L. V. Petrov

Assessment of the competitiveness of the radical and nonradical mechanisms in the acid-catalyzed oxidation of styrene epoxide

The oxidizability value of styrene epoxide as the ratio k2/√k6, where k2 and k6 are the propagation and termination rate constants of the epoxide oxidation chain, respectively, was calculated from experimental data on the oxidation of neat styrene epoxide with oxygen in the presence of the initiator dicumyl peroxide in a quartz reactor of a manometric unit. Alternative calculations of the oxidizability value with the use of two procedures and two experimental setups yielded close values of k2/√k6 = 0.333exp(−22.5 kJ mol−1/RT) and k2/√k6 = 0.18exp(−22.1 kJ mol−1/RT)(l/(mol s))1/2 (393–413 K), which characterize a quite high stability of styrene epoxide toward oxidation by peroxide radicals. With allowance for the new data, it was concluded that the radical mechanism is unfeasible under the conditions of the earlier-studied mild acid-catalyzed oxidation of styrene epoxide (333–348 K).

Effect of polar solvents on the conversion of styrene epoxide in the presence of p-toluenesulfonic acid

The addition of tert-butyl alcohol to a styrene epoxide and catalyst (p-toluenesulfonic acid) solution in acetonitrile accelerates the acid-catalyzed total conversion of epoxide and simultaneous oxygen absorption by this binary system (BS). The introduction of water into the alcohol solution of BS increases the oxidation rate to an even greater extent. Experiments with the indicator m-nitroaniline showed that the addition of alcohol and water decreased the deprotonating ability, i.e., the acidity of the solution. The attempt was made to rationalize the paradoxical situation, at which the decline in acidity is accompanied by enhancement of the acidcatalyzed reaction of the epoxide conversion and oxidation, in terms of the participation of the protonated alcohol in the intermediate complex with epoxide.

Mild oxidation of styrene epoxide in the presence of trace perchloric acid

Perchloric acid in a tert-butanol solution with 10 vol % chlorobenzene exhibits an almost three orders of magnitude higher activity in comparison with para-toluenesulfonic acid (TSA) as a catalyst for the parallel styrene epoxide (SE) heterolysis and homolysis processes. There is a substantial difference between the reactions mediated by these catalysts: rate curves for the overall consumption in the presence of perchloric acid (SE heterolysis) yield straight lines in the log [SE]-time coordinates, but the first-order rate constant drops with an increase in [SE]. However, the oxygen uptake rate increases with [SE]. In the case of TSA, neither overall consumption nor oxidation rate depended on [SE] at [SE] > [TSA]; i.e., the reaction was zeroorder in SE.

Inhibition of the oxidation of styrene epoxide by potassium iodide and bromide in an acidic solution

The inhibiting action of potassium iodide and bromide on the oxidation of the binary system of styrene epoxide + p-toluenesulfonic acid and on the hydroperoxide decomposition in the presence of the binary system was revealed. The inhibition mechanism is complex. During the course of the inhibition, the active form of the inhibitor is regenerated, which interacts, according to the kinetic data, with the transient species formed in the binary mixture.

Effect of hydrogenation on the oxidation resistance of decene oligomers

The kinetics of autoxidation and initiated oxidation of PAO-2, PAO-4, PAO-6, and PAO-10+ decene oligomer fractions at 140°C after a hydrogenation process was studied. Key reactions in the mechanism of oxidation were identified; the numerical values of the kinetic parameters were determined, and mathematical models, which quantitatively described the experimental data on the consumption of oxygen and the buildup of hydroperoxides during the course of the oxidation of the test samples, were obtained. The oxidation resistances of hydrogenated fractions were compared with each other. It was found that the kinetic parameters of the test samples were similar, and the oxidation of all of the hydrogenated oligomers occurred by approximately the same processes. Using the PAO-2 fraction at 120, 130, and 140°C as an example, the oxidizability of hydrogenated and unhydrogenated samples was compared. It was found that hydrogenation improved all of the kinetic characteristics and, consequently, increased the oxidation resistance of oligomers. However, the oligomers remained readily oxidizable substances, particularly, at elevated temperatures.

