The present invention provides a process for the preparation of fluorobenzenesulfonyl chlorides.
BACKGROUND OF THE INVENTION
The sulphonyl containing molecules, especially the molecules containing sulphonyl halide groups, are of considerable commercial interest as intermediates of drugs, photographic dyes and agrochemicals.
The J. Chem. Soc, Perkin Trans. 1, 1978, 1378-1380 describes a process for the preparation of arene sulphonyl chloride from arene sulphonyl fluoride by reaction of corresponding arene sulphonyl fluoride with aluminium chloride in presence of 1, 2-dichloroethane at reflux temperature. The yields of arene sulphonyl chloride obtained from respective arene sulphonyl fluorides range from 58% to 98%.
The present inventors, upon working on present invention, have observed that high temperature of more than 50°C during reaction of corresponding arene sulphonyl fluoride of Formula I with aluminium chloride aids in formation of dimeric impurities, thus resulting in poor yields of arene sulphonyl chloride of Formula II.
F a
o=s=o o=s=o


J "Fn
Formula I Formula II
where n ranges from 1 to 5.

"Fn

Thus, the present inventors have found an inexpensive, easy and industrially favorable method for the preparation of fluorobenzenesulfonyl chlorides.

SUMMARY OF THE INVENTION
The present invention provides a process for the preparation of a compound of Formula II, comprising,
a) contacting a compound of Formula I with aluminium chloride at a
temperature in the range of 0°C to 50°C to obtain the compound of Formula
II, and
F a
I I

o=s=o o=s=o

Formula I Formula II
b) isolating the compound of Formula II obtained from step a), where n ranges from 1 to 5.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for the preparation of a compound of Formula II, comprising,
a) contacting a compound of Formula I with aluminium chloride at a temperature in the range of 0°C to 50°C to obtain the compound of Formula II, and
F a
I I
o=s=o o=s=o


^

^^

Formula I Formula II
b) isolating the compound of Formula II obtained from step a), where n ranges from 1 to 5.
The compound of Formula I, which is used as a starting material may be commercially obtained or, for example, may be prepared by method disclosed in Indian Patent application No.201611029628.
The contacting of compound of Formula I with aluminium chloride take place in presence or absence of a solvent. The solvent may be dichloromethane or 1,2 dichloroethane. The step a) takes place at the temperature range of 0°C to 50°C for 1 to 4hours, preferably for 2 to 3 hours.The aluminium chloride used as chlorinating agent is anhydrous.
The compound of Formula II is isolated by any method known in the art, for example, acid-base neutralization, distillation, evaporation, fractional distillation and column chromatography or mixture thereof.
In a preferred embodiment,the 2, 6-difluorobenzenesulfonyl fluoride is reacted with aluminum chloride in presence of dichloromethane. The reaction is monitored for completion by Gas Chromatography. After completion of the reaction, the reaction mass is poured into 10% hydrochloric acid in water and the organic layer is separated. The aqueous layer is extracted with dichloromethane twice. The organic layers thus obtained are combined, dried and evaporated to obtain the crude product. The crude product is fractionally distilled through 30cm column packed with glass beads at 4-5mmHg to obtain the titled compound.

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.
EXAMPLE
Preparation of 2,6-difluorobenzenesulphonyl chloride
The dichloromethane (150 mL) was charged into a 1L round bottom flask andaluminum chloride (116 g) was added to it to obtain a suspension. To the suspension thus obtained was added 2, 6-difluorobenzenesulfonyl fluoride (114 g)in dichloromethane (350 mL). The reaction was monitored for completion by Gas Chromatography. After completion of the reaction, the reaction mass was poured into 500mLof 10% hydrochloric acid in water and the organic layer was separated. The aqueous layer was extracted twice with dichloromethane (250 mL X 2).The organic layers were combined, dried and evaporated to obtain the crude product. The crude product was fractionally distilled through 30cm column packed with glass beads at 4-5mmHg to obtain the titled compound. Yield (%): 85 Purity (%): 99

WE CLAIM:

1. A process for the preparation of a compound of Formula II, comprising,
a) contacting a compound of Formula I with aluminium chloride at a temperature in the range of 0°C to 50°C to obtain the compound of Formula II, and

F 1 a
c 1
A o o=s=o
r 1 ■""
k^ rn k^ n
F ormula I Formula II
b) isolating the compound of Formula II obtained from step a), where n ranges from 1 to 5.
2. The process as claimed in claim 1, wherein the aluminium chloride is anhydrous.
3. The process as claimed in claim 1, wherein the step a) is carried out in presence or absence of a solvent.
4. The process as claimed in claim 3, wherein the solvent is selected from the group consisting of dichloromethane and 1, 2 dichloroethane.
5. The process as claimed in claim 1, wherein the reaction is carried out in a time period of 1 to 4 hours.

6. The process as claimed in claim 1, wherein the reaction is carried out in a time period of 2 to 3 hours.
7. The process as claimed in claim 1, wherein the compound of formula I is 2,6-difluorobenzenesulphonyl fluoride.
8. The process as claimed in claim 1, wherein the compound of formula II is 2,6-difluorobenzenesulphonyl chloride.