Oxidation Of Primary Alcohols Research Articles

Direct Oxidation of Primary Alcohols to Carboxylic Acids

AbstractOxidation of primary alcohols to carboxylic acids is a fundamental transformation in organic chemistry, yet despite its simplicity, extensive use, and relationship to pH, it remains a subject of active research for synthetic organic chemists. Since 2013, a great number of new methods have emerged that utilize transition-metal compounds as catalysts for acceptorless dehydrogenation of alcohols to carboxylates. The interest in this reaction is explained by its atom economy, which is in accord with the principles of sustainability and green chemistry. Therefore, the methods for the direct synthesis of carboxylic acids from alcohols is ripe for a modern survey, which we provide in this review.1 Introduction2 Thermodynamics of Primary Alcohol Oxidation3 Oxometalate Oxidation4 Transfer Dehydrogenation5 Acceptorless Dehydrogenation6 Electrochemical Methods7 Outlook

Sensitive Method for the Identification of Potential Sensitizing Impurities in Reaction Mixtures by Fluorescent Nitrobenzoxadiazole-Labeled Glutathione.

Allergic contact dermatitis is a critical issue in the development of new chemicals. Minor impurities with strong skin-sensitizing properties can be generated as byproducts. However, it is very difficult to identify these skin sensitizers in product mixtures. In this study, fluorescent nitrobenzoxadiazole-labeled glutathione (NBD-GSH) was synthesized to identify small amounts of skin sensitizers in reaction mixtures. Twelve known skin sensitizers and three nonsensitizers were reacted with NBD-GSH. Adducts formed only with the skin sensitizers, which allowed for their detection by a fluorescence detector. Liquid chromatography-mass spectrometry (LC-MS) analyses showed that NBD-GSH reacted with the skin sensitizers via its thiol and amino groups. An adduct of NBD-GSH with the strong skin sensitizer 1-chloro-2,4-dinitrobenzene was detected with a limit of detection of 6 × 10-8 mol/L by high-performance liquid chromatography with fluorescence detection. When a reaction mixture from primary alcohol oxidation was incubated with NBD-GSH, a NBD-GSH adduct formed with skin-sensitizing aldehyde impurities and could be specifically detected by LC-MS with fluorescence detection. This method will be useful for detection and identification of small amounts of skin sensitizers in raw materials, intermediates, reaction mixtures, and end products in the chemical industry.

(Invited) Uncovering the Role of Alkaline Pretreatment for Hydroxide Exchange Membrane Fuel Cells

As an emerging alternative to proton exchange membrane fuel cells, hydroxide exchange membrane fuel cells (HEMFCs) can use more cost-effective platinum-group-metal-free (PGM-free) catalysts, bipolar plates, and other components.1 Taking advantage of the recent significant progress in hydroxide exchange membranes (HEMs) and optimized electrodes based on hydroxide exchange membrane ionomers (HEIs), HEMFCs achieved unprecedented performance and the record of peak power density was updated frequently in the past few years. Interestingly, nearly all membrane electrode assemblies (MEAs) with satisfactory performances reported in the literature were pretreated with alkaline solutions such as KOH before cell assembly.Here we show that the most crucial role of the alkaline soak is to remove carboxylates that are generated from the oxidation of primary alcohols, used as solvents for ionomers and/or catalyst inks, by platinum/palladium catalysts during membrane electrode assembly fabrication. These carboxylates are difficult or impossible to eliminate by self-purging processes. We also show that bicarbonates are an adequate replacement for the most frequently used strong bases for the pretreatment. As shown in Figure 1, the pretreatment effect can be seen in the shape of polarization curves. And Figure 2 depicts the electrochemical purging process in HEMFCs for acetate and carbonate/bicarbonate, respectively. As a result, alkaline pretreatment is unnecessary for catalysts that do not oxidize primary alcohols. In fact, membrane electrode assemblies with Pt/Pd-free catalysts deliver a better performance without the alkaline pretreatment: a voltage of 0.64 V at 1.0 A/cm2 and a peak power density of 0.69 W/cm2 in H2/O2. References B. P. Setzler, Z. Zhuang, J. A. Wittkopf, and Y. Yan, Nat Nanotechnol, 11 (12), 1020-1025 (2016). Figure 1

Bioinspired Radical-Mediated Transition-Metal-Free Synthesis of N-Heterocycles under Visible Light.

