Cycloalkanes, oxidation with oxygen

Other examples of nitroxyl radicals such as TEMPO [3Id, j] have been used successfully in several examples of environmentally friendly liquid-phase oxidations with. oxygen. Sheldon et al. have reported on the use of N-hydroxysaccharin as an alternative to NHPI in the oxidation of cycloalkanes to dicarboxylic acids [31h]. Other examples include the aerobial oxidation in the presence of NHPI, o-phenanthroline and bromine, in an acetonitrile/CCU solvent and in the absence of metals, at 100 °C. The selectivity was 75% to AA and 22% to cyclohexanone, at 48% cyclohexane conversion [31i]. 

Recently, Corma et al. have patented a process of oxidizing cycloalkane with molecular oxygen to produce cycloalkanol and/or cycloalkanone in the presence of hydrotalcite-intercalated heteropoly anion [Co MnCo (H20)039] (M = W or Mo), which comprised one cobalt as a central atom and another as a substitute of a W=0 fragment in the Keggin structure [98]. At 130 °C and 0.5 MPa, 64 and 24% selectivity to cyclohexanone and cyclohexanol, respectively, was achieved at cyclohexane conversion about 5%. This catalytic system could be of practical importance provided a true heterogeneous nature of catalysis and good catalyst recyclability had been proved. Unfortunately, this information was lacking in [98]. 

Similar stoichiometric reactions can be conducted with other organic substrates. Beside mechanistic importance, such reactions are a convenient way for estimating the potential of a-oxygen oxidation. For that, various organic substrates were tested for their room temperature interaction with a-oxygen to identify the primary oxidation products extracted from the surface. Substrates included alkanes, cycloalkanes, alkenes and aromatics [121,122]. Analysis of products showed that in all cases selective formation of hydroxylated compounds took place. 

Uncatalysed oxidation of cycloalkanes and alkylarenes by molecular oxygen with acetaldehyde as sacrificial co-reductant occurs efficiently in supercritical carbon dioxide under mild multiphase conditions.252... 

Gasoline hydrocarbons volatilized to the atmosphere quickly undergo photochemical oxidation. The hydrocarbons are oxidized by reaction with molecular oxygen (which attacks the ring structure of aromatics), ozone (which reacts rapidly with alkenes but slowly with aromatics), and hydroxyl and nitrate radicals (which initiate side-chain oxidation reactions) (Stephens 1973). Alkanes, isoalkanes, and cycloalkanes have half-lives on the order of 1-10 days, whereas alkenes, cycloalkenes, and substituted benzenes have half- lives of less than 1 day (EPA 1979a). Photochemical oxidation products include aldehydes, hydroxy compounds, nitro compounds, and peroxyacyl nitrates (Cupitt 1980 EPA 1979a Stephens 1973). 

The oxidation of cycloalkanes or alkylarenes with molecular oxygen and acetaldehyde as a co-reductant takes place efficiently in scC02 under mild conditions. No catalyst is required and high-pressure ATR-FTIR online measurements showed that a radical reaction pathway was heterogeneously initiated by the stainless steel of the reactor walls (Equation 4.34) [67]. 

To mimic the Cytochrome P450 properties with MePc embedded in zeolites, the oxygenation of alkanes and cycloalkanes has been studied frequently. Occasionally, iodosobenzcnc (PhOI) has been used as oxidant [6] Alternatively, t-butyl hydroperoxide... 

Maldotti, A., Molinari, A., Varani, G., et al. (2002). Immobilization of (n-Bu4N)4Wio032 on Mesoporous MCM-41 and Amorphous Silicas for Photocatalytic Oxidation of Cycloalkanes with Molecular Oxygen, J. Catal, 209, pp. 210-216. 

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