Method for preparing 1,2-benzisothiazole-3 (2H) ketone-2-butyl-1,1-dioxide

A method for preparing 1,2-benzisothiazole-3 (2H) ketone-2-butyl-1,1-dioxide is characterized in that the method uses soluble saccharin dehydrate and n-butyl bromide as raw materials, reaction is performed under the effect of a composite catalyst at the temperature of 70-90 DEG C for 4-8 hours, a product precipitates after cooling, and centrifugal separation and drying are performed to obtain a high-purity white crystal finished product, wherein the composite catalyst is prepared by mixing water and fatty amine by the mole ratio of 1:0.02-1:5. The method has the advantages that the composite catalyst with the fatty amine as a main ingredient is adopted to prepare the 1,2-benzisothiazole-3(2H) ketone-2-butyl-1,1-dioxide for the first time, and a solvent is not needed for reaction, the product precipitates after reaction and cooling, and centrifugal separation and drying are performed to obtain the high-purity white crystal finished product, the step of removing a reaction solvent and non-reacted raw materials through distillation is omitted, ethyl alcohol for twice re-crystallization is not needed, accordingly a synthesis process is simplified, production cost is greatly reduced, environmental pollution caused by usage of a large amount of organic solvent is also avoided, and a green preparation process is achieved.