Kinetics of the liquid-phase oxidation of 2-hydroxycyclohexanone

The kinetics of oxygen uptake in the azobisisobutyronitrile-initiated oxidation of 2-hydroxycy-clohexanone (RCH(OH)C(O)R) at 323 K has been investigated (chlorobenzene solvent, [RCH(OH)C(O)R] = 0.15-1.30 mol/L, initiation rate of w _i = 0.016–0.473 mol L^?1 s^?1). The effective oxidizability parameter k _{p, eff}(2k _t,eff)^?0.5 has been determined by solving the inverse kinetic problem using the entire data array obtained while varying [RCH(OH)C(O)R] and w _i. The rate constants of chain propagation and termination and the equilibrium constant of the addition of the hydroxyperoxyl radical to the ketoalcohol have been derived from the dependence of the oxidizability parameter on the substrate concentration. The rate constant of bimolecular chain initiation has been calculated to be k ₀ = 9.7 × 10^?7 L mol^?1 s^?1. The ratio of the rate constants of quadratic-law peroxyl radical recombination reactions without and with chain termination (k _eff′/k _t,eff′) increases with increasing [RCH(OH)C(O)R], passes through a maximum at a substrate concentration of 0.8 mol/L, and then falls off. It is demonstrated that this effect is due to the variation of the proportions of the hydroperoxyl and organic (1-hydroxy-2-oxocyclohexylperoxyl or 1,2-dihydroxy-1-cyclo-hexylperoxyl) radicals in the reaction medium.     

Crystallographic Parameters of Special Grain Boundaries in Multicrystalline Silicon

Crystallography Reports - The orientation of grains and the special boundaries formed by them in multicrystalline silicon has been studied by electron backscattered diffraction. It is found that...     

Purification of aqueous glyoxal from organic acids by ion exchange

A procedure for the purification of aqueous glyoxal (obtained by the partial oxidation of glycol) from carboxylic acids was described. Mono- and dibasic organic acids can be removed from solution without any substantial losses of glyoxal by using weakly basic EDE-10P and AN-31 anionites. A mechanism of the adsorption of carboxylic acids on weak resins was suggested based on the IR spectra recorded in a study of AN-31 anion-exchange resin. Using this method of purification also allowed the removal of the glyoxal condensation products from solution.     

Kinetics and mechanism of the liquid-phase oxidation of <Emphasis Type="Italic">n</Emphasis>-carboxylic acids

Short reaction chains participate in the oxidation of C₃-C₆, C₈, C₁₀, and C₁₂ n-carboxylic acids. The quadratic-law recombination of peroxy radicals occurs both without and with chain termination. The ratio of the rate constants of these reactions increases to k′/k _t = 4.5 on passing from propanoic acid to pentanoic acid, and then it decreases almost to zero for dodecanoic acid. The anomalous variation of the k′/k _t ratio is explained by the fact that the radicals resulting from carboxylic acid oxidation at the CH bonds nearest to the functional group make different contributions to the recombination process, depending on the carbon chain length. The cross recombination of secondary hydrocarbon peroxy radicals with the HO₂^· radicals resulting from the oxidation of carboxylic acids at the β-C-H bonds proceeds without chain termination.     

Reactivity of the C-H bonds of methyl hexanoate toward the <Emphasis Type="Italic">tert</Emphasis>-butylperoxy radical

The kinetics of oxygen uptake and the kinetics of accumulation of methyl hexanoate oxidation products in the presence of tert-butyl hydroperoxide have been investigated to determine the partial rate constants for the interaction of the tert-butylperoxy radical with C-H bonds of the ester at 373 K. The ester group deactivates the C-H bonds in the 2- and 3-positions and does not deactivate the same bonds in the 5-position, which are similar in reactivity to the methylenic C-H bonds of hydrocarbons. The C-H bonds of the methoxyl group of methyl hexanoate are substantially more reactive than the C-H bonds of the methyl group.     

Luminescence of aluminoborosilicate glasses doped with Gd3+ ions

The two-photon absorption that leads to the ultraviolet upconversion luminescence in the SiO₂-Al₂O₃-B₂O₃-Na₂O₃-Zr₂O: Cd³⁺ glass has been investigated. The inference has been made that no photon cascade emission takes place under excitation by monochromatic light corresponding to the maximum of the absorption band of the Cd³⁺ ion (204 nm). The mechanisms of concentration quenching and energy transfer between Cd³⁺ ions and optically active defects of the aluminoborosilicate glass have been discussed.     

Hydrogen peroxide formation in the oxidation of carbonyl-containing compounds at β-CH bonds

The concepts of the selective inhibition of reactions with the participation of HO ₂^· radicals by nitrobenzene in accordance with a cyclic mechanism were supported using cyclohexanol oxidation as an example. It was demonstrated that the nitroxyl radical generated from nitrobenzene selectively reacts with HO₂ ^· to form hydrogen peroxide and nitrobenzene. A decrease in the rates of oxidation of esters, carboxylic acids, and ketones with specially chosen structures in the presence of nitrobenzene, as well as the detection of H₂O₂ and corresponding ,-unsaturated compounds among the reaction products, indicated that the degradation of -peroxyl radicals of the above compounds occurred under conditions of the liquid-phase oxidation of organic substances that result in the formation of the HO₂^· radical and an unsaturated compound.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 814–820.Original Russian Text Copyright © 2004 by Nepomnyashchikh, Nosacheva, Perkel.     

Onset Temperatures and Kinetics of Quartz Glass Crystallization

Crystallography Reports - A complex analysis of the crystallization of quartz glass from quartzites of the Bural-Sardyk deposit (the Eastern Sayan) has been performed. A mineralogical and...     

Quartz concentrates from quartzites of the Eastern Sayan

Results from studying quartzites of the Bural–Sardyk deposit in the quartz province adjacent to Lake Baikal are presented. These quartzites are a potential source of quartz raw material. The most promising quartzites of the deposit are briefly described. The effect heat treatment has on the depth of chemical enrichment is determined. The prospects of using quartzites in the production of quartz concentrate are examined.     

Control of the Lyapunov exponents of dynamical systems in the plane with incomplete observation

Control linear systems in the plane are studied under the assumption of incomplete observation and incomplete control. In this situation ordinary static output controls may fail to stabilize the system. That is why special dynamic output feedback controls with finitely many states (hybrid feedback controls) are applied. Necessary and sufficient conditions are offered that guarantee exponential convergence/divergence of the solutions at an arbitrary rate. It is also shown that the general case can be reduced to two particular cases which are treated in detail.