DESC:FIELD
The present disclosure relates to a process for the preparation of 2,6-dichloro-4-nitrophenol.
BACKGROUND
2,6-Dichloro-4-nitrophenol is an important intermediate in the agrochemical and the pharmaceutical industry.
2,6-Dichloro-4-nitrophenol can be prepared by nitration of 2,6-dichlorophenol using a mixture of nitric acid and sulphuric acid. However, this process is associated with the formation of by-products. Similarly, 2,6-dichloro-4-nitrophenol can be prepared by chlorination of 4-nitrophenol, which is a relatively expensive raw material. Further, this method involves formation of various unwanted isomers, such as 2,5-dichloro-4-nitrophenol, 2-chloro-4-nitrophenol, and 2,3,6-trichloro-4-nitrophenol, which are difficult to separate from 2,6-dichloro-4-nitrophenol.
Thus, the conventional processes for the preparation of 2,6-dichloro-4-nitrophenol are associated with drawbacks such as complex reaction procedures, and use of costly raw material. The conventional processes also involve tedious purification steps and provide a product with low yield and low purity.
There is, therefore, felt a need to provide a simple, efficient, and economical process for the preparation of 2,6-dichloro-4-nitrophenol with high yield and in high purity.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a simple and efficient process for the preparation of 2,6-dichloro-4-nitrophenol.
Yet another object of the present disclosure is to provide an economical and eco-friendly process for the preparation of 2,6-dichloro-4-nitrophenol with high yield, and in high purity.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure is related to the process of preparing 2,6-dichloro-4-nitro phenol.
2,6-Dichlorophenol is sulphonylated using sulphuric acid at a temperature in the range of 100°C to 150°C for a period of time in the range of 0.5 hour to 5 hours to obtain a first resultant mixture. Water is added to the first resultant mixture and the diluted mixture is cooled to a temperature in the range of 40°C to 70°C to obtain a second mixture comprising 3,5-dichloro-hydroxybenzenesulphonic acid.
Nitration of 3,5-dichloro-hydroxybenzenesulphonic acid is carried out by adding nitric acid at a pre-determined rate to the second mixture under stirring, while maintaining the temperature of the reaction mixture in the range of 40°C to 70°C, followed by stirring for period of time in the range of 0.5 hour to 4 hours to obtain a second resultant mixture. The second resultant mixture is cooled to a temperature in the range of 20°C to 30°C and further stirred for 1 hour to 2 hours to obtain a slurry comprising a solid fraction and a liquid fraction. The solid fraction is separated from the slurry by filtration to obtain a residue comprising crude 2,6-dichloro-4-nitrophenol. The residue is washed with water, followed by drying under reduced pressure to obtain 2,6-dichloro-4-nitrophenol with a yield in the range of 85% to 95% and with purity in the range of 98% to 99.9%.
The ratio of the amount of 2,6-dichlorophenol and the amount of sulphuric acid is in the range of 1:1 to 1:5.
The ratio of the amount of sulphuric acid and the amount of water is in the range of 1:0.5 to 1:5.
The molar ratio of 2,6-dichlorophenol and nitric acid is in the range of 1:1 to 1:1.2. Nitric acid is slowly added to the second mixture, wherein the rate of addition is in the range of 0.1 to 1 mole of nitric acid per mole of 2,6-dichlorophenol per hour, typically 0.22 mole.
The process of the present disclosure does not employ an organic fluid medium. Further, the separation or the purification of intermediates is not required in the process of the present disclosure. Furthermore, the process also provides 2,6-dichloro-4-nitrophenol with high yield and in high purity.
DETAILED DESCRIPTION
2,6-Dichloro-4-nitrophenol is an important raw material in the agrochemical and the pharmaceutical industry. The present disclosure envisages a simple, efficient, and economical process for the preparation of 2,6-dichloro-4-nitrophenol with high yield, and in high purity.
The present disclosure provides a process for the preparation of 2,6-dichloro-4-nitrophenol (I).

