Hydroxyl radical formation upon dark oxidation of reduced iron minerals: Effects of iron species and environmental factors

Dark formation of hydroxyl radical upon oxidation of reduced iron minerals plays an important role in the degradation and transformation of organic and inorganic pollutants. Herein, we compared the hydroxyl radical formation from various reduced iron minerals at different redox conditions. OH production was generally observed from the oxidation of reduced iron minerals, following the order: mackinawite (FeS) > reduced nontronite (iron-bearing smectite clay) > pyrite (FeS₂) > siderite (FeCO₃). Structural Fe²⁺ and dissolved O₂ play critical roles in OH production from reduced iron minerals. OH production increases with decreasing pH, and Cl^? has little effect on this process. More importantly, dissolved organic matter significantly enhances OH production, especially under O₂ purging, highlighting the importance of this process in ambient environments. This sunlight-independent pathway in which OH forms during oxidation of reduced iron minerals is helpful for understanding the degradation and transformation of various inorganic and organic pollutants in the redox-fluctuation environments.     

Potentiometric and antimicrobial studies on the asymmetric Schiff bases and their binuclear Ni(II) and Fe(III) complexes; synthesis and characterization of the complexes

The protonation constants of two nitro-Schiff bases SB¹, SB² and three asymmetric tetradentate diimines H₂L¹, H₂L² and H₂L³ and the stability constants of their ML type binuclear Ni(II) and Fe(III) complexes have been determined potentiometrically. The asymmetric diimines are (2OH) RCHNC₆H₄CHNR′ (2OH) type compounds [where R = R′ = phenyl for H₂L¹; R = naphthyl, R′ = phenyl for H₂L² and R = R′ = naphthyl for H₂L³]. The effect of tautomeric forms on the acid-base properties of the diimines has been investigated and discussed. In addition, dimeric and binuclear Ni(II) and Fe(III) complexes of the diimines have been synthesized and characterized by physical and spectroscopic techniques. Also, in vitro antimicrobial activities of the diimines and the complexes have been evaluated against three bacteria: Micrococcus luteus (NRLL B-4375), Bacillus cereus (RSKK 863), Escherichia coli (ATCC 11230) and the fungus: Candida albicans (ATCC 10239).     

The electrochemical advanced oxidation processes coupling of oxidants for organic pollutants degradation: A mini-review

The electrochemical advanced oxidation processes(EAOPs) have been extensively applied in the treatment of organic pollutants degradation.Herein,the mini review provides the coupling systems about EAOPs and different oxidants(e.g.,persulfate(PS),peroxymonosulfate(PMS),and ozone(O_3)),including EAOPs-PS systems,EAOPs-PMS systems,EAOPs-peroxone systems,and photoelectro-oxidants systems,for the organic compounds degradation.The coupling system of EAOPs with oxidants is an effective way to improve the generated free radicals(e.g.,HO~·and SO_4~(·-)) concentration and to accelerate pollutant degradation.In this review,we make a summary of the homogeneous and heterogeneous EAOPs-oxidant processes.The reaction mechanisms of EAOPs combined with different oxidants are elucidated in detail,as well as the synergistic effect for improving the degradation and mineralization efficiency.     

New insight in the O2 activation by nano Fe/Cu bimetals: The synergistic role of Cu(0) and Fe(II)

This study demonstrated that as-synthesized nano Fe/Cu bimetals could achieve significant enhancement in the degradation of diclofenac (DCF), as compared to much slow removal of DCF by Cu(II) or zero valent iron nanoparticles (nZVI), respectively. Further observations on the evolution of O₂ activation process by nano Fe/Cu bimetals was conducted stretching to the preparation phase (started by nZVI/Cu²⁺). Interesting breakpoints were observed with obvious sudden increase in the DCF degradation efficiency and decrease in solution pH, as the original nZVI just consumed up to Fe(II) and Cu(II) appeared again. It suggested that the four-electrons reaction of O₂ and Cu-deposited nZVI would occur to generate water prior to the breakpoints, while Cu(0) and Fe(II) would play most important role in activation of O₂ afterwards. Through the electron spin resonance (ESR) analysis and quenching experiments, OH was identified as the responsible reactive species. Further time-dependent quantifications in the cases of Cu(0)/Fe(II) systems were carried out. It was found that the OH accumulation was positively and linearly correlated with nCu dose, Fe(II) consumption, and Fe(II) dose, respectively. Since either Cu(0) or Fe(II) would be inefficient in activating oxygen to produce OH, a stage-evolution mechanism of O₂ activated by nano Fe/Cu bimetals was proposed involving: (a) Rapid consumption of Fe(0) and release of Fe(II) based on the Cu-Fe galvanic corrosion, (b) adsorption and transformation of O₂ to O₂²⁻ at the nCu surface, and (c) Fe(II)-catalyzed activation of the adsorbed O₂²⁻ to OH.     