A redox-active iminoquinone motif connected with π-delocalized pyrene core has been reported that can perform efficient two-electron oxidation of a class of substrates. The design of the molecule was inspired by the organic redox cofactor topaquinone (TPQ), which executes amine oxidation in the enzyme, copper amine oxidase. Easy oxidation of both primary and secondary alcohols happened in the presence of catalytic KOtBu, which could reduce the ligand backbone to its iminosemiquinonate form under photoinduced conditions. Moreover, this easy oxidation of alcohols under aerobic condition could be elegantly extended to multi-component, one-pot coupling for the synthesis of quinoline and pyrimidine. This organocatalytic approach is very mild (70 °C, 8 h) compared to a multitude of transition-metal catalysts that have been used to prepare these heterocycles. A detailed mechanistic study proves the intermediacy of the iminosemiquinonate-type radical and a critical hydrogen atom transfer step to be involved in the dehydrogenation reaction.

Magnetic spent coffee ground as an efficient and green catalyst for aerobic oxidation of alcohols and tandem oxidative Groebke–Blackburn–Bienaymé reaction

In this work, magnetic spent coffee ground as a green, inexpensive, and abundant material was synthesized and characterized by a variety of techniques, including X-ray diffraction pattern, thermal gravimetric analysis, scanning electron microscopy, energy-dispersive spectroscopy, inductively coupled plasma optical emission spectrometry, and Fourier transform infrared spectroscopy. The magnetic spent coffee ground was successfully utilized as a catalyst in aerobic oxidation of primary and secondary benzylic alcohols and tandem oxidative Groebke–Blackburn–Bienayme reaction.

Catalytic Selective Oxidation of Primary and Secondary Alcohols Using Nonheme [Iron(III)(Pyridine‐Containing Ligand)] Complexes

The selective oxidation of different primary and secondary alcohols to carbonyl compounds by hydrogen peroxide was found to be catalyzed in conversion ranging from good to excellent by an iron(III) complex of a pyridine‐containing macrocyclic ligand (Pc‐L), without the need of any additive. The choice of the counteranion (Cl, Br, OTf) appeared to be of fundamental importance and the best results in terms of selectivity (up to 99 %) and conversion (up to 98 %) were obtained using the well‐characterized [Fe(III)(Br)2(Pc‐L)]Br complex, 4c. Magnetic moments in solid‐state, also confirmed in solution ([D6]DMSO) by Evans NMR method, were calculated and point out to an iron metal center in the high spin state of 5/2. The crystal structure shows that the iron(III) center is coordinated by the four nitrogen atoms of the macrocycle and two bromide anions to form a distorted octahedral coordination environment. The catalytic oxidation of benzyl alcohol in acetonitrile was found occurring with better conversions and selectivities than in other solvents. The reaction proved to be quite general, tolerating aromatic and aliphatic alcohols, although very low yields were obtained for terminal aliphatic alcohols. Preliminary mechanistic studies are in agreement with a catalytic cycle promoted by a high‐spin iron complex.

Catalytic alcohol oxidation using cationic Schiff base manganeseIII complexes with flexible diamino bridge

Four Schiff base manganese(III) complexes with derivatives of [(R,R)-N,N’-bis(salicy1idene)-1,2-cyclohexanediaminato)] including substituents on salicylaldehyde such as 3-methoxy, 3,5-di-tert-butyl and 3,5-chloro were synthesized and characterized using a combination of IR, UV–Vis, and HR ESI-MS techniques. The catalytic activity of these complexes was tested in the oxidation of 1-phenylethanol to acetophenone, revealing very good performances for all of the four manganese complexes. The catalytic reactions were carried out in the presence of tert-butyl hydroperoxide (TBHP) as oxidant and imidazole as co-catalyst. Complex Mn-4, bearing electron withdrawing [(R,R)-N,N’-bis(3,5-di-chloro-salicylidene)-1,2-cyclohexanediaminato)] ligand was found to be the most stable of the tested Mn(III) complexes and was selected for the oxidation of several primary and secondary alcohols.

Effective and selective aerobic oxidation of primary and secondary alcohols using CoFe2O4@HT@Imine‐CuII and TEMPO in the air atmosphere

In this study, we present a versatile and easy procedure for modifying a cobalt ferrite nanoparticle step by step. A new nanocatalyst was prepared via CuII immobilized onto CoFe2O4@HT@Imine. The catalyst was fully characterized by Fourier‐transform infrared (FT‐IR), energy‐dispersive X‐ray spectroscopy (EDX), field emission scanning electron microscopy (FE‐SEM), X‐ray diffraction (XRD), and vibrating sample magnetometer (VSM) analyses. The current procedure as a green protocol offers benefits including a simple operational method, an excellent yield of products, mild reaction conditions, minimum chemical wastes, and short reaction times. Without any significant reduction in the catalytic performance, up to five recyclability cycles of the catalyst were obtained. The optimization results suggest that the best condition in the oxidation of benzyl alcohol derivatives is 0.003 g of the CoFe2O4@HT@Imine‐CuII catalyst, TEMPO, at 70°C under solvent‐free condition and air.

