Metal-free Oxidation Research Articles

Vitamin B9 derived nitrogen-doped graphene for metal-free aerobic oxidation of biomass-derived chemicals

A superior carbocatalyst ultrahigh N-doped graphene (NG) was prepared by a novel self-sacrificial templating method of one-step annealing vitamin B9. The NG catalyst with pyrolysis temperature of 800 °C (abbreviated VB9-NG-800) has an ultrahigh nitrogen content of 13.5 wt% and demonstrated the highest activity for the oxidation of bio-based alcohols and terpenes with molecular oxygen without any additives. Systematic characterizations and quantum-chemical calculations further manifested that high contents of graphitic N and pyridinic N species in VB9-NG-800 promoted the generation of O2− active species from molecular oxygen effortlessly, resulting in excellent catalytic performance for aerobic oxidation.

Metal-free photocatalytic aerobic oxidation of biomass-based furfural derivatives to prepare γ-butyrolactone

A heterogeneous metal-free photocatalytic system was developed for photocatalytic aerobic oxidation of biomass-based furfural derivatives to prepare γ-butyrolactone under mild conditions (visible light, room temperature, no base, and O2 balloon).

Aerobic oxidation and oxidative esterification of alcohols through cooperative catalysis under metal-free conditions.

The ABNO@PMO-IL-Br material obtained by anchoring 9-azabicyclo[3.3.1]nonane-3-one N-oxyl (keto-ABNO) within the mesopores of periodic mesoporous organosilica with bridged imidazolium groups is a robust bifunctional catalyst for the metal-free aerobic oxidation of numerous primary and secondary alcohols under oxygen balloon reaction conditions. The catalyst, furthermore, can be successfully employed in the first metal-free self-esterification of primary aliphatic alcohols affording valued esters.

Boosting activity of molecular oxygen by pyridinium-based photocatalysts for metal-free alcohol oxidation

Pyridinium molecules are developed as electron- and energy-transfer mediators to boost the activity of air oxygen and thus achieve highly efficient photocatalytic oxidation of alcohols without any noble metal and additional co-catalysts/additives under mild conditions.

A proof of concept for cooperation from the quinone groups adjacent to N sites during the metal-free oxidation of glycerol by nitrogen-rich graphene oxide

A catalytic active site already present in an organic molecule was chemically tagged on the GO surface to prove the role of quinone groups adjacent to N sites in nitrogen-rich carbon materials for the metal-free oxidation of glycerol.

Synergistic catalysis within core-shell Fe3O4@SiO2 functionalized with triethylene glycol (TEG)-imidazolium ionic liquid and tetramethylpiperidine N-oxyl (TEMPO) boosting selective aerobic oxidation of alcohols

HypothesisIt is expected that incorporation of 2, 2, 6, 6-tetra-methyl piperidine-N-oxyl radical (TEMPO) and an imidazolium bromide bearing hydrophilic triethylene glycol (TEG) groups on Fe3O4@SiO2 core–shell may not only result in a novel highly water-dispersible/magnetically separable multi-functional catalyst system for metal-free aerobic oxidation of alcohols, which operates through a synergistic relay pathway, but it could potentially provide a strong platform for simultaneous separation and recycling of all components. ExperimentsThe catalyst was prepared by anchoring TEMPO moieties onto a magnetic core–shell Fe3O4@SiO2 functionalized with an ionic liquid bearing TEG groups. The materials was characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, thermal gravimetric analysis, and elemental analysis. The performance of the catalyst was evaluated and quantitatively measured in the aerobic oxidation of alcohols in water. FindingsThe catalyst exhibited excellent and stable colloidal dispersion in water and high performance in the aerobic oxidation of various types of alcohols under metal- and halogen-free reaction conditions. As hypothesized, strong synergistic effect between functionalized components was seen in the described reaction. The catalyst displayed excellent dual-adjustable-selectivity in the oxidation of primary alcohols to either the corresponding aldehydes or carboxylic acids by tuning the reaction solvent and/or reaction time and excellent recycling behavior through a “double-separation-strategy”.

Catalytic oxidation of small organic molecules by cold plasma in solution in the presence of molecular iron complexes\u2020

The plasma-mediated decomposition of volatile organic compounds has previously been investigated in the gas phase with metal oxides as heterogeneous catalysts. While the reactive species in plasma itself are well investigated, very little is known about the influence of metal catalysts in solution. Here, we present initial investigations on the time-dependent plasma-supported oxidation of benzyl alcohol, benzaldehyde and phenol in the presence of molecular iron complexes in solution. Products were identified by HPLC, ESI-MS, FT-IR, and ^{1}hbox {H NMR} spectroscopy. Compared to metal-free oxidation of the substrates, which is caused by reactive oxygen species and leads to a mixture of products, the metal-mediated reactions lead to one product cleanly, and faster than in the metal-free reactions. Most noteworthy, even catalytic amounts of metal complexes induce these clean transformations. The findings described here bear important implications for plasma-supported industrial waste transformations, as well as for plasma-mediated applications in biomedicine, given the fact that iron is the most abundant redox-active metal in the human body.

