Inorganic oxides reagents

Table 7. Preparation of thiophene 1,1-dioxides by oxidation with inorganic oxidizing reagents...

Potassium ferricyanide-mediated oxidation Potassium ferricyanide is a relatively mild inorganic oxidizing reagent that is used widely for the conversion of bis(thiol) to disulphides (5, 6, 8). Since K3Fe(CN)g is slightly light sensitive, reactions are best conducted in the dark. Oxidation side products are possible when Met or Trp residues are present in the substrate (89,90). 

Heterogeneous reactions facilitated by supported reagents on inorganic oxide surfaces have received attention in recent years, both in the laboratory as well as in industry. Although the first description of the surface-mediated chemical transformation dates back to 1924 [13], it was not until almost half a century later that the technique received extensive attention with the appearance of several reviews, books and account articles [14—22],... 

Rate constants for the reaction of cytochrome f with inorganic oxidants are independent of pH when it is between 6.5-8.0 [150]. At pH < 6.5 protonation does have an effect, and with for example [Co(phen)3] there is a decrease and [Fe(CN)g] an increase in rate constants. From the kinetics cytochrome f shows no association with positively charged [Co(phen)j], and no competitive inhibition is observed with [Pt(NH3)6]" or [(NH3)5CoNH2Co(NH3)5] " [150]. It is possible therefore to study the effect of these reagents on the reaction of cytochrome f(II) with PCu(II), which... 

In this unusual and new synthetic approach the surface of the inorganic oxide does not behave as a new medium for dispersion of reagents but as a particular kind of ligand that by binding, in various ways, surface organometallic molecular fragments or species controls both the kinetic and the selectivity of the reactions taking place on the surface. 

Epoxides have been prepared on occasion by the action of certain inorganic oxidizing agents on suitable olefins. A notable example is ohromie oxide n anhydrous modia. Knowledge concerning the exart mode of action of such reagents is still incomplete, and for the purpose of epoxide synthesis they are of limited utility. For this reason only a brief discussion will be presented here. 

Thus, in the fine chemicals industry, reduction of ketones and aldehydes relies mainly on the use of complex metal hydrides that require time-consuming workup of reaction mixtures and produce significant amounts of inorganic and organic wastes. Similarly, the oxidation of alcohols into carbonyls is traditionally performed with stoichiometric inorganic oxidants, notably Cr(VI) reagents or a catalyst in combination with a stoichiometric oxidant [1]. 

The oxidation of primary and secondary alcohols into the corresponding carbonyl compounds plays a central role in organic synthesis [1, 139, 140]. Traditional methods for performing such transformations generally involve the use of stoichiometric quantities of inorganic oxidants, notably chromium(VI) reagents [141]. However, from both an economic and environmental viewpoint, atom efficient, catalytic methods that employ clean oxidants such as 02 and H202 are more desirable. 

To overcome the problems of toxicity and work-up associated with many inorganic oxidants, it would be advantageous to develop a catalytic supported oxidant. Towards this aim, chromium(III)-impregnated Nafion 511 (NAFK) has been used as a catalytic oxidant in the presence of t-butyl hydix)peroxide. This reagent gives good yields of ketones (80-100%), but unfortunately oxidation of primary alcohols leads to the formation of complex mixtures. 

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