Trends in oxidation and buildup of conversion products of the hydroquinone–styrene epoxide–p-toluenesulfonic acid ternary system in a polar solution

Addition of 1,4-dihydroxybenzene (hydroquinone) to the styrene epoxide–para-toluenesulfonic acid binary system subjected to oxidation in a solution of 90 vol % tert-butanol with 10 vol % chlorobenzene increases the styrene epoxide consumption rate and the rate of oxygen uptake by the system and leads to buildup of benzaldehyde. The ratio of the O2 uptake rate to the overall rate of styrene epoxide consumption in the hydroquinone–styrene epoxide–para-toluenesulfonic acid ternary system is (VO2/VSE) ≈ 0.24 (343K), which is 3.5 times that for the epoxide–acid binary system.

Oxidation of the aniline–styrene epoxide- p -toluenesulfonic acid ternary system in polar solvents: Trends and mechanism

Investigation of the kinetics of oxygen absorption by the aniline–styrene epoxide-p-toluenesulfonic acid ternary system (TS) in an acetonitrile solution led to a simple equation for the oxidation rate: VTS = k[aniline]0 • [epoxide]0[acid]1 at [aniline], [epoxide] ≫ [acid], k = 0.77 × 10–3s–1, and 343 K. The data obtained indicated that a complex of the three starting reagents formed before oxidation. In a mixed solvent containing tert-butanol, the dependence of VTS on its composition was extremum. A scheme was suggested that explained the change in the dependence VTS = k′[aniline]–0.63[epoxide]0.86[acid]1 in the mixed solvent by the decomposition of the complex in the presence of alcohol.

The role of labile products of styrene epoxide conversion in its oxidation in polar acid medium

Phenylacetaldehyde (PAA) and benzyl alcohol (BAl) are formed in oxygen atmosphere from styrene epoxide in the presence of p- toluenesulfonic acid (TSA) in a solution of 90 vol % tert-butanol with 10 vol % chlorobenzene (BUC). The ratio of the propagation (k2) to the termination (k6) rate constants has been measured to be k2/√k6 = 8.6 × × 10−3 (L/(mol s))1/2 at 343 K by the method of initiated oxidation of PAA in a BUC solution. One of the products of the radical chain PAA oxidation is BA. This reaction leads to BAl accumulation during the conjugated oxidation of PAA with the epoxide in an acid alcohol medium. The contribution of BAl formed to the oxidation is almost unnoticeable.

Inhibition of mild oxidation of styrene epoxide by oxygen in acidic alcohol solution by halide ions

Alkyl-substituted ammonium and lithium chlorides inhibit oxygen consumption in the oxidation of styrene epoxide in the presence of p-toluenesulfonic acid in a tert-butanol-chlorobenzene (9: 1, v/v) solution at 343 K. The inhibitory effect of chlorides is the same for tetramethylammonium, benzyltriethylammonium, and lithium chlorides, thus suggesting the inhibiting action of the anion. The oxidation inhibition effect of ammonium fluoride is ∼2.5 times as strong as that of the chlorides. The main finding of the study is the simultaneous retardation of oxidation and acid-catalyzed heterolytic epoxide consumption by the chloride and iodide anions.

Oxidative transformations of p-chloro- and p-fluorostyrene epoxides in the presence of p-toluenesulfonic acid

Mild oxidation of two halogenated styrene epoxides, 2-(4-chlorophenyl)oxirane (CSE) and 2-(4-fluorophenyl)oxirane (FSE), was studied in the presence of p-toluenesulfonic acid (TSA). Hydrogen peroxide and p-chlorobenzaldehyde are the products of CSE oxidation. The kinetics of the overall CSE consumption and oxidation of CSE and FSE are identical to those revealed earlier for the oxidation of styrene epoxide (SE). The consumption and oxidation rates do not depend on the epoxide concentration (zero order) and are proportional to the TSA concentration. At 343 K, the oxidation rate of CSE and FSE are higher than that for SE by factors of 2 and 7, respectively. The introduction of the halogen atoms in the p-position on the phenyl ring accelerates the oxidation.