FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
SYNTHESIS OF RESORCYLIC ACID
GHARDA CHEMICALS LTD
an Indian company
of B-27/29, MIDC
Dombivli (E), Thane - 421 203
Maharashtra, India.
Inventors:
l.MATHUR SUCHET S
2. PARKAR SURESHKUMAR D
3. DAMANIA PRAGNESH D
4. JAGTAP NAND KISHOR S 5.KALIRAJAN A.
6. KHAMKAR RAHUL H.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the Disclosure
The present disclosure relates to a process for the synthesis of resorcylic acid. More particularly, the present disclosure relates to a process for the synthesis of resorcylic acid from resorcinol.
Background
Resorcylic acid, also known as 2, 6-dihydroxybenzoic acid is an important chemical that is widely used in the preparation of substances such as pharmaceuticals, colorants and pesticides. Derivatives of 2, 6-dihydroxybenzoic acid such as methyl 2, 6-dimethoxy benzoate and 2, 6-dimethoxybenzoic acid are valuable intermediates in the manufacture of pharmaceuticals such as 2, 6-dimethoxy penicillin. Further, 2, 6-dihydroxybenzoic acid also assumes industrial significance as it is widely used in the manufacture of pesticides such as bispyribac-sodium and herbicides such as KIH-2023.
Numerous methods have been developed until now for the preparation of 2, 6-dihydroxybenzoic acid. The carbonation of phenols, also known as Kolbe-Schmitt reaction is carried out by reacting alkali phenoxide and carbon dioxide in a strongly alkaline medium, such as KOH to prepare 2, 6-dihydroxybenzoic acid is known in the art. In this reaction, the product formation varies in relative amounts with respect to the reaction conditions such as temperature and pressure. Further, substitution of potassium phenoxide in place of sodium phenoxide also alters the product formation.
Further, methods for the preparation of 2, 6-dihydroxybenzoic acid by direct carboxylation of resorcinol have also been reported. Heating resorcinol with excess sodium or potassium hydrogen carbonate in water, for a very short period of time, facilitates the exclusive preparation of 2, 4-dihydroxybenzoic acid, with the potassium salt giving the higher yield of the product. It is found that, prolonged (about 41 hours) heating of resorcinol with potassium hydrogen carbonate and carbon dioxide gives 50 % 2, 4-dihydroxybenzoic acid and 36 % 2, 6-dihydroxybenzoic acid. Further, increasing the reaction temperature by substituting glycerol with water, as the reaction

medium, does not influence either the course or the extent of the reaction. Even further, increasing the pressure of carbon dioxide to 27 atmospheres accelerates the reaction and affords quantitative carboxylation at 120-130 °C; with 48 % of the product being 2, 6-dihydroxybenzoic acid. Moreover, use of mono- or di-potassium derivatives of resorcinol gives almost similar results.
Resorcinol is particularly considered as a desirable and readily available starting material for the preparation of 2, 6-dihydroxybenzoic acid. As per the conventional. methods, resorcinol is treated with carbon dioxide in the presence of a base to give a mixture of 2, 4-dihydroxybenzoic acid and 2, 6-dihydroxybenzoic acid. This reaction (Kolbe-Schmitt) may be carried out in the presence or absence of solvents such as hydrocarbons, ketones, pyridine, quinolines, dioxan, polyhydric alcohols and water. Furthermore, it is often necessary to conduct the reaction under certain pressure in order to attain adequate reaction temperature. Still further, under most experimental conditions 2, 4-dihydroxybenzoic acid is the major product, whereas 2, 6-dihydroxybenzoic acid is obtained in a small and variable amount.
GB 9165481963 discloses the synthesis of 2, 6-dihydroxybenzoic acid by carboxylating andydrous mono-potassium salt of resorcinol, at 130 °C, in the presence of a solvent having the formula RCON(R1)2 ,where R is hydrogen or a lower alkyl group and R is a lower alkyl group having 1 to 4 carbon atoms. N, N'-dimethylformamide and N, N'-diethylformamide are the preferable solvents choices. An alkali salt of resorcinol may be formed in situ by reacting resorcinol with alkali metal hydroxide, carbonate or bicarbonate. Isolation of 2, 6-dihydroxybenzoic acid is effected by acidification with hydrochloric acid followed by fractional crystallization.
US 5304677 discloses synthesis of 2, 6-dihydroxybenzoic acid by dissolving resorcinol in a suitable solvent followed by blowing carbon dioxide into the solution in the presence of a basic compound until the absorption of carbon dioxide ceases. Alcohols, alkoxy-alcohols, dimethylformamide, water and mixtures thereof may be used as solvents. The basic compound may be potassium carbonate, potassium

