Official Volatile Oils. BP 1958
Compiled by Ivor Hughes
Part 1 of 2.
OIL OF TURPENTINE.
Official Source : The oleo-resin obtained from various species of Pinus. Two important species are :
1.Pinus palustris Mill. (American Turpentine.
2. Pinus pinaster Ait., also known as P. maritime Lam (French Turpentine).
Geographical Source : South-East U.S.A. and South-West France.
Preparation. The preparation of this oil from the oleo-resin (turpentine) which yields it, and also the production of this oleo-resin, present several special features. In the pine trees yielding the oleo-resin, the wood normally contains only a few oleo-resin ducts, from which the yield would be negligible. However, following superficial injury the cambium produces new wood containing a large number of oleo-resin ducts. These pour forth a copious secretion to serve as a protective covering for the newly-formed tissue. The production and collection of this injury-produced (or pathological) oleo-resin is confined chiefly to the U.S.A. and France, where the following methods are in vogue;
1. American Turpentine
Production and collection proceed as follows:During winter a cavity or "box" is made in the tree trunk about 30 cm. above the ground. The box resembles in shape a wide open mouth with its long axis at about 35� to the horizontal, the depth of the mouth being about 25 cm. and the capacity rather more than a litre. In early spring as soon as the oleo-resin begins to exude from the "lips" of the box, the bark immediately above the box is stripped off to a height of about 30 cm. and the denuded area is hacked. The copious exudation which follows trickles down into the box, from which it is removed monthly by a dipper. During the whole of the summer and autumn months the denuded area is extended each week by hacking off along its upper border about 2 cm. of bark, which maintains the flow. By the beginning of winter this flow has ceased, and the height of the denuded area has reached about 75 cm. Towards the end of winter a new box is made about 45 cm. above the first, i.e. about 30 cm. below the upper border of last year's denudation, thus leaving a similar distance for the flow. Above this box the bark is stripped and hacked weekly as before. This continues until October, but fewer dippings are necessary to empty the box (usually about five). The process is repeated along similar lines for a third and fourth year, the yield gradually diminishing, and only about three dippings are necessary to empty the box.
By this time the upper border is more than 200 cm. from the ground, and difficulties of access, coupled with diminution of yield, render further tappings after the fourth year uneconomical. The number of boxes per tree varies from 1 to 4 according to its age and size; usually there are 2, filling simultaneously. In addition to the oleo-resin removed from the box, which is called dip, some of it partly dries at the surface, and is removed by scraping�this is called scrape, the "gum thus" of English pharmacy. The average yield per tree in the first year of tapping is about 6-5 kilogram. of dip, containing about 20 per cent of oil and 75 per cent of resin, the remainder being foreign matter (water, wood chips, etc.), and about 1-7 kilogram. of scrape, containing about 10 per cent of oil and 80 per cent of resin. In the three succeeding years the amount of dip falls rapidly to about 2-5 kilogrm. in the fourth year, with a lower proportion of oil, whereas the amount of the less valuable scrape increases slightly to about 2-5 kilogrm. Further, the resin progressively darkens in colour, and thus becomes less valuable.
The above system of tapping, called the box system, was exclusively used in America until recent years, and is still very common. Its disadvantages, which will be discussed later, have led to a more general adoption of the French method, called the cup and gutter system, which will now be described.
2. French Turpentine.This oleo-resin is obtained almost exclusively from the Cluster (Maritime) Pine (Pinus pinaster). It is cultivated in the south-west of France, in the Departments of Les Landes, La Gironde, Le Lot et Garonne, Les Charentes and Le Dordogne. The total annual production is about 7 million gallons of oil of turpentine and 100,000 tons of resin: 40 per cent is exported, 10 per cent to this country and the remainder principally to Germany and Belgium. In France the oleo-resin is collected in a "cup," closely resembling a small flower-pot without the hole. Tapping begins in February, when an incision about 9 cm. wide is made in the tree, a short distance above the ground. Into this incision a short zinc gutter is fitted, to convey the oleo-resin into the cup placed on the ground below. The initial exudation soon ceases, and from that time onwards until November, thin shavings of bark are removed at intervals to maintain the flow. By the end of the season the denuded area extends about 60 cm. above the original incision. The process is repeated between the February and November following, and again for the third and fourth year, but in each of these the area denuded is increased to about 90 cm. Thereafter, collection ceases owing to the difficulty of access and the reduction of yield.