Silica supported potassium oxide catalyst for dehydration of 2-picolinamide to form 2-cyanopyridine

The dehydration of 2-picolinamide to produce 2-cyanopyridine was investigated thoroughly using silica supported potassium oxide as a heterogeneous catalyst. Both large specific surface area and pore size of SiO_2 (B) contributed to the favorable catalytic performance for the synthesis of 2-CP. In addition, the yield of 2-CP showed the linear relationship with the amounts of medium basicity of the catalysts,demonstrating that medium basic sites were the active sites of silica supported potassium oxide catalysts. The catalysts were further characterized by XRD and FT-IR to clarify the active species. The results indicated the Si—O—K group produced by the reaction of K_2CO_3 with Si—OH was the active species, which was further evidenced by the adjustment of the amount of Si—OH by silylation and hydroxylation procedure.     

Palladium-catalyzed direct ortho CX bond construction via CH activation of azobenzenes: Synthesis of (E)-1,2-b(2,6-dibromo(chloro)-phenyl)diazene

A palladium-catalyzed direct CX bond formation of azobenzenes with 1,3-dibromo-5,5-dimethylhydantoin or trichloro isocyanuric acid via CH activation has been developed. The reaction could proceed smoothly under an air atmosphere at 110 °C in the presence of Pd(Ph₃P)₄ in DCE and 13 examples of products were obtained.     

Advances in amide and thioamide assisted C(sp3)H functionalization

CH activation is gaining substantial attention from synthetic and process chemists in recent years. Regio- and stereo-selective CH functionalization particularly facilitated by carboxylic acids and derivatives as directing groups has been progressing to an extent that this transformation could be conceived as one of the steps to assemble molecules in modern retrosynthetic analysis. This digest paper covers the most recent developments in C(sp³)H functionalization using carboxylic acid derivatives such as amides or thioamides as a directing group and highlights new reaction discoveries and applications. The content of this review is organized based on the types of directing groups and the mechanism by which the C(sp³)H bond is believed to be activated.     

A synthesis of cephalostatin 1

A synthesis of cephalostatin 1 from hecogenin is described in detail. The gram-scale synthesis of south part features a Baeyer–Villiger oxidation of hecogenin to 16,20-diol, a selective oxidation of C16OH with Dess–Martin periodinane, a Rh(I)-catalyzed C15C16 double bond shift to C14C15 position, and a Hg(OAc)₂-mediated spiroketal formation from cyclic enol ethers with alkenyl side chain at 2-position. Key transformations in the synthesis of north part, also on gram scale, include an abnormal Baeyer–Villiger oxidation of hecogenin to the corresponding dinorcholanic lactone, where a catalytic amount of iodine acts as a traceless and catalytic switch, an umpolung of steroidal 22-aldehyde to forge C22C23 bond with good stereochemical control, a cascade spiroketal-forming process to establish DEF rings in one operation, and a selective oxidation of C3OH. There are also other noteworthy transformations that, although not used in our final route, are valuable and could be applied to other syntheses, including: intra- or intermolecular S_N2′ processes of C14-heteroatom-substituted C15C16 alkenes, an unprecedented rearrangement of β-adduct of D-ring dienes and singlet oxygen, a chelation-controlled methylallylation of C23 aldehyde, and so on.     

