Benzoylperoxy Radical Research Articles

Synthesis of Metal Xanthene‐Bridged Bis‐corroles and their Catalytic Activity in Aerobic Baeyer‐Villiger Oxidation Reaction

AbstractThe metal (M=Co, Cu, Mn, Sn, Fe) xanthene‐bridged bis‐corroles (M2XBC) were synthesized and used for catalyzing aerobic Baeyer‐Villiger (B‐V) oxidation of cyclic ketones to corresponding lactones. It turns out iron (IV) bis‐corrole complex (Fe2XBC) exhibited excellent activity and selectivity towards the B‐V oxidation of various cyclic ketones at very low catalyst loading. The yield of ϵ‐caprolactone could reach 98% with only 0.005 mol% catalyst. The turnover number (TON) of the Fe2XBC catalyst could even be up to 17400 in a gram‐scale oxidation of cyclohexanone, showing the promising for industrial usage. Moreover, the existences of benzoyl radical and benzoylperoxy radical in the reaction were proved by ESI‐HRMS spectra and electron paramagnetic resonance (EPR) spectra. A plausible radical mechanism for the metal bis‐corrole catalyzed aerobic B‐V oxidation of cyclohexanone in the presence benzaldehyde additive was proposed.

Investigation of the formation of benzoyl peroxide, benzoic anhydride, and other potential aerosol products from gas–phase reactions of benzoylperoxy radicals

The secondary organic aerosol (SOA) products of the reaction of benzaldehyde with Cl atoms and with OH radicals in air in the absence of NOx were investigated in an environmental chamber in order to better understand the possible role of organic peroxy radical self-reactions in SOA formation. SOA products and authentic standards were analyzed using mass spectrometry and liquid chromatography, and results show that the yields of benzoyl peroxide (C6H5C(O)OO(O)CC6H5) and benzoic anhydride (C6H5C(O)O(O)CC6H5), two potential products from the gas-phase self-reaction of benzoylperoxy radicals (C6H5C(O)OO·), were less than 0.1%. This is in contrast to results of recent studies that have shown that the gas-phase self-reactions of β-nitrooxyperoxy radicals formed from reactions of isoprene with NO3 radicals form dialkyl peroxides that contribute significantly to gas-phase and SOA products. Such reactions have also been proposed to explain the gas-phase formation of extremely low volatility dimers from autooxidation of terpenes. The results obtained here indicate that, at least for benzoylperoxy radicals, the self-reactions form only benzoyloxy radicals. Analyses of SOA composition and volatility were inconclusive, but it appears that the SOA may consist primarily of oligomers formed through heterogeneous/multiphase reactions possibly involving some combination of phenol, benzaldehyde, benzoic acid, and peroxybenzoic acid.

The benzaldehyde oxidation paradox explained by the interception of peroxy radical by benzyl alcohol

Benzaldehyde readily undergoes autoxidation to form benzoic acid on exposure to air at room temperature. Yet it can be formed in high yield from, for example, benzyl alcohol by oxidation using a variety of procedures and catalysts. Here we report the evidence to resolve this apparent paradox. It is confirmed that benzyl alcohol (and a number of other alcohols), even at low concentrations in benzaldehyde, inhibits the autoxidation. Furthermore we report on the structural features required for inhibition. Electron paramagnetic resonance spin trapping experiments demonstrate that benzyl alcohol intercepts, by hydrogen atom transfer, the benzoylperoxy radicals that play a key role in benzaldehyde autoxidation. A similar inhibition effect has also been observed for the aliphatic octanal/1-octanol system.

Infrared absorption of gaseous benzoylperoxy radical C6H5C(O)OO recorded with a step-scan Fourier-transform spectrometer

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of benzoyl radical, C(6)H(5)CO, with O(2). C(6)H(5)CO was produced either from photolysis of acetophenone, C(6)H(5)C(O)CH(3), at 248 nm, or from photolysis of a mixture of benzaldehyde, C(6)H(5)CHO, and Cl(2) at 355 nm. Two intense bands near 1830 and 1226 cm(-1) are assigned to the C=O stretching (ν(6)) and the C-C stretching mixed with C-H deformation (ν(13)) modes, and two weaker bands near 1187 and 1108 cm(-1) are assigned to the ν(14) (C-H deformation) and ν(16) (O-O stretching /C-H deformation) modes of C(6)H(5)C(O)OO, the benzoylperoxy radical. These observed vibrational wave numbers and relative infrared intensities agree with those reported for syn-C(6)H(5)C(O)OO isolated in solid Ar and values predicted for syn-C(6)H(5)C(O)OO with the B3LYP/cc-pVTZ method. The simulated rotational contours of the two intense bands based on rotational parameters predicted with the B3LYP∕cc-pVTZ method fit satisfactorily with experimental results.

