The invention relates to a method for synthesizing 5-bromoindole. The method comprises the following steps of: (1) dissolving indole into alcoholic organic solvents, adding an
aqueous solution of
sodium hydrogensulfite or
potassium hydrogensulfite, reacting for 15 to 20h, filtering a reaction solution, washing, and
drying to obtain an intermediate I; (2) mixing the intermediate I and
acetic anhydride, raising the temperature to 68 to 75 DEG C, reacting for 2 to 3h, adding ester or
benzene organic solvents, reacting for 0.5 to 1h, cooling to
room temperature after the reaction is finished, filtering, washing, and
drying to obtain an intermediate II; and (3) dissolving the intermediate II into water, adding
bromine at the temperature of between 0 and 5 DEG C, keeping the reaction for 1 to 3h, raising to
room temperature, continuing to react for 1 to 2h, adding the
aqueous solution of
sodium hydrogensulfite or
potassium hydrogensulfite, reacting for 10 to 30min, adding an
aqueous solution of
sodium hydroxide or
potassium hydroxide, refluxing for 12 to 18h, cooling a reaction solution, precipitating crystals, filtering, washing, and
drying to obtain a product, namely the 5-bromoindole. The method is low in cost consumption and is simple, and the quality of the product is high.