Miscellaneous Redox Reactions

Quantitative data for the reactions discussed here will be found in Table 3. The reaction between hexachloroiridate(iv) and pentacyanocobaltate(ii) has been investigated, the process involving two stages, the rapid first step yielding a dinuclear intermediate which disappears in the slower second reaction. Under the experimental conditions used ( 10 M reagent concentrations), the rate of formation of the intermediate was too fast for measurement in the flow apparatus, the second-order rate constant being estimated at 10 1 mol s . The metastable intermediate is considered to be the complex CUIrClCoCChOs formed by an inner-sphere reaction. 

The overall reaction products, hexachloroiridate(m) and hydroxopenta-cyanocobaltate(m), are found after the second stage where there is a Co—Cl bond fission  

At high concentrations of mercury(u), however, a second pathway must be invoked, in which the hydrido-complex may react directly with the Hg(CN)2, The same reaction products are given with Co(CN)5 , although here the reaction is slower, possibly owing to the requirement of the initial dismutation 

Disproportionation of ammine(pyridine)ruthenium(m) complexes has been observed in alkaline media. At pH 8 solutions of the complex (HjI sRu py +, which are almost colourless in more acidic conditions, show a marked colour which resembles that of the corresponding ruthenium(n) complexes, the effect 

The reduction reactions of trans-PthiCli (where L = PEts, piperidine, or SEta) and of /ra j-PtLBr4 with bis-(o-phenylene)-bis(dimethylarsine) [ = (diars)] -nickel(n) and -palladium(n) have been examined in methanol. In the presence of halide ions (Y = Cl or Br ) in solution, the nickel complex reacts, 

Quantitative rate data for reactions discussed in this section are given in Tables 3 and 4. The use of the ion [Ru(NH3)6] + as an outer-sphere reductant is much in evidence. The effect of sodium polystyrene sulphonate and sodium polyethylene on the rate of reduction of the series of complexes [Co(en)2(Cl)A] + (A = py, HjO, or NH3), [Co(en)2Cla]+, and [(NH3)6CoBrp+ has been investigated, for comparison with known effects in inner-sphere reactions. Though acceleration factors were found for both mechanisms, activation parameters reveal that for outer-sphere a lowering of Aff and for inner-sphere a more favourable AS are responsible. With [Ru(NH3)b] + in large excess, the consumption of horse heart ferricytochrome c obeys the rate law 

Gould has studied the [RuCNHa),] reduction of a series of cobalt(m) oxidants which offer no sites for inner-sphere attack and therefore also react by an outer-sphere mechanism with V +, Eu +, and Cr +. The second-order rate constants for reduction of a common oxidant decrease in the order knvi ky k rx kcr. Moreover, linear relationships found are  

In the search for systems capable of yielding first-order rate constants for intramolecular electron transfer, Taube appears to have had most success. Mixed dinuclear cobalt(iii)-ruthenium(ui) complexes have been prepared with pyridine-carboxylato-bridging ligands. Fast reduction by Eu + or [RuCNHa) generates a cobalt(iii)-ruthenium(ii) dinuclear complex, which then disappears by a first-order process, taken to be intramolecular electron-transfer. The greatest rate from these early studies is found for the nicotinate complex (14). Some success has been 

It now seems likely that a distinction between one- and two-equivalent oxidants can be made on the basis of the rate law for reaction with mercury(i) dimer. Both types of reaction are first-order in oxidant but in the case of two-equivalent oxidants an inverse [Hg ]-dependence is observed. Thus with [Ru(bipy)3] + the reaction 

Reaction with [Fe(phen)3] + is entirely analogous and so are many of the previously studied systems. Two-equivalent oxidants, e.g. BrOi and Tl , react according to the rate law 

Quantitative rate data for reactions discussed in this section are given in Table 3. Several systems involving the reductant [Ru(NH8)fl] +, which, unless oxidation is slow compared with the loss of NH3, is constrained to react via an outer-sphere mechanism. A test for mechanisms of this type has recently been described in a cross-section correlation which accommodates deviations of a from 0.5 in the Marcus expression, and in the case of the oxidation of 

Equilibrium and kinetic studies have been made on the reactions between Np and the complexes [Ru(NH3)g] + and [Ru(NH3)5(OHa)] +. No hydrogen-ion dependences have been observed and the reactions were carried out in trifluoromethanesulphonate media which as a counter ion excludes complex formation and also eliminates any side effects due to the Ru -ClOj reaction. Rate parameters for the forward reactions (X = NH3 or HgO), 

Studies were made with both lithium and sodium perchlorate as counter ions the rates were sensitive to the nature of the cation present, being lower in 