The schematic description of the process of the present disclosure is provided in Scheme 1.
Scheme 1: Process for the preparation of 2,6-dichloro-4-nitrophenol (I)

The process of the present disclosure for the preparing 2,6-dichloro-4-nitrophenol is described in detail herein below:
2,6-Dichlorophenol (II) is sulphonylated using sulphuric acid, at a temperature in the range of 100°C to 150°C, for period of time in the range of 0.5 hour to 5 hours to obtain a first resultant mixture. Typically, the reaction of 2,6-dichlorophenol (II) with sulphuric acid is carried out at 120°C.
Water is added to the first resultant mixture, and the diluted mixture is cooled to a temperature in the range of 40°C to 70°C to obtain a second mixture comprising 3,5-dichloro-4-hydroxybenzenesulphonic acid (III). Typically, the first mixture is cooled to 50°C.
Further, nitration of 3,5-dichloro-hydroxybenzenesulphonic acid is carried out by adding nitric acid under stirring to the second mixture at a pre-determined rate, while maintaining temperature of the reaction mixture in the range of 40°C to 70°C, followed by stirring for a period of time in the range of 0.5 hour to 4 hours to obtain a second resultant mixture. The second resultant mixture is cooled to a temperature in the range of 20°C to 30°C and is stirred for 1 hour to 2 hours to obtain a slurry comprising a solid fraction and a liquid fraction.
The solid fraction is separated from the slurry by filtration to obtain a residue comprising crude 2,6-dichloro-4-nitrophenol. The residue is washed with water, and dried under reduced pressure to obtain 2,6-dichloro-4-nitrophenol (I).
The yield of 2,6-dichloro-4-nitrophenol (I) obtained by the process of the present disclosure is in the range of 85% to 95% and purity is in the range of 98% to 99.5%. Thus, the process of the present disclosure provides 2,6-dichloro-4-nitrophenol (I) in high yield and with high purity.
In accordance with the embodiments of the present disclosure, the ratio of the amount of 2,6-dichlorophenol (II) and the amount of sulphuric acid is in the range of 1:1 to 1:5.
In accordance with the preferred embodiments of the present disclosure, the ratio of the amount of 2,6-dichlorophenol (II) and the amount of sulphuric acid is in the range of 1:1 to 1:3.
In accordance with one embodiment of the present disclosure, the ratio of the amount of 2,6-dichlorophenol (II) and the amount of sulphuric acid is 1:1.75.
In accordance with second embodiment of the present disclosure, the ratio of the amount of 2,6-dichlorophenol (II) and the amount of sulphuric acid is 1:1.
In accordance with the embodiments of the present disclosure, the concentration of sulphuric acid used in a sulphonylation step is in the range of 95% w/w to 99% w/w.
In accordance with one embodiment of the present disclosure, the concentration of sulphuric acid used in the sulphonylation step is 98% w/w.
In accordance with one embodiment of the present disclosure, in the step of sulphonylation, 2,6-dichlorophenol (II) is added slowly over a prolonged period to sulphuric acid.
In accordance with the embodiments of the present disclosure, in the step of adding water to the first resultant mixture, the ratio of the amount of sulphuric acid and water is in the range of 1:0.5 to 1:5.
In accordance with the preferred embodiments of the present disclosure, in the step of adding water to the first resultant mixture, the ratio of the amount of sulphuric acid and water is in the range of 1:1.5 to 1:3.5.
In accordance with one embodiment of the present disclosure, in the step of adding water to the first resultant mixture, the ratio of the amount of sulphuric acid and water is 1:2.
In accordance with another embodiment of the present disclosure, in the step of adding water to the first resultant mixture, the ratio of the amount of sulphuric acid and water is 1:2.8.
In accordance with the embodiments of the present disclosure, 3,5-dichloro-4-hydroxybenzenesulphonic acid (III) produced in the sulphonylation step is not separated from the second mixture. The second mixture containing 3,5-dichloro-4-hydroxybenzenesulphonic acid (III) is directly taken to the next step.
In accordance with the embodiments of the present disclosure, the molar ratio of 2,6-dichlorophenol and nitric acid is in the range of 1:1 to 1:1.2.
In accordance with one embodiment of the present disclosure the molar ratio of 2,6-dichlorophenol and nitric acid is 1:1.1.
In accordance with the embodiments of the present disclosure, the concentration of the nitric acid used in the nitrating step is 98% w/w.
