Green Oxidant Research Articles

Sulfate radical anion-induced benzylic oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines.

A mild, operationally convenient, and practical method for the synthesis of synthetically useful N-arylsulfonylimines from N-(arylsulfonyl)benzylamines using K2S2O8 in the presence of pyridine as a base is reported herein. In addition, a "one-pot" tandem synthesis of pharmaceutically relevant N-heterocycles by the reaction of N-arylsulfonylimines, generated in situ with ortho-substituted anilines is also reported. The key features of the protocol include the use of a green oxidant, a short reaction time (30 min), chromatography-free isolation, scalability, and economical, delivering N-arylsulfonylimines in excellent yields of up to 96%. While the oxidation of N-aryl(benzyl)amines to N-arylimines using K2S2O8 is reported to be problematic, the oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines using K2S2O8 has been achieved for the first time. The dual role of the sulfate radical anion (SO4·-), including hydrogen atom abstraction (HAT) and single electron transfer (SET), is proposed to be involved in the plausible reaction mechanism.

Green Synthesis of α-Keton Thiol Ester via Photocatalytic Oxidative Radical Addition of Thioic Acid to Alkene.

α-Keton sulfides are versatile building blocks in organic synthesis. From thioic acids and alkenes, we were able to develop the direct synthesis of α-keton thiol esters via photocatalytic oxidative radical additions. This reaction well matches the idea of green chemistry. It takes the advantage of thioxanthone as an inexpensive organic photocatalyst, O2 as a green oxidant, EtOAc as a green solvent, and visible light as a sustainable energy source, and the only byproduct is water.

Synthesis of Green Cerium Oxide Nanoparticles Using Plant Waste from Colocasia esculenta for Seed Germination of Mung Bean (Vigna radiata)

Synthesis of cerium oxide (CeO2) nanoparticles (NPs) via biological approach has received a lot of interest to reduce the harmful effects of chemical synthesis. In the present study, Colocasia esculenta leaf extract facilitated the preparation of CeO2-NPs by using the sol-gel technique. The crystal structural of CeO2-NPs was proven by X-ray powder diffraction (XRD) investigation to be cubic with size of 2.94 nm according to Debye–Scherrer equation. As demonstrated in the transmission electron microscopy (TEM) image, CeO2-NPs have a spherical form with an average size of 2.04 nm which is almost consistent with a finding from XRD analysis. Energy dispersive X-ray (EDX) measurements exhibited high-intensity peaks attributed to Ce and oxygen and further proved the creation of CeO2-NPs. The Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of Ce-O stretching, indicating the formation of CeO2-NPs. Functional groups of O-H, C-O, and C=O peaks were found in a spectrum due to the phytochemical components that were responsible for reducing and stabilizing during the synthesis process of CeO2-NPs. The examined UV-visible spectra exhibited the absorbance peak at 213 nm. The synthesized NPs produced in this study were further investigated for mung bean seed germination, whereby the influence of grain germination and growth rate demonstrated the significant finding.

An efficient and green synthesis of 2-phenylquinazolin-4(3H)-ones via t-BuONa-mediated oxidative condensation of 2-aminobenzamides and benzyl alcohols under solvent- and transition metal-free conditions

Abstract Quinazolinone synthesis usually requires employing sensitive substrates, hazardous solvents, large excess oxidants, and expensive catalysts. In this study, an efficient and environmentally benign pathway was developed to synthesize 2-phenylquinazolin-4(3H)-one via oxidative coupling between commercially available and stable chemicals, including 2-aminobenzamide and benzyl alcohol without toxic oxidizing agents and transition-metal catalysts. A high yield of the desired product (up to 84%) was obtained at 120°C for 24 h in the presence of oxygen as a green oxidant and t-BuONa as a base. Importantly, the study scope was expanded toward successfully producing various 2-phenylquinazolin-4(3H)-one derivatives in moderate-to-good yields. Furthermore, control experiments proposed that the conversion involved the initial partial oxidation of benzyl alcohol to the benzaldehyde intermediate under basic conditions, followed by the condensation, intramolecular nucleophilic addition, and oxidative dehydrogenation to 2-phenylquinazolin-4(3H)-one.

