DESC:This application is a cognate application of the provisional specification filed at the Indian Patent Office under Application No. 202321083443 on 07/12/2023 and Provisional Specification filed at the Indian Patent Office under Application No. 202321083444on 07/12/2023.
FIELD
The present disclosure relates to a process for the preparation of herbicide intermediates. Particularly, the present disclosure relates to a process for the preparation of 1,2,3-trichlorobenzene.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
1,2,3-trichlorobenzene is an organochlorine compound used as an intermediate for the production of pesticides, pigments, dyes, degreasing agent lubricants, and the like. 1,2,3-trichlorobenzene is also used as a solvent for high-melting products and coolant in electrical installations and glass tempering. 1,2,3-trichloronitrobenzene is represented as formula (I) below:

Formula I
Generally, dichloro nitrobenzene is used as a starting material for the preparation of 1,2,3-trichlorobenzene. Also, dichloro nitrobenzenes are important intermediates for the synthesis of pharmaceuticals and herbicides. Conventionally, dichloro nitrobenzenes are usually obtained by nitration of 1,2-dichlorobenzene. The conventional processes for the nitration of 1,2-dichlorobenzene give exclusively a mixture of 2,3-dichloronitrobenzene (2,3-DCNB) and 3,4-dichloronitrobenzene (3,4-DCNB). However, there is also a demand for 2,5-dichloronitrobenzene derivative. 2,3-dichloronitrobenzene is used as an intermediate in the synthesis of pharmaceuticals and herbicides. 2,5-dichloronitrobenzene is used as an intermediate in the production of dyes, antimicrobials as well as for the preparation of 2,5-dichloroaniline.
Further, the conventional methods for the preparation of 1,2,3-trichlorobenzene are associated with drawbacks such as having impurities and a low yield of the product. These conventional processes require use of expensive reagents and require further purification which is not economical. Another drawback includes the generation of hazardous by-products or using harsh reaction conditions and energy intensive reaction conditions. The impurities in the final product may affect the efficacy, safety, and stability of the final product.
Therefore, there is felt a need to provide a process for the preparation of 1,2,3-trichlorobenzene that mitigates the aforestated drawbacks or at least provides a useful alternative.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the background or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for the preparation of herbicide intermediates, particularly, 1,2,3-trichlorobenzene.
Yet another object of the present disclosure is to provide a process for the preparation of 1,2,3-trichlorobenzene from 2,3-dichloronitrobenzene.
Still another object of the present disclosure is to provide a process for the chlorination of ortho nitro chlorobenzene which selectively provides 2,3-dichloronitrobenzene and 2,5-dichloronitrobenzene.
Yet another object of the present disclosure is to provide a process for the preparation of 1,2,3-trichlorobenzene with a comparatively better purity and better yield.
Still another object of the present disclosure is to provide a simple, cost-effective and environment friendly process for the preparation of 1,2,3-trichlorobenzene.
Yet another object of the present disclosure is to provide a process for the preparation of 1,2,3-trichlorobenzene that is commercially scalable.
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 relates to a process for the preparation of herbicide intermediates. Particularly, the present disclosure relates to a process for the preparation of 1,2,3-trichlorobenzene. The process comprises chlorinating ortho nitro chlorobenzene with a first chlorinating agent in the presence of a catalyst at a first predetermined temperature for a first predetermined time period to obtain a mixture of 2,3-dichloronitrobenzene and 2,5-dichloronitrobenzene. 2,3-dichloronitrobenzene is separated from the mixture to obtain a separated 2,3-dichloronitrobenzene. The separated 2,3-dichloronitrobenzene is denitrochlorinated by using a second chlorinating agent optionally in the presence of a halide salt at a second predetermined temperature for a second predetermined time period to obtain 1,2,3-trichlorobenzene.
The first chlorinating agent and the second chlorinating agent is chlorine gas.
The chlorine gas is passed at a flow rate in the range of 0.05 m3/h to 0.5 m3/h.
In an embodiment of the present disclosure, the chlorine gas is passed at a flow rate in the range of 0.08 m3/h to 0.2 m3/h.
The catalyst is selected from the group consisting of ferric chloride (FeCl3) and iron (Fe) powder.
A molar ratio of ortho nitro chlorobenzene to the catalyst is in the range of 1:0.01 to 1:0.05.
In an embodiment of the present disclosure, the molar ratio of ortho nitro chlorobenzene to the catalyst is in the range of 1:0.015 to 1:0.03.
The halide salt is selected from the group consisting of calcium chloride, potassium chloride and a mixture thereof.
A molar ratio of 2,3-dichloronitrobenzene to the halide salt is in the range of 1:0.05 to 1:0.5.
In an embodiment of the present disclosure, the molar ratio of 2,3-dichloronitrobenzene to the halide salt is in the range of 1:0.08 to 1:0.2.
