Olfactory Delights Marilyn C. Sbrollini Miss Porter's School, Farmington, CT 06032 Throughout history people have been intrigued by the aromatic essences given off by certain resins, barks, flowers. herbs, and animal products s&h as musk, civet, and amber: gris. Perfumes have always been gifts fit for royalty, as evidenced by the essences buried in the tombs of the Egyptian pharaohs, the Wisemen's gifts of frankincense and myrrh, Queen Elizabeth's Hungary Water, and Napolean's lavish use of Eau de Cologne. No wonder i t enhances one's ego t o dab a little of the currently popular Giorgio on one's pulse points or to spray a bit of Lauren behind one's ears. There are even those who claim that the use of scent cannot only elevate one's own mood, hut also it can exert an influence on the people with whom one interacts. Perfumes Commercial perfumes usually consist of three parts: a blend of essential oils (possibly u p to 200 or so), a solvent (also called a diluent), and a fixative that binds all the ingredients into a unified whole, slows the vaporization process, and gives the perfume a lasting quality. Historically, essential oils were obtained from natural products from exotic parts of the world. Frankincense and myrrh, obtained from the gum resin of trees in Africa and Asia, have a lone histom of use as an incense and nerfume ingredient. ~out1;ern~ r & e with its perfect growing season and soils s u n ~ l i e dessential oils from rose. iasmine. lavender. tuberose, and violet, to name a few. ~ n g i i n dprovided oil of lavender and peppermint, British India supplied patchouli from the leaves of the patchouli plant, and Sicily provided the oil of citron and orange. Civet came from the glandular secretion of the civet cat of India and Africa and musk from a gland of the male deer, native to the mountains of China and India. T o provide the coveted musk, excessive hunting of the musk deer has brought i t near extinction (1). The essential oils used in perfumes have been extracted from the plant substances in a variety of ways. Steam distillation, for example, is a process by which steam is passed around plant material. The essential oils are vaporized by the hot water and are collected as the vaoors condense in immiscible layers. Lemon, orange, and bergamont are separated via a method called ex~ression.Pressure on the nee1 is used to liberate the oil loiated in tiny glands below the epidermis. Maceration is useful in extracting essential oils stable to heat. Flowers are immersed in warm liquid fat; then the fat is strained. After the process is repeated several times to intensify the aroma, a fixative is added, and the cooled product is used to condition the skinas wellas add fragrance. A cold extraction method is more suitable for flowers whose oils would be destroyed by heat. In this method, called enteurafe. a thin laver of flowers is soread in fat on elass plates. stacks of plates are arranged in an airtight arrLgement. Fresh flowers continuouslv renlace the old ones until the fat is saturated with aroma: ~ < fragrance e is removed from the fat bv extraction with nure alcohol. The alcohol is then evaporatkd to leave the perfume as a residue. Soluent extraction, usually with petroleum ether, is an efficient method of extracting the aromatics from plant parts. After the solvent is percolated through freshly cut flowers and evaporated, strong alcohol is then used to dissolve the residue. Cooling the absolute results in the precipitation of wax-
es and other undesirable elements and leaves the desired essential oils in the alcohol (2). Extracting oils is a time-consuming, low-yield process, which given the increasing cost of labor, has a precarious future. Most of the blossoms must be hand picked a t just the right moment of ripeness. I t can take thousands of netals t o make one pound of oil. 1.aborarory synthesis of'essential oils began in the late 1800's when the process of isolating natural aromatics and duplicating their bdors was begun.-1n 1876 Tiemann synthesized vanilla (1) the flavor and odor component of the vanilla bean: +-wK CHO 1
Vanilla, once an expensive item, soon became one of our most common and useful flavoring and odorant agents. Since this beginning there was rapid progress that continues today as the perfume chemist duplicates and sometimes improves upon large numbers of essential oils (3). Essential oils are complicated mixtures that may make u p alcohols, ethers, aldehydes, ketones, esters, lactones, castor oil products, terpenes, and paraffins. The hexagon ring originallywas thought to be the odor-producing agent common to all essential oils. Later many substances were found that caused odor but lacked the hexagon shape. One important group of chemicals common to many essential oils is the terpenes. Terpenes (C10H16)are composed of two units of isoprene (2). (Isoprene is also the monomer of natural rubher.) Two isoprenes CH.
