Method for preparing 2, 3-dichloromaleic anhydride

The invention provides a method for preparing 2, 3-dichloromaleic anhydride, which comprises the following steps: in one reaction vessel, firstly using dichloromalealdehydic acid as raw materials, using selenium dioxide as catalysts, carrying out oxidation reaction with aqueous hydrogen peroxide solution with the concentration between 20 percent and 50 percent for 6 to 24 hours under the condition between 60 DEG C and 70 DEG C, and synthesizing 2, 3-dichloromaleic anhydride; then, adding toluene into the prepared 2, 3-dichloromaleic anhydride, bringing out water through boiling at 110 DEG C, next, adding acetic anhydride into the mixture, carrying out dehydration reaction at 120 DEG C, steaming out the toluene and the acetic anhydride in a system and acetic acid generated in reaction after the dehydration reaction is carried out for 2 to 4 hours, and preparing and obtaining the 2, 3-dichloromaleic anhydride. The method has the beneficial effects that the dichloromalealdehydic acid which has a low price and ca