Heterogeneous catalysts for esterification reaction

Sodium silicate from rice husk ash was functionalized with different silylating agents to produce silica with –CH2–Cl (labelled as RHACCl), –CH2–NH2 (labelled as RHAPrNH2) and –CH2–SH (labelled as RHAPrSH) end groups via a novel one–pot synthesis. Saccharine (Sac) and Melamine (Mela) were immobilized onto RHACCl to form RHAC-Sac and RHAPrMela. The functionalized –CH2–SH group in RHAPrSH was oxidized to sulfonic acid, –CH2–SO3H (labelled as RHAPrSO3H) with hydrogen peroxide at room temperature. The catalysts showed good textural and structural properties. RHAC-Sac, RHAPrMela, RHAPrSO3H, RHA–Blank (as control) as well as homogenous Sac and homogenous Mela were used as catalysts in the esterification reaction. The catalytic activity was found to follow the sequence: RHAPrSO3H > RHAPrMela > homogenous Sac > RHAC–Sac > homogenous Mela > RHA–Blank. The catalysts were easily regenerated and could be reused several times without loss of catalytic activity.