Subsequent Oxidation Research Articles

Enhanced mineralization of nitrophenols by a novel C@ZVAl-PS based sequential reduction-oxidation process

Widely employed nitrophenols (NPs) are refractory and antioxidant due to their strong electron-withdrawing group (-NO2). Actually, NPs are readily reduced to aminophenols (APs). However, APs remain toxic and necessitate further treatment. Herein, we utilized a novel sequential reduction-oxidation system of carbon-modified zero-valent aluminum (C@ZVAl) combined with persulfate (PS) for the thorough removal of both NPs and APs. The results demonstrated that p-nitrophenol (PNP, up to 1000 mg/L) exhibited complete reduction to p-aminophenol (PAP), and then over 98.0 % of PAP could be effectively oxidized, in the meantime the removal rate of chemical oxygen demand (COD) was as high as 95.9 %. Based on the SEM and XPS characterizations, we found that C@ZVAl has exceptionally high reactivity that generates massive electrons and reduces PNP to PAP through accelerated electron transfer. In the subsequent oxidation step, PS can be rapidly activated by C@ZVAl to generate SO4− radicals for PAP oxidization. Meanwhile, the mineralization of COD proceeds. The temporal binding of reduction and oxidation can be regulated by varying the PS dosing time. Namely, the appropriate delay in PS dosing facilitates sufficient reduction to provide enough reactants for oxidation, favoring the mineralization of PNP and COD. More crucially, dinitrodiazophenol (DDNP) in an actual explosive wastewater without any pretreatment can be effectively mineralized by this sequential reduction-oxidation system, affirming the excellent performance of this process in practical applications. In conclusion, the C@ZVAl-PS based sequential reduction-oxidation looks very promising for enhanced mineralization of nitro-substituted organic contaminants.

Oxidation of Eugenol Derivatives with KMnO4 and CrO3

AbstractThis study aims to delineate the synthesis of eugenol derivatives, starting with hydroxyl group protection and then the subsequent oxidation stages. Initially, eugenol underwent conversion into acetyleugenol and benzyleugenol during the protection phase. Subsequently, a kinetic oxidation of acetyleugenol with KMnO4 via GC-MS analysis resulted in the identification of four compounds. The kinetic investigation indicated the primary formation of diolacetyleugenol, succeeded by aldehyde eugenol, which further gets converted into its respective carboxylic acid. Additionally, acetyleugenol and benzyleugenol underwent oxidation with CrO3, yielding the corresponding carboxylic acids.

Environmental stability and ageing of ScN thin films from XPS Ar+ depth profiling

A basic knowledge on chemical stability and reactivity of a wide band gap ScN semiconductor in the presence of air atmosphere, where O2 and H2O represent the main degradation or corrosive agents, is of vital importance for a long-term performance of ScN-based devices for thermoelectric applications. Here, we present a systematic XPS Ar+ depth profiling analysis and optical and TEM characterizations of naturally room temperature air-aged thin ScN films prepared by a high-temperature DC sputtering on MgO(001) and SiO2 substrates. We find that superior crystalline quality ScN/MgO films degrade weakly after their quick initial surface oxidation and/or hydrolysis. Their oxidation is rather local and associated with the film-penetrating void-like interfaces. Significant initial surface oxidation and subsequent bulk oxidation after ageing is, however, observed for polycrystalline ScN/SiO2 films. Ab initio calculations of pure ScN and ScN with diluted nitrogen vacancies and/or substitutional oxygen impurities, which assist our experimental research, reveal pronounced impact of these defects on the ScN electronic structure. The modeled compositions reflect homogeneously and weakly oxidized films, while the real films correspond to relatively pure ScN crystallites with interfaces rich in oxygen.

Challenging Aromaticity: Revealing a Thioesterase Domain in a Fungal Nonreducing Polyketide Synthase Governing the Production of 3-Methylene Isochromanone.