The first predetermined temperature is in the range of 50 °C to 150 °C.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 60 °C to 120 °C.
The first predetermined time period is in the range of 5 hours to 20 hours.
In an embodiment of the present disclosure, the first predetermined time period is in the range of 8 hours to 12 hours.
The second predetermined temperature is in the range of 100 °C to 250 °C.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 150 °C to 220 °C.
The second predetermined time period is in the range of 5 hours to 20 hours.
In an embodiment of the present disclosure, the second predetermined time period is in the range of 6 hours to 15 hours.
A mass ratio of 2,5-dichloronitrobenzene to 2,3-dichloronitrobenzene in the mixture is in the range of 60:40 to 65:35.
In an embodiment of the present disclosure, the step (b) of separating 2,3-dichloronitrobenzene from the mixture is carried out by fractional distillation to obtain a fraction of pure 2,5-dichloronitrobenzene and a fraction of pure 2,3- dichloronitrobenzene.
In another embodiment of the present disclosure, the step (b) of separating 2,3-dichloronitrobenzene from the mixture is carried out by fractional distillation followed by melt-crystallization to obtain a fraction of pure 2,5-dichloronitrobenzene and a fraction of pure 2,3- dichloronitrobenzene.
In accordance with the present disclosure, a yield of 1,2,3-trichlorobenzene is in the range of 70 mole% to 95 mole% and a purity of 1,2,3-trichlorobenzene is in the range of 98% to 99.9%.
DETAILED DESCRIPTION
The present disclosure relates to a process for the preparation of herbicide intermediates. Particularly, the present disclosure relates to a process for the preparation of 1,2,3-trichlorobenzene.
Embodiments, of the present disclosure, will now be described herein. Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Generally, dichloro nitrobenzene is used as a starting material for the preparation of 1,2,3-trichlorobenzene. Also, dichloro nitrobenzenes are important intermediates for the synthesis of pharmaceuticals and herbicides. Conventionally, dichloro nitrobenzenes are usually obtained by nitration of 1,2-dichlorobenzene. The conventional processes for the nitration of 1,2-dichlorobenzene give exclusively a mixture of 2,3-dichloronitrobenzene (2,3-DCNB) and 3,4-dichloronitrobenzene (3,4-DCNB). However, there is also a demand for the 2,5-dichloronitrobenzene derivative. 2,3-dichloronitrobenzene is used as an intermediate in the synthesis of pharmaceuticals and herbicides. 2,5-dichloronitrobenzene is used as an intermediate in the production of dyes, antimicrobials as well as for the preparation of 2,5-dichloroaniline.
Further, the conventional methods for the preparation of 1,2,3-trichlorobenzene are associated with drawbacks such as having impurities and a low yield of the product. These conventional processes require use of expensive reagents and require further purification which is not economical. Another drawback includes the generation of hazardous by-products or using harsh reaction conditions and energy intensive reaction conditions. The impurities in the final product may affect the efficacy, safety, and stability of the final product.
The present disclosure provides a process for the preparation of herbicide intermediates. Particularly, the present disclosure provides an improved process for the preparation of 1,2,3-trichlorobenzene.
The process of the present disclosure is simple, environment friendly, economical, and results in improved yield and higher purity of 1,2,3-trichlorobenzene.
The process for the preparation of 1,2,3-trichlorobenzene comprises the following steps:
a) chlorinating ortho nitro chlorobenzene with a first chlorinating agent in the presence of a catalyst at a first predetermined temperature for a first predetermined time period to obtain a mixture of 2,3-dichloronitrobenzene and 2,5-dichloronitrobenzene;
b) separating 2,3-dichloronitrobenzene from the mixture to obtain a separated 2,3-dichloronitrobenzene; and
c) denitrochlorinating the separated 2,3-dichloronitrobenzene by using a second chlorinating agent optionally in the presence of a halide salt at a second predetermined temperature for a second predetermined time period to obtain 1,2,3-trichlorobenzene.
The process for the preparation of 1,2,3-trichlorobenzene is described in detail as:
Step (a): A predetermined amount of ortho nitro chlorobenzene (ONCB) is reacted with a first chlorinating agent in the presence of a catalyst at a first predetermined temperature for a first predetermined time period to obtain a mixture of 2,3-dichloronitrobenzene and 2,5-dichloronitrobenzene.
In an embodiment of the present disclosure, the process for the preparation of 2,3-dichloronitrobenzene comprises charging a predetermined amount of ortho nitro chlorobenzene (ONCB) in a reactor followed by adding a predetermined amount of a catalyst to obtain a reaction mass. The reaction mass is heated at a first predetermined temperature followed by passing a chlorinating agent through the heated mass at a predetermined flow rate at the first predetermined temperature for a first predetermined time period to obtain a mixture comprising 2,3-dichloronitrobenzene (2,3-DCNB), 2,5-dichloronitrobenzene (2,5-DCNB) and unreacted o-nitro chloro benzene (ONCB).
