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 ALKYL THIOACETATES”

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 provides a process for preparation of alkyl thioacetates represented as compound of Formula I,

Formula I

BACKGROUND OF THE INVENTION
Alkyl thioacetates used as intermediates for organic molecules in the pharmaceutical and agricultural industries.
CN108774160A discloses a process for preparation of methylmercaptan ethyl acid esters and thiodiglycolic acid diester using methionine and halogenated acetic acids as raw material.
Journal of the Chemical Society [Section] C: Organic (1970), (15), 2016-22 discloses a method for preparing methyl(methylthio)acetates by reacting methyl thioglycolate with methyl iodide.
The conventional processes involve use of expensive reagents whose recovery and recycling are very difficult and tedious, and thereby increase the cost of production during commercial scaleups.
Thus, there is the need in the art for preparing commercially feasible process for the preparation of alkyl thioacetates. The present invention provides a cost effective and environment friendly process for the preparation of alkyl thioacetates.

OBJECT OF THE INVENTION
The object of the present invention is to provide an alternative and cost-effective process for preparation of alkyl thioacetates of formula I using metal methyl sulfate.

SUMMARY OF THE INVENTION
In an aspect, the present invention provides a process for preparation of a compound of formula I,

Formula I
wherein R1, R2, R3 and R4 represents hydrogen, methyl or ethyl and n is an integer 0-4, R represents C1-C8 alkyl group,
comprising the steps of reacting alkyl mercaptoacetate of formula II,

Formula II
with a metal methyl sulfate in presence of an aqueous alkali hydroxide to obtain a compound of formula I.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a cost-effective and an industrially applicable process for preparation of alkyl methylthioacetates.
As used herein, the alkali hydroxide may be selected from a group consisting of sodium hydroxide, potassium hydroxide, cesium hydroxide, and magnesium hydroxide or a like.
As used herein, the “metal methyl sulfate” preferably refers to a metal methyl sulfate produced as waste in industrially known methods. The metal methyl sulfate, particularly, recycled metal methyl sulfate is selected from recycled metal methyl sulfate such as sodium methyl sulfate or potassium methyl sulfate. The preferred metal methyl sulfate is sodium methyl sulfate.
As used herein, the “alkyl mercaptoacetates or compound of formula II” is selected from a group comprising methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, isopentyl thioglycolate, hexyl thioglycolate, heptyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, methyl 3-mercaptopropionate, ethyl 3-mercaptopropionate, propyl 3-mercaptopropionate, methyl 3-mercaptobutanoate and methyl 3-mercapto-2-methyl propanoate or a like.
As used herein, the “alkyl thioacetates” or “a compound of Formula I” selected from a group comprising methyl 2-(methylthio)acetate, ethyl 2-(methylthio)acetate, propyl 2-(methylthio)acetate, butyl 2-(methylthio)acetate, isopentyl 2-(methylthio)acetate, hexyl 2-(methylthio)acetate, heptyl 2-(methylthio)acetate, octyl 2-(methylthio)acetate, isooctyl 2-(methylthio)acetate, methyl 3-(methylthio)propionate, ethyl 3-(methylthio)propionate, propyl 3-(methylthio)propionate, methyl 3-(methylthio)butanoate and methyl 3-(methylthio)-2-methylpropanoate or a like.
In an embodiment of the present invention, the reaction of alkyl mercaptoacetates of formula II is carried out with a metal methyl sulfate in presence of an aqueous alkali hydroxide to form a compound of Formula I.
In another embodiment of the present invention, the reaction of alkyl mercaptoacetates of formula II is carried out with a metal methyl sulfates in presence of aqueous alkali hydroxide and solvent to form a compound of Formula I.
In a preferred embodiment of the present invention, the reaction of methyl thioglycolate is carried out with a sodium methyl sulphate in the presence of aqueous sodium hydroxide to form a methyl 2-(methylthio)acetate.
In a preferred embodiment of the present invention, the reaction of ethyl thioglycolate is carried out with a sodium methyl sulphate in the presence of aqueous sodium hydroxide to form ethyl 2-(methylthio)acetate.
In a preferred embodiment of the present invention, the reaction of methyl thioglycolate is carried out with potassium methyl sulphate in presence of aqueous potassium hydroxide to form a methyl 2-(methylthio)acetate.
In an embodiment of the present invention, the reaction is carried out at a temperature in the range from 0 to 80?, preferably 35-45?.
In an embodiment of the present invention, the aqueous solution of alkali hydroxide has concentration of 10 to 48%, preferably 20-25%.
In an embodiment of the present invention, the reaction is carried out in absence of a solvent.
In an embodiment of the present invention, the reaction is carried out in presence of a solvent.
The ‘solvent’ is selected from water, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, tert-butanol or like; alkyl acetates such as methyl acetate, ethyl acetate, propyl acetate or like; hydrocarbons such as toluene, xylene or like; chlorohydrocarbon such as chloroform, dichloromethane, dichloroethane or like, ethers such as diethyl ether, dimethyl ether, tetrahydrofuran; ketone such as acetone and methyl ethyl ketone, glyme such as monoglyme and diglyme.
In an embodiment, the compound of formula I is obtained with a yield of at least 85%, preferably more than 90%.
In an embodiment, the compound of formula I is obtained with a purity of at least 95%, preferably more than 97%.
As used herein, the term “isolating” refers to the method used to isolate the compound from the reaction mixture. The isolation is carried out using any of the process consisting of extraction, filtration, decantation, washing, dryings or combination thereof.
The completion of the reaction may be monitored by suitable chromatographic technique such as gas chromatography (GC).
The alkyl mercaptoacetates of formula II is used herein as starting material can be prepared by any of the methods known in the art or can be obtained commercially.
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 2-(methylthio)acetate.
Methyl thioglycolate (10g) and sodium methyl sulphate (15.6g) were added in aqueous solution of sodium hydroxide (5.5g) at 15-20°C. The reaction was allowed to proceed at 35 to 45°C for 10-12 hours. After reaction completion, extracted with dichloromethane, dried using sodium sulphate to obtain title compound.
Yield: 88%; Purity: 98%

