Alcohol dehydrogenase catalyzes the oxidation of ethanol to acetaldehyde, which is further oxidized to acetic acid (as the acetate ion), a normal metabolite.
Today the dominant process for the manufacture of acetaldehyde is the Wacker process, developed between 1957 and 1959, which catalyzes the oxidation of ethylene to acetaldehyde.
The prototype of this reaction is the conversion of acetaldehyde to β-hydroxybutyraldehyde, or aldol.
Some of the more important have been lumped together in a box (Figure 3): acetaldehyde, acrylonitrile, acetic acid, acetic anhydride, the list bringing together substances that have complex interrelations.
Pure acetaldehyde is a colourless, flammable liquid with a pungent, fruity odour; it boils at 20.8 °C (69.4 °F).
The first step of this reaction is the production of an enolate ion (as in formation of the keto enol tautomeric mixture), but this anion then reacts with a second molecule of acetaldehyde to give the product as shown below: These examples illustrate the importance of acid base catalysis in organic reactions.
The resulting accumulation of the highly toxic acetaldehyde results in such symptoms as flushing, nausea, vomiting, a sudden sharp drop of blood pressure, pounding of the heart, and even a feeling of impending death.
Nevertheless, the equilibrium always exists, and every molecule of acetaldehyde (as well as any other aldehyde or ketone with an α-hydrogen) is converted to the enol form (and back again) several times per second.
Ethanol could have been shown in Figure 3 between ethylene and the block containing acetaldehyde and several related chemicals.
Palladium chloride together with salts of copper in the +1 oxidation state forms a homogeneous catalyst for oxidizing ethylene to acetaldehyde (Wacker process), but commercial use of this process has been abandoned.
Commercial n-butyl alcohol is made by fermentation of corn (maize) or molasses or by condensation and reduction of acetaldehyde.
