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In this paper, five recombinant strains: GS115-LacA, GS115-LacB, GS115-LacC, KM71H-Lcc1 and GS115-Lcc2 were selected to produce laccase isozymes with high activities, which reached 13,001 U/L, 10,254 U/L, 11,495 U/L, 9924 U/L and 10,031 U/L on 15th, respectively. Then, we investigated the specificity of several recombinant laccase isozymes for the degradation of endocrine disrupting chemicals (phenolic compounds). The results showed that LacB had the most efficient in degradation of bisphenol A and octyl phenol, while Lcc1 degraded 4-n-octylphenol, gossypol and hydroquinone better. Finally, the effects of degradation conditions were optimized, which shown that the degradation rates of phenolic compounds increased with the optimum temperature and pH by different laccases were different, which were closely related to their enzymatic properties. Under the optimum reaction conditions, the degradation rate of bisphenol A, gossypol, 4-n-octylphenol, octyl phenol and hydroquinone were 95.4%, 93.2%, 89.6%, 71.0% and 91.9% at 8 h, 8 h, 12 h, 24 h and 1 h, respectively. Furthermore, the recombinant laccases were used to degrade phenolic compounds in several laccase/mediator systems, which ABTS and vanillin showed most enhancement on degradation rates and reduction of degradation times. In LacB-ABTS and Lcc1-guaiacol/vanillin systems, the degradation rates of five phenolic compounds reached the maximum with totally 100% within 4 h. All of the results open up promising perspectives for the degradation and oxidative biotransformation of typical phenolic pollutants in the environment.

Herein, a highly sensitive electrochemical immunosensor was presented for the cardiac troponin I (cTnI) determination using a multifunctional covalent organic framework-based nanocomposite (HRP-Ab2-Au-COF) as the signal amplification probe. The spherical COF with a large surface area was synthesized in a short time by a simple solution-based method at room temperature. The good biocompatibility, low toxicity, and high stability in water of the COF guarantee its application in biosensing. Besides, its high porosity makes it an excellent carrier for loading abundant horseradish peroxidase (HRP). The modified gold nanoparticles on the surface of COF not only provide a load platform for secondary antibody (Ab2) but also improve the conductivity of COF. Under the synergistic effect of the hydrogen peroxide (H2O2) and HRP, hydroquinone (HQ) in the solution is catalytically oxidized to benzoquinone (BQ), which is then reduced on the electrode surface to generate the electrochemical signal. The designed probes not only show the specific recognition behavior of Ab2 to cTnI but also improve the sensitivity of the biosensing system due to the signal amplification caused by the excellent enzyme catalytic performance of HRP. Based on the H2O2-HRP-HQ signal amplification system, the biosensor for cTnI was fabricated and exhibited a linear response as a function of logarithmic cTnI concentration ranging from 5 pg/mL to 10 ng/mL, and the detection limit was 1.7 pg/mL. Moreover, the biosensor exhibited excellent recovery and reproducibility in the actual sample testing. This work provided a simple approach to determine cTnI quantitatively in practical samples and broadened the utilization scope of the COF-based nanocomposite in the electrochemical immunosensor.

The alkylation process involves two competitive paths of O- and C-alkylation and achieving better selectivity for desired products is a very challenging problem. The development of new process for ...

In this work, we showed that aquacobalamin (H2OCbl) undergoes decomposition in the presence of glucose oxidase and glucose under aerobic conditions at pH 6.3. This process is contributed by two reactions performed by glucose oxidase, i.e. (i) H2OCbl transformation to cob(II)alamin in the course of the reaction with reduced form of glucose oxidase, and (ii) hydrogen peroxide generation. Further reaction between cob(II)alamin and H2O2 results in macrocycle destruction. Although the reaction between H2OCbl and reduced glucose oxidase is slow, it is accelerated by several phenols and 1,4-benzoquinone. The most pronounced effect of 1,4-benzoquinone and hydroquinone can be explained by the formation of complexes with reduced glucose oxidase, which are more reactive toward H2OCbl than initial reduced glucose oxidase. 1,4-benzoquinone accelerates H2OCbl decomposition in glucose oxidase/glucose system as well.