In the step of nitrating, the addition of nitric acid to the second mixture containing 3,5-dichloro-4-hydroxybenzenesulphonic acid (III) is carried out at a rate in the range of 0.1 to 1 mole of nitric acid per mole of 2,6-dichlorophenol per hour.
In accordance with one embodiment of the present disclosure, in the step of nitrating, the addition of nitric acid is carried out at 50°C at a rate of 0.22 moles of nitric acid per mole of 2,6-dichlorophenol per hour.
In accordance with the embodiments of the present disclosure, the rate of addition of nitric acid to the second mixture containing 3,5-dichloro-4-hydroxybenzenesulphonic acid (III) is controlled in such a way that the temperature of the reaction mixture is maintained in the range of 40°C to 70°C.
It is observed that controlling the temperature in the range of 40°C to 70°C during this addition provides 2,6-dichloro-4-nitrophenol (I) of high purity by limiting the formation of impurities.
In accordance with the embodiments of the present disclosure, crude 2,6-dichloro-4-nitrophenol (I) is washed with water to obtain pure product. No further step of purification is required as 2,6-dichloro-4-nitrophenol obtained has a purity in the range of 98% to 99.5%. The process of the present disclosure does not use any organic fluid medium to carry out sulphonation step and nitration step. Further, the process of the present disclosure does not use the organic fluid medium for the purification. Thus, the process of present disclosure is environment-friendly. Further, the step of sulphonating uses the heat generated during the sulphonation reaction. Therefore, the process of present disclosure is less energy intense. The process of the present disclosure does not require intermediate separation, and purification. Hence, the process of the present disclosure is efficient. Overall, the present process has short reaction cycle and reduces production costs. The process of the present disclosure uses commonly available and inexpensive reagents. Hence, the process of the present disclosure is simple, efficient, and economical.
The disclosure will now be described with reference to the accompanying examples which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
Examples
Example 1: Preparation of 2,6-dichloro-4-nitrophenol (I) from 2,6-dichlorophenol (II)
2,6-Dichlorophenol (800 kg) was added to a glass lined reactor containing 1400 kg of H2SO4 (98%) under stirring. Due to the exothermic reaction between 2,6-dichlorophenol and sulphuric acid, the temperature of the mixture rose to 100oC. The mixture was further heated at 120oC and was maintained at this temperature for 1 hour to obtain a first resultant mixture. The first resultant mixture was monitored for consumption of 2,6-dichlorophenol by thin layer chromatography (TLC). After the complete consumption of 2,6-dichlorophenol, the first resultant mixture was diluted with 2750 kg of water and diluted mixture was cooled to 50oC to obtain a second mixture comprising 3,5-dichloro-4-hydroxybenzenesulphonic acid.
350 kg of HNO3 (98%) was added to the second mixture comprising 3,5-dichloro-4-hydroxybenzenesulphonic acid under stirring at 50oC over a period of 5 hours, i.e. at a rate of 0.22 moles of nitric acid per mole of 2,6-dichlorophenol per hour. The reaction mixture was further stirred at 50oC for 1 hour to obtain a second resultant mixture. The second resultant mixture was monitored for consumption of 3,5-dichloro-4-hydroxybenzenesulphonic acid by thin layer chromatography (TLC).
After complete consumption of 3,5-dichloro-4-hydroxybenzenesulphonic acid, the second resultant mixture was cooled to 35oC, and stirred for 1 hour to obtain a slurry comprising a solid fraction and a liquid fraction. The solid fraction was separated from the slurry by filtration to obtain a residue comprising crude 2,6-dichloro-4-nitrophenol, which was washed with water (700 litres × 2), and dried under reduced pressure to obtain 920 kg of 2,6-dichloro-4-nitrophenol with an yield of 90.1% and purity of 98.5% by HPLC. The melting point of 2,6-dichloro-4-nitrophenol was found to be in the range of 130°C to 133°C.
Examples 2 and 3
Examples 2 and 3 were carried out using same experimental procedure as described in Example I.
Example II: To determine effect of ratio of amount of H2SO4 to the amount of 2,6-dichlorophenol, the preparation of I was carried out using the ratio of 1:1 instead of 1:1.75 used in Example I.
Example III: To determine effect of ratio of H2SO4 to water used for dilution, the preparation of I was carried out using the ratio of H2SO4 to water of 1:2.8 instead of 1:2.
The results are summarized in Table 1.

