Alumina solid support

Jeevarajan, A. S., L. D. Kispert et al. (1993b). An ENDOR study of carotenoid cation radicals on silica-alumina solid support. Chem. Phys. Lett. 209 269-274. 

To accelerate the reactions rates and to increase their yields, sometimes microwave-assisted procedures are applied. The first mention of using a solvent-free microwave procedure was in [55]. The authors described the synthesis of 1,3,5-triarylpyrazoline by the cyclization of chalcones with phenylhydrazine on a basic alumina solid support. The target heterocycles were synthesized under microwave irradiation in high yields (up to 85%) in 1-2 min instead of 3 h in the case of thermal activation. Another publication [56] deals with the rapid (2-12 min) solvent-phase cyclization of naphthyl-substituted chalcones 41 and hydrazines 42 in a microwave field yielding the appropriate pyrazolines 43 quantitatively (Scheme 2.10). 

Transition metals absorbed onto a solid support metal Pd,Pt, Ni, Rh support Carbon, alumina, silica solvent EtOH, EtOAc, Et20, hexanes, etc. 

The allcylation of a number of aromatic compounds through the use of a chloroa-luminate(III) ionic liquid on a solid support has been investigated by Holderich and co-workers [87, 88]. Here the allcylation of aromatic compounds such as benzene, toluene, naphthalene, and phenol with dodecene was performed using the ionic liquid [BMIM]C1/A1C13 supported on silica, alumina, and zirconia. With benzene, monoalkylated dodecylbenzenes were obtained (Scheme 5.1-56). 

Once the membrane was successfully produced, it was analysed for characterisation and scanning. The sol-gel technique was successfully used to obtain a crack-free unsupported membrane, which was expected to have pore size of 1-2 nm. The development of the crack-free membrane may not have the same strength without strong, solid support. The next stage of this work was to characterise the fabricated membrane. Hie objectives of this study were to develop a zirconia-coated 7-alumina membrane with inorganic porous support by the sol-gel method and to characterise the surface morphology of the membrane and ceramic support. 

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. 

It is noted that the Diels-Alder reaction has been done with supercritical CO2 as a solvent. Diels-Alder reactions on solid supports have also been reported, and zeolites have been used in conjunction with catalytic agents.Alumina has been used to promote Diels-Alder reactions. 

Adsorption of carotenoids on activated silica-alumina results in their chemical oxidation and carotenoid radical formation. Tumbling of carotenoid molecules adsorbed on solid support is restricted, but the methyl groups can rotate. This rotation is the only type of dynamic processes which is evident in the CW ENDOR spectrum. 

The amount of Lewis acid to be used is depicted as an effective amount and a minimum limit of 0.5 mole equivalent with respect to the sulfmated compound concentration was mentioned. A wide variety of Lewis acids was mentioned to be useful for the present invention in the patent document, but only copper (II) compounds were claimed. The way in which the Lewis acid is used (either as a homogeneous or a heterogeneous phase), was reported to be irrelevant. So, it could be employed in solution in the reaction medium or insoluble as powders or on a solid support, such as alumina or a zeolite. The Lewis acid is supposed to be acting as a catalyst in the desulfination process. The temperature and pressure conditions for this reaction are substantially higher than the microbial conditions. The temperature and pressure conditions did not form part of any claim, but the document stipulates values between 50°C and 100°C, and 10 and 15psi, respectively. The quantitative effectiveness or conversion values of this reaction were not given, but it looks like it would diminish the advantages of a biocatalytic process. 

Most of the parallel reactions described in Schemes 4.23 and 4.24 were performed as dry-media reactions, in the absence of any solvent. In many cases, the starting materials and/or reagents were supported on an inorganic solid support, such as silica gel, alumina, or clay, that absorbs microwave energy or acts as a catalyst for the reaction (see also Section 4.1). In this context, an interesting method for the optimization of silica-supported reactions has been described [83], The reagents were co-spotted neat or in solution onto a thin-layer chromatographic (TLC) plate. 

Varma and coworkers have explored the use of hypervalent iodine compounds on solid support for the first time and developed a facile oxidative procedure that rapidly converts alcohols to the corresponding carbonyl compounds using alumina-sup-ported IBD under solvent-free conditions and MW irradiation in almost quantitative yields [108]. The use of alumina as a support improved the yields markedly as compared to neat IBD (Scheme 6.33). 1,2-Benzenedimethanol, under these conditions, undergoes cyclization to afford l(3H)-isobenzofuranone. 

The practical applications of NaBH4 reductions on mineral surfaces for in situ generated SchifFs bases have been successfully demonstrated. The solid-state reductive amination of carbonyl compounds on various inorganic solid supports such as alumina, clay, silica etc. and especially on K 10 clay surface rapidly afford secondary and tertiary amines [126]. Clay behaves as a Lewis acid and also provides water from its interlayers thus enhancing the reducing ability of NaBH4 [22],... 

Among various solid supports (K10, acidic alumina, zeolite HY, silica gel) silica gel proved to be the best after irradiation for 4 min the reactions led to yields ranging from 62 to 94%. 

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],... 

Solid supports such as silica gel and alumina have also been used in the generation of 1,3-dipoles to obtain heterocyclic compounds. However, changes in regios-electivity were not observed under microwave irradiation conditions. The regioselec-tivity can be modified by changing the polarity of the solid support [90], De la Hoz reported the reaction of pyridinium dicyanomethylidene ylide (130) with ethyl phenyl-propiolate (73), and found that the selectivity changes from 88 12 to 98 2 when the support is changed from celite, to neutral bentonite (Scheme 9.39). 

The first thing you need is an adsorbant, a porous material that can suck up liquids and solutions. Paper, silica gel, alumina (ultrafine aluminum oxide), corn starch and kitty litter (unused) are all fine adsorbants. Only the first three are used for chromatography. You may or may not need a solid support with these. Paper hangs together, is fairly stiff, and can stand up by itself. Silica gel, alumina, corn starch, and kitty litter are more or less powders and will need a solid support to hold them. 

Although beyond the scope of this book, a vast amount of work has been directed to supporting homogeneous catalysts on solid supports including silica, alumina and zeolites, and functionalized dendrimers and polymers [19]. These give rise to so-called solid-liquid biphasic catalysis and in cases where the substrate and product are both liquids or gases then co-solvents are not always required. In many ways solvent-free synthesis represents the ideal method but currently solvent-free methods can only be applied to a limited number of reactions [20],... 

Mayoral and colleagues210 studied the same reaction catalyzed by a menthoxyaluminum catalyst supported on silica gel and alumina. The catalyst was prepared by treatment of the solid support with diethylaluminum chloride and (—)-menthol. The silica-supported catalyst proved more active than the alumina-supported catalyst. The reaction rates and enantioselectivities depended strongly on the amount of (—)-menthol used. The highest ee obtained was 31% at 81% conversion (endo/exo = 10/90). 

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