Clean Oxidation Research Articles

Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects

Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects

Visible-Light-Mediated Oxidative Amidation of Aldehydes by Using Magnetic CdS Quantum Dots as a Photocatalyst.

A magnetic CdS quantum dot (Fe3 O4 /polydopamine (PDA)/CdS) was synthesized through a facile and convenient method from inexpensive starting materials. Characterization of the prepared catalyst was performed by means of FTIR spectroscopy, XRD, SEM, TEM, energy-dispersive X-ray spectroscopy, and vibrating-sample magnetometer techniques. Fe3 O4 /PDA/CdS was found to be a highly active photocatalyst for the amidation of aromatic aldehydes by using air as a clean oxidant under mild conditions. The photocatalyst can be recovered by magnetic separation and successfully reused for five cycles without considerable loss of its catalytic activity.

AIBN‐Initiated Oxidative Deoximation Reaction: A Metal‐Free and Environmentally‐Friendly Protocol

AbstractAIBN, a very common free radical initiator, was found to be efficient for oxidative deoximation reactions. The process could employ molecular oxygen as the mild, clean and safe oxidant in most cases and did not involve any transition metals. The applied initiator loading was as low as 2 mol%. This work reports a relatively green method for deoximation reactions and may be very practical for large‐scale applications.

Dual-catalyst engineered porous organic framework for visible-light triggered, metal-free and aerobic sp3 C[sbnd]H activation in highly synergistic and recyclable fashion

Photoredox and organo-catalysis denote powerful construction tools for new classes of carbon–carbon bonds, where incisive amalgamation of both the approaches over a single, recyclable platform can bring about synergic and eco-friendly reactions under mild conditions. Aiming at enamine-based photoredox catalysis for atom-economic and metal-free sp3 CH activation, an amide-based two-dimensional (2D) porous organic framework (POF) is devised. The pendent NH2 groups are judiciously anchored with two catalytic stations viz. Rose Bengal and L-proline, through stepwise variation of solid phase peptide synthesis. The dual-catalyst engineered POF represents a fully organic material that synergistically performs visible-light triggered oxidative Mannich reaction to produce biorelevant heterocycle β-amino ketone in excellent yield at room temperature, using oxygen as clean and selective oxidant. Importantly, activity of this bi-functionalized catalyst compares favorably well to individual homogeneous counterparts. The covalently modified framework demonstrates economic viability via gram-scale synthesis besides admirable reusability, and proves to be effective for nineteen varieties of substrates. The photocatalytic path is detailed from efficient energy transfer from host polymer to substrate in light of experimental and theoretical studies, which provides proof-of-concept to the photo-organo combined mechanism. The material benefits heterogenising two homogeneous catalysts, besides excluding additional steps of conventional Mannich reactions, and offers a step-forward to smart and green cross-dehydrogenative coupling reactions.

Copper(ii)-catalyzed and acid-promoted highly regioselective oxidation of tautomerizable C(sp3)-H bonds adjacent to 3,4-dihydroisoquinolines using air (O2) as a clean oxidant.

A mild, efficient and eco-friendly method for the oxidation of 1-Bn-DHIQs to 1-Bz-DHIQs without concomitant excessive oxidation of 1-Bz-DHIQs to 1-Bz-IQs is very important for the syntheses of 1-Bz-DHIQ alkaloids and analogues. In this article, we developed a novel Cu(ii)-catalyzed and acid-promoted highly regioselective oxidation of tautomerizable C(sp3)–H bonds adjacent to the C-1 positions of various 1-Bn-DHIQs. It was observed that when 0.2 equiv. of Cu(OAc)2·2H2O was used as the catalyst, 3.0 equiv. of AcOH was used as the additive and air (O2) was used as a clean oxidant, various 1-Bn-DHIQs could be efficiently oxidized to corresponding 1-Bz-DHIQs at 25 °C in DMSO. Especially, almost no concomitant excessive oxidation of 1-Bz-DHIQs to 1-Bz-IQs was observed during the above reaction. In addition, this method was successfully applied in the first total synthesis of the alkaloid canelillinoxine.

