Lewis acids INDEX

The mineral talc is extremely soft (Mohs hardness = 1), has good sHp, a density of 2.7 to 2.8 g/cm, and a refractive index of 1.58. It is relatively inert and nonreactive with conventional acids and bases. It is soluble in hydroduoric acid. Although it has a pH in water of 9.0 to 9.5, talc has Lewis acid sites on its surface and at elevated temperatures is a mild catalyst for oxidation, depolymerization, and cross-linking of polymers. 

S / V CONTENTS Preface, Robert W. Hay. Structure and Function of Manganese-Containing Biomolecules, David C. Weather-bum. Repertories of Metal Ions as Lewis Acid Catalysts in Organic Reactions, Junghan Suh. The Multicopper-Enzyme Ascorbate Oxidase, Albrecht Messerschmidt. The Bioinorganic Chemistry of Aluminum, Tomas Kiss and Etelka Farkas. The Role of Nitric Oxide in Animal Physiology, Anthony R. Butler, Frederick Flitney and Peter Rhodes. Index. 

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

Chatteijee, A. 2006. A reactivity index study to rationalize the effect of dopants on Bronsted and Lewis acidity occurring in MeAlPOs. J. Mol. Graphics Model. 24 262-270. 

Library of Congress Cataloging in Publication Data. Main entry under title Theoretical inorganic chemistry. (Topics in current chemistry 56). Bibliography p, Includes index. CONTENTS Jorgensen, C. K. Continuum effects indicated by hard and soft antibases (Lewis acids) and bases. - Brunner, H. Stereochemistry of the reactions of optically active organometallic transition metal compounds, [etc.]. 1. Chemistry, Physical and theoretical- Addresses, essays, lectures. I. Series. 

In summary, it is inferred that the low-index (1100) faces are almost un-reactive and that the exposed Fe3+ ions have very weak Lewis acidity. 

Stronger Lewis acid sites associated with TiJ+ centers exist only on higher-index faces or on defects such as edges and steps. 

FA of data matrices containing 35 physicochemical constants and empirical parameters of solvent polarity (c/ Chapter 7) for 85 solvents has been carried out by Svoboda et al. [140]. An orthogonal set of four parameters was extracted from these data, which could be correlated to solvent polarity as expressed by the Kirkwood function (fir — l)/(2fir + 1), to solvent polarizability as expressed by the refractive index function (rfi — + ), as well as to the solvent Lewis acidity and basicity. Thus,... 

Friedel and Crafts themselves observed that aluminum chloride is by no means the only specific catalyst in the Friedel-Crafts reaction. A number of other acidic metal halides could also be employed however, these were less reactive. The strength or coordinating power of different Lewis acids can vary widely against different Lewis bases. Hence it is extremely difficult to establish a scale of strength of Lewis acids in a manner analogous to that used for Brpnsted acids. Despite the difficulties, a number of qualitative orders of reactivity have been proposed. A comparative study of the activity of various Friedel-Crafts catalysts was performed by Olah and coworkers. Thus the activity index (the lowest temperature at which reaction occurs) of a large number of Lewis acid halides was measured using the benzylation reaction as the probe. 

Copolymerization initiated by A proceeds readily at low temperatures and gives isobutene—isoprene copolymers structurally identical to those prepared commercially utilizing a conventional Lewis-acid initiator. That is to say, there is no incorporation of isoprene in a 1,2- or 3,4-fashion, as would be anticipated at least in part for a Ziegler—Natta process. As with polyisobutene, lower temperatures result in higher molecular weights (polydispersities 2) while materials with high M values and a low polydisper-sity index could be obtained only at very low contents of isoprene. consistent with observations that chain-transfer processes are extremely facile following isoprene incorporation. - ... 

CONTENTS Preface, Mark Lautens. Photocyclization and Phofocycloaddition Reactions of 4- and 2-Pyrones, Frederick G. West. Intramolecular I4+3) Cycloaddition Reactions, Michael Harman. Lewis Acid Catalyzed [2+2] Cycloaddition Reactions of Vinyl Sulfides and Their Analogues Catalytic Asymmetric [2+2] Cycloaddition Reactions, Koichi Narasaka and Yujiro Hayashi. Vinylbo-ranes as Diels-Alder Dienophiles, Daniel A. Singleton. Preparation and Exo-Selective [4+2] Cycloaddition Reactions of Cobaloxime-Substituted 1,3-Dienes, MarkE. Welker, Marcus W. Wright, Heather L. Stokes, B. Matthew Richardson, Torrey A Adams, Terrence L. Smalley, Stacia P. Vaughn, Ginger J. Lohr, Louise Liable-Sands, and Arnold L. Rheingold. Index. 

In catalytic biomass cmiversion, the dehydration of polyol moieties is a key reaction, forming either an olefin bond, an ether, or a carbonyl group (after tautomerization). This type of reactimi usually requires the aid of acid catalysis. Both Br0nsted and Lewis acids are known to catalyze dehydration. The most famous dehydration in the context of biomass conversion is the formation of HMF from six-carbon sugars. As can be seen in Fig. 12, HMF from fructose (or glucose) preserves the F.C value of 1.17, while the FI index falls from 2 to 1. Similarly, pentoses lead to furfural in aqueous media under acid catalysis. The catalytic formation of HMF and furfural from hexoses and pentoses, respectively, and HMF production directly from cellulose, have been reported frequently over... 

A further distinction that should be kept in mind is between those parameters that clearly pertain to solvents, such as those derived from bulk properties (refractive index, electrical permittivity, rate and equilibrium constants of reactions in the solvent, UV/visible or IR frequency shifts of solutes), and those that relate to molecules in solntion, such as those derived from enthalpies of reactions in dilute solution in an inert solvent. The donor number DN and Drago s E, E, C, Cg acidity and basicity parameters for Lewis acids and bases are examples of the latter kind. 

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