Solid montmorillonite

In conclusion, in spite of the heterogeneous conditions, solid montmorillonite can facilitate the Michael additions of silyl ketene acetals and silyl enol ethers to enoates, enones, and ynoates. Montmorillonite proved to be an alternative to conventional, moisture-sensitive homogeneous acids which are frequently troublesome in manipulation and work-up. 

Highly active immobilized palladium catalysts modified with a rigid C,N,C-pincer carbene ligand were successfully applied in the coupling of aryl halides to terminal acetylenes. The homogeneous catalyst was immobilized on three types of solids - montmorillonite K-10, bentonite A, and bentonite B - by the solvent-impregnation method. No significant differences were observed in the catalytic efficiency between the various supports. The reactivity of the system is relatively constant after as many as five cycles [68]. 

Reductive alkylation of primary amines to secondary amines has also been carried out using iridium and rhodium complexes supported on solid montmorillonites. ... 

A lamellar solid of especial interest is montmorillonite, a clay mineral. 

To obtain a high viscosity at a much lower clay concentration, certain water-soluble vinyl polymers called clay extenders can be used. In addition to increasing the yield of sodium montmorillonite, clay extenders serve as flocculants for other clay solids. The flocculated solids are much easier to separate using solids control equipment. 

Sorption of plutonium (l.fixlO-11 M) and americium (2xl0-9 M) in artificial groundwater (salt concentration 300 mg/liter total carbonate 120 mg/liter Ref. 59) on some geologic minerals, quartz, biotite, o apatite, o attapulgite, montmorillonite. Dashed lines indicate the range for major minerals in igneous rocks. Experimental conditions room temperature, particle size 0.04-0.06 mm, solid/liquid ratio 6-10 g/1, aerated system, contact time 6 days. 

The synthesis of imidazoles is another reaction where the assistance of microwaves has been intensely investigated. Apart from the first synthesis described since 1995 [40-42], recently a combinatorial synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles has been described on inorganic solid support imder solvent-free conditions [43]. Different aldehydes and 1,2 dicarbonyl compounds 42 (mainly benzil and analogues) were reacted in the presence of ammonium acetate to give the trisubstituted ring 43. When a primary amine was added to the mixture, the tetrasubstituted imidazoles were obtained (Scheme 13). The reaction was done by adsorption of the reagent on a solid support, such as silica gel, alumina, montmorillonite KIO, bentonite or alumina followed by microwave irradiation for 20 min in an open vial (multimode reactor). The authors observed that when a non-acid support was used, addition of acetic acid was necessary to obtain good yields of the products. 

This equation shows that activity of Ca + is related to pH, concentration of H2CO3 and temperature. Because pH is related to the concentration of Cl for the equilibrium curves 1 and 2 in Fig. 2.14, the relationship between the concentrations of Ca " " and Cl" can be derived for calcite-albite-sericite-K-feldspar-quartz equilibrium (curves 4 and 7 in Fig. 2.14) and calcite-albite-sericite-Na-montmorillonite-quartz equilibrium (curves 5 and 8 in Fig. 2.14) with constant w2h2C03- The range of zh2C03 in the solution in equilibrium with calcite is assumed to be 10 to 10 . The other equilibrium curves for the assemblage including Ca minerals are also drawn (Fig. 2.14). These assemblages are wairakite-albite-sericite-K-feldspar-quartz (curve 3), Ca-montmotillonite-albite-sericite-Na-montmorillonite-quartz (curve 6), Ca-montmorillonite-albite-sericite-K-feldspar-quartz (curve 9) and anhydrite (curve 10). The effect of solid solution on the equilibrium curves is not considered because of the lack of thermochemical data of solid solution. 

In this chapter, we demonstrate the potential of such agents as catalysts/promoters in key steps for the derivatization of sugars. The most significant catalytic approaches in carbohydrate chemistry that use aluminosilicate porous materials, namely zeolites and montmorillonite clays, are reviewed and discussed. Silica gel is a porous solid silicate that has also been used for heterogeneous catalysis of organic reactions in general. We include here its usefulness as promoter and reagent support for the reactions under consideration. 