Thioesterase (TE) domain exerts a great influence over the structure of the final product and TE-released nonreduced polyketides (nrPKs) retain aromaticity. 3-Methylene isochromanones are lactones with a unique olefin at C3 that disrupts the aromaticity, whose biosynthetic details are speculative. Our study unveils the complete biosynthesis of ascochin, in which the construction of the 3-methylene isochromanone backbone is achieved by a nonreducing polyketide synthase (nrPKS) alone and two subsequent oxidations are involved. Intriguingly, the TEAscD serves as a gatekeeper to direct the product release toward formation of nonaromatic 3-methylene isochromanone, rather than the typical aromatic product.

Antimony-assisted controlled growth of PtSe2 ribbon arrays for enhanced hydrogen evolution reaction

In this study, we report the successful synthesis of few-layer parallel PtSe2 ribbons on an Au foil employing a surface melting strategy via the chemical vapor deposition growth method at 650 °C. The controlled formation of parallel ribbons was directed by the Au steps generated through antimony treatment. These ribbons exhibit an average length of exceeding 100 μm and a width of approximately 100 nm across a substantial area. Electrocatalysis measurements showcase the catalytic performance of PtSe2 ribbons grown on Au foil, which can be further augmented through subsequent oxidation treatment. This investigation introduces an effective growth method for few-layer ribbons at low temperatures and broadens the scope of employing the substrate-guided strategies for the synthesis of one-dimensional materials. Additionally, it underscores the potential of PtSe2 ribbons as an electrocatalyst for hydrogen evolution.

Efficient reduction-oxidation coupling degradation of nitroaromatic compounds in continuous flow processes

Nitroaromatic compounds (NACs) with electron-withdrawing nitro (-NO2) groups are typical refractory pollutants. Despite advanced oxidation processes (AOPs) being appealing degradation technologies, inefficient ring-opening oxidation of NACs and practical large-scale applications remain challenges. Here we tackle these challenges by designing a reduction-oxidation coupling (ROC) degradation process in LaFe0.95Cu0.05O3@carbon fiber cloth (LFCO@CFC)/PMS/Vis continuous flow system. Cu doping enhances the photoelectron transfer, thus triggering the -NO2 photoreduction and breaking the barriers in the ring opening. Also, it modulates surface electronic configuration to generate radicals and non-radicals for subsequent oxidation of reduction products. Based on this, the ROC process can effectively remove and mineralize NACs under the environmental background. More importantly, the LFCO catalyst outperformed most of the recently reported catalysts with lower cost (13.72 CNY/ton) and higher processing capacity (3600 t/month). Furthermore, the high scalability, material durability, and catalytic activity of LFCO@CFC under various realistic environmental conditions prove the potential ability for large-scale applications.

Theoretical study of the reaction of organic peroxyl radicals with alkenes and their accretion products involved in the atmospheric nucleation

Organic peroxy radicals, including alkyl peroxy radicals (RO2) and acyl peroxy radicals (RC(O)O2), are crucial intermediates in the atmospheric photochemical reactions of volatile organic compounds and directly or indirectly affect the distribution of other species (e.g., HO2 radicals, NOx, OH radicals, and alkenes). However, the atmospheric reactions of organic peroxyl radicals with alkenes (RO2 + alkene reactions) are not fully understood. The present study used theoretical calculations to investigate the reaction mechanisms of various organic peroxy radicals with different alkenes, with the aim of clarifying the influence of molecular structure on RO2 + alkene and RC(O)O2 + alkene reactions. Furthermore, we investigated the nucleation mechanisms of the subsequent oxidation products. The results show that the reaction rate constants for RC(O)O2 + alkene reactions are 1–6 orders of magnitude higher than those for RO2 + alkene reactions. The addition products formed by organic peroxy radicals with alkenes not only undergo monomolecular reactions to generate epoxides, but also participate in O2 addition to yield the accretion products ROOR’. H2SO4 molecules synergistically interact with low-volatility ROOR’ to grow clusters up to the 1–2 nm scale, and the ROOR’ molecules can form pure organic clusters larger than 1 nm, even in the absence of H2SO4 molecules. Our study provides a new perspective on the formation of accretion products in the atmosphere and their involvement in new particle formation.

