JOURNAL OF CHEMICAL EDUCATION
0
THE ROLE OF ESSENTIAL OILS IN MODERN INDUSTRY EDWARD E. LANGENAU Fritzsche Brothers, Inc., New York, New York
IN THE normal course of study of organic chemistry in our colleges and universities, the student often obtains hut little info~mationconcerning essential oils and their role in modern industry. Many graduate students have only a vague conception of what constitutes an essential oil and frequently underestimate their importance in the history and development of organic chemistry. Bare statements in our textbooks such as "Anethole is the chief constituent of anise oil" or "Synthetic coumarin is manufactured for use in the perfume and flavor industries" hardly do justice t o the contribution of essential oils and related products to "Chemistry-the key to better living." Substances commonly known as 'Loils" may he classified in three main divisions: first, the mineral oils, derived from petroleum; second, the fixed or vegetable oils, consisting for the most part of glycerides; third, the volatile or essential o i l s d o called because they were believed to represent the quintessence of the odor and flavor of the botanical, whether produced from the flower, the leaves, the wood, the root, the seed, or the fruit. Like many other natural products, these essential oils have long been a challenge to the organic chemists of the world. Many of the great names in chemistry can he found in the roster of those who interested themselves in essential oils and related products:
Dumas, Liehig, Wohler, Perkin, Tieman, Reimer, Tilden, Baur, Wallach, Semmler, Wagner, Bouveault and Blank, Grignard, Merwin and PondorR, Ruzicka, Carothers, and others. A great number of investigations have been undertaken to discover and identify the constituents of complex essential oils; the subsequent syntheses of many of the naturally occurring chemical substances have resulted in the manufacture and widespread use of these synthetics. Although the essential-oil industry must he considered small in terms of tonnage, its products (derived from almost every corner of the world) are used by many industries. The obvious applications of essential oils and related products include: (1)the medic.inal use of the oils per se; (2) the preparation of perfumes for extracts, soaps, lotions, facial creams, and other toiletries; and (3) the preparation of flavors. The average American would find it very difficult t o spend one day of his life without coming in contact with some product which has been made more pleasant, more salable, and more satisfying through the use of essential oils and related products. The chemist who enters our industry usually is impressed by the low yields of oil obtained from the botanicals. As a student he has become accustomed t o the high yields demanded in the manufacturing
JUNE, 1952
processes of synthetic chemicals. Let us consider a few examples to illustrate this point more clearly. When processed with modern equipment, a ton of lemon fruit will give about 6-7 pounds of essential oil, a yield of approximately 0.3 per cent; yet California alone produces annually an average of about 600,000 pounds of this oil. The average annual production of oil of peppermint in the United States is close to 1,000,000 pounds; yet the yield of oil (depending on the dryness of the herb a t the time of distillation) is usually but 0.3 to 0.4 per cent, only rarely as high as 1 per cent. It is, of course, difficult to generalize, but we may say that a yield of 1to 2 per cent may be considered normal for the production of most essential oils by steam distillation; in some cases it is much lower (e. g., one pound of rose oil is obtained from 4000 pounds of rose petals, a yield of about 0.025 per cent) and in some cases it is much higher (e. g., oil of cloves, distilled from the buds, about 16 per cent). Commercially, the yield is an important factor in the cost of an oil. In the analytical evaluation of botanicals as raw materials for essential oils, a laboratory steam-distillation is usually carried out. The most convenient and available type of apparatus employed is the so-called "Clevenger trap for the determination of essential oils." Two types are available: one for oils lighter than water, and one for oils heavier than water. This apparatus is official in both the
231
"United States Pharmacopoeia" and the "National Formulary." In the essential-oil industry, it is used extensively as such or in some slightly modified form. Typical of such commercial application is the practice of Fritzsche Brothers, Inc., of New York: before a botanical is distilled in their Clifton, New Jersey, plant, a determination of the volatile oil content is made, using the Clevenger apparatus; the quality of the resulting oil as well as the yield is thus established before commercial production is undertaken. Most essential oils are obtained by steam distillation. Basically this is a process wherein two immiscible liquids are heated until the combined vapor pressure of the two components is equal to atmospheric pressure. A mixture of vapors then distills off and, after condeusation, separates intot he two immiscible liquid phases. Other complex factors are, of course, involved, such as hydro diffusion of the oil from the oil cells through the plant tissue into the water; partial solubility of the oils in the aqueous phase, etc. Using the Clevenger apparatus, the distillation waters are automatically cohobated, that is, returned to the still to be stripped of suspended and dissolved oil by further distillation. In most cases the botanical must first be reduced to a coarse powder to permit the more rapid distillation of the oil. The grinding should be done immediately prior to distillation to minimize the loss of the more volatile portions of the essential oil.
