Field of the invention
The present invention provides a process for preparation of 2-bromo-3,3,3-trifluoro-1-propene and intermediates thereof.
Background of the invention
Bromotrifluoropropenes such as 2-bromo-3,3,3-trifluoro-l-propene is a very useful fire extinguisher and has desirable low ozone depletion potential (ODP) and global warming potential (GWP).
2-Bromo-3,3,3-trifluoro-l-propene may be used as an intermediate for preparing several refrigerants, or preferably used for preparing tetrafluoropropenes. Several methods are known in the prior art for preparation of 2-bromo-3,3,3 -trifluoro-1 -propene.
Japanese Pat. Pub. No. 2001-322955 discloses a process for preparation of 2-bromo-3,3,3-trifluoropropene from l,2-dibromo-3,3,3-trifluoropropane in presence of alkali metal hydroxide at 30-130°C by using water as a solvent.
The main disadvantage of the above process is that the use of water as a solvent makes the product isolation very difficult.
Chinese Pat. Pub. No. 102964207 discloses a process for preparation of 2-
bromo-3,3,3-trifluoropropene from l,2-dibromo-3,3,3-trifluoropropane in presence
of sodium hydroxide (30%) and a phase transfer catalyst selected from
tetrabutylammonium bromide, benzyltriethylammonium chloride,
tetrabutylammonium chloride, tetrabutyl ammonium hydrogen sulfate, tributylamine and linear polyethylene glycol.
The present invention provides a cost effective, industrially viable and safe process for preparation of 2-bromo-3,3,3-trifluoropropene and intermediates thereof.

Object of the invention
The main object of the present invention is to provide a cost effective, industrially viable and safe process for preparation of 2-bromo-3,3,3-trifluoropropene and intermediates thereof.
Summary of the invention
In first aspect, the present invention provides a process for preparation of 2-bromo-3,3,3-trifluoropropene comprising the steps of:
a) contacting a compound of Formula I,
Formula I wherein X represents F, CI, Br or I,
with hydrogen fluoride in presence of co-precipitated chromia/alumina catalyst to obtain 3,3,3-trifluoropropene;
b) brominating 3,3,3-trifluoropropene to 2,3-dibromo-1,1,1-
trifluoropropane; and
c) dehydrohalogenating 2,3-dibromo-l,l,l-trifluoropropane with a base in
presence of a phase transfer catalyst to obtain 2-bromo-3,3,3-trifluoropropene.
wherein the phase transfer catalyst is selected from a group consisting of trioctylmethyl ammonium halide and trioctylmethyl ammonium hydrogen sulfate.
In second aspect, the present invention provides a process for preparation of 3,3,3-trifluoropropene comprising, contacting a compound of Formula I,
,CX3
Formula I wherein X represents F, CI, Br or I,

with hydrogen fluoride in presence of co-precipitated chromia/alumina catalyst to obtain 3,3,3-trifluoropropene.
In third aspect, the present invention provides a process for preparation of 2-bromo-3,3,3-trifluoropropene comprising the step of dehydrohalogenating 2,3-dibromo-1,1,1-trifluoropropane with a base in presence of a phase transfer, wherein the phase transfer catalyst is selected from the group consisting of trioctylmethyl ammonium halide and trioctylmethyl ammonium hydrogen sulfate.
Detailed description of the invention
The term "phase transfer catalyst" used in the present invention refers to trioctylmethyl ammonium halides or trioctylmethyl ammonium hydrogen sulfate. Examples of trioctylmethyl ammonium halides includes trioctylmethyl ammonium chloride, trioctylmethyl ammonium iodide, trioctylmethyl ammonium bromide and trioctylmethyl ammonium fluoride.
The step of de-hydrohalogenation is optionally carried out in absence of solvent.
The term "base" as used in the present invention refers to an organic or an inorganic base or the mixtures thereof. Examples of inorganic base includes alkali metal hydroxides selected from lithium hydroxide, sodium hydroxide, potassium hydroxide and alkaline earth metal hydroxides selected from calcium hydroxide and magnesium hydroxide. The organic bases are selected from the group consisting of alkali metal alkoxides, and the like. Examples of alkali metal alkoxide includes sodium methoxide, sodium ethoxide, sodium propoxide, sodium isopropoxide, sodium butoxide, sodium tertiary butoxide or potassium methoxide, potassium ethoxide, potassium propoxide, potassium isopropoxide, potassium butoxide, potassium tertiary butoxide and the like.
In an embodiment, the present invention provides a process for preparation of 2-bromo-3,3,3-trifluoropropene comprising the step of contacting 2,3-dibromo-l,l, 1-trifluoropropane with a base in presence of phase transfer