Tungstate ion (WO42-) confined in hydrophilic/hydrophobic nanomaterials functionalized brönsted acidic ionic liquid as highly active catalyst in the selective aerobic oxidation of alcohols in water

A Brönsted acidic Ionic Liquid containing tungstate anion functionalized polysiloxane network (PMO-IL-WO42-) was synthesized by simple self-condensation of tungstic acid and zwitterionic organosilane precursor possessing both imidazolium and sulfonate groups. Characterization by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), thermal gravimetric analysis TGA, nitrogen porosimetry, solid-state NMR spectroscopy and elemental analysis confirmed that both imidazolium cation and tungstate anion of zwitterion are successfully incorporated inside the organosilica framework. The catalytic activity of resulting hybrid PMO-IL- WO42- material was studied in the selective aerobic oxidation of primary and secondary alcohols using an atmospheric pressure of air in pure water. Due to the ionic liquid-based charged surface containing hydrophilic sulfonic acid and tungstate group, the synergistic hydrophilic/hydrophobic and redox effect of PMO-IL-WO42- as water-friendly catalyst facilitates and enhances the activity and selectivity toward the target oxidative products in water and proved to have a particularly broad substrate scope for reliable aerobic oxidation reaction. Furthermore, the catalyst showed outstanding stability and could be easily separated and reused at least ten reactions run under the same conditions as fresh catalyst without any loss of catalytic activity and product selectivity.

Conversion Mechanisms of Nitroxyl Radical (TEMPO), Oxoammonium Cation, and Hydroxylamine in Aqueous Solutions: Two-Dimensional Correlation Ultraviolet-Visible Spectroscopy.

Oxidation reactions of alcohols have been of interest due to their broad applications in different fields. Oxoammonium cation (TEMPO+) of 2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPO) is a high-potential oxidant for the selective oxidation of primary alcohols, with hydroxylamine (TEMPOH) as a side product. TEMPO or TEMPO+ has been widely applied for various reactions. However, the conversion mechanisms among TEMPO, TEMPO+, and TEMPOH are not well understood and remain controversial, due to complications in the direct observation of the reactions. In this work, two-dimensional correlation (2D-COS) UV-visible (UV-Vis) spectroscopy is applied to examine the correlations between the characteristic bands of each species, to obtain insights into the complete reaction mechanisms. Series of dynamic UV-Vis spectra of solutions under different external perturbations (as a function of reaction time) were recorded and used in the generation of 2D-COS synchronous and asynchronous maps. The key UV-Vis band assignments are as follows: 250 nm and 400 nm for TEMPO, 290 nm and 480 nm for TEMPO+, and 200 nm and 315 nm for TEMPOH. The results indicate that the conversion between TEMPO and TEMPOH in acidic solution is a reversible process, which reaches an equilibrium state after two hours. However, the reaction becomes irreversible after three hours, due to a higher degree of irreversible protonation of TEMPOH to form TEMPOH-H+. Fast conversion from TEMPO to TEMPO+ is observed when sodium hypochlorite co-oxidant is added. The synproportionation-disproportionation also reaches an equilibrium. However, there is no evidence of the conversion from TEMPOH to TEMPO+ under the reaction conditions. At high reaction temperature, the formation of TEMPOH occurs first from TEMPO+ decomposition, followed by TEMPO decomposition. These detailed mechanisms are beneficial in designing the optimum process conditions for the oxidation of specific alcohols.

Cubic nanocasted polyaniline-ordered mesoporous carbon composite and its application for enhanced catalytic activity of palladium nanoparticles in the aerobic oxidation of alcohols in water

A novel polyaniline-ordered mesoporous carbon composite (PANI/OMC) was prepared through a two-step nanocasting technique in the presence of KIT-6 as template. The material exhibits high surface area, accessible mesoporous structure as well as improved basicity and redox potential arising from the presence of polyaniline as a nitrogen-containing polymer. It was successfully used as an effective support for preparation of a Pd nanoparticle (Pd NPs) supported catalyst (Pd@PANI/OMC), which was then employed as a powerful catalyst in the aerobic oxidation of primary alcohols, affording the corresponding carboxylic acids in good to excellent yields in pure water. This excellent catalytic performance can be attributed to the synergism of the large surface area and highly dispersed Pd NPs derived from the extraordinary features of the support. Morphology, structure, and composition of the materials were characterized by N2 adsorption–desorption analysis, electron microscopy (TEM, SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FT-IR).