In accordance with an embodiment of the present disclosure, the schematic representation for the process of chlorination of ortho nitro chlorobenzene is illustrated as scheme I below:

Scheme I
The first chlorinating agent is chlorine gas.
The chlorine gas is passed at a flow rate in the range of 0.05 m3/h to 0.5 m3/h. In an embodiment of the present disclosure, the chlorine gas is passed at a flow rate in the range of 0.08 m3/h to 0.2 m3/h. In an exemplary embodiment of the present disclosure, the chlorine gas is passed at the flow rate of 0.1 m3/h.
The catalyst is selected from the group consisting of ferric chloride (FeCl3) and iron (Fe) powder. In an exemplary embodiment of the present disclosure, the catalyst is ferric chloride (FeCl3). In another exemplary embodiment of the present disclosure, the catalyst is iron (Fe) powder.
A molar ratio of ortho nitro chlorobenzene to the catalyst is in the range of 1:0.01 to 1:0.05. In an embodiment of the present disclosure, the molar ratio of ortho nitro chlorobenzene to the catalyst is in the range of 1:0.015 to 1:0.03. In an exemplary embodiment of the present disclosure, the molar ratio of ortho nitro chlorobenzene to the catalyst is 1:0.02.
The first predetermined temperature is in the range of 50 °C to 150 °C. In an embodiment of the present disclosure, the first predetermined temperature is in the range of 60 °C to 120 °C. In an exemplary embodiment of the present disclosure, the first predetermined temperature is 100 °C. In another exemplary embodiment of the present disclosure, the first predetermined temperature is 80 °C. In an exemplary embodiment of the present disclosure, the first predetermined temperature is 60 °C.
The first predetermined time period is in the range of 8 hours to 12 hours. In an exemplary embodiment of the present disclosure, the first predetermined time period is 10 hours.
Step (b): 2,3-dichloronitrobenzene is separated from the mixture obtained in step (a) to obtain a separated 2,3-dichloronitrobenzene.
In an embodiment of the present disclosure the mixture obtained in step (a) is drowned in 1N HCl solution and is further washed with water till the washing becomes acid free.
In one embodiment of the present disclosure, the combined washings wherein the products present are extracted with a solvent followed by fractional distillation to obtain a pure 2,5-dichloronitrobenzene and 2,3- dichloronitrobenzene.
In another embodiment of the present disclosure, the step (b) of separating 2,3-dichloronitrobenzene from the mixture is carried out by fractional distillation followed by melt-crystallization to obtain a fraction of pure 2,5-dichloronitrobenzene and a fraction of pure 2,3- dichloronitrobenzene.
In an embodiment of the present disclosure, the solvent is ethylene dichloride (EDC).
In an embodiment of the present disclosure, the fractional distillation is carried out by using a fractionating column which is efficient. Initially, ortho nitro chlorobenzene (ONCB) comes out, later 2,5-DCNB and then 2,3-DCNB. The higher chlorinated products are left in the residue.
In an embodiment of the present disclosure, the reaction is monitored by gas chromatography (GC).
In an embodiment of the present disclosure, the product mixture is analysed for a predetermined weight gain of the reactant to determine the termination of the reaction.
In an embodiment of the present disclosure, the pure 2,3-dichloronitrobenzene is taken for denitrochlorination to get 1,2,3-trichlorobenzene.
In an embodiment of the present disclosure, the pure 2,5-dichloronitrobenzene is taken for reduction to make 2,5-dichloroaniline which is further used for the preparation of Dicamba (3,6-dichloro-2-methoxybenzoic acid).
Thus, total utilization of all the products makes the process of the present disclosure environment friendly. The reactant ONCB used in the preparation of 2,3-dichloronitrobenzene is cheaper, thereby making the process of the present disclosure economic.
Step (c): A predetermined amount of 2,3-dichloronitrobenzene and optionally, a predetermined amount of halide salt are mixed to obtain a reaction mixture. The reaction mixture is heated at a second predetermined temperature to obtain a heated reaction mixture followed by passing a predetermined amount of a second chlorinating agent through the heated reaction mixture at the second predetermined temperature for a second predetermined time period to obtain 1,2,3- trichlorobenzene.
In accordance with an embodiment of the present disclosure, the schematic representation for the preparation of 1,2,3-trichlorobenzene is illustrated as Scheme II below:

Scheme II
The halide salt is selected from the group consisting of calcium chloride, potassium chloride and a mixture thereof. In an exemplary embodiment of the present disclosure, the halide salt is calcium chloride. In an exemplary embodiment of the present disclosure, the halide salt is potassium chloride. In an exemplary embodiment of the present disclosure, the halide salt is the mixture of calcium chloride and potassium chloride.
