Inorganic asymmetric oxidation

Various heterogeneous asymmetric oxidation reactions using inorganic supports are listed in Table 2.2. A few selected examples will be described herein on the basis of reachon type. 

Table 2.2 Examples of heterogeneous asymmetric oxidation using inorganic supports. 

A completely different type of inorganic membrane also has its origin in the nuclear industry the asymmetric alumina membranes obtained by the anodic oxidation of an aluminum sheet were first developed for uranium enrichment... 

The transition metal based catalytic species derived from hydrogen peroxide or alkyl hydroperoxides are currently regarded as the most active oxidants for the majority of inorganic and organic substrates " An understanding of the mechanism of these processes is therefore a crucial point in the chemistry of catalytic oxidations. This knowledge allows one to predict not only the nature of the products in a given process, but also the stereochemical outcome in asymmetric reactions. 

The catalytic cycle for the asymmetric dihydroxylation is shown in Figure 20. The reaction is carried out in a 1/1 t-butanol/water mixture to solubilize the potassium ferricyanide/potassium carbonate used as the oxidant. The solvent mixture, normally miscible, separates into two liquid phases upon addition of the inorganic reagents. 

Later on, Liang and coworkers successfully employed trichloroisocyanuric acid (TCCA) as a new type of stoichiometric oxidant for the asymmetric epoxidation of acyclic enones in the presence of 10 mol% of catalyst 4 (Scheme 5.6) [9]. The desired epoxy ketones were obtained in good yields (69-93%) with high enantioselectivities (73-93% ee) under nonaqueous solid-liquid conditions [9b]. In this reaction, TCCA reacts with an inorganic base (KOH) to form a hypochlorite salt, which is transferred to the organic phase by the phase-transfer catalyst and oxidizes... 

Pt(IV) than Pd(n) [49], An interesting system, with asymmetric inorganic membranes, was used for selective metal ion separation. The membrane phase was a self-assembled monolayer of alkyl thiols as a hydrophobic phase for a trialkyl phosphate and phosphine oxide-based metal ion carrier. This organic mixture was attached on alumina porous supports with thin layers of gold. The thin membrane layer gave high fluxes and high selectivity, while metal ions transport was carrier limited [50]. 

Ultraflltraiion membranes are commonly asymmetric (skinned) polymeric membranes prepared by the phase inversion process. Materials commercially made into membranes include cellulose nitrate, cellulose acetate, polysulfone. aramids, polyvinylidene fluoride, and nctylonitrile polymers and copolymers. Inorganic meni-braues of hydrous zirconium oxide deposited on a tubular carbon backing are also commercially available. 

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