Terpineol is any of four isomeric monoterpenoids. Terpenoids are terpene that are modified by the addition of a functional group, in this case, an alcohol. Terpineols have been isolated from a variety of sources such as cardamom, cajuput oil, pine oil, and petitgrain oil. Four isomers exist: ñ-terpineol, ò-terpineol, ó-terpineol, and terpinen-4-ol. ò-Terpineol and ó-terpineol differ only by the location of the double bond. Terpineol is usually a mixture of these isomers with ñ-terpineol as the major constituent.
Terpineol has a pleasant odor similar to lilac and is a common ingredient in perfumes, cosmetics, and flavors. ñ-Terpineol is one of the two most abundant aroma constituents of lapsang souchong tea; the ñ-terpineol originates in the pine smoke used to dry the tea. (+)-ñ-Terpineol is a chemical constituent of skullcap.
Although it is naturally occurring, terpineol is commonly manufactured from alpha-pinene, which is hydrated in the presence of sulfuric acid.
An alternative route starts from limonene:
Limonene reacts with trifluoroacetic acid in a Markovnikov addition to a trifluoroacetate intermediate, which is easily hydrolyzed with sodium hydroxide to ñ-terpineol with 7% selectivity. Side-products are ò-terpineol in a mixture of the cis isomer, the trans isomer, and 4-terpineol.
The biosynthesis of ñ-terpineol proceeds from geranyl pyrophosphate, which releases pyrophosphate to give the terpinyl cation. This carbocation is the precursor to many terpenes and terpenoids. Its hydrolysis gives terpineol.