Nucleophilic substitution on silica surfaces

Untertitel:Comparison of the reactivity of alpha- versus gamma-chlorosubstituted silanes in the reaction with sodium azide
Autoren:Keppeler, Miriam (Universität Ulm); Holzbock, Juergen (Universität Ulm); Akbarzadeh, Johanna; Peterlik, Herwig; Huesing, Nicola (Universität Ulm)
Abstrakt:Azido-group functionalized, hierarchically organized meso-/macroporous silica gels have been prepared through co-condensation of tetrakis(2-hydroxyethyl)orthosilicate with chloromethyltrimethoxysilane or 3-(chloropropyl)-triethoxysilane and subsequent conversion of the chloro groups. Azido functionalities have been obtained by nucleophilic substitution of the surface-bound chloro moieties with NaN3 in N,N-dimethylformamide. A strong dependence of the later azide density (N-3 groups nm(-2)) in the final material on the reaction conditions, such as temperature and time, but also on the spacer length (methylene versus propyl) of the organofunctional silane has been observed. In principle, the nucleophilic substitution benefits from higher reaction temperatures and times. However, while gamma-azido groups seem to be stable over a wide range of reaction temperatures and longer reaction times, alpha-azido moieties tend to decompose at temperatures above 60 degrees C. The structural features of the monolithic gels and the azide functionalities on the surface were determined by IR-ATR-spectroscopy, elemental analyses, N-2-sorption analyses, small angle X-ray scattering and transmission electron microscopy.
Anzahl der Seiten:6
Journaltitel:Journal of the Ceramic Society of Japan (JCS-Japan)
Peer reviewed:true
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