Efficient co-production of glucose and carboxylated cellulose nanocrystals from cellulose-rich biomass waste residues via low enzymatic pre-hydrolysis and persulfate oxidation

Carboxylated cellulose nanocrystals (cCNCs) can be prepared directly from biomass in a one-step ammonium persulfate (APS) oxidation. However, the cellulose in the biomass is not fully utilized because APS oxidation degrades the cellulose amorphous regions. In this paper, to improve cellulose utilization rate, a two-step method (enzymatic pre-hydrolysis and APS oxidation) was developed to co-produce fermentable sugar and cCNCs from xylooligosaccharides manufacturing waste residue (XOR) of corncob. Enzymatic pre-hydrolysis produced 26.1 g of glucose per 100 g of XOR with a cellulase loading of 5 FPU/g cellulose in 24 h. Subsequent oxidation produced 22.9 g cCNCs with 0.5 M APS in 8 h. In contrast, the one-step APS method only produced 28.3 g cCNCs per 100 g of XOR. The total cellulose utilization rate by the two-step method increased by 73 % compared to the one-step APS method. Structural characteristics of cCNCs prepared by the two-step method were slightly different from those of the one-step method, but good properties were maintained. Therefore, the co-production method could prepare glucose and cCNCs with stable properties from XOR with a greatly improved cellulose utilization rate.

Intensification of fructose dehydration into 5‐HMF and subsequent oxidation to 2,5‐FDCA using ultrasound

AbstractUltrasound‐assisted dehydration of fructose into 5‐hydroxymethylfurfural (5‐HMF) and subsequent oxidation to furandicarboxylic acid (2, 5‐FDCA) is studied in the current work with the main objective being to elucidate the effectiveness of ultrasound for intensified synthesis. The effect of reaction parameters like ultrasound power, duty cycle, reaction time, reaction temperature, solid to solvent ratio, and fructose concentration on the dehydration of fructose into 5‐HMF has been studied. Optimized conditions established were ultrasonic power of 140 W, duty cycle of 60%, reaction time of 60 min, temperature of 100°C, and fructose:dimethylsulfoxide (DMSO) ratio of 3:100 (g/mL), which resulted in the highest 5‐HMF yield of 96% and fructose conversion of 100%. The conventional method carried out at optimized conditions resulted in only 13.5% as 5‐HMF yield. The obtained 5‐HMF was further oxidized to FDCA using Pd/C as the catalyst, H2O/DMSO as solvent, and K2CO3 as a base also using ultrasonic irradiation at 140 W power and 22 kHz frequency in the presence and absence of O2 as oxidant. 100% conversion of 5‐ HMF was obtained in 30 min and 4 h using ultrasound in the presence of O2 and in absence of O2, respectively. 75% conversion of 5‐HMF was observed using the conventional method in 5 h in the presence of O2. Overall, the intensification benefits of using ultrasound at both steps of synthesis has been successfully elucidated.

Rhodium(III)-Catalyzed Intramolecular Cyclization and Sequential Aromatization of Ynamides with Propargyl Esters: Access to 2,5-Dihydropyrroles and Pyrroles.

Disclosed herein is a rhodium(III)-catalyzed intramolecular cyclization of ynamides with propargyl esters. A variety of highly functionalized 2,5-dihydropyrroles were obtained in moderate to good yields with high E/Z selectivities. Subsequent oxidation of the products gave valuable pyrrole derivatives. Additionally, scale-up reactions and late-stage derivatizations highlight the potential synthetic utility of this methodology.

