Peroxidative oxidations, of alcohols

Hydrogen peroxide is an inexpensive oxidant, but it requires a catalyst to effect oxidation of an alcohol to the ketone. Removal of the catalyst then becomes an issue. Ronny Neumann of the Weizmann Institute of Science reports (J. Am. Chem. Soc. 2004,126, 884) the development of a hybrid organic-tungsten polyoxometalate complex that is not soluble in organic solvents, but that nonetheless catalyzes the hydrogen peroxide oxidation of alcohols to ketones. The solid catalyst is removed by filtration after the completion of the reaction. The catalyst retained its activity after five recyles. 

Enantioselective, multiple centers 153, 166,189 Hydroamination Intermolecular Alkene 30 Alkyne 1 Intramolecular Alkene 30 Alkyne 13,170 Hydrogen peroxide Oxidation of alcohols 26, 86 Hydrogenolysis of epoxide 1 Hydrozirconation 32... 

Oxidations with nickel peroxide Oxidation of alcohols s. 17, 225... 

Aerobic and peroxidative oxidations of alcohols, in particular of benzylic alcohols, are typical model reactions due to their importance and generality inexpensive O2, H2O2 or tejt-butyl hydroperoxide (TBHP) oxidants, and simple procedures are usually involved. In this section, an overview of some interesting catalytic systems, which were lately introduced into the field of alcohol oxidation, is presented. This concerns mainly homogeneous systems, since recent advances on heterogeneous catalysts are included in Section 8. Moreover, a glance at new substrates and oxidants which could successfully be used in a near future and make a difference in terms of efficiency, selectivity, economy and/or sustainability of the processes, is also presented. 

Pigiel PJ, Kirillov AM, Guedes da Silva MFC, Lasri J, Pombeiro AJL. Self-assembled dicopper(II) diethanolaminate cores for mild aerobic and peroxidative oxidation of alcohols. Dalton Trans. 2010 39 9879-9888. 

Petoxycatboxyhc acids have been obtained from the hydrolysis of stable o2onides with catboxyhc acids, pethydtolysis of acyhinida2ohdes, reaction of ketenes with hydrogen peroxide, electrochemical oxidation of alcohols and catboxyhc acids, and oxidation of catboxyhc acids with oxygen in the presence of o2one (181). 

This ladical-geneiating reaction has been used in synthetic apphcations, eg, aioyloxylation of olefins and aromatics, oxidation of alcohols to aldehydes, etc (52,187). Only alkyl radicals, R-, are produced from aliphatic diacyl peroxides, since decarboxylation occurs during or very shortiy after oxygen—oxygen bond scission in the transition state (187,188,199). For example, diacetyl peroxide is well known as a source of methyl radicals (206). 

Induced oxidation of alcohols by hydrogen peroxide was studied by Kolthoff and Medalia . According to their measurements the value of F-, increases with the increase in the concentration of ethanol, while it decreases with increase in the acid concentration (see Table 16). In acetic acid medium the value of F[ is considerably lower. Chloride ions effectively suppress the induced oxidation of alcohols. The main product of the oxidation of ethanol is acetaldehyde which can be further oxidized to acetic acid. The data on the induced oxidation of alcohol (H2A) can be interpreted by reactions (53), (98), (99) and (57). 

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

Before showing how direct peroxidation of active group works, it should be mentioned that platinum catalyses oxidation of alcohols at ambient temperature in aldehydes (provided they are primary). The exothermicity of the reaction is sufficient to cause the alcohol to combust by heating a thread of platinum at a high temperature. Note that 2-butanol (but not isopropanol) is classified in list B, producing peroxides that become expiosive at a certain concentration in the lists of peroxidable compounds set up by Du Pont de Nemours company (see p.261). 

Oxidation of alcohol produces hydrogen peroxide and carbonyl compound simultaneously (aldehyde and ketone from primary and secondary alcohols, respectively). Carbonyl compound is formed as a result of alkylhydroxyperoxyl radical decomposition... 

The ALDs are a subset of the superfamily of medium-chain dehydrogenases/reductases (MDR). They are widely distributed, cytosolic, zinc-containing enzymes that utilize the pyridine nucleotide [NAD(P)+] as the catalytic cofactor to reversibly catalyze the oxidation of alcohols to aldehydes in a variety of substrates. Both endobiotic and xenobiotic alcohols can serve as substrates. Examples include (72) ethanol, retinol, other aliphatic alcohols, lipid peroxidation products, and hydroxysteroids (73). 

Peroxide oxidation of primary and secondary alcohols (Table 10.31)... 

Tungsten-catalysed oxidation of alcohols by hydrogen peroxide is achieved in high yield in the presence of tetra-n-butylammonium hydrogen sulphate [20-22]. Secondary alcohols are converted into ketones (>90%) [e.g. 21], but primary alcohols generally are oxidized completely to the carboxylic acids [21], Aldehydes are also oxidized to the carboxylic acids [e.g. 21]. In contrast, using procedure 10.7.8.B, which is adaptable to scale up, benzyl alcohols are converted into the aldehydes benzoic acids are only formed with an excess of hydrogen peroxide [22],... 

Common alcohol oxidation methods employ stoichiometric amounts of toxic and reactive oxidants like Cr03, hypervalent iodine reagents (Dess-Martin) and peracids that pose severe safety and environmental hazards in large-scale industrial reactions. Therefore, a variety of catalytic methods for the oxidation of alcohols to aldehydes, ketones or carboxylic acids have been developed employing hydrogen peroxide or alkyl hydroperoxides as stoichiometric oxygen sources in the presence of catalytic amounts of a metal catalyst. The commonly used catalysts for alcohol oxidation are different MoAV(VI), Mn(II), Cr(VI), Re(Vn), Fe(II) and Ru complexes . A selection of published known alcohol oxidations with different catalysts will be presented here. 

Silicon and gennaninm peroxides TABLE 8. Oxidation of alcohols with BTSP in the presence of RuCl2(PPh3)3... 

Several mechanisms for the peroxide oxidation of organosilanes to alcohols are compared. Without doubt, the reaction proceeds via anionic, pentacoordinate silicate species, but a profound difference is found between in vacuo and solvated reaction profiles, as expected. In the solvents investigated (CH2CI2 and MeOH), the most favorable mechanism is addition of peroxide anion to a fluorosilane used as starting material or formed in situ, followed by a concerted migration and dissociation of hydroxide anion. In the gas phase, and possibly in very nonpolar solvents, concerted addition-migration of H2O2 to a pentacoordinate fluorosilicate is also plausible. ... 

An inner-sphere hydrogen atom abstraction from the alcohol by a peroxo metal complex, thus forming a coordinated ketyl radical [(CH3)2—C —O—V(0)(00H)]" , has been proposed for the aerobic oxidation of alcohols catalyzed by peroxidic molybdenum and vanadium derivatives (Scheme 16). While in the case of Mo-catalyzed reaction the H2O2 produced is quantitatively converted to products (ketone and H2O), in the vanadium mediated process, hydrogen peroxide accumulates . In this latter case, the direct involvement of a vanadium monoperoxo species has been substantiated by ESI-MS data. 

Organic Solvent- and HaUde-Free Oxidation of Alcohols with Aqueous Hydrogen Peroxide (Sato et al., 1997)... 

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