The present invention provides a process for preparation of perfluoropropyl vinyl ether. Perfluoropropyl vinyl ether is a thermoplastic used in wide variety of applications.

BACKGROUND OF THE INVENTION
Perfluoroalkylvinyl ethers, the modified fluoropolymer have excellent chemical resistance, corrosion resistance, low temperature performance, and therefore are widely used in industry.
U.S. 3,896,179 discloses a process for preparation of perfluoroalkylvinyl ethers using corresponding acyl fluorides by decarboxylation up to 300°C in the presence of an activator, such as, zinc oxide and a salifying agent. It involves formation of considerable amount of secondary and tertiary isomers of the vinyl ether compounds that are highly undesirable and can act as a chain-transfer agents in the subsequent copolymerization.
U.S. 4,772,756 provides a process for preparation of perfluoroalkylvinyl ether using fluoroalkoxyperfluoroacyl fluoride in a solvent in presence of a salifying agent and dimethyl formamide as catalyst. The process require longer reaction time and poses many health hazards.
JP2877166B2 discloses a process for preparation of hexafluoropropene oxide dimer using a mixture of hexafluoropropene and hexafluoropropene oxide in presence of urea as a catalyst and an amine as a co-catalyst.
CN10187728A discloses a process for preparation of perfluoroalkylvinyl ether from hexafluoropropene (HFP) which involves oxidation of hexafluoropropene to form hexafluoropropylene oxide (HFPO). The process is extremely slow and complex and involve multiple separation column to purify product streams.
U.S. 4,303,593 discloses a process for dimerization of a mixture of HFP and HFPO to form HFPO dimer in presence of a catalyst and a copper complex-forming agent. The copper complex used in the process increases the overall process cost.
CN105017467 provides a process for preparation of perfluoroalkoxy polytetrafluoroethylene comprising pyrolysing tetrafluoroethylene to hexafluoropropylene, then oxidising it to hexafluoropropene oxide, isomerising to perfluorodipropionyl peroxide, followed by its addition to hexafluoropropylene to form perfluoroalkoxyacylfluoride and subsequent decarboxylation to obtain perfluoroalkylvinyl ether. The process involves multiple steps and silent about process yield.
The cited references have several drawback such as use of unnecessary co-catalysts, require complex systems, long reaction time and does not provide satisfactorily yield.
Therefore, there is a need to develop a process, that is, economical and industrially viable and overcome the drawback of existing processes.

OBJECT OF THE INVENTION
The main object of present invention is to provide a cost-effective and a scalable process for preparation of perfluoropropyl vinyl ether by circumventing the use of a co-catalyst and introducing a step of recycling HFP thereby increasing the overall efficiency of the process at industrial scale.

