Technical Production of Aldehydes by Continuous Bleach Oxidation of Alcohols Catalyzed by 4-Hydroxy-TEMPO

Continuous Flow Oxidation of Alcohols Using TEMPO/NaOCl for the Selective and Scalable Synthesis of Aldehydes

A simple and benign continuous flow oxidation protocol for the selective conversion of primary and secondary alcohols into their respective aldehyde and ketone products is reported. This approach makes use of catalytic amounts of TEMPO in combination with sodium bromide and sodium hypochlorite in a biphasic solvent system. A variety of substrates are tolerated including those containing heterocycles based on potentially sensitive nitrogen and sulfur moieties. The flow approach can be coupled with inline reactive extraction by formation of the carbonyl-bisulfite adduct which aids in separation of remaining substrate or other impurities. Process robustness is evaluated for the preparation of phenylpropanal at decagram scale, a trifluoromethylated oxazole building block as well as a late-stage intermediate for the anti-HIV drug maraviroc which demonstrates the potential value of this continuous oxidation method.

Synergistic Effect of Photocatalyst CdS and Thermalcatalyst Cr2O3-Al2O3 for Selective Oxidation of Aromatic Alcohols into Corresponding Aldehydes

Selective transformation of alcohols to corresponding aldehydes has a crucial significance under mild conditions in industrial manufacturing. Herein, a novel photothermal catalyst (Cr₂O₃-Al₂O₃)/CdS (CAO/CdS) was successfully synthesized by coupling two-dimensional Cr₂O₃-Al₂O₃ (CAO) nanosheets and one-dimensional CdS nanorods. The CAO/CdS was characterized in detail. The synergistic effect of thermal catalyst CAO and photocatalyst CdS on the transformation of aromatic alcohols into aldehydes was verified. The result exhibited that alcohols could be oxidized into corresponding aldehydes efficiently under visible light illumination due to photocatalysis of CdS and thermal catalysis of CAO. CAO can weaken the bonds of O-H and C-Hα of alcohol at low temperatures, and CdS can produce active substances (·O₂^- and h⁺) for oxidizing alcohols to aldehydes under visible light illumination. The benzaldehyde yield increased about three times. It is proposed that the work has significant theoretical and practical values in photocatalysis studies.

Continuous flow oxidation of benzylic and aliphatic alcohols using bleach: process improvement by precise pH adjustment in flow with CO2

Commercial bleach neutralization using CO₂ enhanced the oxidation rate of benzylic and aliphatic alcohols to their corresponding aldehydes and ketones.

Amino acid-assisted synthesis of In2S3 hierarchical architectures for selective oxidation of aromatic alcohols to aromatic aldehydes

Flowerlike-In₂S₃ photocatalyst was prepared via a biosynthesis technique and showed high activity toward the selective oxidation of aromatic alcohols.

Redox-Flow Batteries: From Metals to Organic Redox-Active Materials

Research on redox-flow batteries (RFBs) is currently experiencing a significant upturn, stimulated by the growing need to store increasing quantities of sustainably generated electrical energy. RFBs are promising candidates for the creation of smart grids, particularly when combined with photovoltaics and wind farms. To achieve the goal of "green", safe, and cost-efficient energy storage, research has shifted from metal-based materials to organic active materials in recent years. This Review presents an overview of various flow-battery systems. Relevant studies concerning their history are discussed as well as their development over the last few years from the classical inorganic, to organic/inorganic, to RFBs with organic redox-active cathode and anode materials. Available technologies are analyzed in terms of their technical, economic, and environmental aspects; the advantages and limitations of these systems are also discussed. Further technological challenges and prospective research possibilities are highlighted.

Continuous Flow Aerobic Alcohol Oxidation Reactions Using a Heterogeneous Ru(OH) x /Al2O3 Catalyst

Ru(OH) x /Al2O3 is among the more versatile catalysts for aerobic alcohol oxidation and dehydrogenation of nitrogen heterocycles. Here, we describe the translation of batch reactions to a continuous-flow method that enables high steady-state conversion and single-pass yields in the oxidation of benzylic alcohols and dehydrogenation of indoline. A dilute source of O2 (8% in N2) was used to ensure that the reaction mixture, which employs toluene as the solvent, is nonflammable throughout the process. A packed bed reactor was operated isothermally in an up-flow orientation, allowing good liquid-solid contact. Deactivation of the catalyst during the reaction was modeled empirically, and this model was used to achieve high conversion and yield during extended operation in the aerobic oxidation of 2-thiophene methanol (99+% continuous yield over 72 h).

CuCl/DABCO/4-HO-TEMPO-catalyzed aerobic oxidative synthesis of 2-substituted quinazolines and 4H-3,1-benzoxazines

The Cu/N-ligand/TEMPO catalytic system was first applied to the aerobic oxidative synthesis of heterocycles. As demonstrated, 2-substituted quinazolines and 4H-3,1-benzoxazines were synthesized efficiently from the one-pot reaction of aldehydes with 2-aminobenzylamines and 2-aminobenzyl alcohols, respectively, by employing CuCl/DABCO/4-HO-TEMPO as the catalysts and oxygen as the terminal oxidant.

A biphasic oxidation of alcohols to aldehydes and ketones using a simplified packed-bed microreactor

We demonstrate the preparation and characterization of a simplified packed-bed microreactor using an immobilized TEMPO catalyst shown to oxidize primary and secondary alcohols via the biphasic Anelli-Montanari protocol. Oxidations occurred in high yields with great stability over time. We observed that plugs of aqueous oxidant and organic alcohol entered the reactor as plugs but merged into an emulsion on the packed-bed. The emulsion coalesced into larger plugs upon exiting the reactor, leaving the organic product separate from the aqueous by-products. Furthermore, the microreactor oxidized a wide range of alcohols and remained active in excess of 100 trials without showing any loss of catalytic activity.

Green oxidations with laccase–mediator systems

Laccases are oxidase enzymes produced by ‘white rot’ fungi as part of a complex armoury of redox enzymes used to break down lignin – part of the carbon cycle of nature. Laccases alone or in combination with redox co-catalysts have been shown to oxidize xenobiotic compounds under conditions that can be described as ‘green’. This paper describes some novel oxidations using the laccase–mediator method and some current limitations to the use of this technology.