Aromatic Oxidation Research Articles

Platinum meso-tetraphenylporphyrin (Pt(II)TPP) mediated the efficient oxidation of alkyl aromatics to ketones in the presence of tert-butyl hydroperoxide

Platinum meso-tetraphenylporphyrin (Pt(II)TPP) mediated the efficient oxidation of alkyl aromatics to ketones in the presence of tert-butyl hydroperoxide

Performance and Evaluating the Characteristics of Flexible Pavements by Using Shredded Aggregate

Abstract: Now-a-days it is necessary to utilize the wastes effectively with technical development in each field. The old abandoned tyres from cars, trucks, farm and construction equipment and off road vehicles are stockpiled throughout the country. This leads to various environmental problems which include air pollution associated with open burning of tyres and other harmful contaminants like (polycyclic aromatic hydrocarbon, dioxin, furans and oxides of nitrogen) and aesthetic pollution. They are non biodegradable; The waste rubber tyre has become a problem of disposal. Due to increase in demand of automobiles in our daily lives, rubber tyre waste is also increasing simultaneously which results in disposal of rubber waste in landfill. The rubber takes more time to decompose and also leads to land pollution. So in this project the waste rubber can be reused in road construction works by partially replacing with coarse aggregate with bitumen in percentage (5, 10, 15, 20, 25 and 30) and carried out different test result based on it. This is not only to minimize the pollution occurred due to waste tyres but also minimizes the use of conventional aggregate which is available in exhaustible quantity. The addition of rubber tyre in flexible pavements enhances the properties of road surfaces as well as it reduces the rubber tyre waste from the land and decreases the self-weight of the bitumen mix.

Low temperature oxidation chemistry of n-butylbenzene in n-decane/n-butylbenzene mixture: Product characterization and kinetic modeling study

n-Alkanes and aromatics are two essential components in transportation fuels and have distinct oxidation reactivities. Due to products with different chemical functionalities generated in oxidation of n-alkanes and aromatics, the interaction kinetics may significantly affect the overall reactivity as well as product distributions. This work investigated the oxidation chemistry of the mixture of n-decane and n-butylbenzene, both of which are C10 hydrocarbons commonly used as jet fuel surrogate components. The experiments were conducted in a jet stirred reactor at pressure of 1 atm, the temperature range of 450–850 K, and the equivalence ratios of 0.5, 1.0 and 2.0. Key low temperature oxidation intermediates and radicals, including C10-cyclic ethers, C10-ketohydroperoxides, C10-ketodihydroperoxide, C10-diketohydroperoxide, benzyl hydroperoxide, methyl peroxy radical and methyl hydroperoxide, were detected by using synchrotron vacuum ultraviolet photoionization mass spectrometry. A detailed kinetic model was developed and validated against the speciation data in this work. Results reveal that the reactions of n-decane greatly enhance the low temperature oxidation reactivity of n-butylbenzene by efficiently producing reactive radicals, such as OH radicals. Besides, the reactions of n-butylbenzene play an inhibiting role in low temperature oxidation reactivity of n-decane. The measured intermediates, such as C10-cyclic ethers, C10-ketohydroperoxides and C10-ketodihydroperoxide, provide experimental evidence to validate the first, second and third O2-addition reactions, respectively. Due to the addition of n-decane, the evolution profiles of aromatic intermediates as a function of temperature are quite different from the cases of pure n-butylbenzene oxidation. For example, the formation of benzene, phenol and benzaldehyde at low temperatures is significantly enhanced, whose mole fractions present negative temperature coefficient behaviours. Finally, the reaction pathways of the binary fuel to produce C5C1 alkenes, alkynes, aldehydes, alcohols, acids and peroxides were analysed.

Abstract 2471 Supercharged Heme: Unmasking a New Regime of Aromatic Oxidation by an Emergent Superfamily

Abstract 2471 Supercharged Heme: Unmasking a New Regime of Aromatic Oxidation by an Emergent Superfamily

Formation of Polystyrene Coated Persulfate Slow-Release Candles for Polycyclic Aromatic Hydrocarbon Oxidation in Water

Formation of Polystyrene Coated Persulfate Slow-Release Candles for Polycyclic Aromatic Hydrocarbon Oxidation in Water

Reviewing Air Pollutants Generated during the Pyrolysis of Solid Waste for Biofuel and Biochar Production: Toward Cleaner Production Practices

