Clay immobilization

A stereoselective insertion of phenyldiazoacetate-derived carbene into the a-C-H bond of tetrahydrofuran, catalyzed by a laponite clay-immobilized chiral bis(oxazoline) copper complex, depicted below, was also described <07OL731>. 

General conditions 150 mg of clay was dispersed in toluene over 1 h at RT. The solvent was removed by vacuum and an MMAO heptane solution was added (MMAO = 22.5 mmol). The mixture was stirred over 90 min at RT and the solid clay/MMAO product was dried in vacuum. Then the Fe precatalyst (4.6 imol) was added to preform a clay-immobilized iron-based catalyst. 

In addition, two synthesis strategies were studied (Figure 6.11). In route 1, the clay was first reacted with an MMAO heptane solution and then, after saturation with the monomer, the polymerization initiated by the addition of Fe precatalyst. Instead, in route 2, the precatalyst was activated by using the clay-immobilized cocatalyst and the polymerization initiated by monomer addition. The catalytic activities with the different montmorillonites and precatalysts used, following polymerization routes 1 and 2, are summarized in Figure 6.12. 

Schematic illustration of routes for the synthesis of MMAO-modified clay and clay-immobilized 2,6-bis(imino) pyridyl iron (II) catalysts for PE nanocomposites. (Adapted from Leone, G. et al., /. Polym. Sci., Part A Polym. Chem., 47,548,2009.)...

A drawback of A and B homogeneous catalytic systems is their broad molecular mass distribution, coupled to a relevant amount of a fraction with a low molar mass. Very interestingly, the clay-immobilized catalysts displayed not only a much higher activity due to a maximum dispersion of active sites within the silicate host and a longer polymerization lifetime, but also an increase of high molar mass fraction polymers because of a decrease of chain transfer rates or a redistribution of the active center populations (Figure 6.13). 

Although these examples show the possible immobilization on clays and mesoporous zeolites, the most widely used support for salen complexes has... 

In the case of the reaction between N-acryloyloxazolidin-2-one and cy-clopentadiene, both catalysts showed activities and enantioselectivities similar to those observed in homogeneous phase. However, a reversal of the major endo enantiomer obtained with the immobilized 6a-Cu(OTf)2 catalyst, with regard to the homogeneous phase reaction, was noted. Although this support effect on the enantioselectivity remains unexplained, it resembles the surface effect on enantioselectivity of cyclopropanation reaction with clay supports [58]. 

Species held on a surface by ion exchange (such as calcium ions on clay) are also immobile in groundwater. As with physically adsorbed species, they may be replaced by ions with a greater affinity to the solid surface. 

Mobility of The Anion-Free Water. It is well known that water in the electrical double layer is under a field strength of 10 -10 V/cm and that the water has low dielectric constants (36). Since anion-free water is thought to be the water in the electrical double layer between the clay and the bulk solution, at high electrolyte concentrations, the double layer is compressed therefore, the water inside is likely quite immobile. At low electrolyte concentrations, the electrical double layer is more diffuse, the anion-free water is expected to be less immobile. Since the evaluation of the shaly formation properties requires the knowledge of the immobile water, experiments were conducted to find out the conditions for the anion-free water to become mobile. 

By definition, the anion-free water is free of salt. When pressure is applied to a clay-brine slurry to force out water (as that described in the experimental section), the solution that flows out of the cell should maintain the same chloride concentration as the brine s if the anion-free water is immobile. Otherwise, the concentration of the chloride decreases. Pressure forces water to flow through the pores with a certain velocity meanwhile, the pore size... 

In order to increase the flow rate without too much pressure, Experiment 4 was performed with a Fann filter press which has a wider cross sectional area. A constant air pressure of 100 psi was applied, the flow rate was 26 times that of Experiment 1 while the NaCl concentration was only slightly higher than that of Experiment 1. Although the flow rate was much increased in Experiment 4, the result was similar to Experiment 1. The water retained in the clay (Column 8) determined by drying was found to be close to the amount of anion-free water. The porosity of the sediment was 0.4 and the average pore diameter was 4466 X. It was concluded from this experiment, that the anion-free water was immobile even at 100 psi and 7.4 ft/day. The pore size distributionQof the sample showed 90% of the pores to have a diameter above 350 A and less than 3% of the pores to have a diameter below 100 X (Figure 4). 

Ru(II)BINAP was sulfonated and immobilized by the supported-aqueous-phase technique.208-210 Immobilization of Ru(II)BINAP by ion exchange of the sulfonated complex on anionic minerals was also reported.211 The complex is only present at the outer surface and is not intercalated within the interlamel-lar space of the clay. 

Layered materials are of special interest for bio-immobilization due to the accessibility of large internal and external surface areas, potential to confine biomolecules within regularly organized interlayer spaces, and processing of colloidal dispersions for the fabrication of protein-clay films for electrochemical catalysis [83-90], These studies indicate that layered materials can serve as efficient support matrices to maintain the native structure and function of the immobilized biomolecules. Current trends in the synthesis of functional biopolymer nano composites based on layered materials (specifically layered double hydroxides) have been discussed in excellent reviews by Ruiz-Hitzky [5] and Duan [6] herein we focus specifically on the fabrication of bio-inorganic lamellar nanocomposites based on the exfoliation and ordered restacking of aminopropyl-functionalized magnesium phyllosilicate (AMP) in the presence of various biomolecules [91]. 

Clay minerals or phyllosilicates are lamellar natural and synthetic materials with high surface area, cation exchange and swelling properties, exfoliation ability, variable surface charge density and hydrophobic/hydrophilic character [85], They are good host structures for intercalation or adsorption of organic molecules and macromolecules, particularly proteins. On the basis of the natural adsorption of proteins by clay minerals and various clay complexes that occurs in soils, many authors have investigated the use of clay and clay-derived materials as matrices for the immobilization of enzymes, either for environmental chemistry purpose or in the chemical and material industries. 

Jackbean urease was immobilized on kaolinite and montmorillonite [98]. The amounts of urease required for maximum immobilization were 70 and 90 mg g 1 of kaolinite and montmorillonite, respectively. The Km values of immobilized urease (25.1-60.8 mM) were of the same order of magnitude as that of free urease (29.4 mM) but one order of magnitude higher than those of soil urease (1.77-2.90 mM). Immobilization of urease on clay surfaces leads to increases in the kinetic constants. 

Copper(II) nitrate immobilized on K 10 clay (claycop)-hydrogen peroxide system is an effective oxidant for a variety of substrates and provides excellent yields (Scheme 6.31) [104] wherein the maintenance of pH of the reaction mixture is not required. 

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