Oxidação de olefinas, fenóis e anilinas catalisada por compostos de metais de transição

Abstract

Cobalt- and manganese-substituted ferrites were used as heterogeneous catalysts for liquid-phase aerobic oxidations of various monoterpenic alkenes. The materials were prepared by co-precipitation and characterized by Mössbauer spectroscopy, powder X-ray diffractometry, magnetization measurements, and elemental analysis. The results show that isomorphic substitution of iron in the ferrite crystalline structure occurs preferentially at octahedral positions and strongly affects its catalytic properties in the oxidation of monoterpenes. Various valuable oxygenated monoterpenic compounds were obtained with high combined selectivities (75-95%) at ca. 40% substrate conversions. Oxidations of â-pinene and 3-carene lead almost exclusively to allylic mono-oxygenated derivatives, while limonene and á-pinene give both epoxides and allylic products. The use of inexpensive catalyst and oxidant, solvent free conditions, and high final product concentrations (ca. 40 wt.%) are significant practical advantages of this environment-friendly process. The catalysts undergo no metal leaching and can be easily recovered by the application of an external magnet and re-used. A simple, low cost and highly selective method for the synthesis of mono bromophenols from phenol and electron-rich phenolic compounds has been developed. Bromide ions are used as halogenating agents, dioxygen as a final oxidant, and Cu(OAc)2 as a catalyst. Nuclear oxybromination of unprotected aromatic primary amines catalyzed by Cu(OAc)2 under mild conditions has been developed, in which bromide ions are used as halogenating agents and dioxygen as a final oxidant. The catalyst shows not only high regioselectivity for para- or ortho isomers but also a remarkable chemoselectivity for monobromination. Oxychlorination of aniline can also be performed under similar conditions, albeit with lower selectivities, with N-phenylacetamide being the main by-product. This simple catalytic method represents ecologically benign and economically attractive synthetic pathway to expensive low-volume aromatic haloamines.