Molecular-sieve catalysts for the selective oxidation of linear alkanes bymolecular oxygen

Terminally oxidized hydrocarbons are of considerable interest as potential feedstocks for the chemical and pharmaceutical industry, but the selective oxidation of only the terminal methyl groups in alkanes remains a challengi ng task. It is accomplished with high efficiency and selectivity by some en zymes; but inorganic catalysts, although inferior in overall performance un der benign conditions, offer significant advantages from a processing stand point(1). Controlled partial oxidation is easier to achieve with 'sacrifici al' oxidants, such as hydrogen peroxide(2), alkyl hydroperoxides or iodosyl benzene(3), than with molecular oxygen or air. These sacrificial oxidants, themselves the product of oxidation reactions, have been used in catalytic systems involving: tailored transition-metal complexes in either a homogene ous state(4-6), encapsulated in molecular sieves(7-9) or anchored to the in ner surfaces of porous siliceous supports(10). Here we report the design an d performance of two aluminophosphate molecular sieves containing isolated, four-coordinated Co(III) or Mn(III) ions that are substituted into the fra mework and act, in concert with the surrounding framework structure, as reg ioselective catalysts for the oxidation of linear alkanes by molecular oxyg en. The catalysts operate at temperatures between 373 K and 403 K through a classical free-radical chain-autoxidation mechanism. They are thus able to use molecular oxygen as oxidant, which, in combination with their good ove rall performance, raises the prospect of using this type of selective inorg anic catalyst for industrial oxidation processes.