Copper-catalyzed in situ oxidative-coupling for one-pot synthesis of 5-aryl-1,4-disubstituted 1,2,3-triazoles under mild conditions.

A new reaction system with CuCl as catalyst, TEA as base and O2/chloramine-T as oxidant was developed for one-pot in situ oxidative-coupling to synthesize 5-aryl-1,4-disubstituted 1,2,3-triazoles in this paper. A variety of 5-arylated-1,2,3-triazole compounds could be efficiently prepared directly from the readily accessible organic azides, terminal alkynes and arylboronic acids. Advantages of the method include use of low-cost catalyst, clean oxidant, less-toxic additive, and low reaction temperature. Importantly, due to avoiding harsh strong basic reagents and high temperatures, the presented method can offer mild conditions for multi-component synthesis of 5-aryl-1,2,3-triazoles from the designed structurally complicated alkynyl or azide donors bearing natural product motifs and sensitive functional groups.

Mesoporous Silica Nanoparticles Supported Atomically Precise Palladium Nanoclusters Catalyzed Aerobic Oxidation of Alcohols in Water

The first mesoporous silica nanoparticles (MSNs) supported atomically precise palladium nanoclusters catalyzed alcohol oxidation reactions in water have been achieved. The catalysts was synthesized with simple impregnation method and well characterized by TEM, FT-IR, XPS anddiffuse reflectance optical spectrum and the results proved that the Pd nanoclustersimmobilized into the pores of MSNs.The as-prepared catalyst show excellent activity for the alcohol oxidation reactions with high yield under extremely mild aqueous conditions utilizes 1 atmosphere of molecular oxygen as sole oxidant. The features of clean system, gram-scale oxidation and easy recovery catalyst make this method cost effectively and environmentally benign.

Mesoporous Silica Nanoparticles Supported Atomically Precise Palladium Nanoclusters Catalyzed Aerobic Oxidation of Alcohols in Water

The first mesoporous silica nanoparticles (MSNs) supported atomically precise palladium nanoclusters catalyzed alcohol oxidation reactions in water have been achieved. The catalysts was synthesized with simple impregnation method and well characterized by TEM, FT-IR, XPS anddiffuse reflectance optical spectrum and the results proved that the Pd nanoclustersimmobilized into the pores of MSNs.The as-prepared catalyst show excellent activity for the alcohol oxidation reactions with high yield under extremely mild aqueous conditions utilizes 1 atmosphere of molecular oxygen as sole oxidant. The features of clean system, gram-scale oxidation and easy recovery catalyst make this method cost effectively and environmentally benign.

Catalytic behavior of the WOx-ZrO2 system in the clean selective oxidation of diphenyl sulfide (DPS)

WOx-ZrO2 (ZWx) based catalysts were prepared by equilibrium adsorption in basic condition (pH 10) with W content of 10.5, 19.7 and 27.0 wt.%, using hydrous zirconia [ZrO2(383)] as support. In order to determine the soluble fraction of W species which did not interact with the surface, samples were leached with NH3, dried and re-calcined [ZWx(NH3)y]. The W content was determined by spectrophotometric method, before and after the leaching. All catalysts were characterized by textural analysis (BET), X-ray diffraction (XRD) and Raman spectroscopy; the acidic strength was determined by potentiometric titration with n-butylamine.The catalytic behavior was analyzed for the selective oxidation of diphenyl sulfide (DPS) to diphenyl sulfoxide (DPSO) or diphenyl sulfone (DPSO2) using H2O2 as oxidizing agent. High conversion of DPS (∼100 %) and selectivity to DPSO2 (>90 %) at 60 min of reaction time were obtained for the ZWx series of catalysts. The ZWx(NH3)y series (W content: 3.65, 6.50 and 7.50 wt.%, respectively) also showed high selectivity to diphenyl sulfone but the maximum conversion (∼100 %) was achieved with reaction times longer (30 min) than those of the ZWx (10 min) samples.Polytungstate species strongly interacting with the support, identified by Raman spectroscopy in both series of samples, are considered the active phases.

