FIELD OF INVENTION
The present invention relates to a process for preparation of perfluoroalkyl halide. More
particularly, the present invention relates to a process for preparation of perfluoroalkyl halide by heating metal salt of ester of fluorine and iodine in presence of sulpholane.
BACKGROUND OF INVENTION
Perfluoroalkyl halide such as trifluoromethyl iodide is a useful chemical with molecular formula CF3I. CF3I is a potential fire suppression flooding agent for in-fight aircraft and electronic equipment fires, a fluorine-containing intermediate compound for introducing a trifluoromethyl group in producing surfactants, chemicals and pharmaceuticals, and the like Halon 1301, Halon 1211. Conventional fire extinguishers destroy the ozone layer, or cause global temperature rise by a greenhouse effect. Use of such extinguishers are being prohibited by environmental protection laws. On the other hand, trifluoromethyl iodide which have significantly shorter life in the air, causes negligibly ozone layer destruction and global temperature elevation. Therefore trifluoromethyl iodide is promising for use as the fire extinguisher.
Various methods have been reported for the synthesis of trifluoromethyl iodide. Prior to the invention the methods known for the preparation of trifluoromethyl iodide have involved or required one or more of expensive and/or not readily available reactants, multi-steps processes, processes with low selectivity for trifluoromethyl iodide with low yields, product containing high CO2 percentage and processes limited to lab scale production quantities.
In the article "Study on a novel catalytic reaction and its mechanism for CF3I synthesis", Nagasaki, Noritaka et al.. Catalyst Today (2004), 88 (3-4), 121-126, a vapour phase production process has synthesized CF3I by the reaction between CHF3 with I2 in the presence of a catalyst including alkali metal salts, which are supported on an activated carbon carrier.
JP 52068110 teaches that CF3I is prepared in high yield by vapor-phase reaction of Freon-23

with iodine in the presence of alkali or alkali earth metal salts. Thus, 200 ml/min Freon-23 is introduced to iodine, the resulting gaseous mixture of Freon 23 and iodine (iodine/Freon = 2.2 molar) is passed over 800 ml active carbon containing 7.5% KF for 10 hrs at 500 degree C to give 57.8% CF3I.
In DE 1805457, CF3I and C2F5I have been prepared from the corresponding bromides and KI without solvents. Thus, 0.3 mole CF3Br are passed through a layer of 3 mole KI of 6-8 micron particle size at 500 degree C to give 15% of CF3I, 0.3% of C2F5I and 85% of CF3Br which is then recycled.
"Preparation and properties of ZnBr(CF3)2L- a convenient route for the preparation of CF3I", Naumann, Dieter; et al, Journal of Fluorine Chemistry (1994), 67 (1), 91-3 discloses CF3Br as a starting material to synthesized CF3I in a multi-step reaction protocol. ZnBr(CF3)2L (L=DMF, MeCN) is prepared by the reactions of CF3Br with elemental Zn in better than 60% yield. The reaction of ZnBr(CF3)2DMF with iodine monochloride in DMF solution yield pure CF3I in better than 70% yield.
In a similar approach, disclosed in EP 0266281 and US patent 4794200, CF3I is prepared from CF3Br by contact with a metal or an alkali metal dithionate and SO2 in solution followed by filtration and treatment with iodine in a carboxylic or sulphonic acid. Thus, Zn, NaOH and SO2 in DMF in a Parr apparatus were pressurized with 3.7 bar CF3Br and the mixture stirred for 2 hrs whereupon the product was heated at 120 degree C over 9 hrs with iodine in HOAc during which CF3I (32%) was generated and recovered.
A direct synthesis of CF3I by direct iodination of CF3CO2H with iodine has been claimed using a flow reactor over various salt impregnated catalysts, such as copper iodide on activated carbon, in "Synthesis of CF3I by direct iodination of CF3COOH on solid catalyst", Lee, Kyong-Hwan et al, Hwahak Konghak (2001), 39(2), 144-149. In this experiment, the effects of support types, salt types and salt contents for the manufactured catalysts and also those of reaction

