The invention discloses a preparation method of high-purity
bromoxynil octanoate. According to a
reaction sequence, the preparation method successively comprises bromination reaction and
esterification reaction steps, and comprises the following steps: adding water and cyanophenol into a reaction container, and dropwise adding
hydrogen peroxide and
bromine, controlling a dropwise adding temperature to be 20-100 DEG C, heat-insulating reacting for 1-2 hours, sampling, after the reaction is qualified, adding
sodium carbonate to break the excessive
hydrogen peroxide, and then adding a
solvent, dropwise adding caustic soda liquid and caprylyl
chloride simultaneously, controlling a
reaction temperature to be 0-50 DEG C, after dropwise adding, heat-insulating reacting for 1-2 hours, sampling, controlling by neutralizing, washing by the water after qualified, recovering the
solvent, sampling and detecting, discharging and barreling after qualified. The bromination is firstly performed, and the esterification is performed in the reaction. The reaction is controllable. Existing problems that the
esterification reaction is firstly performed so that the space resistance of an octoate group islarge and the reaction activity thereof is weaker than the reaction activity of a phenolic hydroxyl group are solved. The bromination is also performed firstly without using an expensive catalyst, and excessive caprylyl
chloride does not need to be recovered by warming at the same time, so the
recovery difficulty is reduced.