Method of preparing fluoroaromatic compounds

A method of preparing 2-chloro-4,5-difluorobenzoic acid (VII) according to the following reaction, which comprises:

• (a) providing a mixture of 4-chloro-1-methyl-4,5,5-trifluorocyclohexene (IIIa) and 5-chloro-1-methyl-4,4,5-trifluorocyclohexene (IIIb) by reacting chlorotrifluoroethylene (CTFE) (I) and isoprene (II) at temperature range of 390 to 480.degree. C. through continuous vapor phase condensation in a flow reactor and distilling the resultant;
• (b) dehydrohalogenating said mixture in the presence of alkali metal hydroxide and a phase transition catalyst to form 3,4-difluorotoluene (IV);
• (c) reacting said 3,4-difluorotoluene with chlorine gas in the presence of catalysts consisting of ferro-shaving and ferric chloride at temperature range of -10 to 40.degree. C. without using any organic solvent to form 2-chloro-4,5-difluorotoluene (V);
• (d) photo-reacting said 2-chloro-4,5-difluorotoluene with chlorine gas under a lighting mercury lamp at temperature range of 80 to 140.degree. C. without using any organic solvent to form 2-chloro-4,5-difluorobenzotrichloride (VI);
• and
• (e) reacting said 2-chloro-4,5-difluorobenzotrichloride with aqueous acid solution at temperature range of 35 to 80.degree. C. without using any organic solvent:
• ##STR4## wherein Me represents a methyl group.

A method of preparing 2-chloro-4,5-difluorobenzoyl chloride (VIII) according to the following reaction, which comprises:

• (a) providing a mixture of 4-chloro-1-methyl-4,5,5-trifluorocyclohexene (IIIa) and 5-chloro-1-methyl-4,4,5-trifluorocyclohexene (IIIb) by reacting chlorotrifluoroethylene (CTFE) (I) and isoprene (II ) at temperature range of 390 to 480.degree. C. through continuous vapor phase condensation in a flow reactor and distilling the resultant;
• (b) dehydrohalogenating said mixture in the presence of alkali metal hydroxide and a phase transition catalyst to form 3,4-difluorotoluene (IV);
• (c) reacting said 3,4-difluorotoluene with chlorine gas in the presence of catalysts consisting of ferro-shaving and ferric chloride at temperature range of -10 to 40.degree. C. without using any organic solvent to form 2-chloro-4,5-difluorotoluene (V);
• (d) photo-reacting said 2-chloro-4,5-difluorotoluene with chlorine gas under a lighting mercury lamp at temperature range of 80 to 140.degree. C. without using any organic solvent to form 2-chloro-4,5-difluorobenzotrichloride (VI;:
• and
• (e) reacting said 2-chloro-4,5-difluorobenzotrichloride with zinc oxide:
• ##STR5## wherein Me represents a methyl group.