Silica aminopropyl groups

Figure 2. Scheme illustrating (A) amine-silanol and (B) amine-amine interactions and (C) single site or site-isolated 3-aminopropyl groups grafted onto mesoporous silica [20]. 

Figure 3. Synthetic scheme to produce silica containing site-isolated aminopropyl groups through molecular imprinting approach [29].

Figure 5. Synthetic route to site-isolated 3-aminopropyl groups functionalized on mesoporous silica through use of 3-arninopropyltrimethoxysilane with bulky trityl group protected amine that serves as spacer [20].

Table 1. Grafting of 3-aminopropyl groups on mesoporous silica obtained in polar-protic, polar-aprotic and non-polar solvents, surface area and catalytic efficiency for Nitroaldol condensation of 4-hydroxybenzaldehyde and nitromethane [22]. 

Figure 16. Pictorial representation of Pd(ll) metal ions complexed to the 3-aminopropyl groups grafted onto mesoporous silica wall [74],...

There is also rapid development in the domain of standard silica-based zeolites. Their versatility can be extended by imprinting. For instance, Davis and Katz [15] recently successfully carried out imprinting and obtained a silica framework with pore walls anchoring three aminopropyl groups in cavities. Another achievement was reported by Ramamurthy, Schefer and coworkers [16]. The latter authors were able to obtain 90% diastereomeric excess of a product of the photochemical reaction in a commercially available zeolite containing chiral tropolone ether 433 in its pores. 

Many types of chiral stationary phase are available. Pirkle columns contain a silica support with bonded aminopropyl groups used to bind a derivative of D-phenyl-glycine. These phases are relatively unstable and the selectivity coefficient is close to one. More recently, chiral separations have been performed on optically active resins or cyclodextrins (oligosaccharides) bonded to silica gel through a small hydrocarbon chain linker (Fig. 3.11). These cyclodextrins possess an internal cavity that is hydro-phobic while the external part is hydrophilic. These molecules allow the selective inclusion of a great variety of compounds that can form diastereoisomers at the surface of the chiral phase leading to reversible complexes. 

Electroosmotic velocities of buffered solutions are shown for a bare silica capillaiy and one with aminopropyl groups (silica—Si—CHiCHiCHjNlL) covalently attached to the wall. A positive sign means that flow is toward the cathode. Explain the signs and relative magnitudes of the velocities. 

Attempts have recently been made to prepare solid acids by loading triflic acid into various inert oxides including silica,184 titania,185,186 and zirconia.187,188 Silica functionalized with anchored aminopropyl groups was also used to immobilize triflic acid.189 These new catalysts have been tested in a variety of organic transformations, such as alkane-alkene alkylation, Friedel-Crafts acylation, alkene dimerization, and acetalization. Silica nanoboxes prepared by dealumination of Na-X- and Ca-A-type zeolites were also loaded with triflic acid up to 32 wt%.190 The materials were thoroughly characterized but have not been tested as catalysts. 

Furthermore, MCM-41, MCM-48, and SBA-15 silica materials have been lined/ functionalized with, for example, alkyl,104 105 amino or aminopropyl groups,106-120 diamine,121,122 triamine,122,123 ethylenediamine,124 imidazole,120,125-127 triazol,120 A-benzylidenebutan-1 -amine,128 malonamide,129 carboxy(late),108,112,114... 

Hybrid silica materials were prepared via a sol-gel pathway at pH 9. The influence of anionic surfactant (SDS) was studied by comparing templated materials (TbSn series) with hybrid materials obtained without surfactant (Tbn series). Two mechanisms of mesostructure formation can be considered as represented on Fig. 2. The pka of aminopropyl chain is about 10.6 in the reaction mixture propyl-amines are partially protonated. Electrostatic interactions between dodecylsulfate anion and NH and sodium cation neutralization may then occur, resulting in the condensation of the silica structure around surfactant micelles and aminopropyl groups at the surface of the pores. The other mechanism is SDS chains complex-ation by P-CD cavity, which wonld result in P-CD gronps located at the surface of the pores and aminopropyl less accessible, due to steric hindrance caused by P-CD bulky groups. A complete characterization of the prodncts and adsorption capacities will help nnderstanding the formation mechanism of mesoporons hybrid silica. 

This may be explained as follows the SDS interacts with the maximum of partially protonated aminopropyl groups, by electrostatic interactions between dodecylsulfate anion and and sodium cation neutralization. The remaining amino groups are entrapped into the silica network. The amount of P-CD moieties incorporated depend on the initial molar ratio of P-CD APS, and not of the presence or not of SDS. P-CD groups may not interact with SDS. We can say, that for these hybrid materials, the templated mechanism is a S P one (S for anionic surfactant, P for cationic aminosilica species). 

The prominent goal of these studies was the detection of interactions between substrate and silyl esters with different organic groups R. The model substrates used include various kinds of silica, alumina, titania in addition to typical sandstones and silicon wafers. With respect to a contribution in the first conference report [3] one example may suffice here to demonstrate the procedure and the importance of the result obtained. The example concerns the treatment of a silicon wafer surface with 3-aminopropyltriethoxysilane (APTES) aimed at the detection of covalent bonding and possible interaction of the functional aminopropyl group with reactive surface centers. The method of choice is a... 

Silica gel with bonded aminopropyl groups (concentration of aminogroups is 0.8 mmol/g) with specific surface area s = 180 m /g and Silasorb Amin (CzR) with s = 200 m /g as initial adsorbents and fullerene Ceo (more than 99% purity) were used for the modification of silica surface. 

The self-aldol condensation of unmodified aldehydes in toluene catalyzed by propylamines supported on mesoporous silica FSM-16 (surface area 881 iirg has been reported.The aminopropyl groups (propylamine, N-methylpropylamine and A. A -diciliylpropylaiiiinc) were anchored on FSM-16 silica by post-modification methodology by using 3-aminopropyl-, A -methyl-3-aminopropyl- and A, A -diethyl-3-aminopropyltriethoxysilane respectively (Scheme 3.3). ... 

Related materials can be prepared in which the polysaccharides are linked to a silica support by covalently bound tether groups. For example, silica derivatized by 3-aminopropyl groups can be linked to polysaccharides using diisocyanates. These materials seem to adopt organized structural patterns on the surface, and this factor is believed to contribute to their resolving power. The precise structural basis of the chiral recognition and discrimination of derivatized polysaccharides has not been elucidated, but it appears that in addition to polar interactions, tt-tt stacking is important for aromatic compounds. ... 

Synthesis of modified silica 56 Two different types of low surface area silica were employed. The silica Fractosil 2500 (grain size = 80 pm) from Merck AG has a macroporous structure with relatively large pores (>250 nm) and a surface area (BET) of 8.3m g . The monosphere silica from Merck exhibits a spherical non-porous structure with a surface area (BET) of only 1.7 m gThe silica species were functionalized with 3-aminopropyl groups (-0.5 mmol per g Si02) on the surface as follows. The silica was dried in vacuum (<1 Pa at 200 °C). A total of 20 g of silica was charged in a 250-mL round-bottomed flask with 150 mL dried w-xylene. 2.2 g (10 mmol) 3-amino-propyltriethoxysilane was added, and the mixture was refluxed for 8 h. The filtered product was washed thoroughly with acetone. The solid 56 was dried under vacuum at 80 °C. 

The sorbents used in ion exchange SPE are PS-DVB based or silica based with bonding of different ionizable functional groups such as sulfonic acid, carboxylic acid for cation exchange, or aminopropyl group for anion exchange. 

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