hydroxide or sodium carbonate and is used approximately in an amount equimolar to resorcinol. The reaction may be carried out within a temperature range of 100 to 200 °C under atmospheric pressure or under carbon dioxide gas pressure of 30 kg/cm2. The patent also discloses decomposition of 2, 4-dihydroxybenzoic acid from the resultant mixture by acidification of the basic aqueous solution with an organic or a mineral acid to a pH between 5 and 7 and heating the mixture from 90 °C to the boiling temperature of the aqueous solution. After completion of the decomposition reaction, sulfuric acid is added to the mixture to attain a pH of 3 which is followed by filtering off the insoluble matter. Sulfuric acid is further added to the filtrate until the pH value reaches 1, after which the 2, 6-dihydroxybenzoic acid is finally isolated by filtration at 5°C.
The prior art methods for the preparation of 2, 6-dihydroxybenzoic acid, however, suffer from several disadvantages such as presence of high impurity content, low yield and low cost-effectiveness. Accordingly, there is felt a need for a process for the preparation of 2, 6-dihydroxybenzoic acid, that overcomes at least one drawbacks associated with the prior art methods.
Objects
Some of the objects of the present disclosure which at least one embodiment is adapted to provide, are described herein below:
It is an object of the present disclosure to provide a process for the preparation of 2, 6-dihydroxybenzoic acid which is of high purity.
It is another object of the present disclosure to provide a process for the preparation of 2, 6-dihydroxybenzoic acid, which is high yielding.
It is yet another object of the present disclosure to provide a process for the preparation of 2, 6-dihydroxybenzoic acid, which is environment-friendly.

It is still another object of the present disclosure to provide a process for the preparation of 2, 6-dihydroxybenzoic acid, which is economical.
Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.
Summary:
In accordance with the present disclosure there is provided a process for the preparation of 2, 6-dihydroxybenzoic acid, said process comprises the following steps:
• carboxylating resorcinof in the presence of carbon dioxide and at least one base in at least one solvent at a temperature ranging between 100 and 200 °C to obtain a mixture containing 2, 6-dihydroxybenzoic acid, 2, 4-dihydroxybenzoic acid and 4, 6-dihydroxyisophthalic acid; and
• acidifying said mixture with at least one acid to obtain 2, 6-dihydroxybenzoic acid,
wherein said process characterized in that the acidifying step comprises adjusting the pH of said mixture < 1, and the purity of said 2, 6-dihydroxybenzoic acid is > 95 %.
Typically, said process comprising:
• carboxylating resorcinol in the presence of carbon dioxide and at least one base in at least one solvent at a temperature ranging between 100 and 200 °C to obtain a mixture containing 2, 6-dihydroxybenzoic acid, 2, 4-dihydroxybenzoic acid and 4, 6-dihydroxyisophthalic acid;
• maintaining said mixture at a temperature of 140 °C to 180°C for a period of 1 to 10 hours;

• cooling the mixture to obtain a cooled mixture;
• acidifying said cooled mixture to a pH 5.5 to 6 with an acid followed by maintaining at 90-110 °C for a period of 1 to 20 hours to obtain an acidified mass and cooling said mass;
• adjusting the pH of said mass to 2 to 3 with an acid followed by filtering, washing and drying to obtain a solid mass and a filtrate; and
• adding an acid to said filtrate to adjust the pH to 0.8 to 1 followed by stirring, cooling, filtering, washing and drying to obtain 2, 6-dihydroxybenzoic acid having purity > 95 %.
Typically, the step of carboxylation is carried out at a temperature ranging between 140 and 180 °C.
Typically, said acid is selected from the group consisting of hydrochloric acid, sulphuric acid and acetic acid.
Typically, said base is selected from the group consisting of potassium carbonate, potassium hydroxide, sodium carbonate and combinations thereof.
Typically, the solvent is selected from the group consisting of toluene, N, N-dimethylforrnamide, N, N-diethylformamide, ethanol, methanol, acetone, water and combinations thereof.
Typically, the step of carboxylation is carried out in a reactor having a pressure ranging between 5 kg/cm and 45 kg/cm .
Typically, the drying is carried out at a temperature ranging between 40 to 70°C.