Spontaneous Osteogenic Differentiation of Human Mesenchymal Stem Cells by Tuna-Bone-Derived Hydroxyapatite Composites with Green Tea Polyphenol-Reduced Graphene Oxide.

In recent years, bone tissue engineering (BTE) has made significant progress in promoting the direct and functional connection between bone and graft, including osseointegration and osteoconduction, to facilitate the healing of damaged bone tissues. Herein, we introduce a new, environmentally friendly, and cost-effective method for synthesizing reduced graphene oxide (rGO) and hydroxyapatite (HAp). The method uses epigallocatechin-3-O-gallate (EGCG) as a reducing agent to synthesize rGO (E-rGO), and HAp powder is obtained from Atlantic bluefin tuna (Thunnus thynnus). The physicochemical analysis indicated that the E-rGO/HAp composites had exceptional properties for use as BTE scaffolds, as well as high purity. Moreover, we discovered that E-rGO/HAp composites facilitated not only the proliferation, but also early and late osteogenic differentiation of human mesenchymal stem cells (hMSCs). Our work suggests that E-rGO/HAp composites may play a significant role in promoting the spontaneous osteogenic differentiation of hMSCs, and we envision that E-rGO/HAp composites could serve as promising candidates for BTE scaffolds, stem-cell differentiation stimulators, and implantable device components because of their biocompatible and bioactive properties. Overall, we suggest a new approach for developing cost-effective and environmentally friendly E-rGO/HAp composite materials for BTE application.

Green and continuous aerobic oxidation of ethylbenzene over homogeneous and heterogeneous NHPI in a micro-packed bed reactor

Aerobic oxidation of ethylbenzene (EB) has emerged as a promising strategy for the selective synthesis of acetophenone (AP) in line with green chemistry. The integration of flow chemistry into the pharmaceutical industry has been facilitated by recent advancements in microreactor technology. In this work, a continuous micro-packed bed reactor platform is developed to determine the kinetics of aerobic EB oxidation in the presence of N-hydroxyphthalimide (NHPI). The microreactor system offers enhanced gas–liquid mass transfer, leading to a 2-order-of-magnitude increase in the space–time yield of EB oxidation compared to traditional batch reactors. Furthermore, the organic catalyst NHPI is covalently anchored on commercial activated carbon through an imidization reaction. The synthetic heterogeneous catalysts exhibit excellent performance in terms of AP yield of 87.4 % and TOF value of 2.21 h−1 for continuous aerobic EB oxidation.

Green synthesis, formation mechanism and oxidation of Ti3SiC2 powder from bamboo charcoal, Ti and Si

Using low-cost and highly reactive bamboo charcoal, Ti and Si elemental powders as starting materials, Ti3SiC2 powder was synthesized via a simple and cost-efficient pressureless sintering technique in argon atmosphere. The influences of synthesis temperature, holding time and Si content on the Ti3SiC2 content of the synthesized products were investigated, and the analysis indicated that the relative content of Ti3SiC2 reached 98.9 wt% with a molar ratio of 3Ti/1.2Si/2.2C at 1400 °C for 1.5 h. The Ti3SiC2 with good crystallinity and homogeneous nanolayered structure was synthesized at lower temperatures due to the high reactivity and high specific surface area of bamboo charcoal. The non-isothermal oxidation behavior showed that Ti3SiC2 powder was stable in air below 540 °C. With the temperature increasing up to 1300 °C, continuous and dense TiO2 and SiO2 oxidation layers were formed on the surface of Ti3SiC2 particles, which conferred good oxidation resistance to Ti3SiC2 powder.

