FIELD OF INVENTION:
The present invention relates to a process for the preparation of heptafluoroisopropyl iodide followed by purification of the product and recovery of iodine.
BACKGROUND OF INVENTION:
Heptafluoroisopropyl iodide is an important intermediate in the synthesis of agrochemicals. Heptafluoroisopropyl iodide has been prepared by decarboxylation of silver salts of corresponding perfluoro-carboxylic acid in the presence of excess iodine. This method is unfit for large scale manufacture as it uses a costly metal and involves solid handling.
Journal of the Chemical Society, 3779-86; 1961 describes addition of iodine monofluoride to perfluoroolefin by the reaction of perfluoroolefin with iodine and iodine pentafluoride. Iodine pentafluoride is prepared from elementary fluorine. Fluorine, as well as iodine pentafluoride, are the substances dangerous to handle and expensive. The process for the preparation of heptafluoroisopropyl iodide by the reaction of hexafluoropropene, an alkali metal fluoride and iodine at 140-200 °C temperature in a polar aprotic solvent followed by purification of product and recovery of iodine.
Journal of Organic Chemistry, 27, 1813-14; 1962 and U.S. pat. No. 3,052,732 describes a synthesis of some perfluoroiodides by the reaction of fluoro-olefins with alkali metal fluoride and iodine in acetonitrile at 25-250 °C but yields are not satisfactory due to low conversion and formation of dimerization products in large amounts.
Polish patent PL 157347 (1992) also describes the a process in dimethylformamide but the solubility of alkali metal iodide formed in the reaction in DMF makes the recovery of iodine and DMF very difficult also the isolation of product from DMF is not smooth.. According to US pat. No. 3,829,512 (1974) and 5,481,028 (1996) heptafluoroisopropyl iodide can be prepared by the reaction of hexafluoropropene with mixture of I2/C12 and HF at 0-200 °C in the presence of antimony halides or borontrifluoride as catalyst. These processes have disadvantages of requiring antimony salts, which is not an environmental friendly chemical and borontrifluoride with HF, which is dangerous to handle.
In all these processes the elemental iodine or compound of iodine mainly contributes to the cost of
product.
There arise a need to provide a cost effective and environment friendly process for the preparation of heptafluoroisopropyl iodide with recovery of iodine from the iodide present in the reaaion residue after isolation of product.
OBJECTIVE OF THE PRESENT INVENTION:
An object of the present invention is to provide a process for the preparation of heptafluoroisopropyl iodide.
Another object of the present invention is to provide a process for the preparation of heptafluoroisopropyl iodide with recovery of iodine to reduce the effluent load.
Another object of the present invention is to provide a cost effeaive and environment friendly process for the preparation of heptafluoroisopropyl iodide.
SUMMARY OF THE INVENTION:
The present invention relates to a process for the preparation of heptafluoroisopropyl iodide by reacting hexafluoropropene with iodine and alkali metal fluoride in presence of an aprotic solvent at a temperature of 140 °C to 200 °C.
Part of iodine used in the reaction gets converted to the product and part is converted into iodine salt of the alkali metal fluoride used. Some of the iodine is also remain unreaaed, which is solubilized in the solvent. The iodine is recovered from the salt. The recovered iodine is further purified to be reused. The iodine remaining with the solvent is also recovered and reused. The solvent recovered is also reused for further reactions with dissolved iodine remaining in the solvent.
STATEMENT OF THE INVENTION:
Accordingly, the present invention provides a process for the preparation of heptafluoroisopropyl iodide comprising reacting hexafluoropropene with an alkali metal fluoride and iodine in presence of an aprotic solvent at a temperature of 140 °C to 200 °C.
DETAILED DESCRIPTION OF THE INVENTION:
The present invention provide a process for the preparation of heptafluoroisopropyl iodide by reacting hexafluoropropene with iodine and alkali metal fluoride. The alkali metal fluoride is selected from lithium fluoride, sodium fluoride, potassium fluoride, potassium hydrogen fluoride and cesium fluoride. The preferred alkali metal fluoride is potassium fluoride. The theoretical mole ratio of alkali metal fluoride, iodine and hexafluoropropene is 1:1:1 but in practice the alkali metal fluoride is employed in excess, 1.25-10 moles per mole of iodine, preferably 2-3 moles per mole of iodine. The alkali metal fluoride having a high surface area is used in the reaction. The alkali metal fluoride, which are hygroscopic in nature are dried. It is preferred to use spray dried alkali metal fluoride. It is preferred to use alkali metal fluoride having water content less than 1000 ppm. The hexafluoropropene can be employed in excess 0.9-1.25 moles per mole of iodine to increase consumption of iodine. The reaction is carried out at 140 to 200 °C and preferably at a temperature ranging from 170 °C to 190 °C. The reaction is carried out under autogeneous pressure of the solvent at the reaction temperature. An appropriate solvent medium is used to carry out the process cost effectively. Some of the preferred solvents are nitrobenzene and benzonitrile, preferrably nitrobenzene. The ratio of the amount of iodine and nitrobenzene ranges from 1:1 to 1:4 by weight.