A simple and efficient metal free, additive, or base free dehydrogenation of tetrahydroisoquinolines using oxygen as a clean oxidant

Metal free dehydrogenation of various substituted tetrahydroisoquinolines via a simple and convenient metal free, atom economical route for the synthesis of corresponding isoquinolines under oxygen atmosphere in N-methyl-2-pyrollidone (NMP) is described. Metal free dehydrogenation was carried out without the use of additive or base. A scope of the methodology was demonstrated for a number of aryl and heteroaryl substitutions present at C1 position and ester moiety at C3 position and was found to be good substrates. Substituted isoquinolines (3a–3h) and their esters (3i–3m) were synthesized in very good to excellent yields.

Clean and Selective Oxidation of Alcohols with Oxone and Phase-Transfer Catalysts in Water

A new, simple, metal-free, and eco-friendly procedure has been proposed for the oxidation of alcohols with Oxone (potassium peroxymonosulfate) in water in the presence of six phase-transfer catalysts (PTC). Phase-transfer catalysts were found to display high catalytic activity in water solution. Furthermore, the oxidation of alcohols was also carried out with relatively good conversion and selectivity in water without any catalyst.

Magnetite nanoparticles-catalyzed synthesis of conductive poly(p-aminodiphenylamine)

Para-aminodiphenylamine (p-ADPA) was successfully polymerized by simple, economical and environmentally improved procedure. Magnetite nanoparticles (Fe3O4 NPs) were found to successfully catalyze the oxidation of p-ADPA in the presence of hydrogen peroxide (H2O2), an eco-friendly and clean oxidant, with a very small amount of ammonium peroxydisulfate (APS) as an initiator. In this manner, the amount of by-products occurring during the reaction is drastically reduced. The oxidation of p-ADPA proceeded also in the absence of Fe3O4 NPs, but far more slowly than the catalyzed process. The influence of the mass ratio Fe3O4NPs/p-ADPA on the properties of products was systematically studied by different characterization techniques. Spectroscopic measurements (UV-Vis-NIR, FTIR, Raman, EPR) indicate that the polymerization products are polyaniline emeraldine salt-like polymers and their measured electrical conductivity is one of the highest values reported in the literature for p-ADPA oligomerization/polymerization products (1.8∙10-2 S cm-1). X-ray powder diffraction (XRPD) measurements revealed highly crystalline structure of Poly(p-ADPA) samples synthesized with Fe3O4 NPs, while scanning electron microscopy (SEM) showed layered and prismatic-shaped particles as prevailing in their morphology.

Catalytic activity of bis p-nitro A2B (oxo)Mn(V) corroles towards oxygen transfer reaction to sulphides

The 5 A2B Mn(III) corroles have been synthesized, fully characterized and used for oxygen atom transfer (OAT) from isolated (oxo)manganese(V)corrole to sulfide. Oxidation of Mn(III) were carried out using ozone, a clean oxidant, which resulted in the isolation of the 5 red- coloured (oxo)manganese(V) corroles. The stoichiometric OAT to a different p-thioanisoles gave a mechanistic insight. The electron withdrawing and electron donating group containing phenyl group substituents on C10meso carbon were synthesized to gain effect of substituents on the rate constant. The rate constant suggests the disproportionation reaction for OAT from (oxo)manganese(V) corrole to (oxo)manganese(IV) and (oxo)manganese(VI) corroles. Newly synthesized free bases were characterised by 1H NMR, UV–visible spectroscopy. Manganese(III) corrole, (oxo)manganese(V) corrole were characterized by UV–visible spectroscopy. Self-decay and oxygen atom transfer to sulfide rate constant were determined using UV–visible spectroscopy. Electrochemistry of these Mn(III) corroles shows the effect of meso phenyl substituents on the oxidation potential of Mn(III) corroles. DFT calculation of these synthesized Mn(III) corroles have been carried out and HOMO-LUMO gap varies with the substituents on meso carbons.