Typically, the purity of 2, 6-dihydroxybenzoic acid is > 99%.
In one embodiment the process include the step of decarboxylation of 2, 4-dihydroxy benzoic acid and 4, 6-dihydroxyisophthalic acid to obtain resorcinol and recycling of said resorcinol.
Detailed Description:
The present disclosure provides a process for the preparation of 2, 6-dihydroxybenzoic acid using resorcinol as the starting material. The process involves the following steps:
In the first step, resorcinol is carboxylated in the presence of carbon dioxide and at least one base in at least one solvent at a temperature ranging between 100 and 200 °C to obtain a mixture containing 2, 6-dihydroxybenzoic acid, 2, 4-dihydroxybenzoic acid and 4, 6-dihydroxyisophthalic acid. The obtained mixture is acidified with at least one acid to obtain 2, 6-dihydroxybenzoic acid. The acidifying step involves adjusting the pH of the mixture < 1. The purity of 2, 6-dihydroxybenzoic acid obtained by the process of the present disclosure is > 95 %, preferably greater than 99%. The acid is selected from the group consisting of hydrochloric acid, sulphuric acid and acetic acid, whereas the base is selected from the group consisting of potassium carbonate, potassium hydroxide, sodium carbonate and combinations thereof and the solvent is selected from the group consisting of toluene, N, N-dimethylformamide, N, N-diethylformamide, ethanol, methanol, acetone, water and combinations thereof. In accordance with the present disclosure the step of carboxylating is carried out at a temperature ranging between 140 and 180 °C. Typically, the step of carboxylation is carried out in a reactor having a pressure ranging between 5 kg/cm2 and 45 kg/cm2.
In one embodiment the process involves the following steps:
• carboxylating resorcinol in the presence of carbon dioxide and at least one base in at least one solvent at a temperature ranging between 100 and 200 °C to

obtain a mixture containing 2, 6-dihydroxybenzoic acid, 2, 4-dihydroxybenzoic acid and 4, 6-dihydroxyisophthalic acid;
• maintaining said mixture at a temperature of 140 °C to 180°C for a period of 1 to 10 hours;
• cooling the mixture to obtain a cooled mixture;
• acidifying said cooled mixture to a pH 5.5 to 6 with an acid followed by maintaining at 90-110 °C for a period of 1 to 20 hours to obtain an acidified mass and cooling said mass;
• adjusting the pH of said mass to 2 to 3 with an acid followed by filtering, washing and drying to obtain a solid mass and a filtrate; and
• adding an acid to said filtrate to adjust the pH to 0.8 to 1 followed by stirring, cooling, filtering, washing and drying to obtain 2, 6-dihydroxybenzoic acid having purity > 95 %.
The drying step is carried out at a temperature ranging between 40 and 70°C.
In one embodiment the process include the step of decarboxylation of 2, 4-dihydroxy benzoic acid and 4, 6-dihydroxyisophthalic acid to obtain resorcinol and recycling of
said resorcinol.
The disclosure is further illustrated by way of the following non limiting examples.
Example 1:
Preparation of 2,6-dihydroxybenzoic acid:
A mixture of resorcinol (110 grams, 1.0 mole), toluene (250 ml) and potassium hydroxide (65.1 grams of 86 %, 1.0 mole) was stirred in a reactor to which a Dean & Stark apparatus was installed to obtain a mass. The obtained mass was dehydrated by

