ASPECTS OF THE SYNTHESIS, CHARACTERIZATION AND METAL-LIGAND STOICHIOMETRY OF AMINOPROPYL, NITROBENZAMIDE, AND 8-QUINOLINOL SILICA-GELS

Surface modification of several silica gels with a number of silanes was studied, as well as further reactions of the modified surfaces. Complete reaction of aminopropylsilane was easily achieved if surface silanols were in excess. Triethoxysilylpropyl-p-nitrobenzamide (TESPN) reacts with difficulty, and complete reactions occurred only with long reaction time (at least 12 h). The maximum coverage of 100-Angstrom pore silica gel by TESPN was found to be about 1.7 mu mol/m(2), considerably less than the 3-4 mu mol/m(2) of available silanol sites, probably due to steric effects of the large silane. Even at this maximum coverage, further reaction of the modified silica with trimethylsilyl capping groups occurred, with additional coverage of about 1.0 mu mol/m(2). The maximum amount of silylpropylamido-p-phenylazo-8-quinolinol that could be bound to silica gel was found to be about 1.0 mu mol/m(2), again probably limited by steric effects of the large 8-quinolinol (oxine) moiety. Virtually complete conversion of parent nitrobenzamide silica gel (NBSG) to 8-quinolinol silica gel (QSG) could be achieved if NBSG coverage was less than about 0.7 mu mol/m(2). QSG materials were found to have a 2 oxine to 1 copper(II) stoichiometry, even with surface coverages as low as 0.16 mu mol/m(2)