NATURAL CHEMICAL RESOURCES OF AUSTRALIAN PLANT PRODUCTS. PART XI* A. R. PENFOLD, CURATOR AND ECONOMIC CHEMIST,SYDNEY TECANOLOOICAI. MUSEUM, SYDNEY. AUSTRALIA
I n this article the isolation and identification of naturally occurring 8diketones i s discussed. Attention is called to the commercial production and unique walue of o tea-tree oil (Melalauca alternifolia) in medical and dental prectice. The commercial production of two well-known essential oil commodities, Western Australian sandalwood oil, and ihe concrete otto of boronia in the State of Western Australia, as well as the interesting nature of their chemical comfiosition are described. The remarkable features of some Australian essential-oiGyielding plants abnormally rich in the aldehydes, cilral and citronellal, and the economic walue of Eucalyptus oil residues rich i n cuminal, phellandral, cryptal, etc., are rm'med. The occurrence of imfiortant fihysiological forms of well-known Auslralian trees, Eucalyptus dines, and Geijera pamiflora, are of singular interest. These forms are indistinguishable both on morphological grounds and in the jield, but are readily separated according to the composition of the respective essential oils. . . . . . Before proceeding to discuss additional Australian plants and their essential oils, I propose to review some of the information set forth in Part I of this series. On page 1204 of Part I* reference was made to the essential oil of Barkhousia angustifolia, and the occurrence therein of a new phenol to the extent of 757& Since that date, this interesting substance has been critically examined by a team of investigators, with the result that the socalled phenol has been shown to be a B-diketone of the formula C1,HvO3 (not CloHIaOa as previously reported), and called angustione. It was found that while the boiling point remained constant the specific gravity and refractive index varied within considerable limits with preparations of the diketone separated from different consignments of oil. The specific gravities varied from 1.085 to 1.1054 and the refractive index showed extreme limits of 1.5130 and 1.5288. These marked differences were subsequently shown to be due to the angustione just mentioned and a closely related diketone of the formula CllH1403. These two ketones are the first naturally occurring 0-diketones which have been investigated. The chemical and physical characters are compared in the following table. Formula CI~HI~OI CdLOs Boiling Point 129' (15 mm.) 126-127' (11mm.) Specific Gravity, 201.089 1.103 Refractive Index. 20" 1.5087 1.5313 -5 56' -2.03" Optical Rotation * Part I was published in J. CWM. Eouc., 6. 1195-205 (July-Aug.. 1929). 429
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They have been shown to be fairly widely distributed in Australian essential oils, having been observed in some of the eucalyptus and boronia oils. No economic value has yet been found for these interesting bodies which are readily characterized by the orange-red coloration given with ferric chloride in alcoholic solution, the crystalline amino derivative produced by reaction with ammonia and the characteristic purplish crystalline copper compound. I t is interesting to note that these substances are readily soluble in dilute alkali solutions by which they are removed from the crude oils. It will be necessary for future workers to investirate closely the constituents removed by dilute alkali solutions in order to determine if the substances are acidic, phenolic, or diketonic. For those especially interested in the chemistry of these naturally occumng substances, reference should be made to the J. Chem. Sac., 1930, pp. 1185201, and 1931,287-94.
