Form 2
THE PATENTS ACT 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2002
COMPLETE SPECIFICATION
(See Section 10;Rule 13)
TITLE
A process for the selective isolation of 2-mercapto-6-halobenzoic acid
APPLICANTS
GODREJ AGROVET LIMITED,
Pirojshanagar, Eastern Express Highway, Vikhroli (East), Mumbai 400079, Maharashtra, India, an Indian Company
INVENTORS
Under Section 28(2)
Dr Naik Parag Vilas, Iyer Ramaswamy, Dr Ramraj Velaswamy Munuswamy, Dr Vyas Brahmanand Ambashankar, Dr Mistry Keki Bamanshaw and Godrej Nadir Burjor, all of Godrej Agrovet Limited, Pirojshanagar, Eastern Express Highway, Vikhroli (East), Mumbai 400079, Maharashtra, India, all Indian Nationals
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:
6-9-2004 19-NOV 2003

FIELD OF INVENTION
This invention relates to a process for the selective
isolation of 2-mercapto-6-halobenzoic acid of the formula I:
COOH

Formula I
wherein X is halogen atom such as chloro, bromo or iodo.
PRIOR ART

(Japanese Patent No Hei3-17386 teaches the synthesis of 2-mercapto-6-halobenzoic acid of the formula 1 from 2-amino-6-
halotoluene via multiple reaction steps. The resulting reaction mass is a mixture of compound of the formula I and 2,2'-dithio bis-(6-


wherein X is as defined above and is extremely sensitive to air oxidation and hence unstable on storage. This is due to the labile nature of compound of the fomnula I which is easily oxidised to compound of the formula !!. The Japanese patent also teaches reduction of compound of the formula II to compound of the formula I with metal catalysts which add lo the cost of the process. Besides it also involves tedious operating and storage conditions along with long term pioblems such as catalyst poisoning. Hence, the process is time consuming and is not convenient and commercially viabie for industrial scale manufacture of the compound of the formula I.
The compounds of the formula I find immense use in the synthesis of pheny-thio-pyrimidines which possesses excellent activity against annual and perennial weeds, the compounds of the formula I also may be employed in the preparation of fungicides for therapeutic use.

OBJECTS OF INVENTION
An object of the invention is to provide a process for the selective isolation of 2-mercapto-6-halo benzoic acid of the formula I which is simple and easy to carry out
Another object of the invention is to provide a process for the selective isolation of 2-mercapto-6-halo benzoic acid of the fonnula I which is efficient, economical and commercially viable.
Another object of the invention is to provide a process for the selective isolation of 2-mereapto-6-halo benzoic acid of the formula I which is less time consuming
Another object of the invention is to provide a process for the selective isolation of 2-mercapto-6-halo benzoic acid of the fonnula I which may be employed for separation of compound of the formula 1 from compound of the formula 11 if the former gets

oxidised to the latter during storage or accidental contact with air and results in mixture of the two.
DESCRIPTION OF INVENTION
According to the invention there is provided a process for the selective isolation of 2-mercapto-6-halo benzoic acid of the


formula I:

COOH

Formula I
Formula 11

wherein X is halogen atom such as chloro, bromo or iodo from a mixture of compound of the formula I and 2,2'-dithio bis-(6-halo)benzoic acid of the formula II:


wherein X is as defined above by treating the mixture with a chlorinated organic solvent such as herein described at 10°C to 60°C followed by filtering out the precipitate containing the compound of the formula II.
The chlorinated organic solvent used in the process of the invention may be methylene chloride, ethylene chloride, chloroform or carbon tetrachloride or mixtures thereof, preferably methylene chloride or mixture of methylene chloride and chloroform.
Preferably the mixture of compounds of the formulae I and II may be treated at 25°C to 40°C.
According to the process of the invention it is possible to achieve extremely effective selective isolation of compound of the formula I from a mixture of compounds of the formulae I and II. The compound of the formula II may be easily filtered out and separated from the reaction and the chlorinated organic solvent may be recovered from the filtrate by fractional distillation. The compound of the formula I is obtained in crystallized state on

complete recovery of the chlorinated organic solvent. The process of the invention is simple and easy to carry out. It is also efficient and economical and commercially viable. Also, the process is completed in a very short time. The chlorinated organic solvents used in the process are very cheap and readily available. The process of the invention may be advantageously employed if the 2-mercapto-6-halo benzoic acid of the fonnula I gets oxidized to its disulfide namely 2,2'-dithio bis-(6-halo) benzoic acid of the formula II during storage or even by accidental air contact and compound of the formula I is to be separated from the mixture.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof.
Example 1 250 g of a mixture of 2-Mercapto-6-halobenzoic acid and 2,2'-dithio bis~(6-haio)benzoic acid (Black-brown oily solid) obtained by the procedure of Japanese Patent No Hei3 -173863,

was taken in a reactor fitted with a stirrer and condenser assembly. Methylene chloride (1000ml) was added to the mixture slowly using a dropping funnel followed by stirring continuously at 40°C for 15 minutes. The insoluble solid fraction containing 2)2'-dithio bis-(6-halo)benzoie acid was filtered out (Gray coloured precipitate we.ghing 24.86 g). The filtrate (Yellow-ot ange coloured solution) containing 2-mercapto-6-halobenzoic acid was subjected to fractional distillation to recover methylene chloride. On complete recovery of methylene chloride, 2-mercapto-6-ha!obenzoic acid (Yellow coloured solid weighing 225.14 g) was obtained in pure state, dried under high vacuum and stored in a vacuum-sealed container.
Example 2 25 g of a mixture of 2-mei capto-6-halobenzoic aci i and 2,2'-dithio bis-(6-halo)benzoic acid (Black-brown oily solid) obtained by the procedure of Japanese Patent No Hei3 -173863, was taken in an Erlenmeyer flask. A mixture of methylene chloride and chloroform (100 ml, 70:30% by volume) was added to the flask followed by shaking the flask on an orfoitol shaker for 60 minutes at 25°C The

insoluble solid precipitate containing 2,2-dithio bis-(6-halo)benzoic acid was filtered out ( Gray coloured precipitate weighing 2.07 g). The organic layer containing 2-mercapto-6-halobenzoic ac d was subjected to fractional distillation to recover the solvents. On complete recovery of the solvents, 2-mercapto-6-halobenzoic acid (Yellow coloured solid weighing 22.93 g) was obtained in pure state, dried under vacuum and stored in a vacuum-sealed container.

We Claim:
1. A process of the selective isolation of 2-mercapto-6-
halo benzoic acid of the formula I:
COOH

wherein X is halogen atom such as chloro, bromo or iodo from a mixture of compound of the formula I and 2,2'-dithio bis-(6-halo)benzoic acid of the formula II:

Formula II
wherein X is as defined above by treating the mixture with a chlorinated organic solvent such as herein described at 10 to 60°C followed by filtering out the precipitate containing the compound of the formula II

2. A process as claimed in claim 1, wherein the chlorinated organic solvent is methylene chloride or mixture of methylene chloride and chloroform.
3. A process as claimed in claim 1 or 2, wherein the mixture is treated with a chlorinated organic solvent at 25°C to 40°C.
4. A process for the selective isolation of 2-mercapto-6-halo benzoic acid of the formula I:
COOH

Formula I
wherein X is halogen atom such as chloro, bromo or iodo substantially as
herein described particularly with reference to Examples 1 and 2.
Dated this 5th day of June 2003
(Jose M A ) of
Khaitan & Co
Agent for the Applicants