Palladium(II)-catalyzed allylic acetoxylation has been the focus of extensive development and investigation. Methods that use molecular oxygen (O2) as the terminal oxidant typically benefit from the use of benzoquinone (BQ) and a transition-metal (TM) cocatalyst, such as Co(salophen), to support oxidation of Pd0 during catalytic turnover. We previously showed that Pd(OAc)2 and 4,5-diazafluoren-9-one (DAF) as an ancillary ligand catalyze allylic oxidation with O2 in the absence of cocatalysts. Herein, we show that BQ enhances DAF/Pd(OAc)2 catalytic activity, nearly matching the performance of reactions that include both BQ and Co(salophen). These observations are complemented by mechanistic studies of DAF/Pd(OAc)2 catalyst systems under three different oxidation conditions: (1) O2 alone, (2) O2 with cocatalytic BQ, and (3) O2 with cocatalytic BQ and Co(salophen). The beneficial effect of BQ in the absence of Co(salophen) is traced to synergistic roles of O2 and BQ, both of which are capable of oxidizing Pd0 to PdII The reaction of O2 generates H2O2 as a byproduct, which can oxidize hydroquinone to quinone in the presence of PdII NMR spectroscopic studies, however, show that hydroquinone is the predominant redox state of the quinone cocatalyst in the absence of Co(salophen), while inclusion of Co(salophen) maintains oxidized quinone throughout the reaction, resulting in better reaction performance.

For current carbon-supported Pt catalysts in vehicle proton exchange membrane fuel cells (PEMFCs), the insufficient stability and durability of carbon supports are severe limitations under operating conditions. This paper adopts the accelerated stress test (AST) method to study the carbon corrosion of catalysts, which is significant to efficiently select the catalysts supports in fuel cells. Graphitized carbon blacks with various surface properties are heated under different conditions, followed by evaluation of their antioxidation capacity with the AST. It is shown that optimally graphitized carbon blacks demonstrate superior stability, retaining a constant quinone/hydroquinone (QH) transition peak potential for over 70,000 AST cycles. A Pt catalyst supported on the selected graphitized carbon exhibits excellent durability at both the rotating disk electrode (RDE) and membrane electrode assembly (MEA) levels. The final specific mass activity (MA) of the optimum catalyst is 47.87 mA/mgPt, which is 2.06 times that of commercial Pt/C (23.31 mA/mgPt) in the RDE tests. The final maximum power density of the optimum catalyst is 525.68 mW/cm2, which is 305.52 mW/cm2 higher than that of commercial Pt/C after undergoing the AST during the MEA measurements. These results prove that the rational surface features of carbon supports play a vital role in improving the overall fuel cell performance by realizing uniform dispersion of Pt nanoparticles, resisting corrosion, and reinforcing metal–support interactions.

The competitive hydrogenation and hydrodeoxygenation (HDO) of dihydroxybenzene isomers, catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene) and hydroquinone (1,4-dihydroxybenzene), was studied in the liquid phase over a Rh/silica catalyst at 323 K and 3 barg hydrogen pressure. Under competitive hydrogenation conditions an order of reactivity of ortho > para > meta was observed. Catechol initially inhibited resorcinol and hydroquinone hydrogenation but not HDO suggesting separate sites for hydrogenation and HDO. When resorcinol and hydroquinone were reacted competitively, HDO became the favoured reaction. The data suggested that cyclohexane and cyclohexanone were primary products. At low dihydroxybenzene (DHB) conversion the ratio of HDO products was dependent upon DHB isomer. When all three DHB isomers were reacted together, initially 86% of the HDO yield came from catechol with the rest from hydroquinone. When resorcinol finally reacted, HDO products were produced first. Reaction of DHB isomers in pairs using deuterium instead of hydrogen revealed changes in kinetic isotope effect (KIE). The presence of competing reactants had a dramatic effect on the energetics of hydrogenation and HDO reactions of individual components, reinforcing the view that hydrogenation and HDO are mechanistically separate. This effect on reaction energetics observed when more than one substrate was present, highlights the limitations of studying one single model compound as a route to understanding the processes required for the upgrading of a true bio-oil feed.