In an embodiment of the present disclosure, a molar ratio of 2,3-dichloronitrobenzene to the halide salt is in the range of 1:0.05 to 1:0.5. In a preferred embodiment of the present disclosure, the molar ratio of 2,3-dichloronitrobenzene to the halide salt is in the range of 1:0.08 to 1:0.2. In an exemplary embodiment of the present disclosure, the molar ratio of 2,3-dichloronitrobenzene to the halide salt is 1:0.1.
The second chlorinating agent is chlorine gas.
The second predetermined temperature is in the range of 100 °C to 250 °C. In an embodiment of the present disclosure, the second predetermined temperature is in the range of 150 °C to 220 °C. In an exemplary embodiment of the present disclosure, the second predetermined temperature is 180 °C. In another exemplary embodiment of the present disclosure, the second predetermined temperature is 200 °C.
The second predetermined time period is in the range of 5 hours to 20 hours. In an embodiment of the present disclosure, the second predetermined time period is in the range of 6 hours to 15 hours. In an exemplary embodiment of the present disclosure, the second predetermined time period is 11 hours. In another exemplary embodiment, the second predetermined time period is 13 hours. In yet another exemplary embodiment, the second predetermined time period is 8 hours.
In accordance with the present disclosure, the off gases such as nitryl chloride formed as by product during the reaction and excess chlorine in the reaction is scrubbed in alkali or acid.
In an embodiment of the present disclosure, the product 1,2,3-trichlorobenzene is isolated by fractional distillation with or without any workup procedure.
In another embodiment of the present disclosure, the product 1,2,3-trichlorobenzene is isolated by fractional distillation after workup with a mixture of water and dichloromethane.
In accordance with the present disclosure, the yield of 1,2,3-trichlorobenzene is in the range of 70 mole% to 95 mole%.
In accordance with the present disclosure, the purity of 1,2,3-trichlorobenzene is in the range of 98% to 99.9%.
The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments are scalable to industrial/commercial process.
EXPERIMENTAL DETAILS
Experiment 1: Process for the chlorination of ortho nitro chlorobenzene in accordance with the present disclosure:
EXAMPLE 1:
1 mole of ONCB (ortho nitro chlorobenzene) was chlorinated by passing chlorine gas at 0.1 m3/h for 10 hours in the presence of 2 mole % FeCl3 at 100 °C to obtain a mixture of 2,5-dichloronitrobenzene and 2,3-dichloronitrobenzene. After the desired weight gain (34.5 gm/m) of 0.9 to 0.95 m/m chlorine or when less than 10 % unreacted ONCB was evident by GC, the reaction was terminated. The typical GC analysis showed a reaction mass comprising 8.288 % starting material ONCB, 56.218 % of 2,5-dichloro-nitro-benzene (2,5-DCNB) and 29.535 % of 2,3-dichloro-nitrobenzene (2,3-DCNB).
The so obtained ratio of 2,5 DCNB to 2,3 DCNB was 65.9: 34.1.
The reaction mass was worked up by drowning in 1N HCl (20 ml/m twice) to remove FeCl3, and then washed with water till acid free filtrate was obtained. Ethylene dichloride (EDC) extraction (50 ml/m total EDC used) was done to extract the material present in an aqueous layer. After extraction with EDC at least twice, the combined EDC layer was concentrated to obtain EDC concentrated mass which was about 181 g. The GC shows 8.351 % unreacted ONCB; 56.701 % 2,5-DCNB; 29.363 % 2,3-DCNB and 5.58 % more chlorinated high retention peaks.
This material was fractionated by using efficient fractionating column under vacuum. Fractionation was carried out up to 150 °C pot, 130 °C vapor and 5 to 20 mm Hg pressure. Initially ONCB comes out, later 2,5-DCNB and then 2,3-DCNB. The higher chlorinated products were left in the residue.
Fractionation by using efficient fractionating column:
The material as obtained from example 1 was subjected to fractionation with 5-feet height 1inch dia-glass column with structured packing. The column was charged with 1085.6 g of the material and collected in different cuts as per GC analysis up to 170 °C reaction mass temperature and 10 to 20 mm. Hg. Pressure. The different cuts obtained of 97 to 99 % purity 2,5-DCNB was 344 g and 96 to 98 % purity 2,3-DCNB cuts was 205 g.
The remaining impure cuts were taken for fractionation in the next batch.
The material as obtained from example 1 was also subjected to fractionation with 10-feet height 1-inch dia-glass column with structured packing. The column was charged with 8420 g material and collected in different cuts as per GC analysis. This gave 336 g of 98 to 99.6 % pure ONCB, 2310 g of 97 to 99.6 % pure 2,5-DCNB and 1211 g of 97 to 99.8 % pure 2,3-DCNB.
