Pentafluorobenzyl bromide → Pentafluoro-benzyl 2,2-dimethyl-3-(2-chloro-2-p-chloro-phenyl-vinyl)-cyclopropanecarboxylate

10.7 g (0.033 mol) of the potassium salt of 2,2-dimethyl-3-(2-chloro-2-p-chlorophenyl-vinyl)-cyclopropanecarboxylic acid were dissolved in 100 ml of dimethylformamide and the solution was heated to 120° C., together with 6.8 g (0.026 mol) of pentafluorobenzyl bromide, for 3 hours. After the reaction had ended, the dimethylformamide was distilled off in vacuo and the residue which remained was taken up in 200 ml of methylene chloride. The methylene chloride solution was then extracted by shaking twice with 100 ml of water each time, the organic phase was dried over sodium sulphate and the solvent was stripped off in vacuo. Last residues of solvent were removed by brief incipient distillation at a bath temperature of 60° C./1 mm Hg. 9.0 g (74.4% of theory) of pentafluoro-benzyl 2,2-dimethyl-3-(2-chloro-2-p-chloro-phenyl-vinyl)-cyclopropanecarboxylate were obtained as a yellow oil with the refractive index nD25 :1.5382.