Field of the invention
The present invention provides a process for preparation of 1,1,1,2-tetrachlorodifluoroethane in liquid phase reaction.

Background of the invention
Tetrachlorodifluoroethanes are substantially less toxic than the related alkyl chlorides and thus have been widely used in the industry especially as solvent and as chemical intermediate.
There are a few processes known for preparation of 1,1,1,2-tetrachlorodifluoroethane
U.S. Patent No. 2,566,163 discloses a process for preparation of tetrachlorodifluoroethane by reacting ethylene fluoride and chlorine in presence of actinic rays while maintaining temperature above 300°C. Due to very high temperature range the process is not economical.
U.S. Patent No. 7,282,120 provides a process for preparation of 1,1,1,2-tetrachlorodifluoroethane using photochlorination of chloro-1,1-difluoroethane in gas phase. However, photochlorination reaction provides a mixture of isomers and lack selectivity.
U.S. Patent No. 8,536,387 provides a process comprising an addition reaction of elemental fluorine to tetrachloroethylene. The addition reaction predominantly gives 1,1,2,2-tetrachloro-1,2-difluoroethane as major product whereas 1,1,1,2-tetrachlorodifluoroethane is present in very small amount. An additional step is required to isomerise 1,1,2,2-terachloro-1,2-difluoroethane to 1,1,1,2-tetrachlorodifluoroethane using aluminium chloride as catalyst.
Thus it is an object of the present invention to provide a new process for producing 1,1,1,2-tetrachlorodifluoroethane with a high reaction rate and selectivity.

Object of the invention
The present invention provides a simple, safe and economic process for preparing 1,1,1,2-tetrachlorodifluoroethane by reacting 1,1-dichloro-2,2-difluoroethene with an electrophilic chlorinating agent at low temperature.

Summary of the invention
The present invention provides a process for selectively preparing 1,1,1,2-tetrachlorodifluoroethane comprising the step of reacting 1,1-dichloro-2,2-difluoroethene with an electrophilic chlorinating agent.

Detailed description of the invention
As used herein, “electrophilic chlorinating agent” is selected from a group consisting of elemental chlorine, sulfuryl chloride, oxalyl chloride, phosphorous pentachloride, phosphorous trichloride, triphenyl phosphine dichloride or like.
Electrophilic chlorinating agent is preferably elemental chlorine. The elemental chlorine may optionally be used as a mixture with one or more carrier gases (e.g. nitrogen). Any carrier gases are suitably inert gases, suitably inert to chlorine and suitably also inert to any other starting materials, products, or reagents of the methods of the invention.
The molar ratio of compound of chlorinating agent to compound of 1,1,-dichloro-2,2-difluoroethene is selected in the range of 0.9-1.5, preferably 0.95-1.05.
The step of reacting 1,1,-dichloro-2,2-difluoroethene with a electrophilic chlorinating agent is carried out in an inert solvent.
The inert solvent is selected from a group consisting of hydrocarbons such as toluene, hexane, xylene or like, a polar solvent such as dimethyl formamide, dimethyl sulfoxide, sulfolane, 1,4-dioxane or like, a halogenated hydrocarbon such as trichloroethane, dichloromethane, trichloromethane, tetrachloromethane, chlorofluoroalkanes or the like or mixture thereof. The chlorination is carried out in presence of tetrachloromethane and 1,1,1-trichloro-2,2,2,-trifluoroethane.
The solvent can be used in the ratio of 1: 10 to 1: 5 with respect to 1,1-dichloro-2,2-difluoroethene.
The step of reacting 1,1-dichloro-2,2-difluoroethene with an electrophilic chlorinating agent is carried out at temperature in the range 0 to 30°C in presence of an inert solvent.
It is known that at high temperature degradation and decomposition is higher for almost all molecules. The present invention provides a process to prepare 1,1,1,2-tetrachlorodifluoroethane at very low temperature which prevents formation of by-products and degradation and help in improvement of yield.
The present invention is very economical and safe, as the operating temperature is very low.
The chlorination is preferably carried out in liquid phase.
The present invention provides a process for preparation of 1,1,1,2-tetrachlorodifluoroethane, comprising the steps of:
a) adding 1,1-dichloro-2,2-difluoroethene to an inert solvent at a temperature of 0°C to 25°C to obtain a homogenous mixture;
b) passing chlorine to the homogenous mixture of step a);
c) distilling 1,1,1,2-tetrachlorodifluoroethane from step b).
1,1,1,2-tetrachlorodifluoroethane obtained is having purity greater than 95%, preferably greater than 98%.
1,1,1,2-tetrachlorodifluoroethane is isolated by any method known in the art, for example, chemical separation, extraction, acid-base neutralization, distillation, evaporation, column chromatography and filtration or a mixture thereof.
1,1,1,2-tetrachlorodifluoroethane may be isolated or can be used in-situ for preparation of other compounds.
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.
The preferred method for analysis for present invention is gas chromatography.
1,1-Dichloro-2,2-difluoroethene of present invention can be prepared or 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 1,1,1,2-tetrachlorodifluoroethane
Tetrachloromethane (50ml) was cooled to 0°C. 1,1-dichloro-2,2-difluoroethene (30g) was passed into the flask and stirred well. Chlorine gas (16g) was slowly purged into the reaction mixture continuously. After complete addition of chlorine gas, reaction mass was stirred for one hour. The progress of the reaction was monitored by gas chromatography. After completion of the reaction, the reaction mass was dried and distilled to obtain 1,1,1,2-tetrachlorodifluoroethane.
GC purity: 97%
Selectivity: 95%