removing water from side arm of the Dean and Stark apparatus. After no more water was observed in the side arm of the Dean and Stark apparatus, toluene was completely distilled and N,N-dimethylformarnide (330 ml) was added to obtain a solution. The resultant solution was transferred to a dry stainless steel pressure reactor, pressurized using a carbon dioxide gas and heated to 150 °C to obtain a reaction mixture. The obtained reaction mixture was held at 150 °C for 6 hours under a carbon dioxide gas pressure of 9 kg/cm2.
The mixture was cooled to 50 °C, carbon dioxide pressure was released and carbon dioxide was vented into alkali scrubber. The mixture was then transferred to a glass reactor and N, N-dimethylformamide was distilled at 110°C liquid temperature and 10 mm Hg pressure to obtain a reaction mass. The resultant mass was cooled to ambient temperature and dissolved in water. The HPLC composition of the reaction mass was of 56.61 %-2,6-dihydroxybenzoic acid, 4.97 %-2,4-dihydroxybenzoic acid, 9.32 % resorcinol, 12.73% 4,6-dihydroxyisophthalic acid.
The aqueous mass was acidified to a pH value of 5.5 to 6 with concentrated hydrochloric acid and maintained at 100 °C for 6 hours. The reaction progress was monitored by HPLC.
The mass was cooled to 30 °C, acidified with cone, hydrochloric acid to pH 2.85, filtered, washed & dried at 60°C to get 15.35 g dry solids (HPLC comp = 95.2% 4,6-dihydroxyisophthalic acid, 2.97% 2,6-dihydroxybenzoic acid). Filtrate of 2.85 pH was neutralized to a pH value of 0.8 to 1 using concentrated hydrochloric acid, cooled to 10°C and filtered, washed with water. The wet solid was dried at 60°C to get 53.9 grams of solid with 96.1 % 2,6-dihydroxy benzoic acid by HPLC.
Example-2
A mixture of 220 grams resorcinol (2.0 mole), 1300 ml 50 % (v/v) aqueous ethanol and 276 grams (2.0 mole) potassium carbonate was added in a dry stainless steel high-pressure reactor. Reactor was pressurized to 5 kg using carbon dioxide and heated to 170 °C. The mixture was held at 170 °C for 5 hours keeping carbon dioxide pressure of 38- 39 kg/cm2.

The reaction mixture was cooled to ambient temperature and carbon dioxide was
released and vented in alkali scrubber.
The mixture was then transferred to a glass reactor and analyzed by HPLC.
HPLC composition: 38.43 %-2,6-dihydroxybenzoic acid, 34.6 %-2,4-
dihydroxybenzoic acid, 9.40 % resorcinol & 16.42 % 4,6-dihydroxyisophthalic acid.
The mixture was neutralized to pH = 5.5 to 6 by concentrated hydrochloric acid at 30 °C and ethanol/water was then distilled from the mixture at 100°C liquid temperature. The reaction mixture was further maintained at reflux for 12.5 hours with adding concentrated hydrochloric acid to maintain the pH value 5.5 to 6.
After 12.5 hours maintenance at 100 °C, the composition of the reaction mass by HPLC was 55.25 %-2,6-dihydroxybenzoic acid, 3.6 %-2,4-dihydroxybenzoic acid, 20.35% resorcinol & 19.90 % 4,6-dihydroxyisophthalic acid.
After completion of decomposition of 2,4-dihydroxybenzoic acid, concentrated hydrochloride acid was added to the mixture until the pH value reached to 2.83. The obtained solids were filtered and wet solid was further slurried in water. To this, concentrated hydrochloric acid was added until pH value of 0.90 was reached. Solids were filtered, washed and dried at 60 °C till constant weight to get 11.8 grams dry solids. (HPLC composition was 93.5 % of 4,6- dihydroxyisophthalic acid & 5.84 % 2,6-dihydroxy benzoic acid).
Filtrate of pH 2.83 was fiirther acidified with concentrated hydrochloric acid until pH value reached 0.9 to 1.0 and stirred for 1 hr. The resultant slurry was cooled to 0 °C, stirred for 1 hour and filtered. The wet cake was further re-slurried in water, stirred at 55 - 60 °C for 1 hour, cooled to 0 °C and filtered. Solid was washed with chilled water and dried at 60 °C till constant weight to get 99.2 grams dry solid of 2,6-dihydroxybenzoic acid. (96.4 % purity by HPLC)

