Principal relationships of the heterogeneous catalytic oxidation of benzene and its derivatives

The results of investigations into the processes involved in the heterogeneous catalytic oxidation of benzene and its derivatives at the L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, are summarized. The mechanisms of the full and partial oxidation of benzene, toluene, and their halogen derivatives are discussed. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, Kiev. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 133–147, May–June, 1998.     

Experimental and modeling study of the oxidation of benzene

This paper describes an experimental and modeling study of the oxidation of benzene. The low‐temperature oxidation was studied in a continuous flow stirred tank reactor with carbon‐containing products analyzed by gas chromatography. The following experimental conditions were used: 923 K, 1 atm, fuel equivalence ratios from 1.9 to 3.6, concentrations of benzene from 4 to 4.5%, and residence times ranging from 1 to 10 s corresponding to benzene conversion yields from 6 to 45%. The ignition delays of benzene–oxygen–argon mixtures with fuel equivalence ratios from 1 to 3 were measured behind shock waves. Reflected shock waves permitted to obtain temperatures from 1230 to 1970 K and pressures from 6.5 to 9.5 atm. A detailed mechanism has been proposed and allows us to reproduce satisfactorily our experimental results, as well as some data of the literature obtained in other conditions, such as in a plug flow reactor or in a laminar premixed flame. The main reaction paths have been determined for the four series of measurements by sensitivity and flux analyses. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 503–524, 2003     

Chemical transformations of the photochemical 1,3-adducts of benzene and anisole to cyclobutenes

The photochemical 1,3-adduct of benzene to cis-3,4-dichlorocyclobutene has been transformed in four steps to 2,5-endo-10-oxotricyclo[4.3.1.0^2,5]deca-3,8-diene 1. The key reaction is the acid catalyzed addition of water to the photoadduct 2 which gives the 3,4-dichloroalcohol 3 corresponding to 1. Similarly the photochemical 1,3-adduct of benzene to cyclobutene has also been cleaved with acid. A more convenient synthesis of 1 is provided by the photochemical 1,3-addition of anisole to cis-3,4-dichlorocyclobutene and the treatment of the adduct with acid. The 3,4-dichloro derivative of 1 is thereby obtained directly. Probable mechanisms for these transformations are discussed.     

Mechanism of photochemical reduction of chromium(VI) by alcohols and its environmental aspects

The idea of photochemical abatement of the Cr(VI) pollution has been verified by investigating the photoreduction mediated by aliphatic alcohols under conditions mimicking the environmental ones. Effects of the alcohol nature, pH and presence of oxygen are analysed. The time-resolved spectra are used to follow the generation of the transient chromium Cr(V), Cr(IV) and Cr(II) species and the R₁R₂CHOH√⁺ radicals. A direct interaction between chromate(VI) and an electron donor is a precondition of the photoreduction via the photoinduced electron transfer (PET). Two pathways of the PET are identified: one-electron transfer for intermolecular and two-electron transfer for the intramolecular systems. In the case of the alcohol mediators the option is pH-controlled.     

Effect of photochemical oxidation on polypropylene phosphorescence

Phosphorescence from polyolefins was studied from the aspects of excitation and emission wavelength and lifetime. Effects of photochemical oxidation on polypropylene phosphorescence are discussed in contrast to the effects of thermal oxidation.     

Electrochemical oxidation of benzene to phenol

Gas-phase electrochemistry: The direct hydroxylation of benzene to phenol was investigated using an electrochemical cell. The production of phenol over a VO(x) anode was found to be significant at 50?°C. The resultant current efficiency for phenol production and selectivity toward phenol reached 76.5 and 94.7?%, respectively.     

A quantum-chemical investigation of deoxypeganine and its salts II. The photochemical oxidation of deoxypeganine hydrochloride

The stability of deoxypeganine hydrochloride under the action of light has been established. The kinetics of the oxidation of deoxypeganine hydrochloride in aqueous solution in the presence of deoxyvasicinone hydrochloride have been studied. The structures and electronic conformations of hypothetical models of the salt DOP HCl in the ground and excited states have been considered by the MO LCAO method in the AM1 approximation. The difference in the resistance of the molecules of the base deoxypeganine and its hydrochloride to photochemical oxidation is discussed on the basis of the results of experiments and calculations.     

The reactive state in the photochemical 1,3-addition of benzene and alkylbenzenes to cycloalkenes

Quantum yield measurements for the photochemical 1,3-addition of benzene and alkylbenzenes to cyclobutene and cyclopentene allow the reactive state to be narrowly defined.     

A quantum-chemical investigation of deoxypeganine and its salts II. The photochemical oxidation of deoxypeganine hydrochloride

The stability of deoxypeganine hydrochloride under the action of light has been established. The kinetics of the oxidation of deoxypeganine hydrochloride in aqueous solution in the presence of deoxyvasicinone hydrochloride have been studied. The structures and electronic conformations of hypothetical models of the salt DOP HCl in the ground and excited states have been considered by the MO LCAO method in the AM1 approximation. The difference in the resistance of the molecules of the base deoxypeganine and its hydrochloride to photochemical oxidation is discussed on the basis of the results of experiments and calculations.Abbreviations HPLC high-performance liquid chromatography - MO LCAO molecular orbitals as linear combinations of atomic orbitals - AM1 Austin Model 1 - DOP HCl deoxypeganine hydrochloride - DOV HCl deoxyvasicinone hydrochloride Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 729–733, September–October, 1993.     

Influence of oxygen pressure on the photochemical oxidation of phenol

The influence of the oxygen pressure on the photochemical oxidation of phenol is investigated. It is shown that raising the oxygen pressure from 0.1 to 0.7 MPa leads to an increase in the photochemical oxidation of phenol by a factor of approximately 3.7.     

Mutual effect of benzene and maleic anhydride in selective heterogeneous catalytic oxidation of benzene

It is shown that in the oxidation of benzene (B) by molecular oxygen over a vanadium-molybdenum oxide catalyst the introduction of maleic anhydride (MA) into the reaction mixture suppresses the formation of carbon oxides but does not alter the rate for formation of MA from B. It has been found by programmed thermal desorption that B and MA are adsorbed at different active sites on the catalyst.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 622–626, September–October, 1988.We thank Yu. I. Pyatnitskii for discussion of the paper.     

Pseudorotation and the environmental effects of the phosphorescence lifetime of benzene

The strong temperature dependence of the phosphorescent decay rate of benzene is attributed to pseudorotational motion of benzene which has the lowered D_2h symmetry in the triplet state. This model accounts for the unusual deuterium effect of the activation energy, the very large pre-exponential factor, the low onset temperature, and the solvent effects.     

Activation energies in catalytic oxidation of benzene

The existence of a linear correlation between the apparent activation energy of benzene disappearance and the primary selectivity was demonstrated for a series of vanadia based catalysts. Analysis of this correlation leads to the conclusion that the activation energies of reaction 1 as well as activation energies of reaction 2 in benzene oxidation scheme do not differ significantly over a series of these catalysts.

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