Field of the invention
The present invention provides a process for preparation of tetrafluoropropene by reacting difluoromethane with difluorochloroethene in the presence of an activated aluminium catalyst, and intermediates thereof.
Background of the invention
Fluoropropenes, especially 1,1,1,2-tetrafluoropropene, being environmentally benign are developed to replace chlorofluorocarbons for use in the industry as refrigerants, solvents, cleaning agents, foam expansion agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing agents, sterilizers and power cycle working fluids.
Several processes are known in literature for the preparation of tetrafluoropropene involving addition of fluoromethylene derivative to ethylene derivative.
U.S. Patent No. 5,157,171 discloses a process for the addition of CHCl2F to CF2-CF2 using a modified aluminium chloride catalyst. Although relatively efficient, the products of these processes are a varied mixture of chlorofluorocarbons, including the configurational isomers of hydrochlorofluorocarbons. Thus, a separation step is required to obtain a commercially viable product hydrofluorocarbon.
U.S. Patent No. 8,258,353 discloses processes for preparation of fluoropropenes by reacting chloroethylene or chlorofluoroethylene and methane, chloromethane, fluoromethane or chlorofluoromethane at elevated pressures.
U.S. Patent Publication No. 20080027250 discloses processes for preparation of fluoropropenes by reacting a hydrofluoromethane selected from the group consisting of CH2F2 and CH3F, with a fluoroolefin selected from the group consisting of CF2-CF2, ClFC-CF2 and CF3CF-CF2, in the presence of an aluminium catalyst.
All the processes known in literature for preparation of tetrafluoropropene involves terminal ethylene derivatives. The present inventors have evolved a process which involves the use of hydrogen containing ethylene derivatives to produce tetrafluoropropene under mild reaction conditions.
Object of the invention
The present invention provides a simple, economic and industrially viable process for preparation of tetrafluoropropene by reacting difluoromethane with difluorochloroethene in the presence of an activated aluminium catalyst.

Summary of the invention
The first aspect of present invention provides a process for preparation of 1,1,1,2-tetrafluoropropene comprising the steps of:
a) fluorinating trichloroethene to obtain 1,2-dichloro-1,1-difluoroethane;
b) dehydrohalogenating 1,2-dichloro-1,1-difluoroethane to obtain difluorochloroethene;
c) reacting difluorochloroethene with difluoromethane to obtain 3-chloro-1,1,1,2-tetrafluoropropane;
d) dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.
Second aspect of present invention provides a process for preparation of a 1,1,1,2-tetrafluoropropene comprising the steps of:
a) dehydrohalogenating 1,2-dichloro-1,1-difluoroethane to obtain difluorochloroethene;
b) reacting difluorochloroethene with difluoromethane to obtain 3-chloro-1,1,1,2-tetrafluoropropane;
c) dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.
Third aspect of present invention provides a process for preparation of a 1,1,1,2-tetrafluoropropene comprising the steps of:
a) reacting difluorochloroethene with difluoromethane to obtain 3-chloro-1,1,1,2-tetrafluoropropane;
b) dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.
Fourth aspect of present invention provides a process for preparation of 1,1,1,2-tetrafluoropropene comprising the steps of dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.

