Rate parameter oxidation

A kinetic study of the electrophilic substitution of pyridine-N-oxides has also been carried out50b,c. Rate-acidity dependencies were unfortunately given in graphical form only and the rate parameters (determined mostly over a 30 °C range) are given in Table 4b. There is considerable confusion in Tables 3 and 5 of the original paper, where the rate coefficients are labelled as referring to the free base. In fact the rate coefficients for the first three substituted compounds in... 

RATE PARAMETERS FOR REACTION OF PYRIDINE-N-OXIDES WITH HN03-H2S04... 

Rate parameters for ligand replacement processes in octahedral complexes of metals in oxidation state three. J. O. Edwards, F. Monacelli and G. Ortaggi, Inorg. Chim. Acta, 1974,11,47-104 (368). 

RATE PARAMETERS FOR THE OXIDATION OF Fe(ll) BY VARIOUS EDTA AND HEDTA... 

RATE PARAMETERS FOR FIRST STAGE OF THE OXIDATION OF OLEFINS BY PERMANGANATE... 

ACIDITY-DEPENDENCES AND RATE PARAMETERS FOR THE CHROMIC ACID OXIDATION... 

The rate of oxidation is reduced by one half on addition of manganous ions and the following Arrhenius parameters were recorded... 

Section 3 deals with reactions in which at least one of the reactants is an inorganic compound. Many of the processes considered also involve organic compounds, but autocatalytic oxidations and flames, polymerisation and reactions of metals themselves and of certain unstable ionic species, e.g. the solvated electron, are discussed in later sections. Where appropriate, the effects of low and high energy radiation are considered, as are gas and condensed phase systems but not fully heterogeneous processes or solid reactions. Rate parameters of individual elementary steps, as well as of overall reactions, are given if available. 

The yields and rates of oxidation by DMDO under these in situ conditions depend on pH and other reaction parameters.90... 

This reaction is very exothermic (A// —180 to —200kJ mol-1) and, therefore, seems to be very probable from the thermochemical point of estimation. The pre-exponential factor is expected to be low due to the concentration of the energy on three bonds at the moment of TS formation (see Chapter 3). To demonstrate that this reaction is responsible for the oxidative destruction of polymers, PP and PE were oxidized in chlorobenzene with an initiator and analyzed for the rates of oxidation, destruction (viscosimetrically), and double bond formation (by the reaction with ozone) [131]. It was found that (i) polymer degradation and formation of double bonds occur concurrently with oxidation (ii) the rates of all three processes are proportional to v 1/2, (iii) independent of p02, and (iv) vs = vdbf in PE and vs = 1.6vdbf in PP (vdbf is the rate of double bond formation). Thus, the rates of destruction and formation of double bonds, as well as the kinetic parameters of these reactions, are close, which corroborates with the proposed mechanism of polymer destruction. Therefore, the rate of peroxyl macromolecules degradation obeys the kinetic equation ... 

In connection with practical situations where CO oxidation is important, we must also consider the perennial question of how to connect the low pressure results onto those at high pressure. Qualitatively this has been done for the CO oxidation reaction but it would still be worthwhile to attempt a numerical prediction of high pressure results based on low-pressure rate parameters. A very nice paper modeling steady-state CO oxidation data over a supported Pt catalyst at CO and O2 pressures of several torr has very recently appeared (.25). Extension of this work to other systems in warranted and, even though unresolved questions continue to exist, every indication is that the high and low pressure data can be reliably modeled with the same rate parameters if no adsorption - desorption equilibria are assumed. 

In reality, it is believed that the oxidation of carbonaceous surfaces occurs through adsorption of oxygen, either immediately releasing a carbon monoxide or carbon dioxide molecule or forming a stable surface oxygen complex that may later desorb as CO or C02. Various multi-step reaction schemes have been formulated to describe this process, but the experimental and theoretical information available to-date has been insufficient to specify any surface oxidation mechanism and associated set of rate parameters with any degree of confidence. As an example, Mitchell [50] has proposed the following surface reaction mechanism ... 