Thermochemistry and Reaction Paths in the Oxidation Reaction of Benzoyl Radical: C6H5C•(═O)

Alkyl substituted aromatics are present in fuels and in the environment because they are major intermediates in the oxidation or combustion of gasoline, jet, and other engine fuels. The major reaction pathways for oxidation of this class of molecules is through loss of a benzyl hydrogen atom on the alkyl group via abstraction reactions. One of the major intermediates in the combustion and atmospheric oxidation of the benzyl radicals is benzaldehyde, which rapidly loses the weakly bound aldehydic hydrogen to form a resonance stabilized benzoyl radical (C6H5C(•)═O). A detailed study of the thermochemistry of intermediates and the oxidation reaction paths of the benzoyl radical with dioxygen is presented in this study. Structures and enthalpies of formation for important stable species, intermediate radicals, and transition state structures resulting from the benzoyl radical +O2 association reaction are reported along with reaction paths and barriers. Enthalpies, ΔfH298(0), are calculated using ab initio (G3MP2B3) and density functional (DFT at B3LYP/6-311G(d,p)) calculations, group additivity (GA), and literature data. Bond energies on the benzoyl and benzoyl-peroxy systems are also reported and compared to hydrocarbon systems. The reaction of benzoyl with O2 has a number of low energy reaction channels that are not currently considered in either atmospheric chemistry or combustion models. The reaction paths include exothermic, chain branching reactions to a number of unsaturated oxygenated hydrocarbon intermediates along with formation of CO2. The initial reaction of the C6H5C(•)═O radical with O2 forms a chemically activated benzoyl peroxy radical with 37 kcal mol(-1) internal energy; this is significantly more energy than the 21 kcal mol(-1) involved in the benzyl or allyl + O2 systems. This deeper well results in a number of chemical activation reaction paths, leading to highly exothermic reactions to phenoxy radical + CO2 products.

Study of a Benzoylperoxy Radical in the Gas Phase: Ultraviolet Spectrum and C6H5C(O)O2+ HO2Reaction between 295 and 357 K

This work reports the ultraviolet absorption spectrum and the kinetic determinations of the reactions 2C(6)H(5)C(O)O(2) → products (I) and C(6)H(5)C(O)O(2) + HO(2) → C(6)H(5)C(O)O(2)H + O(2) (IIa), → C(6)H(5)C(O)OH + O(3) (IIb), → C(6)H(5)C(O)O + OH + O(2) (IIc). Experiments were performed using a laser photolysis technique coupled with UV-visible absorption detection over the pressure range of 80-120 Torr and the temperature range of 293-357 K. The UV spectrum was determined relative to the known cross section of the ethylperoxy radical C(2)H(5)O(2) at 250 nm. Kinetic data were obtained by simulating the temporal behavior of the UV absorption at 245-260 nm. At room temperature, the rate constant value of reaction I (cm(3)·molecule(-1)·s(-1)) was found to be k(I) = (1.5 ± 0.6) × 10(-11). The Arrhenius expression for reaction II is (cm(3)·molecule(-1)·s(-1)) k(II)(T) = (1.10 ± 0.20) × 10(-11) exp(364 ± 200/T). The branching ratios β(O3) and β(OH), respectively, of reactions IIb and IIc are evaluated at different temperatures; β(O3) increases from 0.15 ± 0.05 at room temperature to 0.40 ± 0.05 at 357 K, whereas β(OH) remains constant at 0.20 ± 0.05. To confirm the mechanism of reaction II, a theoretical study was performed at the B3LYP/6-311++G(2d,pd) level of theory followed by CBS-QB3 energy calculations.

Matrix Isolation and IR Characterization of the Benzoyl and Benzoylperoxy Radicals

AbstractThe benzoyl radical 1 was synthesized in argon matrices by the thermal reaction of the phenyl radical 2 with CO. The IR spectrum with the C=O str. vibration at 1824.4 cm–1 is in good agreement with DFT calculations. The formation of 1 is reversible and UV irradiation results in the cleavage back to 2 and CO. The benzoyl radical 1 can react with molecular oxygen in the matrix to produce the benzoylperoxy radical 3. Radical 3 was also characterized by IR spectroscopy in combination with DFT calculations.

