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.