Verbenone

Verbenone is a natural organic compound classified as a terpene which plays an important role in the control of the Southern pine bark beetle.

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Chemistry

Verbenone is a bicyclic ketone which is found naturally in a variety of plants. It is the primary constituent of the oil of Spanish verbena, hence its name; it is also found in the oil of rosemary. It has a pleasant characteristic odor. It is nearly insoluble in water, but miscible with most organic solvents.^[1]

Verbenone can be readily prepared synthetically by the oxidation of the more common terpene α-pinene:^[2]

Verbenone can then be converted into chrysanthenone through a photochemical rearrangement reaction:^[3]

Use for insect control

The Southern pine bark beetle (Dendroctonus frontalis) is a major threat to pine trees in the southeastern United States. Its reproductive cycle is controlled by varying ratios of certain natural chemicals, including verbenone. To reproduce, pine bark beetles aggregate in large numbers in their host pine trees. At the beginning of an attack, various chemicals produced by infested trees and by the beetles attract additional beetles of the same species. When the numbers of adults and larvae approach the maximum that the tree can support, antiaggregation signal chemicals are produced to keep additional beetles away. Forest managers frequently try to control infestations of the Southern pine bark beetle by cutting down and sometimes burning infested trees and nearby healthy trees. They then hang verbenone pouches on nearby susceptible healthy trees to repel and confuse the beetles.^[4]

Other uses

Because of its pleasant aroma, verbenone (or essential oils high in verbenone content) are used in perfumery, aromatherapy, herbal teas, spices and herbal remedies. The L-isomer is used as a cough suppressant under then name levoverbenone. Verbenone may have also have antimicrobial properties.^[5]

References

1. ^ Merck Index, 11th Edition, 9862.
2. ^ Glidden, U.S. Patent 2,911,442 (1959).
3. ^ "Photochemical transformations of unsaturated bicyclic ketones. Verbenone and its photodynamic products of ultraviolet irradiation." William F. Erman J. Am. Chem. Soc.; 1967; 89(15); 3828-3841. Abstract
4. ^ U.S. Environmental Protection Agency Pesticide Fact Sheet #128986.
5. ^ "Chemical composition and antimicrobial activity of Rosmarinus officinalis L. essential oil obtained via supercritical fluid extraction." Santoyo S, Cavero S, Jaime L, Ibanez E, Senorans FJ, Reglero G. J Food Prot. 2005 Apr;68(4):790-5. Abstract