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Tea Trees Under this head reference was made to the essential oil of Melaleuca nlternifolia, which was about to be placed on the markets of the world. Since that date, the oil has achieved a reputation for itself by the remarkable results which have been obtained by its use in medical and dental practice. Of course, those engaged in its commercial exploitation have protected themselves by marketingthe oil under thename of "Titrol" andits suspension in soap solution as "Melasol" and "Intol." The essential oil was shown to possess a Rideal-Walker coefficient of 11, and to be non-toxic and non-irritant. Its great value in surgical work has been due to its
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cutting within a period of twelve months. Undoubtedly the State of New South Wales possesses a very important asset in this tea tree. There are two very interesting commercial essential oils which emanate from the State of Western Australia. I refer to the well-known Australian sandalwood oil and the concrete otto of boronia. Sandalwood as is well known has been much sought after by Eastern nations since the earliest periods when the wood was used for carving and for incense. Even today i t is still used in the East for similar purposes. The occurrence of sandalwood in the world is almost entirely confined to India, the Eastern Asiatic Archipelago, and the western and northern portions of Australia, including Queensland. A great deal has been written concerning sandalwood and its essential oil, but I intend to c o n h e my remarks primarily t o the Australian product. The well-known East Indian sandalwood oil of commerce is obtained by the distillation of the wood of Santalum album and since the Great War of 1914-18, i t has become practically a monopoly of the Mysore (India) Government. There has unfortunately been considerable controversy regarding the correct botanical derivation of the West Australian sandalwood tree. The writer is not a trained botanist and, therefore, is compelled to recognize the determination of the Royal Botanic Gardens, Kew, which is Eucarya spicata (Sprague and Summerhayes) (Syn Fusanus spicatus, R.Br.; Santalum spicatum, A.Dc.; S . cygnorum, Miq.). Then again the controversy has not been confined to its botanical origin alone, but the question of its chemical composition has
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been similarly debated. I do not wish to bore readers with the various controversial views. Great credit, however, is due to the persevering efforts of the Western Australian manufacturers, especially during the past ten years, which have resulted in the marketing of an excellent quality of oil second to none. It has to be remembered, too, that the present high quality of commercial oil has been attained only by careful selection of raw material and rectification of the crude oils. This achievement can best be appreciated when a perusal of the literature reveals that early samples contained only 75y0 of sesquiterpene alcohols as compared with 95y0 of these bodies in the present-day commercial article. The East Indian oil, of course, contains approximately 90% of sesquiterpene alcohol in its crude condition, although it contains small amounts of other alcohols, yet i t is generally considered to consist essentially of the sesquiterpene alcohols a- and 8-santalol. The Western Australian oil undoubtedly contains santalol, but to a much less extent, approximately 60y0. The remainder consists of a very closely allied sesquiterpene alcohol which is now under investigation. According to Mr. H. V. Marr, who has written much on this subject, the sandalwood industry of Western Australia dates back to 1846, when the fist record of exportation shows that four tons of wood, valued a t S50, were exported. This writer stated that until the establishment of the Mysore monopoly, trade in sandalwood from Western Australia to other countries proceeded without any interference from the government. Large tracts of forests were denuded of sandalwood and shipped away
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along the coasts of Western Australia to eastern markets. The district from which the best quality of sandalwood has been cut in recent years, and which produces the best wood is an area embracing Kalgoorlie, Kanowna, Laverton, and Mt. Morgan districts. Some idea of the state of the trade in sandalwood in Western Australia is shown by the statistics puhlished by the Western Australian Forestry Department. From the years 1845 to 1922, the total exports of sandalwood amounted to 350,034 tons valued a t £3,298,100. As is generally known, the essential oil is obtained from the wood of the tree, the butt, and the roots. The production of the oil has increased considerably from 6870 lb. weight in 1921 to about 100,000 lb. weight in 1930. Large quantities of the Western Australian oil are forwarded to America for use in the soap industry. While treating of sandalwood oil I should not overlook the oil of Santalum lanceolatum, another sandalwood tree which occurs in Western Australia, and plentifully in certain parts of Queensland. It contains about 90y0 of a sesquiterpene alcohol C15HZ40 of unknown constitution, possessing the following characters: Boiling Point Specific Gravity Optical Rotation Refractive Index, 20'
153-154" (3 mm.) 0.9474 -66.7" 1 .5074
I t is highly levo-rotatory and yields a beautiful well-defined crystalline allophanate, of melting point 114'. The oil was used to a limited extent by Western Australian manufacturers to bring up the levo-rotation of their commercial sandalwood oil produced from Eucarya spicata. I understand its use in this cxmection has now been discontinued. The oil, apparently. is not used a t all a t the present time, but the wood is exported in cousiderable quantities to the East for incense purposes. The oil is still under investigation. I cannot see why i t should not he used to a much greater extent for purposes similar to commercial sandalwood oil derived from other sources.
