The present invention relates to a process for preparation of 2,3,3,3-tetrafluoroprop ene.
BACKGROUND OF THE INVENTION
Fluoro olefins play an important role as refrigerants. In recent years a fluoro olefin viz. 2,3,3,3-tetrafluoropropene (HFO-1234yf) has attracted attention as a new refrigerant to replace another fluorinated refrigerants.
U.S. Patent No. 2,931,840 describes a process for preparation of HFO-1234yf by heating and decomposing a mixture of methyl chloride and chlorodifluoromethane or tetrafluoroethylene at a temperature from 700 to 950°C by a common heating means such as an electric heater in a reactor.
The said patent has followed free radical mechanism, therefore, the said process results in low yield due to formation of several by-products.
There are several other patents available in literature which avoid the free radical mechanism process and most of references utilize 1,1,1,2,3-pentafluoropropane (245eb) as a key intermediate for synthesizing HFO-1234yf
U.S. Patent No. 6,548,719 discloses a process for producing fluoro olefins by dehydrofluorinating a hydrofluorocarbon in the presence of a phase transfer catalyst without using any solvent or diluent.
U.S. Patent No. 7,560,602 discloses a process for producing 2,3,3,3-tetrafluoropropene by catalytic dehydrofluonnation of 1,1,1,2,3-pentafluoropropane (245eb) in the presence of alumina and chromium oxide catalysts.
U.S. Patent No. 8710282 discloses a process for producing 2,3,3,3-tetrafluoropropene by dehydrofluonnation of 1,1,1,2,3-pentafluoropropane (245eb) in the presence of potassium hydroxide.

Inventors of the present invention has discovered a novel intermediate
namely "2-bromo-l, 1,1,2-tetrafluoropropane" for synthesizing 2,3,3,3-
tetrafluoropropene. The said novel intermediate can also be used as a refrigerant.
OBJECT OF THE INVENTION
The object of the present invention is to provide a process for preparation of 2,3,3,3-tetrafluoropropene.
SUMMARY OF THE INVENTION
A first aspect of the present invention provides a process for preparation of 2,3,3,3-tetrafluoropropene comprising the step of de-hydrobrominating 2-bromo-1,1,1,2-tetrafluoropropane to 2,3,3,3-tetrafluoropropene.
A second aspect of the present invention provides a process for preparation of 2,3,3,3-tetrafluoropropene comprising the steps of:
i) fluorinating 2-bromo-3,3,3-trifluoropropene to obtain 2-bromo-l, 1,1,2-tetrafluoropropane; and
ii) de-hydrobrominating 2-bromo-l, 1,1,2-tetrafluoropropane to obtain 2,3,3,3-tetrafluoroprop ene.
A third aspect of the present invention provides a novel intermediate namely 2-bromo-1,1,1,2-tetrafluoropropane.
A fourth aspect of the present invention provides a process for preparation of 2-bromo-1,1,1,2-tetrafluoropropane comprising the step of fluorinating 2-bromo-3,3,3-trifluoropropene to obtain 2-bromo-l, 1,1,2-tetrafluoropropane.