NaC104 than in LiC104, probably owing to medium effects. Such effects are also observed in the hydrogen-ion dependence, which may be described in the form 

The reduction of vanadium(v) by titanium(m) in acidic perchlorate (or chloride) media occurs in three steps, two of which are important in the presence of excess reductant. Solutions of titanium(m) were prepared in chloride media owing to the reduction of ClOr. The reaction 

Propan-2-ol is oxidized to acetone by two equivalents of Ag. The reaction is rapid and shows a first-order dependence on [Ag j, suggesting that direct participation of Ag in the reaction is unlikely. Disproportionation of Ag to form Ag and Agi i with direct oxidation by Ag would result in a second-order dependence on Ag. Stabilization of the tervalent form by a strong complex with alcohol can also be discounted since this would result in a zero-order dependence on alcohol, and not the first-order dependence observed. It is concluded that the reaction involves direct attack of Ag on propan-2-ol. Rate retardation by the addition of Ag was shown to be inconsistent with the formation of oxidatively inert Ag -ROH complexes and was explained by the existence of a back reaction in the rate-determining steps 

The formulation [Ag radical] can be considered as existing in a solvent cage. Oxidation then proceeds when the radical diffuses out of the cage to be further oxidized to acetone by a second mole of Ag . The rate data show that the oxidative reactivity of AgOH+ towards propan-2-ol is much less than that of Ag +. Comparison of activation parameters with those for propan-2-ol oxidations by other oxidants reveals no relation to the standard redox potential. 

In the corresponding reaction of 4,4 -biphenyldiol (10), which is also very rapid and was studied at 0 °C, a free-energy correlation between the rates of oxidation by Mn, Ce and Ag and the standard redox potentials was considered fortuitous in the light of the different mechanisms and pathways involved with different metal ions. Assuming a second-order rate law, the rate constant for the reaction with Ag  

In the formation of COa from the silver(ii) oxidation of formic acid, the experimental rate law at constant [H+] and excess substrate is 

To explain the dependence on H+], it was necessary to take into account the presence of the hydrolysed species AgOH+ and AgOH + in the mechanism  

---

Table 4 Rate constants and activation parameters for miscellaneous redox reactions for units see Table 1)...

Only transformations in the longest linear sequence (LLS) are considered. The term skeleton constructions refers to C-C and C-O bond formations (notwithstanding redox reactions) that directly introduce native structural features of the bryostatins without further modification. The term other functional group manipulations refers to steps that indirectly introduce native structural elements, the interconversion of functional groups (e.g., the introduction and removal of auxiliaries) and miscellaneous transformations that do not involve skeleton construction... 

Miscellaneous Transformations. Aromatic aldehydes and nitriles like acetonitrile or benzonitrile are converted by CIbSII to secondary amides, through a redox reaction (eq 3). When acrylonitrile is used instead, the product is an imino aldehyde (eq 4). 

The different applications have been classified by reaction type oxidation (sect. 2.1-2.3), hydrogenation (sect. 2.4), environmental (sect. 2.5) and miscellaneous (sect. 2.6). The environmental applications have been grouped together in view of the present relevance of this field. It includes total oxidation of organic compounds and CO, redox processes such as CO+NO reaction and NO/N2O decomposition. 

Miscellaneous Reactions of LR. Under particular conditions, certain carbonyl compounds and other substrates react with LR to form thiophosphonates or heterocycles, which fact throws some hght on the mechanism of thionation reactions with LR. Carbinols undergo nucleophilic substitution with LR to form the corresponding thiols. The redox properties of LR can be utilized to prepare dithiolactones from dialdehydes (eq 22), a-0X0 thioamides from nitro ketones (eq 23), or sulfides from sulfoxides. ... 

Miscellaneous kinetic studies of solvolysis in binary aqueous mixtures have included those of the [Co(NH3)5(dmso)] + cation in seventy-one such mixtures, of the /rans-[Co(dmgH)2Cl(N02)] anion and its methylglyoximate analogue in ethanol- and propan-2-ol-water, of [Cr(sal)3] and of ajffy5-tetra-(p-sulphonato-phenyl)porphineiron(m) in ethanol-water, of the 5,6-dimethylbenzimidazoIe derivative of methylcobalamin, of the acid-catalysed hydrolysis of (BHJ- in acetonitrile containing small amounts of water, and of the rate-determining aquation prior to redox of the [Mn(ox)2(OH2)a] anion in aqueous dimethylformamide. A kinetic study of the reaction of thallium(m) with dimethylformamide indicates caution in the use of this co-solvent in binary aqueous mixtures at elevated temperatures or in the presence of oxidants. ... 

---