Field of the invention
The present invention provides a process for the preparation of compound of Formula I.

Formula I

Background of the invention

The Journal of the Electrochemical Society, 148(6) E262-E266 (2001) simply mentions perfluorination of hexafluorobutanol in presence of anhydrous hydrogen fluoride to form n-perfluorobutyryl fluoride. According to the paper, perfluorobutyrl fluoride is the only product formed, as seen in the mass spectra.

While working on the present invention, the inventors have found that the electrochemical fluorination of hexafluorobutanol in the presence of anhydrous hydrogen fluoride forms n-perfluorobutyryl fluoride along with other products. The other products formed are lower fluorinated / partially fluorinated acid fluorides, perfluoro hydrocarbons such as perfluoromethane, perfluoroethane and perfluoropropane. The inventors have successfully isolated n-perfluorobutyryl fluoride and converted the same to the compound of Formula I.

Summary of the invention

The present invention provides a process for the preparation of a compound of Formula I, comprising:
a) contacting a compound of Formula IV with methanol to obtain a compound of Formula III;
b) contacting anhydrous hydrogen fluoride and the compound of Formula III in an electrochemical fluorination cell to obtain a compound of Formula II;
c) contacting methanol with the compound of Formula II to obtain a compound of Formula I; and
d) isolating the compound of Formula I obtained from step c).

Formula IV Formula III

Formula II Formula I

Detailed description of the invention

The present invention provides a process for the preparation of a compound of Formula I, comprising:
a) contacting a compound of Formula IV with methanol to obtain a compound of Formula III;
b) contacting anhydrous hydrogen fluoride and the compound of Formula III in an electrochemical fluorination cell to obtain a compound of Formula II;
c) contacting methanol with the compound of Formula II to obtain a compound of Formula I; and
d) isolating the compound of Formula I obtained from step c).

Formula IV Formula III

Formula II Formula I

The compound of Formula IV may be obtained commercially or may be prepared by any method known in the art, for example, as disclosed in US 3,446,858.
The step a) is carried out in the presence of free radical initiators selected from the group consisting benzoyl peroxide, diisopropyl peroxydicarbonate, di-t-butyl peroxide, t-butylperoxy-2-ethyl hexanoate and azobisisobutyronitrile.

The compound of Formula IV is contacted with methanol and a free radical initiator at a temperature in the range of 40°C to 120°C for 0.5 hours to 4 hours.
In an embodiment, electrochemical fluorination is carried out using an electrolytic cell made of stainless steel having a reflux cooler maintained at a temperature in the range of -30°C to 0°C. The reflux cooler is arranged in the upper portion of the reactor. The cathode and anode of the electrochemical cell are made of nickel plates of 1 mm thickness which are alternately arranged so that the distance between every two adjacent plates is in the range of 1.3mm to 5mm.

The step c) is carried out at a temperature in the range of 10°C to 30°C.

The compound of Formula I is isolated by any of the methods known in the art, for example, distillation, evaporation and layer separation or mixture thereof.

The compound of Formula I as obtained by the process of the present invention has a purity greater than 95 %, preferably greater 99% by gas chromatography.

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.

The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.

Examples
Example 1: Preparation of hexafluorobutanol
Benzoyl peroxide (24.3g, 0.1 mole) and technical grade methanol (1056g, 33 mole) were added to an autoclave. The autoclave was cooled to –50oC using liquid nitrogen. Hexafluoropropene (900g, 6 mole) was added to the autoclave. The temperature was raised to 120oC. The contents were agitated at 120oC for 3 hours. The autoclave was cooled to 20-30oC and unreacted hexafluoropropene (240g) was vented off. Fractionation of the reaction mixture was carried out to obtain the title compound (728g).
Yield (%) = 91
Purity (%) = 98

Example 2: Preparation of methyl heptafluorobutanoate
Hexafluorobutanol as obtained in Example 1 was added to an electrolytic cell. Anhydrous hydrogen fluoride (1800g) and hexafluorobutanol (250g) were fed sequentially in a lot of 10 to 15 g over a period of 20 hours, into the electrolytic cell, and a voltage of 5volts to 6volts was applied across the electrode. The electrolysis was carried out with the cell voltage of 5.2 volts and cell temperature of 5oC to 6oC. The electrolysis temperature was kept constant by adjusting the temperature of a cooling medium for cooling the electrolytic cell. Chilled water was used as a cooling medium. The cell current was decreased gradually as fluorination proceeded. The effluent gases from the cell were passed over sodium fluoride pellets to trap the hydrogen fluoride coming along with the product and then bubbled through two stainless steel traps containing methanol which were maintained at 50oC. The gaseous products which did not react with methanol were charged into potassium hydroxide solution and were vented off. The alkaline solution was brought to 7.5 pH, and was concentrated. It was extracted repeatedly with isopropyl alcohol. This was subsequently hydrolysed with sulphuric acid and esterified with methanol to get the product. The ester from the methanol scrubber was analysed by gas chromatography. After complete consumption of methanol, the content of the traps were fractionated. The fraction which boils at 81oC was the title compound.
Purity (%) = 99.9

WE CLAIM:
1. A process for the preparation of a compound of Formula I, comprising:
a) contacting a compound of Formula IV with methanol to obtain a compound of Formula III;
b) contacting anhydrous hydrogen fluoride and the compound of Formula III in an electrochemical fluorination cell to obtain a compound of Formula II;
c) contacting methanol with the compound of Formula II to obtain a compound of Formula I; and
d) isolating the compound of Formula I obtained from step c).

Formula IV Formula III

Formula II Formula I

2. The process as claimed in claim 1, wherein step a) is carried out in the presence of free radical initiators selected from the group consisting of benzoyl peroxide, diisopropyl peroxydicarbonate, di-t-butyl peroxide, t-butylperoxy-2-ethyl hexanoate and azobisisobutyronitrile.

3. The process as claimed in claim 1, wherein step a) is carried out at a temperature in the range of 40°C to 120°C for 0.5 hours to 4 hours.

4. The process as claimed in claim 1, wherein step b) is carried out at a temperature in the range of -30°C to 0°C .

5. The process as claimed in claim 1, wherein step c) is carried out at a temperature in the range of 10°C to 30°C.