The cup is supported by long nails driven into the tree after the first flow has ceased, and it is repeatedly raised with the gutter so that the oleo-resin is collected before it has much time to evaporate or become incrusted on the trunk. The cups are emptied every three weeks, and the scrape removed in the autumn. The number of cups per tree varies according to age and tapping interval. The trees yield *oleo-resin from the 15th to the 60th year or longer. To ensure continuity of flow it is important that tapping should not be too drastic, or commenced too early; a favourable age is between the 25th and 30th year. Although in some instances as many as six areas are tapped simultaneously on one tree, such treatment shortens its life, and it is much more satisfactory to tap from one area at a time, and to allow a rest of 3 or 4 years before incising a second area. Although the annual yield of oleo-resin per cup is rather less than that obtained per box, the cup system has compensating advantages which render it preferable, viz. �
(a) The cup can be raised whenever the flow ceases, so that the oleo-resin, having a shortened distance to travel, does not lose so much volatile oil or form as much of the less valuable scrape.
(b) The trees can be tapped over many years, and the total yield far exceeds that from the box system.
(c) Production can be steadily increased without interruption, the unproductive period (about 25 years) being easily bridged by rotation-planting. With the box system replacement cannot keep pace with the rapid destruction of the trees.
(d) When exhausted of oleo-resin, the tree is still valuable as timber, whereas the box system considerably reduces this value.
The principle of the cup and gutter method is illustrated; in this experimental working, V-shaped incisions were made. The cup and gutter are shown.
Distillation of the Oleo-resin. The oleo-resin and scrape from the forests are despatched in barrels to the factories. In some areas they are distilled together, but in others they receive separate treatment. The apparatus used ranges from primitive fire-heated stills of small capacity to large modern stills. In the former, the two are mixed with water, and heating and distillation allowed to proceed until about 140� C. is reached. Water is then slowly run in through a pipe opening into the top of the still, and heating continued, until the temperature reaches about 170� C. at which stage all the volatile oil has distilled. The molten resin in the still is then run off through wire sieves (Nos. 150-200) made of special metal to resist the action of the resin. The cooling apparatus attached to the still usually consists of a water-cooled coil leading to a tank. Modern plant works along similar lines, sometimes a current of steam replacing the running stream of water.
The simple application of either of the above methods produces a dark-coloured resin, owing to the great difficulty in removing suspended foreign matter from the molten resin, which is very viscid. Consequently it is usual to subject the oleo-resin to a preliminary process of purification before it is distilled; it is first warmed to render it fluid, then allowed to form a sediment, and finally filtered under pressure. Centrifugal machines have also been devised for the purpose. The volatile oil produced is oil of turpentine, and the resin is known variously as colophony, colophony resin, resin, or rosin. The oil contains traces of resin mechanically carried over during distillation, which although unobjectionable in ordinary use must be removed from oil intended for medicinal use. This is effected by re-distillation with water and potassium carbonate, and the fluid product constitutes the official Oil of Turpentine.
Constituents:Pinene, the dextro- and laevo- forms-'in American oil, and chiefly the few-form in French oil. Camphene, and traces of resin acids and other oxidation products such as camphoric aldehyde (giving the characteristic odour of old oil of turpentine) are also present.
Adulteration:Oil of Turpentine is commonly adulterated with a fraction of petroleum spirit which boils over the same range. Oil of Turpentine absorbs a large proportion of iodine whereas petroleum spirit absorbs very little. The determination of the iodine value forms therefore an important means of detecting adulteration with petroleum spirit. Special conditions are prescribed for the determination to prevent loss of oil of turpentine by volatilization. Other reported adulterants are (1) a product of destructive distillation of colophony; it causes the oil to leave a permanent stain on paper, and (2) wood turpentine, obtained by distillation from the roots and stumps of various species of Pinus; it has a higher weight per ml. and a lower iodine value than oil of turpentine.
