PLANT SOURCES OF CAMPHOR, BORNEOL, AND CINEOL (EUCALYPTOL).
Reading edition
Owing to the presence in large quantities of the compounds camphor, borneol, and cineol in the oils to be described in this bulletin, the usual sources of these compounds are herewith presented, together with their commercial uses.
The occurrence of camphor in the vegetable kingdom as a component of volatile oils has been noted chiefly in such plant families as the Lauraceæ, Compositæ, Labiatæ, and Zinziberaceæ. The source of commercial camphor at present is the camphor tree, Cinnamomum camphora (Laurus camphora), indigenous to Japan and Formosa. This tree has been introduced into the United States and experiments are now being conducted in Florida for the production of camphor, with some degree of success.
Two modifications of camphor occur in nature, the commercial variety, or dextrogyrate (rotating the plane of polarization to the right), and the levogyrate (having the opposite rotation). Comparatively few plants native to this country have been found to yield camphor. Whittelsey[1] has recently succeeded in isolating and identifying levo camphor in considerable quantities from the oil of a western sagebrush (Artemisia cana Pursh., family Compositæ). Camphor has been observed in the native plant Sassafras variifolium (Sassafras officinalis), a tree belonging to the family Lauraceæ. According to Power and Kleber,[2] sassafras oil contains from 6 to 8 per cent of dextro camphor. Traces of camphor have also been observed in tansy oil,[3] obtained from Tanacetum vulgare, a plant which is cultivated in the Eastern States for its volatile oil.
Borneol, or Borneo camphor, is closely related to camphor and possesses very similar properties. It is derived chiefly from the Borneo camphor tree (Dryobalanops aromatica (D. camphora), family Dipterocarpaceæ), and is found in crude crystalline condition in the natural cavities of the wood.[4] Blumea balsamifera (family Compositæ), a shrubby plant[5] native to India, also yields considerable quantities of borneol,[6] known to the natives as ngai camphor. The presence of borneol in plants native to this country is restricted to a few species, where it appears in the free condition only as a trace, being found more widely distributed as esters. It has been found in small quantities in the oil of red cedar (Juniperus virginiana),[7] and in thuja oil from the arborvitæ (Thuja occidentalis),[8] both trees being found abundantly in various sections of the United States. Small quantities have been found in the oils of other native plants, such as the goldenrod (Solidago canadensis),[9] Virginia snakeroot (Aristolochia serpentaria),[10] Texas snakeroot (Aristolochia reticulata),[11] Canada snakeroot (Asarum canadense),[12] tansy (Tanacetum vulgare),[13] and sweet gum (Liquidambar styraciflua).[14] As its acetic acid ester, it occurs in the oils of a large number of species of pines and firs.
Borneol and camphor occur occasionally together in the same oils. Their association is not surprising, since the relationship of the two compounds is very close. By oxidation borneol is readily converted into camphor. The two compounds have been observed together in the oil of cardamon,[15] distilled from the seeds of Amomum cardamomum; also in the oil of rosemary, from the plant Rosmarinus officinalis,[16] and in spike oil, obtained from Lavandula spica,[17] the latter two belonging to the mint family.
Cineol, or eucalyptol, is found chiefly in the volatile oils from various species of the eucalyptus tree and is the principal constituent of many of these oils. The blue gum tree (Eucalyptus globulus), belonging to the family Myrtaceæ and introduced abundantly in the western part of the United States, furnishes a volatile oil of which more than one-half is cineol. Other important sources also are cajuput oil[18] and niaouli oil[19] from Melaleuca leucadendron (M. viridiflora), a plant indigenous to India. Only a few native aromatic plants are known to yield volatile oils which contain cineol and in only a very few cases has this constituent been found to be present in any quantity. It is known to occur in the oil of the California laurel, or mountain laurel (Umbellularia californica),[20] where it is present to the extent of about 20 per cent. Among other native plants in which cineol is known to occur in small quantities is the composite Achillea millefolium,[21] commonly known as milfoil or yarrow. Peppermint oil from Mentha piperita[22] and sage oil from Salvia officinalis[23] are said to contain small quantities of this constituent.
Camphor, borneol, and cineol are found in considerable quantities in volatile oils which have been distilled from three unutilized aromatic plants of the United States, which will be discussed fully in the subsequent pages of this bulletin.