Method for preparing 3-sulfydryl coumarin

The invention discloses a method for preparing 3-sulfydryl coumarin. The method comprises the following steps: in an alkali liquid, enabling o-chlorobenzaldehyde and mercaptoacetic acid as raw materials to react at 85-115 DEGC for 3-6 hours, wherein the mole ratio of o-chlorobenzaldehyde to mercaptoacetic acid is 1:(1.1-1.3), and the amount of the alkali is 2.5-3.5 mole times of mercaptoacetic acid; after the reaction, adding concentrated hydrochloric acid to acidify till the pH value of the reaction product (kettle liquid) is 3-4, filtering, and drying, thereby obtaining a crude product 3-sulfydryl coumarin; re-crystallizing the crude product 3-sulfydryl coumarin by using absolute ethyl alcohol, performing vacuum suction filtration, washing, and drying, thereby obtaining 3-sulfydryl coumarin. The method for preparing 3-sulfydryl coumarin has the characteristics of wide raw material source, low production cost, simple process, low reaction temperature, high yield, applicability to scale production, and the like.