Bimetal-carbon engineering for polypropylene conversion into hydrocarbons and ketones in a Fenton-like system

Fenton-like reaction with targeted reactive species was tested for up-cycling of waste plastics to value-added chemicals and we demonstrated a bimetal-carbon-activated peroxymonosulfate (PMS) Fenton-like system for effectively converting polypropylene into hydrocarbons and ketones. In a hydrothermal reaction process at 160 °C for 14 h, directional polypropylene conversion was achieved at a selectivity of 80 wt% hydrocarbons and ketones in the products. The distribution of Cu-Mg bimetallic sites on a carbon substrate exhibited a synergistic effect, and their catalytic activation of PMS induced specific generation of •OH-dominated reactive species. The target reactive species controlled the oxidizing capacity of the system. The efficient breaking of C-C/C-H bond in polypropylene and the subsequent further oxidation under mild conditions led to the dominated products of hydrocarbons and ketones. This study provides an attractive approach for upcycling waste plastics, thus promoting circular economy and carbon reduction.

Self-assembled Co(II) and Co(III) [M2L3] helicates and [M4L6] tetrahedra from an unsymmetrical quaterpyridine ligand.

In order to bind guest molecules with exquisite selectivity, biological host molecules often employ low symmetry binding pockets. The majority of metallosupramolecular assemblies, however, rely on symmetrical ligands to form high-symmetry assemblies that enclosing similarly symmetrical cavities. Here we employ an unsymmetrical quaterpyridine ligand in combination with cobalt(II) to form a mixture of low-symmetry [M2L3] helicates and [M4L6] tetrahedra and their subsequent oxidation to Co(III)-containing assemblies.

Modular Enantioselective Total Syntheses of the erythro-7,9-Dihydroxy- and 9-Hydroxy-7-Keto-8,4'-Oxyneolignans.

A modular, enantioselective approach to access the bioactive 7,9-dihydroxy- and 9-hydroxy-7-keto-8,4'-oxyneolignans is disclosed, which employs stereoselective Mitsunobu reactions of enantiopure 2-aryl-1,3-dioxan-5-ols and functionalized phenols. The enantiopure dioxanols are prepared through Sharpless asymmetric dihydroxylation of protected coniferyl or sinapyl alcohols and subsequent benzylidene acetal formation. Through a mix-and-match coupling approach, six of the eight possible erythro-7,9-dihydroxy-8,4'-oxyneolignan enantiomeric natural products (bearing a C-1' hydroxypropyl chain) were generated following sequential deprotection. Subsequent benzylic oxidation afforded the 7-keto-derivatives, resulting in enantioselective syntheses of each enantiomer of the natural products asprenol B and icariol A1.

Stereoselective Synthesis of meso- and l,l-Diaminopimelic Acids from Enone-Derived α-Amino Acids.

The stereoselective synthesis of meso-diaminopimelic acid (meso-DAP), the key cross-linking amino acid of the peptidoglycan cell wall layer in Gram-negative bacteria, and its biological precursor, l,l-DAP, is described. The key step involved stereoselective reduction of a common enone-derived amino acid by substrate- or reagent-based control. Overman rearrangement of the resulting allylic alcohols, concurrent alkene hydrogenation and trichloroacetamide reduction, and subsequent ruthenium-catalyzed arene oxidation completed the synthesis of each stereoisomer. The synthetic utility of this approach was demonstrated with the efficient preparation of an l,l-DAP-derived dipeptide.

Integrated Struvite Precipitation and Fenton Oxidation for Nutrient Recovery and Refractory Organic Removal in Palm Oil Mill Effluent

Anaerobically treated palm oil mill effluent (AnT-POME), containing a high concentration of ammoniacal-nitrogen (NH4+-N) and soluble chemical oxygen demand (sCOD) was subjected to sequential processes of struvite precipitation to recover NH4+-N and Fenton oxidation for sCOD removal. The optimization of treatment was conducted through response surface methodology (RSM). Under optimized struvite precipitation conditions (Mg2+/NH4+, PO43−/NH4+ molar ratios: 1; pH 8.2 ± 0.1), NH4+-N concentration decreased to 41 ± 7.1 mg L−1 from an initial 298 ± 41 mg L−1 (78.8 ± 1.6 % removal). Field emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX) confirmed NH4+-N was recovered as struvite. Subsequent Fenton oxidation under the optimized conditions (H2O2 dosage: 2680 mg L−1; molar ratio of Fe2+/H2O2: 0.8; reaction time: 56 min) reduced sCOD concentration to 308 ± 46 mg L−1 from an initial 1350 ± 336 mg L−1 (76.0 ± 1.0 % removal). The transparent appearance of treated AnT-POME validated the removal of sCOD responsible for the initial brownish appearance. Models derived from RSM demonstrated significance, with high coefficients of determination (R2 = 0.99). Overall, integrated struvite precipitation and Fenton oxidation effectively removed NH4+-N and sCOD from AnT-POME, contributing to nutrient recovery and environmental sustainability.