catalyst, wherein the phase transfer catalyst is selected from the group consisting of trioctylmethyl ammonium halide and trioctylmethyl ammonium hydrogen sulfate.
The phase transfer catalyst is used in 1 to 10 mole percentage. The phase transfer catalyst of the present invention can be easily recovered and reused.
The reaction is carried out at a temperature in the range of 45°C to 80°C for 30 minutes to 5 hours.
The alkali metal hydroxides and alkaline earth metal hydroxides are typically used in the form of an aqueous solution, prepared by dissolving the base in water having a concentration of 5% to 50% (w/v).
2-Bromo-3,3,3-trifluoropropene is isolated by using techniques known in the art for example distillation, evaporation, column chromatography and layer separation or a combination thereof.
The term "about" used hereinabove refers to the 10% variation from the specified parameter.
The present invention provides a process for preparation of 3,3,3-trifluoropropene, comprising the step of contacting a compound of Formula I with hydrogen fluoride in presence of co-precipitated chromia/alumina catalyst,
Formula I wherein X represents F, CI, Br or I.
The compound of Formula I represents any halo propane wherein X is F, CI, Br or I. Preferably, X is F or CI. Examples of compounds of Formula I include 1,1,1,3 -tetrachloropropane, 1,1,3 -trichloro-1 -fluoropropane, 1,3 -dichloro-1,1-difluoropropane, 3-chloro-l,l,l-trifluoropropane and 1,1,1,3-tetrafluoropropane.
In an embodiment, the present invention provides a process for preparation of 3,3,3-trifluoropropene, comprising the step of contacting 1,1,1,3-

tetrachloropropane with hydrogen fluoride in presence of co-precipitated chromia/alumina catalyst.
In another embodiment of the present invention, the step of contacting involves fluorination and de-hydrohalogenation.
In another embodiment of the present invention, the step of fluorination and de-hydrohalogenation is carried out simultaneously.
In an embodiment of the present invention, the step of fluorination and de-hydrohalogenation is carried out at a temperature ranging from about 200 to about 400°C.
In an embodiment of the present invention, the step of fluorination and de-hydrohalogenation is carried out at atmospheric pressure.
The hydrogen fluoride is essentially anhydrous hydrogen fluoride.
The molar ratio of 1,1,1,3-tetrachloropropane to hydrogen fluoride is selected in the range of 1:4 to 1:20.
In another embodiment, the co-precipitated chromia/alumina catalyst used in the present invention is essentially amorphous. The co-precipitated chromia/alumina catalyst used in the present invention may attain some degree of crystallinity over a period of time at high temperature.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst is impregnated with zinc, nickel, magnesium or salts thereof.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst is impregnated with zinc chloride.
In another embodiment of the present invention, the process of co-precipitation is performed using a base selected from ammonium hydroxide, sodium hydroxide and potassium hydroxide.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst contain chromium-aluminium in the atomic ratio of 1:1

to 1:14 and the amount of zinc compound impregnated ranges from about 2% to about 12%.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst contains about 20% to about 25% of chromia, about 70% to about 75%) of alumina and about 4% to about 6% of zinc chloride.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst contains about 22% to about 24% of chromia, about 71% to about 73%) of alumina and about 4% to about 6% of zinc chloride.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst has loss on ignition (LOI) of less than 20% at a maximum temperature of 375°C.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst has crush strength of more than 5Kg/cm2.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst has surface area of about 160 to about 300m2/g before it is subjected to pre-treatment with hydrogen fluoride.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst has surface area of at least 250m2/g before it is subjected to pre-treatment with hydrogen fluoride.
In another embodiment of the present invention, the co-precipitated chromia/alumina catalyst has bulk density ranging from about 0.8 to about 0.95Kg/l.
In another embodiment of the present invention, the chromia/alumina catalyst is in the form of pellets, granules or sticks of appropriate size for use in fixed bed or fluidised bed. The catalyst may be supported or unsupported.
In a preferred embodiment of the present invention, the chromia/alumina catalyst is present as a fixed bed.
In another embodiment of the present invention, the process is either carried out batch-wise or continuous in the vapour phase.