Photochemistry of 9‐fluorenone oxime phenylglyoxylate: a combined TRIR, TREPR and ab initio study

AbstractThe photochemistry of 9‐fluorenone oxime phenylglyoxylate (1) in tetrachloromethane was investigated by a variety of time‐resolved methods [STEP‐SCAN TRIR and time‐resolved EPR (TREPR)]. Photolysis of 1 yields the benzoyl radical, carbon dioxide and the fluorene‐9‐iminyl radical on pulsed irradiation (λ = 355 nm). All radicals have a lifetime in the range of microseconds and can be detected within the rise time of our time‐resolved equipment before undergoing recombination or reactions with the solvent. The benzoyl radical shows a strong absorption ($(\tilde \nu$C=O = 1824 cm−) in the IR spectrum. Upon purging the solution with oxygen, the benzoyl radical is quenched to yield the benzoylperoxy radical ($(\tilde \nu$C=O = 1814 cm−), which has a lifetime that is several microseconds longer than that of the benzoyl radical. Owing to the lack of a good IR chromophore, the fluorene‐9‐iminyl radical is not detected by IR spectroscopy. It can, however, be detected by TREPR spectroscopy, which allows the detection of a 1 : 1 : 1 triplet of the fluorene‐9‐iminyl radical at 3456 G and a 1 : 2 : 1 triplet of the benzoyl radical at 3460 G. Copyright © 2004 John Wiley & Sons, Ltd.

Alpha-hydroxy ketones and sunlight, a novel effluent treatment?

There is a need for cheap and simple methods to destroy recalcitrant pollutants such as dyes in waste water. It is shown that the radicals produced from the UV A and B photolysis of alpha-hydroxy ketones are capable of completely bleaching a wide range of azo dyes (Orange II, Amaranth, Evans Blue, Direct Green 26 and Direct Red 80). It is found that complete bleaching occurs when the ratio of [ketone]/[azo groups] is greater than 2.6–7.6 dependent on dye structure and occurs over a wide pH range (2–11 investigated). Sunlight may be used as a light source and bleaching occurs in minutes. Mechanistic investigation shows that in the presence of air the bleach reaction is predominately a 1-electron oxidation induced by the benzoyl peroxy radical. From reaction with phenols of known electropotential, the reduction potential of the benzoyl peroxy radical is estimated as ∼1.9V v NHE. It is also shown that the benzoyl peroxy radical can undergo oxygen atom transfer reactions. In the absence of air a 1-electron reduction by the alpha-hydroxy radical [E(acetone, H+/2-hydroxy-2-propyl) = −1.4V v NHE] is the main reaction. Thus the system may be switched from oxidative to reductive by removal of oxygen. Initial products are given for both oxidative and reductive routes. First cost estimates look attractive.

Studies on reactivity of benzoyl and benzoylperoxy radicals produced by laser flash photolysis of dibenzoyldiazene in aerated solutions

Photolysis of dibenzoyldiazene gives benzoyl radicals. In aerated solutions, the benzoyl radicals react with oxygen to yield benzoylperoxy radicals. Spin trapping studies indicate that 5,5′dimethyl-1-pyrroline N-oxide reacts with the benzoylperoxy radicals to produce the adduct which exhibits ESR parameters, AN = 13.8 G and AHβ = 10.1 G. Laser photolysis studies reveal that the rate constants for the reaction between the benzoyl radical and oxygen are ca. 4 × 109 M-1 s-1 in toluene, acetone, and ethyl acetate. The benzoylperoxy radicals undergo one-electron oxidation of tetramethyl-p-phenylenediamine, TMPD, to give an ion pair. The ion pair has an absorption spectrum similar to that of the TMPD cation radical. The formation of the ion pair is detected by monitoring the absorbance change at 600 nm after laser pulsing. From the kinetic studies for the formation of the ion pair in the presence of olefins, the bimolecular rate constants for reactions between several olefins and the benzoylperoxy radical are determined. The electrophilic addition of the benzoylperoxy radicals to olefins is discussed in comparison with the addition reactions of thiyl radicals to olefins. The detection and determination of the dipole moments of both the benzoylperoxy radicals and the ion pair are carried out with the use of the time-resolved microwave dielectric absorption technique. The distance between the positive and negative ions in the ion pair is estimated as 0.20 nm.

Radiation-induced reactions of benzoyl chloride and acrylates in solution. A pulse radiolysis study

Using electron pulse radiolysis with optical detection, the radiation-induced reactions of benzoyl chloride and acrylates were studied in tetrahydrofuran and acetonitrile solution at room temperature. In both solvents electron transfer leads to the formation of transient radical anions of acrylates (k≈2–3×1010 dm3 mol−1 s−1) and of benzoyl chloride (k≈3×1010 dm3 mol−1 s−1). The latter dissociates into chloride ion and the benzoyl radical (k=3×106 s−1), whereas the acrylate anion transforms by protonation into a ketyl-type radical. In mixed solutions a fast electron transfer from acrylate anions to benzoyl chloride is found (k≈1×1010 dm3 mol−1 s−1). The benzoyl chloride anion reacts with the monomer (k=2.8×109 dm3 mol−1 s−1) with simultaneous release of Cl−, forming species which may initiate polymerization. In the presence of oxygen the formation of benzoylperoxy radicals (k=1.6×109 dm3 mol−1 s−1), showing a strong absorption band in the near-UV (λmax=400 nm), is observed.

