-B

The process as described in Example-25 above was repeated except the catalyst used was 2.O g sulfuric acid. The product Triclopyr-butoxyethyl ester was obtained with 90.02% yield and 99.3% purity.

EXAMPLES-26 to 28

The process as described in Example-25 above was repeated except the molar ratio of triclopyr to 2-butoxyethanol was changed. The results are tabulated in the following Table.

Preparation of Triclopyr-Butoxyethyl ester by transesterification from Triclopyr-alkyl esters

A solvent-less process has been developed for preparation of triclopyr- butoxyethyl ester. As per said process, Triclopyr-butoxyethyl ester is prepared by transesterification from triclopyr-Ci-3-alkyl ester by heating a mixture of triclopyr- Ci-3-alkyl ester with 2-butoxyethanol in presence of a catalyst. Preparation by transesterification from ethyl- or methyl ester is preferable due to commercial reasons. The catalysts used in the process include titanium n-butoxide, methane sulfonic acid p-toluene sulfonic acid and sulfuric acid.

Preparation of Triclopyr-Butoxyethyl ester by transesterification from Triclopyr-Ethyl ester

As per said process, Triclopyr-butoxyethyl ester is prepared by transesterification from triclopyr-ethyl ester by heating a mixture of triclopyr-ethyl ester with 2-butoxyethanol in presence of a catalyst. Ethanol framed during the reaction is distilled out simultaneously. Excess of 2-butoxyethanol is also removed by distillation. The catalyst is removed by washing the reaction mass with water. Small fraction of the product dissolved during water-washing is recovered by back extraction with ethylene dichloride. Ethylene dichloride is then removed by distillation under vacuum to obtain triclopyr-butoxyethyl ester with 95-97% purity.

EXAMPLE-29

In a 250 ml 3-necked round bottom flask equipped with . a magnetic stirrer and connected to a distillation set up, 0.253 moles of 2- butoxyethanol was taken. It was heated to 9O⁰C. 0.168 moles of triclopyr-ethyl ester was added with stirring maintaining the temperature at 90⁰C to form a clear solution. The mixture was heated to 120⁰C and 1 ml of titanium butoxide catalyst was added. Ethanol formed during trans-esterification was distilled out under vacuum. The temperature of the reaction mass was increased to 150⁰C. After 7 hrs., the reaction mass was analyzed and 92% conversion was observed. Excess of 2- butoxyethanol was removed by distillation. The reaction mixture was poured in water to remove catalyst. Some product dissolved in water washings was recovered by back-extraction with 100 ml ethylene dichloride which was dried over anhydrous sodium sulfate and solvent was removed by distillation to obtain Triclopyr-butoxyethyl ester with 85.35% recovery.

EXAMPLE-30

The process as described in Example-29 above was repeated except the catalyst used was 1-ml of methanesulfonic acid. Triclopyr-butoxyethyl ester obtained with 87.85% yield and 96% purity.

EXAMPLE-31

The process as described in Example-29 above was repeated except the catalyst used was 1 g of p-toluenesulfonic acid. Triclopyr-butoxyethyl ester obtained with 90.3% yield and 97% purity.

EXAMPLE-31 -A

The process as described in Example-29 above was repeated except the catalyst used was 1-ml of sulfuric acid. Triclopyr-butoxyethyl ester obtained with 82.10% yield and 84.7% purity.

Preparation of Triclopyr-Butoxyethyl ester by transesterification from Triclopyr-Methyl ester

EXAMPLE-32

In a 250 ml 3-necked round bottom flask equipped with a magnetic stirrer and connected to a distillation set up, 0.554 moles of 2- butoxyethanol was taken. It was heated to 9O⁰C. 0.364 moles of triclopyr-methyl ester was added with stirring maintaining the temperature at 90⁰C to form a clear solution. The mixture was heated to 120⁰C and 1 ml of titanium butoxide catalyst was added. Methanol formed during trans-esterification was distilled out under vacuum. The temperature of the reaction mass was increased to 150⁰C. After 7 hrs., the reaction mass was analyzed and 98% conversion was observed. Excess of 2 -butoxyethanol was removed by distillation. The reaction mixture was poured in water to remove catalyst. Some product dissolved in water washings was recovered by back-extraction with 100 ml ethylene dichloride which was dried over anhydrous sodium sulfate and solvent was removed by distillation to obtain Triclopyr-butoxyethyl ester with 96% yield and 98.5% purity.