I
CH,=C-CH=CH, 2
join together to form different structural and geometrically shaped molecules of different aromas. Oxygen can also be introduced into the molecule to make an "oxygenated terpene" in both cylic and aliphatic forms. Citral, (3),
3
an oxygenated aliphatic terpene found in the peel of the orange, lemon, and lime and in lemon grass, is responsible for a pleasant lemon odor. Menthol (4) is a cyclicoxygenated terpene
4
and the recognizable constituent in oil of peppermint. Many, but not all, the essential oils contain terpene or terpenerelated compounds (4). Sometimes it is desirable to remove terpenes partially from the essential oil mixture, for they Volume 64 Number 9
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Figure 1. Pepperminty molecules fit into a wedgs-shaped cavity and come equipped with a polarized group of atoms capable of forming H bonds wilh a hydrogen in the receptor site.
may mask the odor of a more desirable component, decrease the solubility of the oil in alcohol and water, and erode the stabilitv of the mixture over time (5). The most common solvent used in perfumes is ethyl nlrohol. Its percentage determines whether the framance is classified as a perfume, cologne, or splash. Perfumes contain 20 to .lOOi essential oils with the remainder alcohol. Colognes contain between :I and 5 5 essential oils, RO to 9070alcohol. and the remainder is water. Splnshes contain about 2*i essentiuloil.60 to809 alcohul. and the rrmainder is water. l h e solvent a& as a diluent. Some of the scents that have a disagreeable odor when concentrated become pleasurable when diluted. The alcohol vaporizes and carries with it some molecules of essential oils (2). The fixative is an impo&nt stabilizing component of a perfume. Natural fixatives exist in both animal substances (such as civet from civet cat, castor from heaver, musk from deer musk. and ambereris from the sperm whale) and plant material rsuch as henjoin from the h&k and leaf of theipier hush ofeastern United Statesand theorrisroot from the root of the Spanish iris). Today synthetic stabilizers have been substituted for many of the natural ones (2). Olfaction Scientists haveheen more successful in synthesizing nature's fragrances than in understanding the physiology of the sense of smell. There are mvriad theories ~ronosed . . bv investigators to explain olfacation, but there is no general aereement. Moore classifies the theories into two cateeories: vrbrational theories and chemical theories (3). The;ihrational theories are based on the idea that molecules absorb or emit vibrations which, in turn, affect the olfactory nerve endings. Chemical theories involve a chemical reaction between-the odoriferous molecule and the olfactory receptor. The activating molecule must be volatile (to reach the nose), fat soluble (to dissolve through the lipid layer of the cell membrane of the nerve cell, and, a t least to a slight extent, water soluble (to become part of the watery solution that bathes the nerve endings). Factors such as a reactive functional eroun. .,unsaturation. the reaction of a molecule with an enzyme, the formation weak addition compounds, and v the establishment of H bonds have heen DroDosed to ~ l a in a role in the chemical reaction (3). ~ e c e n i e v a e n c ehoweier, , supports a stereochemical theory of odor. Amoore et al. (6) propose that the sense of smell is based t o a large extent on the geometry of molecules. Seven primary odors have been identified, each capable of being detected by a complementarilv shaped receptor site high in the nose. The primary odo; families (camphorous, musky, floral, pepp&minty, ethereal, pungent, and putrid) lack similarity in empirical and structural formulasiyet, they do share roughly the same molecular shape and size, with charge sometimes an addi800
Journal of Chemical Education
Figure 2. Unrelated camphorlike odors fit into the same bowl-shaped receptor site.
tional important component. Seven kinds of receptor sites exist in the olfactory cells of the nose. When a molecule of the correct size and shane fitsinto a com~lementarvrece~tor 1.)~ o m i l e xodors site, an iypulse is initiated. (See result when a molecule fits into more than one kind of site (troadside intoa wide receptor siteand end-on inton narrow sire). X-rav diffraction. infrared spertroscopv, and electronbeam probes have enahled invescgators to- build models of the seven primary odors. When the shapes of molecules producing camphoraceous odors were compared, i t was clear that they all shared roughly the same spherical shape. (See Fig 2.) The other odor families were similarly tested and their common geometry realized. Direct proof was added when researchers probed into the olfactory nerve cells of the frog using microelectrodes. Different cells were found to respond selectively to different odors. The frog has eight primary receptor sites (6). The body chemistry of the perfume wearer plays an important role and often adds subtle changes to the final scent. In some instances there are marked differences between two individuals wearing the same fragrance (8). Perfume Artistry The perfume artist is s~eciallvtrained to recoenize verv slight 'ariations in smell.'~rmedwith a palette of over 500 different precious essential oils, the artist creates perfumes with unique personalities and usually divides perfumes into fragrance families. Each family is associated with its own emotion-evoking effect. The floral family (which when properly blended is reported to be psychologically calming) consists of the essential oils from flowers such as rose, jamine, gardenia, lilac, lily of the valley, and tuberose, to name a few. The green family, including eucalyptus, pine, citrus, lavender, rosemary, camphor. .and basil. lends sharoness and is said to be invieorat& ing. The animal family of musk, civet, ambergris, and castoreum evoke mystery and desire. The spicy-woody family of oak-moss, sandlewood, myrrh, cedar, cinnamon, and clove is refreshine. Perfumes usuallv contain two main scents which are rounded out with other essential oils to give harmony (7). Make Your Own Fragrance I t is possible, economical, and fun to create your own fragrance. The following activities are modified and simplified versions of those used in the perfume industry. Follow-