Design and introduction of quaternary ammonium hydroxide‐functionalized graphene oxide quantum dots as a pseudo-homogeneous catalyst for epoxidation of α,β-unsaturated ketones

In present work, design and synthesis of a novel pseudo-homogeneous catalyst is described. For this purpose, amine-functionalized graphene oxide quantum dots (N-GOQDs) were prepared from graphene oxide (GO) by a facile one-step oxidative fragmentation approach. The prepared N-GOQDs were then modified with quaternary ammonium hydroxide groups. Various characterization techniques clearly revealed that the quaternary ammonium hydroxide‐functionalized GOQDs (N-GOQDs/OH−) have been successfully synthesized. TEM image revealed that the GOQDs particles are almost regularly spherical in shape and mono-dispersed with particle sizes < 10 nm. The efficiency of the synthesized N-GOQDs/OH− as a pseudo-homogeneous catalyst in epoxidation of α,β-unsaturated ketones in the presence of aqueous H2O2 as an oxidant at room temperature was investigated. The corresponding epoxide products were obtained in good to high yields. This procedure has the advantages of a green oxidant, high yields, involvement of non-toxic reagents and reusability of the catalyst without discernible loss in activity.

Visible-Light Photocatalytic CO2-to-CO and H2O-to-H2O2 by g-C3N4/Cu2O-Pd S-Scheme Heterojunctions.

Visible-light photocatalytic conversion of CO2-to-fuels for green electricity is sustainably attractive for alleviating carbon emissions. Photocatalytic CO2-to-CO frequently suffered from relatively low yields, mainly due to ineffective charge transfer rates. A new approach for photocatalytic CO2-to-CO enhanced with effective H+ from H2O-to-H2O2 through the water oxidation reaction (WOR) has been studied in the present work. Here, the nano palladium (9 wt %), serving as a cocatalyst, dispersed on the g-C3N4/Cu2O heterojunctions (i.e., g-C3N4/Cu2O-Pd) has been prepared to facilitate charge separation for the two-electron reduction of CO2 to CO. Experimentally, the g-C3N4/Cu2O-Pd heterojunctions have a higher photocatalytic H2O-to-H2O2 yield than the g-C3N4/Cu2O heterojunction by 5.3 times. The photocatalytic WOR provides sufficient electrons (e-) and H+ (2H2O → H2O2 + 2H+) for CO2-to-CO (CO2(aq) + 2H+ + 2e- → CO(g) + H2O(l)). Relatively high photocatalytic yields of H2O2 (34.0 μmol/mg) and CO (14.6 μmol/mg) affected by the heterojunctions can be achieved. Also, the heterojunctions have a high photostability with a photocatalytic generated CO/H2 ratio of 1.75 approximately. This visible-light photocatalytic CO2-to-CO and H2O-to-H2O2 by the new g-C3N4/Cu2O-Pd S-scheme heterojunctions demonstrates the feasibility of the zero carbon emission approach with additional green oxidant (H2O2) generation.

Nickel-Carbon Bond Oxygenation with Green Oxidants via High-Valent Nickel Species.

Described herein is the synthesis of the NiII complex (tBuMe2tacn)NiII(cycloneophyl) (tBuMe2tacn = 1-tert-butyl-4,7-dimethyl-1,4,7-triazacyclononane, cycloneophyl = -CH2CMe2-o-C6H4-) and its reactivity with dioxygen and peroxides. The new tBuMe2tacn ligand is designed to enhance the oxidatively induced bond-forming reactivity of high-valent Ni intermediates. Tunable chemoselectivity for Csp2-O vs Csp2-Csp3 bond formation was achieved by selecting the appropriate solvent and reaction conditions. Importantly, the use of cumene hydroperoxide and meta-chloroperbenzoic acid suggests a heterolytic O-O bond cleavage upon reaction with (tBuMe2tacn)NiII(cycloneophyl). Mechanistic studies using isotopically labeled H2O2 support the generation of a high-valent Ni-oxygen species via an inner-sphere mechanism and subsequent reductive elimination to form the Csp2-O bond. Kinetic studies of the exceptionally fast Csp2-O bond-forming reaction reveal a first-order dependence on both (tBuMe2tacn)NiII(cycloneophyl) and H2O2, and thus an overall second-order reaction. Eyring analysis further suggests that the oxidation of the NiII complex by H2O2 is the rate-determining step, which can be modulated by the presence of coordinating solvents. Moreover, computational studies fully support the conclusions drawn from experimental results. Overall, this study reveals for the first time the ability to control the oxidatively induced C-C vs C-O bond formation reactions at a Ni center. Importantly, the described system merges the known organometallic reactivity of Ni with the biomimetic oxidative transformations resembling oxygenases and peroxidases, and involving high-valent metal-oxygen intermediates, which is a novel approach that should lead to unprecedented oxidative catalytic transformations.