Example 2: Preparation of 1,1,1,2-tetrachlorodifluoroethane
1,1,1-trichloro-2,2,2-trifluoroethane (50ml) was taken in a flask at 20°C. 1,1-dichloro-2,2-difluoroethene (30g) was passed into the flask and stirred well. Chlorine gas (16g) was slowly purged into the reaction mixture continuously. After complete addition of chlorine gas, reaction mass was stirred for one hour. The progress of the reaction was monitored by gas chromatography. After completion of the reaction, the reaction mass was dried and distilled to obtain 1,1,1,2-tetrachlorodifluoroethane.
GC purity: 96%
Selectivity: 94%

WE CLAIM:
1. A process for selectively preparing 1,1,1,2-tetrachlorodifluoroethane, comprising the step of reacting 1,1-dichloro-2,2-difluoroethene with an electrophilic chlorinating agent.
2. A process for preparation of 1,1,1,2-tetrachlorodifluoroethane, comprising the steps of:
a) adding 1,1-dichloro-2,2-difluoroethene to an inert solvent at a temperature of 0°C to 25°C to obtain a homogenous mixture;
b) passing electrophilic chlorinating agent to the homogenous mixture of step a); and
c) isolating 1,1,1,2-tetrachlorodifluoroethane from step b).
3. The process as claimed in claim 1 and 2, wherein electrophilic chlorinating agent is selected from a group consisting of elemental chlorine, sulfuryl chloride, oxalyl chloride, phosphorous pentachloride, phosphorous trichloride and triphenyl phosphine dichloride or a mixture thereof.
4. The process as claimed in claim 1 and 2, wherein the step of reacting 1,1,-dichloro-2,2-difluoroethene with a electrophilic chlorinating agent is carried out in an inert solvent selected from a group consisting of toluene, hexane, xylene dimethyl formamide, dimethyl sulfoxide, sulfolane, 1,4-dioxane, trichloroethane, dichloromethane, trichloromethane, tetrachloromethane and chlorofluoroalkanes or a mixture thereof.
5. The process as claimed in claim 1 and 2, wherein the step of reacting 1,1-dichloro-2,2-difluoroethene with an electrophilic chlorinating agent is carried out at a temperature selected in the range 0 to 30°C.
6. The process as claimed in claim 1 and 2, wherein the chlorination is carried out in liquid phase.

7. The process as claimed in claim 1 and 2, wherein 1,1,1,2-tetrachlorodifluoroethane is obtained with a purity greater than 95%.
8. The process as claimed in claim 1 and 2, wherein 1,1,1,2-tetrachlorodifluoroethane is isolated using chemical separation, extraction, acid-base neutralization, distillation, evaporation, column chromatography and filtration or a combination thereof.