Epoxidation of propylene by hydrogen peroxide catalyzed by the silanol‐functionalized polyoxometalates‐supported ferrate: Electronic structure, bonding feature, and reaction mechanism

AbstractHydrogen peroxide (H2O2), as clean oxidant, has been disregarded due to its low efficiency and selectivity for the oxidation of olefins. In the present paper, the redox‐important ferrate anion (FeO42−) has been anchored to a silanol‐decorated polyoxometalates (POM) to form a single site‐supported Fe‐POM catalyst. Possible reaction mechanisms for the epoxidation of propylene with H2O2 catalyzed by the Fe‐POM catalyst have been investigated based on density functional theory with the M06L functional. The study of molecular geometry, electronic structure, and bonding feature shows that the Fe‐POM complex can be viewed as a high‐valent Fe‐oxo (FeO) species. The propylene molecule was activated by the Fe‐POM catalyst via an effective electron transfer from propylene to the Fe‐POM catalyst to form a cation propylene radical. Due to the high reactivity of radical species, the calculated activation energy barrier is only 4.50 kcal mol−1 for epoxidation of propylene to epoxypropane catalyzed by the Fe‐POM catalyst. Subsequently, the calculated free energy profiles show that H2O2 was decomposed into a H2O molecule and a surface O species over the Fe‐POM catalyst, and the remaining O atom attaches to the exposed Fe center, resulting in the replenishing of the Fe‐POM catalyst via a two‐state reaction pathway. The calculated activation energy barrier for this process is 23.42 kcal mol−1, and thus, decomposition of H2O2 is the rate‐determining step for the whole reaction. The Fe center serves as an electron acceptor, accepting electrons from the binding propylene molecule to form radical species in the first half of the reaction and, in the role of electron donor in the remaining reaction steps to eliminate the radical feature, reduces the reactivity and stops the reaction at the stage of the desired epoxypropane product.

Synthesis and Characterization of CoxOy–MnCO3 and CoxOy–Mn2O3 Catalysts: A Comparative Catalytic Assessment Towards the Aerial Oxidation of Various Kinds of Alcohols

CoxOy–manganese carbonate (X%)(CoxOy–MnCO3 catalysts (X = 1–7)) were synthesized via a straightforward co-precipitation strategy followed by calcination at 300 °C. Upon calcination at 500 °C, these were transformed to CoxOy–dimanganese trioxide i.e., (X%)CoxOy–Mn2O3. A relative catalytic evaluation was conducted to compare the catalytic efficiency of the two prepared catalysts for aerial oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using O2 molecule as a clean oxidant without utilizing any additives or alkalis. Amongst the different percentages of doping with CoxOy (0–7% wt./wt.) on MnCO3 support, the (1%)CoxOy–MnCO3 catalyst exhibited the highest catalytic activity. The influence of catalyst loading, calcination temperature, reaction time, and temperature and catalyst dosage was thoroughly assessed to find the optimum conditions of oxidation of benzyl alcohol (BzOH) for getting the highest catalytic efficiency. The (1%)CoxOy–MnCO3 catalyst which calcined at 300 °C displayed the best effectiveness and possessed the largest specific surface area i.e., 108.4 m2/g, which suggested that the calcination process and specific surface area play a vital role in this transformation. A 100% conversion of BzOH along with BzH selectivity >99% was achieved after just 20 min. Notably, the attained specific activity was found to be considerably larger than the previously-reported cobalt-containing catalysts for this transformation. The scope of this oxidation reaction was expanded to various alcohols containing aromatic, aliphatic, allylic, and heterocyclic alcohols without any further oxidation i.e., carboxylic acid formation. The scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) specific surface area analytical techniques were used to characterize the prepared catalysts. The obtained catalyst could be easily regenerated and reused for six consecutive runs without substantial decline in its efficiency.

