Phenyl-modified silica matrix

Figure 40.9 Schematic representation of the pore structure in the phenyl-modified silica matrix (SiO-Ph).

This reaction has been modified extensively to proceed under different conditions. For example, it has been performed in liquid crystalline matrixes, sg in zeolite,in supercritical C02, on a silica gel surface, or in the presence of cyclo-dextrin. In addition, this reaction has been catalyzed by photoacid. Moreover, this reaction has been extended to various substrates other than the regular phenyl (or aryl) esters as described earlier. 

Reversed-phase extractions are used to enrich nonpolar compounds from a polar sample matrix. The extraction is based on interactions between carbon-hydrogen bonds from the compound and the sorbent. These hydrophobic interactions are shown in Figure 9.1a, and have been discussed in Section 3.5.2. Most organic compounds contain carbon-hydrogen-rich groups and will, therefore, be retained. Exceptions are ionized compounds or compounds with relatively many polar functional groups. Silica-based materials modified with C2, C4, C8, C18, cyclohexyl, phenyl, and cyano groups are examples of reversed-phase sorbents (see Table 9.3 for their structures). 

---