Oxidation state during reaction

Among the most active transition metals are Mo and V, and both are effective in their highest oxidation state during reaction. Linden and Farona have foimd that Mo(V) is inactive for the epoxidation reaction and that V(IV) is converted to V (V) when contacted with a hydroperoxide [467]. The metals are added as compounds soluble in the reaction mixture, for example, Mo(CO)6, MoO2(acac), and VO(acac)2 (acac = monoanion of acetylacetone). Sheldon and Van Doom [266] have found that irrespective of the starting material, all molybdenum catalysts give rise to a common compound, a 1,2-diol complex (Fig. 1.11b). This is formed... 

A (a) This is a metathesis or double displacement reaction. Elements do not change oxidation states during this reaction. It is not an oxidation-reduction reaction. 

The oxidation states of palladium on 7-alumina during methane combustion were investigated by Demoulin et al. (2003), who observed that, regardless of its initial state, palladium reached the same (equilibrium) state during reaction. Palladium was found to be partly oxidized during methane combustion. 

Zinc does not undergo a change in oxidation state during enzymatic catalysis even though it participates in oxidoreduction reactions, e.g., as a component of alcohol dehydrogenase. The zinc cation has a stable. 

The role of copper in the oxidative half-reaction has been debated for some years, since the Cu ion in CAO is redox active. However, studies involving isotope effect measurements of CAO catalysis,of the inhibition of CAO by CO, and of substitution of the copper content of CAO with other metal ions, " have all implied that this site remains in its -f2 oxidation state during normal turnover. That would mean that O2 reacts with TOPANH2 directly, without being activated by precoordination to Cu(I). 

Activation of the Phillips catalyst directly by ethylene monomer was further investigated by XPS and TPD-MS methods in order to shed some light on the reaction mechanisms during the induction period. Deconvolution of the XPS spectra for industrial Phillips Cr/silica catalysts treated in ethylene atmosphere at RT for 2 h revealed that surface chromium species presented in three oxidatimi states surface chromate Cr(Vl)0 c,surf species surface-stabilized trivalent Cr(III) species and surface-stabilized Cr(II) species. Compared to the original catalyst before ethylene treatment, about one-third of chromate Cr(VIX) c,surf species (i.e., ca. 22.6% of the whole surface Cr) was reduced to Cr species in lower oxidation states during the ethylene treatment, even under ambient conditions [67]. 

Secondary metabolites frequently change their oxidation state during the biosynthesis or degradation of the molecule. The processes may be classified according to the type of enzyme involved and their mechanism of action such as hydrogenation and dehydrogenation reactions. 

At current densities which are higher than the limiting diffusion current of process (11), hafiiium dissolves also in the form of HfCU complexes [8]. We have pointed out repeatedly that the formation of complexes of different oxidation states during anodic dissolution is an undesirable effect in the melts of a heteroligand composition, because a disproportionation reaction will occur in the bulk and at the melt surface on account of the convection of fluoride ions liberated during cathodic discharge [1,9] ... 

The most commonly employed and convenient methods for studying nonlinear chemical dynamics employ potentiometric techniques. Electrochemical methods offer speed, low cost and, in many cases, excellent selectivity and sensitivity. A platinum electrode and a reference electrode are all that is required for any system with a species that changes its oxidation state during the reaction. The potential E is given by the Nemst equation ... 

A reducing agent is a substance that has the potentiai to cause another substance to be reduced. Reducing agents lose electrons they attain a more positive oxidation state during an oxidation-reduction reaction. Therefore, the reducing agent is the oxidized substance. 

Oxides of transition metals, mainly Cr, Mn, Co, Ni, Fe, Cu, and V are employed in the oxidation of organic compounds. Deep oxidation reactions over these metal oxides are considered to be catalyzed by lattice oxygen. A common feature of these metal oxides is the presence of multiple oxidation states. During catalysis, the metal may be reduced by the hydrocarbon and reoxidized by oxygen. It may cycle between two or more oxidation states thus operating in a redox cycle (Mars-van Krevelen mechanism) [12]. However, the actual mechanism of a working catalyst may involve many steps in a number of consecutive or parallel reactions. Because of its low volatility and low toxicity, MnOjc has received the attention of many researchers. 

---