Around 300,000 tons of turpentine are isolated from plant materials, mainly Pine species. From these 300,000 tons circa 100,000 tons are used as starting material for the production of aroma chemicals. Turpentine mainly consists of a mixture of monoterpenes, hydrocarbons with 10 carbon atoms, from which the most important are alpha- and beta-pinene. Sometimes turpentine is used as such for the production of aroma chemicals, for instance for alpha-terpineol and isoborneol. More often the defined monoterpenes are isolated by fractional distillation before use. A small review of some important aroma chemicals produced from turpentine or alpha/beta-pinene will be given below.
alpha-Terpineol
alpha-Terpineol is manufactured in at least two ways: (a) by
hydration of turpentine (alpha- and beta-pinene) with sulphuric acid
at roomtemperature to terpine hydrate and subsequently dehydration of
this hydrate with phosphoric acid and simultaneously
steamdistillation of alpha-terpineol, and (b) direct mono-hydration
of turpentine in acetone with a low concentration of sulphuric acid
at elevated temperature.
Isoborneol
Isoborneol is produced by converting turpentine with a titaniumoxide
catalyst to camphene and hydration of camphene with sulphuric acid.
This reaction is often carried out in the presence of acetic acid
under the formation of isobornyl acetate.
Geraniol-nerol
beta-Pinene is pyrolyzed in the gasphase at high temperature to
myrcene. Hydrochloric acid is added to myrcene in the presence of a
copper chloride catalyst to form geranyl/neryl chloride, which in
turn are reacted with sodium acetate to form the corresponding
acetate. Geranyl/neryl acetates are saponified to the alcohols.
Linalool
alpha-Pinene is hydrogenated to cis-pinane, which is oxygenated with
a peroxide to cis-pinanol. This pinanol subsequently is pyrolized at
high temperature to linalool.
Myrcenol
Myrcenol is manufactured from myrcene by hydration of its
sulphurdioxide-adduct with sulphuric acid and removing of the
sulphurdioxide under reduced pressure.
Dihydromyrcenol
Dihydromycenol is produced from alpha-pinene via cis-pinane (see
Linalool), by pyrolizing it to dihydromyrcene and consequently (a)
addition of formic acid to a mixture of dihydromyrcenol and its
formate, or (b) direct hydration of dihydromyrcene with a high
concentration of sulphuric acid.
Reprinted by Leffingwell & Associates, 2006, with Permission