SUMMARY OF THE INVENTION
First aspect of the present invention provides an improved process for preparation of perfluoropropyl vinyl ether comprising the steps of:
a) epoxidation of hexafluoropropene using epoxidising agent in presence of a phase transfer catalyst to obtain a mixture of hexafluoropropene and hexafluoropropene oxide;
b) oligomerisation of a mixture of hexafluoropropene and hexafluoropropene oxide with a catalyst in a solvent to obtain a mixture 1;
c) isolating hexafluoropropene oxide dimer from mixture 1; and
d) reacting hexafluoropropene oxide dimer with a base in a solvent to isolate perfluoropropyl vinyl ether.
Second aspect of the present invention provides a process for preparation of perfluoropropyl vinyl ether comprising the steps of:
a) oligomerisation of a mixture of hexafluoropropene and hexafluoropropene oxide with a catalyst in a solvent to obtain mixture 1;
b) isolating hexafluoropropene oxide dimer from mixture 1; and
c) reacting hexafluoropropene oxide dimer with a base in a solvent to isolate perfluoropropyl vinyl ether.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, “Mixture of hexafluoropropene and hexafluoropropene oxide” refers to a mixture containing a sum of hexafluoropropene and hexafluoropropene oxide greater than 90%.
As used herein, “Mixture 1” refers to a mixture comprising hexafluoropropene and hexafluoropropene oxide, hexafluoropropene oxide dimer, polymers and solvent.
As used herein, “Epoxidising agent” refers to oxidising agents selected from a group consisting of sodium hypochlorite, sodium chlorite, sodium chlorate, sodium perchlorate, potassium hypochlorite, potassium chlorite, potassium perchlorate, potassium hypochlorite, potassium permanganate, peroxybenzoic acid, peroxyformic acid, peroxyacetic acid, meta-chloroperbenzoic acid, or the like.
As used herein, “oligomerisation” refers to dimerization, trimerisation or polymerisation. Preferably, oligomerisation refers to dimerization.
As used herein, “HFP” refers to hexafluoropropene.
As used herein, “HFPO” refers to hexafluoropropene oxide.
As used herein, “HFPO dimer” refers to hexafluoropropene oxide dimer.
As used herein, “Phase transfer catalyst” refers to a compounds selected from a group consisting of tetrabutyl ammonium chloride, tetra butyl ammonium bromide, trimethybutylethylammonium bromide, crown-6, tetraoctyl ammonium chloride, trioctylmethyl ammonium chloride or like.
The solvent used in oligomerisation and in reaction of hexafluoropropene oxide dimer with a base may be selected from a group consisting of monoglyme, diglyme, toluene, acetonitrile, tetrahydrofuran or like or a mixture thereof.
In one embodiment, the percentage of hexafluoropropene oxide in a mixture of hexafluoropropene and hexafluoropropene oxide may range from 50-80%.
In another embodiment, the mixture of hexafluoropropene and hexafluoropropene oxide may contain other components up to 3%.
In another embodiment, the epoxidation of hexafluoropropene using epoxidising agent is carried out at a temperature range of -10 to 10°C.
In a preferred embodiment, the epoxidation of hexafluoropropene using epoxidising agent is carried out in a temperature range selected from 0-5°C.
In another embodiment, the concentration of epoxidising agent is in the range of 10-12%.
In another embodiment, the epoxidising agent is added slowly using dosage pump in the reactor.
In another embodiment, the epoxidation of hexafluoropropene with epoxidising agent is carried in presence of a base.
The base for present invention may be selected from a group consisting of sodium carbonate, potassium carbonate, potassium hydrogen sulphate, sodium hydrogen sulphate or like or mixture thereof.
In one embodiment, epoxidation of hexafluoropropene with epoxidising agent is carried out in a solvent.
In preferred embodiment, the epoxidation is carried out in toluene as solvent.
In another embodiment, the gaseous phase of step a) is vented out and collected at -78°C after reaction to obtain a mixture of hexafluoropropene and hexafluoropropene oxide.
In an embodiment of the present invention, the step of oligomerisation of a mixture of hexafluoropropene and hexafluoropropene oxide is carried out using a catalyst in a solvent.
In another embodiment, a mixture of hexafluoropropene and hexafluoropropene oxide is reacted with a catalyst at a temperature ranging from 0-10°C.
The catalyst is selected from a group consisting of tetraalkylurea such as tetramethylurea or tetraethylurea.
In another embodiment, a mixture of hexafluoropropene and hexafluoropropene oxide is slowly added to the solvent at -10 to 30°C.
In preferred embodiment, the step of oligomerisation is carried out in diglyme as a solvent.
It is known that hexafluoropropene and hexafluoropropene oxide are very close boiling and are difficult to separate from their mixture.
In another embodiment of the present invention, the unreacted HFP in the step of oligomerisation from a mixture of HFP and HFPO to HFPO dimer is recycled back to the reactor).
In another embodiment of the present invention, HFP is recycled from mixture 1.
In another embodiment of the present invention, the gaseous phase of mixture 1 may be vented out and collected at below -25°C to recycle HFP.
In another embodiment of the present invention, 50 to 90% of HFP is recovered and recycled to the step a) of the process.
In another embodiment of the present invention, the catalyst and the solvent are also recovered and used in subsequent batches.
In another embodiment of the present invention, the process is carried out in batch, continuous or semi-continuous reactor.
In another embodiment of the present invention, the purity of isolated hexafluoropropene oxide dimer is greater than 90%.
In another embodiment of the present invention, the hexafluoropropene oxide dimer is isolated by separation and distillation.
In another embodiment of the present invention, the reaction of hexafluoropropene oxide dimer and base is carried out in presence of solvent.
Hexafluoropropene oxide dimer upon treatment with a base in diglyme as solvent gives perfluoropropylvinyl ether.
The reaction of hexafluoropropene dimer and base is carried out at a temperature ranging from 130-140°C.
In another embodiment of the present invention, the purity of isolated perfluoropropyl vinyl ether ranges from 85 to 98%.
The isolation technique used for present invention may be selected from a group consisting of chemical separation, distillation, reactive distillation, condensation, filtration, crystallization or like or combination 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.
The reagents used in the above process are 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
Step 1: Preparation of hexafluoropropene oxide
Hexafluoropropene (460g) was added in a reactor containing toluene (160g), aqueous sodium carbonate (800g) and trioctylmethylammonium chloride (1.4g) at -5°C. Sodium hypochlorite (10%) was slowly added in the reactor-using pump. The reaction mixture was stirred for half an hour to an hour at the same temperature. The gaseous organic phase was vented out and collected in a trap maintained at -78°C. The aqueous phase was extracted with solvent to remove entrapped organic. The trap material was analysed which shows a mixture of hexafluoropropene and hexafluoropropene oxide.
Analysis: GC purity
HFPO: 72%
HFP: 26%
Others: 2%
Yield: 53%
Step 2: Preparation of hexafluoropropene oxide dimer
The mixture of hexafluoropropene and hexafluoropropene oxide (100g) was passed in a reactor containing diglyme (78g) and tetramethylurea (4.615g) at -30°C. The reaction mixture was stirred at 5-10°C for 3-5 hours. After complete conversion, gaseous phase of reactor was vented and collected at -30°C. The organic phase and fluorous layer were separated. The fluorous layer was taken for distillation to isolate hexafluoropropene oxide dimer. Hexafluoropropene was recovered and recycled back to the step a).
Analysis: GC purity
HFPO dimer: 90%
Yield: 50%
Step 3: Preparation of perfluoropropyl vinyl ether
Hexafluoropropene oxide dimer dimer (30g), diglyme (50g) and sodium carbonate (20g) were taken in a round bottom flask. The reaction mixture was heated to 140°C and stirred for one hour. Perfluoropropyl vinyl ether was separated from reaction mixture by reactive distillation.
Yield: 73%
Purity: 89%

