DESC:FIELD OF THE INVENTION
The present invention provides a process for the preparation of 1-nitro-4-(trifluoromethoxy)benzene.

BACKGROUND OF THE INVENTION
1-Nitro-4-trifluoromethoxybenzene is a useful intermediate in pharmaceuticals, pesticides, dyes, liquid crystal materials and electronic chemicals.
J. Am. Chem. Soc. 1987, 109, 3708-3713 provides a process for preparation of 1-nitro-4-(trifluoromethoxy)benzene by nitration of (trifluoromethoxy)benzene in the presence of nitronium tetrafluoroborate in nitromethane.
Chinese Publication No. 107266321 discloses a process for preparation of 1-nitro-4-(trifluoromethoxy)benzene by nitration of (trifluoromethoxy)benzene using fuming mixture of sulphuric acid and nitric acid.
PCT Publication No. 2016125185 discloses a process for preparation of 1-nitro-4-(trifluoromethoxy)benzene by nitration of (trifluoromethoxy)benzene using nitric acid. It was found that these already known processes inadvertently involves the formation of undesired 1-nitro-2-(trifluoromethoxy)benzene isomer that is very difficult to remove from the desired product owing to its close boiling point.
Therefore, there is a need in the art to provide a process that limits or eliminates the formation of the undesired 1-nitro-2-(trifluoromethoxy)benzene isomer.
The present invention provides an alternative process for preparation of 1-nitro-4-(trifluoromethoxy)benzene that has minimized the formation of undesired isomer thereby making the process cost effective and commercially viable.

OBJECT OF THE INVENTION
The main object of the present invention is to provide a simple, cost effective and commercially viable process for preparation of 1-nitro-4-(trifluoromethoxy)benzene that has minimized the formation of undesired isomer.

SUMMARY OF THE INVENTION
The present invention provides a process for preparation of 1-nitro-4-(trifluoromethoxy)benzene, comprising a step of fluorinating 4-(chlorodifluoromethoxy)-1-nitrobenzene.