The difference in H2 selectivity between Pt and Rh can be explained by the relative instability of the OH species on Rh surfaces. For the H2-O2-H2O reaction system on both and Rh, the elementary reaction steps have been identified and reaction rate parameters have been determined using laser induced fluorescence (LIF) to monitor the formation of OH radicals during hydrogen oxidation and water decomposition at high surface temperatures. These results have been fit to a model based on the mechanism (22). From these LIF experiments, it has been demonstrated that the formation of OH by reaction 10b is much less favorable on Rh than on Pt. This explains why Rh catalysts give significantly higher H2 selectivities than Pt catalysts in our methane oxidation experiments. 

By combining rate parameters from these 0-H studies with rate parameters from the hterature for the various steps in CO oxidation over Pt and Rh catalysts, we have developed a model based on the surface reaction mechanism outlined in... 

While oxidation of S(IV) in solution in the presence of 02 has been known for many years, there has been considerable controversy concerning the rates, mechanisms, and effects of catalysts such as Fe3+ and Mn2+, particularly under atmospheric conditions. However, studies over the past decade carried out in a number of laboratories, particularly those of Hoffmann and coworkers (e.g., Hoffmann and Boyce, 1983 and references therein) Martin and co-workers (1994 and references therein), have identified the various parameters that determine the overall rate of oxidation. As we shall see, the mechanism and kinetics are so complex that past confusion is understandable. 

Table 10.5 provides performance data regarding the SCWO process. Typical destruction efficiencies (DEs) for a number of compounds are also summarized in Table 10.5, which indicates that the DE could be affected by various parameters such as temperature, pressure, reaction time, oxidant type, and feed concentration. Feed concentrations can slightly increase the DE in supercritical oxidation processes. For SCWO, the oxidation rates appear to be first order and zero order with respect to the reactant and oxygen concentration, respectively. Depending upon reaction conditions and reactants involved, the rate of oxidation varies considerably. Pressure is another factor that can affect the oxidation rate in supercritical water. At a given temperature, pressure variations directly affect the properties of water, and in turn change the reactant concentrations. Furthermore, the properties of water are strong functions of temperature and pressure near its critical point. 

The oxidation of benzoin with cerium(IV) in perchloric acid solution is proposed to involve an interaction between Ce4+(aq.) ions and the keto alcohol, resulting in the formation of free radicals. The final product is benzoic acid.66 The rate of oxidation of crotyl alcohol with cerium(IV) is independent of the concentration of Ce(IV). The reaction induced polymerization of acrylonitrile indicating the formation of free radicals. The kinetics and activation parameters for the reaction have been determined.67 For the Ir(III)-catalysed oxidation of methyl ketones68 and cyclic ketones69 with Ce(IV) perchlorate, successive formation of complex between the reductant and Ce(IV) and then with the catalyst has been proposed. Results showed that in acidic solutions, iridium(III) is a more efficient catalyst than osmium and ruthenium compounds. 

Rates of oxidation of para-substituted arylphosphines with singlet oxygen show good correlation with the Hammett a parameter (p = —1.53) and with the Tolman electronic parameter. The only products are the corresponding phosphine oxides. However, for ortho-substituted phosphines with electron-donating substituents, there are two products, namely a phosphinate formed by intramolecular insertion and phosphine oxide. Kinetic analyses demonstrated that both products are formed from the same intermediate, a phosphadioxirane. VT NMR experiments showed that perox-idic intermediates can only be detected for highly hindered and very electron-rich arylphosphines 243... 

The specificity of flavopapains III and V has been examined by measuring the kinetics of oxidation of a series of dihydronicotinamides, including the N-substituted methyl-, ethyl-, n-butyl-, n-pentyl-, n-hexyl-, benzyl- and j3-phenylethyl compounds. The variations made in the R substituent on the ring nitrogen of the dihydronicotinamides had less than a five-fold effect on kcat/Km. Also, the rate parameters measured indicated that flavopapains III and V were much less effective as catalysts for dihydronicotinamide oxidation than... 

Table I. Rate Parameters for the Oxidation of Dihydronicotinamides by Flavopapain IV6 and the Model Flavin 7-Acetyl-10-Methylisoalloxazine...

Table III. Product Ratios and Rate Parameters for the Oxidation of NADH and Deuterated NADH Derivatives by Flavopapain IV...

An analysis of the kinetics of CO oxidation by 02 over Rh catalysts based on a model which accounts for the individual elementary reaction steps has been presented by Oh et al. [24]. A significant feature of the model is that the rate expressions used to describe the elementary steps and the rate parameters associated with these steps are all drawn from surface science... 

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