Detailed description of the invention
As used herein, the step of fluorination is carried out using hydrogen fluoride optionally in the presence of fluorination catalyst.
The fluorination catalyst can be selected from a group consisting of antimony, tin, aluminium, iron, chromium, nickel based chlorides, fluorides and chlorofluorides, oxyfluorides or mixture thereof.
As used herein, the step of dehydrohalogenating 1,2-dichloro-1,1-difluoroethane, is carried out either using a base in presence of a phase transfer catalyst or using a dehydrohalogenation catalyst.
Phase transfer catalyst can be selected from a group consisting of quaternary ammonium salts such as tetrabutylammonium bromide (TBAB), trimethylbenzylammonium bromide, triethylbenzylammonium bromide, and trioctylmethylammonium chloride (TOMAC); phosphonium salts such as tetrabutylphosphonium chloride (TBPC); crown ethers such as 15-crown 5 and 18-crown 6; and the like. Examples also include known substances such as alkylammonium salts, carboxylic acid salts, and alkylsulfonic acid salts of these, quaternary ammonium salts are preferable, and, for example, tetrabutylammonium bromide, trioctylmethylammonium bromide, Aliquat 336 (registered trademark), or the like can be suitably used.
The base may be selected from a group consisting of carbonates such as sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, aluminium carbonate, hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, magnesium hydroxide and aq. sodium hydroxide or like and mixture thereof.
In a particular embodiment, the dehydrohalogenation of 1,2-dichloro-1,1-difluoroethane is carried out using sodium hydroxide in presence of Aliquat 336.
Preferably, sodium hydroxide in aqueous solution is selected in the range of 20% to 40%.
As used herein, the step of reacting difluorochloroethene with difluoromethane is carried out using an addition catalyst.
The molar ratio of compound of difluorochloroethene to difluoromethane is selected in the range of 1.5-2.5, preferably 1.75-2.25 and more preferably between 1.95-2.05.
Addition catalyst is selected from the group consisting of antimony fluoride fluorochloroantimonates, iron chloride, iron fluoride, nickel chloride, nickel bromide, nickel fluoride, copper fluoride, copper chloride, zinc chloride, zinc bromide, aluminium fluoride or aluminium chloride or aluminium bromide, aluminium chlorofluoride or aluminium bromofluoride or the like.
The reaction of difluorochloroethene with difluoromethane is carried out in a temperature range selected from 20°C to 60°C, preferably in the range 40°C to 45°C in presence of aluminium catalyst.
The aluminium catalyst is preferably activated using a fluorinated substrate selected from hydrogen fluoride, fluorine, trichlorotrifluoroethane, hexafluoropropane, fluorotrichloromethane or like. The fluorinated substrate is preferably fluorotrichloromethane or hexafluoropropene.
The step of reacting difluorochloroethene with difluoromethane may yield a mixture of 2-chloro-1,1,1,3-tetrafluoropropane and 3-chloro-1,1,1,2-tetrafluoropropane. The mixture can be used as such or may be distilled to obtain pure 3-chloro-1,1,1,2-tetrafluoropropane. When mixture is used as such for dehydrohalogenation, it also results in formation of 1,1,1,3-tetrafluoropropene along with desired 1,1,1,2-tetrafluoropropene. The 1,1,1,3-tetrafluoropropene can be distilled out in the final step.
As used herein, the step of dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane is carried out using a metal acetate optionally in a polar aprotic solvent.
As used herein, “metal acetate” refers to alkali acetate salts selected from a group consisting of potassium acetate, sodium acetate, lithium acetate or like and mixture thereof.
Polar aprotic solvent is selected from a group consisting of acetonitrile, diethyl ether, tetrahydrofuran, perfluorotetrahydrofuran, methyl acetate, ethyl acetate, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoramide or the like.
The volatile by products formed in the present reaction after reaction are vented off from reactor before reaction workup. The unreacted halopropane and certain reaction by-products can be recycled back to the reaction vessel to provide a continuous process. Alternatively, fresh halopropane may be supplied to the reaction mixture in order to run the process continuously.
In the present invention, preferred purification technique is distillation and the preferred method for analysis is gas chromatography (GC).
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 1,2-dichloro-1,1-difluoroethane
Freshly prepared antimony pentachloride catalyst (120g) was charged into an autoclave and anhydrous hydrogen fluoride (300g) was passed into the reactor at -10°C. Reactor was steadily warmed to 60°C with constant stirring for 90 minutes. A mixture of hydrogen fluoride and hydrogen chloride was vented at 60°C. Anhydrous hydrogen fluoride (300g) and trichloroethene (1000g) were charged into the reactor and heated to 55°C. After 5 hours, reaction was quenched with ice cold water and the obtained organic layer was separated and analysed by GC.
GC Purity: 92%
Yield: 81%
Example 2: Preparation of 2-chloro-1, 1-difluoroethene
1,2-dichloro-1,1-difluoroethane (700g), aliquat-336 (40g) and 30% aqueous solution of sodium hydroxide (1000g) were charged into the autoclave. Reaction mass was stirred for 24 hours at 35°C. Gaseous product formed was vented and collected at -30°C. Condensed mass was analyzed using gas chromatography.
GC Purity: 98.5%
Yield: 91%
Example 3: Preparation of 3-chloro-1,1,1,2-tetrafluoropropane
Anhydrous aluminium chloride (8g) and fluorotrichloromethane (60g) were charged into autoclave reactor and stirred at 30°C. After 2 hours, volatiles formed are removed through vacuum. difluorochloroethene (70g) and difluoromethane (107g) were charged to the vaccumized reactor at -40°C. Reactor was warmed gently and allowed to stir at 45°C for 12 hours. Volatiles were vented, quenched with ice cold water. The organic and aqueous layer were separated and organic layer was analyzed on GC.
GC Purity: 80%
Yield: 29%
Example 4: Preparation of 1,1,1,2-tetrafluoropropene
3-chloro-1,1,1,2-tetrafluoropropane (75g), potassium acetate (100g) and dimethyl formamide (100ml) were charged in an autoclave. Reaction mixture was heated to 100°C with constant stirring. After 8 hours, gaseous product was vented out and collected at -50°C. The obtained 2,3,3,3-tetrafluoropropene gas was analyzed on GC.
Yield: 73%
Purity by GC: 97%