Combination of H2O2-producing microbial desalination cells and UV/H2O2 advanced oxidation process: Water salinity reduction and microbial inactivation

Microbial desalination cells (MDCs) are bioelectrochemical devices that can recover usable energy and chemicals from organic wastes and concurrently desalinate saltwater. MDCs can also produce the green oxidant, H2O2, through a two-electron oxygen reduction reaction occurring on the cathode electrode. If MDCs producing H2O2 are used in the pretreatment of brackish water or seawater for reverse osmosis (RO) processes, the salinity of feed water can be reduced in MDCs and the MDC-produced H2O2 can be utilized onsite to oxidize organic contaminants or disinfect microorganisms in the feed water. This strategy of using MDC pretreatment may substantially alleviate the energy requirements and biofouling tendency of downstream RO units. Herein, we assessed the applicability of a combination of H2O2-producing MDCs and ultraviolet (UV) or UV254nn -based advanced oxidation process (AOP) (i.e., UV/H2O2) as pretreatment for RO processes. We first examined the effect of catholyte conditions, which is one of the most crucial factors directly affecting the H2O2 composition and decomposition, on the performance of MDCs. Then, we evaluated the microorganism disinfection efficiencies of advanced photo-oxidation processes using H2O2 obtained from MDCs. The MDC investigated herein achieved 93.1% desalination efficiency and > 5.0 mM H2O2 concentration. In addition, UV-based AOP with the produced H2O2 demonstrated up to 15-fold higher inactivation kinetics than that by UV254 nm disinfection alone.

Photocatalytic Synthesis of Hydrogen Peroxide from Molecular Oxygen and Water

Hydrogen peroxide is a powerful and green oxidant that allows for the oxidation of a wide span of organic and inorganic substrates in liquid media under mild reaction conditions, and forms only molecular water and oxygen as end products. Hydrogen peroxide is therefore used in a wide range of applications, for which the well-documented and established anthraquinone autoxidation process is by far the dominating production method at the industrial scale. As this method is highly energy consuming and environmentally costly, the search for more sustainable synthesis methods is of high interest. To this end, the article reviews the basis and the recent development of the photocatalytic synthesis of hydrogen peroxide. Different oxygen reduction and water oxidation mechanisms are discussed, as well as several kinetic models, and the influence of the main key reaction parameters is itemized. A large range of photocatalytic materials is reviewed, with emphasis on titania-based photocatalysts and on high-prospect graphitic carbon nitride-based systems that take advantage of advanced bulk and surface synthetic approaches. Strategies for enhancing the performances of solar-driven photocatalysts are reported, and the search for new, alternative, photocatalytic materials is detailed. Finally, the promise of insitu photocatalytic synthesis of hydrogen peroxide for water treatment and organic synthesis is described, as well as its coupling with enzymes and the direct insitu synthesis of other technical peroxides.

Utilizing Graphene Oxide (GO) Catalysed Cascade in the Synthesis of Tetracyclic Pyrano[3,4‐b]indole Derivatives

AbstractA simple, highly effective synthesis of tetracyclic pyrano[3,4‐b]indoles derivatives from simple 2‐indolylmethanols and trione alkenes has been accomplished through oxa‐Michael addition‐Friedel–Crafts reaction‐cyclization cascade promoted by a cheap and green graphene oxide catalyst. Under mild conditions, the reaction afforded a range of pyrano[3,4‐b]indole scaffolds, which are an important structural unit of different bioactive molecules, in excellent yields. Most importantly, in the cascade reaction of 2‐indolylmethanols with trione alkenes, the nanocatalyst not only activates trione alkene substrates by forming hydrogen‐bonding, but also promotes the following intramolecular ring formation and dehydration. Moreover, graphene oxide showed high recyclability in this reaction and could be used in gram scale synthesis. To the best of our knowledge, graphene oxide is used for the first time in the synthesis of functionalized tetracyclic dihydropyranoindole derivatives.