Terebene:This is prepared from oil of turpentine by shaking the oil (usually mixed with a small proportion of alcohol) with small successive portions of sulphuric acid, separating and rejecting the non-oily liquid and distilling the oily liquid in a current of steam. The optical rotation of terebene is + 2 to - 2. Terebene consists chiefly of dipentene, an optically-inactive form of limonene, produced by the action of the sulphuric acid on the pinene present in oil of turpentine.
OILS CONTAINING OXYGENATED CONSTITUENTS.
In this class the medicinal properties and odour are due to substances containing oxygen in combination with carbon and hydrogen. Most volatile oils belong to this class, and for description they will be classified according to the chemical nature of the principal oxygenated compound present.
1. Oils containing Esters.
Principle of Estimation:Esters are estimated by boiling a known weight of oil with a known excess of semi-normal solution (alcoholic) of potassium hydroxide for one hour under a reflux condenser, and then determining the residual alkali by titration with semi-normal solution of sulphuric acid. The experiment is repeated omitting the oil, and the difference between the two burette readings for the normal solution of sulphuric acid represents the number of ml. of semi-normal solution of potassium hydroxide needed to saponify the ester. From the data, the percentage of ester in the oil can be calculated.
OIL OF SIBERIAN FIR
Botanical Source: The fresh leaves of Abies sibirica Ledeb.
Geographical Source: North-East Russia.
Preparation: By distillation in steam.
Constituents: Bornyl acetate, 30 - 45 per cent, the B.P.C. 1949 requirement being 33 - 45 per cent w/w. Subsidiary constituents are the terpenes pinene, phellan-drene, and camphene.
Tests: The determination of the ester content is the most important for the following reasons:
1. The ester is the medicinally-important constituent.
2. Other pine oils which are likely substitutes or adulterants contain only a small proportion of ester, e.g. oil of pumilio pine only 3 -10 per cent. So the synonym of oil of pine has been given to oil of Siberian fir, to ensure its use when oil of pine, without further qualification, is prescribed.
OIL OF LAVENDER
Geographical Source: Southern Prance, Italy and England.
Preparation: By distillation in steam; yield 0 . 5 per cent..
Constituents: Several esters of linalol, officially calculated as acetate, in the following proportions of Linalyl Acetate. 7 -11 per cent in English oil; official requirement 7 -14 % w/w. 28 - 50 per cent in French oil, official requirement not less than 35 % w/w.
Subsidiary constituents are: The alcohols linalol and geraniol, the terpenes pinene and limonene, a sesquiterpene, and, in English oil, a small proportion of cineole.
Tests and Adulteration: From the above figures it might be presumed that French oil, with its higher content of ester, would be more valuable. On the contrary, ester content alone is not a criterion of value, and the fine odour, which gives English oil its superiority, is probably due more to the kind of ester than to the quantity. Although the ester is always calculated as linalyl acetate (a substance with a bergamot-like odour), it appears from investigations that the true lavender odour is due to linalyl butyrate and proprionate. English oil is richer in both these esters than French, which is valued in commerce according to the ester content, whereas with English oil, odour is the principal criterion of value.
Oil of lavender is frequently adulterated, usually by admixture of genuine oil of lavender with synthetic esters such as ethyl citrate and ethyl phthalate, whereby the ester content is artificially raised.
Oil of spike lavender, from Lavandula latifolia Vill., grown in Spain and France, contains practically no ester, but about 30 per cent of alcohols, chiefly linalol, borneol and geraniol, with terpineol, camphor and cineole. It is used to adulterate oil of lavender�the consequent reduction in ester content being adjusted by the addition of synthetic esters. Spanish oil of lavender is usually a mixture of this kind.
2. Oils containing Alcohols.
From the above table it will be seen that chemical evaluation is prescribed for only one oil, the Pharmacopoeia relying upon physical requirements as an index of a suitable content of alcohol in the case of oils of anise and coriander.
