This review is focused on the use of solid Lewis acids to promote catalytic oxidations. While the concept of using Lewis acids to promote the reaction of organic substrates with oxidizing reagents is widely accepted in homogeneous catalysis, this concept has not become evident and generally used in heterogeneous catalysis until recent days. Certainly the development of new Lewis acid solids active and selective for catalytic oxidations is an urgent need and a challenging scientific target for some substrates especially using environmentally friendly oxidants. Since the replacement of current stoichiometric oxidations for the production of fine chemicals by environmentally benign catalytic oxidations is one of the major tasks in green chemistry, solid Lewis acids are called to play a crucial role to accomplish this goal. In the review, we will see the still important role that stoichiometric oxidations play in our daily life, and how they are being substituted by catalytic oxidations. At this point, three general mechanisms in which Lewis acids are involved will be described, and the material has been organized starting from homogeneous and ending with solid catalysts for heterogeneous oxidations. A bridge between the two will be established by presenting catalytic systems that can fill the gap between the two systems helping to rationalize the nature of the catalytic active sites in solid systems. This review is obviously focused on solid oxidation catalysts, and the core of the review is organized to show the evolution from the simplest strategy for heterogeneizing homogeneous catalysts, i.e., supporting the active species on large surface area solids, to the more elaborate ones in which the active sites are part of the solid structure. Given the importance of metallosilicates, and more specifically titanosilicates, as catalysts in commercial processes, special attention has been paid to these types of materials. Although sufficient references are provided to early seminal work, special emphasis has been given to most recent contributions to this area, particularly of the last 10 years. Patent literature has also been extensively covered in this review. Examples to illustrate the concepts have been selected among recent publications, and an effort has been made to present a series of commercial and near commercial processes based on catalytic oxidations. Finally, two * E-mail: acorma@itq.upv.es. 3837 Chem. Rev. 2002, 102, 3837−3892

Lewis acids as catalysts in oxidation reactions: from homogeneous to heterogeneous systems.

Carbohydrates as ligands: coordination equilibria and structure of the metal complexes

In early spring 1996 our handbook on science and technology of catalysis will be completed. In order to give all scientists working in the fields of kinetics and homogenous or heterogenous catalysis the possibility to have this detailed treatise of the topic on his or her shelf we decided to offer the whole handbook as a set for a reduced price.

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Catalysis science and technology

Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by drying with supercritical CO2. This technique affords low-density (60−130 kg/m3), high-surface-area (600−700 m2/g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction, solid-state NMR, acoustic measurements, and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2−5 nm in diameter and of varying lengths, whereas the aerogels prepared from hydrated Al(NO3)3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5−15 nm ra...

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Synthesis of High-Surface-Area Alumina Aerogels without the Use of Alkoxide Precursors

Evaluation of various types of Al-MCM-41 materials as catalysts in biomass pyrolysis for the production of bio-fuels and chemicals

Synthesis, Characterization, and Catalytic Properties of Mesoporous Tin-Containing Analogs of MCM-41☆

An attempt is made to survey and categorize selective protection and deprotection reactions, so that practicing chemists/biologists may be able to choose a method for the preparation of protected inositol derivatives, depending on their requirement. In addition to being useful for those who work with inositols, it is hoped that this review will help to widen the scope of using cyclitol derivatives for the synthesis of various classes of natural and unnatural compounds with interesting properties. Emphasis is given to the literature published between 1985 and the end of the year 2002, involving selective protection/deprotection of inositol hydroxyl groups.

Regioselective protection and deprotection of inositol hydroxyl groups.

Mesoporous aluminosilicate of the MCM-41 type: its catalytic activity in n-hexane isomerization

The local structural characteristics of Si and Ti sites in ETS-10 as derived from a combination of high-resolution magic angle spinning (MAS) NMR spectroscopic and molecular modeling studies are reported. Pure and highly crystalline ETS-10 and aluminum-substituted ETS-10 (ETAS-10), devoid of impurity ETS-4 phase, were synthesized and fully studied by MAS and multiple-quantum magic angle spinning (MQ-MAS) NMR. More accurate assignments of the experimentally observed 29Si resonances to the crystallographically nonequivalent Si sites are made, and a correlation with T-site geometry is established. 29Si slow MAS NMR is shown to be a very general and powerful methodology to unequivocally establish heteroatom substitution in the zeolite lattice, and this was used to probe the local symmetry and chemical shielding at different Si sites in ETS-10 and ETAS-10. 29Si and 27Al MAS NMR spectral analysis of ETAS-10 is used to confirm that the aluminum substitution occurs only in Si[4Si,0Ti] silicon sites. This, in turn, was used to generate cluster models for computer graphics techniques. The electronic structure of such cluster models and the calculated aluminum substitution energy values pinpoint the topographical location of aluminum in ETAS-10. The acidity of ETAS-10 is predicted on the basis of the quantum chemical cluster model calculations. The first application of MQ-MAS NMR to study cation environments in molecular sieves is also reported and is used in the present study to investigate the local structural characteristics of sodium cations in ETS-10 and ETAS-10.

Anisotropic Chemical Shielding, M-Site Ordering, and Characterization of Extraframework Cations in ETS-10 Studied through MAS/MQ-MAS NMR and Molecular Modeling Techniques

(±)-2,4-Di-O-benzoyl-myo-inositol 1,3,5-orthoformate, on heating in the presence of a base, undergoes transesterification to give 2,4,6-tri-O-benzoyl-myo-inositol 1,3,5-orthoformate and 2-O-benzoyl...

Tanya Das

Papers

Synthesis, Characterization, and Catalytic Properties of Mesoporous Tin-Containing Analogs of MCM-41☆

Regioselective protection and deprotection of inositol hydroxyl groups.

Mesoporous aluminosilicate of the MCM-41 type: its catalytic activity in n-hexane isomerization

Anisotropic Chemical Shielding, M-Site Ordering, and Characterization of Extraframework Cations in ETS-10 Studied through MAS/MQ-MAS NMR and Molecular Modeling Techniques

Reactivity controlled by lattice interactions in crystal: intermolecular acyl transfer in (±)-2,4-di-O-benzoyl-myo-inositol 1,3,5-orthoformate