Example 2: Preparation of ethyl 2-(methylthio)acetate.
Ethyl thioglycolate (10g) and sodium methyl sulphate (18.6g) were added in aqueous solution of sodium hydroxide (5.5g) and toluene (20g) at 15-20°C. The reaction was allowed to proceed at 35 to 45°C for 10-12 hours. After reaction completion, separated the layers, dried the organic layer with sodium sulphate to obtain title compound.
Yield: 85%; Purity: 98%
Example 3: Preparation of ethyl 2-(methylthio)acetate.
Ethyl thioglycolate (17g) and potassium methyl sulphate (21.9g) were added in aqueous solution of potassium hydroxide (9.35g) and toluene (34g) at 15-20°C. The reaction was allowed to proceed at 70 to 80°C. After reaction completion, separated the layers and extracted with fresh toluene, then dried to obtain title compound.
Yield: 70%; Purity: 98%.
,CLAIMS:WE CLAIM:
1. A process for preparation of a compound of formula I,

Formula I
wherein R1, R2, R3 and R4 represents hydrogen, methyl or ethyl and n is an integer 0-4, R represents C1-C8 alkyl group,
comprising reacting alkyl mercaptoacetate of formula II,

Formula II
with a metal methyl sulfate in presence of an aqueous alkali hydroxide to obtain a compound of formula I.
2. The process as claimed in claim 1, wherein the alkali hydroxide is selected from a group consisting of sodium hydroxide, potassium hydroxide, cesium hydroxide, and magnesium hydroxide.
3. The process as claimed in claim 1, wherein the metal methyl sulfate is a recycled metal methyl sulfate selected from the group consisting of sodium methyl sulfate and potassium methyl sulfate.
4. The process as claimed in claim 1, wherein the source of “metal methyl sulfate” used is industry waste.
5. The process as claimed in claim 1, wherein the reaction is carried out at a temperature in the range from 0 to 80?.
6. The process as claimed in claim 1, wherein the reaction is carried out in presence of a solvent selected from the group consisting of water, methanol, ethanol, propanol, isopropyl alcohol, butanol, tert-butanol, methyl acetate, ethyl acetate, propyl acetate, toluene, xylene, chloroform, dichloromethane, dichloroethane, diethyl ether, dimethyl ether, tetrahydrofuran, acetone, methyl ethyl ketone, monoglyme and diglyme.
7. The process as claimed in claim 1, wherein the compound of formula I is obtained with a yield greater than 85% and purity greater than 95%.
Dated this 8th day of March 2024.