CLAIMS:WE CLAIM:
1. An improved process for preparation of perfluoropropyl vinyl ether comprising the steps of:
a) epoxidation of hexafluoropropene using epoxidising agent in presence of phase transfer catalyst to obtain a mixture of hexafluoropropene and hexafluoropropene oxide;
b) oligomerisation of the mixture of hexafluoropropene and hexafluoropropene oxide with a catalyst in a solvent to obtain a mixture 1;
c) isolating hexafluoropropene oxide dimer from mixture 1; and
d) reacting hexafluoropropene oxide dimer with a base in a solvent to isolate perfluoropropyl vinyl ether.
2. A process for preparation of perfluoropropyl vinyl ether comprising the steps of:
a) oligomerisation of a mixture of hexafluoropropene and hexafluoropropene oxide with a catalyst in a solvent to obtain mixture 1;
b) isolating hexafluoropropene oxide dimer from mixture 1; and
c) reacting hexafluoropropene oxide dimer with a base in a solvent to isolate perfluoropropyl vinyl ether.
3. The process as claimed in claim 1, wherein the epoxidising agent is selected from a group consisting of sodium hypochlorite, sodium chlorite, sodium chlorate, sodium perchlorate, potassium hypochlorite, potassium chlorite, potassium perchlorate, potassium hypochlorite, potassium permanganate, peroxybenzoic acid, peroxyformic acid, peroxyacetic acid and meta-chloroperbenzoic acid.
4. The process as claimed in claim 1, wherein the phase transfer catalyst is selected from a group consisting of tetrabutyl ammonium chloride, tetra butyl ammonium bromide, trimethybutylethylammonium bromide, crown-6, tetraoctyl ammonium chloride and trioctylmethyl ammonium chloride.
5. The process as claimed in claim 1, wherein the step a) reaction is carried out at a temperature range of -10 to 10°C.
6. The process as claimed in claims 1 and 2, wherein the catalyst used in oligomerisation is tetra alkylurea selected from a group consisting of tetramethylurea and tetraethylurea.
7. The process as claimed in claims 1 and 2, wherein the oligomerisation is carried at a temperature ranging from 0-10°C.
8. The process as claimed in claims 1 and 2, wherein the base is selected from a group consisting of sodium carbonate, potassium carbonate, potassium hydrogen sulphate and sodium hydrogen sulphate or a mixture thereof.
9. The process as claimed in claims 1 and 2, wherein the reaction of hexafluoropropene oxide dimer with a base is carried at a temperature ranging from 130-140°C.
10. The process as claimed in claims 1 and 2, wherein the solvent used is selected from a group consisting of monoglyme, diglyme, toluene, acetonitrile, tetrahydrofuran or a mixture thereof.

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