The mechanism and kinetic features of hydrodeoxygenation of hydroquinone over the oxygen-defective anatase (a-TiO2) supported gold (Au) catalyst were studied by density functional theory calculatio...

Stochastic collision electrochemistry is a hot topic in single molecule/particle research, which provides an opportunity to investigate the details of the single molecule/particle reaction mechanism that is always masked in ensemble-averaged measurements. In this work, we develop an electrochemical amplification strategy to monitor the electrocatalytic behavior of single G-quadruplex/hemin (GQH) for the reaction between hydrogen peroxide and hydroquinone (HQ) through the collision upon a gold nanoelectrode. The intrinsic peroxidase activities of single GQH were investigated by stochastic collision electrochemical measurements, giving further insights into understanding biocatalytic processes. Based on the unique catalytic activity of GQH, we have also designed a hybridization chain reaction strategy to detect miRNA-15 with good selectivity and sensitivity. This work provided a meaningful strategy to investigate the electrochemical amplification and the broad application for nucleic acid sensing at the single molecule/particle level.

Hybrid composites of phosphomolybdic acid@UiO-66 (PMo12@UiO-66) and Co-substituted phosphomolybdic acid@UiO-66 (PMo11Co@UiO-66) were synthesized using the direct solvothermal method. A variety of characterization results demonstrated that phosphomolybdic acid (PMo12) or Co-substituted phosphomolybdate acid (PMo11Co) clusters are uniformly dispersed in the cages of Zr-based metal-organic UiO-66 frameworks. The catalytic properties of these hybrid composites were investigated by applying the epoxidation of olefins with tert-butyl hydroperoxide as the oxidant. Compared to PMo12@UiO-66, PMo11Co@UiO-66 showed a much higher catalytic activity and was simply recovered by filtration and reused for at least ten runs without significant loss of catalytic activity. Particularly, PMo11Co@UiO-66 can efficiently convert cyclic olefins like limonenes to epoxides, and its selectivity to 1,2-limonene oxide reached 91% in the presence of a radical inhibitor such as hydroquinone. The excellent catalytic activity and stability of the hybrid composite PMo11Co@UiO-66 are mainly attributed to the uniform distribution of highly active PMo11Co units within the smaller cages of UiO-66, to the suitable surface polarity of the hybrid composite for facilitating the access of reagents and solvent, and to the strong interface-interactions between the polyoxometalate and the UiO-66 framework.

Nitrate-intercalated Mg/Cu/Al-layered double hydroxides (LDHs) were successfully synthesized by the co-precipitation method under ultrasonic irradiation as a fast, simple, and low-cost technique. The LDHs were synthesized with six different molar ratios of Cu2+/Mg2+, and then they were characterized by FT-IR, XRD, TGA, ICP, BET, TEM, and FE-SEM analyses. The results showed that the nitrate ions were well intercalated between layers without any carbonate ions. According to the XRD and TGA results, increasing of Cu ions in the LDHs lowered the crystallization and improved the thermal stability of samples at the same time. The morphological studies carried out by FE-SEM and TEM analyses showed the morphological structure similar to the lamellar structure and plate-like shape particles. However, the surface property of binary LDHs, including Al and only one of Cu or Mg elements, was better than ternary ones. Furthermore, this catalyst was used for the phenol hydroxylation using H2O2 as oxidant and water as a solvent. The results exhibit that the CuMg32Al-NO3− catalyst had the best catalytic activity, as well as it was found that the catalyst is active under mild reaction conditions such as the temperature of 65 °C, phenol: oxidant ratio of 2:1, phenol/catalyst = 100, and reaction time of 1 h. Thus, these conditions gave better activity with the conversion of 27%, the selectivity of 92.05% for catechol and hydroquinone, and CAT/HQ ratio of 1.5.

Organo-radical catalysts have recently attracted great interest, and the development of this field can be expected to broaden the applications of organocatalysis. Herein, the first example of a radical-generating system is reported that does not require any photoirradiation, radical initiators, or preactivated substrates. The oxidative C-C-bond cleavage of 2-substituted cyclohexanones was achieved using an azolium salt and a hydroquinone as co-catalysts. A catalytic mechanism was proposed based on the results of diffusion-ordered spectroscopy and cyclic voltammetry measurements, as well as computational studies.