Concrete Otto of Boronia Australians are very proud and fond of their famous flowering plants called horonias, more particularly the well-known Boronia megastigma commonly called the brown boronia of Western Australia. This shrub, which attains a height of about six feet, is found in damp and swampy situations in the southwest of Western Australia, and is noted for its sweet-scented reddish brown flower. This plant is cultivated extensively in Victoria, principally for floral purposes. I n Western Australia, however, its native habitat, enormous areas occur and these have been exploited by several prominent local manufacturers in the production of an excellent concrete otto. It is difficult to estimate the total production of this
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substance but I have computed the annual production to be in the neighborhood of 200 lb. weight of concrete obtained from about 50,000 lb. weight of blossoms. The odor of the concrete is a characteristic one and quite typical of the flower from whicb it is obtained. The writer examined the concrete some years ago and found it to contain the following constituents: triacontane (a parailin of melting point 64"), a glyceride of palmitic and stearic acids, phytosterols, free palmitic, formic, and caprylic acids with small quantities of ethyl alcohol and ethyl formate and unidentified phenolic bodies. These constituents undoubtedly form an excellent fixative or camer for the odoriferous components consisting of an unidentified alcohol and probably p-iouone. It is interesting to note that this is the first reported occurrence of /3ionone in nature. The ionones are well-known synthetic substances produced by the condensation of acetone and citral, noted for their violet odor in dilute alcoholic solutions. Tb:s preliminary evidence was subsequently confirmed by M. Sebastien Sabetay (Comptes rendus, 180, p. 808) who separated a quantity of the actual ketone. Most of the concrete otto is used in Australia where i t forms the basis of some beautiful creations of the perfumer's art. Aldehydes Australia seems to be particularly rich in plants yielding essential oils containing aldehydes. The first one which comes to mind is the wellknown lemon-scented gum of Queensland Eucalyptus citriodora, referred to in the table of commercial-yielding eucalyptus oils ofi' page 1196 of Part I of this series. It was regarded as containing 90-95% of citronellal, but this work has recently been revised. It is usual for chemists to estimate aldehydes in this oil by absorption with 33% solution of sodium bisulfite, despite the fact that it has been shown by many chemists that alcohols and other oxygenated bodies were also absorbed by the bisulfite solution, and therefore are estimated as aldehyde. This oil has recently been re-examined (see Journal Sydney Technical College Chemical Society, 4 , pp. 53-60) and found to contain from 70-85% of citronellal when the aldehyde is estimated by the modified Holtappel method. Then there is Backhousia citriodora, a small tree endemic to Queensland whicb yields an essential oil containing 95% of citral, the richest source of this aldehyde in the world. The tree, unfortunately, grows in insufficient quantities to warrant commercial exploitation. Consignments of the oil were dispatched to Europe many years ago, but although orders have been received of recent date they have not been executed. The tree is cultivated, but in my opinion is too slow in growth, in comparison with Leptospermum citratum (previously described). This oil contains 50% citral and 35% citronella1
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and the plant is remarkable for its rapid growth when grown under favorable conditions. Then there is Eucalyptus staigeriana, the lemon-scented ironbark of the Palmer River District of North Queensland, which contains from 2838% citral and yields a very satisfactory substitute for oil of lemon, particularly for the flavoring of confectionery. Here again very little has been done in connection with the exploitation of this tree but I understand steps are now being taken to produce the oil for commercial purposes. The question arises, of course, as to where there is a sufficiently good market for the product. One of the most interesting groups of aldehydes is that consisting of cuminal, phellandral, and cryptal, found occurring together in a large number of eucalyptus oils, especially those of the "Make" group. The demand for water-white eucalyptus oils to conform to certain requirements of cineol content and the various pharmacopoeias has led to the rectification in Australia of all eucalyptus oils prior to export abroad. These high-boiling residues remaining in the still contain sesquiterpenes, sesquiterpene alcohols, etc., together with considerable quantities of these aldehydes with australol (p-isopropyl phenol). All these constituents possess high phenol coefficients as germicides (cuminal 12.75, phellandral 9.25, cryptal 12, australol 22.51, and consequently these residues are much sought after by the disinfectant manufacturers. These aldehydes are not only of commercial value, but intense academic interest. The constitutions of cumiual and phellandral have been well known for some time, but only comparatively recently (January, 1930) has the constitution of cryptal been determined (4-isopropyl-A2-cyclohexenal). It is singular that these three interesting aldehydes should occur together in the crude oils of Eucalyptus polybractea, Eucalyfitus cneorifolia, hemiphloia, etc. The chemical and physical characters are compared in the following table. Boiling Point Specific Gravity Optical Rotation Refractive Index, 20' Structural Formula
