R. C. Kapoor

Halogen-facilitated preparation of S4(AsF6)2·xSO2(x⩽ 1) and S4(Sb2F11)2, and a convenient synthesis of Se4(AsF6)2 and Se4(Sb2F11)2

Sulfur reacted with an excess of AsF5 at room temperature in the presence of a trace amount of halogen (X2= Cl2, Br2 or I2) or AsCl4AsF6 in SO2 to give S4(AsF6)2·xSO2(x⩽ 1) quantitatively in a few minutes. A similar, but slower, reaction with SbF5 in SO2 or AsF3 at room temperature gave quantitative yields of S4(Sb2F11)2. The vibrational spectra of these salts with tentative assignments are reported. The corresponding preparations of Se4(AsF6)2 and Se4(Sb2F11)2 are also greatly facilitated by the presence of traces of halogen. Reactions of sulfur (or selenium) with SbF5 with and without traces of X2 in SO2 designed to give M4(SbF6)2(M = S or Se) gave products that contained M42+, an unidentified SbV fluoroanion and some SbIII-containing species. A comparative study was made on the effect of solvent, oxidising agent and facilitating reagent on the course of reaction. Possible reaction pathways for oxidation of sulfur (or selenium) by AsF5(or SbF5) with and without the addition of traces of X2 or AsCl4AsF6 have been proposed.

Kinetics and mechanisms of redox reactions in aqueous solution. Part 8. Osmium(VIII) catalysed oxidation of amino acids by alkaline hexacyanoferrate(III)

Amino acids, in the presence of OsVIII as a catalyst, are oxidised by alkaline hexacyanoferrate(III) to aldehydes. There is a zero - order dependence in [Fe(CN)63–], an order less than unity in [amino acid], and a first-order dependence in [OsVIII] and [OH–]. The observed zero - order rate constant was independent of [Fe(CN)64–]. The proposed mechanism envisages the formation of a transient [OsO4(OH)2]2––amino acid complex prior to its rate-limiting interaction with hydroxide ion. The respective values of the equilibrium and rate-limiting constants are reported. The values of the enthalpy and entropy of activation in each case are also estimated.

Kinetics and mechanisms of oxidation by metalions. Part XI(1). Kinetics of the osmium(VIII)-catalysed oxidation of glycols by alkaline hexacyanoferrate(III)

SummaryThe kinetics of the OsVIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN)63−] and first-order dependence in [OsO4]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH−] is a combination of two rate constants; one independent of and the other first-order in [OH−]. These observations are commensurate with a mechanism in which two complexes, [OsO4(H2O)G]− and [OsO4(OH)G]2−, are formed either from [OsO4(H2O)(OH)]− or [OsO4(OH)2]2− and the glycol GH, or by [OsO4(H2O)2] and [OsO4(H2O)(OH)]− and the glycolate ion, G−, which is in equilibrium with the glycol GH through the reaction between GH and OH−. Hence there is an ambiguity about the true path for the formation of the two OsVIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH− ion on the two species of OsVIII-complexes, indicates that the two complexes are structurally different because ΔS‡ changes from the negative (corresponding to k1β1) to positive (related to k2).

Kinetics and mechanism of redox reactions in aqueous solution. Part 3. Oxidation of diols by aquacerium(IV) species in perchlorate solution

Michaelis–Menten kinetics have been observed for the oxidation of diols and 3-methoxybutan-1-ol by aquacerium(IV) ions in acid perchlorate solution of 2 mol dm–3 ionic strength. The reaction has a first-order dependence on cerium(IV) concentration and the rate is accelerated by increasing acidity. An analysis of the equilibrium constants for complex formation between CeIV and the substrates, the rates of disproportionation of the intermediate complexes, and the entropy values associated with the latter suggests the formation of chelate complexes in the oxidation of propane-1,3-, butane-1,3-, and butane-1,4-diols. whereas in the oxidation of pentane-1,5- and hexane-1,6-diols and 3-methoxybutan-1-ol the substrate is believed to act as a unidentate ligand.

Kinetics and mechanism of redox reactions in aqueous solution. Part 1. Silver(I)-catalysed oxidation of cerium(III) by peroxodisulphate ion

The kinetics of the silver(I)-catalysed oxidation of CeIII by [S2O8]2– in 0.5 mol dm–3 sulphuric acid have confirmed a zero-order dependence on [CeIII] and a first-order dependence on [AgI]. However, the order with respect to [S2O82–] is less than one and the reaction is retarded by both hydrogen sulphate ions and sulphuric acid. The probable mechanism of the reaction is discussed.