Table 1:
Examples 2,6-Dichlorophenol H2SO4 HNO3 Water for dilution Yield of I
I 800 kg 1400 kg 350 kg 2750 kg 920 kg
II 800 kg 800 kg 350 kg 1600 kg 890 kg
III 800 kg 1400 kg 350 kg 4000 kg 880 kg
It was observed from Examples I and II that, the yield of I decreases on decreasing the ratio of 2,6-dichlorophenol and H2SO4 from 1:1.75 to 1:1.
Further, it was observed from Examples I and III that, the yield of I decreases on increasing the ratio of H2SO4 and water from 1:2 to 1:2.8.
TECHNICAL ADVANCEMENT
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of 2,6-dicloro-4-nitrophenol, that is;
• simple and efficient;
• provides high yield and high purity; and
• economical and eco-friendly.
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 components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:1. A process for preparing 2,6-dichloro-4-nitrophenol from 2,6-dichlorophenol, said process comprising the following steps:

a. sulphonylating 2,6-dichlorophenol using sulphuric acid at a temperature in the range of 100°C to 150°C for a period of time in the range of 0.5 hour to 5 hours to obtain a first resultant mixture comprising 3,5-dichloro-4-hydroxybenzenesulphonic acid;

b. adding water to said first resultant mixture, and cooling diluted mixture to a temperature in the range of 40°C to 70°C to obtain a second mixture comprising 3,5-dichloro-4-hydroxybenzenesulphonic acid;

c. nitrating 3,5-dichloro-4-hydroxybenzenesulphonic acid by adding nitric acid to said second mixture at a predetermined rate, while maintaining the temperature of the reaction mixture in the range of 40°C to 70°C, followed by stirring for a period of time in the range of 0.5 hour to 5 hours to obtain a second resultant mixture; and

d. cooling said second resultant mixture to a temperature in the range of 20°C to 30°C, followed by stirring for 1 hour to 2 hours to obtain a slurry comprising a solid fraction and a liquid fraction, separating said solid fraction from said slurry to obtain a residue comprising crude 2,6-dichloro-4-nitrophenol, washing said residue with water and drying to obtain 2,6-dichloro-4-nitro phenol with a yield in the range of 85% to 95% and with purity in the range of 98% to 99.5%.

2. The process as claimed in claim 1, wherein the ratio of the amount of 2,6-dichlorophenol to the amount of sulphuric acid is in the range of 1:1 to 1:5.
3. The process as claimed in claim 1, wherein the ratio of the amount of sulphuric acid to the amount water is in the range of 1:0.5 to 1:5.

4. The process as claimed in claim 1, wherein the molar ratio of 2,6-dichlorophenol to nitric acid is in the range of 1:1 to 1:1.2.

5. The process as claimed in claim 1, wherein in process step (c), the predetermined rate of addition of nitric acid is in the range of 0.1 to 1 mole of nitric acid per mole of 2,6-dichlorophenol per hour.

6. The process as claimed in claim 1, wherein in process step (c), the predetermined rate of addition of nitric acid is 0.22 mole of nitric acid per mole of 2,6-dichlorophenol per hour.