Determination of Citrate Ions by Potentiometric Titration with a Copper-Selective Electrode in Monitoring the Production of Citric Acid

A simple and rapid procedure was developed for the potentiometric titration of citrate ions in fermented solutions from citric acid production with the use of a copper-selective electrode.     

Composition and Stability of Peroxide Products of Liquid-Phase Cyclohexanol Oxidation

The kinetics of accumulation of peroxide compounds during noncatalytic cyclohexanol oxidation at 130°C is studied. The oxidation of cyclohexanol at the CH bond in the 1-position yields hydrogen peroxide and 1-hydroxycyclohexyl hydroperoxide along with peroxides resulting from the oxidation of the CH bonds of the alcohol in the 2-, 3-, and 4-positions, namely, cis- and trans-2-, -3- and -4-hydroxycyclohexyl hydroperoxides. Product accumulation curves and the variation of the proportions of cis- and trans-2-, -3-, and -4-hydroxycyclohexyl hydroperoxides as a function of cyclohexanol conversion indicate that these hydroperoxides have different stabilities during oxidation. The highest stability is inherent in cis-2-, trans-2-, and cis-3-hydroxycyclohexyl hydroperoxides, while cis-4-, trans-4-, and trans-3-hydroxycyclohexyl hydroperoxides are characterized by the lowest stability. This fact is explained by the stabilization of the first three isomers by an intramolecular hydrogen bond, which prevents their decomposition involving substrate molecules.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 366–369.Original Russian Text Copyright © 2005 by Puchkov, Buneeva, Perkel’.Based on a report at the XI International Conference on the Chemistry of Organic and Organoelement Peroxides (Moscow, June 24–26, 2003)     

Pathways of Liquid-Phase Oxidation of Cyclohexanol

The kinetics of product accumulation in uncatalyzed oxidation of cyclohexanol at 403 K was studied. Along with the compounds originating from oxidation of cyclohexanol at position 1 (cyclohexanone, hydrogen peroxide, 1-hydroxycyclohexyl hydroperoxide), products formed by oxidation of C-H bonds at positions 2-4 were detected: 2-, 3-, and 4-hydroxycyclohexyl hydroperoxides (cis and trans isomers), 1,2-, 1,3-, and 1,4-dihydroxycyclohexanes (cis and trans isomers), 2- and 4-hydroxycyclohexanones, and 2-cyclohexenone.     

The Reactivity of C–H Bonds in the Cyclohexyloxy Moiety of Cyclohexyl Acetate toward the tert-Butylperoxy Radical

The effect of the functional group on the partial rate constants of the reactions of the tert-butylperoxy radical with CH bonds in the cyclohexyloxy moiety of cyclohexyl acetate at 333 K was studied by the Howard–Ingold method. The ester group activates the CH bond at the 1-position and deactivates the CH bonds at the 3-position and, especially, the 2-position. The reactivity of CH bonds at the 4-position is close to the reactivity of CH bonds in cyclohexane.     

Reactivity of Cyclohexanol CH Bonds toward the tert-Butylperoxy Radical

The effect of the hydroxy group on the partial rate constants of the reactions of the tert-butylperoxy radical with CH bonds in cyclohexanol at 333 K was studied by the Howard–Ingold method. The overall reaction rate constant increased with decreasing alcohol concentration in chlorobenzene because of complex effects of hydrogen bonds at the steps of chain growth and termination. The hydroxy group activates the -CH bond and deactivates the - and -CH bonds. The reactivity of -CH bonds is close to the reactivity of CH bonds in cyclohexane.