Green Oxidation of Isochromans to Isochromanones with Molecular Oxygen Catalyzed by a Tetranuclear Vanadium Cluster

Comprehensive SummaryIsochromanone is the core structure of many bioactive compounds. Direct oxidation of isochromans is one of leading methods for the construction of isochromanones, while most established processes remain suffering from the use of environmentally unfriendly metal oxidants, harsh reaction conditions, and the difficulty in catalyst recycling and product separation. Herein, we report a convenient, cost‐effective, and green method for the synthesis of high‐value added isochromanones via isochroman oxidations with O2 by a novel heterogeneous vanadium cluster catalyst (Cat.1) under mild conditions. This reaction protocol demonstrates high catalytic activity with good catalyst recyclability and reusability for a wide scope of substrates.

Green synthesis and characterization of iron oxide nanoparticles for the removal of heavy metals (Cd2+ and Ni2+) from aqueous solutions with Antimicrobial Investigation

Clove and green Coffee (g-Coffee) extracts were used to synthesize green iron oxide nanoparticles, which were then used to sorb Cd2+ and Ni2+ ions out of an aqueous solution. Investigations with x-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption and desorption (BET), Zeta potential, and scanning electron microscopy were performed to know and understand more about the chemical structure and surface morphology of the produced iron oxide nanoparticles. The characterization revealed that the main component of iron nanoparticles was magnetite when the Clove extract was used as a reducing agent for Fe3+, but both magnetite and hematite were included when the g-Coffee extract was used. Sorption capacity for metal ions was studied as a function of sorbent dosage, metal ion concentration, and sorption period. The maximum Cd2+ adsorption capacity was 78 and 74 mg/g, while that of Ni2+ was 64.8 and 80 mg/g for iron nanoparticles prepared using Clove and g-Coffee, respectively. Different isotherm and kinetic adsorption models were used to fit experimental adsorption data. Adsorption of Cd2+ and Ni2+ on the iron oxide surface was found to be heterogeneous, and the mechanism of chemisorption is involved in the stage of determining the rate. The correlation coefficient R2 and error functions like RMSE, MES and MAE were used to evaluate the best fit models to the experimental adsorption data. The adsorption mechanism was explored using FTIR analysis. Antimicrobial study showed broad spectrum antibacterial activity of the tested nanomaterials against both Gram positive (S. aureus) (25923) and Gram negative (E. coli) (25913) bacteria with increased activity against Gram positive bacteria than Gram negative one and more activity for Green iron oxide nanoparticles prepared from Clove than g-Coffee one.

Visible-Light-Responsive Nano CuO/ZnO Photocatalyst for Chan–Lam Coupling Reaction and Aerobic C(sp3)–H Bond Oxidation

AbstractWhen it comes to heterogeneous photocatalysts, semiconductors are the best candidate with a high potential to respond in visible-light regions. In this study, semiconductor p-n heterojunction, nano CuO/ZnO, was synthesized via a simple, sustainable, and low-cost approach. Photocatalytic activity of the synthesized material with a 2.02 eV band gap was investigated in the Chan–Lam coupling reaction and C(sp3)–H bond oxidation of alkyl aromatic compounds under visible-light irradiation in aqueous solution. In the case of the Chan–Lam coupling reaction, various derivatives of aniline and arylboronic acid successfully took part in the reaction, delivering the desired products in 57–89% yields. In addition, nano CuO/ZnO photocatalyst showed high efficiency in the C(sp3)–H bond oxidation of alkyl aromatic compounds under air as a green oxidant. Noticeably, the photocatalyst showed high performance in the large-scale synthesis of desired products and maintained activity after several uses.