The production of biofuels and biochar through pyrolysis is a promising avenue for sustainable energy generation and waste management. However, this process can inadvertently release various air pollutants into the atmosphere, potentially compromising its environmental benefits. This article provides a comprehensive overview of the gas pollutants associated with pyrolysis for biofuel and biochar production, as well as different variables affecting gas emissions. Key pollutants such as particulate matter (PM), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), carbon monoxide (CO), and nitrogen oxides (NOx) have been discussed in terms of their formations and emissions during pyrolysis processes. Furthermore, major factors influencing pollutant emissions, including feedstock composition, pyrolysis conditions, and combustion technologies have been examined with up-to-date examples. The review highlights the significance of emission control strategies, such as advanced reactor design, catalyst utilization, and the integration of realtime monitoring systems, in mitigating air pollution from pyrolysis processes. By shedding light on the environmental challenges associated with pyrolysis-based biofuel and biochar production, this article aims to encourage the development of cleaner and more sustainable approaches to harness the potential of solid waste conversion technologies.

New mechanism for the participation of aromatic oxidation products in atmospheric nucleation

Oxygenated organic molecules (OOMs) are recognized as important precursors for new particle formation (NPF) in the urban atmosphere. The paper theoretically studied the formation of OOMs by styrene oxidation processes initiated by OH radicals, focusing on the OOMs nucleation mechanism. The results found that in the presence of an H2SO4 molecule, lowly oxygenated organic molecules containing a benzene ring (LOMBs) can form stable clusters and grow to the scale of a critical nucleus through pi–pi stacking and OH hydrogen bonding. In addition, LOMBs are more readily generated in a styrene-oxidized system in the presence/absence of NOx than highly oxygenated organic molecules (HOMs). The reaction of OH radicals with other aromatics containing a branched chain on the benzene ring produces LOMBs to varying degrees, with pi–pi stacking playing an essential role. This result suggests that, in the presence of H2SO4 molecules, LOMBs may play a more significant role in promoting nucleation than HOMs. Our findings serve as a pivotal foundation for future investigations into the oxidation and nucleation processes of diverse aromatics in urban environments.

Manganese/CaCO3-based dual functional catalyst facilitating basic catalysis activity and stability for the selective oxidation of aromatics

The pore engineering of alkaline earth metal carbonates with significant specific surface area (SSA) provides promising opportunities for the optimization of surface bases and further construction of bifunctional catalysts. Herein, Mn/CaCO3, with a high dispersion of Mn species and massive basic sites, is successfully synthesized utilizing a one-pot NaCl-assisted mechanochemistry protocol. To be astonished, the SSA of Mn25/CaCO3 reaches 77 m2/g, nearly ten times more than Mn/CaCO3-Pr (prepared by precipitation). Mn25/CaCO3 exhibits unique synergetic catalysis of basic and redox catalysis in the selective oxidation of ethylbenzene (EB) to acetophenone (AP), illustrating the turnover frequency (TOF) of EB is 3 and 7.1-fold compared to Mn/CaCO3-DP (synthesized by deposition precipitation) and Mn/CaCO3-Pr. The low energy barriers in activating EB for Mn25/CaCO3 are disclosed by density functional theory (DFT), further explaining the interactions of base-redox synergetic effect. This research lays a solid foundation for the exploration of highly efficient selective aerobic oxidation catalysts.

Revisiting Nitroaromatic Drugs: Mechanisms of Bioactivation, Metabolism and Toxicity and Methods to Synthesize Nitroaromatic Fragments

Nitroaromatic drugs represent an important class of therapeutic agents, endowed with different pharmacological properties such as antibacterial, antiprotozoal, anti-Parkinson, anticancer, etc. However, the nitroheterocycle and nitroarene fragments are considered potentially toxic, with reports of mutagenicity and genotoxicity. The bioreduction process of the nitro group plays a central role in the antimicrobial and toxicological mechanism of action of nitroaromatic drugs. This article will review the nitroaromatic drugs approved by the Food and Drug Administration (FDA) in the last 30 years, the mechanisms of bioactivation, metabolism and toxicity and, finally, it will revisit the main methodologies for obtaining the nitroaromatic fragment from aromatic nitration reaction and oxidation of arylamines and/or heteroarylamines.

Organo NHC catalyzed aqueous synthesis of 4β-isoxazole-podophyllotoxins: in vitro anticancer, caspase activation, tubulin polymerization inhibition and molecular docking studies.

