Periodate oxidation kinetics

These oxidants have been used rarely. The kinetics of periodate oxidation of sulphoxides have been studied119,124. In an acid medium the reaction proceeds without catalysis but in alkali a catalyst such as an osmium(VIII) or ruthenium(III) salt is required124. Iodosylbenzene derivatives have also been used for the oxidation of sulphoxides to the sulphone level94,125 (equation 39). In order to use this reaction for the synthesis of sulphones, a ruthenium(III) complex should be used as a catalyst thus quantitative yields are obtained at room temperature in a few minutes. However, column chromatography is required to separate the sulphone from the other products of the reaction. 

Reaction (15) contributes to the chain propagation. The higher rates of this reaction correspond to lower inhibitory efficiencies and lower stoichiometric coefficients of inhibition. The equations describing the induction period, oxidation rate, and kinetics of oxygen consumption for this mechanism when ki5[02] [In] > v i are given here. 

Hence, the copper surface catalyzes the following reactions (a) decomposition of hydroperoxide to free radicals, (b) generation of free radicals by dioxygen, (c) reaction of hydroperoxide with amine, and (d) heterogeneous reaction of dioxygen with amine with free radical formation. All these reactions occur homolytically [13]. The products of amines oxidation additionally retard the oxidation of hydrocarbons after induction period. The kinetic characteristics of these reactions (T-6, T = 398 K, [13]) are presented below. 

Exhaustive studies on well-defined systems are rather scarce (4) nevertheless 3 systems thoroughly analyzed by independant research groups are of outstanding interest a) the quaternization of polyvinylpyridines by alkyl halogenides (20-25) b) the chlorination of polyethylene (13,26-28) c) the basic or acid hydrolysis of PMMA (29-31). On the other hand, neighbouring groups effects have been quantitatively taken into account for the kinetic analysis of periodate oxidation of amylose (32,33). 

The effect of pH on the periodate oxidation of seven anilines has been investigated. " The kinetics of periodate oxidation of aromatic amines have been studied. " - " Periodate oxidation of oxalic acid is catalysed by Mn(II). " The reaction of ethane-1,2-diol with periodate has been investigated under a variety of conditions and the results compared with those of earlier work and analogous studies on pinacol. " The 104 ion is the primary reactant, with H5IO6 as a secondary reactant the reverse is true for pinacol. The complex observed in previous work is shown not to be an intermediate, but rather to deactivate the reactants. 

Oxidation of Mn2+ in aqueous solution appears to occur in a stepwise fashion to Mn02, with MnOOH (8) and Mn304 (9) as possible intermediates. The reaction exhibits the induction period and kinetics characteristic of an au-tocatalytic process (10). Mn(II) is strongly sorbed to the surfaces of the newly formed, insoluble oxides, where its oxidation is greatly facilitated. 

Oxidation of arylmethyl ketoximes by phenyliodoso diacetate in glacial acetic acid was second order overall, first order each in substrate and oxidant.145 Iodine allowed the oxidative dimerization of glycine ester enolates with low to moderate diastereoselec-tivity that is consistent with kinetic control.146 Although malonic acid is not oxidized by iodate under acidic conditions, oxidation proceeds in the presence of catalytic ruthenium(III). A mechanism is put forward to account for the observed orders of reaction.147 The rate of periodate oxidation of m-toluidine in acetone-water increases with ionic strength.148... 

The ruthenate ion-catalysed oxidation of D-galactose and D-xylose by alkaline periodate in an alkaline solution showed a zero-order dependence on reducing sugar and a first-order dependence on ruthenate ion. The first-order dependence of the reaction on periodate and alkali at their low concentrations tends to zero order at higher concentrations. A mechanism consistent with the kinetics has been proposed.138 The kinetics of the periodate oxidation of p-bromoanilinc139 and 4-chloro-2-methylaniline140 have been determined and interpreted. 

In contrast, the periodate oxidation method is a relatively simple process and is unaffected by the presence of carbohydrates. Construction of a kinetic curve is not necessary in the periodate oxidation procedure, which requires only determination of the maximum amount of methanol formation for the calculation of phenolic hydroxyl content. Thus, for routine analysis, the periodate oxidation method may require only measurement of the amount of methanol liberated after 2 and 3 days reaction for isolated lignin and wood samples, respectively (Gierer et al. 1964, Yang and Goring 1980). 

In most of its reactions periodate is a two-electron oxidant, and it is reduced to iodate. Periodate oxidations are normally carried out in aqueous solution, but organic or mixed aqueous-organic solvents can be used (Qureshi and Sklarz ) and in section 1.8 the very limited amount of kinetic data available for mixed solvents is reviewed. 

The only compound containing an active methylene group whose periodate oxidation has been studied kinetically is 2-methyl-l,3-cyclohexanedione (Wolfrom and Bobbitt ). At 22.5 °C and pH 6.2 the kinetics are first-order with respect to each reactant. The same workers showed qualitatively that for the oxidation of 5,5-dimethyl-l,3-cyclohexanedione, the rate reaches a maximum between pH 5 and 6 (phosphate buffers were used). 

Periodate oxidations are much slower in non-aqueous solvents or in mixed aqueous-organic solvents. Very few kinetic studies have been made of the solvent effect. Taylor et al. found that the rate of oxidation of ethane-1,2-diol by periodic acid is reduced by a factor of approximately 12 by the addition of 38 % of ethanol to water. Guthrie studied the oxidation of tra 5-cyclohexane-l,2-diol in dimethylformamide/water mixtures, and found a sharp reduction in rate when the DMF content was increased beyond 20 %. 

Fig. 27.—Rate curves for the periodate oxidation of the Schardinger dextrins V, amylodextrin , 7 A, 0 0,a. The pseudo-time B has been placed on a logarithmic scale in order to facilitate kinetic analysis and to compress a rather wide range of real times ...

Magnetic particles coated with copolymer of acrylamide and acrylonitrile has been prepared. Those particles were used as a matrix for a covalent binding of peroxidase. The periodic-oxidized enzyme was bound to the matrix by immobihza-tion procedure at 4°C for 18 h. The immobihzed enzyme showed relative activity of 86%. The following results were obtained for pH and optimum temperature of the immobilized enzyme - 7.0°C and 30°C, respectively. The analysis of the kinetic parameters of the immobilized enzyme showed values of V - 0.0517 M x 10 s and - 2.3 x 10" M (Yotova et al. 2008). 

A peptide from pyruvate kinase labeled with oADP (55) and one from ferre-doxin-NADP reductase labeled with oNADP (75) have been isolated and characterized. These are exceptions. Despite the large number of papers describing the kinetics of affinity labeling by periodate-oxidized nucleotides, there are very few reports of the identification of particular amino acids labeled by these reagents within determined peptide sequences. For enzyme products other than a Schiff base reducible by NaBHU, the instability of the products in the proteolytic digests of modified enzymes under conditions of peptide purification has precluded isolation of labeled peptides in most cases. 

The model compound, frans-4-chloro-4-octene, was chosen because it possessed the —C1C=CH— group of polychloroprene, but without the repeating 1,5-diene structure of the polymer. The autoxidation was similar to that observed for polychloroprene, although no induction period was observed (cf. hexachlorobutadiene oxidation above). The evolution of HC1 was proportional to the square of the time, but the oxidation kinetics were approximated more closely by the equation... 

F. Sussich and A. Cesaro, The kinetics of periodate oxidation of carbohydrates A calorimetric approach, Carbohydr. Res., 329 (2000) 87-95. 

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