The pure cut of 2,3-DCNB was taken to De-nitro-chlorination for obtaining 1,2,3-trichloro-benzene.
The pure cut of 2,5-DCNB was taken to reduction for obtaining 2,5-DCA (di-chloro Aniline), which was further used for the preparation of Dicamba (3,6-dichloro-2-methoxybenzoic acid).
EXAMPLE 2:
Example 1 was repeated by using 2 mole % Fe-powder as a catalyst (instead of 2 mol % FeCl3) and chlorine gas was passed at 100 °C at 0.1 m3/hour for 10 hours. After passing chlorine gas, 0.93 m/m weight gain was observed and the reaction was terminated.
The GC analysis shows 18.1 % ONCB, 27.1 % of 2,3-DCNB and 47.7 % of 2,5-DCNB.
The ratio of 2,5 DCNB to 2,3 DCNB was observed as 64:36.
This material was fractionated by using efficient fractionating column by following the same procedure of Example 1.
EXAMPLE 3:
Example 1 was repeated by using 2 mole % FeCl3 and chlorine gas was passed at 60 °C (instead of 100 °C) at 0.1 m3/hour for 10 hours. After passing chlorine gas, 0.93 m/m weight gain was observed and the reaction was terminated.
The GC analysis shows 18.4 % ONCB, 52.0 % 2,5-dichloro-nitro-benzene (2,5-DCNB) and 27.2 % 2,3-dichloro-nitrobenzene (2,3-DCNB).
The observed ratio of 2,5 DCNB to 2,3 DCNB was 65.6 : 34.4.
This material was fractionated by using efficient fractionating column by following the same procedure of Example 1.
EXAMPLE 4:
Example 1 was repeated by using 2 mole % FeCl3 and chlorine gas was passed at 80 °C (instead of 100 °C) at 0.1 m3/hour for 10 hours. After passing chlorine gas, 0.93 m/m weight gain was observed and the reaction was terminated.
The GC analysis shows 10.4 % ONCB, 55.9 % 2,5-dichloro-nitro-benzene (2,5-DCNB) and 29.3 % 2,3-dichloro-nitrobenzene (2,3-DCNB).
The ratio of 2,5 DCNB to 2,3 DCNB was 65.6 : 34.4.
This material was fractionated by using efficient fractionating column by following the same procedure of Example 1.
EXAMPLE 5:
Example 1 was repeated by using 1 mole % FeCl3 (instead of 2 mole % FeCl3) and chlorine gas was passed at 100 °C at 0.1 m3/hour for 10 hours. After passing chlorine gas, 0.987 m/m weight gain was observed and the reaction was terminated.
The GC analysis shows 10.0 % ONCB, 55.75 % 2,5-dichloro-nitro-benzene (2,5-DCNB) and 28.98 % 2,3-dichloro-nitrobenzene (2,3-DCNB).
The ratio of 2,5 DCNB to 2,3 DCNB was 65.8 : 34.2.
This material was fractionated by using efficient fractionating column by following the same procedure of Example 1.
EXAMPLE 6:
Example 1 was repeated by using 1 mole % FeCl3 having 0.2 mole% water (instead of 2 mole % FeCl3 without moisture) and chlorine gas was passed at 100 °C at 0.1 m3/hour for 10 hours. After passing chlorine gas, 0.93 m/m weight gain was observed and the reaction was terminated.
The GC analysis shows 6.5 % ONCB, 57.75 % 2,5-dichloro-nitro-benzene (2,5-DCNB) and 29.29 % 2,3-dichloro-nitrobenzene (2,3-DCNB).
The ratio of 2,5 DCNB to 2,3 DCNB was 65.9 : 34.1.
This material was fractionated by using efficient fractionating column by following the same procedure of Example 1.
Some impure cuts from fractionation were re-fractionated or melt crystallized to obtain more pure cuts. Particularly, the first cut from fractionation column containing less content of ONCB, very high content of 2,5 isomer and very less content of 2,3 isomer was melt crystallized to obtain high purity 2,5-isomer (below Example-i). The second cut from the fractionation column containing very less content of ONCB, high content of 2,5-isomer and less content 2,3-isomer was melt crystallized to obtain high purity 2,5-isomer (below Example-ii). The third cut from the fractionation column containing no ONCB, less 2,5 isomer and high 2,3 isomer was melt crystallized to obtain high purity 2,3-isomer (below Example-iii).
Melt crystallization by using 2.25-feet long and 1-inch dia-jacketed glass column with sintered plate:
Example (i): 670 g material having GC analysis as ONCB = 8.8 %, 2,5-DCNB = 91.0 %, 2,3-DCNB = 0.05% was fed in the column at 25 °C and then slowly vacuum was applied up to 200 mm Hg pressure. The column temperature was slowly increased up to 56 °C over 32 hours and collected filtrate cuts as per GC analysis. The purity of 2,5-DCNB obtained was > 99.0 % purity with 50 wt % recovery.