We present, for the first time, the organo-N-heterocyclic carbene (NHC) catalyzed 1,3-dipolar cycloaddition of 4β-O-propargyl podophyllotoxin (1) with in situ aromatic nitrile oxides to afford regioselective 4β-isoxazolepodophyllotoxin hybrids (6a-n) in benign aqueous-organic media. Preliminary anticancer activity results showed that compound 6e displayed superior activity against MCF-7, HeLa and MIA PaCa2 human cell lines compared with podophyllotoxin. Compounds 6j and 6n showed greater activity against the MCF-7 cell line than the positive control. Caspase activation studies revealed that compound 6e at 20 μg ml-1 concentration had greater caspase 3/7 activation in MCF-7 and MIAPaCa2 cells than podophyllotoxin. Furthermore, in vitro tubulin polymerization inhibition studies revealed that compound 6e showed comparable activity with podophyllotoxin. Finally, in silico molecular docking studies of compounds 6e, 6j, 6n and podophyllotoxin on α,β-tubulin (pdb id 1SA0) revealed that compound 6n showed excellent binding energies and inhibition constants compared with podophyllotoxin.

Integrating NiFe bimetal sites into a conjugated microporous polymer for boosting photocatalytic selective aromatic alcohol oxidation

A conjugated porous polymer metalated with Ni and Fe sites (NiFe-CMP) has been rationally designed and synthesized, exhibiting excellent photocatalytic activity and selectivity in the oxidation of aromatic alcohols under visible light irradiation.

Enhanced detection of aromatic oxidation products using NO3 - chemical ionization mass spectrometry with limited nitric acid.

Nitrate ion-based chemical ionization mass spectrometry (NO3 --CIMS) is widely used for detection of highly oxygenated organic molecules (HOMs). HOMs are known to participate in molecular clustering and new particle formation and growth, and hence understanding the formation pathways and amounts of these compounds in the atmosphere is essential. However, the absence of analytical standards prevents robust quantification of HOM concentrations. In addition, nitrate-based ionization is usually very selective towards the most oxygenated molecules and blind to less oxygenated compounds hindering the investigation of molecular formation pathways. Here, we explore varying concentrations of nitric acid reagent gas in the sheath flow of a chemical ionization inlet as a method for detecting a wider range of oxidation products in laboratory-simulated oxidation of benzene and naphthalene. When the concentration of reagent nitric acid is reduced, we observe an increase in signals of many oxidation products for both precursors suggesting that they are not detected at the collision limit. The sensitivity of naphthalene oxidation products is enhanced to a larger extent than that of benzene products. This enhancement in sensitivity has a negative relationship with molecular oxygen content, the oxygen-to-carbon ratio, the oxidation state of carbon, and lowered volatility. In addition, the sensitivity enhancement is lower for species that contain more exchangeable H-atoms, particularly for accretion products. While more experimental investigations are needed for providing the relationship between enhancement ratios and instrumental sensitivities, we suggest this method as a tool for routine check of collision-limited sensitivities and enhanced detection of lower-oxygenated species.

Catalytic Oxidation Mechanism of Toluene on the Ce0.875Zr0.125O2 (110) Surface

Aromatic volatile organic compounds (VOCs) are toxic to public health and contribute to global air pollution; thus, it is urgent to control VOC emissions. Catalytic oxidation technology has been widely investigated to eliminate aromatic VOCs; this technology exhibits high catalytic efficiency even at low temperatures. However, the reaction mechanism of aromatic VOCs’ total oxidation over metal-oxide-based catalysts, which is of great significance in the design of catalysts, is not yet clear. In this study, we systemically calculated the catalytic oxidation mechanism of toluene over the Ce0.875Zr0.125O2 catalyst using density functional theory (DFT). The results show that toluene first loses hydrogen from the methyl group via oxy-dehydrogenation and is gradually oxidized by lattice or adsorbed oxygen to benzyl alcohol, benzaldehyde, and benzoic acid following the Mars-van Krevelen (MVK) mechanism. Afterwards, there is a decarboxylation step to produce phenyl, which is further oxidized to benzoquinone. The rate-determining step then proceeds via the ring-opening reaction, leading to the formation of small molecule intermediates, which are finally oxidized to CO2 and H2O. This work may provide atomic-scale insight into the role of lattice and adsorbed oxygen in catalytic oxidation reactions.

O2 Activation by a Coordinated -NH- Function: Hydrogen Atom Transfer and Aromatic Ring Oxidation.

