Terpineol

Terpineols are a group of chemical compounds of which are found as secondary plant substances at least four ( α -, β -, γ - and δ -terpineol ) course. Chemically, they are monocyclic monoterpene alcohols with molecular formula C10H18O. They are clear, colorless liquids with various characteristic odors. The term terpineol in the singular is often used synonymously for α -terpineol.

Structure

There are at least four structurally terpineols (see figure), which are all tertiary monohydric alcohols. Terpineols are further structural isomer to Pinanol, borneol, myrcenol, dihydrocarveol, nerol, geraniol and linalool.

Properties

α -terpineol is a clear, colorless liquid of high viscosity, boiling at 219 ° C and solidified at 34 ° C. The density is 0.935 g/cm3 (20 ° C). The flash point is 90 ° C. The refractive index is 1.48. In water, α -terpineol is almost insoluble.

The smell of the terpineols is very different, depending on its structure and stereochemistry. Thus, ( R) - ( )- α -terpineol a very intense smell of lilac on; on the other hand smells the stereoisomers of opposite handedness, ( S) - ( -)- α - terpineol, coniferous -like. The thiol derivative Thioterpineol is the material with the lowest known odor threshold.

Occurrence

Terpineols occur in essential oils of many plants, such as laurel, rosemary, aniseed, marjoram, sage and juniper. They are also found in turpentine. The essential oil of turmeric contains up to 500 ppm terpineol, in the seed of the nutmeg Nussbaum occur up to 9600 ppm α -terpineol.

Synthesis

Racemic α -terpineol can be synthesized as follows: isoprene is reacted with methyl acrylate in a Diels -Alder reaction to give racemic 4- methylcyclohex -3-ene -1-carboxylic acid methyl ester. This is due to the low boiling point of isoprene, preferable catalyzed by Lewis acid variant. This results in a Grignard reaction with methyl magnesium bromide ( CH3MgBr, Grignard reagent ) to the hydrolysis α -terpineol as a racemic mixture:

α -terpineol can also be prepared from the cis- trans isomers geraniol and nerol in an acidic environment. β -terpineol is prepared 1,8-dihydroxy -p-menthane.

Technically, α -terpineol by hydration of α - pinene, turpentine oil or with acid ( cis- terpin hydrate yields ) followed by partial dehydration in the presence of weak acids or acid activated silica gel produced.

Reactions

From α - terpineol, formed by hydrogenation of p- menthane- 8 -ol, dehydration results in a mixture of unsaturated terpene hydrocarbons. The most important for the perfume industry is the esterification reaction, especially to terpinyl.

Use

Terpineols are fragrances. They are used, for example, soaps and perfumes. Most often you take a mixture of α - and γ -terpineol for intense scent of lilac.