Oxygen-aluminum bonds reactions with

Strong mineral acids react with clays to hydrolyze aluminum-oxygen bonds. The aluminum dissolves, leaving an altered structure. Protons in the acid also exchange with sodium and other alkali cations, leaving an acidic material. Houdry took advantage of such reactions in making the active acidic catalysts... 

Treatment of the reaction mixture with aqueous acid cleaves the aluminum-oxygen bond and produces cyclohexanol. 

Titanium compounds bonded to the surface OH groups of Mg(OH)2 are mainly inactive. The active sites are the ones associated with the coordinated and unsaturated negative oxygen ions. Reactions with aluminum alkyls activate the catalysts. For high efficiency, special carriers must be used together with a correct balance of the reactants, and proper reaction conditions. Some choice combinations of reactants are ... 

The scheme in Fig. 5.5 indicates that the ligand, for example, oxalate, is adsorbed very fast in comparison to the dissolution reaction thus, adsorption equilibrium may be assumed. The surface chelate formed is able to weaken the original Al-oxygen bonds on the surface of the crystal lattice. The detachment of the oxalato-aluminum species is the slow and rate-determining step the initial sites are completely regenerated subsequent to the detachment step provided that the concentrations of the reactants are kept constant, steady state conditions with regard to the oxide surface species are established (Table 5.1). If, furthermore, the system is far from dissolution equilibrium, the back reaction can be neglected, and constant dissolution rates occur. 

Alone formed by the reaction of lithium aluminum hydride and aluminum chloride in ether cleaves exclusively the carbon-oxygen bond in cyclic monothioketals derived from ketones and mercaptoethanol, and on refluxing in 100% excess for 2 hours produces -hydroxyethyl sulfides (yields 66-91%) on prolonged heating with the reagent these -hydroxyethyl sulfides are further reduced to the corresponding ethyl sulfides (thioethers) (yields 28-81%) [936]. 

The metalloporphyrin-initiated polymerizations are accelerated by the presence of steri-cally hindered Lewis acids [Inoue, 2000 Sugimoto and Inoue, 1999]. The Lewis acid coordinates with the oxygen of monomer to weaken the C— O bond and facilitate nucleophilic attack. The Lewis acid must be sterically hindered to prevent its reaction with the propagating center attached to the prophyrin structure. Thus, aluminm ortho-substituted phenolates such as methylaluminum bis(2,6-di-/-butyl-4-methylphenolate) accelerate the polymerization by factors of 102-103 or higher. Less sterically hindered Lewis acids, including the aluminum phenolates without ortho substituents, are much less effective. 

This problem has been partially overcome by elimination of the phosphorus-oxygen bonds, as, for example, in the poly(phosphinoisocyanates), which have the structure shown in 6.47.42 It is also possible to form poly(metal phosphinates) with repeat unit -M(0PR20)2- by allowing a metal alkoxide to react with a phosphinic acid.43 Typical metal atoms are aluminum, cobalt, chromium, nickel, titanium, and zinc.43 Polymeric phosphine oxides can be prepared by the reactions... 

Previous studies have shown that a trend exists in the behavior of some evaporated metals on polyimide surfaces x-ray and ultraviolet photoelectron (XPS, UPS) as well as high resolution electron energy loss (HREELS) measurements have indicated that while for some metals such as aluminum, titanium and chromium there is bond formation with the PMDA carbonyl oxygen of the polyimide (2, 10-13). other metals such as copper, palladium and gold undergo little reaction or interaction (10,12,14,15). It has, however, since been postulated that metals, in order to adhere well at all to a polymer under a wide variety of conditions, must form metal- polymer bonds (10). 

---