The synthesis of N-heterocyclic carbene-silica nano-particles and its catalytic activity in the cyclization of glycerol

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• 作者：Farook Adam^a ; ^{farook@usm.my} ; Hiba Eltahier Hassan^a ; Kasim Mohammed Hello^b
• 关键词：Carbene&ndash ; silica composite ; Cyclization of glycerol ; Nano-particles ; Acetalization
• 刊名：Journal of the Taiwan Institute of Chemical Engineers
• 出版年：2012
• 期刊代码：P31_18761070
• 类别：ce
• 出版时间：July, 2012
• 卷：43
• 期：4
• 页码：619-630
• 文件大小：1282 K

摘要

1-Butylimidazole (BIm) was successfully immobilized onto rice husk ash via 3-chloropropyltriethoxysilane (CPTES) to produce RHABIm-Cl. The chlorine was easily replaced with sulphate and phosphate anion at room temperature, and these modified catalysts were labeled as RHABIm-HSO₄ and RHABIm-H₂PO₄. The percentage replacement of chlorine was 57%in RHABIm-HSO₄. The RHABIm-HSO₄ had a specific surface area of 194 m² g^鈭?. The ²⁹Si MAS NMR solid-state spectrum showed the presence of Q⁴, Q³, T³ and T² silicon centers were present in RHABIm-HSO₄ and RHABIm-H₂PO₄. RHABIm-H₂PO₄ was used to show the importance of the ionizable proton in the acid catalysis. It showed a higher catalytic activity and selectivity than RHABIm-HSO₄ in the cyclization of glycerol (Gly) to cyclic acetals. The catalytic activities of RHABIm-H₂PO₄ and RHABIm-HSO₄ were determined to be 80 and 75%respectively. The benzaldehyde (Benz) conversion over RHABIm-HSO₄ was achieved in 6 h with high selectivity toward the five-member ring isomer. The kinetic study over RHABIm-HSO₄ showed the reaction obeyed the pseudo-first order rate law. RHABIm-HSO₄ was stable and re-used several times with only minor loss in catalytic activity due to possible leaching of the organic ligand.