Example - 3
A mixture of 220 grams resorcinol (2 mole), 1300 ml of 50 % (v/v) aqueous ethanol, 138 grams (1.0 m) of potassium carbonate was added in a stainless steel high-pressure reactor. The mixture was pressurized to 5 kg using carbon dioxide and heated to 170 °C, the mixture was held at 170 °C for 5 hours with a carbon dioxide pressure of 23 -25 kg/cm2.
The reaction mixture was cooled to ambient temperature, carbon dioxide was released, carbon dioxide was vented in alkali scrubber.
The mixture was neutralized to pH 5.5 to 6 using concentrated sulfuric acid at 30 °C. Ethanol/water was then distilled from the mixture to get 98 -100 °C liquid temperature. The reaction mixture was further maintained at reflux for 11 hours by adding concentrated sulfuric acid to the reaction mixture keeping pH value 5.5 to 6 during heating.
After 11 hours HPLC composition of the mass was 55.72 %-2,6-dihydroxybenzoic acid, 2.81 %-2,4-dihydroxybenzoic acid, 38.14 % resorcinol and 2.15 % 4,6-dihydroxyisophthalic acid as against initial value of 52.47 %-2,6-dihydroxybenzoic acid, 20.20 %-2,4-dihydroxybenzoic acid, 24.2 % resorcinol & 2.47 % 4,6-dihydroxyisophthalic acid).
The mass was cooled to ambient temperature and concentrated sulfuric acid was added to the mixture until the pH value reached 4. The mixture was filtered to remove potassium sulfate. Filtrate was further acidified using concentrated sulfuric acid until pH value reached 0.9 to 1.0. Stirred the mass for 1 hour. The resultant slurry was cooled to 10 °C and stirred for 1 hour & filtered. The wet solid was further reslurried in water, stirred at 55-60 °C for 1 hour, cooled to 25 °C and filtered. Solid was washed with water and dried at 60 °C till constant weight to get 110.4 grams dry solid of 2,6-dihydroxybenzoic acid. (99.1 % purity by HPLC)
The aqueous filtrate was mixed and extracted with methyl ethyl ketone several times. Combined methyl ethyl ketone extract was concentrated under reduced pressure to get

142 grams viscous mass having HPLC composition of 85.7 % resorcinol, 7.8 % -2,6-DHBA, 1.6 % 2,4-dihydroxybenzoic acid and 2.1 % 4,6-dihydroxybenzoic acid. The residue post distillation of methyl ethyl ketone, which was rich in resorcinol, was recycled.
Example-4
The 142 grams of methyl ethyl ketone concentrated mass obtained from example - 3
(1.107 m resorcinol; 0.072 m 2,6-DHBA) was mixed with 90.3 grams fresh resorcinol
(0.821 mole), to adjust the resorcinol quantity to 2 mole, 151.8 grams (1.10m) of
potassium carbonate and 1300 ml of 50 % (v/v) aqueous ethanol.
The mixture was pressurized to 5 kg using carbon dioxide and heated to 170 °C, the
mixture was kept at 170 °C for 5 hours with a carbon dioxide pressure of 23 - 25
kg/cm2.
The reaction mixture was cooled to ambient temperature, carbon dioxide was released,
carbon dioxide was vented in alkali scrubber.
The mixture was neutralized to pH 5.5 to 6 using concentrated sulfuric acid at 30 °C.
Ethanol/water was then distilled from the mixture to get 98-100 °C liquid temperature.
The reaction mixture was further maintained at reflux for 12 hours by adding
concentrated sulfuric acid to the reaction mixture until pH value reached 5.5 to 6
during maintenance.
After 12 hours of maintenance the HPLC composition was 55.48 % -2,6-
dihydroxybenzoic acid, 0.1 % 2,4-dihydroxybenzoic acid, 41.04 % resorcinol and 0.93
% 4,6-dihydroxyisophthalic acid as against initial value of 35.52 % -2,6-
dihydroxybenzoic acid, 30.21 % 2,4-dihydroxybenzoic acid, 26.27 % resorcinol and
6.41 % 4,6-dihydroxyisophthalic acid. 4,6-dihydroisophtahlic acid shows complete
decarboxyaltion at 100 °C using concentrated sulfuric acid.
Concentrated sulfuric acid was added to the mixture until the pH value reached 3.96.
The slurry was equilibrated for 1 hour at 30 °C & filtered to remove potassium sulfate.
Filtrate was further acidified using concentrated sulfuric acid until pH value is reached
0,9 to 1.0 and stirred for 1 hour. The resultant slurry was cooled to 10 °C & stirred for
1 hour, and filtered.