Magmatic sulfide oxidation drives crustal PGE mobilization: Implications for hydrothermal PGE mineralization

Platinum-group elements (PGEs) have a strong affinity for sulfur and tend to accumulate in the deep continental crust, either concentrated within magmatic Cu-Ni-PGE deposits or dispersed throughout disseminated sulfides. However, PGE enrichment in shallow magmatic-hydrothermal systems implies an obscure link to deep sulfide destabilization, which releases PGEs into ore-forming fluids. To bridge this gap, our study investigates the PGE composition of magmatic sulfides with oxidative textures in dacitic rocks from the southwestern Okinawa Trough. We identified three groups of magmatic sulfides, primarily precipitated as Cu-poor monosulfide solid solution (MSS), which formed at distinct stages of magma evolution from deep to shallow crustal levels. Group A sulfides manifest as small-sized inclusions (<30 μm) within most high-Mg olivines, whereas Group B and C sulfides are larger (50–500 μm) and occur within cognate xenoliths of mafic cumulate rocks and the groundmass of host dacites. Group B and C sulfides exhibit distinct oxidative textures and newly-formed mineral assemblages, including magnetite, hematite, goethite, and magnetite ± pyrite, alongside hydrothermal silicate minerals, respectively. We attribute the oxidation process to the infiltration of orthomagmatic fluids exsolved from mafic magma that had underplated the sulfide-bearing felsic magma reservoir, which was nearly solidified. By comparing the chemical compositions between pristine sulfides and their oxidative remnants, we observed extensive mobilization of Pd, Pt, Cu, Ag, Ni, and Co from the altered sulfides of Group B, while Au enrichment occurred as nanoparticles under high oxidation states. In contrast, Au was extracted along with other mobile metals from the altered sulfides of Group C, with Pt remaining in place under more reduced conditions. These distinct scenarios may lead to the formation of PGE-rich and Au-rich fluids, respectively. The formation of deep crustal MSS and subsequent hydrothermal oxidation under varying redox conditions thus provides a viable mechanism for trans-crustal PGE mobilization and inter-element fractionation, typical of PGE-rich magmatic-hydrothermal deposits.

Unusual Photochemistry in Aromatic Dithioimides: Quantitative Thione Reduction Promoted by Ether Solvents.

We report a mechanistic investigation of an aromatic dithioimide (2SS) displaying puzzling yet efficient photochemistry in ether solvents. Perplexingly, 2SS dissolved in ether solvents in a sealed and degassed vial was photochemically converted to the corresponding diimide (2OO), as determined by 1H NMR following product extraction. With no external sources of oxygen in the sample, could the oxygen in 2OO be from the ether itself? To study this unprecedented proposition, we attempt to uncover the ether's involvement in this reaction. As seen by laser-flash photolysis, 2SS appears to first react with the solvent from its singlet excited state. Following the reaction by NMR under rigorously oxygen- and water-free conditions led to the identification of a photoreductive pathway that quantitatively transformed one thione into a methylene to yield 2SH2. Subsequent oxidation of 2SH2 or irradiation of 2SS under air proved that molecular oxygen was indeed necessary to observe an oxidative pathway leading to 2OO, ruling out the initially proposed involvement of an ether oxygen. An explanation of 2SS desulfurization was further revealed through the study of solvent by-products by GC-MS analysis. Supported by DFT calculations, a mechanism is proposed to involve a chain reaction initiated by photochemically generated ether radical.

