Page 157 - Adsorbents fundamentals and applications

142 SILICA GEL, MCM, AND ACTIVATED ALUMINA

Table 6.2. Silanes used for grafting silicas
Chlorosilanes: Trichlorosilane, Cl 3 SiH
Methyltrichlorosilane, Cl 3 SiCH 3
Dimethyldichlorosilane, Cl 2 Si(CH 3 ) 2
Trimethylchlorosilane, ClSi(CH 3 ) 3
Propyltrichlorosilane, Cl 3 SiCH 2 CH 2 CH 2
Octyltrichlorosilane, Cl 3 Si(CH 2 ) 7 CH 3
Octadecyltrichlorosilane, Cl 3 Si(CH 2 ) 17 CH 3
Alkenylsilanes: Vinyltriethoxysilane, (CH 3 CH 2 O) 3 Si−CH=CH 2
Methcryloxypropyltriethoxysilane,
(CH 3 CH 2 O) 3 SiCH 2 CH 2 CH 2 −O−CO−C(CH 3 )=CH 2
Arylsilane: Phenyltriethoxysilane, (CH 3 CH 2 O) 3 SiC 6 H 5

Epoxifunctional Silane: 3-Glyciodoxypropyltrimethoxysilane
(CH 3 O) 3 SiCH 2 CH 2 CH 2 −O−CH 2 CH−O−CH2
N-Functional Silanes: 3-Aminopropyltriethoxysilane,
(CH 3 CH 2 O) 3 SiCH 2 CH 2 CH 2 NH 2
3-Aminopropyldiethoxymethylsilane,
(CH 3 CH 2 O) 3 CH 2 SiCH 2 CH 2 CH 2 NH 2
3-Aminopropylethoxydimethylsilane,
(CH 3 CH 2 O)(CH 2 ) 2 SiCH 2 CH 2 CH 2 NH 2
Cyanopropyltriethoxysilane,
(CH 3 CH 2 O) 3 SiCH 2 CH 2 CH 2 CN
Hexamethyldisilazane,
(CH 3 ) 3 SiNHSi(CH 3 ) 3
S-functional Silane: 3-Mercaptopropyltriethoxysilane,
(CH 3 CH 2 O) 3 SiCH 2 CH 2 CH 2 SH
Cl-functional Silane: Chloropropyltriethoxysilane,
(CH 3 CH 2 O) 3 SiCH 2 CH 2 CH 2 Cl
Courtesy of Vansant et al., 1995.

The organosilanes have the general formula R N −Si−X 4−N ,where Risan
organic group and X is a hydrolyzable ligand. X may be an acyloxy, amine,
halide, or alkoxy group. Chloride, ethoxy, and methoxy are the most-used
X groups.
Silica gels are used in gel permeation chromatography, based on size exclusion
of polymers from the pores. Silica gels have also found use as a polar column
sorbent. Modification of the silica by silanes makes the stationary phase apolar.
Because most interactions are reversed, compared with the pure silica, separations
using these apolar columns are termed “reversed-phase chromatography”.
Amine grafted silicas are promising sorbents for selective adsorption,
especially for applications in environmental control and catalysis. For example,
Lasperas et al. (1997) and Angeletti et al. (1988) used amine function-modified