DETAILED DESCRIPTION OF THE INVENTION
In an embodiment, 4-(chlorodifluoromethoxy)-1-nitrobenzene used in the process of present invention is prepared by a process comprising nitration of (chlorodifluoromethoxy)benzene.
In another embodiment, (chlorodifluoromethoxy)benzene used in the process of the present invention is prepared by a process comprising partial fluorination of (trichloromethoxy)benzene.
In another embodiment, 4-(chlorodifluoromethoxy)-1-nitrobenzene used in the process of present invention is prepared by a process comprising the steps of:
a) partial fluorination of (trichloromethoxy)benzene to give (chlorodifluoromethoxy)benzene; and
b) nitration of (chlorodifluoromethoxy)benzene.
In another embodiment, the present invention provides a process for preparation of 1-nitro-4-(trifluoromethoxy)benzene, comprising the steps of:
a) partial fluorination of (trichloromethoxy)benzene to give (chlorodifluoromethoxy)benzene;
b) nitration of (chlorodifluoromethoxy)benzene to give 4-(chlorodifluoromethoxy)-1-nitrobenzene; and
c) fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene to give 1-nitro-4-(trifluoromethoxy)benzene.
The present invention provides a process for preparation of 1-nitro-4-(trifluoromethoxy)benzene by partially fluorinating (trichloromethoxy)benzene to (chlorodifluoromethoxy)benzene. The nitration of chlorodifluoromethoxybenzene results in selective formation of 4-(chlorodifluoromethoxy)-1-nitrobenzene without the formation of undesired ortho-isomer i.e., 2-(chlorodifluoromethoxy)-1-nitrobenzene.
In another embodiment of the present invention, the step of partial fluorination is carried out in the presence of hydrogen fluoride.
In another embodiment of the present invention, the step of partial fluorination is carried out in the presence of anhydrous hydrogen fluoride.
In another embodiment of the present invention, the step of partial fluorination is carried out in the presence of 2.0 to 2.5 moles of hydrogen fluoride.
In another embodiment of the present invention, the step of partial fluorination is carried out at a temperature of 20°C to 50°C at a pressure of 0 to 5 bars.
In another embodiment of the present invention, the step of partial fluorination is carried out in presence of a catalyst selected from a group consisting of antimony trichloride, antimony pentachloride, antimony trifluoride, tetra-n-butylammonium fluoride, boron trifluoride, perfluoropropanesulfonyl fluoride, perfluorobutanesulfonyl fluoride, perfluoropentanesulfonyl fluoride, perfluoroheptanesulfonyl fluoride, perfluorooctanesulfonyl fluoride or the like.
After completion of step of partial fluorination, the remaining catalyst and HF are quenched, and the mass is distilled to get pure (chlorodifluoromethoxy)benzene. The quenching agents used in the present invention are selected from a group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate or potassium hydroxide, potassium carbonate, potassium bicarbonate or the like.
In an embodiment, (chlorodifluoromethoxy)benzene is obtained with a yield of 85% to 95% with a purity of 95 to 98%.
In another embodiment of the present invention, the step of nitration is carried out using a mixture of sulfuric acid and nitric acid.
In another embodiment of the present invention, the step of nitration is carried out using a mixture of 98% of sulfuric acid and 65-70% of nitric acid.
In another embodiment of the present invention, the step of nitration is carried out at a temperature of 0-5°C.
After completion of nitration, the reaction mass is quenched to get pure 4-(chlorodifluoromethoxy)-1-nitrobenzene.
In an embodiment, 4-(chlorodifluoromethoxy)-1-nitrobenzene is obtained with a yield of 90% to 95% with a purity of 97 to 99%.
In another embodiment of the present invention, the step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene is carried out in the presence of hydrogen fluoride.
In another embodiment of the present invention, the step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene is carried out in the presence of an anhydrous hydrogen fluoride.
In another embodiment of the present invention, the step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene is carried out in the presence of 10 to 15 mole ratio of hydrogen fluoride.
In another embodiment of the present invention, the step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene is carried out at a temperature of 150°C to 160°C at a pressure of 35 to 40 bars.
In another embodiment of the present invention, the step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene is carried out in an autoclave at a temperature of 150°C to 160°C at a pressure of 35 to 40 bars.
In another embodiment of the present invention, the step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene is carried out in presence of a catalyst selected from a group consisting of antimony trichloride, antimony pentachloride, antimony trifluoride, tetra-n-butylammonium fluoride, boron trifluoride perfluoropropanesulfonyl fluoride, perfluorobutanesulfonyl fluoride, perfluoropentanesulfonyl fluoride, perfluorohexanesulfonyl fluoride, perfluoroheptanesulfonyl fluoride, perfluorooctanesulfonyl fluoride or the like.
After completion of step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene, most of HF was recovered and recycled, the remaining catalyst and HF are quenched and the mass is distilled to get pure 1-nitro-4-(trifluoromethoxy)benzene. The quenching agents used in the present invention are selected from a group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate or potassium hydroxide, potassium carbonate, potassium bicarbonate and the like.
In another embodiment, 1-nitro-4-(trifluoromethoxy)benzene is obtained with a yield of 85% to 90% and a purity of 96 to 98%.
In another embodiment, 1-nitro-4-(trifluoromethoxy)benzene obtained in the process of the present invention has 0 to 0.05% of 1-nitro-2-(trifluoromethoxy)benzene isomer.