Redox Approaches to Carbene Generation in Catalytic Cyclopropanation Reactions

AbstractTransition metal‐catalyzed carbene transfer reactions have a century‐old history in organic chemistry and are a primary method for the synthesis of cyclopropanes. Much of the work in this field has focused on the use of diazo compounds and related precursors, which can transfer a carbene fragment to a catalyst with concomitant loss of a stable byproduct. Despite the utility of this approach, there are persistent limitations in the scope of viable carbenes, most notably those lacking stabilizing substituents. By coupling carbene transfer chemistry with two‐electron redox cycles, it is possible to expand the available starting materials that can be used as carbene precursors. In this Minireview, we discuss emerging catalytic reductive cyclopropanation reactions using either gem‐dihaloalkanes or carbonyl compounds. This strategy is inspired by classic stoichiometric transformations, such as the Simmons–Smith cyclopropanation and the Clemmensen reduction, but instead entails the formation of a catalytically generated transition metal carbene or carbenoid. We also present recent efforts to generate carbenes directly from methylene (CR2H2) groups via a formal 1,1‐dehydrogenation. These reactions are currently restricted to substrates containing electron‐withdrawing substituents, which serve to facilitate deprotonation and subsequent oxidation of the anion.

Redox Approaches to Carbene Generation in Catalytic Cyclopropanation Reactions.

Transition metal-catalyzed carbene transfer reactions have a century-old history in organic chemistry and are a primary method for the synthesis of cyclopropanes. Much of the work in this field has focused on the use of diazo compounds and related precursors, which can transfer a carbene fragment to a catalyst with concomitant loss of a stable byproduct. Despite the utility of this approach, there are persistent limitations in the scope of viable carbenes, most notably those lacking stabilizing substituents. By coupling carbene transfer chemistry with two-electron redox cycles, it is possible to expand the available starting materials that can be used as carbene precursors. In this Minireview, we discuss emerging catalytic reductive cyclopropanation reactions using either gem-dihaloalkanes or carbonyl compounds. This strategy is inspired by classic stoichiometric transformations, such as the Simmons-Smith cyclopropanation and the Clemmensen reduction, but instead entails the formation of a catalytically generated transition metal carbene or carbenoid. We also present recent efforts to generate carbenes directly from methylene (CR2H2) groups via a formal 1,1-dehydrogenation. These reactions are currently restricted to substrates containing electron-withdrawing substituents, which serve to facilitate deprotonation and subsequent oxidation of the anion.

Enhanced Photobiocatalytic Cascades at Pickering Droplet Interfaces.

Developing new methods to engineer photobiocatalytic reactions is of utmost significance for artificial photosynthesis, but it remains a grand challenge due to the intrinsic incompatibility of biocatalysts with photocatalysts. In this work, photocatalysts and enzymes were spatially colocalized at Pickering droplet interfaces, where the reaction microenvironment and the spatial distance between two distinct catalysts were exquisitely regulated to achieve unprecedented photobiocatalytic cascade reactions. As proof of the concept, ultrathin graphitic carbon nitride nanosheets loaded with Au nanoparticles were precisely positioned in the outer interfacial layer of Pickering oil droplets to produce H2O2 under light irradiation, while enzymes were exactly placed in the inner interfacial layer to catalyze the subsequent biocatalytic oxidation reactions using in situ formed H2O2 as an oxidant. In the alkene epoxidation and thioether oxidation, our interfacial photobiocatalytic cascades showed a 2.0-5.8-fold higher overall reaction efficiency than the photobiocatalytic cascades in the bulk water phase. It was demonstrated that spatial localization of the photocatalyst and the enzyme at Pickering oil droplet interfaces not only provided their respective preferable reaction environments and intimate proximity for rapid H2O2 transport but also protected the enzyme from oxidative inactivation caused by the photogenerated species. These remarkable interfacial effects contributed to the significantly enhanced photobiocatalytic cascading efficiency. Our work presents an innovative photobiocatalytic reaction system with manifold benefits, providing a cutting-edge platform for solar-driven chemical transformations via photobiocatalysis.