FIELD OF THE INVENTION
The present invention provides a process for preparation of haloalkyl substituted phenol compounds of formula I.

Formula I
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.

BACKGROUND OF THE INVENTION
Haloalkyl substituted phenol compounds of formula (I) are useful in agricultural industry in the preparation of herbicides.
US Patent No. 5892126 discloses a process for preparation of 4-fluoro-3-trifluoromethyl phenol by hydrolysis of corresponding diazonium salt using about 1.3 molar equivalents of copper sulfate solution. The amount of copper sulfate used is very high and is lost during the workup resulting in the increase in the cost of the process at commercial scale ups. It does not disclose any process of recovering the copper sulfate from aqueous solution of diazotization reaction.
The inventors of the present invention have evolved a method of recovering and reusing copper sulfate from the process of preparation of haloalkyl substituted phenols, thereby reducing the cost of running the operations at commercial scales.

SUMMARY OF THE INVENTION
In an aspect, the present invention provides a process for preparation of a compound of Formula (I).

Formula I
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
comprising the steps of:
a) diazotizing a compound of Formula II using diazotizing agent to obtain a reaction mixture;

Formula II
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
b) contacting the reaction mixture of step a) with aqueous copper sulfate pentahydrate solution in presence of a solvent to obtain the compound of formula I; and
c) recovering copper sulfate from step b), wherein recovery of copper sulfate is more than 90%.
In another aspect, the present invention provides a process for preparation of a compound of Formula (I).

Formula I
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
comprising the steps of:
a) diazotizing a compound of formula II using diazotizing agent to obtain a reaction mixture,

Formula II
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
b) contacting the reaction mixture of step-(a) with aqueous copper sulfate pentahydrate solution in presence of a solvent to obtain a reaction mixture containing aqueous and organic layers;
c) separating aqueous and organic layers from step-b).
d) isolating a compound of formula (I) from organic layer;
e) acidifying aqueous layer and isolating copper sulfate, wherein recovery of copper sulfate is more than 90%.
DETAIL DESCRIPTION OF THE INVENTION
As used herein, the term “diazotizing” refers to the reaction of converting aniline into a diazonium ion by treating it with a diazotizing agent in presence of an acid in a solvent, optionally in presence of a stabilizing agent.
As used herein, the “diazotizing agent” refers to nitrous acid formed in situ by reacting nitrites and acid.
Nitrites refers to organic alkyl nitrites such as butyl nitrite, propyl nitrite, tert-butyl nitrite, amyl nitrite and inorganic metal nitrites such as sodium nitrite, potassium nitrite.
As used herein, the term “an acid” refers to hydrochloric acid, sulfuric acid, hydrobromic acid, phosphoric acid or mixtures thereof.
As used herein, the term “stabilizing agent” refers to a compound that prevent the decomposition of diazonium salt in solution. The preferred stabilizing agent for the present invention is urea.
In one embodiment, the aqueous solution of copper sulfate pentahydrate was mixed in an immiscible solvent.
The immiscible solvent used in the process may be selected from a group consisting of organic solvent such as toluene, xylene, hexane or a mixture thereof.
As used herein, the term “aniline” refers to substituted or unsubstituted aminobenzenes.
As used herein, the term “contacting” refers to the step of reacting, mixing, stirring or the like.
As used herein, the term “recovering” refers to the processes used in the art to obtain the compound from the reaction mixture. The process may include but are not limited to filtration, precipitation, decantation, isolation, crystallization, or the like.
As used herein, the term “isolating” refers to process of separating the compound from the mixture and may involve evaporation, filtration, decantation, distillation, layer separation or the like
In an embodiment, the present invention provides a process for the preparation of 4-fluoro-3-(trifluoromethyl) phenol, comprising the steps of:
a) diazotizing 4-fluoro-3-trifluoromethylaniline by using aqueous sodium nitrite in presence of sulfuric acid to obtain reaction mixture;
b) contacting the reaction mixture of step-(a) with aqueous copper sulfate pentahydrate solution and immiscible solvent to isolate 4-fluoro-3-(trifluoromethyl) phenol; and
c) recovering copper sulfate from the aqueous layer using acid, wherein recovery of copper sulfate pentahydrate is greater than 90%.
In another embodiment of the present invention, the process is carried out in presence of aqueous copper sulfate solution having concentration ranging from 20-50% and more preferably ranging from 30-40%.
In another embodiment of the present invention, the process of recovery of copper sulfate involves bringing the pH of the aqueous layer of step c) to 1.5 to 3 by adding sulfuric acid, followed by cooling the reaction mass obtained to 0 to 10°C and isolating 80 to 95% of copper sulfate.
In another embodiment of the present invention, the process of recovery of copper sulfate involves isolating 90-95% of copper sulfate.
The recovered copper sulfate may be analyzed by any method present in the art. The preferred method for present invention is titration for analysis of copper sulfate pentahydrate.
4-fluoro-3-trifluoromethylaniline used as raw material in the process may be prepared from methods given in the art or can be obtained commercially. Chinese patent application 101337911 discloses reduction process of 4-fluoro-3-trifluoromethylnitrobenzene using iron and ammonium chloride in presence of water to obtain 4-fluoro-3-trifluoromethylaniline.
The completion of the reaction may be monitored by any one of chromatographic techniques such as thin layer chromatography (TLC), high pressure liquid chromatography (HPLC), ultra-pressure liquid chromatography (UPLC), gas chromatography (GC), liquid chromatography (LC) and the like.
Unless stated to the contrary, any of the words “comprising”, “comprises” and includes mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it.
Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLE
Preparation of 4-fluoro-3-trifluoromethylphenol
Aqueous sulfuric acid (50%, 33.1g) and 4-fluoro-3-trifluoromethylaniline (5g) were charged in a reaction vessel. Reaction mass was cooled to -5 to 5°C and sodium nitrite aqueous solution (40%, 1.6g) was added dropwise in the reaction mass. After complete addition, urea (1.1g) was added to reaction mass and maintained at 0°C with optimum stirring.
Aqueous solution of copper sulfate pentahydrate (31%, 23.1g) and toluene (21.6g) were added in a separate flask and heated to 85°C. The reaction mixture was added dropwise to the copper sulfate pentahydrate solution maintained at 85°C. Progress of the reaction was monitored by liquid chromatography. After completion of the reaction, the reaction mass was cooled and layers were separated. The organic layer was washed with water and concentrated to get crude 4-fluoro-3-trifluoromethylphenol. The aqueous layer was kept for copper sulfate pentahydrate recovery. The crude material was further purified by vacuum distillation to obtain pure 4-fluoro-3-trifluoromethylphenol.
Yield: 60%
Purity (by LC): 99.0%
Recovery of copper sulfate pentahydrate:
The aqueous layer for copper sulfate was charged in a reaction flask. The sulfuric acid was added to the reaction flask slowly to attain a pH~2. The reaction mass was cooled to below 10°C and stirred for 30 minutes. The cooled mass was filtered to obtain copper sulfate pentahydrate of recovery greater than 90%. The recovered copper sulfate pentahydrate was feasible to use in further batches to product 4-fluoro-3-trifluoromethylphenol.

