Mechanism of osmium(VIII) catalyzed oxidation of tellurium(IV) by alkaline ferricyanide ion

A kinetic and mechanistic study of the osmium(VIII)-catalysed oxidation of crotyl alcohol by hexacyanoferrate(III) in aqueous Alkaline medium

The kinetics and mechanism of the osmium(VIII)-catalysed oxidation of crotyl alcohol by hexacyanoferrate(III) in aqueous alkaline medium is studied. The role of the osmium(VIII) catalyst is delineated to account for the experimental observations. A plausible reaction mechanism is suggested. Activation parameters such as the energy and entropy of activation are evaluated by employing the Eyring equation and are found to be 36.833 kJ mol−1 and −141.518 J K−1 mol−1, respectively.

Kinetic and Mechanistic Aspects of Redox Reactions of Tellurium(Iv) and Tellurium(Vi)

Many kinetic and mechanistic studies are reported on the direct and transition metal ion catalysed oxidation of tellurium(IV) with oxidants like persulphate, periodate, chromium(VI), hexacyanoferrate(III), cerium(IV), manganese(III), cobalt(III) etc. Similar studies on the reduction of tellurium(VI) by different reductants are much fewer. An attempt has been made to discuss in brief up-to-date information available on the nature of tellurium(IV) and tellurium(VI) species as well as kinetic and mechanistic studies on the direct and catalysed oxidation and reduction reactions of tellurium(IV) and tellurium(VI) respectively. The majority of reactions concerned with the oxidation of tellurium(IV) to tellurium(VI) seems to prefer a complementary path to a non-complementary one, in accordance with Schaffer's principle of equivalent change.

Oxidation of Tyrosine by Hexacyanoferrate(III) in Aqueous Ethanoic Acid Medium–A Kinetic and Mechanistic Study

The kinetics of oxidation of tyrosine by Fe(CN)63-have been studied in 40% AcOH-H2O containing 4.0 mol dm-3HCl. The oxidation is made possible by varying the difference in redox potential by adding HCl and AcOH to the reaction mixture. The reaction is first order with respect to [Fe(CN)63-and fractional (0.72) order with respect to [tyrosine]. Increasing the acid concentration at constant chloride concentration accelerates the reaction. The order with respect to acid concentration is nearly two and H2Fe(CN)6-is regarded as the active oxidant. The initially formed product, Fe(CN)64-retards the reaction. A suitable mechanism is proposed and the reaction constants of the different steps involved have been evaluated. Activation parameters have also been calculated with respect to the slow step of the mechanism and discussed.

Glycogen, its chemistry and morphological appearance in the electron microscope.11. The complex formed in the selective contrast staining of glycogen

Selective contrast staining of glycogen in untreated ultrathin sections of aldehyde-fixed tissues, double-fixed with 1% osmium tetroxide containing 0.05 M K3Fe(CN)6 as reported previously (De Bruijn, 1973), may also be obtained by the addition of either K4Fe(CN)6,K3Co(CN)6,K2Ru(CN)6, or K4Os(CN)6. On the other hand, addition of K3Cr(CN)6, K2Ni(CN)4, K3Mn(CN)6, K3Rh(CN)6, K2Pd(CN)4, K2Pt(CN)4, or K3Ir(CN)6 produces no effect. Hexavalent osmium oxide compounds, such as K2OsO4 and OsO3-2 pyridine, react selectively with a native (or acquired) ligand in the aldehyde-fixed glycogen, but do not render it more electron dense than its immediate surroundings. The presence of these osmium oxides is detected and they are rendered more electron dense by an accumulation reaction by the application on ultrathin sections of phosphotungstic acid (PTA) or a mixture of K2OsO4 and K4Fe(CN)6. As selective contrast staining of glycogen is also obtained by double fixation of the aldehyde-fixed tissue with 0.05 M K2OsO4 solutions containing 0.05 M K4Fe(CN)6 or 0.05 M K4Os(CN)6, it is postulated that in such tissue, both the selective reaction of K2OsO4 with the ligand in the aldehyde-fixed glycogen, and the accumulation of heavy metal at the sites occupied by the K2OsO4, occur simultaneously. A proposal for the constitution of this heavy metal osmium/cyanide complex is formulated and arguments are presented that both compounds are formed in the selective contrast stained glycogen areas of such treated tissues. The relative contribution of the components to the final contrast and its complex character is demonstrated by staining ultrathin glutaraldehyde sections intermittently with 0.05 M solutions of K2OsO4 and K4Fe(CN)6; it is shown that after at least three intermittent reactions with both K2OsO4 and K4Fe(CN)6, the glycogen areas in such sections became contrast stained.