The degradation of paracetamol (PCT) in an aqueous medium using the Fenton and photo-Fenton reactions was investigated. The aim of this research was the development of a kinetic model based on a reaction mechanism, which includes two main intermediates of PCT degradation and the local volumetric rate of photon absorption (LVRPA). Ferrioxalate was used as a catalyst and the working pH was adjusted to 5.5 (natural pH). Experimental work was planned through a D-optimal experimental design and performed in a flat plate reactor irradiated by a solar simulator. Hydrogen peroxide (HP) concentration, reaction temperature, and radiation level were the operating parameters. The photo-Fenton reaction allowed to reach a minimum relative PCT concentration of 2.01% compared to 5.04% achieved with Fenton reaction. Moreover, the photo-Fenton system required a 50% shorter reaction time and lower HP concentration than in dark conditions (90 min and 189 mg L-1 vs. 180 min and 334 mg L-1, respectively). The experimental results were used to estimate the kinetic parameters of the proposed kinetic model employing a nonlinear, multi-parameter regression method. The values obtained from the normalized root-mean-square error (14.52, 1.96, 4.36, 13.16, and 8.72 % for PCT, benzoquinone, hydroquinone, HP, and oxalate, respectively) showed a good agreement between the predicted and experimental data.

The construction of a nanozyme that mimics a natural enzyme is a promising strategy to obtain a highly stable catalyst. Laccases are members of copper-containing oxidases, as environmental catalysts, and show significant potential in biotechnology and environmental remediation. In this study, inspired by the active site and electron transfer of laccase, a new laccase mimic (defined as CA-Cu) was synthesized via the coordination of copper with a cysteine (Cys)–aspartic acid (Asp) dipeptide. The as-prepared CA-Cu nanozyme exhibits significant laccase-like activity and catalytic oxidation of a wide range of phenolic pollutants, such as 2,4-dichlorophenol, phenol, p-chlorophenol, 2,6-dimethoxyphenol, hydroquinone, o-nitrophenol and o-aminophenol hydroquinone. It has a similar Km (Michaelis constant), a higher vmax (maximum rate) and better recyclability than laccase at the same mass concentration. In addition, the CA-Cu nanozyme is robust in a broad temperature range (0–100 °C), at extreme pH and under long-term storage. Surprisingly, the catalytic performance of the CA-Cu nanozyme was enhanced under high-salt conditions or at high concentrations of heavy metal ions, which lead to severe loss in the catalytic activity of laccase. We believe that this nanozyme is a promising environmental catalyst for the treatment of phenolic pollutants under high-salt or heavy metal ion conditions.

Hydroquinone is an electron-rich connector, and it contains phenolic hydroxyls similar to electron-deficient 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP). In this paper, two conjugated microporous polymers (THQ and HHQ) were synthesized via the nucleophilic substitution reactions of hydroquinone with cyanuric chloride (CC) and hexachlorocyclotriphosphazene (HCCP). The structures of the CMPs were fully characterized by FT-IR, ss 13C NMR, and elemental analysis. The BET specific surface areas of THQ and HHQ are 71.55 and 24.16 m2 g−1. THQ and HHQ have excellent fluorescence sensing performance for DNP and TNP, respectively, with high Ksv of 6.50 × 104 and 2.30 × 105 L mol−1 and low limit of detections (LODs) of 1.85 × 10−10 and 1.30 × 10−11 mol L−1.

An efficient method for the synthesis of benzannelated macrocyclic di- and triperoxides by cyclocondensation of phenol, catechol, resorcinol or hydroquinone with bis-hydroperoxides and formaldehyde in the presence of lanthanide catalysts has been developed. Additionally, by using flow cytometry, it has been shown for the first time in this work that thus-synthesized macrocyclic di- and triperoxides are efficient apoptosis inducers in the tumor cultures Jurkat, K562 and U937 and in fibroblasts.