Catalytic activity of Mn(III) porphyrin complex supported onto cross linked polymers in the green oxidation of malathion with hydrogen peroxide in aqueous solution

Developing effective, affordable, and recoverable heterogeneous catalysts is one of the foremost challenges in modern chemistry. Mn(III) complexes of 5-(4-aminophenyl) −10, 15, and 20-triphenyl porphyrin 1 immobilized covalently on polymethyl methacrylate (PMMA) 2 and poly(methyl methacrylate –co- styrene) (PMMA/ST) 3 were synthesized, characterized, and applied for degradation of malathion with H2O2 in aqueous solution. Mn(III) porphyrin complex anchored on cross linked polymers 4 and 5 show high catalytic activity for malathion (pesticide) degradation in an aqueous solution with green oxidant H2O2. The catalytic efficacy of malathion degradation was highest with the Mn(III) porphyrin complex covalently anchored on (polymethyl methacrylate-co-styrene) 5. The optimum conditions, including the effect of pH, catalyst concentration, and H2O2 concentration on the degradation of malathion, were investigated. The reuse and stability of catalysts were examined, and the findings proposed that the Mn(III) porphyrin complex 5 has no noticeable changes in the removal efficiency up to five consecutive cycles. GC–MS analyses showed that the degraded compounds and intermediates formed from malathion degradation were non-toxic to E. coli bacteria. For the degradation of dissolved malathion pesticides in an aqueous solution, the use of Mn(III) porphyrin complex 5 in the presence of H2O2 has the potential to be advantageous.

Laccases from Pleurotus ostreatus applied to the oxidation of furfuryl alcohol for the synthesis of key compounds for polymer industry.

Laccases are oxidative enzymes with high synthetic potential. In this work, we prove their value in biocatalysis through the green and selective oxidation of furfuryl alcohol into furfural with the aid of mediators. The influence of different parameters such as pH, enzyme/mediator composition, buffer type, cosolvent tolerance and reaction times were deeply investigated. Under the optimal conditions, 20 mol% of TEMPO as mediator, and 5.8 U mL-1 of laccases POXC and POXA1b from Pleurotus ostreatus allowed to achieve quantitative production of furfural after 16 h. POXC laccase stood out for its ability to catalyze the reaction at pH 6.5, meanwhile POXA1b highlighted for its high stability. Furfural conversions reached excellent values (95%) after 72 h using only 5 mol% of TEMPO at 100 mM. Furthermore, furfuryl alcohol bioamination was successfully achieved employing the amine transaminase from Chromobacterium violaceum, providing furfuryl amine, a key compound for polymer industry, through a one-pot sequential approach.

A Comparative Study of Green and Chemical Cerium Oxide Nanoparticles (CeO2-NPs): From Synthesis, Characterization, and Electrochemical Analysis to Multifaceted Biomedical Applications

A Comparative Study of Green and Chemical Cerium Oxide Nanoparticles (CeO2-NPs): From Synthesis, Characterization, and Electrochemical Analysis to Multifaceted Biomedical Applications

Facile synthesis of CoSi alloy catalysts with rich vacancies for base- and solvent-free aerobic oxidation of aromatic alcohols

The rational design and green synthesis of low-cost, robust, and efficient catalysts for the selective oxidation of various alcohols are highly challenging. Herein, we report a fast and solvent-free arc-melting (AM) method to controllably synthesize a semimetallic CoSi alloy catalyst (denoted as AM-CoSi) that is efficient in the base- and solvent-free oxidation of six types of aromatic alcohols. X-ray absorption fine structure analysis, electron paramagnetic resonance spectroscopy, and aberration-corrected high angle annular dark field scanning transmission electron microscopy confirmed the successful synthesis of AM-CoSi with abundant Si vacancies (Siv). The as-prepared CoSi alloy catalysts exhibit an order of magnitude greater activity in the oxidation of a model reactant, benzyl alcohol (BAL) to benzyl benzoate (BBE), compared with their mono-counterparts, and provide 70% yield of BBE, the highest yield reported to date. Experimental results and density functional theory calculations suggest that the CoSi alloy structure improves the BAL conversion and that Si vacancy is the main contributor to the generation of BBE, based on which a potential reaction pathway is rationally proposed. Furthermore, the CoSi alloy maintains high stability and also exhibits high activity in the selective oxidation of various alcohols with different functional groups. This work demonstrates for the first time that semimetallic CoSi alloys can be robust catalysts for the green oxidation of various alcohols and proviedes a vast opportunity for the rational design and application of other semimetal alloy catalysts.