Biological Oxidation of Alcohols

Oxidation of alcohols to carbonyl compounds may be found in our bodies. Ethanol, for example, is oxidized

in the liver to acetaldehyde(ethanal). The enzyme that catalyses the oxidation of ethanol is called alcohol dehydrogenase.

The rate of oxidation of ethanol in a particular person is constant, regardless of the concentration of alcohol present. Thus ingestion of ethanol from alcoholic beverages at a rate greater than the rate of oxidation results in a build up of ethanol in the bloodstream, leading to intoxication.

Acetaldehyde is further oxidized to acetate(ethanoate) in a reaction catalysed by the enzyme aldehyde dehydrogenase.

Acetate is used by the body in the synthesis of fatty acids and cholesterol.

However, methanol is a poisonous substance that can cause blindness or death from the ingestion of even small amounts. Methanol is oxidized to formaldehyde(methanal) in the body by the same enzyme system that oxidizes ethanol, alcohol dehydrogenase.

formaldehyde is toxic to the retina of the eye and is the cause of blindness from methanol ingestion. Formaldehyde is further oxidized in the body to formate(methanoate).

Formate is not utilized rapidly by the body and collects in the blood as formic acid(methanoic acid). This lowers the pH of the blood below the normal physiological range, resulting in a fatal condition called acidosis.

One treatment for methanol poisoning makes use of the fact that both methanol and ethanol are oxidized in the body by the same enzyme systems. A solution containing ethanol is given to a victim of methanol poisoning. Ethanol is considerably less toxic than methanol, and the ethanol oxidation "ties up" the enzymes, preventing the more harmful methanol oxidation from occurring.