Synthesis And Characterization Of Silica-Supported N,N,N',N'-Tetramethyl-N''-Propyl Guanidine And Its Ionic Liquid

Aminopropylated silica (APS), silica-supported N,N,N',N'-tetramethyl-N''-propyl guanidine (STMPG) and STMPG ionic liquids with different anions including PF6-, CH3COO- and CF3SO3- were prepared. The structures of APS, STMPG and its ionic liquids were characterized by means of FTIR, BET, ¹³C MAS NMR, TG and elemental analysis. The different preparation methods were compared.APS was synthesized separately by liquid-phase method and sol-gel method, and was characterized by means of FTIR, BET, elemental analysis and TG analysis. The surface of silica was pretreated via four kinds of methods to increase the quantity of hydroxyl group content and the result showed that microwave-activating was the most effective method: the number of hydroxyl group on the silica surface increased from 1.08 /nm² to 1.29 /nm². The loading of aminopropyl in the APS synthesized via liquid-phase method was 8.59wt%, the functional group concentration of aminopropyl was 1.49mmol/g and the pKa of APS was 9.3-15.0. The effects of some parameters on the sol-gel process were investigated and the optimal conditions were as follows: tetraethylorthosilicate(TEOS)/H₂O=1/7 (molar ratio), TEOS/EtOH(ethanol)=1/6(molar ratio), aminopropyltriethoxysilane(APTES)/ TEOS=0.07 (mass ratio), T=35℃, pH=9, aging time 72h. APS was extracted with dichloromethane for 4 h and dried at 393 K in vacuum for 6h. The loading and functional group concentration of aminopropyl in the APS synthesized via sol-gel method was 6.88wt% and 1.19mmol/g, respectively. The pKa of APS was 4.8, lower than that of APS synthesized via liquid-phase method.STMPG was prepared through three different methods. One synthetic method started with APS and tetramethylurea(TMU) in the presence of phosphorus oxy chloride (POCl₃). The other two methods started with chloropropyltriethoxysilane (CPTES) and N,N,N',N'-tetramethy lguanidine (TMG). The structure of STMPG was characterized by means of FTIR, Uv-vis, BET, ¹³C MAS NMR, elemental analysis and TG analysis. The results showed that the maximum loading of N,N,N',N'-tetramethyl -N''-propyl guanidine (TMPG) was 8.33 wt%, the functional group concentration of TMPG was 0.53 mmol/g and the pKa of STMPG was 6.8 ⁷.2.STMPG ionic liquids with different anions including PF₆^-, CH₃COO^- and CF₃SO₃^- were prepared through different methods on the basis of STMPG. The structures of the ionic liquids and their precursors were determined by means of FTIR, BET and elemental analysis. The acidity and basicity of the ionic liquids were determined and the results showed that the pKa of [STMPG]CH₃COO was the highest, about 4.8⁶.8.