Benzoyl Radicals Research Articles

Palladium Catalyzed Direct Ortho C‐H Acylation of 4‐Phenylquinazoline Using Methylarenes as Acylation Reagents

AbstractA simple ortho‐acylation of 4‐phenylquinazoline by a Pd‐catalyzed oxidative C−H activation was developed, with moderate yields, in which no prefunctionalized methylarenes were used as acylation reagents. Moreover, this methodology tolerates a wide range of functional groups. Radical scavenging experiments indicate that the acylation involves a benzoyl radical pathway.

Three-component carbonylative Michael addition of aryl bromides using abundant metal-carbonyl under light

Carbonyl compounds are widely found in various chemical reactions and natural products. Herein, a light-driven carbonylative cross-coupling reaction of bromobenzene was reported. Co2(CO)8 was used as an abundant solid carbonyl source to synthesize various Michael addition products with high yields. This reaction has broad substrates scope with good functional group tolerance. The mechanism study indicated that the reaction is achieved by the formation of benzoyl radical from homolytic C–Co cleavage under irradiation.

A comparative study of mechanical crushing and pyrolysis techniques for separation and recovery of discarded polycrystalline silicon photovoltaic modules

With the rapid growth of the photovoltaic (PV) industry, efficient recovery and utilization of discarded polycrystalline silicon PV modules have attracted increasing attention. This study compares the application of mechanical crushing and pyrolysis techniques in the recovery of PV modules. The results indicate that while mechanical crushing can preliminarily disintegrate materials, its effectiveness in separating valuable materials such as silver and aluminum is limited, particularly for particles larger than 1 mm. In contrast, pyrolysis techniques demonstrate outstanding performance in removing organic matter and separating silicon wafers and glass, notably enhancing the recovery rate of large glass particles. However, the brittleness of silicon wafers presents a challenge during pyrolysis. Furthermore, the pyrolysis mechanisms of ethylene-vinyl acetate (EVA) film and backsheet materials are thoroughly discussed. The pyrolysis process of EVA film involves two stages: firstly, the preferential decomposition of acetyl oxygens on ester side chains, followed by further pyrolysis decomposition of the main chain and side chains to generate alkanes. Pyrolysis of polyethylene terephthalate (PET) begins with the generation of methyl and benzoyl radicals, while polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF) pyrolysis initiates with the detachment of head-group units, followed by sequential detachment of chain units. Given the advantages of pyrolysis techniques, this study recommends them as the preferred method for PV module recovery.

Access to N-Fused Quinazolinones by Radical-Promoted Cascade Annulations of Alkenyl N-Cyanamides with Aromatic Aldehydes.

A cascade radical cyclization of alkenyl N-cyanamides with aromatic aldehydes has been achieved for an expeditious synthesis of keto-methylated dihydropyrrolo-quinazolinones. Benzoyl radicals, generated from aryl aldehydes in the presence of di-tert-butyl peroxide (DTBP), promoted the domino annulations leading to distinctive functionalized quinazolinones in good yields. In addition, the robustness of the present protocol is validated by employing heterocyclic and natural product-based aldehydes.

A deep-curing UV-LED light photoinitiator based on diphenylpropanetrione

Benzophenone is a widely used type II photoinitiator, whose application is somewhat limited due to these shortcomings, such as short absorption wavelength, requirement for initiation with a co-initiator like tertiary amine and propensity to yellowing. In this study, 1,3-diphenylpropyltriacetone (DPPT) was synthesized and its photopolymerization was evaluated. Due to the adjacent conjugation of the tricarbonyl group, it has an absorption band at 400–500 nm. The photopolymeirzaition process of DPPT was tested by using real time FT-IR under 365 and 405 nm LED irradiation for various acrylate monomers. Interestingly, the results showed that the initiation efficiency of DPPT was improved by OH-containing monomers or alcohols. ESR-ST and steady-state photolysis experiments demonstrated that the benzoyl radicals were generated, but the photoreaction was expedited by the structure of the addition products of the central carbonyl group of DPPT and alcohol. Furthermore, the DPPT/alcohol initiator could be used for deep curing due to the light bleach property.

Supramolecularly modulated carbon-centered radicals: toward selective oxidation from benzyl alcohol to aldehyde.

