Efficient <i>N</i>-Alkylation of Secondary Amines to Prepare <i>N</i>-Butyl-1,2-benzisothiazolin-3-one Based on Cs Ion Effect with Cs/LTA Zeolite Catalysts

N-Butyl-1,2-benzisothiazolin-3-one (BBIT) is a safe and environmentally friendly new fungicide with wide application prospects in the field of industrial and medical antibacterial. The synthesis route of BBIT by introducing hydrocarbon groups through the N-alkylation reaction on the nitrogen atom of 1,2-benzisothiazolin-3-one (BIT) has been widely concerned. Herein, a series of Cs/LTA zeolite catalysts were developed by an equal volume impregnation method with different cesium metal loadings to catalyze N-alkylation reactions of BIT instead of stoichiometric inorganic bases. The physicochemical properties of both prepared Cs/LTA catalysts and LTA zeolite supports were characterized by XRD, FT-IR, XPS, thermogravimetry (TG), N2-physisorption, and CO2-TPD, and the reaction mechanisms were discussed by DFT calculations. The characterization and DFT results show that the well-dispersed cesium metal on the LTA zeolite is the active site of the BIT reaction. The synergistic interaction of Cs+ interacting with zeolite in the rate-control step of BIT and butyl bromide reduces the reaction barrier of C–N bond construction, thus prioritizing the dehydrogenation step of the product intermediate and improving the selectivity of N-alkylation. Compared with traditional inorganic bases, Cs/LTA catalysts have broad industrial application prospects because of their higher catalytic and environmental performance.