EXAMPLES
Example 1: Partial fluorination of (trichloromethoxy)benzene
(Trichloromethoxy)benzene (312g, 1 mole ratio) was added in an autoclave reactor. Antimony pentachloride catalyst (2.5g, 0.006MR) was added to the reactor and cooled the reaction mass to 0 to 5°C. Anhydrous hydrogen fluoride (74g, 2.5 mole ratio) was charged at 0 to 5°C. The reaction mass was heated in autoclave to 25°C and maintained for 2-3 hours at 20-50°C.
The catalyst and remaining hydrogen fluoride was neutralised with an aqueous solution of sodium bicarbonate (100g, 10%). The layers were separated to get crude product that was distilled to get pure (chlorodifluoromethoxy)benzene.
Yield: 90%, Purity (by GC): 98%
Example 2: Nitration of (Chlorodifluoromethoxy)benzene:
(Chlorodifluoromethoxy)benzene (214g, 98%) and sulphuric acid (180g, 98%) were charged in a reactor. The reaction mass was cooled to 0 to 5°C. Nitric acid (88.5g, 70%) was added to reaction mass in 2-3 hours at 0 to 5°C (Reaction was highly exothermic). The reaction progress was monitored by GC. The reaction mass was quenched into water (500g) and layers were separated to get 4-(chlorodifluoromethoxy)-1-nitrobenzene.
Yield: 95%, Purity (by GC): 99%
Example 3: Fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene
4-(chlorodifluoromethoxy)-1-nitrobenzene (262g, 99%) was charged in an autoclave reactor. Antimony pentachloride catalyst (8g) and hydrogen fluoride (210g) were added at 25°C. The reaction mass was heated to 160°C and 38 Kg/cm2 was autoclave pressure. The reaction mass was maintained for 5-6 hours at 160°C temperature and 38 Kg/cm2 pressure. The reaction mass was cooled to 50°C and vented gas into scrubber (HCl/HF gas). The catalyst and the unreacted hydrogen fluoride were neutralised using an aqueous solution of sodium carbonate (200g, 10%). The layers were separated to get crude product 1-nitro-4-(trifluoromethoxy)benzene and distilled to get pure product.
Yield: 90%, Purity: 99%
Example 4: Fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene
4-(chlorodifluoromethoxy)-1-nitrobenzene (130g, 99%) was charged in an autoclave reactor. Perfluorobutanesulfonyl fluoride (1g) and hydrogen fluoride (100g) were added at 25°C. The reaction mass was heated to 160°C and 38 Kg/cm2 was autoclave pressure. The reaction mass was maintained for 5-6 hours at 160°C temperature and 38 Kg/cm2 pressure. The reaction mass was cooled to 50°C and vented gas into scrubber (HCl/HF gas). The catalyst and the unreacted hydrogen fluoride were neutralised using an aqueous solution of sodium carbonate (100g, 10%). The layers were separated to get crude product 1-nitro-4-(trifluoromethoxy)benzene and distilled to get pure product.
Yield: 90%, Purity: 98%
Comparative example 1: Nitration of (trifluoromethoxy)benzene:
(Trifluoromethoxy)benzene (100g, 99%) and sulphuric acid (62g, 98%) was charged in a reactor. The reaction mass was cooled to 0 to 5°C. Nitric acid (62g, 70%) was added to reaction mass in 2-3 hr at 0 to 5°C (Reaction was highly exothermic). The reaction progress was monitored by GC. The reaction mass was quenched into water (200g) and layers were separated to get crude 1-nitro-4-(trifluoromethoxy)benzene. The crude product was analyzed by GC.
1-nitro-4-(trifluoromethoxy)benzene: 80%
1-nitro-2-(trifluoromethoxy)benzene: 20%
The crude product was further distilled to get pure 1-nitro-4-(trifluoromethoxy)benzene (82g). Yield: 40%;

CLAIMS:WE CLAIM:
1. A process for preparation of 1-nitro-4-(trifluoromethoxy)benzene, comprising a step of fluorinating 4-(chlorodifluoromethoxy)-1-nitrobenzene.

2. The process as claimed in claim 1, wherein the step of fluorination of 4-(chlorodifluoromethoxy)-1-nitrobenzene is carried out at a temperature of 150°C to 160°C and at a pressure range of 35 to 40 bars.

3. The process as claimed in claim 1, wherein the process further comprises a step of preparing 4-(chlorodifluoromethoxy)-1-nitrobenzene by nitration of (chlorodifluoromethoxy)benzene.

4. The process as claimed in claim 1, wherein the process further comprises the steps of:
a) partially fluorinating (trichloromethoxy)benzene to obtain (chlorodifluoromethoxy)benzene; and
b) nitrating (chlorodifluoromethoxy)benzene to obtain 4-(chlorodifluoromethoxy)-1-nitrobenzene.

5. The process as claimed in claims 1 and 4, wherein the step of fluorination is carried out in presence of hydrogen fluoride.

6. The process as claimed in claim 4, wherein the step of fluorination of (trichloromethoxy)benzene is carried out at a temperature of 20°C to 50°C and at a pressure of 0 to 5 bars.

7. The process as claimed in claim 4, wherein the step of nitration is carried out using a mixture of sulfuric acid and nitric acid.

8. The process as claimed in claims 1 and 4, wherein the step of fluorination is carried out in presence of a catalyst selected from a group consisting of antimony trichloride, antimony pentachloride, antimony trifluoride, tetra-n-butylammonium fluoride, boron trifluoride, perfluoropropanesulfonyl fluoride, perfluorobutanesulfonyl fluoride, perfluoropentanesulfonyl fluoride, perfluorohexanesulfonyl fluoride, perfluoroheptanesulfonyl fluoride and perfluorooctanesulfonyl fluoride.