EXAMPLE-33

The process as described in Example-32 above was repeated except the catalyst used was 1-ml of methanesulfonic acid. Triclopyr-butoxyethyl ester obtained with 96.6% yield and 98.8% purity.

EXAMPLE-34

The process as described in Example-32 above was repeated except the catalyst used was 1 g of p-toluenesulfonic acid. Triclopyr-butoxyethyl ester obtained with 96.2% yield and 98.6% purity.

EXAMPLE-35

In a reactor equipped with a mechanical stirrer, thermometer pocket, dean & stark and reflux condenser, 0.554 moles of 2 -butoxyethanol was taken. It was heated to 9O⁰C. 0.364 moles of triclopyr-methyl ester was added with stirring maintaining the temperature at 90⁰C to form a clear solution. The mixture was heated to 125⁰C and 1 ml of titanium butoxide catalyst was added. Methanol formed during trans- esterification was distilled out under vacuum. The temperature of the reaction mass was increased to 145⁰C. After 7 hrs., the reaction mass was analyzed and 98,5% conversion was observed. Excess of 2- butoxyethanol was removed by distillation at higher vacuum. The crude product Triclopyr-butoxyethyl ester was distilled under vacuum to obtain 95% yield and 99.25% purity of the product.

EXAMPLE-35-A

The process as described in Example-35 above was repeated except the catalyst used was 1-ml of sulfuric acid. Triclopyr-butoxyethyl ester obtained with 81.84% yield and 84.25% purity.

EXAMPLE-36

The process as described in Example-35 above was repeated except the catalyst used was 1-ml of methanesulfonic acid. Triclopyr-butoxyethyl ester obtained with 94.5% yield and 99% purity.

EXAMPLE-37

The process as described in Example-35 above was repeated except the catalyst used was 1 g of p-toluenesulfonic acid. Triclopyr-butoxyethyl ester obtained with 95.5% yield and 99.3% purity. Preparation of 2-butoxyethyl chtoroacetate:

2-butoxyethyl chloroacetate is an intermediate for triclopyr. The inventers of present invention have developed a process for preparation of said intermediate by reaction of chloroacetic acid and 2-butoxyethanol in presence of a catalyst. The product obtained has improved purity compared to the product obtained by prior art process.

EXAMPLE-38

In a round bottom flask equipped with a mechanical stirrer, thermometer pocket, dean & stark and reflux condenser arrangement, 2.12 moles of chloroacetic acid in 190 ml toluene was taken. 2.12 moles of 2- butoxyethanol was added. 4 g. of p-toluenesulfonic acid catalyst was added. The mixture was refluxed in an oil bath for 6 hrs. Water during the reaction was removed by dean & stark arrangement. After 6 hrs. the reaction mass was analyzed and it showed 98.5% conversion. The reaction mass was cooled to room temperature and was washed with 150 ml water followed by 200 ml 10% sodium carbonate solution. Finally it was washed with 150 ml water. The organic layer was dried over anhydrous sodium sulfate and decolorized with silica gel. The solvent was removed by vacuum distillation to obtain 2-butoxyethylchloroacetate in 86.24% yield and 98.5% purity.

EXAMPLE-38-A

The process as described in Example 38 above was repeated except that the catalyst used was 4.0 g methanesulfonic acid to obtain 2- butoxyethylchloroacetate in 85.39% yield and 98.2% purity. EXAMPLES-39 & 40

The process as described in Example 38 above was repeated except the molar ratio of chloroacetic acid to 2-butoxyethanol was changed. The results are tabulated in following Table:

EXAMPLE-41

The process as described in Example 38 above was repeated except 95 ml of toluene was used instead of 190 ml. The yield of product obtained was 84.54%.

