The invention discloses a synthesis method of 2, 4, 5-trifluorophenylacetic acid, which comprises the following steps: by taking cheap and easily available o-
chloronitrobenzene as a
raw material, reacting with
sodium nitrate in a
sulfuric acid and
trifluoroacetic acid system, separating generated 2, 4-dinitrochlorobenzene through melt
crystallization, and continuing to synthesize 2, 4-dinitrochlorobenzene in methyl chloroacetate to obtain 2, 4, 5-trifluorophenylacetic acid. The method comprises the following steps: carrying out indirect aromatic
nucleophilic substitution reaction on 2, 4-dinitrophenylacetic acid under the condition of
sodium hydride to generate 5-chloro-2, 4-dinitrophenylacetic acid methyl ester, separating, carrying out fluorination reaction on the 5-chloro-2, 4-dinitrophenylacetic acid methyl ester and
potassium fluoride under the action of a
phase transfer catalyst, carrying out rectification separation to obtain 2, 4, 5-trifluorophenylacetic acid, and carrying out hydrolytic acidification on the 2, 4, 5-trifluorophenylacetic acid in a
sodium hydroxide aqueous solution to obtain 2, 4, 5-trifluorophenylacetic acid. And the process
route is
safer, more environment-friendly, more efficient and lower in cost.