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Turpentine

Update: 6/3/2013

Turpentine is a liquid produced by extracting volatile substances, terpenes, mainly from wood. This can be done in various ways, and since different trees contain different amounts of different terpenes, turpentines vary a great deal in composition.

Fresh turpentine is colourless, but as the terpenes oxidate – which they do readily and continuously – the liquid becomes more of a yellow colour. Turpentine has a strong smell derived from its constituent terpenes.

The oldest way of producing turpentine (gum turpentine) is by distilling it from resin (turpentine gum) extracted from trees. Later, when the supply of turpentine gum fell short of demand, wood turpentine was extracted from stumps and suchlike tree refuse. 
 
Nowadays, apart from specialised grades mainly for artists’ use (balsam turpentine) turpentine is a by-product of the production of pulp. Sulphate turpentine is chilled from the gas emitted when wood chips are pre-heated with steam before digestion. Pine and spruce have the best turpentine yields.
 
Turpentine consists of 45-75% a-pinene (1), 5-30% b-pinene (2), 2-40% 3-carene (3), other turpentines such as limonene and camphene and their oxidation products, such as alcohols and aldehydes.
Terpenes are a group of hydrocarbons which can be regarded as oligomers of isoprene, 2-methyl-1,3-butadiene. They often contain cyclic structures and double bondings, and their derivates are also included in the term “terpenes”.

Terpenes are divided into groups according to the number of isoprene units they contain. Turpentine contains monoterpenes consisting of two isoprene units, while the resin (colophony) remaining after distillation of gum turpentine consists of four units, known as diterpenes.

The ratio between the different terpenes in turpentine varies according to origin. American turpentine contains a good deal more a- and b-pinene than Swedish turpentine, which instead contains 30-40% 3-carene, or Indian turpentine, which can include up to 70% 3-carene. “French turpentine” contains only small amounts of 3-carene. 
 
Turpentine has long been used as a solvent, above all for paints, but its use for this purpose has diminished in favour of petroleum solvents. The latter used often to be called mineral turpentine to distinguish them from turpentines extracted from wood.

In recent years there has been a growth of interest in traditional methods of treating wood in connection with building conservation, which spells a come-back for turpentine, and above all for various balsam turpentines, as dilutants.
The quantity involved, however, is marginal compared with the amount of petroleum solvents used as dilutants/solvents. Many of the odorants and flavouring agents traditionally produced from terpenes extracted from turpentine are also nowadays synthesised less expensively from petroleum raw materials.

Fractionation of turpentine, for example, yields 60-70% a-pinene, 20-25% b-pinene, 3-10% limonene and carene, 3-7% pine oil and a few % miscellaneous substances.
It is above all a-pinene that is used for synthesis to camphor, synthetic pine oil, camphene, linalool and many other substances used as odorants and flavouring agents and as raw materials for pharmaceuticals.

The limonene fraction is sold as a solvent under the name of dipentene. Terpenes are used to make terpene resins and can also be used as fuel.
 
Source: http://apps.kemi.se

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