Zeolites synthesis scheme

For this study, the pH value is fixed to 10. As the specific surface area can be used to express the crystallinity of materials, the scheme represented in Figure 2, which describes the different steps observed during zeolite synthesis, has been also found in the synthesis of... 

Figure 8.11 Synthesis schemes for mesoporous zeolites by carbon templating, directly with...

Figure 12.7 Scheme of equilibration and change of order during a zeolite synthesis [95bj. 

Zeolites are prepared hydrothermal synthesis. A simplified scheme of the zeolites synthesis is depicted in Figure 11.6 The basic ingredients -SiO, Na SiOj or Si(OR) and Al O, NaAlO, or Al(OR)j - together with a structure directing agent (template), usually an amine or surfactant like tetra-alkyl ammonium salt, are added to aqueous alkali (pH 8-12) which results in the sol-gel consisting monomeric and oligomeric silicate species. 

Kunkeler et al. (1997) reported that zeolite HNaY and zeolite-P are active and recyclable heterogeneous catalysts in the Fischer indole synthesis (Scheme 2.12). In certain cases, zeolite-P is capable of producing the linear indole isomer in excess. 

FIGURE 12.2 Synthesis scheme for the preparation of microporous ZTC from zeolite 7 as a template (a) and high-resolution transmission electron microscopy (HRTEM) image of the periodic microporous carbon inverse replica (b) obtained following this procedure. (From Lee, J. et al., Advanced Materials, 18,2073,2006. With permission.)... 

Silica gel or zeolite HY have also been used successfully for the synthesis of imidazoles, isoxazoles, and pyrazoles [59], under irradiation, without solvent (Scheme 8.39). 

For this purpose, Ag zeolite and Ag, developed by Garegg25 and Paulsen,26 respectively, have been widely employed (Scheme 7.6). Reactions using these activators have found practical use in synthetic studies on glycoprotein glycans and glycolipids. For instance, Paulsen reported the chemical synthesis of the core pentasaccharide structure 6 common to all types of Asn-linked glycans, using the Ag... 

Another opportunity to combine two reaction steps towards a one pot synthesis is the epoxidation of a-pinene and the isomerization of the epoxide to campho-lenic aldehyde (Scheme 5.6). Zeolite Ti-Beta seems adequate to deal with both steps as a catalyst [24]. Campholenic aldehyde is the starting material for several sandalwood fragrances. 

Scheme 5 Examples of the zeolite chiral inductor and chiral auxiliary methods for photochemical asymmetric synthesis...

Figure 5.30 Synthetic scheme for the synthesis of [Mn(salen )j within the pores of zeolite Y. (Redrawn from Sabater [187].)...

Further treatment with NH3 at 553 K promoted neither the catalytic performance nor further growth of the Re clusters. Thus the 120 min NH3 treatment gave the best performance of the Re-CVD/HZSM-5 catalyst for phenol synthesis. DFT calculations of Rejo cluster structures embedded in the pore of HZSM-5 revealed the most stabilized structure in the pore of HZSM-5 to be as shown in Scheme 10.4b. The edge-shared Rejo structure may be due to the structure and size of the pore ofthe HZSM-5 zeolite. A broader peak at 5 3.6 ppm than that of fresh HZSM-5 in the Al solid-state NMR spectrum implies a positive interaction between the A1 sites and the Reio clusters inside the pore of HZSM-5. 

The synthesis of phthallocyanines in zeolite Y has been the subject of several publications [52-58]. The different procedures are represented in Scheme 3. In principle, dicyanobenzene is reacted under inert conditions with transition metal zeolites. The latter can be prepared either via ion exchange, or via carbonyl or metallocene impregnation. 

The synthesis of the Y zeolite-encapsulated manganese complex of the salen ligand has been reported recently [51]. It was found to have catalytic activity in the oxidation of cyclohexene, styrene, and stilbene with PhlO. Typically, 1 Mn(salen) is present per 15 supercages, resulting in catalytic turn-overs in the order of 60. The reactions investigated with the respective product yields are given in Scheme 5. Typical oxidation products are epoxides, alcohols and aldehydes. In comparison to the homogeneous case encapsulation seems to lower the reaction rate. From cyclohexene the expected oxidation product cyclohexene oxide is present in excess and is formed on the Mn(salen) site. 2-cyclohexene-l-ol is probably formed on residual Mn cations via a radical mechanism. 

A promising unprecedented application of the chiral enecarbamates Ic in asymmetric synthesis is based on the ship-in-the-bottle strategy, which entails the oxidation of these substrates in zeolite supercages . In this novel concept, presumably dioxetanes intervene as intermediates, as illustrated for the oxidation of the chiral enecarbamate Ic in the NaY zeolite (Scheme 6). By starting with a 50 50 mixture of the diastereomeric enecarbamates (45, 3 R)-lc and (45, 3 5 )-lc, absorbed by the NaY zeolite, its oxidation furnishes the enantiomerically enriched (ee ca 50%) S -methyldesoxybenzoin, whereas the (4R,3 R)-lc and (4R,3 S)-lc diastereomeric mixture affords preferentially (ee ca 47%) the R enantiomer however, racemic methylbenzoin is obtained when the chirality center at the C-4 position in the oxazolidinone is removed. Evidently, appreciable asymmetric induction is mediated by the optically active oxazolidinone auxiliary. 

Japanese workers prepared examples of 2-alkenyl-4,5-oxazolediones 40a and 40b, which are key intermediates in the synthesis of alkenoyl isocyanates 41a and 41b (Scheme 6.13). These reactive monomers are precursors to a variety of functionalized polymers including instantaneously curable compositions. Thus, reaction of oxalyl chloride with acrylamide 39a or methacrylamide 39b affords 40a and 40b isolated as hydrochloride salts in high yields. Subsequent decomposition of the 2-alkenyl-4,5-oxazolediones in the presence of a metal halide or synthetic zeolite affords 41a and 41b contaminated with varying amounts of 42a and 42b. The synthesis and reactions of other 2-substituted 4,5-oxazolediones have been described independently by Speziale and co-workers ° and Sasaki and co-workers. ... 

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