Catalytic oxidation are processes that rely on
catalysts to introduce oxygen into organic and inorganic compounds. Many applications, including the focus of this article, involve oxidation by oxygen. Such processes are conducted on a large scale for the remediation of pollutants, production of valuable chemicals, and the production of energy.
Oxidations of organic compounds
Carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
s,
ketone
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...
s,
epoxides, and
alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
s are often obtained by partial oxidation of
alkane
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...
s and
alkenes with
dioxygen. These intermediates are essential to the production of consumer goods. Partial oxidation is challenging because the most favored reaction between oxygen and hydrocarbons is
combustion.
Oxidations of inorganic compounds
Sulfuric acid is produced from sulfur trioxide which is obtained by oxidation of sulfur dioxide. Food-grade phosphates are generated via oxidation of white phosphorus. Carbon monoxide in automobile exhaust is converted to carbon dioxide in
catalytic converters.
Examples
Industrially important examples include both inorganic and organic substrates.
Catalysts
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
2-Ethylhexanoic acid is the organic compound with the formula CH3(CH2)3CH(C2H5)CO2H. It is a carboxylic acid that is widely used to prepare lipophilic metal derivatives that are soluble in nonpolar organic solvents. 2-Ethylhexanoic acid is a colo ...
, which are highly lipophilic. These catalysts initiate
radical chain reaction
Radical may refer to:
Politics and ideology Politics
*Radical politics, the political intent of fundamental societal change
* Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe an ...
s,
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.
[Mario G. Clerici, Marco Ricci and Giorgio Strukul "Formation of C–O Bonds by Oxidation" in Metal-catalysis in Industrial Organic Processes
Gian Paolo Chiusoli, Peter M Maitlis, Eds. 2006, RSC. .]
Fine chemicals
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.
Biological catalysis
Catalytic oxidations are common in biology, especially since aerobic life subsists on energy obtained by oxidation of organic compounds by air. In contrast to the industrial processes, which are optimized for producing chemical compounds, energy-producing biological oxidations are optimized to produce energy. Many
metalloenzymes mediate these reactions.
Fuel cells, etc
Fuel cell
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
s rely on oxidation of organic compounds (or hydrogen) using catalysts. Catalytic heaters generate flameless heat from a supply of combustible fuel and
oxygen from air as
oxidant.
Challenges
The foremost challenge in catalytic oxidation is the conversion of methane to methanol. Most methane is
stranded, i.e. not located near metropolitan areas. Consequently, it is flared (converted to carbon dioxide). One challenge is that methanol is more easily oxidized than is methane.
Catalytic oxidation with oxygen or air is a major application of
green chemistry. There are however many oxidations that cannot be achieved so straightforwardly. The conversion of propylene to propylene oxide is typically effected using
hydrogen peroxide, not oxygen or air.
References
External links
*https://archive.today/20130626171216/https://portal.navfac.navy.mil/portal/page/portal/NAVFAC/NAVFAC_WW_PP/NAVFAC_NFESC_PP/ENVIRONMENTAL/ERB/THERMCATOX
*http://www.frtr.gov/matrix2/section4/4-59.html
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Catalysis