Application of The Dess-Martin Oxidation in Total Synthesis of Natural Products.

Dess-Martin periodinane (DMP), a commercially available chemical, is frequently utilized as a mild oxidative agent for the selective oxidation of primary and secondary alcohols to their corresponding aldehydes and ketones, respectively. DMP shows several merits over other common oxidative agents such as chromiumand DMSO-based oxidants; thus, it is habitually employed in the total synthesis of natural products. In this review, we try to underscore the applications of DMP as an effective oxidant in an appropriate step (steps) in the multi-step total synthesis of natural products.

Uncommon overoxidative catalytic activity in a new halo‐tolerant alcohol dehydrogenase

AbstractAlcohol dehydrogenases (ADH) are versatile and useful enzymes employed as biocatalysts, especially for the selective oxidation of primary and secondary alcohols, and for the reduction of carbonyl moieties. A new alcohol dehydrogenase (HeADH‐II) has been identified from the genome of the halo‐adapted bacterium Halomonas elongata, which proved stable in the presence of polar organic solvents and salt exposure. Unusual for this class of enzymes, HeADH‐II lacks enantiopreference and is capable of oxidizing both alcohols and aldehydes, enabling a direct overoxidation of primary alcohols to carboxylic acids. HeADH‐II was coupled with a NADH‐oxidase from Lactobacillus pentosus (LpNOX) to increase the process yields and allowing recycling of the cofactor. The enzymatic oxidation of primary alcohols was also paired with in situ condensation of the intermediate aldehydes with hydroxylamine to prepare the corresponding aldoximes, with particular attention to perillartine (a powerful sweetener), whose enzymatic synthesis starting from natural sources, leads to an equally natural product.

Biocatalytic Oxidation of Alcohols

Enzymatic methods for the oxidation of alcohols are critically reviewed. Dehydrogenases and oxidases are the most prominent biocatalysts, enabling the selective oxidation of primary alcohols into aldehydes or acids. In the case of secondary alcohols, region and/or enantioselective oxidation is possible. In this contribution, we outline the current state-of-the-art and discuss current limitations and promising solutions.

Acceptorless dehydrogenative oxidation of primary alcohols to carboxylic acids and reduction of nitroarenes via hydrogen borrowing catalyzed by a novel nanomagnetic silver catalyst

A novel silver nano magnetic catalyst was devised for dehydrogenative oxidation of aromatic and aliphatic alcohols to the corresponding acid with water as the sole oxygen source and hydrogen gas as the only by-product. The designed catalytic system advantages from easy recovery of magnetic materials i.e. magnetic decantation, being economically viable and environmentally friendly. Furthermore, the catalytic reaction is able to reduce aryl nitro compounds in the absence of any reducing agent.

Dioxygen Activation by Internally Aromatic Metallacycle: Crystallographic Structure and Mechanistic Investigations.

SummaryMononuclear metal-peroxo species are invoked as the key intermediates in metalloenzymatic or synthetic catalysis. However, either transience or sluggishness reactivity of synthetic analogs of metal-peroxo species impedes our understanding of oxygen activation mechanism. Herein, we designed and characterized a dioxygen-derived mononuclear osmium-peroxo complex, in which the peroxo ligand is stabilized by internally aromatic metallacycle. We demonstrate that the osmium-peroxo species shows catalytic activity toward promoterless alcohol dehydrogenations. Furthermore, computational studies provide a new mechanism for the osmium-peroxo-mediated alcohol oxidation, starting with the concerted double-hydrogen transfer and followed by the generation of osmium-oxo species. Interestingly, the internally aromatic metallacycle also plays a vital role in catalysis, which mediates the hydrogen transfer from osmium center to the distal oxygen atom of Os–OOH moiety, thus facilitating the Os–OOH→Os=O conversion. We expect that these insights will advance the development of aromatic metallacycle toward aerobic oxidation catalysis.

A Woven Supramolecular Metal-Organic Framework Comprising a Ruthenium Bis(terpyridine) Complex and Cucurbit[8]uril: Enhanced Catalytic Activity toward Alcohol Oxidation.

