Catalyst For Oxidation Of Alcohols Research Articles

Synthesis, Crystal Structure of Tetra-Nuclear Macrocyclic Zn(II) Complex and Its Application as Catalyst for Oxidation of Benzyl Alcohol

A new six coordinated tetra-nuclear macrocyclic Zn(II) complex, ZnL4(Phen)2 (1) (HL= 3-bromo-2-hydroxybenzaldehyde-pyridine-2-carbohydrazone, Phen = 1,10-phenanthroline) has been synthesized by the self-assembly of 3-bromo-2-hydroxybenzaldehyde-pyridine-2-carbohydrazone, Zn(CH3COO)2•2H2O, NaOH and 1,10-phenanthroline in water/ethanol (v:v = 1:3) solution. Complex 1 was characterized by elemental analysis, infra red (IR), and single-crystal X-ray diffraction (XRD) analysis. The results show that Zn1 and Zn1b ions are six-coordinated with a distorted octahedral geometric configuration by four O atoms of two different L ligands and two N atoms of two different L ligands, Zn1a and Zn1c ions are also six-coordinated with a distorted octahedral geometric configuration by two N atoms of two different L ligands, two N atoms of Phen ligands and two O atoms of two different L ligands. Complex (1) forms 3D network structure by the - interaction. The selective oxidation reactions of benzyl alcohols catalyzed by complex (1) was investigated. The highest benzyl alcohol conversion and benzaldehyde selectivity were obtained at 100 °C for 4 h under 5 bar of O2. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Frontispiece: A Perspective on Heterogeneous Catalysts for the Selective Oxidation of Alcohols

In the processes for synthesis of fine chemicals, selective oxidation of alcohols, especially the higher ones, is of great importance. In this regard, heterogeneous catalysts have been applied in different approaches namely, thermocatalysis, electrocatalysis and photocatalysis. Metal- and oxide-based catalysts have been used within these approaches, and despite of advances in the preparation of efficient, there is still a lack of understanding about their dynamics considering the complexity of the catalysts’ surfaces and the mechanism of the reactions. Therefore, it is essential to unravel these properties using advanced operando characterization. In this mini-review, we gathered some of more important works in the field with the aim to give a perspective on the existing challenges needed to provide a fundamental understanding of the catalysts under different reaction conditions. For more information, see the Minireview by S. Najafishirtari, M. Behrens et al. on page 16809.

Fe(II)-phthalocyanine supported on chitosan aerogel as a catalyst for oxidation of alcohols and alkyl arenes

Manipulation of materials is considered as one of the eminent strategies to create desirable catalysts. In this regard, increasing surface area and decreasing dimensions of catalysts have been widely employed on account of effectiveness of these methods. Herein, aerogel form of chitosan as a sustainable, and high aspect ratio compound is employed as a green support for the catalytic purposes. Chitosan aerogel was modified with Fe(II)-phthalocyanine to produce a heterogeneous catalyst for oxidation reactions. The synthesized catalyst promoted the oxidation reactions of alcohols and alkyl arenes to the corresponding aldehydes and ketones using H2O2 as an oxidant in 24 h. The reactions for aliphatic and aromatic alcohols gave turnover numbers of 106–109 at 80 °C and 106–117 at room temperature, respectively. The oxidations of alkyl arenes were carried out with turnover numbers laying in the range of 106–117 at 100 °C. The low toxicity, inexpensive nature, and recycling possibility of the catalyst accompanied by the reaction mild conditions, clean oxidant, and excellent yields offer chitosan aerogel modified with Fe(II)-phthalocyanine as a promising catalyst for oxidation reactions.

Co-N-Si/AC Catalyst for Aerobic Oxidation of Benzyl Alcohols to Esters under Mild Conditions.

A stable, earth-abundant, reusable cobalt-based heterogeneous catalyst is developed for the oxidative esterification of alcohols under ambient conditions, featuring broad substrate scope, providing good to excellent product yields. This protocol enables easy recyclability of the catalyst, measured up to five times without significant loss of efficiency. The active sites of Co-N-Si/AC are proposed to be Co-N species.

Efficient Synthesis of Cu(II)‐N‐Heterocyclic Carbene Complexes in Water and Their Activity Towards Aerobic Alcohol Oxidation

AbstractThe majority of the copper N‐heterocyclic carbene (NHC) complexes contain Cu in a +1 oxidation state. The Cu(II)‐NHC complexes reported so far usually require strict inert atmosphere conditions. In this work, we report a very facile and quantitative preparation of a series of new Cu(II)‐NHC complexes (2 a–c) starting from the inexpensive and readily available Cu(II) salts like Cu(OAc)2 and CuCl2 ⋅ 2H2O with imidazolium salts (1 a–c), wherein 2 b and 2 c were exclusively synthesized in water under aerobic condition. It should be emphasized that this is the first example where Cu(II)‐NHC complexes have been prepared in the aqueous medium. All the complexes have manifested with a heterobidentate C, O chelate type of coordination to Cu(II) centers forming trans‐[Cu(IRpyO)2] (where R=Me, Mes, Dipp) type of complexes where 2 b forms a perfect square planar Cu(II)‐NHC complex. Complexes 2 a–c were evaluated as catalysts for the aerobic oxidation of alcohols.

Intelligent light-responsive and ionic polymer functionalized polyacrylonitrile as an environmental benign catalyst for selective oxidation of benzyl alcohols

Herein, spiropyran (SPA) and 1-vinyl-3-ethylimidazole were firstly grafted as conjugated polymer onto the Polyacrylonitrile fiber (PANF) by reversible addition fragmentation chain transfer (RAFT), and then their imidazole cation were used as exchanger to prepare an intelligent photo-responsive catalyst loaded with intact Keggin hydrogen phosphotungstate (HxPW12O40(3−x) -), which were fully characterized by FT-IR, XPS, SEM, TGA and ICP. The obtained catalysts could efficiently promote the aqueous oxidation of benzyl alcohol in presence of H2O2. The reversible light-responsive property of SPA on fiber renders its hydrophobic microenvironment which is propitious to adsorb organic starting substrates in the reaction process, while the increasing hydrophilicity, derived from the ring opening of SPA by ultraviolet light, can desorb the product completely from the fiber. The whole catalytic process, including reaction stage and work-up stage, does not need any volatile organic solvent and the catalysts could be recycled for 10 times without any significantly loss of activity. Finally, the fiber could be further twinned on the impeller of mechanical stirrer, demonstrating the readily scale-up production potential.

Unrevealing the Mechanism of Aminoxyl Catalyzed Electrochemical Oxidation of Alcohols By Unpolished Glassy Carbon Electrode

2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO, 1) and related aminoxyl derivatives are important catalysts for alcohol oxidation. They are featured in the synthesis of pharmaceuticals and recently found considerable attention for the conversion of hydroxyl bearing biomass-derived feedstocks to value-added products. Aminoxyl compounds undergo facile redox reactions at electrode surfaces, enabling them to mediate electrochemical oxidation of alcohols.The well-known electron transfer reaction of these persistent radicals involves a reversible one electron oxidation to the corresponding oxoammonium species (TEMPO+ , 3), which are relatively strong oxidants. Aminoxyl radicals can also undergo a proton coupled reduction to hydroxylamines (2), which is quasireversible and less known. However, for many of their electrosynthetic reactions, the catalytic cycle involves not only aminoxyl/oxoammonium redox couple, but also formation of hydroxylamines and regeneration of the oxoammonium from the hydroxylamine. This two steps oxidation has been proposed to occur via two distinct pathways: the comproportionation reaction between the hydroxylamine and a second oxoammonium cation to form aminoxyloxyl radical (two) followed by oxidation of aminoxyl radicals to oxoammonium (pathway b), or the two-electron oxidation of the hydroxylamine to the oxoammonium (pathway a). The electron transfer of the hydroxylamine, at the electrode surface, is a quasireversible ill-defined reaction that strongly depends on the electrode material and conditionings, and its detailed understanding is still lacking. Herein, we investigated the electron transfer reaction of TEMPO and its hydroxylamine, is formed during catalytic alcohol oxidation, using the glassy carbon electrodes that treated under different conditions. Well-treated electrode facilitates the electron transfer of hydroxylamine and enables two-electrons oxidation to oxoammonium, whereas on the untreated electrode, two separated one-electron oxidations are observed that enables measuring the rate of generation and consumption of hydroxylamine. Understanding of how each regeneration pathway affects the catalytic behavior made it possible to comprehensively understand all the features of the current profiles obtained under various alcohol oxidation conditions. Figure 1. Possible mechanism for regeneration of oxoammonium during aminoxyl catalyzed alcohol oxidation. Figure 1

A Perspective on Heterogeneous Catalysts for the Selective Oxidation of Alcohols.

Selective oxidation of higher alcohols using heterogeneous catalysts is an important reaction in the synthesis of fine chemicals with added value. Though the process for primary alcohol oxidation is industrially established, there is still a lack of fundamental understanding considering the complexity of the catalysts and their dynamics under reaction conditions, especially when higher alcohols and liquid‐phase reaction media are involved. Additionally, new materials should be developed offering higher activity, selectivity, and stability. This can be achieved by unraveling the structure–performance correlations of these catalysts under reaction conditions. In this regard, researchers are encouraged to develop more advanced characterization techniques to address the complex interplay between the solid surface, the dissolved reactants, and the solvent. In this mini‐review, we report some of the most important approaches taken in the field and give a perspective on how to tackle the complex challenges for different approaches in alcohol oxidation while providing insight into the remaining challenges.

A Synergistic Magnetically Retrievable Inorganic‐Organic Hybrid Metal Oxide Catalyst for Scalable Selective Oxidation of Alcohols to Aldehydes and Ketones

AbstractHerein, we report a synergistic silica coated magnetic Fe3O4 catalyst functionalized with nitrogen rich organic moieties and immobilized with cobalt metal ion (FNP‐5) for selective oxidation of alcohols to aldehydes and ketones using tert‐butyl hydroperoxide (TBHP) as oxidant. The catalyst was rigorously characterized via several techniques which delineate its core‐shell structure, magnetic behavior, phase and crystal structure. The Co(III) acts as the active catalytic center for selective oxidation reaction. The control reactions revealed radical mechanistic pathway assisted by the synergism induced by the inorganic‐organic hybrid nature of FNP‐5. The other features of current protocol involve neat reaction conditions, high TOF values, scalability of product and low E‐factor value (1.92). Moreover, FNP‐5 could be effortlessly separated via an external magnet, displays recyclability over eight catalytic cycles and exhibits structural integrity even after rigorous use. Overall, these results manifest the understanding of synergistic architectures as sustainable surrogates for selective oxidation reactions.

P,N co-doped biomass carbon as a remarkable metal-free catalyst for solvent-free oxidation of benzyl alcohol with ambient air: The key promoting role of N co-doping

Benzaldehyde is an important chemical intermediate, and its production via the oxidation of benzyl alcohol with O2 is highly pursued as an alternative for the existing industrial process to meet the demand of green chemistry. Most of the reported catalytic systems are dependent on the noble/toxic metal catalysts. Herein, a biomass carbon catalyst doped with P and N heteroatoms is prepared by calcinating the phosphoric acid-treated N-containing biomass of soybean flour in N2. In the absence of solvent or additive, the obtained P,N co-doped carbon catalyst exhibits aremarkablecatalyticactivity for oxidation of benzyl alcohol to benzaldehyde with air (99.4% yield, TOF = 62.1 × 10-4 mol BAD/(g catalyst × h reaction time)). The present turnover frequency surpasses all the previously reported ones of similar metal-free carbon catalysts for this reaction. The N co-doping facilitates the P doping into the carbon matrix, favors the formation the catalytic active species and has a remarkable electronic effect on them, which are identified via experiments and DFT calculations.

O-Quinone methide with overcrowded olefinic core as a catalytically-active surrogate of triarylmethylium salt for dehydridative oxidation of benzylic alcohols under aerobic photoirradiation conditions

An o-quinone methide (o-QM) competent as a catalyst for the dehydridative oxidation of benzylic alcohols was developed. The introduction of an overcrowded olefinic component into the o-QM induced structural distortion, beneficial for imparting triarylmethylium character and regenerability. The zwitterionc resonance form of the o-QM, generated via photoexcitation and subsequent relaxation, exerted the dehydridation activity. Density functional theory calculations were conducted to gain insights into the operative catalytic process.

Magneto-structural properties and reliability of (Mn/Ni/Zn) substituted cobalt-copper ferrite heterogeneous catalyst for selective and efficient oxidation of aryl alcohols

Herein, M2+ substituted CoCuFe2O4 (M2+ = Mn, Zn, Ni) ferrites have been synthesized using the sol-gel auto combustion method. The structural, morphological and magnetic studies confirm the phase formation of pure magnetic cubic spinel MCoCuFe2O4 (M2+ = Mn, Zn, Ni) ferrites. The substitution with Mn, Ni and Zn does not show large variation in binding energies obtained from XPS of Cu (2p) that specifies identical copper concentration (Cu0.5) and substitution of only cobalt (Co2+) in Mn-F, Ni-F and Zn-F catalysts. Interestingly, MCoCuFe2O4 magnetic catalysts were explored for selective oxidation of a series of substituted benzyl alcohols. Catalyst Mn-F showed 93% conversion of benzyl alcohol while, Ni-F showed 95% conversion of 4-nitrobenzyl alcohol. Whereas, the catalyst Zn-F was showed 96% conversion for 4-methoxybenzyl alcohol. Additionally the results also indicate an efficient separation and recovery of the magnetic catalysts after four successive reuses without any considerable loss in its catalytic activity.

Bio‐derived nanosilica‐anchored Cu(II)‐organoselenium complex as an efficient retrievable catalyst for alcohol oxidation

AbstractA new copper(II) complex supported onto rice‐husk‐derived nanosilica was prepared from 2,6‐bis((phenylselanyl)methyl)pyridine, salicylaldehyde and copper acetate monohydrate, Cu(OAc)2·H2O. The as‐synthesized complex Cu(II)SeNSe@imine‐nanoSiO2 (Complex I) was extensively characterized with FT‐IR, powder XRD, SEM‐EDX, solid‐state UV‐Vis, ESR, XPS, TGA and BET surface area analysis. The catalytic activity of the complex was explored for alcohol oxidation reactions using H2O2 as oxidant and acetonitrile as solvent. For comparison, we have also prepared an analogous homogeneous catalyst (Complex II) and characterized it with FT‐IR, UV‐Vis, LC‐MS and ESR analyses. Its catalytic activity was also screened to the same reaction. The immobilized catalyst showed better efficiency with 75%–95% isolated yield compared with the homogeneous one for alcohol oxidation with at least five times recyclability without profound loss in activity.

Three-Dimensional Radical Covalent Organic Frameworks as Highly Efficient and Stable Catalysts for Selective Oxidation of Alcohols.

With excellent designability, large accessible inner surface, and high chemical stability, covalent organic frameworks (COFs) are promising candidates as metal-free heterogeneous catalysts. Here, we report two 3D radical-based COFs (JUC-565 and JUC-566) in which radical moieties (TEMPO) are uniformly decorated on the channel walls via a bottom-up approach. Based on grafted functional groups and suitable regular channels, these materials open up the application of COFs as highly efficient and selective metal-free redox catalysts in aerobic oxidation of alcohols to relevant aldehydes or ketones with outstanding turn over frequency (TOF) up to 132 h-1 , which has exceeded other TEMPO-modified catalytic materials tested under similar conditions. These stable COF-based catalysts could be easily recovered and reused for multiple runs. This study promotes potential applications of 3D functional COFs anchored with stable radicals in organic synthesis and material science.

Three‐Dimensional Radical Covalent Organic Frameworks as Highly Efficient and Stable Catalysts for Selective Oxidation of Alcohols

AbstractWith excellent designability, large accessible inner surface, and high chemical stability, covalent organic frameworks (COFs) are promising candidates as metal‐free heterogeneous catalysts. Here, we report two 3D radical‐based COFs (JUC‐565 and JUC‐566) in which radical moieties (TEMPO) are uniformly decorated on the channel walls via a bottom‐up approach. Based on grafted functional groups and suitable regular channels, these materials open up the application of COFs as highly efficient and selective metal‐free redox catalysts in aerobic oxidation of alcohols to relevant aldehydes or ketones with outstanding turn over frequency (TOF) up to 132 h−1, which has exceeded other TEMPO‐modified catalytic materials tested under similar conditions. These stable COF‐based catalysts could be easily recovered and reused for multiple runs. This study promotes potential applications of 3D functional COFs anchored with stable radicals in organic synthesis and material science.

Recyclable Pd‐based polysaccharide catalyst for aerobic oxidation of benzyl alcohol

AbstractPalladium acetate that was heterogenized together with triphenylphosphine trisulfonate ligand on renewable polysaccharides was employed in the aerobic oxidation of benzyl alcohol in three representative solvents—hexane, ethyl acetate, and ethanol. Solvent polarity was found to affect the reaction rate, as both the solubility of benzyl alcohol and oxygen depend on the nature of the solvent. The conversion rate was decreased in the order of hexane > ethanol > ethyl acetate (conversion rates in the presence of the heterogenized iota‐based catalyst after 24 h of reaction were 38, 20, and 15%, respectively). In addition, the nature of the polysaccharide, that is, the type and numbers of functional groups on its backbone, also affected the reaction rate, where xanthan gum yielded the highest conversion rate of 58% in hexane. Finally, though hexane was found to be the preferred solvent for the heterogeneous system, catalytic performance in hexane decreased during recycling while in ethanol it increased due to the formation of palladium nanoparticles. To reveal the structural changes undergone by the catalyst during the reaction, several techniques were used, including energy dispersive X‐ray spectrometry‐scanning electronic microscopy, X‐ray photoelectron spectroscopy, Transition electronic microscopy, and thermal gravimetric analysis. This simple and straightforward heterogenization procedure can be also used for immobilization of different other metal complexes in variety of organic reactions.

Benzyl alcohol to benzaldehyde oxidation on MnOx clusters: Unraveling atomistic features

• Catalytic oxidation of benzyl alcohol to benzaldehyde over MnO x catalysts is analyzed in the DFT framework. • Oxidation reactivity and selectivity over cluster-sized Mn 4 O 8 and Mn 4 O 9 catalytic models is compared. • Catalyst poisoning is addressed by investigating the formation of benzoic acid following that of benzaldehyde. • Reaction steps and the related oxidation pathways are collected and analyzed by an original kinetic approach. • Experimental strategies aimed at decreasing catalyst deactivation hence at increasing selectivity are proposed. The catalytic oxidation of benzyl alcohol with O 2 is a promising option for the production of benzaldehyde, from both environmental and economical viewpoints. In particular, highly dispersed MnO x systems feature good activity and selectivity in a wide range of temperatures, although deactivation phenomena by over-oxidation and/or poisoning of active sites are generally recorded. On this account, a density functional theory study was performed on cluster-sized catalyst models, namely Mn 4 O 8 and over-oxygenated Mn 4 O 9 fragments, to predict the reactivity pattern of MnO x catalysts in the selective aerobic oxidation of benzyl alcohol. Several pathways concur to determine the whole reaction process and all of them were compared to unveil the atomistic details of the alcohol oxidation mechanism. Moreover, assuming that the consecutive formation of benzoic acid affects the activity-stability pattern of the MnO x based catalyst, also the benzaldehyde oxidation mechanism was computationally addressed. A systematic comparison of the benzyl alcohol and benzaldehyde oxidation mechanisms on the Mn 4 O 8 and Mn 4 O 9 fragments reveals some experimental strategies to test the reaction mechanisms and design alternative catalytic routes to decrease undesired parasitic reactions leading to catalyst deactivation. The matching structural, energetic and kinetic data are published in the Data in Brief journal [1].

The catalytic reactivity of titanium dioxide supported on SBA-15 catalyst for selective oxidation of benzyl alcohol

The catalytic reactivity of titanium dioxide supported on SBA-15 catalyst for selective oxidation of benzyl alcohol

Chemically functionalized MIL-101-NH2 with cobalt(II) tetrasulfophthalocyanine: an efficient catalyst for the aerobic oxidation of alcohols and one-pot tandem conversion of alcohols to propargylamines

In this investigation, MIL-101-NH2 chemically functionalized with cobalt(II) tetrasulfophthalocyanine (CoTSPc) through a superior electrostatic interaction reaction. The configuration of the synthesized composite was characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), and inductively coupled plasma optical emission spectrometer (ICP-OES). This spongy composite showed excellent catalytic activity in the aerobic oxidation reaction of primary and secondary benzylic alcohols. The generated catalyst's behavior was examined to synthesize propargylamines via tandem oxidative A3 coupling process to illustrate the maximum potential of the synthesized catalyst. Utilizing air as an oxidant, operational simplicity, easy preparation, apt yielding, non‐hazardous nature of the catalyst, and reusability are the essential advantages of this catalyst.

An efficient heterogeneous Cu(I) complex for the catalytic oxidation of alcohols and sulfides: synthesis, characterization, and investigation of the catalyst activity

A heterogeneous Cu(I) complex was synthesized by reaction of C5H4NC(O)NHP(O)[NHC(CH3)3]2 (L) with CuCl and used as a catalyst for green oxidation of aromatic alcohols and sulfides. According to the characterization results obtained from 31P NMR, UV-Vis, FT-IR, mass, XRD, elemental analysis, and molar conductivity techniques, the chemical formula of the complex (1) was suggested as [CuClL2]. Parameters on the catalytic activity (reaction temperature, the substrate to oxidant molar ratio, catalyst amount, and solvent type) were optimized, using H2O2 as a green oxidant, and excellent conversion amounts (100%) were achieved under optimal conditions. Moreover, the generality and recyclability of the catalyst were tested and confirmed. A comparison between the oxidation results of the alcohol and sulfide in the presence of 1 with other catalysts indicated that in most cases 1 showed better efficiency, in a more reasonable reaction time and conditions.