The reactivity of ketyl radicals and benzoyl radicals, two key intermediates of photo-induced oxidation of benzyl alcohol, can be stabilized by the host-guest interaction of the radicals with cucurbit[7]uril. As a result, the selectivity of photo-induced oxidation from benzyl alcohol to aldehyde is significantly improved by diminishing side reactions and inhibiting the generation of carboxylic acid products. This work presents a new route to modulate the reactivity of radical intermediates, enriching the chemistry of supramolecular intermediates and the toolbox of supramolecular catalysis.

DFT studies of solvent effect in hydrogen abstraction reactions from different allyl-type monomers with benzoyl radical

Inert allyl-type monomers have been widely documented due to reduce degradation chain transfer. Recently, we and others discovered that the [3 + 2] cyclization reaction process by a photo-driven radical reaction, which can accelerate the polymerization. It was discovered that allyl ether monomers had much higher reactivity than other allyl monomers in the suspension photopolymerization initiated by Type I photoinitiator. Since the hydrogen abstraction reaction (HAR) is the initial step of cyclization, and in order to clarify the influence of solvents effect, three allyl-type monomers were employed, containing “O”, “N” and “S” atom as hydrogen donors. The benzoyl radical obtained from cleavage of photoinitiator was chosen as hydrogen acceptors. We explored the hydrogen abstraction reaction in different solvents (methanol, water and DMSO) by quantum chemistry for geometry and energy. An investigation was undertaken regarding the structural orbital by electrostatic potential (ESP) and topological analysis (ELF and LOL). The findings were also combined with the distortion model and transition state theory. We obtained the molecular interactions used independent gradient method in the Hirshfeld molecular density partition (IGMH). The Eckart’s correction allowed to examine the driving factors of the hydrogen abstraction reaction tunnels and these reactions constant rates are determined in the range of 500–2500 K depending on the modified Arrhenius form in different solvents effect. Our results can provide an answer for the different reactivities.

Highly Selective Oxidation of Toluene to Benzaldehyde in Alkaline Systems

For the selective oxidation of toluene to benzaldehyde, the biggest challenge is to prevent the further oxidation of benzaldehyde as toluene conversion increases. Using benzyl benzoate as the solvent and adding benzoate to adjust the alkalinity of the system, the formation of the benzoyl radical can be well inhibited, but the oxidation of toluene is weakened. The decomposition of benzyl benzoate to benzaldehyde can activate the reaction at the initial stage, and the negative influence of alkalinity is avoided to some extent. Therefore, by using atmospheric air as an oxidant, a high selectivity and yield of benzaldehyde can be obtained in a benzyl benzoate catalytic system with alkali as an additive. The mechanism of alkaline regulation and selective oxidation of toluene was investigated by in situ infrared (IR) spectroscopy experiments. The benzaldehyde capacity is defined to characterize the tolerance of benzaldehyde in the system. Catalysts and alkaline regulators can be easily reused with high-boiling solvents, making it a convenient process for product separation and catalyst–alkaline solvent recycling.

Metal- and Additive-Free Synthesis of α-Hydroxyamino Ketones Enabled by Organophotocatalyst

AbstractWe report herein a straightforward method for the synthesis of α-hydroxyamino ketones, which involves the benzoylation reaction of nitrones with 2-benzoyl-2-phenylbenzothiazoline under organophotocatalysis. This method offers access to a variety α-hydroxyamino ketones without the use of any transition-metal catalyst or base. Control experiments suggested that the reaction proceeded through a benzoyl radical addition to nitrone. Benzothiazoline was found to be a more suitable radical precursor than Hantzsch ester.

Piezocatalyzed Decarboxylative Acylation of Quinoxalin-2(1H)-ones Using Ball Milling

The first piezochemically driven decarboxylative coupling of the C–H bond was developed. The agitation of BaTiO3 via ball milling converts mechanical energy into electrical potential, leading to the production of a benzoyl radical via a single-electron transfer pathway analogous to the photocatalytic reaction. This mechanoredox BaTiO3 catalytic strategy to synthesize C3-acylated quinoxalin-2(1H)-ones requires no solvent, a short reaction time, and simple handling skills, exhibiting promising potential in large-scale chemical manufacturing.

