Al III

4 LEWIS ACID-ASSISTED CHIRAL BR0NSTED ACID CATALYSTS 

BINOL derivative SnCl4 complexes are useful not only as artificial cyclases but also as enantioselective protonation reagents for silyl enol ethers. However, their exact structures have not been determined. SnCl4-free BINOL derivatives are 

26 SnCl4 is also superior to 22 SnCl4, and is effective for the enantioselective cyclization of 2-(polyprenyl)phenol derivatives to give polycyclic terpenoids bearing a chroman skeleton.The synthetic utility of 26 SnCl4 is demonstrated by very 

Ishihara, Yamamoto, and coworkers demonstrated that 26 SnCl4 is an artificial cyclase that is useful for not only achiral but also chiral substrates. The diastereo-selective cyclization of ( )-nerolidol (29) has been examined with 1 equiv of the achiral LBA, 2-methoxyphenol (32) SnCl4, in dichloromethane at —78°C (entry 1, Table 12.1). Cyclization of ( )-29 bearing an acid-sensitive allylic hydroxy group gives a complex reaction mixture, and the desired trans-fused 2-oxabicyclo[4.4.0] 

TABLE 12.1. Double Asymmetric Induction in Cyclization of ( )-29 with LBAs 

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Fig. Vni-11. ESCA spectrum of A1 surface showing peaks for the metal, A1(0), and for surface oxidized aluminum, Al(III) (a) freshly abraided sample (b) sample after five days of ambient temperature air exposure showing increased A1(III)/A1(0) ratio due to surface oxidation. (From Instrument Products Division, E. I. du Pont de Nemours, Co., Inc.)...

On the basis of these reagents a procedure of determinations of Al(III), Cr(III), Hg(II), Cd(II), Pb(II) in deferent objects was develop and showed prospect in a subsequent investigation of these compounds. 

Influence of the various factors in static conditions (concentration of heavy metals, both time of contact and ratio of solid and liquid phase, pH of medium) on solution of Pb(II), Cu(II), Cd(II) and Zn(II) from water solutions is studied and the optimal conditions of their extraction by organosilica sorbents modified by ions of Al(III) and Cu(II) are found. 

Al(III) is an example of an aquatic ion that forms a series of hydrated and protonated species. These include AlOrf Al(OH)J, Al(OH)3, and other forms in addition to AP. (For simplicity, we omit the H2O molecules that complete the structures of these complexes.) Most of these species are amphoteric (able to act as an acid or a base). Thus the speciation of Al(III) and many other aquatic ions is sensitive to pH. In this case, an aggregate variable springs from the conservation of mass condition. In the case of dissolved aluminum, the total dissolved aluminum is given by... 

Very few references are available relating to the study of the Al(III)/Al(s) reaction. Most of the earlier studies have been made in molten cryolite.56,57 Armalis and Levinskas58 have reported the overall exchange current density of the reaction under a steady state of deposition and showed that it is a moderately fast reaction. 

Aluminium is also a possible cause of the high frequency of sclerosis and Parkinsonian dementia among the natives of certain regions of South East Asia, where the soils are high in Al(III) and low in Mg2+ and Ca2+. 

A large number of complexes have been prepared in which metalla-/3-diketonate anions coordinate to either metal ions or B(X)(Y) moieties. The chemistry of such metal complexes has been reviewed previously (7). To summarize briefly, tris-chelate complexes (3) of Al(III) or Ga(III)... 

An ionophoretic method was described by Tewari [41] for the study of equilibria in a mixed ligand complex system in solution. This method is based on the movement of a spot of metal ion in an electric field with the complexants added in the background electrolyte at pH 8.5. The concentration of the primary ligand (nitrilo-triacetate) was kept constant, while that of the secondary ligand (penicillamine) was varied. The stability constants of the metal nitrilotriacetate-penicillamine complexes have been found to be 6.26 0.09 and 6.68 0.13 (log K values) for the Al(III) and Th(IV) complexes, respectively, at 35 °C and an ionic strength of 0.1 M. 

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