The invention discloses a preparation method of 3-chloro-2,4,5-trifluorobenzoic acid and application thereof, comprising the following steps: S1: adding
bromine dropwise to 1,2,4-trifluorobenzene at 10-30°C to carry out bromination reaction; S2: adding N-chlorosuccinimide in batches to the obtained 2,4,5-trifluorobromobenzene and concentrated
sulfuric acid at 5-10°C to carry out
substitution reaction and purification; S3: adding
magnesium chips and
tetrahydrofuran to an
anhydrous reaction
bottle, adding the obtained 3-chloro-2,4,5-trifluorobromobenzene under stirring, heating to 35-40°C to initiate reaction, then adding
bromobenzene dropwise, keeping warm and stirring for reaction for 1h, then cooling to 5-10°C, adding
dry ice in batches to carry out
Grignard reaction, adding
ultrapure water when the
system is no longer exothermic, adjusting pH=1, filtering by suction and
drying; and S4: recrystallization. The invention uses 1,2,4-trifluorobenzene as a
raw material, and obtains a target product through bromination, chlorination,
Grignard reaction and recrystallization. The reaction process is simplified, the operation is simple, the reaction is mild, the product yield is more than 90%, the purity is more than 99.9%, the by-products in the reaction process are few, and the production cost is low.