DETAILED DESCRIPTION
The term "about" as used herein indicates 10% deviation in both sides from the specified parameter.
As disclosed herein, the step of fluorination is carried out using hydrogen fluoride optionally in the presence of a catalyst.
The fluorination is carried out either in gas or liquid phase.
The fluorination is carried out at a pressure of about 5 Kg/cm2 to about 20Kg/cm2
The catalyst used for fluorination is based on a metal including a transition metal or an oxide or halide or oxyhalide derivative of such a metal. Preferably, antimony halide is used as a catalyst for fluorination.
The antimony halide may be selected from a group consisting of antimony pentachloride, antimony chlorofluoride, or the like.
The fluorination is carried out at a temperature range of 40°C to 100°C, preferably at a temperature range of 70°C and 90°C for 1 to 50 hours.
The unreacted hydrogen fluoride was recycled back to the reactor.
The step of de-hydrobromination is carried out either using an alkali metal hydroxide or using hydrogen fluoride in presence of a catalyst.
The alkali metal hydroxide used for de-hydrobromination is selected from potassium hydroxide, sodium hydroxide, lithium hydroxide, or the like.
In an embodiment of the present invention the step of de-hydrobromination is carried out using alkali metal hydroxide in presence of a phase transfer catalyst.
The phase transfer catalyst is selected from a group consisting of
Trioctylmonomethylammomum chloride, benzyltriethylammomum chloride,
methyltrioctylammonium chloride, tetra-n-butylammonium chloride, tetra-n-
butylammonium bromide, tetra-n-butylphosphonium chloride,
bis[tris(dimethylamino)phosphine]iminium chloride and

tetratris[tris(dimethylamino)phosphinimino]phosphonium chloride, polyethylene glycol, crown ethers or the like.
The reaction of 2-bromo-l,l,l,2-tetrafluoropropane with alkali metal hydroxide is carried out at a temperature in the range of 30°C to 120°C and at a pressure in the range of 0-30Kg/cm2for few minutes to several hours till the reaction completion.
In one embodiment, the reaction is carried out at a temperature in the range of 50°C to 90°C for 12 hours to 24 hours.
After completion of the reaction, the reaction mixture is cooled at a suitable temperature in the range of -5°C to 10°C and gas phase is collected from reactor to super cooled vessel(-78°C). The outlet crude gas may further be purified to get a pure 2,3,3,3-tetrafluoropropene having purity at least 95% or atleast 99% or atleast 99.5%.
The catalyst used for de-hydrobromination is selected from zirconium catalyst, chromium containing catalyst, or the like.
After completion of the reaction, 2-bromo-l,l,l,2-tetrafluoropropane may be isolated by using any suitable technique known in the art such as layer separation, extraction, distillation and alike or combination thereof.
In an embodiment, the hydrogen bromide formed during the step of de-hydrobromination is converted to bromine that is recycled and reused in the reactor, thereby considerably reducing the cost of operating the process at commercial stage.
The hydrogen bromide is made to react with a strong acid such as sulphuric acid to recover bromine.
The present invention provides a novel intermediate namely 2-bromo-1,1,1,2-tetrafluoropropane.
In one embodiment, 2-bromo-l,l,l,2-tetrafluoropropane characterized by purity greater than 98% and yield not less than 80%.

The reaction may be conducted in a suitable reaction vessel or reactor. Preferably the vessel is comprised of materials which are resistant to corrosion as Hastelloy, Inconel, Monel and/or fluoropolymers linings. The vessel may contain catalyst, for example a fixed or fluid catalyst bed, packed with a suitable catalyst, with suitable means to heat the reaction mixture to the desired reaction temperature.
2-Bromo-3,3,3-trifluoropropene either can be obtained commercially or can be prepared by any methods known in the art.
In one embodiment, 2-bromo-3,3,3-trifluoropropene can be prepared by the method; wherein ethene and tetrachloromethane are reacted to give 1,1,1,3-tetrachloropropane followed by the reaction with chromia-alumina-zinc in the presence of hydrogen fluoride to give 3,3,3-trifluoropropene. Finally, 3,3,3-trifluoropropene is brominated to give 2,3-dibromo-l,l,l-trifluoropropane which upon de-hydrobromination gives 2-bromo-3,3,3-trifluoropropene.
The crude gaseous mixture may further be purified with any type of distillation or with any known techniques based on adsorption or absorption to get a pure 2,3,3,3-tetrafluoropropene.
The completion of the reaction can 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), gas chromatography-mass spectroscopy (GC-MS) and the like.
It is against this and other backgrounds, which shall be filed in a detailed manner in complete specifications, in due course, the present invention is brought out and explained in following non-limiting examples.