A high-performance electrochemical sensing platform based on CuS nano-globules is efficiently developed. The CuS nano-globules are synthesized through a hydrothermal process. All the important physical characteristics of the nanomaterial such as crystal architecture, morphology, topography and composition are investigated. To better demonstrate the electrochemical sensing capability of CuS nano-globules reinforced electrodes, hydroquinone (HQE) is chosen as an analyte. Upon the electrochemical investigation, the CuS-based sensor displayed an enhanced detection limit of 0.135 μM with a linear range of 1–2287 μM. The overall sensing performance of CuS nano-globules-equipped electrode towards HQE is very impressive with good stability and reproducibility. These investigative results evidently indicate the superior electrochemical properties of CuS nano-globules and they can be highly recommended for real-time analysis.

Hydroquinone (HQ) is poorly degradable in the ecological environment and is highly toxic to human health even at a low concentration. The colorimetric method has the advantages of low cost and fast analysis, which provides the possibility for simple and rapid detection of HQ. In this work, a new colorimetric method has been developed for HQ detection based on a peroxidase-like catalyst, α-Fe2O3@CoNi. This sweetsop-like α-Fe2O3@CoNi catalyst enables H2O2 to produce hydroxyl (˙OH), leading to the oxidization of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxTMB. In the presence of HQ, the blue oxTMB is reduced to colorless, which allows for colorimetric detection of HQ in water samples. This method has been validated by detecting HQ in water samples with high selectivity, rapid response, broad detection range (0.50 to 30 μM), and low detection limit (0.16 μM).

Three-dimensional interconnected porous carbon nanosheets were prepared through pyrolyzing sodium D-isoascorbic acid, and were thoroughly characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The specific surface area and pore size distribution of the porous carbon nanosheets were characterized by N2 adsorption desorption. The thickness of the carbon nanosheet was measured by atomic force microscopy (AFM). An electrochemical sensor was fabricated by the modification of the porous carbon nanosheets onto a glassy carbon electrode surface. The electrochemical behaviors of hydroquinone (HQ) and catechol (CA) on the electrochemical sensor were investigated by cyclic voltammetry and differential pulse voltammetry. Under the optimized conditions, the peak currents were found to be linear to the HQ and CA concentrations in the range from 0.4 to 20 μmol L−1, and the detection limits were 0.028 μmol L−1 (HQ) and 0.035 μmol L−1 (CA), respectively.

The catalytic pyrolysis mechanism of the initial lignin depolymerization products will help us develop biomass valorization strategies. How does isomerism influence reactivity, product formation, selectivities, and side reactions? By using imaging photoelectron photoion coincidence (iPEPICO) spectroscopy with synchrotron radiation, we reveal initial, short-lived reactive intermediates driving benzenediol catalytic pyrolysis over H-ZSM-5 catalyst. The detailed reaction mechanism unveils new pathways leading to the most important products and intermediates. Thanks to the two vicinal hydroxyl groups, catechol (o-benzenediol) is readily dehydrated to form fulvenone, a reactive ketene intermediate, and exhibits the highest reactivity. Fulvenone is hydrogenated on the catalyst surface to phenol or is decarbonylated to produce cyclopentadiene. Hydroquinone (p-benzenediol) mostly dehydrogenates to produce p-benzoquinone. Resorcinol, m-benzenediol, is the most stable isomer, because dehydration and dehydrogenation both involve biradicals owing to the meta position of the hydroxyl groups and are unfavorable. The three isomers may also interconvert in a minor reaction channel, which yields small amounts of cyclopentadiene and phenol via dehydroxylation and decarbonylation. We propose a generalized reaction mechanism for benzenediols in lignin catalytic pyrolysis and provide detailed mechanistic insights on how isomerism influences conversion and product formation. The mechanism accounts for processes ranging from decomposition reactions to molecular growth by initial polycyclic aromatic hydrocarbon (PAH) formation steps to yield, e.g., naphthalene. The latter involves a Diels–Alder dimerization of cyclopentadiene, isomerization, and dehydrogenation., Detection of reactive intermediates with synchrotron radiation and photoelectron photoion coincidence methods reveals new mechanistic insights into lignin catalytic pyrolysis. Here we focus on how the isomerism changes the conversion and product formation.

