DESC:FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

“PROCESS FOR PREPARATION OF ESTERS”

SRF LIMITED, AN INDIAN COMPANY,
SECTOR 45, BLOCK-C, UNICREST BUILDING,
GURGAON – 122003,
HARYANA (INDIA)

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to a process for producing aliphatic carboxylic acid esters.
BACKGROUND OF THE INVENTION
Aliphatic carboxylic acid esters, more importantly, the fluorinated aliphatic carboxylic acid esters are useful as surfactant, water and oil repellent agent, pharmaceutical and agricultural synthetic intermediates thereof.
U.S. Pat. No. 5,235,094 discloses a process for preparation of ester by reacting a nucleophile precursor and a diester with ethylenically unsaturated olefin at a temperature of -25°C to 10°C. The process uses alkali metal alkoxide as a nucleophile, dimethyl carbonate as a diester and tetrafluoroethene as an unsaturated olefin to generate an ester along with an alcohol. The process involves using an excess of dimethyl carbonate which should be recycled in the reaction later for achieving a cost effectiveness process, however it is found that presence of an alcohol by-product in the process, hinders separation and thereby recycling of dimethyl carbonate.
The present invention provides an efficient method of separating and recycling dimethyl carbonate in the process of preparation of esters.
OBJECT OF THE INVENTION
The main object of the present invention provides a cost-effective method of separation and recycling of dimethyl carbonate in the process of preparation of esters.
SUMMARY OF THE INVENTION
The present invention provides a method for preparing an ester comprising the steps of:
(a) contacting a mixture of a base and dimethyl carbonate in an organic solvent with an organic precursor;
(b) contacting an acid with the reaction mixture of step a);
(c) recovering the ester from step b) and obtaining acidified spent solvent;
(d) adding an entrainer to the acidified spent solvent;
(e) recovering and recycling back the mixture of dimethyl carbonate and the organic solvent into the step a) reactor; and
(f) recovering and recycling back the entrainer into step d).
DETAILED DESCRIPTION OF THE INVENTION
As used herein the term “ester” refers to the compounds selected from a group consisting of methyl 3-methoxy-2,2,3,3-tetrafluoropropionate, methyl 3-ethoxy-2,2,3,3-tetrafluoropropionate, methyl 3-propoxy-2,2,3,3-tetrafluoropropionate, methyl 3-t-butoxy-2,2,3,3-tetrafluoropropionate; methyl 4-fluorobenzoylacetate; and methyl 3-oxo-3-(thiophen-2-yl)propanoate or the like.
In another embodiment of the present invention, the base is selected from a group consisting of sodium hydride, potassium hydride, sodium methoxide, sodium ethoxide, sodium propoxide, sodium isopropoxide, sodium t-butoxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium isopropoxide and potassium t-butoxide or the like.
In another embodiment of the present invention, the organic solvent is selected from a group consisting of tetrahydrofuran (THF) and dioxane or the like.
In another embodiment of the present invention, the organic precursor is an organic compound to be substituted with an ester group and is selected from a group consisting of tetrafluoroethylene, 2-acetylthiophene and p-fluoroacetophenone or the like.
In another embodiment of the present invention, the entrainer is a chlorinated solvent selected from a group consisting of dichloromethane, trichloromethane, tetrachloromethane and dichloroethane or the like.
In another embodiment of the present invention, dimethyl carbonate is used in a mole ratio of 1.5 to 2.5 with respect to the organic precursor.
In another embodiment of the present invention, 80 to 100% of the excess dimethyl carbonate and the organic solvent is separated from acidified spent solvent and recycled back to the reactor.
In an embodiment, the ester is recovered from the step-b) reaction mixture to obtain acidified spent solvent or spent solvent and followed for recovery of mixture of dimethyl carbonate and organic solvent.
In an embodiment of the present invention, the process provides a preparation of methyl 3-methoxy-2,2,3,3-tetrafluoropropionate comprising the steps of:
(a) contacting a mixture of sodium methoxide and dimethyl carbonate in an organic solvent with tetrafluoroethylene;
(b) contacting an acid with the reaction mixture of step a);
(c) recovering the ester from step b) and obtaining acidified spent solvent;
(d) adding an entrainer to the acidified spent solvent;
(e) recovering and recycling back the mixture of dimethyl carbonate and the organic solvent into the reactor; and
(f) recovering and recycling back chlorinated solvent into step d).
In another embodiment of the present invention, 80-100% of the chlorinated solvent is recovered and recycled.
The recovery and recycling of dimethyl carbonate, organic solvent and the chlorinated solvent results in 60 to 89% reduction in the cost of the process at commercial scale.
In an embodiment, the present invention provides a process for preparation of ester, having yield in the range of 80 to 95%.
In an embodiment, the present invention provides a process for preparation of the ester, having purity greater than 97%, preferably greater than 98%, more preferably greater than 99%, and having impurities in an amount of 0.1 to 0.05%, preferably 0.1 to 0.05%.
The product may be isolated by any method known in the art, for example, chemical separation, extraction, acid-base neutralization, distillation, recrystallization, evaporation, column chromatography and filtration or a mixture thereof.
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 alike.
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: Preparation of methyl 3-methoxy-2,2,3,3-tetrafluoropropionate
Tetrahydrofuran (130 g), dimethyl carbonate (270.5 g) and sodium methoxide (81.2 g) were charged in a reactor and tetrafluoroethylene (158 g) was added at a temperature of 0-10°C. After completion of the reaction, the inert gas was slowly purged into the reactor to remove excess of tetrafluoroethylene. The reaction mixture was acidified using anhydrous HCl (152.8 g), filtered to remove salts. The filtrate was distilled to obtain the product and the spent solvent.
Purification of spent solvent to recover THF and dimethyl carbonate:
Dichloromethane (695 g) was added to the spent solvent and heated the mixture to 40-45°C. The mixture was distilled to obtain a mixture of dimethyl carbonate and tetrahydrofuran. The residual solvent was washed with water and layers were separated to obtain dichloromethane layer, which was recycled into the purification step. The mixture of dimethyl carbonate and tetrahydrofuran was recycled into the reactor part.
Example 2: Preparation of methyl 4-fluorobenzoylacetate
A solution of p-fluoroacetophenone (50 g) in THF (50 g) was added to a preheated mixture of tetrahydrofuran (135 g), dimethyl carbonate (66 g) and sodium hydride (36 g, 60%) in a dry reaction flask. After completion of addition, reaction mass was refluxed for 1 hour. The refluxed mass was cooled and added with a solution of methanol and THF, followed by quenching with saturated ammonium chloride solution under cooling. The reaction mass was acidified using HCl to pH 3 and extracted with DCM (3 X 150 g). The combined organic layer was subjected to distillation to obtain crude material and spent solvent.
Purification of spent solvents to recover THF and dimethyl carbonate:
Dichloromethane was added to the spent solvents and heated the mixture to 40-45°C. The mixture was distilled to obtain a mixture of dimethyl carbonate and tetrahydrofuran. The residual solvent was washed with water and layers were separated to obtain dichloromethane layer, which was recycled into the purification step. The mixture of dimethyl carbonate and tetrahydrofuran was recycled into the reactor part.
Example 3: Preparation of methyl 3-oxo-3-(thiophen-2-yl)propanoate
A solution of 2-acetylthiophene (12.6 g) in THF (100 g) was added to a preheated mixture of tetrahydrofuran (120 g), dimethyl carbonate (36 g) and sodium hydride (12 g, 60%) in a dry reaction flask. After completion of addition, reaction mass was refluxed for 1 hour. The reaction mass was cooled and quenched with water. The reaction mass was acidified using HCl and layers were separated. DCM was added to the aqueous layer and separated the layers. The combined organic layer was distilled to obtain crude material and spent solvents.
Purification of spent solvents to recover THF and dimethyl carbonate:
Dichloromethane was added to the spent solvents and heated the mixture to 40-45°C. The mixture was distilled to obtain a mixture of dimethyl carbonate and tetrahydrofuran. The residual solvent was washed with water and layers were separated to obtain dichloromethane layer, which was recycled into the purification step. The mixture of dimethyl carbonate and tetrahydrofuran was recycled into the reactor part.

