4-Ethylphenol


Ethylphenol is an organic compound with the formula C2H5C6H4OH. It is one of three isomeric ethylphenols. A white solid, it occurs as an impurity in xylenols and as such is used in the production of some commercial phenolic resins. It is also a precursor to 4-vinylphenol.

Production

4-Ethylphenol is produced by careful sulfonation of ethylbenzene to 4-ethylphenylsulfonic acid. The sulfonic acid is subsequently subjected to alkaline fusion, the dissolution of the sulfonic acid in molten alkali metal base. The main steps in the synthesis are shown:

Natural occurrences

In wine and beer, 4-EP is produced by the yeast Brettanomyces. At concentrations greater than 140 μg/L it gives the wine aromas described as barnyard, medicinal, band-aids, and mousy. In certain Belgian beer styles, a high 4-EP level may be desirable; however, very high levels of the compound in wine can render it undrinkable. The level of 4-EP is roughly proportional to Brettanomyces concentration and activity, and can therefore be used as an indicator of the yeast's presence. There are significant differences between strains of Brettanomyces in their ability to produce 4-EP.
4-EP is also a component of castoreum, the exudate from the castor sacs of the mature North American beaver and the Eurasian beaver, used in perfumery.

Biochemistry

4-EP is biosynthesized in two steps from p-coumaric acid. Decarboxylation gives 4-vinylphenol as catalyzed by the enzyme cinnamate decarboxylase. 4-Vinylphenol is further reduced to 4-ethylphenol by the enzyme vinyl phenol reductase. Coumaric acid is sometimes added to microbiological media, enabling the positive identification of Brettanomyces by smell.