Catalytic oxidation

Catalytic oxidation are processes that oxidize compounds using catalysts. Common applications involve oxidation of organic compounds by the oxygen in air. Such processes are conducted on a large scale for the remediation of pollutants, production of valuable chemicals, and the production of energy.

An illustrative catalytic oxidation is the conversion of methanol to the more valuable compound formaldehyde using oxygen in air:

This conversion is very slow in the absence of catalysts. Typical oxidation catalysts are metal oxides and metal carboxylates.

Industrially important examples include both inorganic and organic substrates.

Oxidation catalysis is conducted by both heterogeneous catalysis and homogeneous catalysis. In the heterogeneous processes, gaseous substrate and oxygen (or air) are passed over solid catalysts. Typical catalysts are platinum, and redox-active oxides of iron, vanadium, and molybdenum. In many cases, catalysts are modified with a host of additives or promoters that enhance rates or selectivities.

Important homogeneous catalysts for the oxidation of organic compounds are carboxylates of cobalt, iron, and manganese. To confer good solubility in the organic solvent, these catalysts are often derived from naphthenic acids and ethylhexanoic acid, which are highly lipophilic. These catalysts initiate radical chain reactions, autoxidation that produce organic radicals that combine with oxygen to give hydroperoxide intermediates. Generally the selectivity of oxidation is determined by bond energies. For example, benzylic C-H bonds are replaced by oxygen faster than aromatic C-H bonds.

Many selective oxidation catalysts have been developed for producing fine chemicals of pharmaceutical or academic interest. Nobel Prize–winning examples are the Sharpless epoxidation and the Sharpless dihydroxylation.

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