Example (ii): 690 g material having GC analysis as = ONCB = 0.005 %, 2,5-DCNB = 90.35 %, 2,3-DCNB = 7.75% was fed in the column at 25 °C and then slowly vacuum was applied up to 200 mm Hg pressure. The column temperature was slowly increased up to 60 °C over 58 hours and collected filtrate cuts as per GC analysis. The purity of 2,5-DCNB obtained was > 99.0 % purity with 58 wt % recovery.
Example (iii): 275 g material having GC analysis as = ONCB = nil, 2,5-DCNB = 4.5 %, 2,3-DCNB = 94.25 % was fed in the column at 25 °C and then slowly vacuum was applied up to 200 mm Hg pressure. The column temperature was slowly increased up to 67 °C over 22 hours and collected filtrate cuts as per GC analysis. The purity of 2,3-DCNB obtained was > 99.0 % with 46 wt % recovery.
This shows that the process is economically viable as both the isomers were purified and can be utilized.
Further, to compare the effect of fractionation by using efficient fractionating column on the purity of 2,5 DCNB and 2,3 DCNB, the material obtained in example 1 was subjected to distillation without column.
Distillation without column:
5920 g of material having GC analysis as – ONCB = 1.08 %, 2,5-DCNB = 59.64 %, 2,3-DCNB = 32.62 % was subjected to distillation without any column and distilled in different cuts at 135 °C reaction temperature and 10 mm Hg pressure. None of the distilled cut was pure enough to take it to the next step of de-nitro-chlorination. All cuts GC analysis of 2,5-DCNB was < 70 % and 2,3-DCNB was < 42 %.
From the above trials, it was found that distillation without column was not efficient to high purity 2,5-DCNB and 2,3-DCNB.
COMPARATIVE EXAMPLES:
Comparative Example I: (No catalyst)
When chlorination was performed by using a similar method as disclosed in Example 1 without adding any catalyst at 100 °C, no reaction was observed. Free chlorine came out in the scrubber.
Comparative Example II: (Ferrocene as a catalyst)
1 mole of o-nitrochlorobenzene was charged in a reactor with 2 mole% Ferrocene at 100 °C to obtain a first reaction mixture. Chlorine gas was passed to the first reaction mixture at a flow rate of 0.1 m3/hour and at 100 °C for 5 hours to obtain a product mixture comprising 2,5-dichloronitrobenzene, 2,3-dichloronitrobenzene and unreacted o-chloronitrobenzene. Further, free chlorine was seen in the vent. The observed weight gain was 0.56 m/m.
The GC analysis of the product mixture shows high retention peaks which corresponds to 69.5% of unreacted ONCB, 17.3% of 2,5-DCNB and 9.6% of 2,3-DCNB.
The ratio of 2,5-DCNB to 2,3-DCNB was 64:36.
Comparative Example III: (1 mol% FeCl3 and 1 mol% of S2Cl2)
1 mole of o-nitrochlorobenzene was charged in a reactor with 1 mole% FeCl3 and 1 mole% of S2Cl2 at 100 °C to obtain a first reaction mixture. Chlorine gas was passed to the first reaction mixture at a flow rate of 0.1 m3/hour and at 100 °C for 5 hours to obtain a product mixture comprising 2,5-dichloronitrobenzene, 2,3-dichloronitrobenzene and unreacted o-chloronitrobenzene. Further, the free chlorine was seen in the vent. The observed weight gain was 0.255 m/m. The reaction was terminated to obtain a product mixture.
The GC analysis of the product mixture shows high resolution peaks which corresponds to 80.5% of unreacted ONCB, 11.77% of 2,5-DCNB and 6.56% of 2,3-DCNB.
The ratio of 2,5-DCNB to 2,3-DCNB was 64:36.
Comparative Example IV: (2 mol % FeCl3 at 30 °C)
1 mole of ortho nitro chlorobenzene was chlorinated in presence of 2 mole % FeCl3 at 30 °C over 10 hours. Chlorine gas was passed at 0.1 m3/hour. After passing chlorine gas for 5 hours, further free chlorine seen in the vent. The weight gain was 0.5 m/m, reaction was terminated.
The GC analysis shows 63.8 % starting ONCB, 23.4 % 2,5-dichloro-nitro-benzene (2,5-DCNB) and 12.5% 2,3-dichloro-nitrobenzene (2,3-DCNB).
The ratio of 2,5-DCNB: 2,3-DCNB was 65 : 35.
