Field of the Invention
The present invention provides a process for the preparation of substituted fluorobenzenes.

Background of the Invention
The U.S Patent No. 4,155,940 describes a process for the preparation of a compound of Formula I via bromination of compound of Formula II followed by fluorine-exchange reaction.

Formula I Formula II

The Chinese Patent Publication No. 101643438 describes a process for the preparation of bromofluorobenzenes which involves the decomposition of diazonium salt at high temperature i.e., 120oC. The present inventors have observed that the diazonium saltsare unstable at high temperature and form impurities which reduces the yield of the desired product. The present inventors have observed that treatment of diazonium salt at low temperature leads to higher yield and less effluents, thus providing a far better industrial scale process.

Object of the Invention
The present invention provides a process for the preparation of substituted fluorobenzenes.
Summary of the Invention
The present invention provides a process for the preparation of a compound of Formula I, comprising
a) contacting a compound of Formula III with hydrogen bromide to obtain a reaction mixture,
b) contacting the step a) reaction mixture with copper (I) halide and sodium nitrite to obtain the compound of Formula I, and

Formula I Formula III

c) isolating the compound of Formula I obtained from step b).

Detailed Description of the Invention
In an aspect, the present invention provides a process for the preparation of a compound of Formula I, comprising:
a) contacting a compound of Formula III with hydrogen bromide to obtain a reaction mixture;
b) contacting the step a) reaction mixture with copper (I) halide and sodium nitrite to obtain the compound of Formula I; and

Formula I Formula III
c) isolating the compound of Formula I obtained from step b).

In particular, the present invention provides a process for the preparation of a compound of Formula I, comprising:
a) contacting a compound of Formula III with hydrogen bromide to obtain a reaction mixture;
b) contacting the step a) reaction mixture with copper (I) halide and sodium nitrite to obtain a compound of Formula I; and

Formula I Formula III

c) isolating the compound of Formula I obtained from step b), wherein step b) is carried out at a temperature range of 0oC to 50oC.

The compound of Formula III may be obtained commercially or may be prepared by method as disclosed in prior art, for example US Patent No. 4,725,683.

The step a) may take place in the presence of an acid. The acid may be an inorganic acid. The inorganic acid may be selected from the group consisting of nitric acid, phosphoric acid, sulfuric acid, boric acid, perchloric acid, hydrofluoric acid, hydrochloric acid, hydroiodic acid and hydrobromic acid.

The step b) may be carried out in presence of copper (I) halides selected from the group consisting of copper (I) bromide, copper (I) iodide and copper (I) chloride,
The step a) and step b) may be carried out in presence of water miscible solvents selected from the group consisting of formic acid and acetic acid.

The step b) takes place at a temperature range of 0oC to 50oC for 1hour to12 hours.

The step a) may be done either separately or step a) and step b) may be done in one-pot, wherein step a) product undergoes step b) reaction as such without isolation.

While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLES
Example: 1(a) Preparation of 3-bromo-4-fluorobenzotrifluoride
The sulfuric acid solution (140g, 1.4 mole, 98%) and 140 g de-mineralized water (DM water) were charged in a round-bottomed flask and the temperature of the mixture was maintained at 36°C. The 3-Amino-4-fluorobenzotrifluoride (50 g, 0.279 mole) was added to the reaction mass in 2 minutes and the mixture was stirred. The DM water (100 g) was added to the mixture to obtain slurry mass. The resultant slurry mass was cooled to -2°C using crushed ice salt and sodium nitrite solution (21.2 g, 0.30 mole and 100 g DM water) was added drop wise to the mixture. The mixture was stirred and the temperature was maintained in the range of -5 to 3°C for a period of 10 minutes. The diazo mixture was further maintained at -5 to 3°C for another 1 hour. The dark brown copper bromide and hydrogen bromide solution (4 g, 0.027 mole Cu (I) Br, 96.2 g 47 % hydrogen bromide solution and 100g DM water) were taken together in a round-bottomed flask and the mass was cooled to 0°C. The diazo mixture was contacted with copper bromide solution slowly over the period of 1 to 2 hours and the temperature of the mass was maintained in the range of 0 to 5°C. The resultant mass was stirred and maintained at 0 to 5°C for further 1 hour. The completion of reaction was monitored by gas chromatography (GC). The dichloromethane (200 g) was added to the reaction mass and the mixture was stirred for 15 minutes. The resultant layer was separated, neutralized with 5% sodium bicarbonate solution (100 g) to obtain the titled compound.
Yield (%): 66
Purity(%): 99.63 (by GC)

Example: 1(b) Preparation of 3-bromo-4-fluorobenzotrifluoride
The hydrogen bromide solution (290g, 1.674 mole, 47 %) and 290 g of DM water were charged in a round-bottomed flask at 36°C. The 3-amino-4-fluorobenzotrifluoride (100 g, 0.558 mole) was added to the reaction mass for 5 minutes and the reaction mass was continuously stirred. The Cu(I)Br (8 g, 0.055 mole) was added to the reaction mass. The Sodium nitrite solution (43 g, 0.614 mole and 210 g DM water) was added dropwise to the reaction mass with constant stirring over a period of 1.0 hour and the temperature of the mixture was maintained in the range of 25°C to 30°C. The completion of reaction was monitored by GC. The organic layer was separated, treated with sodium bicarbonate solution (250 g, 5 %) and distilled to obtain the titled compound.
Yield: 66%
Purity:99.6% (by GC)

WE CLAIM:
1. A process for the preparation of a compound of Formula I, comprising:
a) contacting a compound of Formula III with hydrogen bromide to obtain a reaction mixture;
b) contacting the step a) reaction mixture with copper (I) halide and sodium nitrite to obtain a compound of Formula I, and

Formula I Formula III

c) isolating the compound of Formula I obtained from step b).

2. The process as claimed in claim 1, wherein the step b) is carried out at a temperature range of 0oC to 50oC.

3. The process as claimed in claim 1, wherein the step a) is carried out in presence of an acid.

4. The process as claimed in claim 3, wherein the acid is inorganic acid, more preferably sulfuric acid.

5. The process as claimed in claim 5, wherein the preferred copper(I) halide is copper (I) bromide.

6. The process as claimed in claim 1, wherein step a) and step b) are carried out in presence of water miscible solvents selected from the group consisting of formic acid and acetic acid.

7. The process as claimed in claim 1, wherein the step b) is carried out within a time period of 1 hour to 12 hours.

8. The process as claimed in claim 1, wherein the step a) is carried out either separately or step a) and step b) are carried out in one-pot process.