Principle of Estimation:Alcohols are estimated by heating the oil with excess of acetic anhydride and anhydrous sodium acetate for two hours in a flask attached to an air condenser, whereby the alcohol is converted to its acetate. The product, called the acetylated oil, is then washed to remove reagents, dried by shaking with anhydrous sodium sulphate, and filtered. A weighed amount of the acetylated oil is then saponified exactly as described above for esters, and the alcohol content calculated from the data obtained.
OIL OF ANISE
1. The dried ripe fruits of Pimpinella anisum Linn. Fam.: Umbelliferae.
2. The dried ripe fruits of Illicium verum Hook. f. (Star Anise). Fam.: Magnoliaceae.
Geographical Source: 1. South Spain and Russia, 2. Southern China (Kwangsi).
Preparation: By distillation in steam; yield 1.5 to 3.0 % from anise fruits, and 5 per cent from star anise fruits. China Star Oil is normally used for pharmaceutical purposes, Pimpinella Oil being far more expensive.
Constituents: Anethole - an alcohol - 80 to 90 per cent. Subsidiary constituents are methyl-chavicol and anisic acid; in star anise oil, d-pinene and a little l -phellandrene.
Tests: The Pharmacopoeia relies principally upon physical tests, to ensure a suitable content of anethole. For example, the oil is required to freeze at a temperature not below 15� C. Pure anethole melts at 21� C., and the substances accompanying anethole in the oil lower its melting-point in ratio to the amount present, hence departure from the official freezing-point would indicate adulteration.
OIL OF CORIANDER
Preparation: By distillation in steam; yield 0-7 to 1-1 %
Constituents: d-Linalol (coriandrol), 45-65 per cent. Subsidiary constituents are d-pinene, geraniol, borneol and terpinene; the substance to which the characteristic odour is due has not yet been identified.
OIL OF AUSTRALIAN SANDALWOOD
Geographical Source : Western Australia.
Preparation: The oil is prepared by distillation and then rectified. Rectification consists of fractional distillation, whereby part of the terpenes are separated and the alcohol content raised to 90 per cent or more.
Constituents: Santalol and Fusanol isomeric alcohols, the santalols form about half the total.. These alcohols together must form not less than 90 per cent w/w of the oil. Australian sandal wood oil contains therefore the same proportion of alcohols as the East Indian Oil (known simply as Oil of Sandalwood). The constituent alcohols are not quite identical, the East Indian Oil containing a higher proportion of the santalols. The therapeutic effects of the two oils are, however, indistinguishable.
3. Oils containing Alcohols and their Esters.
OIL OP PEPPERMINT
Official Source: The fresh flowering tops of Mentha piperita. Linn.
Geographical Source: U.S.A. (Oregon, Michigan, Indiana, Wayne County), England, France, Germany and Italy.
Preparation: By distillation in steam; yield about 0-25 per cent, highest from fresh herb harvested when minute oily globules are visible on the under-surface of the leaves. The oil is rectified by re-distillation if necessary.
Constituents: Menthol (free and combined) 50-72 % for English Oil, and 48-63% for American Oil, the official requirement being not less than 45-0 per cent w/w of free menthol. Menthyl acetate and isovalerate, 3 to 15 % for English Oil and 5 to 9% forAmerican Oil. (calculated together as acetate), the official requirement being 4-0-9-0 % w/w. Subsidiary constituents are the ketone menthone (8-16 %), the terpenes dipentene, l-limonene and phellandrene, and the sesquiterpene cadinene. Unrectified oil may contain dimethyl sulphide.
Adulteration Both English and American oils (the principal sources) normally satisfy the official requirements. The principal substitute and adulterant is dementholized Japanese oil of peppermint, an important by-product in the manufacture of menthol. This oil contains 5-17 per cent of esters, and 40-54 per cent of menthol free and combined. By adding sufficient menthol, if necessary, to bring the content up to 46 per cent w/w of free menthol, it is possible to produce an oil which fulfils the official quantitative chemical and physical requirements.The Pharmacopoeia therefore includes a colour test which serves to distinguish genuine oil from Japanese mint oil. There are numerous varieties of; M. piperita var. officinalis forma rubescens Camus, known as Black Peppermint, is the one mostly cultivated in England; M. piperita var. vulgaris Sole, known as Black Mint is the variety most cultivated in America, France and Italy.