EXAMPLES Example 1: Process for preparing l,14?3-tetrachloropropane
1300g of (8.452mol) Carbon tetrachloride, 115g of (0.63 lmol) Triethylphosphate, 15.5g of (0.278mol) Iron, 0.4g of Iron chloride were charged in a 2 Litre Hastalloy pressure reactor. The reaction mass was flushed with nitrogen gas at a pressure of 2Kg/cm2 for two times and ethylene was flushed one time at a pressure of 2Kg/cm2. After that reactor was pressurized with ethylene at a pressure of 4Kg/cm2. Then heating and stirring was started, temperature was gradually increased and exothermicity was observed at 90°C. Temperature was raised to 120°C. Ethylene pressure was dropped; when temperature reached to 120°C, ethylene pressure maintained at a pressure of 8Kg/cm2. After 12 hours reaction was stopped and unreacted ethylene was vented, the reaction mass was unloaded and was taken for distillation. Distillation was done under vacuum. Initially unreacted carbon tetrachloride was collected, then product cut 1185g was collected, the catalyst was recycled back for next reaction. Purity (By GC): 98% Yield: 77%
Example 2: Process for preparing 3,3,3-trifluoropropene.
The inconnel Y type tubular reactor was charged with 400 to 500g of Chromia-Alumina-Zinc catalyst. The catalyst was first dried by heating under nitrogen atmosphere at 250°C for 24 hour. Next the pre-fluorination of the catalyst was begun by introducing HF along with nitrogen stream and the temperature was increased to 300°C for 16 hours. During the last 5 hours the nitrogen flow was gradually cut off. Finally, the temperature was reduced to 25°C.
The starting material 1,1,1,3-tetrachloropropane was charged at a rate of 60 ml per hour using dosing pump. On the other side hydrogenfluoride gas was passed

at a rate of 2g per min. The reactor temperature was maintained 225°C to 250°C. The gases exiting the reactor were scrubbed with potassium hydroxide solution to remove acid vapours and the gas was analyzed by GC-MS and GC. The major product was identified as 3,3,3-trifluoropropene. Purity (By GC): 98% Yield: 90%
Example 3: Process for preparing 2,3-dibromo-l,l?l-trifluoropropane
200g (1.25mol) bromine was charged in a three neck round bottom flask, the centre neck equipped with double condenser. Primary condenser was maintained at 0°C and the secondary condenser was maintained at -80°C, side necks were equipped with thermopocket and gas purging tube. Agitation and Cooling was started, at a temperature of 0-3°C. The 126g (1.31) 3,3,3-trifluoroprop-l-ene purging was started. After decolonisation of bromine, reaction was stopped. The product was analyzed using GC-MS and GC. Purity by GC: 98% Yield: 95%
Example 4: Process for preparing 2-bromo-3,3,3-trifluoropropene
60g (0.39Mol) of 26.5%) Sodium hydroxide solution was charged in a three neck round bottom flask, the centre neck was equipped with reflux divider with condenser, side necks were equipped with thermopocket and addition funnel. Then 3g (0.00742Mol) of trioctylmethylammoniumchloride was added. The reaction mass was agitated and heated to 50°C. At 50°C , the 50g (0.1953Mol) of 2, 3-dibromo-l, 1, 1-trifluoropropane addition was started. After completion of addition the temperature was raised to 70°C. The low boiling product refluxed at vapour temperature of 33-34°C in the reflux divider. The 27.5g (0.1571 Mol) 2-bromo-3, 3,

