1911 Encyclopædia Britannica/Eugenol
EUGENOL (allyl guaiacol, eugenic acid), C10H12O2, an odoriferous principle; it is the chief constituent of oil of cloves, and occurs in many other essential oils. It can be synthetically prepared by the reduction of coniferyl alcohol, (HO)(CH3O)C6H3·CH:CH·CH2OH, which occurs in combination with glucose in the glucoside coniferin, C16H22O8. It is a colourless oil boiling at 247° C., and having a spicy odour. On oxidation with potassium permanganate it gives homovanillin, vanillin, &c.; with chromic acid in acetic acid solution it is converted into carbon dioxide and acetic acid, whilst nitric acid oxidizes it to oxalic acid. By the action of alkalis it is converted into iso-eugenol, which on oxidation yields vanillin, the odorous principle of vanilla (q.v.). This transformation of allyl phenols into propenyl phenols is very general (see Ber., 1889, 22, p. 2747; 1890, 23, p. 862). Alkali fusion of eugenol gives protocatechuic acid. The amount of eugenol in oil of cloves can be estimated by acetylation, in presence of pyridine (A. Verley and Fr. Baelsing, Ber., 1901, 34, p. 3359). Chavibetol, an isomer of eugenol, occurs in the ethereal oil obtained from Piper betle.
The structural relations are: