Oxidation Of CH Bonds Research Articles

Role of oxygen vacancy in spinel (FeCoNiCrMn)3O4 high entropy oxides prepared via two different methods for the selective C[sbnd]H bond oxidation of p-chlorotoluene

The selective CH bond oxidation of aromatic hydrocarbon is an interesting but challenging task, it is desirable to develop efficient heterogeneous non-noble metal catalyst for this reaction. Herein, two kinds of spinel (FeCoNiCrMn)3O4 high entropy oxides were fabricated via two different methods (i.e., c-FeCoNiCrMn, prepared by a co-precipitation method, and m-FeCoNiCrMn, prepared by physically mixing method). Different from traditional environmentally-unfriendly Co/Mn/Br system, the prepared catalysts were employed for the selective CH bond oxidation of p-chlorotoluene to p-chlorobenzaldehyde in a green approach. Compared to m-FeCoNiCrMn, c-FeCoNiCrMn have smaller particles size and larger specific surface area, which were related to the enhanced catalytic activity. More importantly, characterization results disclosed that abundant oxygen vacancies were formed over c-FeCoNiCrMn. Such a result facilitated the adsorption of p-chlorotoluene on the catalyst surface and promoted the formation of *ClPhCH2O intermediate as well as the desired p-chlorobenzaldehyde, as revealed by DFT (Density functional theory) calculations. Besides, scavenger tests and EPR (Electron paramagnetic resonance) results indicated that hydroxyl radical derived from H2O2 homolysis was the main active oxidative species for this reaction. This work revealed the role of oxygen vacancy in spinel high entropy oxide and also demonstrated its promising application for the selective CH bond oxidation in an environmentally-benign approach.

Application of chiral Betti base-copper complexes in enantioselective allylic oxidation of olefins, computational studies of the Betti bases, and docking of the resulting chiral allylic esters

Chiral (R)- and (S)-Betti bases have been initially synthesized from resolution of the corresponding racemic mixture by diastereomeric recrystallization method using l-(+)-tartaric acid, and then the copper complexes of the Betti bases have been studied in enantioselective allylic CH bond oxidation of olefins. This kind of ligands gave enantioenriched allylic esters with good to high yields and satisfactory enantioselectivities under optimized conditions. In addition, the thermodynamic stability of the Betti base mixture and binding energy between the racemic Betti bases and l-(+)-tartaric acid in the resolution process have been calculated using the M06–2X method and 6–311++G(d,p) basis set. Furthermore, the bioactivity of the synthesized chiral allylic esters has been investigated towards the PI3Kα enzyme with the use of AutoDock Vina.

A copper-catalyzed oxidative intramolecular cyclization approach for the synthesis of mesoionic [1,2,3]triazo[5,1-a]isoquinoliums

Treatment of 1-alkyl-4-(2-alkynylphenyl)triazoles with copper acetate resulted in the formation of mesoionic [1,2,3]triazo[5,1-a]isoquinoliums via 6-endo-dig cyclization and CH bond oxidation.

Acidic permanganate oxidation of sulfamethoxazole by stepwise electron-proton transfer

Permanganate is a versatile chemical oxidant, and has undergone a dramatic evolution toward deep insight into its reaction mechanism. However, the hydrogen abstraction of the NH bond by permanganate remains unclear. We studied the permanganate oxidation of the emerging micropollutant sulfamethoxazole in acidic aqueous solution. The reaction followed autocatalytic kinetics and demonstrated first-order with respect to each reactant. The presence of HMnO4 accelerated the reaction rate, which was four orders of magnitude higher than that of MnO4−. Based on the identified products, the rate-limiting step was determined to be simple NH bond oxidation by metal-oxo species permanganate. The mechanism was then studied computationally by density functional theory (DFT) using ammonia as the simplest model. Results showed that the NH bond oxidation by MnO4− (32.86 kcal/mol) was a concerted mechanism similar to that of CH bond oxidation, whereas HMnO4 oxidation of the NH bond (10.44 kcal/mol) was a stepwise electron-proton transfer. This reminds us that coordination of Brønsted acid could not only produce the stronger electrophile but also change the reaction mode by avoiding the bond cleavage in electron transfer process.

Synthesis, structural characterization and C[sbnd]H activation property of a tetra-iron(III) cluster

A non-heme tetra-iron cluster, [Fe4III(μ-O)2(μ-OAc)6(2,2′-bpy)2(H2O)2](NO3−)(OH−) (1), [OAc = acetate; 2,2′-bpy = 2,2′-bipyridine] containing oxido- and acetato-bridges was synthesized and structurally characterized by different spectroscopic methods including single crystal X-ray diffraction studies. X-ray crystal structure analysis of 1 revealed that tetra-iron complex was crystallized in monoclinic system with C2/c space group. Each of the Fe centres in 1 was found to exist in octahedral geometry and interconnected by oxido- and acetato-bridges. Bond valence sum (BVS) calculation recommended the existence of iron centres in +3 oxidation state. Variable temperature magnetic measurement authenticated the dominating antiferromagnetic ordering among the iron centres in the solid state of 1. This tetra-iron cluster was also evaluated as an efficient catalytic system towards the oxidation of both linear & cyclic alkanes without production of primary CH bond oxidation products. Oxidation of secondary CH bonds attested the formation of both the corresponding alcohols & ketones in 27–900 TONs. The tetra-iron catalytic system with Alcohol/Ketone values 0.2–1.7 indicated the involvement of freely diffusing carbon-centered radicals rather than metal based oxidant.

Photocatalytic anion oxidation achieves direct aerobic difunctionalization of alkenes leading to β-thiocyanato alcohols

A novel visible light-driven oxidative cascade reaction for the synthesis of β-thiocyanato alcohols via difunctionalization of alkenes is described for the first time. In this protocol inorganic ion thiocyanate was successfully converted into radical through photocatalysis by employing Rose Bengal as a photocatalyst to mediate the single-electron transfer. This hydroxylation process did not need extra reducing agent and the new CS and CO bonds could be constructed in one pot. Molecular oxygen not only was used as an excellent terminal oxidant, but also served as a green oxygen source, which is one of the most ideal processes to realize CH bond oxidation functionalization. Moreover, the reaction also proceeded very well under irradiation of sunlight.

Chemoselective oxidation and deprotection of para-methoxybenzylic position with (diacetoxyiodo)benzene in acetic-trifluoroacetic acid

(Diacetoxyiodo)benzene in the presence of acetic–trifluoroacetic acid in THF has been developed for the chemoselective para-methoxybenzylic CH bond oxidation to provide aryl carbonyl compounds at room temperature. The reaction condition is also applicable for the chemoselective deprotection of para-methoxybenzyl (PMB) ether in the presence of benzyl ether.

Mechanistic study for the selective oxidation of benzene and toluene catalyzed by Fe(ClO4)2 in an H2O2-H2O-CH3CN system

Iron(II) perchlorate in an H2O-H2O2-CH3CN mixture was used to efficiently carry out CH bond activations of benzene to form phenol and/or hydroquinone, and of toluene to form benzaldehyde, benzyl alcohol, o-cresol, p-cresol, and/or methyl-p-benzoquinone. The reactions were facilely tuned and controlled to selectively yield either a single or double oxygenation of benzene as well as a sp3 or sp2 CH bond oxidation of toluene. On the basis of H/D kinetic isotope effect data, we determined the aromatic oxidation to mostly proceed by way of formation of an arene oxide or a σ-complex intermediate from high-valence iron species and to then undergo a 1,2-hydride shift, i.e., NIH-shift rearrangement.

