Abstract: In this paper, a microchannel method was used to generate liquid bromine in situ in a polytetrafluoroethylene hose by the reverse disproportionation reaction of HBr and NaBrO₃ in aqueous solution, which was directly added to the reaction system to react with 5,5-dimethylhydantoin, and the pH value of the system was controlled by adding NaOH solution to prepare 1,3-dibromo-5,5-dimethylhydantoin (DBDMH). The post-treatment of the reaction is simple, and the target compound is obtained by filtration and water washing. Then, the synthesized dibromohydantoin is used as a bromination reagent to introduce a bromine atom at the 5-position of the compound (6-methoxynaphthalen-2-yl) propan-1-one to obtain a key intermediate for the preparation of S-naproxen. The bromination reaction is completed in 30 minutes, which is simple and efficient, with good selectivity and high yield. The method of continuous flow in-situ generation of bromine used in this experiment provides a new approach for aqueous phase system experiments involving liquid bromine in undergraduate university chemistry experiments. The subsequent bromination reaction shows that dibromohydantoin has obvious advantages as a bromination reagent compared to NBS and liquid bromine. This experiment combines the principles and operations of organic chemistry and inorganic chemistry experiments, strengthens the concept of organic acids and bases in theory, and strengthens the training of basic skills in organic synthesis in operation. It is a comprehensive chemistry experiment suitable for senior undergraduate students.

Key words: Hydantoin-based disinfectants, Reverse disproportionation reaction, Microchannel reactor, Bromination reaction