Exceptionally Long Lifetimes of Strongly Entangled Acyl–Trityl Radical Pairs Photochemically Generated in Crystalline Trityl Ketones

Triplet acyl-alkyl radical pairs generated by pulsed laser excitation within the constraints of their nanocrystalline ketone precursors were recently introduced as a potential platform for the robust and repeated instantiation of spin qubit pairs for applications in quantum information science. Here, we report the transient spectroscopy of a series of nanocrystalline trityl-alkyl and trityl-aryl ketones capable of generating correlated triplet radical pairs with persistent triphenylmethyl radicals forced to remain within bonding distances of highly reactive acyl radicals. Whereas triplet trityl-acyl radical pairs decay by competing product-forming decarbonylation and intersystem crossing, triplet trityl-benzoyl radical pairs have lifetimes of up to ca. 4 ms and exclusively regenerate the starting ketone. We propose that these long lifetimes are the result of the short inter-radical distances and the colinear orientation of the two singly occupied orbitals, which are expected to result in large singlet-triplet energy gaps, large zero-field splitting parameters, and a poor geometry for spin-obit coupling. Ketones generating trityl-benzoyl radical pairs demonstrate promising performance along multiple dimensions that are crucial for quantum information science.

Quinazoline-Assisted Acylation with Aldehydes through Pd(II)-Catalyzed C(sp2)–H Activation

An efficient quinazoline-assisted ortho-aroylation of 4-phenylquinazolines with aromatic aldehydes has been developed using Pd(OAc)2 as the catalyst in presence of tert-butyl hydroperoxide (TBHP). This work provides an efficient strategy to synthesis of arylketones, giving yields of up to 90%. Meanwhile, the reaction system exhibits good functional group tolerance and a wide substrate scope. Radical trapping and control experiments suggest that the aroylation reaction involves a benzoyl radical pathway.

Direct Aroylation of Olefins through a Cobalt/Photoredox-Catalyzed Decarboxylative and Dehydrogenative Coupling with α-Oxo Acids.

A photoredox/cobalt dual catalytic procedure has been developed that allows benzoylation of olefins. Here the photoredox catalyst effects the decarboxylation of α-ketoacids to form benzoyl radicals. After addition of this radical to styrenes, the cobalt catalyst abstracts a H-atom. Hydrogen evolution from the putative cobalt hydride intermediate allows a Heck-like aroylation without the need for a stoichiometric oxidant. Mechanistic studies reveal that electronically different styrenes lead to a curved Hammett plot, thus suggesting a change in product-determining step in the catalytic mechanism.

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.

Aerobic Baeyer‐Villiger Oxidation Catalyzed by Metal Corroles

AbstractMetal corrole catalyzed Baeyer‐Villiger oxidation reaction was successfully achieved for the first time. Among all tested Co, Mn, Fe and Cu complexes of 5, 10, 15‐Tris (pentafluorophenyl) corrole, Fe complex [Fe(tpfc)Cl] exhibited the best activity, and the highest yield was observed for six membered cyclic ketones. Preliminary results suggest that Fe(tpfc)Cl may act as an initiator for dehydrogenation of benzaldehyde to generate benzoyl radical, which will form peroxybenzoic acid under molecular oxygen atmosphere. The oxidation of Fe(tpfc)Cl catalyst by peroxybenzoic acid produces high‐valent iron‐oxo corrole intermediate. The iron‐oxo corrole is attacked by cyclohexanone to form a Criegee adduct, which will finally generate ϵ‐caprolactone product to finish the catalytic cycle. The 4 A‐MS additive may accelerate the production of perbenzoic acid and significantly improve the reaction yield.

Metal-free visible-light-driven cascade cyclization reaction to synthesize 2-oxindoles via benzoyl and phenylsulfinyl radicals with acrylamide derivatives.

A metal-free visible-light-driven cascade cyclization reaction to synthesize 3-methyl-3-acetophenone-2-oxindoles and 3-methyl-3-(methylsulfonyl)benzene-2-oxindoles in yields up to 96% and 99%, via benzoyl and phenylsulfinyl radicals with acrylamide derivatives is reported, respectively. Extensive studies, including gram-scale, radical capture and isotope experiments, were performed to indicate that the reaction may involve a radical process.

Pd and photoredox dual catalysis assisted decarboxylative ortho-benzoylation of N-phenyl-7-azaindoles.

