SYNTHESIS AND SIMPLE METHOD OF CHARACTERIZATION OF ALDEHYDE-SILICA GEL

Abstract

Two approaches to the functionalization of the silica gel surface have been proposed, which make it possible to obtain materials with covalently immobilized highly reactive aldehyde groups. Immobilization of aldehyde groups in the first case is achieved by the click-reaction of azido-alkyne cycloaddition of 4-(prop-2-in-1-yloxy)benzaldehyde and 3-azidopropyl silica gel. In the second case, surface modification is performed by the alkylation reaction of hydroxybenzaldehydes with 3-chloropropyl silica gel. The obtained silica gel samples were characterized by infrared spectroscopy and thermogravimetric analysis data. In IR spectra absorption bands determination of aldehyde groups on the silica gel surface using 2.4 -dinitrophenylhydrazine has been proposed. The proposed method is based on the condensation reaction between the aldehyde groups grafted on the surface and 2.4 -dinitrophenylhydrazine. The quantitative estimation of the grafted aldehyde groups is suggested to be calculated by the difference between the initial amount of 2.4-dinitrophenylhydrazine and the amount remaining in the solution after the reaction. The necessity of maintaining a constant acidity of the medium by adding H2SO4 was established. It is shown that at λ = 315 nm the Bouguer-Beer-Lambert Law is satisfied in the concentration range 2.5∙10-5 to 12.5∙10-5 M. The correctness of the proposed method was checked using the procedure of operative control of the correctness of the results of chemical analysis. This procedure provides the determination of aldehyde groups in the modified material by multiply varying the silica gel weight and using the root-mean-square deviation of the repeatability of measurement results as an error characteristic. The proposed method for determining the aldehyde groups was tested on all silica gel samples. It was shown that by varying the conditions of surface modification it is possible to obtain materials with different functional capacity for aldehyde groups.