Cobalt-catalyzed oxidation of activated hydrocarbons under an atmosphere of oxygen.

Abstract

Liquid phase oxidation of organic substrates under an atmosphere of oxygen catalyzed by metal complexes is reviewed in Chapter 1. Also included in the review are homogeneous and heterogeneous catalysis and free radical autoxidation reactions. The selective catalytic oxidation of aromatic hydrocarbons is described in Chapter 2. Anhydrous CoCl$\sb2$, CoCl$\sb2$/CrCl$\sb3$, or CoCl$\sb2$/ZrCl$\sb4$ were used as the catalysts to oxidize a variety of substrates in the presence of diglyme or a mixture of diglyme and MEK (1:3). These substrates included substituted toluenes and other benzylic hydrocarbons. The reactions afforded fair to excellent yields of the product aldehydes or ketones under mild conditions. It was discovered that the selectivity of these reactions is strongly influenced by the catalyst and the solvent. Selective catalytic oxidation of ethers and cyclic acetals using cobalt chloride is described in Chapter 3. The oxidation of cyclic ethers gives the corresponding lactones in reasonable to excellent yields. However, 2,3-dihydrobenzofuran leads to no reaction. Oxidation of acyclic alkyl benzyl ethers to the corresponding esters afforded yields which were dependent on the stability of the alkyl radicals. The more stable the alkyl radical, the lower the yield of the ester obtained. In addition, oxidation of acyclic and heterocyclic ethers is described. An investigation of the reaction mechanism of this process was also studied. Finally, the oxidation of 2-substituted 1,3-dioxolanes afforded high yields of formate esters and acids. It was found that the presence of catalytic amounts of ZnCl$\sb2$ promoted the rate of oxidation.