The directing group assisted decarboxylative ortho-benzoylation of N-aryl-7-azaindoles with α-keto acids has been achieved by synergistic visible light promoted photoredox and palladium catalysis. The approach tenders rapid entry to aryl ketone architectures from simple α-keto acid precursors via the in situ generation of a benzoyl radical intermediate. The transformation provides a range of ortho-benzoylated N-aryl-7-azaindoles, with excellent site-selectivity and good functional group compatibility under mild reaction conditions. Biological target predictions indicate that these molecules may serve as potential anti-cancer and anti-viral agents.

An approach of quantum chemical methods for the development and substantiation of the structure of new piperidine compounds

The main research direction uses computational computer programs that establish the structural features of new modified piperidine compounds. The analysis of molecular models of piperidine derivatives using the semiempirical PM3 method of the HyperChem program (version 8.0.8) shows the practicality of synthesizing seven drugs and thermodynamic stability for the structures. All compounds have one nucleophilic reaction (oxygen in benzoyl radical) based on the calculations of the piperidine charges and their derivatives. The chemical stability of piperidine derivatives directly depends on the highest occupied molecular orbital (HOMO) energy gap and the lowest unoccupied molecular orbital (LUMO). All investigated model structures 4, 6, 7, 10 are nucleophiles. Compounds 2, 3, and 15 acts as electrophiles, attributed to the absence of benzyloxy radical in their structure. Based on the calculations of dipole moments, all the considered compounds have high polarity and will be readily soluble in almost all polar solvents: water and alcohol. This confirms the possibility of obtaining various dosage forms based on the investigated compounds on an industrial scale.

Decarboxylative/Oxidative Amidation of Aryl α-Ketocarboxylic Acids with Nitroarenes and Nitroso Compounds in Aqueous Medium.

The decarboxylative/oxidative amidation of aryl α-ketocarboxylic acids with 5-aryl-3-nitroisoxazole-4-carboxylates and substituted dinitrobenzenes under oxidative aqueous conditions to afford N-aryl amides is described. The reaction is suggested to proceed via a radical pathway in which a benzoyl nitroxyl radical, the key intermediate formed from reaction between nitroarene and benzoyl radical from glyoxalic acid, couples with hydroxyl radical from water to produce amide. Mechanistic insight allowed the scope of the strategy to be expanded to the synthesis of amides via reaction between aryl α-ketocarboxylic acids and nitroso compounds.

Pressure-dependent kinetics on benzoyl radical + O2 and its implications for low temperature oxidation of benzaldehyde

Toluene is present in significant amounts of the aromatic compounds of real-fuel. Its fundamental combustion characteristics have attracted much attention. Benzaldehyde is a key intermediate in toluene oxidation and could have a potential impact in the construction of a toluene kinetic mechanism. Unfortunately, the understanding of benzaldehyde oxidation mechanism has not as yet reached consensus in the combustion community. Benzoyl as primary intermediate of benzaldehyde after H-atom abstraction, the recognition of its consumption pathway is to direct dissociation in both high- and low-temperature regimes, without considering the reaction channels of C6H5ĊO + 3O2. In order to clarify the importance of this acyl radical addition to oxygen reaction in aldehydes oxidation particularly at low temperatures. The potential energy surface of C6H5ĊO + 3O2 was evaluated at the DLPNO-CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level of theory. RRKM/ME calculations were performed on the C6H5ĊO + 3O2 reaction using thermochemical and kinetic parameters obtained from the ab-initio calculations, with micro-canonical variational transition state theory for treatment of barrierless kinetics. Impact of the newly calculated reaction channels on auto-ignition and oxidation of benzaldehyde was investigated computationally. Current results reveal that the benzaldehyde sub-mechanisms derived from different sources take on distinguished sensitivity for updating the C6H5ĊO + 3O2 kinetics. Thermodynamic analysis was carried out to interpret the dependence of benzaldehyde model performance on C6H5ĊO + 3O2 kinetics. Thermodynamic parameters of benzoyl radical was calculated by the compounded methods of G3, G4 and CBS-APNO due to the excessive effect on equilibrium of reaction for benzoyl consumption. Our results indicate that more accurate determination of thermochemistry of benzoyl is critical to improve the model capability of benzaldehyde in prediction of ignition delay time and identification of species evolution at lower temperature in particular.