The development of cost effective and efficient nanomaterials with enzyme mimetics and photocatalytic activity has achieved tremendous research interest in the quantitative detection as well as removal of toxic environmental pollutants. CuS nanoparticles decorated MoS2 sheets were successfully synthesized adopting a simple hydrothermal technique and using low-cost materials. The nanocomposite was successfully used as an efficient catalyst for the selective detection and removal of a toxic phenolic compound like hydroquinone (HQ). The CuS–MoS2 nanocomposite catalyzed the oxidation of different chromogenic substrates like 3,3′,5,5′-tetramethylbenzidine, 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)diammonium salt, and o-phenylenediamine in the presence of H2O2, indicating its peroxidase-like activity as natural Horseradish peroxidase (HRP). The catalytic performance of the nanozyme was further investigated through the typical Michaelis−Menten kinetics. The results showed that the proposed sensor exhibited improved catalytic properties with a wide linear relationship (0.4–50 μM) and a low detection limit of 3.68 μM for HQ detection in aqueous medium. Meanwhile, the mechanism of HQ sensing in the presence of CuS–MoS2 nanozyme was systematically investigated. Moreover, the CuS–MoS2 nanozyme possessed significant photocatalytic activity and 83% HQ decomposition was achieved within 240 min under irradiation of natural sunlight. The mechanism of enhanced photocatalytic degradation of HQ through the formation of ˙OH radicals as reactive species was evidenced by analyzing the formation of fluorescent active molecules on the addition of terephthalic acid and by high-resolution mass spectrometry. Thus CuS–MoS2 represents a new and promising HQ sensing material in a highly sensitive and fast manner as well as an efficient photocatalyst for the degradation of HQ to its non-toxic products under natural sunlight irradiation.

Non-natural photoenzymatic reactions reported to date have depended on the excitation of electron donor-acceptor complexes formed between substrates and cofactors within protein active sites to facilitate electron transfer. While this mechanism has unlocked new reactivity, it limits the types of substrates that can be involved in this area of catalysis. Here we demonstrate that direct excitation of flavin hydroquinone within "ene"-reductase active sites enables new substrates to participate in photoenzymatic reactions. We found that by using photoexcitation these enzymes gain the ability to reduce acrylamides through a single electron transfer mechanism.

Palladium(II)-catalyzed oxidation reactions represent an important class of methods for selective modification and functionalization of organic molecules. This field has benefitted greatly from the discovery of ancillary ligands that expand the scope, reactivity, and selectivity in these reactions; however, ancillary ligands also commonly poison these reactions. The different influences of ligands in these reactions remain poorly understood. For example, over the 60-year history of this field, the PdII/0 redox potentials for catalytically relevant Pd complexes have never been determined. Here, we report the unexpected discovery of (L)PdII(OAc)2-mediated oxidation of hydroquinones, the microscopic reverse of quinone-mediated oxidation of Pd0 commonly employed in PdII-catalyzed oxidation reactions. Analysis of redox equilibria arising from the reaction of (L)Pd(OAc)2 and hydroquinones (L = bathocuproine, 4,5-diazafluoren-9-one), generating reduced (L)Pd species and benzoquinones, provides the basis for determination of (L)PdII(OAc)2 reduction potentials. Experimental results are complemented by density functional theory calculations to show how a series of nitrogen-based ligands modulate the (L)PdII(OAc)2 reduction potential, thereby tuning the ability of PdII to serve as an effective oxidant of organic molecules in catalytic reactions.

