Ethylenimine in the synthetic routes of a new silylating agent: chelating ability of nitrogen and sulfur donor atoms after anchoring onto the surface of silica gel

Using a heterogeneous route, the precursor silylating agent 3-mercaptopropyltrimethoxysilane (mts) was first grafted onto silica gel and then condensed to one molecule of ethylenimine (etn). In the homogeneous route, mts reacted with etn to yield 3-trimethoxypropylthioethylamine (mptt), which was covalently anchored onto silica gel. In both cases, the new silylating agent displayed a chelating moiety containing nitrogen and sulfur basic centres. The amount of nitrogen immobilized was 1.73 and 1.74 mmol g(-1) silica for the heterogeneous and homogeneous methods, respectively. In both routes of synthesis nu(N-H) stretching bands appeared at 3361 and 3284 cm(-1) with the absence of a nu(S-H) stretching band. C-13 NMR Of the new silylating agent, (CH3O)(3)SiCH2CH2CH2SCH2CH2CH2NH2, showed chemical shifts for methoxy groups at 50.0 ppm and signals at 8.4, 23.0, 34.4, 36.1 and 41.2 ppm for the sequence of carbons from the silicon atom to the NH, group at the end of the organic chain. The H-1 NMR spectrum presented a singlet peak which was attributed to methoxy groups at 3.52 ppm; a triplet at 2.76, quintet at 1.64 ppm, multiplet at 2.49 and triplet at 0.65 ppm were assigned to hydrogen atoms bonded to carbons in the same sequence as above. A broad amidic proton peak appeared at 1.08 ppm. C-13 NMR-CPMAS (cross-polarization magic-angle spinning) of the immobilized surface gave a series of peaks similar to those of the free silylating agent. Thermal and elemental analyses confirmed the covalent attachment of the organic species onto the silica gel surface. The chelating moiety formed by basic centre atoms of the pendant groups on the silica surface have a pronounced ability to extract divalent copper from aqueous solution. (C) 2000 Elsevier Science Ltd All rights reserved.