conditions such as reaction temperature, contact time and feeding mole ratio of reactant was tested. It has been reported that a longer contact time lead to the higher yield of CF3I. The optimized reaction conditions are: I2/CF3COOH mole ratio is above 1 and reaction temperature is about 400 degree C. Active carbon as a support shows better performance than alumina. For the salt impregnated on support, the best results of both salt content and salt type are 7.5 wt. percentages and Cul type respectively. In the reaction conditions, the catalyst was readily deactivated.
In "A simple novel method for the preparation of trifluoromethyl iodide and diiododifluoromethane", Su, Debao et al, Journal of the Chemical Society, Chemical Communications (1992), (U) 807-8, CF3I has been synthesized in 70-80% yield by treatment of XCF2CO2Me(X=Cl or Br) with iodine in the presence of potassium fluoride and copper (I) iodide. If KI is used instead of KF under similar conditions, CF2I2 is obtained in 50-60% yields without traces of Mel.
Therefore there exists a need for an alternative process for preparation of trifluromethyl iodide which is fairly simple and inexpensive as compared to the processes of the prior art. The process of the present invention is a one-step process which utilizes cheaper and/or readily available reactants. The process can be commercially adopted. Most of prior art methods result in products contaminated with CO2. The present invention provides a process for the commercial synthesis of very pure trifluoromethyl iodide which is free from CO2 contamination.
OBJECTIVES
The objective of the present invention is to provide a simple and inexpensive process which
utilizes cheaper and/or readily available reactants.
Another objective of the present invention is to provide a process which can be easily adopted
on a commercial scale and the product so formed do not require further purification step.
Yet another objective of the present invention is to provide a process wherein the product is
free from CO2 contamination.

STATEMENT OF INVENTION
Accordingly, the present invention relates to a process for the preparation of perfluoroalkyl halide wherein said process comprises heating a metal salt of ester of fluorine and iodine in presence of sulpholane,
SUMMARY OF INVENTION
The present invention relates to a process for the preparation of perfluoroalkyl halide. More particularly, the present invention relates to a process for preparation of perfluoroalkyl halide such as trifluoromethyl iodide. Trifluoromethyl iodide is prepared by heating potassium trifluoroacetate and iodine in presence of sulpholane. The molar ratio of potassium trifluoroacetate to iodine is in the range of 1:2 to 1:0.8 and the molar ratio of sulpholane to potassium trifluoroacetate is in the range of 1:0.5 to 1:2, more preferably in the molar ratio of 1:1. The reaction mixture is heated at a temperature ranging from 130 to 210 degree C, preferably at a temperature range of 140 to 170 degree C under atmospheric atmosphere for a period of 4 to 10 hours, more preferably for a period of 7 to 9 hours to obtain the trifluoromethyl iodide gas. After completion of the reaction, the colourless, odourless trifluoromethyl iodide gas is collected by passing through a trap containing aqueous sodium hydroxide or aqueous potassium hydroxide.
Trifluoromethyl iodide obtained by the process of present invention does not require any purification step. Yield of the product is very high i.e 78 to 81% with a high purity of 99%. The process is more economic as compared to the prior art as it uses inexpensive metal salt of trifluoroacetate. Further, the use of sulpholane is economical which is very cheap, easy to dehydrate, recover and recycle for reused. Hence it can be used commercially. The product also contain less than 1% of CO2 as impurity.
DETAILED DESCRIPTION OF INVENTION
The present invention relates to a process for preparation of perfluoroalkyl halide by heating metal salt of ester of fluorine and halogen in presence of sulpholane. More particularly, the