An encapsulation-structured Fe2O3@meso-ZSM-5 (Fe@MZ5) was fabricated by confining Fe2O3 nanoparticles (ca. 4 nm) within the ordered mesopores of hierarchical ZSM-5 zeolite (meso-ZSM-5), with ferric oleate and amphiphilic organosilane as the iron source and meso-porogen, respectively. For comparison, catalysts with Fe2O3 (ca. 12 nm) encapsulated in intra-crystal holes of meso-ZSM-5 and with MCM-41 or ZSM-5 phase as the shell were also prepared via sequential desilication and recrystallization at different pH values and temperatures. Catalytic phenol hydroxylation performance of the as-prepared catalysts using H2O2 as oxidant was compared. Among the encapsulation-structured catalysts, Fe@MZ5 showed the highest phenol conversion and hydroquinone selectivity, which were enhanced by two times compared to the Fe-oxide impregnated ZSM-5 (Fe/Z5). Moreover, the Fe-leaching amount of Fe@MZ5 was only 3% of that for Fe/Z5. The influence of reaction parameters, reusability, and · OH scavenging ability of the catalysts were also investigated. Based on the above results, the structure-performance relationship of these new catalysts was preliminarily described.

The use of molecular oxygen in palladium‐catalyzed oxidation reactions is highly widespread in organic chemistry. However, the direct reoxidation of palladium by O2 is often kinetically unfavored, thus leading the deactivation of the palladium catalyst during the catalytic cycle. In the present work, we report a highly selective palladium‐catalyzed carbocyclization of bisallenes to seven‐membered heterocycles under atmospheric pressure of O2. The use of a homogenous hybrid catalyst (Co(salophen)‐HQ, HQ=hydroquinone) significantly promotes efficient electron transfer between the palladium catalyst and O2 through a low‐energy pathway. This aerobic oxidative transformation shows broad substrate scope and functional group compatibility and allowed the preparation of O‐containing seven‐membered rings in good yields in most cases., Heterocycles: We report a PdII‐catalyzed oxidative carbocyclization of the rationally designed bisallenes using molecular oxygen. By applying a bifunctional catalyst (Co(salophen)‐HQ) as an efficient electron‐transfer mediator, bisallenes are effectively converted to the corresponding seven‐membered carbocycles in good yields (see scheme).

Direct hydroxylation of benzene to phenol with dioxygen is a green route for synthesis of phenol. The higher bonding energies of C–H in benzene and O–O in dioxygen make metal-free catalysis a challenge. A novel metal-free catalyst of quinone-cylcohexanone-formaldehyde polymer was rationally designed and prepared. The polymer was characterized with FT-IR, XRD, Raman, SEM, 13C NMR and XPS. Abundant oxygen functional groups of cyclic ketonic, quinone carbonyl and hydroquinone were found on the surface of polymer. The catalytic performances for hydroxylation of benzene to phenol with dioxygen over the metal-free catalyst were investigated and a phenol yielding of 11.4% was achieved. Moreover, the reaction mechanism was proposed.

As synthesized AgBr nanoparticles (NPs) and g-C3N4 nanosheets were synthesized and coupled to obtain the AgBr-g-C3N4 catalyst, It showed a boosted activity in the photodegradation of methyl orange (MO) in aqueous solution (1.6 and 1.3 times greater than just the AgBr and g-C3N4 NPs in the initial degradation experiments without any optimization, respectively). The composite was characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), cyclic voltammetry (CV), etc. The modified carbon paste electrode by the composite showed a significant increase in peak current, confirming a significant increase in charge transfer between the semiconductors of the coupled system. The bandgap energies of the samples were estimated by both DRS and CV methods. The composite with an AgBr:g-C3N4 mole ratio of 2:1 showed the best photocatalytic activity. The initial pH of the MO solution was changed from 6.5 to 5.5 during the photodegradation process. Experimental design by RSM was used for the study of the interaction effects between the influencing variables. The conditions of the optimized run were: pH: 3.5, Catalyst dosage: 0.9 g/L, Time: 83 min, CMO: 3.2 ppm, while those of the central point were: pH: 6.1, Catalyst dosage: 0.99 g/L, Time: 82.50 min, CMO: 2.9 ppm. Various degradation intermediates such as benzene, phenol, catechol, hydroquinone, aniline, dimethylamine, benzoquinone, p-amino phenol, ethendiol, ethylene glycol, oxalic acid, maleic acid, 1-propenoic acid, sulfate, etc. were detected by GC-Mass. Further attacking of hydroxyl and superoxide radicals can easily mineralize these intermediates to water, carbon dioxide, and other inorganic species.