Visible light induced efficient activation of persulfate by a carbon quantum dots (CQDs) modified γ-Fe2O3 catalyst

In this study, a carbon quantum dots modified maghemite catalyst (CQDs@γ-Fe₂O₃) has been synthesized by a one-step solvothermal method for efficient persulfate (PDS) activation under visible light irradiation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) characterization indicated that the formation of heterojunction structure between CQDs and γ-Fe₂O₃ effectively reduced the catalyst band gap (E_g), favoring the separation rate of electrons and holes, leading to remarkable efficient sulfamethoxazole (SMX) degradation as compared to the dark-CQDs@γ-Fe₂O₃/PDS and vis-γ-Fe₂O₃/PDS systems. The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe³⁺. Electron paramagnetic resonance (EPR) and radical scavenging experiments demonstrated that both OH and SO₄⁻ were generated in the reaction system, while OH was relatively more dominant than SO₄⁻ for SMX degradation. Finally, the reaction mechanism in the vis-CQDs@γ-Fe₂O₃/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle. CQDs would enrich the photo-generated electrons from γ-Fe₂O₃, causing efficient interfacial generation of surface-bond Fe²⁺ and reduction of adsorbed Fe³⁺. This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.     

Efficient Fe(III)/Fe(II) cycling triggered by MoO2 in Fenton reaction for the degradation of dye molecules and the reduction of Cr(VI)

In this work, we develop an inorganic cocatalyst of commercial MoO₂ application in Fenton reaction, which can significantly enhance the Fe(III)/Fe(II) cycling efficiency to improve the oxidation activity for the remediation of Lissamine rhodamine B (L-RhB).     

Crystal structure,conformation and vibrational characteristics of diethyl 4,4′-disulfanediylbis(6-methyl-2-phenylpyrimidine-5-carboxylate) – A new pharmaceutical cure

The crystal and molecular structures of diethyl 4,4′-disulfanediylbis(6-methyl-2-phenylpyrimidine-5-carboxylate) have been determined by X-ray diffraction and quantum chemical DFT analysis. The title compound crystallizes in orthorhombic Pbca (D_2h¹⁵) space group, with one molecule in the asymmetric unit. The molecular structure of the studied compound has been determined using the DFT B3LYP/6-311G(2d,2p) approach and compared to that derived from X-ray studies. The IR and Raman spectra have been measured and their wavenumbers have been compared to those calculated for the optimized geometry of the studied compound. The characteristic vibrations of the 4,4′-dithiobispyrimidine N₂C₄SSC₄N₂ skeleton have been identified and on this basis the correlation between the disulfide bridge conformation and vibrational data have been discussed.     

DDQ-promoted C(sp3)H phosphorylation of cycloheptatriene

An efficient and convenient C(sp³)H phosphorylation has been achieved via the DDQ-promoted cross-dehydrogenative coupling between cycloheptatriene and P(O)H compounds at room temperature. This transformation provides a direct synthetic route to the construction of C(sp³)P bonds with good functional group compatibility, leading to the formation of cyclohepta-2,4,6-trien-1-ylphosphonates in up to 99% yield.     

An ab initio study of the valence tautomerism of type B mesoionic rings

The MP2 calculated Gibbs free energies of a series of type B mesoionic rings and their acyclic valence tautomers suggest that in the gas phase the relative stability of the mesoionic ring increases with single bond strength (SS > RNNR > OO). Inclusion of aqueous solvation in the calculations further favours the stability of the mesoionic ring by ～10–15 kcal mol^?1. Replacement of CR groups at ring positions by nitrogen atoms results in a significant increase in the relative stability of the mesoionic ring. Calculations of aromatic stabilization energy (ASE), together with the Bird aromaticity index (I₅), suggest that aromaticity decreases with aza substitution and the increase in relative stability is attributable to charge stabilisation by the electronegative nitrogen atoms, which more than compensates for any loss of aromaticity.     

Efficient decomposition of sulfamethoxazole in a novel neutral Fered-Fenton like/oxalate system based on effective heterogeneous-homogeneous iron cycle

In this study, efficient sulfamethoxazole (SMX) degradation was demonstrated in a novel neutral Fered-Fenton like/oxalate (electro-Fe²⁺/PDS/Ox, Fered-FL/Ox) system adopting pre-anodized Ti@TiO₂ cathode. Optimization of operational parameters was conducted and the whole reaction mechanism based on the critical solid-liquid interfacial reactions was explored. An efficient neutral heterogeneous-homogenous iron cycle would exist in the Fered-FL/Ox system, depending on the formation of specific COTi bonds through the inner sphere surface complex (ISSC) of Fe(C₂O₄)₃³⁻. It would induce ultrafast electron transfer from the cathode to the Fe^III core, effectively accelerating the neutral Fenton-like reactions and complete mineralization of SMX with relative low dosage of ferrous catalyst and applied voltage. The result of this study is expected to supply a good alternative in treating complex neutral industrial wastewaters     