In another embodiment of the present invention, the process is carried out using the same catalytic bed comprising co-precipitated chromia/alumina catalyst for "N" number of times without loss of yield and selectivity. The table 1 shows the yield data of the reaction carried out at "N" number of times on the same catalytic bed.
Table-1

SNo N Raw material input (g) Yield %

1,1,1,3 -tetrachlorpropane HF
1 1 360 323 89.53
2 5 316 260 87.59
3 10 435 650 86.29
4 15 383 467 88.11
In an embodiment of the present invention, the co-precipitated chromia/alumina catalyst was regenerated, the process for recovery of the catalyst comprises the steps of:
a) drying the catalyst under inert atmosphere at 250-375°C for 4-10 hour;
b) simultaneously introducing air into the reactor for 24-48 Hours and;
c) reducing the temperature to 25-40°C.
The inert atmosphere can be attained using nitrogen or argon. The recovered co-precipitated chromia/alumina catalyst is very stable, does not undergo charring and can be stored for a long time, which makes the process highly suitable at industrial scale.
In another embodiment, the catalyst was first dried by heating under nitrogen atmosphere at 250°C for about 24 Hour. The dried catalyst was pre-fluorinated by introducing HF along with nitrogen stream and the temperature was

increased to 300°C. During the last 5 hours the nitrogen flow was gradually cut off. Finally, the temperature was reduced to 25°C to obtain the pre-fluorinated catalyst.
3,3,3-Trifluoropropene can be isolated by using techniques known in the art for example distillation.
The co-precipitated chromia/alumina catalyst used in the present invention is either procured commercially or is prepared by the method disclosed in WO/2001/074483 and Journal of fluorine chemistry 1999, 95, pp, 177-180, which are included as references.
The process may be carried out in a reactor made from the material resistant to corrosion such as Inconel® and Hastalloy.
Unless stated to the contrary, any of the words "comprising" and "comprises" 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 examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.
1,1,1,3-tetrachloropropane used as a starting material is commercially available or can be prepared by the method as disclosed in U.S. Pat. No. 4605802.
Trioctylmethyl ammonium chloride and trioctylmethyl ammonium hydrogen sulfate used as phase transfer catalyst are easily available on commercial scale.
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: Pre-fluorination of catalyst
The 500g of zinc chloride impregnated co-precipitated chromia-alumina catalyst was charged in a reactor. The catalyst was first dried by heating under nitrogen atmosphere at 250°C for 24 Hour. The dried catalyst was pre-fluorinated by introducing hydrogen fluoride (HF) along with nitrogen stream and the temperature was raised to 300°C and stirred for 16 hours at the same temperature. During the last 5 hours the nitrogen supply was gradually cut off. Finally, the temperature was reduced to 25°C to obtain pre-fluorinated catalyst. Example 2: Preparation of 3,3,3-trifluoropropene
The pre-fluorinated catalyst (600g) was charged in a reactor. 1,1,1,3-tetrachloropropane (360g) was then charged at a feed rate of 60 ml per hour. Simultaneously, the hydrogen fluoride gas (323g) was passed at a feed rate of 2g per minute. The reactor temperature was maintained at 225°C to 250°C. The progress of the reaction was monitored by gas chromatography. The gases exiting the reactor were scrubbed with potassium hydroxide solution to remove acid vapours and 180g of the title compound i.e., 3,3,3-trifluoropropene was obtained.
Yield: 94%; Purity: 98% (by gas chromatography).
Recovery of zinc/chromia/alumina catalyst
The used zinc chloride impregnated chromia/alumina catalyst (600g) obtained from example 2 was dried by heating under nitrogen atmosphere at 350°C for 4 Hour. Simultaneously the air was introduced into the reactor for 28 Hours and the temperature was reduced to 25°C. Then airflow was stopped and the 550g of catalyst was recovered.
Yield: 90% w/w. Example 3: Preparation 2, 3-Dibromo-l, 1,1-trifluoropropane
Bromine (200g (1.25mol)) was charged in a reactor equipped with condenser maintained at 0°C the secondary condenser maintained at -80°C. 3,3,3-

