作者: Véronique Dufaud , Mark E. Davis
DOI: 10.1021/JA034594S
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摘要: Catalytic materials bearing multiple sulfonic acid functional groups and positioned at varying distances from one another on the surface of mesoporous solids are prepared to explore effects that spatial arrangement active sites have catalytic activity selectivity. A series organosiloxane precursors containing either disulfide or sulfonate ester functionalities (synthons eventual groups) synthesized. From these molecular precursors, a variety organic−inorganic hybrid, mesostructured SBA-15 silica using postsynthetic grafting procedure leads modified silicas: [Si]CH_2CH_2CH_2SS-pyridyl, 2·SBA, [Si]CH_2CH_2CH_2SSCH_2CH_2CH_2[Si], 3·SBA, [Si]CH_2CH_2(C_6H_4)(SO_2)OCH_2CH_3, 4·SBA, [Si]CH_2CH_2(C_6H_4)(SO_2)OC_6H_4O(SO_2)(C_6H_4)CH_2CH_2[Si], 6·SBA ([Si] = (⋮SiO)_x(RO)_(3-x)Si, where x 1, 2). By subsequent chemical derivatization grafted species, thiol silicas obtained. The characterized by spectroscopic (^(13)C ^(29)Si CP MAS NMR, X-ray diffraction) quantitative (TGA/DTA, elemental analysis, capacity titration) techniques. In all cases, organic fragment precursor molecule is onto solid without measurable decomposition, are, in general, attached oxide siloxane bridges. species 2·SBA 3·SBA reduced corresponding thiols 7·SBA 8·SBA, respectively, 4·SBA transformed aryl acids 11·SBA 12·SBA, respectively. 8·SBA differ only terms level control groups. Both further oxidation with hydrogen peroxide produce alkyl 9·SBA 10·SBA, performances (with exception 12·SBA) tested as catalysts for condensation reaction phenol acetone bisphenol A. material 10·SBA derived cleavage dipropyl more than not its monosite analogue 9·SBA, but also presumably stronger 11·SBA. It appears cooperative effect between two proximal may be operating this reaction.