Lewis aridity

Figure 8. Bronsted acidity ( ) and Lewis acidity (O) of La zeolites pretreated at 900° C and rehydrated, against cation contents/unit celt. Bronsted aridity (c) and Lewis aridity ( ) of the Na-8.7 zeolite pretreated at 800°C and rehydrated are also plotted...

Selected spectra of pyridine on various samples at 473 K are depicted in Figure 2. It can be seen that both Brpnsted and Lewis acid sites were present on each sample. The ratio of these two types of add sites, measured by the ratio of absorbances of the respective bands, was different, however. Similar Brpnsted and Lewis acidity was found for the ion-exchanged samples (e.g., Ag/AL= 0.97 for Fc2Na-Mont). For the pillared samples, Lewis aridity predominated (Ag/AL= 0.27 and 0.12 for Al -PILC and Fe2Al j -PILC, respectively). Negligible Brpnsted acidity was found for the parent Na-Mont. 

It has been shown by X-ray crystallographic and NMR studies of aldehyde-Lewis arid complexes that a Lewis arid does not coordinate along the C=0 bond axis [76, 85], Moreover, according to the nature of the Lewis acid and the stoichiometry, several types of complexes can be generated [85, 86], When considering the nucleophilic attack on complexed carbonyl compounds, the various interactions at transition state must be estimated. Indeed, the presence of the Lewis acid can provide new nonbonded interactions with the incoming reagent. 

The main Lewis arid employed industrially to synthesize ethylbenzene is formed of the Aia3/HCl system. The general mechanism of its action in a Fricdel/Crafts type reaction can be illustrated as follows ... 

Like carbon dioxide, sulfur dioxide behaves as a Lewis acid by accepting a pair of electrons from the Lewis base water. The Lewis arid-base adduct rearranges to form sulfurous acid in a manner exactly analogous to the rearrangement of the carbon dioxide-water adduct to form carbonic acid that is presented on page 700 of the textbook. 

What is the proposed mechanism of initiation of polymerization, by the Lewis arid like aluminum chloride or bromide through an auto ionization process ... 

Sax, N.I., arid Lewis, R.J. (1988) Dangerous Properties of Industrial Materials, 7th edn, Van Nostrand Reinhold, New York. 

Trudell, M. R., Marowitch, J.M., Thomson, D.G., Fulton, C. W. Hoffmann, R. E. (1994). In situ bioremediation at a wood-preserving site in cold, semi-arid climate feasibility and field pilot design. In Bioremediation of Chlorinated and Polycyclic Aromatic Hydrocarbon Compounds, ed. R. E. Hinchee, A. Leeson, L. Semprini S. K. Ong, pp. 99-116. Boca Raton, FL Lewis Publishers. 

Thus, B(0H)3 is a Lewis add rather than a Bronsted acid (see Chapter 1). Because boron adsorbs most effectively in the pH 8 to 9 range on A1 and Fe oxides and silicate minerals, its availability is generally low in coarse-textured, acid-leached soils and in calcareous soils. Deficiency in add soils is the result of boron depletion by leaching, while deficiency in calcareous soils is caused by strong adsorption and predpitation as relatively insoluble Ca borate salts. In contrast, B toxicity is most commonly found in alkaline soils of arid regions these soils often contain high levels of Na which forms quite soluble borate salts. A lack of rainfall allows soluble borate to accumulate to phytotoxic levels. 

Clark-Lewis J W, Porter L J 1972 Phytochemical survey of the heartwood flavonoids of of Acacia species from arid zones of Australia. Aust J Chem 25 1943-1955... 

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