Herein, we disclose a unique method of oxidation of a 1,4-naphthoquinone ring in air. We report that (1,4-naphthoquinone)-NH-N=C(OH)Ph (H3L) coordinated to octahedral ruthenium(II) and osmium(II) ions activates an 3O2 molecule spontaneously. Hydrogen atom transfer (HAT) from the -NH- function of H3L to 3O2 and subsequent (2e + 2H+) oxidation forming (1,3,4-trioxonaphthalen)=N-N=C(OH)Ph (HLOX) have been established. The H3L → HLOX transformation occurs via (3-hydroperoxy-1,4-naphthoquinone)=N-N=C(O-)Ph (HLOOH-) as an intermediate. The primary step is HAT generating H2L•- and hydroperoxide (OOH•) radicals. H2L•- is delocalized over the aromatic ring and incites coupling reactions via ortho carbon and produces coordinated HLOOH-. In solution, the homolytic cleavage of the peroxo bond leads to aromatic ring oxidation, affording LOX-. Ruthenium(II) and osmium(II) complexes of the types [MII(H2L-)(PPh3)2X], [MII(HLOOH-)(PPh3)2X], and trans-[MII(LOX-)(PPh3)2X] were successfully isolated in good yields. Notably, the cyclic voltammograms of all of the complexes exhibit reversible anodic waves due to MIII/MII redox couples. The rate constants of the [MII(H2L-)(PPh3)2X] → [MII(HLOOH-)(PPh3)2X] conversions determined by time-driven UV-vis spectroscopy in dry CH2Cl2, wet CH2Cl2, and D2O wet CH2Cl2 in air at 298 K follow the order > > . It is established that the rate constants are dependent on the 3O2 content of the solution but not on the concentration of the complex.

Insights into the Peroxide-Bicyclic Intermediate Pathway of Aromatic Photooxidation: Experimental Yields and NOx-Dependency of Ring-Opening and Ring-Retaining Products.

Aromatic hydrocarbons are important contributors to the formation of ozone and secondary organic aerosols in urban environments. The different parallel pathways in aromatic oxidation, however, remain inadequately understood. Here, we investigated the production yields and chemical distributions of gas-phase tracer products during the photooxidation of alkylbenzenes at atmospheric OH levels with NOx present using high-resolution mass spectrometers. The peroxide-bicyclic intermediate pathway emerged as the major pathway in aromatic oxidation, accounting for 52.1 ± 12.6%, 66.1 ± 16.6%, and 81.4 ± 24.3% of the total OH oxidation of toluene, m-xylene, and 1,3,5-trimethylbenzene, respectively. Notably, the yields of bicyclic nitrates produced from the reactions of bicyclic peroxy radicals (BPRs) with NO were considerably lower (3-5 times) than what the current mechanism predicted. Alongside traditional ring-opening products formed through the bicyclic pathway (dicarbonyls and furanones), we identified a significant proportion of carbonyl olefinic acids generated via the 1,5-aldehydic H-shift occurring in subsequent reactions of BPRs + NO, contributing 4-7% of the carbon flow in aromatic oxidation. Moreover, the observed NOx-dependencies of ring-opening and ring-retaining product yields provide insights into the competitive nature of reactions involving BPRs with NO, HO2, and RO2, which determine the refined product distributions and offer an explanation for the discrepancies between the experimental and model-based results.

Low temperature chemistry of 1,2,4-trimethylbenzene in a blend with n-heptane

As a representative aromatic component of practical fuels, understanding the low temperature chemistry of 1,2,4-trimethylbenzene under the reaction environment of fuel mixtures is necessary to improve the ignition and combustion process. In this work, low temperature oxidation of 1,2,4-trimethylbenzene was examined in a jet stirred reactor with reactants of n-heptane and 1,2,4-trimethybenzene in a fuel mixture (1:1 in mole, 500–800 K, ϕ = 0.5, τ = 2.0 s, p = 1 bar). Chemical species and their mole fraction evolution with reaction temperatures were recorded by the time of flight molecular beam mass spectrometer using synchrotron vacuum ultraviolet radiation as photon ionization source. Molecular structures of 56 species were identified by comparing the species ionization energies and the photonionization efficiency curves. 25 chemical formula of monocyclic oxygenated aromatics and oxygenated polycyclic aromatic hydrocarbons (OPAH) are detected, and 12 of them are identified. Some of the OPAHs are more toxic than the polycyclic aromatic hydrocarbons, indicating the importance of revealing their formation pathways in low temperature oxidation of aromatics. Numerical simulations using the latest kinetic model from Lawrence Livermore National Laboratory well predict the mole fractions of the reactants and most intermediates, but many monocyclic oxygenated aromatics and OPAHs are missing. The detection and identification of key monocyclic oxygenated aromatics (e.g., peroxides, aldehydes, dialdehydes, and ketohydroperoxides of 1,2,4-trimethylbenzene) provide important clues to unravel the low temperature oxidation pathways of alkylated aromatics like 1,2,4-trimethylbenzene. For monocyclic oxygenated aromatics and OPAHs that are missing in the kinetic model, potential formation pathways were proposed based on the molecular structure information, which might be useful for future kinetic model development.

