Synthesis method of 2-butyl-1,2-benzisothiazolin-3-one

The invention discloses a synthesis method of 2-butyl-1,2-benzisothiazolin-3-one. The synthesis method comprises the following steps: by taking bis-sulpho-cyanophenyl and alcohol as raw materials, carrying out a Pinner reaction to generate a Pinner salt under acid catalysis, hydrolyzing the Pinner salt to generate bis-sulpho-benzoate, recovering the catalyst and the alcohol, adding alcohol solvents, adding n-butylamine in the reaction solution and carrying out an amidation reaction, and recovering the solvent under a reduced pressure to obtain 2,2'-dithio-dibenzamide; dissolving 2,2'-dithio-dibenzamide in an organic solvent, adding a chlorination agent and cyclizing to generate 2-butyl-1,2-benzisothiazolin-3-one. According to the synthesis method disclosed by the invention, environment-friendly raw materials are used, thus reducing environment pollution; meanwhile, the whole synthesis process of the synthesis method disclosed by the invention is a one-pot method, a middle separation process is not needed, the operation is convenient, the whole reaction process is high in yield, the purity of the obtained target product is also relatively high; the synthesis method is low in pollution, high in yield and high in purity.