Trifluoroprop-1-ene (126g (1.31)) was purged in the reactor . After decolourisation of bromine reaction was stopped. The product was analysed using GC-MS and GC. Purity: 98% by GC (Area %); Yield: 95% Example 4: Preparation 2-bromo-3,3,3-trifluoro-l-propene
Trioctylmethylammonium chloride (3g) was added to an aqueous solution of sodium hydroxide (60g; 26.5%). 2,3-Dibromo-l,l,l-trifluoropropane (50g) was added slowly to the reaction mixture at a temperature of 50°C. The temperature of the reaction mixture was raised to 70°C. The low boiling product refluxed at vapour temperature of about 33 to 34°C in the reflux divider. 2-Bromo-3, 3, 3-trifluoroprop-1-ene (27.5g) was collected in the reflux divider. The collected product was analysed using gas chromatography (GC).
Purity: 99.2% by GC (Area %); Yield: 85%

WE CLAIM:
1. A process for preparation of 2-bromo-3,3,3-trifluoropropene, comprising the steps of: a) contacting a compound of Formula I,

Formula I wherein X represents F, CI, Br or I,
with hydrogen fluoride in presence of co-precipitated chromia/alumina catalyst to obtain 3,3,3-trifluoropropene;
b) brominating 3,3,3-trifluoropropene to obtain 2,3-dibromo-l,l,l-
trifluoropropane; and
c) dehydrohalogenating 2,3-dibromo-l,l,l-trifluoropropane with a base in
presence of a phase transfer catalyst to obtain 2-bromo-3,3,3-trifluoropropene,
wherein the phase transfer catalyst is selected from a group consisting of trioctylmethyl ammonium halide and trioctylmethyl ammonium hydrogen sulfate.
2. A process for preparation of 3,3,3-trifluoropropene comprising contacting a
compound of Formula I,
.^^ .cx3
Formula I wherein X represents F, CI, Br or I, with hydrogen fluoride in presence of co-precipitated chromia/alumina catalyst to obtain 3,3,3-trifluoropropene.
3. A process for preparation of 2-bromo-3,3,3-trifluoropropene, comprising the step
of dehydrohalogenating 2,3-dibromo-1,1,1 -trifluoropropane with a base in presence
of a phase transfer catalyst.

wherein the phase transfer catalyst is selected from the group consisting of trioctylmethyl ammonium halide and trioctylmethyl ammonium hydrogen sulfate.
4. The process as claimed in claim 1 and 3 wherein, base used is selected from a
group consisting of alkali metal hydroxides, preferably lithium hydroxide, sodium
hydroxide or potassium hydroxide.
5. The process as claimed in claim 1 and 2, wherein, the co-precipitated
chromia/alumina catalyst is impregnated with zinc, nickel, magnesium or salts
thereof.
6. The process as claimed in claim 1 and 2, wherein, the process of co-precipitation
is carried out using a base selected from a group consisting of ammonium
hydroxide, sodium hydroxide and potassium hydroxide.
7. The process as claimed in claim 1 and 2, wherein, the co-precipitated chromia/alumina catalyst contain chromium-aluminium in the atomic ratio of 1:1 to 1:14 and the amount of zinc compound impregnated ranges from about 2% to about 12%.
8. The process as claimed in claim 1 and 2, wherein, the co-precipitated chromia/alumina catalyst contains 20% to 25% of chromia, 70% to 75% of alumina and 4% to 6% of zinc chloride.
9. The process as claimed in claim 1 and 2, wherein, the co-precipitated chromia/alumina catalyst has surface area of about 160 to about 300m2/g before it is subjected to pre-treatment with hydrogen fluoride.

10. The process as claimed in claim 1 and 2, wherein, the co-precipitated chromia/alumina catalyst has bulk density ranging from 0.8 to 0.95Kg/l.