FIELD OF THE INVENTION
The present invention provides an improved process for the preparation of 2,2-difluorocyclopropane carboxylic acid derivatives of Formula I using mixture of solvents.

Formula I
wherein R1 is substituted or unsubstituted alkyl or aryl group

BACKGROUND OF THE INVENTION
The 2,2-difluorocyclopropane carboxylic acid derivatives are used as intermediate for complex organic molecules in the pharmaceutical or agricultural industries.
There are several methods known for the preparation of 2,2-difluorocyclopropane carboxylic acid derivatives.
Journal of Medicinal Chemistry, 30(6), 1074-90; 1987, describes a process for preparation of difluorocyclopropane carboxylic acid by reacting 1,1-difluoro-2-vinylcyclopropane with potassium permanganate and sodium bicarbonate.
Journal of Fluorine Chemistry, 126(3), 339-343; 2005, discloses a process for the preparation of 2,2-difluorocyclopropanecarboxylic acid by refluxing 2,2-difluorocyclopropanecarboxylic acid butyl ester in four equivalents of aqueous sodium hydroxide for overnight.
Journal of Organic Chemistry, 76(9), 3450-3456; 2011, discloses a process for preparation of 2,2-difluorocyclopropanecarboxylic acid by refluxing n-butyl-2,2-difluorocyclopropanecarboxylate with three equivalents of an aqueous potassium hydroxide for 10 hours.
The above cited processes take long hours and are performed using large excess of alkali metal hydroxides in water that would require large quantities of acid for neutralization leading to the degradation of the product.
Thus with this state of the art in mind, there is a need to provide improved process over the existing one. The present invention provides a simple, safe and improved cost effective method for preparing 2,2-difluorocyclopropane carboxylic acid derivatives.

OBJECT OF THE INVENTION
The main object of the present invention is to provide an industrially viable process for the preparation of 2,2-difluorocyclopropane carboxylic acid derivatives.

SUMMARY OF THE INVENTION
The present invention provides an improved process for preparation of a compound of Formula I,

Formula I
wherein R1 is substituted or unsubstituted alkyl or aryl group,
comprising the step of reacting a compound of Formula II,

Formula II
wherein R1 and R2 are substituted or unsubstituted alkyl or aryl group,
with a base in a solvent to obtain compound of Formula I.

DETAILED DESCRIPTION OF THE INVENTION
In an embodiment of the present invention, the compound of Formula II is reacted with a base selected from a group consisting of alkali metal and alkaline earth metal hydroxides, carbonates, bicarbonates.
The preferred base used in the step a) is selected from the group consisting of sodium carbonate, potassium carbonate, lithium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate or mixture(s) thereof.
In a preferred embodiment, the base used in the process of present invention is selected from an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide.
In an embodiment, the present invention is performed using 2.2 to 3.5 equivalents of the base.
In another embodiment, the present invention is performed using 2.2 to 2.8 equivalents of the base.
In another embodiment, the process of the present invention is carried out in a solvent selected from a group consisting water and a polar organic solvent.
The polar organic solvent can be selected from a group consisting of methanol, ethanol, isopropanol, tertiary butanol, pentanol, acetonitrile, and tetrahydrofuran or a mixtures thereof.
In a preferred embodiment, the process of the present invention is carried out in a mixture water and a polar aprotic organic solvent.
The aprotic polar organic solvent can be selected from a group consisting of dimethyl ether of diethylene glycol (diglyme), polyethylene glycol, polypropylene glycol, polytetramethylene glycol or polytetramethylene ether glycol, anisole, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, and 1-4-dimethoxybenzene or a mixtures thereof.
In another embodiment of the present invention, the solvent used is recovered, recycled and reused.
In an embodiment of the present invention, the process resulted in the formation of an alcohol as a by-product that is recovered and recycled.
In a particular embodiment, the present invention provides an improved process for preparation of 2,2-difluorocyclopropane carboxylic acid comprising the steps of reacting butyl 2,2-difluorocyclopropane-1-carboxylate with sodium hydroxide in presence of water and diglyme to obtain 2,2-difluorocyclopropane carboxylic acid.
In another particular embodiment of the present invention, the butanol produced as a by-product in the process is recovered and recycled.
The compound of Formula I is isolated by using techniques known in the art for example distillation, evaporation, column chromatography and layer separation or combination thereof.
In an embodiment, the hydrolysis of compound of Formula II is carried out at a temperature range of 25-35°C.
The hydrolysis of compound of Formula II is carried out within a time period of 2 to 5 hours.
The compound of Formula I so obtained by the present invention has a purity greater than 95 %, more preferably greater than 98 %, most preferably greater than 99.6 % by gas chromatography.
The compound of formula II used in the process can be obtained commercially or can be prepared by reacting an alkyl acrylate with methyl chlorodifluoro acetate and potassium bromide in a solvent in presence of a phase transfer catalyst to obtain an alkyl-2,2-difluorocyclopropane-1-caboxylate.
In another embodiment, the compound of formula II is prepared by reacting an alkyl acrylate with methyl chlorodifluoro acetate and potassium bromide in a solvent in presence of a phase transfer catalyst, which is then in situ treated with a base to obtain the compound of formula I.
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.

EXAMPLES
Example 1: Process of preparation for 2,2-difluorocyclopropane carboxylic acid
An aqueous solution of sodium hydroxide (21g), diglyme (412g) and butyl 2,2-difluorocyclopropane-1-carboxylate (37.2g) were added to a reactor and stirred at 25°C for 3 hours to obtain a reaction mass. The progress of the reaction mass was monitored by gas chromatography. After completion of the reaction, dichloromethane was added to the reaction mass to extract diglyme and the same extraction was repeated for three times to ensure complete extraction of diglyme from aqueous phase. The aqueous mass was neutralized using 10% hydrochloride acid (191g) and extracted with methyl tertiary butyl ether. The organic layer was concentrated to get a crude acid. Further, crude acid was purified by hexane to obtain the titled compound having purity of 99.6%.

CLAIMS:WE CLAIM:
1. A process for preparation of a compound of Formula I,

Formula I
wherein R1 is substituted or unsubstituted alkyl or aryl group,
comprising a step of reacting a compound of Formula II,

Formula II
wherein R1 and R2 are substituted or unsubstituted alkyl or aryl group,
with a base in a mixture of water and polar organic solvent to obtain the compound of Formula I.
2. The process as claimed in claim 1, wherein the polar organic solvent is selected from a group consisting of methanol, ethanol, isopropanol, tertiary butanol, pentanol, acetonitrile, tetrahydrofuran, diglyme, paraformaldehyde, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene ether glycol, anisole, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene and 1-4-dimethoxybenzene or a mixtures thereof.
3. The process as claimed in claim 1, wherein the base is selected from a group consisting of alkali metal and alkaline earth metal hydroxides, carbonates and bicarbonates.
4. The process as claimed in claim 3, wherein the base is selected from the group consisting of sodium carbonate, potassium carbonate, lithium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate or a mixture(s) thereof.
5. The process as claimed in claim 1, wherein the reaction is carried out at a temperature selected in the range of 20 to 35°C.
6. The process as claimed in claim 1, wherein the reaction is carried out using 2.2 to 3.5 equivalents of the base.