The product is isolated from the reaction mixture by simply stripping of the product from the reaction mixture. The stripping is carried out after filtering the reaction mass to remove the solids to the produa is stripped of directly from the reaction mixture and the solids is separated thereafter. Part of iodine used in the reaaion gets converted to the produa and part is converted into iodine salt of the alkali metal fluoride used. Some of the iodine is also remain unreaaed, which is solubilized in the solvent. It is important to recover the iodine from the iodide salt. The recovery of iodine from the salt is carried out using a displacement reagent such as chlorine. The recovered iodine is further purified to be reused. The iodine remaining with the solvent is also recovered and reused. It is also possible to reuse the solvent for further reactions with dissolved iodine remaining in the solvent.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.
Example 1
A 2000 ml Hastelloy autoclave is loaded with iodine (500 gm, 1.97 mol), anhydrous potassium fluoride (228.5 gm, 3.94 mol), nitrobenzene (1150 gm) and hexafluoropropene (324 gm, 2.16 mol) and heated with stirring at 180 °C. The pressure of the autoclave decreases from 38 kg/cm2 to 15 kg/cm2 in six hours. After boiling off the reaction mixture, obtained 550g crude product, analysis by GC indicates 95 % product, 3 % dimer and 2 % unreacted hexafluoropropene .The crude product is purified by distillation to get 470 gm heptafluoroisopropyl iodide of 99.9 % purity. The residue in the autoclave is filtered to get 425 gm solid (mixture of KF and KI) and 1050 gm nitrobenzene containing 2.38 % unreacted iodine.
Example 2
A 2000 ml Hastelloy autoclave is loaded with iodine (475 gm, 1.87 mol), anhydrous potassium fluoride (228.5 gm, 3.94 mol), nitrobenzene containing 2.38 % iodine obtained from example 1 (1050 gm), fresh nitrobenzene (125 gm) and hexafluoropropene (324 gm, 2.16 mol) and heated with stirring at 180 °C. The pressure of the autoclave decreases from 40 kg/cm2 to 15.2 kg/cm2 in six hours. After boiling off the reaction mixture, obtained 524 gm crude product, analysis by GC indicates 90 % product, 4 % dimer and 6 % unreacted hexafluoropropene. The crude product is purified by distillation to get 435 gm heptafluoroisopropyl iodide of 99.9 % purity. The residue in the autoclave is filtered to get 395 gm solid (mixture of KF and KI) and 1118 gm nitrobenzene with 7.68 % unreacted iodine.
Example 3
The mixture of potassium fluoride and potassium iodide obtained from example 1 and 2 (828 gm) is dissolved in water to make three litters clear solution. Chlorine gas (125 gm) is passed into this solution slowly in two hours followed by filtration to get 510 gm crude iodine. Iodometric analysis of crude iodine indicated 85 % iodine. The crude iodine is sublimed with calcium oxide (500 gm) and 402 gm to obtain pure iodine with 99 % purity.
Example 4
A 2000 ml Hastelloy autoclave is loaded with recovered iodine (500 gm, 1.97 mol), anhydrous potassium fluoride (228.5 gm, 3.94 mol), fresh nitrobenzene (1150 gm) and hexafluoropropene (300
gm, 2 mol) and heated with stirring at 180 °C. The pressure of the autoclave decreases from 37 kg/cm2 to 9 kg/cm2 in six hours. After boiling off the reaaion mixture, obtained 535 gm crude product. Analysis by GC indicated 94.7 % produa, 3.5 % dimer and 1.8 % unreaaed hexafluoropropene .The crude produa is purified by distillation to get 447 gm heptafluoroisopropyl iodide of 99.9 % purity. The residue in the autoclave is filtered to get 400 gm solid (mixture of KF and KI) and 1075 gm nitrobenzene with 2.41 % unreaaed iodine.
ADVANTAGES:
1. The main advantage of the process is to use of an aprotic solvent, namely nitrobenzene, resulting
in improving the yield of the of the produa.
2. The process is environment friendly as the used iodine is recovered and reused thus reducing the
effluent load.
3. The recovery of iodine makes the process cost effective.
4. The process uses no hazardous or difficult to handle materials.

We claim:
1. A process for preparation of heptafluoroisopropyl iodide comprising reacting hexafluoropropene with an alkali metal fluoride and iodine in presence of an aprotic solvent at a temperature of 140°C to 200°C.
2. The process as claimed in claim 1, wherein the alkali metal fluoride is selected from the group consisting of lithium fluoride, sodium fluoride, potassium fluoride, potassium hydrogen fluoride and cesium fluoride.
3. The process as claimed in claim 1, wherein the alkali metal fluoride used is in the range of 2 to 10 moles per mole of iodine.
4. The process as claimed in claim 1, wherein the alkali metal fluoride used is in the range of 2 to 3 moles per mole of iodine.
5. The process as claimed in claim 1, wherein the alkali metal fluoride used is spray dried alkali metal fluoride.
6. The process as claimed in claim 1, wherein the alkali metal fluoride has water content less than 1000 ppm.
7. The process as claimed in claim 1, wherein the hexafluoropropene used is in the range of 1.2 to 1.25 moles per mole of iodine.
8. The process as claimed in claim 1, wherein the reaction is carried out at a temperature of 170°C to 190°C.
9. The process as claimed in claim 1, wherein the reaction is carried out at a pressure ranging from 9 Kg/cm2 to 40Kg/cm2.
10. The process as claimed in claim 1, wherein the aprotic solvent used is nitrobenzene.
11. The process as claimed in claim 1, wherein the ratio of the amount of iodine and nitrobenzene ranges from 1:1 to 1:4 by weight.
12. The process for preparation of heptafluoroisopropyl iodide substantially as herein before described with reference to accompanying specification.