A Convenient Access to Functionalized Oxazol-2-One-5-Carboxylates from β-Aminoalcohols Through NBS-Light Mediated Oxidation of Cis- or Trans-N-Alkyloxazolidinones

An efficient methodology is developed involving a metal-free oxidation of cis or trans-trisubstituted oxazolidin-2-ones in the presence of NBS under light irradiation for the synthesis of N-alkyl oxazol-2-one-5-carboxylates. The mild conditions employed enable the efficient and rapid synthesis of a variety of those compounds in satisfactory yields.

Quinone-amine polymers derived N and O dual doped carbocatalyst for metal-free benzyl alcohol aerobic oxidation

Carbon-based materials are promising environmentally benign heterogeneous catalysts for metal-free catalysis. Aerobic oxidation of benzylic alcohol to aldehydes over carbocatalyst under mild reaction condition is still a great challenge. In the present work, quinone-amine based carbon (QAC) was rationally prepared from the qiunone-amine polymer. The QAC catalyst showed excellent catalytic efficiency for oxidation of benzyl alcohol to benzaldehyde in water. The TOF can reach 29.7 × 10−4 mol∙g-1 h-1 at room temperature under 1 bar O2. To our best knowledge, this is highest activity of metal-free carbocatalyst for the titled reaction. The doped O afforded active sites to enhance activity while doped N offered the radical confinement effect to guarantee the selectivity. The present results demonstrate the QAC catalyst is promising carbon materials for “green catalysis” of aerobic selective oxidation of benzyl alcohol to benzaldehyde.

Bio-based green solvent for metal-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfural over nitric acid-modified starch

The non-toxic biologic material of expanded corn starch (ECS)-supported nitric acid (ECS-HNO3 and ECS-NH2-HNO3) has been prepared via simple procedures. Both the materials are used as heterogeneous catalysts for the selective aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) with an up to 98% yield in γ-butyrolactone (GBL, a bio-based green solvent) containing as little as 10% (v/v) acetic acid (AcOH) after less than 5 h under ambient pressure of dioxygen at 50 oC. The ECS-NH2-HNO3 proved to be more stable than ECS-HNO3 and was repeatedly used five times with almost no change in its catalytic performance.

4-Dimethylaminopyridine-Catalyzed Metal-Free Aerobic Oxidation of Aryl α-Halo Esters to Aryl α-Keto Esters.

A novel, metal-free aerobic oxidation method is described. 4-Dimethylaminopyridine (DMAP) successfully catalyzed the oxidation of aryl α-halo esters to corresponding aryl α-keto esters (up to 95% yield) under mild reaction conditions (Li2CO3, dimethylacetamide, air, and room temperature). A mechanism has been proposed where the oxidation proceeds through a [3 + 2] cycloaddition between O2 in an air atmosphere and pyridinium ylides. The ylides are supposedly generated from aryl α-halo esters and DMAP in the presence of carbonates. Based on the plausible mechanism, the potential of DMAP as a catalyst in oxidation reactions was extended.

Single-phase Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 and Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 nanoparticles as efficient photocatalysts for the reduction of Cr(VI) and degradation of methylene blue dye

We report for the first time the use of noble metal-free multi-component equiatomic oxide as photocatalysts with excellent performance for natural sunlight driven degradation of Cr(VI) and methylene blue dye. The multi-component oxide nanoparticles with a composition Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 and Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 were synthesized by simple co-precipitation followed by peptization in acid to obtain nanoparticle sol and calcined at 500 °C. The nanopowders were characterized by x-ray diffraction (XRD), UV–Visible spectroscopy (UV–Vis), and high-resolution transmission electron microscopy (HRTEM). The complete (∼100%) reduction of Cr(VI) to Cr(III) was observed after 90 and 100 min for the calcined Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 and Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 respectively, under exposure to natural sunlight. In addition, 70% degradation of methylene blue is observed in 180 min. The effective photocatalytic activity of multi-component oxides can be attributed to their unique composition containing five components in equimolar amounts. The role of oxygen vacancies in photocatalytic reduction of Cr(VI) and the degradation of methylene blue is also discussed.

