FIELD OF THE INVENTION The present invention provides a reactive distillation process for the preparation of 1 , 1, 1 , 2, 3, 3, 3-heptafluoro-2-bromoropane.

BACKGROUND OF THE INVENTION

The 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane is a key starting material for preparing polyhaloalkylated aromatics. The polyhaloalkylated aromatics are becoming increasingly important, as lipophilic building blocks in agrochemical or pharmaceutical active ingredients. The polyhaloalkyl substituents increase the lipophilicity and therefore the membrane permeability of the entire active ingredient molecule.

The US Publication Nos. 2004/0092762 and 2004/0092781 provide a process for the preparation of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane by heating dried mixture of tetramethylenesulphone and potassium fluoride with 1 , 2-dibromohexafluoropropane up to 175°C under nitrogen atmosphere and at a pressure of 13.5 bar. The 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane so obtained is allegedly 95.8 % pure.

The FR Patent Application No. 1357392 provides a process for the preparation of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane by heating a suspension of potassium fluoride and 1 , 2-dibromohexafluoropropane in N, N-dimethylformamide to about 90°C. The 1, 1 , 1 , 2, 3, 3, 3-heptafiuoro-2-bromopropane is distilled into a cooled container. This process allegedly yields only 55% of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane over an elongated time period of 16 hours. Indian Patent Application No. 753/DEL/2010 further discloses a process for the preparation of 4- heptafluoroisopropyl-2-methyl aniline by the reaction of ortho-toluidine with 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane.

The present inventors have observed that the reaction did not proceed to completion when potassium fluoride and 1 , 2-dibromohexafiuoropropane were reacted in N, N- dimethyl form amide at about 90°C. Thus resulting in low yield of 1, 1 , 1 , 2, 3, 3, 3- heptafluoro-2-bromopropane. Further, 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane was obtained in poor yield and low purity when potassium fluoride and 1 , 2- dibromohexafluoropropane were heated in N, N-dimethylformamide to about 140°C, cooled, decompressed and distilled. It was thus desirable to find a selective process for the preparation of 1 , 1 , 1 , 2, 3, 3, 3- heptafluoro-2-bromopropane with which a good productive output by volume can be achieved and which minimizes the need for purification operations and drastic reaction conditions like high pressure and temperature without compromising on yield and purity.

OBJECTIVE OF THE INVENTION

The main object of the present invention is to provide a reactive distillation process for the preparation of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromoropane.

SUMMARY OF THE INVENTION

The present inventors have found that the reactive distillation of 1 , 1 , 1 , 2, 3, 3, 3- heptafluoro-2-bromopropane by heating potassium fluoride and 1 , 2- dibromohexafluoropropane in N, N-dimethylformamide at a temperature in the range of about 90°C to about 150°C yields high and efficient output of 1 , 1 , 1 , 2, 3, 3, 3- heptafluoro-2-bromopropane without adhering to harsh reaction conditions like high temperature and pressure. The reactive distillation of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2- bromopropane is particularly advantageous in a continuous mode wherein the simultaneous formation and continuous isolation/removal of 1 , 1 , 1 , 2, 3, 3, 3- heptafluoro-2-bromopropane from the reactive zone eliminates any side reactions thereby resulting in high yield and purity. The "reactive distillation" comprises the simultaneous production and continuous isolation/removal of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane from the reactive zone.

In an aspect, the present invention provides a process for preparation of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane comprising; a) reacting 1, 2-dibromohexafiuoropropane and an alkali metal fluoride in presence of an amide solvent; and b) isolating 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane by reactive distillation.

DETAILED DESCRIPTION OF THE INVENTION In an embodiment, the present invention provides a process for preparation of 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane comprising; a) reacting 1 , 2-dibromohexafiuoropropane and an alkali metal fluoride in presence of an amide solvent; and b) isolating 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane by reactive distillation. The alkali metal fluoride is selected from the group consisting of sodium fluoride, potassium fluoride and cesium fluoride or a mixture thereof. The alkali metal fluoride may be in granular form or in powdered form. The amide solvent is selected from the group consisting of N, N-dimethylformamide, methylpyrrolidone, N- methylformamide, dimethylacetamide, 2-pyrrolidone and N- vinylpyrrolidone or a mixture thereof.

The reaction of 1 , 2-dibromohexafluoropropane and an alkali metal fluoride is carried out at a temperature in the range of about 70°C to about 170°C, preferably in the range of about 90°C to about 150°C for a time period in the range of about 10 minutes to about 10 hours.

The 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane is isolated by reactive distillation. The reactive distillation is carried out at a temperature in the range of about 80°C to about 160°C, preferably in the range of about 90°C to about 150°C.

In further aspect, the 4-heptafluoroisopropyl-2-methyl aniline is prepared by the reaction of ortho-toluidine with 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane, wherein 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane is prepared by present invention.

While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

EXAMPLES

Example 1 : Preparation of 1 , 1 , 1 , 2, 3, 3, 3-Heptafluoro-2-bromopropane N, N-dimethylformamide (942 g), potassium fluoride (232 g) and 1 , 2- dibromohexafluoropropane (622 g) were taken together in a two-liter autoclave attached with one meter packed column. The column was maintained at atmospheric pressure. The temperature at the column head was maintained in the range of about 15°C to about 20°C. The reaction mixture was heated to about 90°C. The temperature of the reaction was increased slowly to about 140°C. The 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2- bromopropane was distilled simultaneously and continuously from the top of the column for about 3 hours.

Comparative Examples

1. Preparation of 1 , 1 , 1 , 2, 3, 3, 3-Heptafluoro-2-bromopropane N, N-dimethylformamide (937 g), potassium fluoride (232 g) and 1 , 2- dibromohexafluoropropane (620 g) were taken together in a two-liter autoclave. The temperature of the reaction mixture was increased slowly to about 140°C. The reaction mixture was maintained at about 140°C for about 10 minutes. The contents were cooled to 0°C and decompressed. The 1 , 1 , 1 , 2, 3, 3, 3-heptafluoro-2-bromopropane was distilled into the cold trap.

2. Preparation of 1 , 1 , 1 , 2, 3, 3, 3-Heptafluoro-2-bromopropane

N, N-dimethylformamide (850 g), potassium fluoride (204 g) and 1 , 2- dibromohexafluoropropane (563 g) were taken together in a two-liter autoclave. The temperature of the reaction mixture was increased slowly to about 140°C. The reaction mixture was maintained at about 140°C for about 90 minutes. The contents were cooled to 0°C and decompressed. The 1 , 1 , 1 , 2, 3, 3, 3-heptaftuoro-2-bromopropane was distilled into the cold trap.