Recyclable Pd(II)complex catalyzed oxidative sp2 C[sbnd]H bond acylation of 2-aryl pyridines with toluene derivatives

A recyclable polymer–anchored Pd(II) complex C was synthesized and characterized using different spectroscopic techniques. In addition the catalytic efficiency of the Pd (II) complex C was evaluated for ortho-acylation of 2-aryl pyridines with toluene derivatives to form aryl ketones via cross dehydrogenative coupling. In this catalytic process toluene acts as an effective coupling partner upon sp3 CH bond oxidation for sp2 CH bond acylation of 2-aryl pyridines in the presence of Pd(II)/TBHP system on water. Furthermore, the catalyst C was highly stable and could be easily recovered and reused for four cycles with no significant decrease in its activity and selectivity.

Iron-catalyzed oxidation of unreactive C[sbnd]H bonds: Utilizing bio-inspired axial ligand modification to increase catalyst stability

Three different bio-inspired Fe(II) complexes are applied as powerful catalysts for the oxidation of unreactive CH bonds under ambient conditions. Cyclohexane as the main model substrate is oxidized to cyclohexanol, cyclohexyl hydroperoxide, and cyclohexanone. Alcohol+cyclohexyl hydroperoxide to ketone ratios ((A+H)/K) of up to 26 are obtained with comparatively high turnovers of up to 43. Bio-inspired modification of the Fe(II) complexes in the axial positions is used to increase catalyst stability toward hydrogen peroxide, leading to an increase in turnovers of up to 34%. Several parameters for the catalytic oxidation are investigated, e.g., the amount and type of oxidant, reaction temperature, and the relative catalyst concentration. Among others, 9,10-dihydroantracene and 2,3-dimethylbutane are used as substrates for the catalytic CH bond oxidation.

ChemInform Abstract: Catalytic Asymmetric Synthesis of Allylic Alcohols and Derivatives and Their Applications in Organic Synthesis

AbstractReview: ca. 570 refs.

Heme-iron oxygenases: powerful industrial biocatalysts?

Are cytochrome P450 enzymes powerful industrial biocatalysts? Next to market demands, well-defined enzyme functionalities and process parameters allow generalizations on the basis of process windows. These can provide useful guidelines for the design of improved biocatalysts. Oxygenase-catalyzed reactions are of special interest for selective C-H bond oxidation. The versatile class of cytochrome P450 mono-oxygenases attracts particular attention, and impressive advances have been achieved with respect to mechanistic insight, enzyme activity, stability, and specificity. Recent major achievements include significant increases in productivities, yields, and rates of catalytic turnover as well as modification of substrate specificity and efficient multistep reactions in whole-cell biocatalysts. For some biocatalysts, these parameters are already of an industrially useful magnitude.

ChemInform Abstract: Mechanism of Dioxirane Oxidation of CH Bonds: Application to Homo‐ and Heterosubstituted Alkanes as a Model of the Oxidation of Peptides

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Mechanism of Dioxirane Oxidation of CH Bonds: Application to Homo- and Heterosubstituted Alkanes as a Model of the Oxidation of Peptides

Ab initio methods have been employed to study the oxidation of the CH bonds in homo- (1a−d) and heterosubstituted alkanes (2a−d, 3a,b) by the parent dioxirane as a model for the dioxirane oxidation of proteins. The study involved methane (1a), ethane (1b), propane (1c), isobutane (1d), methylamine (2a), methanol (2b), ethanol (2c), acetaldehyde (2d), glycolaldehyde (3a), and a peptide model, N-formylglycine amide (3b). Geometries were optimized at DFT (B3LYP) and MP2 levels of theory using 6-31G* and 6-311+G** basis sets. Stationary points were characterized by vibrational frequency analysis. Final energies for the oxidation of 1a were obtained at the MP4(SDTQ)/6-311+G** and QCISD(T)/6-311+G** levels. A new mechanism of the oxidation reconciling the apparently contradictory experimental data was found. The reaction proceeds via a highly polar asynchronous transition state, which is common for either concerted oxygen insertion into the CH bond and formation of a radical pair (alkyl radical + α-hydroxyalkox...