Volatile oil

Volatile oils• different from fixed– secreted in oil cells in specialised structures

• ducts, gland, cell or glandular hairs– frequently associated with other substances

• gums, resins (resinify on exposure to air)

• mainly terpenoid– some phenol ethers and phenols

• Terpenoids– based on the 5C isoprene unit

– Monoterpenes• most important, most volatile

– di-, tri-, sesquiterpenes also important

• contain 2 condensed 5C units head-tail

Monoterpene components

• Hydrocarbons

• Alcohols

• Aldehydes

– all produced via the terpenoid pathway

• Ketones

Citral

• Esters

• Oxides

Sesquiterpenes (C15)

Hydrocarbons Phenols Phenolic esters

Anethole

Chemical and physical properties

• volatile liquids with no colour– keep in amber bottles with minimum air

• odour• asymetric centres, isomers with optical activity

– only one isomer occurs naturally• refractive index normally high

– is a means to characterise the oil• miscible in water and soluble in organic solvents

– more soluble if contains –OH fatty acids• reasonably heat stable

– can be steam distilled• tend to be used as solvents for resins

Families• Economically only a few family groups are

commercially useful

[1] LabiataeLavender, Mentha Sp.

• oil occurs in special organs – synthesized in glandular trichomes (mint)

[2] UmbelliferaeFruits (best if ripe): anise, caraway, fennel, coriander

• found in “vittae” in the outer layer is characteristic

[3] PinaceaePine, juniper

• found in resin ducts in outer old xylem or bark• released when bark removed

[4] RutaceaeCitrus fruits

• typical ductless sacs in outer part of fruit – rind• less stable, need more care

[5] LauraceaeCinnamon, camphor

• from region immediately below bark

Usesas inhalations, orally, gargles, mouthwashes, trans-dermally

[1] Flavours & carminatives[2] Local stimulants and antiseptics

(containing phenols)[3] Perfumes[4] Insect repellant, antimating device[5] Starting materials