EXAMPLE-42

The process as described in Example 39 above was repeated except that 95 ml 'of toluene was used instead of 190 ml. The yield of product obtained was 87.09%.

EXAMPLE-43

In a round bottom flask equipped with a mechanical stirrer, thermometer pocket and reflux condenser arrangement with vacuum facility was taken 1.0582 moles of chloroacetic acid and 1.0582 moles of 2-butoxyethanol. 2.0 g. of p-toluenesulfonic acid catalyst was added. The mixture was heated in a water bath at 65-70⁰C under 600-630 mm Hg. During the reaction water was removed through the condenser. After 3 hrs of heating, the conversion was found to be 96.5%. The reaction mass was cooled to room temperature and was washed with 200 ml water. The organic layer was dried over anhydrous sodium sulfate. The product obtained was off-white in color in 80.16% yield and 98.02% purity.

EXAMPLE-44

The process as described in Example-43 above was repeated except that the molar ratio of chloroacetic acid to 2-butoxyethanol was changed to 1 : 1.05. The yield of the product obtained was 83.56%.

EXAMPLE-45

In a round bottom flask equipped with mechanical stirrer and thermometer pocket, 2.1 16 moles of chloroacetic acid and 2.116 moles of 2-butoxyethanol were taken. 7.0 g 98% sulfuric acid was added as a catalyst as well as water acceptor. The mixture was heated to 90-105⁰C in an oil bath for 4 hrs. conversion was found to be 60%. The reaction mass was cooled and washed with 150 ml water followed by 200 ml of 10% sodium carbonate and finally with 150 ml water. The organic layer was dried over anhydrous sodium sulfate and decolorized with silica gel to obtain 2-butoxyethyl chloroacetate in 61.70% yield and 97% purity. EXAMPLE-46

In a round bottom flask equipped with mechanical stirrer and thermometer pocket, 2.1 16 moles of chloroacetic acid and 2. JL 16 moles of 2-butoxyethanol were taken. Molecular sieve was used as water absorber. 4.0 g of p-toluenesulfonic acid catalyst was added. The ^■21

reaction mixture was heated to 80-1 lOoC in an oil bath for 5 hrs. Conversion was found to be 65%. The organic product was cooled to room temperature and was given washing with 150 ml water followed by 200 ml of 10% sodium carbonate solution and finally with 150 ml water. The product was dried over anhydrous sodium sulfate and decolorized with charcoal treatment to obtain the product with 55.87% yield and 96% purity.

EXAMPLE-47

The process as described in Example 46 above was repeated except that sodium sulfate was used as water absorber instead of molecular sieve. The product was obtained with 51.01% yield and 95% purity.

EXAMPLE-48

The process as described in Example 38 was repeated except that 465 ml toluene was used instead of 190 ml. The yield of the product was found to be 90.12%.

EXAMPLE-49

The process as described in Example 39 was repeated except that 465 ml toluene was used instead of 190 ml. The yield of the product was found to be 92.31%.

EXAMPLE-50

The process as described in Example 40 was repeated except that 465 ml toluene was used instead of 190 ml. The yield of the product was found to be 94.5%. Preparation of Triclopyr-butoxyethyl ester from 2-butoxyethyl chloroacetate and sodium salt of 3,5,6-trichloro-2-pyridinol.

2-butoxyethyl ester of chloroacetic acid is reacted with sodium salt of 3,5,6-trichloro-2-pyridinol in presence of tetrabutylammonium bromide which is an inexpensive well known phase transfer catalyst used extensively.

As opposed to the prior art process, the inventors of this invention have developed a process wherein the reaction between sodium salt of 3,5,6- trichloro-2-pyridinol and 2-butoxyethyl ester of chloroacetic acid is carried out in presence of catalyst without solvent, thereby avoiding extra consumption of energy and solvent losses.

The process of present invention though requires solvent for separation of the product after reaction, the quantity required thereof is very less compared to the process of prior art.

