Gas-phase circulation preparation method for 2-(4-bromomethylphenyl)propionic acid

The invention discloses a gas-phase circulation preparation method for 2-(4-bromomethylphenyl)propionic acid. The gas-phase circulation preparation method comprises the following steps: feeding hydrobromic acid, paraformaldehyde and 2-phenylpropionic acid in a bromoethylation reactor and adding a solvent and a Lewis acid catalyst as reaction materials; adding water into a hydrogen bromide gas generator, adding phosphorus tribromide drop by drop, and allowing generated hydrogen bromide gas to enter a buffer device; after heating of the bromoethylation reactor, allowing a gas phase of the reaction materials to enter a condenser for condensation, combining uncondensed gas with hydrogen bromide gas discharged from the buffer device, then allowing the obtained gas mixture to enter a gas circulation pump, and conveying the gas mixture to the bottom of the bromoethylation reactor by the gas circulation pump so as to realize gas-phase circulation; and after a reaction is completed, subjectinga reaction liquid in the