Aromatic aldehyde oxidation by hexacyanoferrate(III) catalyzed by Ru(VI) in alkaline medium

In this study, the selective oxidation of aromatic aldehydes has been investigated using Ru(VI) as a catalyst and hexacyanoferrate (III) as a cooxidant in an alkaline medium. The reaction order with respect to the oxidant and the aromatic aldehyde is complex while the reaction order with respect to Ru(VI) is one. The proposed mechanism presents two catalytic cycles for the two active species of the catalyst. In each cycle, Ru(VI) species forms a complex with the anion of hydrated benzaldehyde which decomposes to form benzoic acid. The function of hexacyanoferrate(III) is the regeneration of catalyst species. A quantitative structure–activity relationship was analyzed using the Hammett equation for decomposition complex step. This analysis showed that deactivating groups in para- position enhances this process.

Insights into ethylbenzene oxidation catalyzed by transition-metal oxides: Crucial role of hydroperoxide transformation

Selective oxidation of aromatics via a free-radical process is a crucial ingredient in the chemical industry, in which the transformation of hydroperoxide was considered the key step to facilitate the reaction. In this study, the aerobic oxidation of ethylbenzene (EB) to acetophenone (AcPO) catalyzed by carbon nitrides (CNx) supported the transition-metal oxides was performed. Among these catalysts, Co3O4/CNx displayed the highest activity with 48.09 % EB conversion and 77.8 % AcPO selectivity, due to the efficient decomposition of 1-phenylethyl hydroperoxide (PEHP). Notably, in the case of CuO/CNx, the relatively low EB conversion (19.8 %) and high selectivity of AcPO (70.2 %) were observed, while almost no PEHP was detected. Further mechanism investigations revealed that the decomposition of hydroperoxide over CuO/CNx was too fast to generate the reactive free-radicals, which could not efficiently facilitate the propagation steps. Moreover, the addition of tert-butyl hydroperoxide (TBHP) participated in the α-H abstraction of EB and facilitated of radical propagation, showing the distinguished activities over Co3O4/CNx and CuO/CNx.

Aerobic oxidation of alkyl aromatics to ketones catalyzed by biomimetic copper complex and N-hydroxyphthalimide (NHPI) under mild conditions

A galactose oxidase-like copper complex (CuIIL) (Ligand: N, N′-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2′-diaminobiphenyl) was synthesized and used to catalyze the aerobic oxidation of alkyl aromatics to ketones in presence of N-hydroxyphthalimide (NHPI). The catalytic system exhibited excellent performance and tolerance under mild conditions. Mechanistic studies indicated that NHPI could be activated smoothly to generate phthalimide N-oxyl (PINO) radical in the presence of CuIIL. The kinetic isotope effect (KIE) studies showed that the generation of PINO radical was the rate-determining step.

Influence of Polycyclic Aromatic Compounds and Oxidation States of Soot Organics on the Metabolome of Human-Lung Cells (A549): Implications for Vehicle Fuel Selection.

Decades of research have established the toxicity of soot particles resulting from incomplete combustion. However, the unique chemical compounds responsible for adverse health effects have remained uncertain. This study utilized mass spectrometry to analyze the chemical composition of extracted soot organics at three oxidation states, aiming to establish quantitative relationships between potentially toxic chemicals and their impact on human alveolar basal epithelial cells (A549) through metabolomics-based evaluations. Targeted analysis using MS/MS indicated that particles with a medium oxidation state contained the highest total abundance of compounds, particularly oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) composed of fused benzene rings and unsaturated carbonyls, which may cause oxidative stress, characterized by the upregulation of three specific metabolites. Further investigation focused on three specific OPAH standards: 1,4-naphthoquinone, 9-fluorenone, and anthranone. Pathway analysis indicated that exposure to these compounds affected transcriptional functions, the tricarboxylic acid cycle, cell proliferation, and the oxidative stress response. Biodiesel combustion emissions had higher concentrations of PAHs, OPAHs, and nitrogen-containing PAHs (NPAHs) compared with other fuels. Quinones and 9,10-anthraquinone were identified as the dominant compounds within the OPAH category. This knowledge enhances our understanding of the compounds contributing to adverse health effects observed in epidemiological studies and highlights the role of aerosol composition in toxicity.