Oxidation Organocatalysts

Oxidation Organocatalysts

The action of introducing an organic substance into oxygen or dehydrogenating during the reaction of an organic substance is called oxidation. The essence of the oxidation reaction is that the substance loses electrons. The catalyst for the catalytic oxidation reaction is called oxidation organocatalysts.

Applications

Oxidation organocatalysts can catalyze a variety of reactions. They are generally classified into the organocatalysts that catalyze chemical oxidation reactions and the organocatalysts that catalyze biological reactions. Chemical oxidation organocatalysts generally include nitro, nitroso, peroxyacid, and complex oxidizing agents with inorganic oxides. Biology oxidation organocatalysts are usually enzymes.

• Free radical oxidation： An important catalyst for the chemical oxidation reaction is a carboxylate. In order to impart good solubility of these catalysts in organic solvents, these catalysts are typically derived from highly lipophilic naphthenic acids and ethylhexanoic acid. These catalysts initiate a free radical chain reaction which automatically oxidizes to produce an organic group bonded to oxygen to give a hydroperoxide intermediate. Generally, the selectivity of oxidation is determined by the bond energy. For example, a benzyl C-H bond is replaced by oxygen faster than an aromatic C-H bond.
• Molecular oxygen oxidation: Hydrocarbon-catalyzed molecular oxygen oxidation technology is superior to traditional inorganic oxidant oxidation technology in both experimental and industrial research. At present, catalysts for molecular oxygen oxidation can be classified into the following two categories. One type is metal porphyrin-based biomimetic catalysts, which first activate oxygen before oxidizing the substrate. Another type of catalyst is to first activate the substrate and then combine with oxygen to form an oxidation product, such as a hydroxylamine organic catalyst. Hydroxylamine catalysts have the advantages of relatively mild reaction conditions, wide applicability of substrates, wide range of catalytic activity, and a wide variety of nitrogen-oxygen radical initiators, which can achieve metal-free or solvent-free catalytic oxidation. It has attractive application prospects in the field of hydrocarbon catalytic oxidation.
• Alcohol oxidation: Alcohol oxidation is an important reaction in organic synthesis. Alcohols are oxidized to give carbonyl compounds such as aldehydes, ketones and acids, which are widely used in fine chemical experiments and industrial production. Metal-organic frameworks (MOFs) have become a research hotspot in the field of alcohol oxidation catalysis due to their large specific surface area, porosity, tunability of pore size and structural diversity. For example, oxidation of benzyl alcohol is an important chemical reaction and one of the most commonly used methods for the preparation of benzaldehyde. A cobalt-based metal organic framework catalyst can catalyze the oxidation of benzyl alcohol. Selective oxidation of alcohols to the corresponding carbonyl compounds is also a very important functional group conversion reaction in organic synthesis. For example, the small organic molecule 2,2,6,6-tetramethylpiperidine nitroxyl TEMPO can effectively catalyze the high selectivity of air to oxidize alcohol to the corresponding aldehyde.
• Oxidative desulfurization and denitrification: The organic sulfoxide catalyst can form a stable complex in combination with unstable intermediates such as HNO₂ and H₂SO₃ to form a stable product by oxidation. And the complex can be decomposed so that the catalyst freely binds to the unstable intermediate formed by the new dissolution of the contaminant molecules. At the same time, the organic sulfoxide can extract the acid. Figure 1. Cobalt-based metal organic framework catalyst

  Figure 1. Cobalt-based metal organic framework catalyst

References

1. Hudlický, Miloš (1990). “Oxidations in Organic Chemistry.” American Chemical Society. p.456. ISBN 0-8412-1780-7.
2. Wertz, S.; Studer, A.(2013).”Nitroxide-catalyzed transition-metal-free aerobic oxidation processes” Green Chem. 15, 3116-3134.
3. Neuenschwander, U., Tuna, N., Aellig, C., Mania, P.(2010) ” Understanding selective oxidations”. Chimia.64, 225-230.