Synthesis of 2,3,5,6-tetrasubstituted pyridines via selective three-component reactions of aldehyde and two different enaminones

The three-component synthesis of structurally unsymmetrical pyridines with polysubstituted structure has been realized via the catalytic system consisting of CuI and KHSO₄. The employment of two different enaminones is the main factor allowing the successful [3+2+1] construction of the pyridine ring based on the formation of two CC and one CN bonds.     

Stereocontrolled concise synthesis of (±)-halosaline through intramolecular C-H amination

Total synthesis of 2-(2-hydroxyalkyl)-piperidine alkaloid (±)-halosaline is described from 7-octen-4-ol using a Rh-catalyzed chemo- and diastereo-selective intramolecular CH amination of sulfamate ester, ring-closing metathesis, and S_N2 displacement reaction of the six-membered ring sulfamidate as the key steps.     

InP quantum dots on g-C3N4 nanosheets to promote molecular oxygen activation under visible light

Largely limited by the high dissociation energy of the OO bond, the photocatalytic molecular oxygen activation is highly challenged, which restrains the application of photocatalytic oxidation technology for atmospheric pollutants removal. Herein, we design and fabricate the InP QDs/g-C₃N₄ compounds. The introduction of InP QDs promotes the charge transfer within the interface resulting in the effective separation of photo-generated carriers. Furthermore, InP QDs greatly facilitates the activation of molecular oxygen and promote the formation of O₂⁻ under visible-light illumination. These conclusions are identified by experimental and calculation results. Hence, NO can be combined with the O₂⁻ to form OONO intermediate to direct conversion into NO₃⁻. As a result, the NO removal ratio of g-C₃N₄ has a onefold increase after InP QDs loaded and the generation of NO₂ is effectively inhibited. This work may provide a strategy to design highly efficient materials for molecular oxygen activation.     

Enhanced visible light photocatalytic activity of CeO2@Zn0.5Cd0.5S by facile Ce(IV)/Ce(III) cycle

In this study, CeO₂@Zn_0.5Cd_0.5S heterostructure (Ce@ZCS) is synthesized via a simple two-step hydrothermal method. The effect of CeO₂ loading on the visible-light photoactivity of Zn_0.5Cd_0.5S is mainly investigated. It is found that Ce@ZCS shows a 1.9 times activity as high as ZCS for the MB degradation. The improved activity mainly results from the significant enhanced charge separation by CeO₂, in which the electron transfer is obviously promoted by the facile Ce(IV)/Ce(III) cycle. The excited electrons of ZCS is easy to transfer to CeO₂, thus obviously increasing the charge separation of ZCS. The accepted electrons by CeO₂ may easily be captured by the adsorbed O₂ to form O₂⁻, and then O₂⁻ could combine with H⁺/H₂O to form HO₂, and OH. Finally, O₂⁻, h⁺ and OH are confirmed as the major oxidative species in photocatalytic reaction for Ce@ZCS, and a possible photocatalytic mechanism is proposed. The cheap, efficient Ce@ZCS photocatalyst could be applied for practical waste water treatment.     

Stereoselective synthesis of novel functionalized cyclohexanone derivatives via the condensation of aromatic aldehydes with acetoacetamide and the influence of the ortho-effect and autocondensation

A simple, inexpensive and stereoselective synthesis of novel functionalized cyclohexanone derivatives via the reaction of acetoacetamide with aromatic aldehydes in ethanol at room temperature is described. Additionally, the presence of substituents such as NO₂ and Cl in the ortho-position of the aldehyde aromatic ring resulted in the formation of novel piperidines. The use of Lewis acids such as iron(III) chloride and bismuth(III) nitrate as catalysts led to autocondensation of acetoacetamide and the formation of 2,4-dimethyl-6-oxo-1,6-dihydropyridine-3-carboxamide.