Engineering donor-acceptor conjugated organic polymers with boron nitride to enhance photocatalytic performance towards visible-light-driven metal-free selective oxidation of sulfides

In this work, a novel heterojunction photocatalyst (BN@TTCOP) was designed and fabricated by a facile in situ growth of boron nitride (BN) on donor-acceptor type thiophene-triazine based conjugated organic polymer (TTCOP). Results revealed that the incorporation of BN could simultaneously boost light harvesting and narrow bandgap structure. More importantly, the separation efficiency and interfacial transfer rate of photogenerated charge carriers of the TTCOP were greatly promoted since negatively charged BN might exceptionally attract photogenerated holes from the surface of TTCOP by electrostatic interaction between them. Benefiting from these features, BN@TTCOP heterojunctions exhibited superior photocatalytic activity under visible-light illumination for metal-free selective oxidation of sulfides; the highest activity reached to >99 % of conversion, which was nearly 2 times higher than that of pristine TTCOP. Further analyses unveiled that the mechanism for the photooxidation is probably triggered by photogenerated superoxide radical. This study highlights a promising strategy for enhancing photocatalytic performance.

Visible-Light-Responsive Anthraquinone Functionalized Covalent Organic Frameworks for Metal-Free Selective Oxidation of Sulfides: Effects of Morphology and Structure

Visible-light-responsive covalent organic frameworks (COFs) as photocatalysts for metal-free organic reactions are highly desirable due to their structural controllability and molecular functionali...

SYNTHESIS OF UREA-HYDROGEN PEROXIDE AND ITS APPLICATION FOR PREPARING THIOSULFINATE

The Urea-Hydrogen Peroxide complex (UHP) was synthesized from urea and hydrogen peroxide, characterized by FT-IR. This UHP complex could be employed as an oxidizing agent for metal-free oxidation reaction of disulfides to thiosulfinate compounds. This protocol was carried out under very mild conditions at 0oC in CH3CO2H solvent, was efficient and compatible with a range of alkyl, aryl or allyl disulfides to afford direct access to thiosulfinate compounds in very good yields up to 92% and high selectivities.

Acid-Promoted Intramolecular Decarbonylative Coupling Reactions of Unstrained Ketones: A Modular Approach to Synthesis of Acridines and Diaryl Ketones.

Herein, we reported Lewis acid- or Brønsted acid-promoted intramolecular C(sp2)-C(sp2) bond cleavage and a novel C(sp2)-C(sp2) bond-forming cascade reaction to synthesize the acridine motif. The metal-free oxidation of the alkyne motif generated the in situ ketone group extracted via a decarbonylation reaction. The mechanistic studies revealed that the electrophilic N-iodo species triggered key decarbonylation reactions via consecutive dearomatization/aromatization reactions. In addition, we exploited this acid-promoted C-C bond activation system with internal alkynes to synthesize bis(heteroaryl) ketones.

Hummers’ and Brodie’s graphene oxides as photocatalysts for phenol degradation

Undoped metal-free graphene oxide (GO) materials prepared by either a modified Hummers’ (GO-H) or a Brodie’s (GO-B) method were tested as photocatalysts in aqueous solution for the oxidative conversion of phenol. In the dark, the adsorptive capacity of GO-B towards phenol (~35%) was higher than that of GO-H (~15%). Upon near-UV/Vis irradiation, GO-H was able to remove 21% of phenol after 180 min, mostly through adsorption. On the other hand, by using less energetic visible irradiation, GO-B removed as much as 95% in just 90 min. By thorough characterization of the prepared materials (SEM, HRTEM, TGA, TPD, Raman, XRD, XPS and photoluminescence) the observed performances could be explained in terms of their different surface chemistries. The GO-B presents the lower concentration of oxygen functional groups (in particular carbonyl groups as revealed by XPS) and it has a considerably higher photocatalytic activity compared to GO-H. Photoluminescence (PL) of liquid dispersions and XRD analysis of powders showed lower PL intensity and smaller interlayer distance for GO-B relative to GO-H, respectively: this suggests lower electron-hole recombination and enhanced electron transfer in GO-B, in support of its boosted photocatalytic activity. Reusability tests showed no efficiency loss after a second usage cycle and over three runs under visible irradiation, which was in line with the similarity of the XPS spectra of the fresh and used GO-B materials. Moreover, scavenging studies revealed that holes and hydroxyl radicals were the main reactive species in play during the photocatalytic process. The obtained results, establish for the first time, that GO prepared by Brodie’s method is an active and stable undoped metal-free photocatalyst for phenol degradation in aqueous solutions, opening new paths for the application of more sustainable and metal-free materials for water treatment solutions.

Kraft lignin derived S and O co-doped porous graphene for metal-free benzylic alcohol oxidation

S and O co-doped graphene derived from lignin carbonization achieved 95.9% yield of benzaldehyde in metal-free oxidation of benzyl alcohol.

Sterically driven metal-free oxidation of 2,7-di-tert-butylpyrene

A new metal-free ortho oxidation of 2,7-di-tert-butylpyrene provides in high yield the corresponding 4,5-dione and 4,5,9,10-tetraone in environmentally benign solvents.

A practical route to azo compounds by metal-free aerobic oxidation of arylhydrazides using an NOx system

Metal-free aerobic oxidation of aryl hydrazides catalyzed by NOx was developed for the practical and environment friendly synthesis of azo compounds.