This invention discloses a method for preparing cis-1,2-dibromoethylene based on steric hindrance, belonging to the field of technical
organic synthesis. The method includes the following steps: (a) providing reactors A and B connected in series.
Bromine is added to reactor A, and a
solvent and configuration-
selective catalyst are added to reactor B. This invention employs a series
reactor system. Under the synergistic effect of a
copper /
crown ether composite catalyst and
ultraviolet light, a
highly selective addition reaction of
acetylene with
bromine is achieved by controlling the
solvent system,
reaction temperature, and material ratio. Using
acetonitrile or perfluoroalkane as
solvent, and
copper chloride and crown ethers (such as 15-crown-5) as catalysts, the reaction is carried out at 30-80℃ under 200-400nm
ultraviolet light. The selectivity of cis-1,2-dibromoethylene is ≥95%, which has advantages such as mild
reaction conditions, solvent recyclability, and suitability for industrial production. Furthermore, the cis selectivity is improved to ≥95%; the content of the byproduct
tetrabromoethane is <0.5%; and the solvent
recovery rate is >98%.