present invention relates to a process for the preparation of perfluoroalkyl halide such as trifluoromethyl iodide. Trifluoromethyl iodide is prepared by heating potassium trifluoroacetate and iodine in presence of sulpholane. The molar ratio of potassium trifluoroacetate to iodine is in the range of 1:2 to 1:0.8 and the molar ratio of sulpholane to potassium trifluoroacetate is in the range of 1:0.5 to 1:2 more preferably in the molar ratio of 1:1. The reaction mixture is heated at a temperature ranging from 130 to 210 degree C, preferably at a temperature range of 140 to 170 degree C under atmospheric atmosphere for a period of 4 to 10 hours, more preferably for a period of 7 to 9 hours to obtain the trifluoromethyl iodide gas. After completion of the reaction, the colourless, odourless trifluoromethyl iodide gas is collected by passing through a trap containing aqueous sodium hydroxide or aqueous potassium hydroxide.
Trifluoromethyl iodide obtained by the process of present invention does not require any purification step. Yield of the product is very high i.e 78 to 81% with a high purity of 99%. The process is more economic as compared to the prior art as it uses inexpensive metal salt of trifluoroacetate. Further, the use of sulpholane is economical which is very cheap, easy to dehydrate, recover and recycle for reuse. Hence it can be used commercially. The product also contain less than 1% of CO2 as impurity.
The process can be utilized for preparation of perfluoroalkyl bromide as well.
The following examples is given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention in any manner.
EXAMPLE 1
Preparation of trifluoromethyl iodide
A three neck 1 liter flask equipped with a stirrer was charged with lOOg potassium trifluoroacetate, 200g sulpholane and 184g iodine. The mixture was heated at a temperature of 160 degree Celsius for 8 hours to obtain trifluoromethyl iodide gas. The gas is collected by

passing through a trap containing aqueous sodium hydroxide.
The process yield 81% of trifluoromethyl iodide. The product is analyzed by GC-MS and
found to be 99% purity. The product contains less than 1% carbon dioxide as impurity.
Results
Expected CO2 generated 28.9g
Yield=100-105g (78-81%)
Purity (by GC-MS) > 99%
CO2 < (1%) theoretical @ CO2 of generated 28.9g
ADVANTAGES OF THE INVENTION
1. The process uses liquid solvent, sulpholane which is cheap and commercially available material.
2. Sulpholane is easy to dehydrate, recover and recycle for reuse.
3. The process uses a simple, one-step process for preparation of perfluoroalkyl halide.
4. No purification step is required.
5. The process uses inexpensive reactants such as potassium trifluoroacetate.
6. The product contain less than 1% of CO2 as impurity.
7. High yield of perfluoroalkyl halide with 78 to 81%.
8. High purity of perfluoroalkyl halide upto 99%.

We claim:
1. A process for the preparation of perfluoroalkyl halide wherein said process comprises: heating a metal salt of ester of fluorine and iodine in presence of sulpholane.
2. The process as claimed in claim 1, wherein the perfluoroalkyl halide prepared by said process is trifluoromethyl iodide.
3. The process as claimed in claim 1 or 2, wherein the metal salt of ester of fluorine for the preparation of trifluoromethyl iodide is potassium trifluoroacetate.
4. The process as claimed in claim 1, wherein the metal salt of ester of fluorine and iodine is heated at a temperature ranging from 130 to 210 degree Celsius.
5. The process as claimed in claim 1, wherein the metal salt of ester of fluorine and iodine is heated for a period ranging from 4 to 10 hours.
6. The process as claimed in claim 1, wherein the metal salt of ester of fluorine and iodine are in
the molar ratio ranging between 1:2 to 1:0.8,
7. The process as claimed in claim 1, wherein the sulpholane and metal salt of ester of
fluorine are in the molar ratio ranging between 1:0.5 to 1:2.
8. The process as claimed in claim 1, wherein the perfluoroalkyl halide is collected by passing through a trap containing aqueous alkali hydroxide.
9. The process as claimed in claim 8, wherein the aqueous alkali hydroxide is selected from a group consisting of aqueous sodium hydroxide and aqueous potassium hydroxide.
10. The process for preparation of perfluoroalkyl halide substantially as herein described
with reference to the foregoing example.