From the various aforesaid Examples it was observed that the chlorination of ONCB was incomplete without any catalyst. Further, the process of chlorination of ONCB does not go to completion by using 2 mole % FeCl3 as a catalyst at a low temperature of 30 °C. It is further observed that minimum temperature required to achieve satisfactory level of chlorination is 60 °C and the optimum temperature where free chlorine is very negligible in the scrubber is 100 °C. Furthermore, it is evident that Fe-metal works equally well as FeCl3 for the chlorination reaction of ONCB wherein minimum 2 mole % FeCl3 is required for the efficient chlorination.
Experiment 2: Preparation of 1,2,3-trichlorobenzene in accordance with the present disclosure:
Example (i) – Preparation of 1,2,3-trichlorobenzene by using calcium chloride
In a reactor, 2 moles of 2, 3 dichloro nitro benzene (2, 3 DCNB) and 0.2 moles of anhydrous calcium chloride were mixed to obtain a mixture. The mixture was heated to 180 °C followed by passing chlorine gas through the heated mixture at 180 °C for 11 hours to obtain a product mixture comprising 1,2,3- trichlorobenzene. Off gases were scrubbed in a suitable scrubber. The product 1,2,3- trichlorobenzene was isolated by fractional distillation as such without any workup procedure.
Yield of 1,2,3-trichloro-benzene obtained was greater than 75 m % and purity was not less than 99.5 %.
Example (ii) – Preparation of 1, 2, 3 trichlorobenzene by using calcium chloride
In a reactor, 0.5 moles of 2, 3 dichloro nitro benzene (2, 3 DCNB) and 0.05 moles of calcium chloride were mixed to obtain a mixture. The mixture was heated to 180 °C followed by passing chlorine gas at 180 °C for 11 hours to obtain a product mixture comprising 1,2,3- trichlorobenzene. Off gases were scrubbed in alkali or acid.
The product 1,2,3- trichlorobenzene was isolated by fractional distillation after extraction by mixture of water and dichloromethane workup.
Yield of 1,2,3-trichloro-benzene obtained was greater than 75 m % and purity was not less than 99.5 %.
Example (iii) - Preparation of 1, 2, 3 trichlorobenzene by using potassium chloride
In a reactor, 2 moles of 2, 3 dichloro nitro benzene (2, 3 DCNB) and 0.2 moles of potassium chloride were mixed to obtain a mixture. The mixture was heated at 180 °C followed by passing chlorine gas at 180 °C for 13 hours to obtain a product mixture comprising 1,2,3- trichlorobenzene. Off gases were scrubbed in a suitable scrubber. The product 1,2,3- trichlorobenzene was isolated by fractional distillation as such without any workup procedure.
Yield of 1,2,3-trichloro-benzene obtained was greater than 75 m % and purity was not less than 99.5 %.
Example (iv) - Preparation of 1, 2, 3 trichlorobenzene without using halide salt
In a reactor, 2 moles of 2,3 dichloro nitro benzene (2, 3 DCNB) was heated to 180 °C followed by passing chlorine gas for 13 hours to obtain a product mixture comprising 1,2,3- trichlorobenzene. Off gases were scrubbed in a suitable scrubber. The product 1,2,3- trichlorobenzene was isolated by fractional distillation as such without any workup procedure.
Yield of 1,2,3-trichloro-benzene obtained was greater than 75 m % and purity was not less than 99.5 %.
Example (v) – Preparation of 1,2,3-trichlorobenzene by using mixture of Anhydrous calcium chloride and potassium chloride
In a reactor, 2 moles of 2, 3 dichloro nitro benzene (2, 3 DCNB) and 0.1 moles of anhydrous calcium chloride + 0.1 moles of KCl were mixed to obtain a mixture. The mixture was heated at 180 °C followed by passing chlorine gas through the heated mixture at 180 °C for 11 hours to obtain a product mixture comprising 1,2,3- trichlorobenzene. Off gases were scrubbed in a suitable scrubber. The product 1,2,3- trichlorobenzene was isolated by fractional distillation as such without any workup procedure.
Yield of 1,2,3-trichloro-benzene obtained was greater than 75 m % and purity was not less than 99.5 %.
Example (vi) - Preparation of 1, 2, 3 trichlorobenzene without using halide salt
In a reactor, 2 moles of 2,3 dichloro nitro benzene (2, 3 DCNB) was heated to 200 °C followed by passing chlorine gas for 8 hours to obtain a product mixture comprising 1,2,3- trichlorobenzene. Off gases were scrubbed in a suitable scrubber. The product 1,2,3- trichlorobenzene was isolated by fractional distillation as such without any workup procedure.
Yield of 1,2,3-trichloro-benzene obtained was greater than 75 m % and purity was not less than 99.5 %.
