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 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 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.
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.
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 is manufactured from myrcene by hydration of its sulphurdioxide-adduct with sulphuric acid and removing of the sulphurdioxide under reduced pressure.
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