Alcohol oxidation complexes, equilibrium formation

A study of the relaxational transitions and related heat capacity anomalies for galactose and fructose has been described which employs calorimetric methods. The kinetics of solution oxidation of L-ascorbic acid have been studied using an isothermal microcalorimeter. Differential scanning calorimetry (DSC) has been used to measure solid state co-crystallization of sugar alcohols (xylitol, o-sorbitol and D-mannitol), and the thermal behaviour of anticoagulant heparins. Thermal measurements indicate a role for the structural transition from hydrated P-CD to dehydrated P-CD. Calorimetry was used to establish thermodynamic parameters for (1 1) complexation equilibrium of citric acid and P-CD in water. Several thermal techniques were used to study the decomposition of p-CD inclusion complexes of ferrocene and derivatives. DSC and derivative thermogravimetric measurements have been reported for crystalline cytidine and deoxycytidine. Heats of formation have been determined for a-D-glucose esters and compared with semiempirical quantum mechanical calculations. ... 

This two-electron oxidation of an alcohol occurs with a concomitant two-electron reduction of PtCli to PtCl4, although prolonged photolysis leads to complete reduction to platinum metal. The initial quantum yield for PtCli" disappearance is 4 times greater than the initial PtCl4 appearance quantum yield, which is consistent with the equilibrium formation of PtCls by the condisproportionation of PtCli and PtCli . The aldehyde and ketone likely arise from a ) -hydrogen transfer reaction from an intermediate platinum alkoxide complex/ ... 

In real systems (hydrocarbon-02-catalyst), various oxidation products, such as alcohols, aldehydes, ketones, bifunctional compounds, are formed in the course of oxidation. Many of them readily react with ion-oxidants in oxidative reactions. Therefore, radicals are generated via several routes in the developed oxidative process, and the ratio of rates of these processes changes with the development of the process [5], The products of hydrocarbon oxidation interact with the catalyst and change the ligand sphere around the transition metal ion. This phenomenon was studied for the decomposition of sec-decyl hydroperoxide to free radicals catalyzed by cupric stearate in the presence of alcohol, ketone, and carbon acid [70-74], The addition of all these compounds was found to lower the effective rate constant of catalytic hydroperoxide decomposition. The experimental data are in agreement with the following scheme of the parallel equilibrium reactions with the formation of Cu-hydroperoxide complexes with a lower activity. 

Chromium(III) catalyses the cerium(IV) oxidation of primary and secondary alcohols in a mixture of H2SO4 and HC104. Kinetic results have been interpreted in terms of the formation of chromium(IV) in a reversible equilibrium, which forms a complex with the alcohol. Internal oxidation-reduction occurs in a rate-determining step to give aldehyde or ketone and regenerate the catalyst in the +3 state. The oxidation of ethanol under similar conditions has also been studied. ... 

The first example reported in the literature is the cyclization of dihydrobilin to octadehydrocorrin [51-54]. The reaction is catalyzed by the presence of nickel or cobalt salts. As in the case of corrole and its metal complexes such ring closure reaction has been carried out in alcoholic solution, it is oxidative and base catalyzed. It has been demonstrated that the formation of the corrin ring is part of an equilibrium where the oxidative ring closure is coupled with a reductive ring opening reaction [55]. 

ABSTRACT. The electrochemical behaviour of tetraazamacrocyc-lic Ni(II) complexes containing a pendant amino group has been studied by cyclic voltammetry at glassy carbon electrodes in function of pH and kind of solvent. The internal pH-dependent equilibrium between the open and chelated form of the pendant arm, the influence of solvent on the heterogenous kinetics of Ni(III)/Ni(II) redox couple in these complexes, formation of the modified electrode in strongly alkaline solutions and its application to the electrocatalytic oxidation of simple alcohols have been studied and discussed. 

The catalysts applied to alkene epoxidation in fluorinated alcohol solvents can be subdivided into those which are metal/chalconide-based and those which are purely organic in nature (Scheme 4.5). The former comprise arsanes/arsane oxides [27,28], arsonic acids [29, 30], seleninic acids/diselenides ]31-35], and rhenium compounds such as Re207 and MTO (methylrhenium trioxide) ]36,37]. As shown in Scheme 4.5, their catalytic activity is ascribed to the intermediate formation of, for example, perseleninic/perarsonic adds or bisperoxorhenium complexes. In other words, their catalytic effect is due to the equilibrium transformation of hydrogen peroxide to kmetically more active peroxidic spedes. 

The mechanism of picolinic acid (PA)-catalysed oxidation of formic acid by chro-mium(VI) involves the formation of a Cr(VI)-PA chelate complex in a pre-equilibrium step followed by attack at the Cr(VI) centre by the substrate, leading to a ternary complex within which electron transfer occurs giving a Cr(IV)-PA complex and CO2. The Cr(IV)-PA complex reacts faster with the substrate, ultimately giving rise to a Cr(III)-PA complex. The reaction is catalysed by anionic surfactants and inhibited by cationic surfactants. The oxidation of alcohols by modified oxochromium(VI)-amine reagents has been reviewed. ... 

Many metals can be transformed into alkoxides by relatively simple procedmes of anodic oxidation in alcohol-based media. A thermostated electrochemical cell without subdivision of cathodic and anodic space is used as reaction vessel. The process is nm with direct current, using for regulation of voltage the same potentiostat equipment that is common for biochemical electrophoresis experiments. The reaction proceeds in conditions close to equilibrium (if 3 V) only for the late transition metals, for example, Cu, Co, and Ni [81], and involves complexation with the anions of electrolyte at the anode and formation of the alkoxide via metathesis at the cathode ... 

The formed complexes (Ci] resembled an ester-like species involving both alcohol and chromium (VI). This ester is unstable and is in equilibrium with the protonated substrate and chromic acid [28]. Convincing arguments for formation of that ester were documented elsewhere [6,13,17,26,124], this being a characteristic feature of common redox processes involving chromium (VI) oxidant. The ester-like complexes formed between chromic acid and polysaccharides may be in cyclic or non-cyclic forms depending on the nature of both the substrate and the formed intermediate species (Cr or Cr ) as well as on the nature of the complex formed between the oxidant and the reductant substrate (1 1 or 1 2 intermediate complex). 

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