Typically, in the process of present invention, 2-butoxyethyl chloroacetate, sodium salt of 3,5,6-trichloropyridinol and catalyst are mixed and the mixture is maintained at 55-65⁰C under stirring. The resulting product is washed with hot water, filtered and extracted with solvent. The organic layer is separated and dried over anhydrous sodium sulfate and optionally decolorized with silica gel. The solvent is then removed by vacuum distillation to obtain Triclopyr-butoxyethyl ester in 90-94% yield. The product may be extracted in any suitable solvent and the solution of Triclopyr-butoxyethyl ester may be used directly for preparing formulation. EXAMPLE-51

0.445 moles 2-butoxyethyl chloroacetate was taken in a reactor which was provided with a mechanical stirrer, thermometer pocket and a condenser. 0.445 moles sodium salt of 3,5,6-trichloro-2-ρyridinol and 4.5 g. of tetrabutylammonium bromide were added to it. The reactor was placed in a water bath to maintain temperature of the reaction mixture at 55⁰C under constant stirring. After reaction, the amount of 2- butoxyethyl chloroacetate present in the mixture was found to be less than 0.5%. The resultant product was washed with 200 ml hot water and was filtered. The product was then extracted with 200 ml hexane. The organic layer was separated, dried over anhydrous sodium sulfate and decolorized with silica gel. Hexane was removed by vacuum distillation to obtain Triclopyr-butoxyethyl ester with 90% yield and 91% purity.

EXAMPLES-52 & 53

The process as described in Example-51 aboye was repeated except the molar ratio of reactants[sodium salt of 3,5,6-trichloro-2-pyridinol : 2- butoxyethyl chloroacetate] was taken as given in the following table. The results obtained are also given therein.

Claims

CLAIMS:

1. A process for preparation of triclopyr by hydrolysis of triclopyr-alkyl ester comprising steps including:

(i) heating an aqueous slurry of said ester with an alkali;

(ii) cooling the reaction mass to room temperature;

(iii) adding a decolorizing agent;

(iv) acidifying the reaction mass for precipitation of the product and filtration thereof.

2. A process as claimed in claim- 1, wherein the triclopyr-alkyl ester is Ci-3 alkyl ester.

3. A process as claimed in any of the claims 1 or 2, wherein aqueous slurry of triclopyr-alkyl ester has a concentration in the range of 5-15 wt%.

4. A process as claimed in any of the claims 1-3, wherein the molar ratio of triclopyr-alkyl ester to alkali is 1 : (1-2).

5. A process as claimed in claim- 1, wherein the decolorizing agent is NaOCl or H₂O₂.

6. A process as claimed in claim- 1, wherein the reaction mass is acidified to pH 1-2 for precipitation of the product.

7. A process for preparation of triclopyr-butoxyethyl ester by reaction of triclopyr and 2-butoxyethanol in presence of p-toluenesulfonic acid as catalyst.

8. A process as claimed in claim 7, except that the catalyst used is methane sulfonic acid.

9. A process as claimed in claim 7 except that the catalyst used is sulfuric acid.

10. A process as claimed in any of the claims 7-9, wherein the molar ratio of triclopyr : 2-butoxyethanol is 1 : (1-1.2).

1 1. A process as claimed in any of the claims 7-10, wherein the catalyst is used in the range of 0.5 - 5.0 mole% based on the moles of triclopyr.

12. A process as claimed in any of the claims 7-11, wherein the reaction is carried out by:

(i) refluxing the mixture of triclopyr, 2-butoxyethanol and catalyst in solvent at 110- 115⁰C and simultaneously removing water during the reaction preferably by azeotropic distillation thereof; (ii) cooling the reaction mass to room temperature; (iii) washing reaction mass with water and separating phases; (iv) back-extracting the fraction of the product dissolved in washings into a water-immiscible organic solvent; (v) removing solvent by distillation preferably under reduced pressure.

13. A process for preparation of triclopyr-butoxyethyl ester by transesterification from triclopyr-Ci-3-alkyl ester by heating a mixture of triclopyr-Ci-3-alkyl ester with 2-butoxyethanol in presence of titanium n- butoxide as a catalyst.