Example (vii) - Preparation of 1, 2, 3 trichlorobenzene without using halide salt
In a reactor, 2 moles of 2,3 dichloro nitro benzene (2, 3 DCNB) was heated to 200 °C followed by passing chlorine gas for 8 hours to obtain a product mixture comprising 1,2,3- trichlorobenzene. Off gases were scrubbed in a suitable scrubber. The product 1,2,3- trichlorobenzene was isolated by fractional distillation after workup and extraction with solvent.
Yield of 1,2,3-trichloro-benzene obtained was greater than 75 m % and purity was not less than 99.5 %.
TECHNICAL ADVANCEMENT
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of a process for the preparation of a herbicide intermediate i.e. 1,2,3- trichlorobenzene, that
• is simple, cost effective and environment friendly;
• provides 1,2,3- trichlorobenzene having a comparatively better purity and yield;
• is a one pot reaction;
• does not employ acids or bases as reagents;
• high purity product is obtained by fractional distillation and low purity fractions are recycled so as to minimize the loss of product; and
• by-product gases are scrubbed and used in diazotization reaction.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following 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 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.
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 invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
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 given for various physical parameters, dimensions, and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions, and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment 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:WE CLAIM:
1. A process for the preparation of 1,2,3-trichlorobenzene, said process comprising the following steps:
a) chlorinating ortho nitro chlorobenzene with a first chlorinating agent in the presence of a catalyst at a first predetermined temperature for a first predetermined time period to obtain a mixture of 2,3-dichloronitrobenzene and 2,5-dichloronitrobenzene;
b) separating 2,3-dichloronitrobenzene from said mixture to obtain a separated 2,3-dichloronitrobenzene; and
c) denitrochlorinating said separated 2,3-dichloronitrobenzene by using a second chlorinating agent optionally in the presence of a halide salt at a second predetermined temperature for a second predetermined time period to obtain 1,2,3-trichlorobenzene.
2. The process as claimed in claim 1, wherein said first chlorinating agent and said second chlorinating agent is chlorine gas.
3. The process as claimed in claim 2, wherein said chlorine gas is passed at a flow rate in the range of 0.05 m3/h to 0.5 m3/h.
4. The process as claimed in claim 2, wherein said chlorine gas is passed at a flow rate in the range of 0.08 m3/h to 0.2 m3/h.
5. The process as claimed in claim 1, wherein said catalyst is selected from the group consisting of ferric chloride (FeCl3) and iron (Fe) powder.
6. The process as claimed in claim 1, wherein a molar ratio of ortho nitro chlorobenzene to said catalyst is in the range of 1:0.01 to 1:0.05.
7. The process as claimed in claim 1, wherein a molar ratio of ortho nitro chlorobenzene to said catalyst is in the range of 1:0.015 to 1:0.03.
8. The process as claimed in claim 1, wherein said halide salt is selected from the group consisting of calcium chloride, potassium chloride and a mixture thereof.
9. The process as claimed in claim 1, wherein a molar ratio of 2,3-dichloronitrobenzene to said halide salt is in the range of 1:0.05 to 1:0.5.
10. The process as claimed in claim 1, wherein a molar ratio of 2,3-dichloronitrobenzene to said halide salt is in the range of 1:0.08 to 1:0.2.
11. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 50 °C to 150 °C.
12. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 60 °C to 120 °C.
13. The process as claimed in claim 1, wherein said first predetermined time period is in the range of 8 hours to 12 hours.
14. The process as claimed in claim 1, wherein said second predetermined temperature is in the range of 100 °C to 250 °C.
15. The process as claimed in claim 1, wherein said second predetermined temperature is in the range of 150 °C to 220 °C.
16. The process as claimed in claim 1, wherein said second predetermined time period is in the range of 5 hours to 20 hours.
17. The process as claimed in claim 1, wherein said second predetermined time period is in the range of 6 hours to 15 hours.
18. The process as claimed in claim 1, wherein a mass ratio of 2,5-dichloronitrobenzene to 2,3-dichloronitrobenzene in said mixture is in the range of 60:40 to 65:35.
19. The process as claimed in claim 1, wherein said step (b) of separating 2,3-dichloronitrobenzene from said mixture is carried out by fractional distillation to obtain a fraction of pure 2,5-dichloronitrobenzene and a fraction of pure 2,3- dichloronitrobenzene.
20. The process as claimed in claim 1, wherein said step (b) of separating 2,3-dichloronitrobenzene from said mixture is carried out by fractional distillation followed by melt-crystallization to obtain a fraction of pure 2,5-dichloronitrobenzene and a fraction of pure 2,3- dichloronitrobenzene.
21. The process as claimed in claim 1, wherein a yield of 1,2,3-trichlorobenzene is in the range of 70 mole% to 95 mole% and a purity of 1,2,3-trichlorobenzene is in the range of 98% to 99.9%.

Dated this 13th day of March, 2024

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R.K.DEWAN & CO.
AUTHORIZED AGENT OF APPLICANT

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT CHENNAI