Frontispiece: Room‐Temperature Laser Synthesis in Liquid of Oxide, Metal‐Oxide Core‐Shells, and Doped Oxide Nanoparticles

Laser synthesis of colloids emerged in recent years as a versatile approach to access a library of clean oxide nanoparticles relying on only four main strategies running at room temperature and ambient pressure: laser ablation in liquid, laser fragmentation in liquid, laser melting in liquid and laser defect-engineering in liquid. Here, established laser-based methodologies are reviewed through the presentation of a panorama of oxide nanoparticles. For more information, see the Review by V. Amendola, S. Barcikowski et al. on page 9206 ff.

Room-Temperature Laser Synthesis in Liquid of Oxide, Metal-Oxide Core-Shells, and Doped Oxide Nanoparticles.

Although oxide nanoparticles are ubiquitous in science and technology, a multitude of compositions, phases, structures, and doping levels exist, each one requiring a variety of conditions for their synthesis and modification. Besides, experimental procedures are frequently dominated by high temperatures or pressures and by chemical contaminants or waste. In recent years, laser synthesis of colloids emerged as a versatile approach to access a library of clean oxide nanoparticles relying on only four main strategies running at room temperature and ambient pressure: laser ablation in liquid, laser fragmentation in liquid, laser melting in liquid and laser defect‐engineering in liquid. Here, established laser‐based methodologies are reviewed through the presentation of a panorama of oxide nanoparticles which include pure oxidic phases, as well as unconventional structures like defective or doped oxides, non‐equilibrium compounds, metal‐oxide core–shells and other anisotropic morphologies. So far, these materials showed several useful properties that are discussed with special emphasis on catalytic, biomedical and optical application. Yet, given the endless number of mixed compounds accessible by the laser‐assisted methodologies, there is still a lot of room to expand the library of nano‐crystals and to refine the control over products as well as to improve the understanding of the whole process of nanoparticle formation. To that end, this review aims to identify the perspectives and unique opportunities of laser‐based synthesis and processing of colloids for future studies of oxide nanomaterial‐oriented sciences.

Synthesis of Pd-M@HCS(M = Co, Ni, Cu) Bimetallic Catalysts and Their Catalytic Performance for Direct Synthesis of H2O2

Hydrogen peroxide (H2O2), as a clean and green oxidant, is widely used in many fields. The direct synthesis of H2O2 (DSHP) from H2 and O2 has attracted most research interest because it relates to a facile, environmentally friendly, and economic process. Yolk–shell Pd-M@HCS (hollow carbon sphere) (M = Co, Ni, Cu) nanocatalysts, in which the bimetal nanoparticle is the core and porous carbon works as the shell layer, are reported in this work. It was found that catalytic activities were enhanced because of the introduced M metals. Additionally, the different mass ratios of Pd to Co (mPd/mCo) were further investigated to improve the catalytic performance for the DSHP. When mPd/mCo was 4.4, the prepared Pd-Co@HCS-(4.4) catalyst, with an average Pd nanoparticle size of 7.30 nm, provided the highest H2O2 selectivity of 87% and H2O2 productivity of 1996 mmolgPd−1·h−1, which were increased by 24% and 253%, respectively, compared to Pd@HCS.

Selective Oxyfunctionalisation Reactions Driven by Sulfite Oxidase‐Catalysed In Situ Generation of H2O2

AbstractH2O2 can be accepted by several peroxygenases as a clean oxidant, able to supply both the necessary electrons and oxygen atom at the same time. The biocatalysts, in turn, are able to catalyse an array of interesting oxygen insertion reactions at enantio‐ and regio‐selectivities hard to attain with classical chemical methods. The sensitivity of most peroxygenases towards H2O2, however, requires this oxidant to be generated in situ. Here, we suggest the application of (modified) sulfite oxidases to couple the oxidation of sulfites to the reduction of oxygen. This enables us to use calcium sulfite, an industrial waste product from scrubbing flue gases, as an electron donor to reduce oxygen. This will supply the required peroxide in a controlled manner and enables us to perform these challenging reactions at the expense of simple salts.

Preparation of nanoscale zero-valent metal for catalyzed clean oxidation of hydroxypropyl guar gum at a wide pH range

Preparation of nanoscale zero-valent metal for catalyzed clean oxidation of hydroxypropyl guar gum at a wide pH range