Autooxidation cyclohexane

The reactions depicted in Fig. 32 are most often carried out at low temperatures. The incursion of a thermal process at elevated temperatures has occasionally been observed. In some cases the thermal oxygenation products are identical to the photochemical products and in other cases are different. For example, when 2,3-dimethyl-2-butene/02 NaY is warmed above — 20 °C a reaction was observed which led to pinacolone (3,3-dimethyl-2-butanone) as the major product.98,110 Pin-acolone is not formed in the photochemical reaction at the same temperature. On the other hand, identical products were observed in the thermal and photochemical intrazeolite oxygenations of cyclohexane.114,133 135 These intrazeolite thermal processes occur at temperatures well below that necessary to induce a classical autooxidation process in solution. Consequently, the strong electrostatic stabilization of oxygen CT complexes may also play a role in the thermal oxygenations. Indeed, the increase in reactivity of the thermal oxygenation of cyclohexane with increasing intrazeolite electrostatic field led to the conclusion that initiation of both the thermal and photochemically activated processes occur by the same CT mechanism.134 Identical kinetic isotope effects (kH/kD — 5.5+0.2) for the thermal and photochemical processes appears to support this conclusion.133... 

Radical hydroxylation of hydrocarbons by autooxidation yields alcohols (major products), ketones, and acids (minor products). Cyclohexanol, for example, is formed in 90% yield from cyclohexane and peroxyacetic acid (275). The high -ol/-one ratio at low conversions can sometimes be used as a partial diagnostic tool to distinguish between the radical and electrophilic pathways. The predominant reaction of electrophilic radicals, such as HO, ROO, and CH 3 is H-atom abstraction from reactants (S-H) or peracids, as exemplified by the following ... 

Figure 10-6 Reaction steps to make adipic add by autooxidation of cyclohexane. Adipic add is a key ingredient in Nylon.

CoAPO-5 has been used to oxidize cyclohexane and n-hexane in the presence of acetic acid to give cyclohexyl acetate and hexyl-2-acetate respectively [189]. The active site is regenerated by oxidation of Co(II) to Co(III) by acetic acid. Another example concerns the autooxidation of p-cresol to p-hydroxybenzaldehyde in methanolic sodium hydroxyide solution [190]. 

Molecular oxygen can also oxidize a variety of organic compounds, including hydrocarbons, aldehydes, amines, ethers and ketones. These autooxidation reactions can be used to make a variety of small molecules and a number of industrial processes rely on the controlled oxidation of organics using molecular oxygen (often with a metal catalyst). Examples include the formation of phenol and acetone from cumene (isopropylbenzene) and cyclohexanone from cyclohexane. Phenol is a popular starting material for a number... 

Hermans, L, Peelers, J. and Jacobs, P. (2008). Origin of Byproducts during the Catalytic Autooxidation of Cyclohexane, J. Phys. Chem. A., 112, pp. 1747-1753. 

In systems where such radicals appear (alcohols, amines, some unsaturated compounds), variable-valence metal ions manifests themselves as catalysts for chain termination (see Chapter 11). The reaction of the ions with peroxyl radicals appears also in the composition of the oxidation products, especially at the early stages of oxidation. For example, the only primary oxidation product of cyclohexane autooxidation is hydroperoxide the other products, in particular, alcohol and ketone, appear later as the decomposition products of hydroperoxide. In the presence of stearates of such metals as cobalt, iron, and manganese, all three products (ROOH, ROH, and ketone) appear immediately with the beginning of oxidation and in the initial period (when ROOH decomposition is insignificant), they are formed in parallel with a constant rate. The ratio of rates of their formation is determined by the catalyst. The reason for this behavior is evidently related to the fast reaction of R02 with the catalyst. Thus, the reaction of peroxyl radicals widi variable-valence ions manifests itself in the kinetics as well (the induction period appears imder certain conditions), and alcohol and ketone are formed in parallel with ROOH from R02 among the oxidation products. 

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