TEMPO silica-entrapped

In other cases, organic modification of the sol gel cages markedly protects the entrapped molecular dopant from degradation by external reactants, as shown for instance by the entrapment of the radical 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO). This is a highly active catalyst which in the NaOCl oxidation of alcohols to carbonyls in a CH2CI2-H20 biphasic system becomes highly stabilized upon sol gel entrapment in an ORMOSIL matrix it progressively loses it activity when entrapped at the external surface of commercial silica.25... 

The chemical entrapment of TEMPO moiety in the sol-gel silica hybrid material is performed in two steps reductive amination of 4-oxo-TEMPO with 3-aminopropyl-trimethoxysilane (APTMS) followed by sol-gel co-poly-condensation of the TEMPO-funcionalized alkoxide thereby obtained with methyl-trimethoxysilane (MTMS) catalyzed by fluoride (Figure 6.2). 

The procedure is easily reproduced and can be applied to a variety of readily available olefins to afford valuable a-hydroxyacids (Table 6.3). The method offers a practical alternative to the use of cyanohydrins currently employed in industrial processes and further demonstrates the synthetic benefit of entrapping the TEMPO catalyst inside the nanocages of hydrophobized porous silica, where the radical catalytic molecules are highly protected from degradation. " Silia Cat TEMPO is a trademark of SdiCycle Inc., Quebec City, Canada. 

TEMPO to solid supports such as silica [13, 14] and the mesoporous silica, MCM-41 [15] or by entrapping TEMPO in sol-gel [16]. Alternatively, in our group we developed an oligomeric TEMPO (Scheme 4.3), derived from Chimassorb 944 [17]. 

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