3-trifluoroprop-l-ene product was collected in the reflux divider. The collected product was analysed using GC-MS and GC. Purity (By GC): 99.20% Yield: 80.46%
Example 5: Process for preparing 2-bromo-l,14?2-tetrafluoropropane
A freshly prepared SbCb (350g), anhydrous hydrogen fluoride (400g) and 2-bromo-3,3,3-trifluoropropene (100g) were charged in a 2 lit Hastalloy reactor and slowly heated and maintained at 85°C for 4 hours. After 4 hours the hot reaction mixture was slowly vented off into ice water. After completion of venting, the aqueous layer was separated. The bottom layer consisting of crude organic of about 108g with the area composition of 85% of 2-bromo-1,1,1,2-tetrafluoropropane and 13%) of 2-bromo-3,3,3,-trifluoropropene by GC. The crude was further distilled to obtain pure 2-bromo-1,1,1,2-tetrafluoropropane. Purity(by GC):98% Yield: 80%
Example 6: Process for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf)
2-bromo-1,1,1,2-tetrafluoropropane (80g) was added to a mixture of aqueous sodium hydroxide (125g; 45%) and polyethylene glycol (3ml) in a 450ml Hastelloy reactor equipped with a mechanical agitator and coupled with a thermowell. The reaction mixture was slowly heated to 85°C and maintained for 24 hours. After 24 hours, the reactor was cooled to 10°C. The gas phase was collected from the reactor to a super cooled vessel (-78°C). The output crude gas was analyzed by GC. The crude material was further distilled to get pure HFO-1234yf Purity (by GC): 99.7% Yield: 85%

Recovery of Bromine
The hydrogen bromide formed during the reaction is passed through strong acid such as sulfuric acid to recover bromine that is recycled and reused in the process.

WE CLAIM:

1.A process for preparation of 2,3,3,3-tetrafluoropropene, comprising the step of de-hydrobrominating 2-bromo-l,l,l,2-tetrafluoropropane to obtain 2,3,3,3-tetrafluoroprop ene.
2. A process for preparation of 2,3,3,3-tetrafluoropropene comprising the steps of:
i) fluorinating 2-bromo-3,3,3-trifluoropropene to obtain 2-bromo-l, 1,1,2-tetrafluoropropane; and
ii) de-hydrobrominating 2-bromo-l, 1,1,2-tetrafluoropropane to obtain 2,3,3,3-tetrafluoropropene.
3. A novel compound of formula 1,
Br
F
2-bromo-l, 1,1,2-tetrafluoropropane (formula 1).
4. A process for preparation of 2-bromo-l, 1,1,2-tetrafluoropropane,
comprising the step of fluorinating 2-bromo-3,3,3-trifluoropropene to obtain 2-
bromo-1,1,1,2-tetrafluoropropane.
5. The process as claimed in claim 1 & 2, wherein the step of de-
hydrobromination is carried out using alkali metal hydroxide, preferably potassium

hydroxide, sodium hydroxide or lithium hydroxide or using hydrogen fluoride with a catalyst, preferably zirconium or chromium containing catalyst.
6. The process as claimed in claim 1 & 2, wherein the step of de-hydrobromination is carried out using alkali metal hydroxide in presence of phase transfer catalyst, selected from a group consisting of trioctylmonomethylammonium chloride, benzyltriethylammonium chloride, methyltrioctylammonium chloride, tetra-n-butylammonium chloride, tetra-n-butyl ammonium bromide, tetra-n-butylphosphonium chloride, bis[tris(dimethylamino)phosphine]iminium chloride, tetratris[tris(dimethylamino)phosphinimino]phosphonium chloride, polyethylene glycol and crown ethers.
7. The process as claimed in claim 1 & 2, wherein de-hydrobromination is carried out at a temperature in the range of 30°C to 120°C and at a pressure in the range of 0-30Kg/cm2.
8. The process as claimed in claim 2 & 4, wherein the step of fluorination is carried out using hydrogen fluoride.
9. The process as claimed in claim 2 & 4, wherein the fluorination is carried out at a pressure in the range of 5 Kg/cm2 to 20Kg/cm2 and at a temperature in the rangeof40°Ctol00°C.

10. The process as claimed in claim 2 & 4, wherein the unreacted hydrogen fluoride was recycled back to the reactor.