The self-assembly of a diamondoid woven supramolecular metal-organic framework wSMOF-1 has been achieved from intertwined [Ru(tpy)2 ]2+ (tpy=2,2',6',2''-terpyridine) complex M1 and cucurbit[8]uril (CB[8]) in water, where the intermolecular dimers formed by the appended aromatic arms of M1 are encapsulated in CB[8]. wSMOF-1 exhibits ordered pore periodicity in both water and the solid state, as confirmed by a combination of 1 H NMR spectroscopy, UV-vis absorption, isothermal titration calorimetry, dynamic light scattering, small angle X-ray scattering and selected area electron diffraction experiments. The woven framework has a pore aperture of 2.1 nm, which allows for the free access of both secondary and primary alcohols and tert-butyl hydroperoxide (TBHP). Compared with the control molecule [Ru(tpy)2 ]Cl2 , the [Ru(tpy)2 ]2+ unit of wSMOF-1 exhibits a remarkably higher heterogeneous catalysis activity for the oxidation of alcohols by TBHP in n-hexane. For the oxidation of 1-phenylethan-1-ol, the yield of acetophenone was increased from 10 % to 95 %.

Synthesis of mesoporous NiO/Bi2WO6 nanocomposite for selective oxidation of alcohols

Mesoporous NiO/Bi2WO6 nanocomposite has been synthesized and found to be an efficient catalyst for the oxidation of primary and secondary benzylic alcohols under mild conditions. The mean particle size of the nanocomposite, determined by SEM and TEM, is about 60 nm. The BET analysis shows a narrow pore-size distribution of 6–9 nm and specific surface area of 73 m2g-1, which is much higher than its individual components, i.e. Bi2WO6 and NiO nanoparticles. This mesoporous structure facilitates the access of bulky molecules to the active sites of the catalyst, increasing the catalytic activity. In this study, the effects of oxidant, reaction time, solvent, amount of catalyst, and catalyst reusability have been investigated. The results reveal that the synthesized nanocomposite shows a significant improvement in the oxidation of benzylic alcohols to their corresponding aldehydes under mild conditions with the selectivity over 99% and higher conversion percentage compared to its individual components. Additionally, the results of this study suggest that the conversions of substituted benzyl alcohols are dependent on the position of substituents on the ring. The catalyst can be recycled five times and reused for oxidation of alcohols without significant loss of activity.

Design and development of natural and biocompatible raffinose-Cu2O magnetic nanoparticles as a heterogeneous nanocatalyst for the selective oxidation of alcohols

Natural polymers are recently playing a vital role as a support for the noble metals. In the present study, raffinose from the classes of oligosaccharide polymer with a high capacity of magnetization was used as active support for the copper metal. The copper immobilized on the raffinose-based magnetic nanoparticles (MNPs) which can be used as a recyclable heterogeneous nanocatalyst for the selective oxidation of primary benzyl alcohols (PBA) to benzaldehyde (BAD) derivatives. The morphology and structure of the recoverable magnetic nanocatalyst were characterized using different microscopic and spectroscopic techniques including FT-IR, GC, VSM, XRD, TEM, TGA, FESEM and EDS analyses. Also, the optimum conditions of co-reactant, reaction time, oxidant, temperature and amount of the nanocatalyst for oxidation reaction were investigated. Moreover, the Fe3O4@raffinose-Cu2O NPs had a significant effect to enhance yield and reduce the reaction time.

Enhanced singlet oxygen generation by hybrid Mn-doped nanocomposites for selective photo-oxidation of benzylic alcohols

Transition-metal ions doped nanocrystals (NCs), specifically Mn-doped NCs, hold great potential in the field of photocatalysis, especially, to improve photocatalytic performance for singlet oxygen (1O2) generation. Here, we report the design of a novel Mn-doped NC-based nanocomposites, specifically, silica-coated Mn-doped CdS/ZnS NCs decorated with Pt NCs (denoted as Mn-NCs@SiO2-Pt), which enhance photocatalytic 1O2 generation. Owing to the long-lived Mn excited state (on the order of ms), the energy-transfer between Mn-NCs and molecular oxygen is facilitated with the assistance of the Pt NCs adhered to the Mn-NC@SiO2 surface. Therefore, the Mn-NCs@SiO2-Pt composites, integrate the advantages of Mn-doped NCs, a protective silica layer, and Pt NCs to exhibit excellent catalytic activity and selectivity for the selective oxidation of primary benzylic alcohols to aldehydes through an 1O2 engaged oxidation process under visible-light irradiation. This work paves the way for enhancing catalytic performance via facilitated energy transfer relaxation by utilizing the long-lived excited-state of Mn2+ dopant ions in nanocomposites.