The wet solid was further reslurried in water, stirred at 55-60 °C for 1 hour, cooled to 25 °C & filtered. Solid was washed with water and dried at 60 °C till constant weight to get 76.5 grams dry cake of 2,6-dihydroxybenzoic acid. (99.0 % purity by HPLC).
Example-5
After performing the main reaction and isolation of 2,6-dihydroxy benzoic acid, as
given in the example 3 and 4, aqueous filtrate was recycled.
Aqueous filtrate was neutralized to pH 7 using potassium carbonate & then it was
treated with charcoal & filtered off charcoal. The content of resorcinol in aqueous
filtrate was determined by HPLC and the shortfall of resorcinol for a batch size of 2.0
mole of resorcinol was compensated by adding fresh resorcinol and carboxylation was
conducted as per the process given in the example 3 and 4.
The yield of 2,6-dihydroxy benzoic acid was 33 % (use of fresh resorcinol), 35 %
after first recycle of aqueous filtrate and 32 % after second recycle of aqueous filtrate.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not

of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
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 a 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.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications 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 modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

WE CLAIM:
1. A process for the preparation of 2, 6-dihydroxybenzoic acid, said process comprising the following steps:
i. carboxylating resorcinol in the presence of carbon dioxide and at least one base in at least one solvent at a temperature ranging between 100 and 200°C to obtain a mixture containing 2, 6-dihydroxybenzoic acid, 2, 4-dihydroxybenzoic acid and 4, 6-dihydroxyisophthalic acid; and
ii. acidifying said mixture with at least one acid to obtain 2, 6-dihydroxybenzoic acid,
wherein said process characterized in that the acidifying step comprises adjusting the pH of said mixture < 1, and the purity of said 2, 6-dihydroxybenzoic acid is > 95 %.
2. The process as claimed in claim 1, wherein said process comprising:
- carboxylating resorcinol in the presence of carbon dioxide and at least one base in at least one solvent at a temperature ranging between 100 and 200 °C to obtain a mixture containing 2, 6-dihydroxybenzoic acid, 2, 4-dihydroxybenzoic acid and 4, 6-dihydroxyisophthalic acid;
- maintaining said mixture at a temperature of 140 °C to 180°C for a period of 1 to 10 hours;
- cooling the mixture to obtain a cooled mixture;
- acidifying said cooled mixture to a pH 5.5 to 6 with an acid followed by maintaining at 90-110 °C for a period of 1 to 20 hours to obtain an acidified mass and cooling said mass;

- adjusting the pH of said mass to 2 to 3 with an acid followed by filtering, washing and drying to obtain a solid mass and a filtrate; and
- adding an acid to said filtrate to adjust the pH to 0.8 to 1 followed by stirring, cooling, filtering, washing and drying to obtain 2, 6-dihydroxybenzoic acid having purity > 95 %.

3. The process as claimed in claim 1 or 2, wherein the step of carboxylation is carried out at a temperature ranging between 140 and 180 °C.
4. The process as claimed in claim 1 or 2, wherein said acid is selected from the group consisting of hydrochloric acid, sulphuric acid and acetic acid.
5. The process as claimed in claim 1 or 2, wherein said base is selected from the group consisting of potassium carbonate, potassium hydroxide, sodium carbonate and combinations thereof.
6. The process as claimed in claim 1 or 2, wherein the solvent is selected from the group consisting of toluene, N, N-dimethylformamide, N, N-diethylformamide, ethanol, methanol, acetone, water and combinations thereof.
7. The process as claimed in claim 1 or 2, wherein the step of carboxylation is carried out in a reactor having a pressure ranging between 5 kg/cm and 45 kg/cm2.
8. The process as claimed in claim 2, wherein the drying is carried out at a temperature ranging between 40 to 70°C.
9. The process as claimed in claim 1 or 2, wherein the purity of 2, 6-dihydroxybenzoic acid is > 99%.

10. The process as claimed in claim 1 or 2, include the step of decarboxylation of 2, 4- dihydroxy benzoic acid and 4, 6-dihydroxyisophthalic acid to obtain resorcinol and recycling of said resorcinol.