Subsequently, Goncalves cl al.97 reported the acetylation of glycerol with acetic acid performed over different solid acids, including montmorillonite K-10 and such acid zeolites as HZSM-5 and HUSY. Among the siliceous porous materials examined, montmorillonite K-10 gave the best performance, with 96% conversion into the mono-, di- and tri-acetylated derivatives. When zeolites were used, the conversion was lower than with the other catalysts, giving a 30% conversion for HZSM-5 and only 14% for HUSY. However, selectivity for the primary monoacetylated product,... 

K. Motokura, N. Nakagiri, T. Mizugaki, K. Ebitani, and K. Kaneda, Nucleophilic substitution reactions of alcohols with use of montmorillonite catalysts as solid Br0nsted acids, J. Org. Chem., 72 (2007) 6006-6015. 

K. Toshima, Y. Ushiki, G. Matsuo, and S. Matsumura, Environmentally benign aryl C-glycosidations of unprotected sugars using montmorillonite K-10 as a solid acid, Tetrahedron Lett., 38 (1997) 7375-7378. 

A facile method for the oxidation of alcohols to carbonyl compounds has been reported by Varma et al. using montmorillonite K 10 clay-supported iron(III) nitrate (clayfen) under solvent-free conditions [100], This MW-expedited reaction presumably proceeds via the intermediacy of nitrosonium ions. Interestingly, no carboxylic acids are formed in the oxidation of primary alcohols. The simple solvent-free experimental procedure involves mixing of neat substrates with clayfen and a brief exposure of the reaction mixture to irradiation in a MW oven for 15-60 s. This rapid, ma-nipulatively simple, inexpensive and selective procedure avoids the use of excess solvents and toxic oxidants (Scheme 6.30) [100]. Solid state use of clayfen has afforded higher yields and the amounts used are half of that used by Laszlo et al. [17,19]. 

Addition of a solid acid catalyst such as Montmorillonite K10 increased the yield significantly under the action of either thermal heating (64%) or MW irradiation (66%) [52 c]. Under the latter conditions the reaction time was reduced. Comparable results were obtained for the synthesis of aminocoumarins 39-42 (Tab. 7.3) [53]. 

Reaction of pyrones under dassical conditions requires the use of high temperatures to obtain low to moderate yields. The Diels-Alder reaction of pyrones has been performed in a commercial microwave oven under solvent-free conditions on solid supports such as silica gel, montmorillonite, fitrol clay and alumina. The reaction time was dramatically reduced - from 4 h to 4 min (Scheme 9.9) [50],... 

The dispersion and solid-state ion exchange of ZnCl2 on to the surface of NaY zeolite by use of microwave irradiation [17] and modification of the surface of active carbon as catalyst support by means of microwave induced treatment have also been reported [18]. The ion-exchange reactions of both cationic (montmorillonites) and anionic clays (layered double hydroxides) were greatly accelerated under conditions of microwave heating compared with other techniques currently available [19.]... 

Ogawa M, Shirai H, Kuroda K, Kato C (1992) Solid-state intercalation of naphthalene and anthracene into alkylammonium-montmorillonites. Clays Clay Miner 40 485-490... 

The long-term goal of this investigation is an understanding of the effect of a particular mode of adsorption on montmorillonite which ensures that under pressure the clay platelets align parallel to a solid surface even under saline conditions. This is an important phenomenon in petroleum recovery processes. 

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

The recovery of M2D-C3-0-(E0)n-CH3 after exposure to various solid media has been investigated by API-MS, high performance liquid chromatography light scattering mass detection (HPLC-LSD) and HPLC-APCI-MS methods [10]. Recoveries with extraction immediately following application were determined (surfactant concentration 0.1%, surfactant/solid lOmgg-1) with complete recoveries obtained on all media other than the clays illite and montmorillonite (Table 5.5.2) [10]. 

The structural integrity of M2D-C3-0-(E0)ra-CH3 was maintained for all solid media investigated, as confirmed by qualitative analysis of the flow injection analysis (FIA) API-MS spectra (example shown in Fig. 2.8.10a). Intercalation of the surfactant solution between the clay layers was considered as the likely cause of the reduced recovery on montmorillonite (74%), according to experimental observations and... 

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