,CLAIMS:

WE CLAIM:
1. A method for preparing an ester comprising the steps of:
(a) contacting a mixture of a base and dimethyl carbonate in an organic solvent with an organic precursor;
(b) contacting an acid with the reaction mixture of step a);
(c) recovering the ester from step b) and obtaining acidified spent solvent;
(d) adding an entrainer to the acidified spent solvent;
(e) recovering and recycling back the mixture of dimethyl carbonate and the organic solvent into the step a) reactor; and
(f) recovering and recycling back the entrainer into step d).
2. The process as claimed in claim 1, wherein the base is selected from a group consisting of sodium hydride, potassium hydride, sodium methoxide, sodium ethoxide, sodium propoxide, sodium isopropoxide, sodium t-butoxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium isopropoxide and potassium t-butoxide.
3. The process as claimed in claim 1, wherein the organic solvent is selected from a group consisting of tetrahydrofuran and dioxane.
4. The process as claimed in claim 1, wherein the organic precursor is selected from a group consisting of tetrafluoroethylene, 2-acetylthiophene and p-fluoroacetophenone.
5. The process as claimed in claim 1, wherein the entrainer is a chlorinated solvent selected from a group consisting of dichloromethane, trichloromethane, tetrachloromethane and dichloroethane.
6. The process as claimed in claim 1, wherein the dimethyl carbonate is used in a mole ratio of 1.5 to 2.5 with respect to the organic precursor.
7. The process as claimed in claim 1, wherein the 80 to 100% of the excess dimethyl carbonate and the organic solvent is separated and recycled back to the reactor.
8. The process as claimed in claim 1, wherein the ester is prepared with a yield in the range of 80 to 95%.
9. The process as claimed in claim 1, wherein the ester is prepared with a purity greater than 97%.
10. The process as claimed in claim 1, wherein the ester is prepared with impurities in an amount of from 0.1 to 0.5%.
Dated this 20th day of December 2022.