Hydrogen peroxide as primary oxidant

Variations of Oxidant Hydrogen Peroxide as Primary Oxidant... 

Scheme 1.15 Postulated formation of peroxyimidic acid in the asymmetric epoxidation reaction using hydrogen peroxide as primary oxidant...

The first highly enantioselective epoxidation of cyclic enones was developed by List et al. by using hydrogen peroxide as the oxidant and a chiral primary amine salt as the organocatalyst. A series of primary amine salts were investigated for this reaction and the best results were obtained with a quinine-derived primary amine salt, which provided excellent enantioselectivities of up to 99% ee for a variety of cyclic enones, as shown in Scheme 7.7. 

Under microwave irradiation and applying MCM-41-immobilized nano-iron oxide higher activity is observed [148]. In this case also, primary aliphatic alcohols could be oxidized. The TON for the selective oxidation of 1-octanol to 1-octanal reached to 46 with 99% selectivity. Hou and coworkers reported in 2006 an iron coordination polymer [Fe(fcz)2Cl2]-2CH30H with fez = l-(2,4-difluorophenyl)-l,l-bis[(l//-l,2,4-triazol-l-yl)methyl]ethanol which catalyzed the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as oxidant in 87% yield and up to 100% selectivity [149]. An alternative approach is based on the use of heteropoly acids, whereby the incorporation of vanadium and iron into a molybdo-phosphoric acid catalyst led to high yields for the oxidation of various alcohols (up to 94%) with molecular oxygen [150]. 

Traube [15,16] performed the next important step in understanding of the oxidation mechanism. He studied the oxidation of metals in water and proposed hydrogen peroxide as the primary product of oxidation. Traube proposed the following scheme of metal oxidation ... 

A molecule of linear alkyl ether possesses a very convenient geometry for intramolecular hydrogen atom abstraction by the peroxyl radical. Therefore, chain propagation is performed by two ways in oxidized ethers intermolecular and intramolecular. As a result, two peroxides as primary intermediates are formed from ether due to oxidation, namely, hydroperoxide and dihydroperoxide [62],... 

The selective oxidation of saturated hydrocarbons is a reaction of high industrial importance. Besides a variety of other oxidants, hydrogen peroxide as a very clean oxidant has also been used for these purposes . As an example, in 1989 Moiseev and coworkers reported on the vanadium(V)-catalyzed oxidation of cyclohexane with hydrogen peroxide (Scheme 146) . When the reaction was carried out in acetic acid cyclohexanol and cyclohexanone were formed, bnt conversions were very poor and did not exceed 13%. Employing CF3COOH as solvent, complete conversions could be obtained within 5 min-ntes. Here, cyclohexyl trifluoroacetate was the main product (85% of the products formed) resulting from the reaction of cyclohexanol (the primary product of the oxidation) with CF3COOH. 

The subject is highly relevant in the search for more effective, safe and economical activation methods, employing hydrogen peroxide as the primary oxidant source. 

The problem of heavy metal contamination of effluent streams which can result from the use of homogeneous catalysts, whilst not insurmountable, can be eliminated by the use of heterogeneous catalysts such as titanium silicalite205 and phosphotungstic acid on alumina206 with hydrogen peroxide as the primary oxidant. 

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