Preparation method of 2-phenyl-1,1-dioxo-1,2-benzisothiazole-3(2H)-one

The invention relates to a preparation method of 2-phenyl-1,1-dioxo-1,2-benzisothiazole-3(2H)-one. The preparation method comprises the following steps: (1) mixing aniline, water and a fluoboric acid aqueous solution, then dropwise adding a sodium nitrite aqueous solution while stirring at the temperature of 0-5 DEG C, heating to room temperature after dropwise adding is finished, continuing stirring and reacting for 1-2 hours, and carrying out suction filtration to obtain benzenediazonium tetrafluoroborate; (2) stirring and mixing 1,1-dioxo-1,2-benzisothiazole-3(2H)-one, alkali, a copper salt catalyst and a solvent at the temperature from minus 5 DEG C to 5 DEG C, then adding the benzenediazonium tetrafluoroborate in batches, reacting for 6-8 hours while stirring at the temperature from minus 5 DEG C to room temperature, and after reaction is finished, extracting, drying, removing the solvent by evaporation, and carrying out recrystallization to obtain the final product. The copper salt is used as the cataly