WE CLAIM:

1. A process for preparation of a compound of Formula (I).

Formula I
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
comprising the steps of:
a) diazotizing a compound of Formula II using diazotizing agent to obtain a reaction mixture;

Formula II
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
b) contacting the reaction mixture of step a) with aqueous copper sulfate pentahydrate solution in presence of a solvent to obtain the compound of formula I; and
c) recovering copper sulfate from step b), wherein recovery of copper sulfate is more than 90%.
2. A process for preparation of a compound of Formula (I).

Formula I
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
comprising the steps of:
a) diazotizing a compound of formula II using diazotizing agent to obtain a reaction mixture,

Formula II
wherein X represents a halogen group selected from fluoro, chloro, bromo and iodo and R1 represents C1-C3 alkyl group substituted with at least one fluorine atom.
b) contacting the reaction mixture of step-(a) with aqueous copper sulfate pentahydrate solution in presence of a solvent to obtain a reaction mixture containing aqueous and organic layers;
c) separating aqueous and organic layers from step-b).
d) isolating a compound of formula (I) from organic layer;
e) acidifying aqueous layer and isolating copper sulfate, wherein recovery of copper sulfate is more than 90%.
3. The process as claimed in claim 1 and claim 2, wherein diazotizing agent is prepared in situ using nitrite and acid.

4. The process as claimed in claim 3, wherein nitrite is selected from a group consisting of butyl nitrite, propyl nitrite, tert-butyl nitrite, amyl nitrite, sodium nitrite and potassium nitrite or a mixture thereof.
5. The process as claimed in claim 3, wherein the acid used in step a) is selected from a group consisting of hydrochloric acid, sulfuric acid, hydrobromic acid and phosphoric acid or a mixture thereof.

6. The process as claimed in claims 1 and claim 2, wherein the aqueous copper sulfate solution is having concentration selected in the range of 20-50%.

7. The process as claimed in claim 1 and claim 2, wherein the step b) is carried out in presence of a water immiscible solvent selected from a group consisting of toluene, xylene and hexane.