Precise N‑Alkylation via Cs-LTA Zeolites: Mechanistic Insights and Green Catalytic Synthesis of High-Yield BBIT...

The precise synthesis of the industrial bactericide N-butyl-1,2-benzisothiazolin-3-one (BBIT) is primarily achieved through catalytic N-alkylation reactions. In this study, a multistep ion-exchange approach was utilized to produce Cs⁺ modified LTA zeolites (Cs-LTA) as precise catalysts for the selective N-alkylation of 1,2-benzisothiazolin-3-one (BIT) using bromobutane, resulting in high-efficiency BBIT synthesis. A systematic optimization of ion-exchange cycles and calcination temperatures facilitated precise control over Cs⁺ dispersion and basic site density within the zeolite framework. XRD, XPS, CO₂-TPD, and ²⁷Al NMR characterizations verified that the incorporation of Cs⁺ enhanced both the strength of basicity and structural stability through covalent Si-O-Cs bonds, thereby minimizing metal leaching. Under optimized conditions, the Cs-LTA/3 catalyst achieved a BIT conversion rate of 99.21% and a BBIT selectivity of 92.67%. Notably, the catalyst maintained over 80% activity after five cycles, demonstrating superior performance compared to impregnated counterparts. In situ Raman spectroscopy and kinetic analyses revealed a synergistic mechanism: Cs⁺ activates the C-Br bond in bromobutane, producing an electron-deficient alkene intermediate, while the zeolitic basic sites dehydrogenate BIT to generate a nucleophilic amine species, collectively reducing the calcination energy barrier. This research establishes a sustainable catalytic system that overcomes the limitations of homogeneous bases and transition-metal catalysts, providing insights into the strategic design of zeolite-based catalysts for green organic synthesis.