Curninnl
Pkrllondrol
Clyml
110' (10 mm.) 0.982 (15") Inactive 1.5287 CHO
90' (5 mm.) 0.9412 (20°) -130.85" 1.4912 CHO
98-100' (10 mm.) 0.9442 (209) -76.2" 1.4830 CHO
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Physiological Forms In my first article (see footnote, page 429) mention was made of the interesting series of physiological forms or varieties which had been observed in the case of the broad-leafed peppermint, Eucalyfitzu dines. These forms are indistinguishable both on morphological grounds and in the field from the type, but are readily separated according to the composition of the respective essential oils. Since that date other interesting examples of a similar character have been brought to light, the most notable and recent one being Geijera pamiflora. This small rutaceous tree, commonly known as the "wilga" or "Australian willow" is endemic to Australia. It is one of the best shade trees in the Western Districts of New South Wales, and stands drought conditions better than any other. It is an extremely handsome tree as will be observed from the illustration, possessing dense, spreading, pendulous foliage which in many parts practically touch the ground. The tree is widely distributed, growing in all States of the Commonwealth except Tasmania. Owing to the tree being abundant in the drought-stricken areas, the foliage, especially when other fodders become scarce, has frequently been relished by sheep. It is a not uncommon sight in Western New South Wales to observe trees which have been kept neatly trimmed by stock. It is the intention to limit my remarks to the essential oil obtained from the leaves of this interesting tree, and not to discuss the value of the "wilga" as a fodder tree, about which so much conflicting evidence has been published. Geijera Parviflora New South Wales
Yield of Oil Color of Oil Specific Gravity Optical Rotation Refractive Index, 20"
0.5% Pale yellow 0.86720.876 +42" to +50.85" 1.4743-1.4750
Quecnslond
0651.2% Dark green to blue 0.907-0.9181 About -6' 1.4987-1.5005
The examination of essential oils obtained from leaves and terminal branchlets from trees growing in various parts of New South Wales and Queensland has revealed a marked difference in the chemical composition of the oil from the two States (in this connection it is well to note that the division of the states is purely political or arbitrary). The New South Wales material was found to yield an essential oil of bright yellow color, quite mobile, with a pleasant but characteristic terpenic odor, to the extent of about 0.470. It contained pinene and camphene to the extent of 80%. On the other hand, the oils obtained from material collected a t Eidsvold, Queensland, varied from a dark green to a deep blue in color, according to the content of that fascinating blue hydrocarbon, azulene. The essential oil was obtained to the extent of 0.6-1.18% on leaves containing about 10-
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13% of moisture. These oils were very viscous and possessed a sickly odor of linalool with a new hydrocarbon of the tentative formula CllHls (boiling point 198-19g0 a t 774 mm.). The wide variation in the chemical and physical constants is readily observed in the foregoing table. Botanists up to the present time have been unable to separate the New South Wales and Queensland trees on morphological evidence. The writer has not yet had an opportunity of examining the trees in the field and as i t will be some time before such an opportunity presents itself, he has adopted the course of looking upon the New South Wales tree as a form of the Queensland one which is accepted as the type. That one is merely a form of the other is supported by the additional evidence that material collected from various parts of Queensland bore a close resemblance to the oil from the New South Wales trees, and appeared to be of an intermediate character. The New South Wales essential oil is a very excellent source of dcamphene. I mentioned earlier in this article that stock frequently relish the leaves of "wilga," but, according to competent observers resident in the parts of the country wbere the tree abounds, there are certain trees which sheep will readily eat and others which they reject. It was thought that an examination of the essential oil might reveal the reason, and although samples submitted by the Department of Agriculture, a t Nyngan, New South Wales, and marked "readily eaten by stock" and "not readily eaten by stock" were separately examined, no differences could be detected in the romposition of the essential oils, beyond the observation that the terpenes separated from the oil obtained from the former were highly fluorescent. I t is evident, therefore, that any differencesmust besoughtfor in the other chemical constituents of the leaves. The other constituents of the Queensland oil, such as the hydrocarbon and sesquiterpenes, are worthy of further investigation and the former is now receiving attention. While writing of the Geeera, i t is worthy of note that another tree of the same family, called Geijera salicifolia, which attains a height of 60-80 ft. with a girth of Cr8 ft. and known as the "willow-leafed wilga," yielded on steam distillation about 1.27% of a rare phenol ether called phloracetophenone dimethyl ether, of melting point 82-83', The oil is, therefore, remarkable for the high content of this substance, being the richest source recorded up to the present time. The only other known source of this interesting substance is the essential oil of Blumea balsamifera.