WE CLAIM:
1. A process for preparation of 1,1,1,2-tetrafluoropropene, comprising the steps of:
a) fluorinating trichloroethene to obtain 1,2-dichloro-1,1-difluoroethane;
b) dehydrohalogenating 1,2-dichloro-1,1-difluoroethane to obtain difluorochloroethene;
c) reacting difluorochloroethene with difluoromethane to obtain 3-chloro-1,1,1,2-tetrafluoropropane;
d) dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.

2. A process for preparation of 1,1,1,2-tetrafluoropropene, comprising the steps of:
a) dehydrohalogenating 1,2-dichloro-1,1-difluoroethane to obtain difluorochloroethene;
b) reacting difluorochloroethene with difluoromethane to obtain 3-chloro-1,1,1,2-tetrafluoropropane;
c) dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.

3. A process for preparation of 1,1,1,2-tetrafluoropropene, comprising the steps of:
a) reacting difluorochloroethene with difluoromethane to obtain 3-chloro-1,1,1,2-tetrafluoropropane;
b) dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.

4. A process for preparation of 1,1,1,2-tetrafluoropropene, comprising the step of dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane to obtain 1,1,1,2-tetrafluoropropene.
5. The process as claimed in claim 1, wherein the step of fluorination is carried out using hydrogen fluoride.

6. The process as claimed in claim 1 and 2, wherein the step of dehydrohalogenating 1,2-dichloro-1,1-difluoroethane is carried out using a base in presence of a phase transfer catalyst, or using a dehydrohalogenation catalyst.

7. The process as claimed in claim 6, wherein the base is selected from a group consisting of sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, aluminium carbonate, sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, magnesium hydroxide and aqueous sodium hydroxide or a mixture thereof.

8. The process as claimed in claim 1, 2 and 3, wherein the step of reacting difluorochloroethene with difluoromethane is carried out using an addition catalyst selected from a group consisting of antimony fluoride, fluorochloroantimonates, iron chloride, iron fluoride, nickel chloride, nickel bromide, nickel fluoride, copper fluoride, copper chloride, zinc chloride, zinc bromide, aluminium fluoride, aluminium chloride, aluminium bromide, aluminium chlorofluoride and aluminium bromofluoride or a mixture thereof.

9. The process as claimed in claim 1, 2 and 3, wherein the step of reacting difluorochloroethene with difluoromethane is carried out using an aluminium catalyst activated using a fluorinated substrate selected from hydrogen fluoride, fluorine, trichlorotrifluoroethane, hexafluoropropne, fluorotrichloromethane.

10. The process as claimed in claim 1, 2, 3 and 4, wherein the step of dehydrohalogenating 3-chloro-1,1,1,2-tetrafluoropropane is carried out using a metal acetate selected from a group consisting of potassium acetate, sodium acetate and lithium acetate or a mixture thereof.