Oxidation of ethers to esters by photo-irradiation with benzil and oxygen

A novel method for the conversion of ethers to esters by photo-oxidation using benzil and molecular oxygen, and its plausible reaction mechanism participated by benzoylperoxy radical are described.

Kinetic behaviour of benzoylperoxy radicals in the presence of NO and NO 2

Benzoyl peroxynitrate (C 6H 5C(O)O 2NO 2) was prepared in situ in a 420 l photoreactor by continuous photolysis of Cl 2/C 6H 5CHO/O 2/NO 2/N 2 mixtures. From the loss of benzoyl peroxynitrate in the presence of different amounts of NO and NO 2, rate constants of the reaction C 6H 5C(O)O 2NO 2 (+M)→C 6H 5C(O)O 2+NO 2 (+M) (−2) and rate constant ratios k 2 k 1 of the reactions C 6H 5C(O)O 2+NO 2 (+M)→C 6H 5C(O)O 2NO 2 (+M) (2) and C 6H 5C(O)O 2+NO→products (1) were determined. The temperature and pressure dependence of k −2 can be described by the expressions developed by Troe and co-workers with the following parameters: k 0/[N 2]=3.4×10 −2exp(−92.6 kJ mol −1/ RT) cm 3 molecule −1 s −1, k ∞=1.1×10 17 exp(−117.0 kJ mol −1/ RT) s −1, F c=0.25. The ratio k 2 k 1 is 0.63±0.07 in the temperature range 310–322 K and in 1000 mbar N 2.

ベンゾイルペルオキシラジカルの反応性

ベンゾイルペルオキシラジカルの反応性

Liquid-phase oxidation of 2-butene in the presence of benzaldehyde

The co-oxidation of cis- and trans-2-butene and benzaldehyde at 110 °C has been carried out in benzene and the mechanism of epoxide formation has been investigated by examining the ratio of cis- to trans-epoxides. The results indicate that epoxides were formed by two mechanisms, one involving the benzoylperoxy radical to give about half cis and half trans epoxides and the other by stereospecific epoxidation with perbenzoic acid. Experimental results show that the stereospecific character of epoxidation increases with the reaction time and the concentration of benzaldehyde, but does not depend on the concentration of 2-butene.

Absolute rate constants for hydrocarbon autoxidation. XIII. Aldehydes: photo-oxidation, co-oxidation, and inhibition

The oxidations of acetaldehyde, heptanal, octanal, cyclohexanecarboxaldehyde, pivaldehyde, and benzaldehyde in chlorobenzene at 0 °C have been studied. These aldehydes oxidize at similar rates under similar conditions because there are compensating changes in the rate constants for chain propagation (kp) and chain termination (2kt). The termination rate constants increase from ∼7 × 106 M−1 s−1 for pivaldehyde and cyclohexanecarboxaldehyde to ∼2 × 109 M−1 s−1 for benzaldehyde. The propagation rate constants increase from ∼1 × 103 M−1 s−1 for pivaldehyde to ∼1 × 104 M−1 s−1 for benzaldehyde.The rate of oxidation of the aldehydes was decreased by the addition of 1,4-cyclohexadiene, tetralin, tetralin hydroperoxide, cumene, cumene hydroperoxide, t-butyl hydroperoxide, and 2,6-di-t-butyl-4-methylphenol. As a result of product analysis and absolute rate constant measurements, it is concluded that the peroxy radicals derived from aldehydes are considerably more reactive in hydrogen atom abstraction from hydrocarbons than are the peroxy radicals derived from the hydrocarbons. In the abstraction from cyclohexadiene, the acylperoxy radicals appear to be from 15 to 70 times as reactive, and the benzoylperoxy radicals about 800–900 times as reactive, as the hydroperoxy radical. The differences in reactivity are very much less pronounced in the abstraction from 2,6-di-t-butyl-4-methylphenol.The great ease of oxidation of all aldehydes, and particularly benzaldehyde, is due at least in part to the high reactivity of the peroxy radicals formed in these reactions.

LIQUID-PHASE OXIDATION OF CYCLOHEXENE IN THE PRESENCE OF BENZALDEHYDE

The kinetics, at room temperature, of the oxidation of cyclohexene in the presence of benzaldehyde have been measured, and the nature of the products when this oxidation was performed at 70 and 110 °C has been studied. The results indicate that the attack of benzoyl peroxy radical on the double bond of cyclohexene retards the rate of oxygen absorption and also causes epoxidation of cyclohexene. The epoxidation of cyclohexene by peroxybenzoic acid (produced from aldehyde) seems to proceed simultaneously with the epoxidation by peroxy radicals during the oxidation of cyclohexene in the presence of benzaldehyde.