14. A process as claimed in claim 13, except that the catalyst used is methanesulfonic acid.

15. A process as claimed in claim 13, except that the catalyst used is p- toluenesulfonic acid.

16. A process as claimed in claim 13, except that the catalyst used is sulfuric acid.

17. A process as claimed in any of the claims 13-16, wherein the molar ratio of triclopyr-alkyl ester to 2-butoxyethanol is 1 : (1-2).

18. A process as claimed in claim 17, wherein the catalyst is used in the range of 0.5 - 5.0 mole% based on the moles of triclopyr alkyl ester.

19. A process as claimed in any of the claims 13-18, wherein triclopyr- butoxyethyl ester is obtained by:

(i) heating 2-butoxyethanol to 85-120⁰C;

(ii) adding triclopyr-alkyl ester and stirring;

(iii) adding catalyst and stirring at 120-160⁰C;

(iv) removing alkanol formed during reaction by simultaneous distillation preferably under reduced pressure;

(v) removing unreacted/ excess 2-butoxyethanol by distillation under reduced pressure;

(vi) washing reaction mass with water to remove catalyst and allowing aqueous and organic phases to separate;

(vii) back-extracting the fraction of product dissolved in water-washing;

(viii) removing the solvent by distillation preferably under reduced pressure.

20. A process for preparation of 2-butoxyethyl chloroacetate by reaction of chloroacetic acid and 2-butoxyethanol in presence of p-toluene sulfonic acid as catalyst.

21. A process as claimed in claim 20, except that the catalyst used is methane sulfonic acid.

22. A process as claimed in any of the claims 20 or 21, wherein the molar ratio of chloroacetic acid to 2-butoxyethanol taken is 1 : (1-1.5).

23. A process as claimed in any of the claims 20-22, wherein the catalyst is used in the range of 0.5 - 5.0 mole% based on the moles of chloroacetic acid.

24. A process as claimed in any of the claims 20-23, wherein 2- butoxyethyl chloroacetate is obtained by:

(i) refluxing the mixture of 2-butoxyethanol, chloroacetic acid, catalyst and solvent at 110-115⁰C and simultaneously removing water preferably by azeotropic distillation;

(ii) cooling the reaction mass to room temperature;

(iii) washing the reaction mass with water followed by mild alkali and again with water;

(iv) optionally drying the organic phase over a water absorbent/ adsorbent and decolorizing;

(v) removing the solvent by distillation preferably under reduced

0 pressure.

25. A process as claimed in any of the claims 20-23, wherein 2- butoxyethyl chloroacetate is obtained by:

(i) heating the mixture of 2-butoxyethanol, chloroacetic acid and catalyst at 60-75⁰C under 600-630 mm Hg and simultaneously removing water; (ii) cooling the reaction mass to room temperature;

(iii) washing the reaction mass with water followed by mild alkali and again with water; IQ

(iv) optionally drying the organic phase over a water absorbent/adsorbent and decolorizing.

26. A process for preparation of Triclopyr-butoxyethyl ester comprising steps of :

(i) reacting 2-butoxyethyl chloroacetate with sodium salt of 3,5,6- trichloropyridinol in presence of a phase transfer catalyst;

(ii) washing the resultant product with water;

(iii) extracting the product with a solvent;

(iv) separating the organic phase and optionally drying it with a drying agent &/or decolorizing;

(v) removing the solvent by distillation.

27. A process as claimed in claim 26, wherein the molar ratio- of sodium salt of 3,5,6-trichloropyridinol to 2-butoxyethyl chloroacetate is 1 : (1- 1.5).

28. A process as claimed in any of the claims 26 or 27, wherein the catalyst used is tetrabutylammonium bromide.

29. A process as claimed in any of the claims 26-28, wherein the catalyst is used in the range of 0.5 - 5.0 mole% based on the moles of sodium salt of 3,5,6-trichloropyridinol.

30. A process as claimed in claim 26, excluding any of the steps (ii) or (V) .

31. A process described in any of the specific examples disclosed in this specification.