The chemical compound pinene is a bicyclic terpene (C10H16, 136.24 g/mol ) known as a monoterpene. There are two structural isomers found in nature: a-pinene and -pinene. Both forms are present in many essential oils but are mostly obtained from turpentine (obtained by the dry distillation of wood or other dry botanical material). Turpentine contains 58%-65% a-pinene and about 30% of -pinene. Both pinenes are hydrocarbons and have a molecular weight of 136.23, and contain 88.16% of carbon, 11.84% of hydrogen.

The a pinene obtained in North American oils is largely dextrorotary whereas the European oils are levorotary. The majority of B pinene, irrespective of its origin, is levorotary. As examples, a pinene and pinene are found in Cedar Wood oil, orange oil, mandarin peel oil and in many fragrances. Like many essential oil constituents, the pinenes are thermally labile and need to separated by gas chromatography with considerable caution.

As the name suggests, both forms are important constituents of pine resin; they are also found in the resins of many other conifers, and more widely in other plants. Both are also used by many insects in their chemical communication system.

Pinene has been found in coriander oil, lemon oil, cumin oil, American peppermint oil, and oil of Levant wormseed.

a-Pinene has frequently been found in other oils, but its optical rotation has not been recorded. Thus in Venetian turpentine oil, in the pine tar oil from Finland, in the oil from the leaves and twigs of Larix americana, in Thuja oil, in juniper oil, in the oil from the resin of Callitris verrucosa, in matico oil, in pilea oil, in the oil from Canada snake-root, in boldo leaf oil, in cinnamon root oil, in the oil from Pichurim beans (?), in sassafras oil, the oil from sassafras leaves, in the oils from laurel leaves, massoy bark and Japanese pepper (?), in the oils of bergamot and lemon, in several elemi oils, in oil of myrrh, in the oil from the berries of Schinus molle, in the oils from the following species of Eucalyptus, viz., acmenoides, affinis, aggregata, albens, amygdalina, angophoroides, apiculata, Baeuerleni, bicolor, Bosistoana, Bridgesiana, Cambagei, camphor a, capi-tellata, cinerea, cneorifolia, conica, cordata, corymbosa, crebra, dealbata, dives, dumosa, eugenioides, eximia, fastigiata, Fletcher/, fraxinoides, Globulus, goniocalyx, gracilis, hemilampra, hemiphloia, intermedia, intertexta, lactea, Iongifolia, Lueh-manniana, Macarthuri, macrorrhyncha, maculata, maculosa, Maideni, melanophloia, melliodora, microcorys, microtheca, Morrisii, nova-anglica, odorata, oleosa, ovalifolia, o. var. lan-ceolata, paniculata, pendula, pilularis, polyanthema, polybractea, populifolia, propinqua, pulverulenta, punctata, p. var. didyma, quadrangulata, radiata, resin if era, Risdoni, robusta, Rossi, rostrata, r. var. boreal is, rubida, saligna, siderophloia, sider-oxylon, s. var. pal lens, Smithii, squamosa, stricta, Stuartiana, tereticornis, tessellaris, trachyphloia, umbra, viminalis, viridis and Woollsiana, in French parsley oil, rosemary oil, sage oil, in the oils of Thymus capitatus and Satureja Thymbra, in oil of spike, in golden rod oil, and in the oil of Helichrysum Stcechas.

a-Pinene is a colorless, mobile liquid, which, like most terpenes, undergoes autoxidation upon standing by taking oxygen from the air and partly resinifies. It is readily converted into other terpenes. Thus by a higher temperature (250 to 270) it is changed into dipentene, by moist hydrogen chloride into dipentene or its dihydrochloride, by means of alcoholic sulphuric acid into terpinolene and terpinene, presumably through the dipentene as an intermediate stage. Through the action of dry hydrogen halides a-pinene is changed to derivatives of camphor, a reaction that has become of great importance in the artifical production of camphor.

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