Modulating Basicity in Mg-Al Oxides for Selective N‑Alkylation of BIT with Improved Catalytic Performance

Heterogeneous catalytic N-alkylation has increasingly been recognized as a sustainable approach for the formation of C-N bonds, particularly in the synthesis of high-value nitrogen compounds. Based on the characteristic that calcined hydrotalcites exhibit basic sites of varying strengths depending on their Mg/Al molar ratios, this study employed Mg-Al layered double hydroxides (LDHs) as precursors to synthesize a series of layered double oxides (LDOs) with different Mg/Al ratios via high-temperature topotactic transformation. These LDOs were then used as solid base catalysts to investigate the mechanistic influence of basic site strength on the N-alkylation of 1,2-benzisothiazolin-3-one (BIT) for the selective synthesis of N-butyl-1,2-benzisothiazolin-3-one (BBIT). Notably, Mg₄Al₁O-600 showcased superior catalytic activity, achieving a BIT conversion rate of 61.66% and a BBIT yield of 42.81% within 20 h. A structure-property correlation analysis suggests that the abundant medium-strength basic sites function as active centers for selective N-alkylation, thereby significantly improving selectivity toward BBIT. The predominant catalytic mechanism is identified as an S_N2 nucleophilic substitution. Additionally, kinetic analysis indicates that the reaction is largely influenced by the coupled mass transfer and reaction behavior of BIT.