Silicon-aluminium exchange reaction

The regioselectivity of the double nucleophilic addition of ketene silyl acetals to a,/3-unsaturated imines has been found to be highly dependent on the subtle difference in the reactivities of the ketene silyl acetals the factors are mainly derived from the ability of the ketene silyl acetals to undergo the silicon-aluminium exchange reaction, where the aluminium enolate preferentially undergoes 1,4-addition.209... 

The tlrree impurities, iron, silicon and aluminium are present in the metal produced by the Kroll reduction of zirconium tetrachloride by magnesium to the extent of about 1100 ppm. After dre iodide refining process tire levels of these impurities are 350, 130 aird 700ppm respectively. The relative stabilities of the iodides of these metals compared to that of zirconium can be calculated from the exchange reactions... 

All the T-atom positions in the faujasite structure are equivalent and there should be no discrimination on this basis. Since the cations take part in the reaction with SICI4 (Eq.l), the cation location could influence the rate of the isomorphic substitution reaction. The dealumination reaction could proceed via two consecutive reaction steps (ref.8). The first step could be the rupture of one Si - Cl bond and formation of a Si - 0 bond and a chloride salt of the charge compensating cation. This step is exothermic and can proceed at mild reaction temperatures (ref.8). The second step is the aluminium-silicon exchange with concomitant formation of a aluminium chloro complex. This conversion is also exothermic (ref.8) and can proceed during the posttreatment. 

---