Peppermint
Figure 3. Distillation setup
iue the nrescribed ~rocedureswill not make a product as pure or concentrated as the essential oils commercially available: however, the ~ r o d u c t can s be blended successfully with experimentation into delightful, personal, fragrant concoctions. Some of the rarer essential oils can be purchased at a cost of $7.00 for 0.25 fluid ounces and used along with those extracted in the lab. Expression and Extraction by Soluent. Oil of orange (oil of lemon can be prepared in a similar fashion) can be prepared by a procedure detailed by Plummer (9).Place the peel of an orange in a 400-mL beaker. Add 100 mL of vodka as a solvent. (The denaturing.. ingredient in laboratory ethanol gives it an undesirable scent.) Warm below the buill l a m m due to ina nuint ,,n a hot d a t e for 15 min. Aoord open . th~jlammabilityof the alcohol. Once the extract has cooled, Dour into a centrifuge tube, and centrifuge. Collect the clear iiquid, and store in tightly sealed darkbottle. Steam Distillation of Oil of Peppermint. Fill a separatory funnel with the leaves of fresh peppermint? Place 250 mL of water into the distilling flask, and assemble the apparatus as shown in Figure 3. Run the steam distillation until 100 mL of the peppermint-scented distillate has been collected. Store the scented liquid in a tightly capped, dark bottle. This procedure can he repeated with rosemary leaves to collect oil of rosemary. Extraction Using Almond Oil. Oil of rose geranium can be extracted from the scented rose geranium plant1 using a method described by Plummer (9). Cover the bottom of a auart iar with cotton halls. Saturate with 50 mL of oil of ilmonb.2Add a second layer and saturate with an additional 50 mL of almond oil. Take petals from arose-scented geranium or any flower with a strong scent. Bruise the leaves and fill the jar to the brim with torn leaves. Cap tightly, andleave ~
a
'
Check your local nursery for peppermint and scented geranium plants. Almond oil and storax are available from a perfume supplier like Bauer and Beckwith's Soap Opera. 319 State Street, Madison, Wi 53703 (800-251-SOAP). Available from the Soap Opera. 'Some suggestions for starting essential oils to be order from a perfume supplier are oil of musk, oil of sandalwood, oil of orrisroot, rose, jasmine, turberose, lilac, gardenia, bay rum, lavender, clove, and cinnamon.
in the sun until the leaves appear withered. Remove old leaves and renlace with fresh ones (about everv other dav). After about three weeks when the scent of thcoil is strong, remove all ~ e t a l .ssaueeze .. the oil from the cotton balls into a dark hottle., add 1 teaspoon of liquid storax as a lixative, and cao . tiehtlv. - .One ID of musk Der 30 mL of oil could be used in place of the s t o r a ~ . ~ Enfleuraee. Oil of lilac can he extracted using the enfleue 8-in. rage procedire outlined by Plummer (9). ~ s s e m b l two cake tins. Melt 1 CUD of lard in a 400-mL beaker on a hot plate. Add 2 tearpoons tinrturr of henroin.'l)ividr the meltrd lard hetween twornke tins, and allow tomol. Gather fresh lilac floamers, nnd fill hoth tins to thr brim with blosa~ms. Invert one container over the other, and tape in place to hold an airtight seal. I'lare tins in Zioloc baas. andadd a weiaht to hold the seal. Change the flowers everisecond day, andkeep up the process as long as the lilacs are in bloom. At the end of the absorption time, remove the flowers. Heat the lard gently over water and strain between layers of cheesecloth. Cool. Chop the lard into pieces, and drop into a quart jar. Add 250 mL of vodka or Everclear (a oroduct sold in liquor stores). Cap tightly, and keep in anaccessible place so that it can he shaken daily for a month. This aging period is necessary to transfer the scent from the lard to the alcohol. When the scent is satisfactory, add 4 drops of sandalwood as a fixative. Pour into cologne bottles, and stopper tightly. Creatlng Fragrances-Some Starter Formulas Uslng Your Extractions After-Shave Lotion. Usina- the oils you extracted, blend some rosrmary, lemun, and orange in equal amounts. If you like the scent, add an eaual amount of dilurnt with fixative.? Since your extracted essential oils will be of varying concentrations, you may have to experiment to get the right blend. These are the basic ingredients of Hungary Water, which sells for $4per ounce. Stopper tightly, and age in a dark place for 3 months. Experiment with mixtures of rosemary, orange, rose garanium, and a drop of musk. If you like the scent, complete your cologne according to the directions for Hungary Water. Cologne. Combine ingredients of rose geranium with oil of lilac or lily of the valley. Add a drop of musk and equal amounts of diluent with fixative. Bottle, stopper, and age for 3 months. Creating a Personal Fragrance. For this experiment you will use the essential oils that have been p u r c h a ~ e d Use .~ only a drop because the purchased oils are concentrated and costly. Smell the available oils from the bottles and find those that appeal you. When you have found a family that you like, experiment with blending 2 or 3 of the oils together by placing a drop of each on your skin and mixing them with adrop of diluent with your finger. Keep a record of those you mixed. Allow the scent to remain on your skin for 5 min and then record your reactions. Wash the scent away, rest your olfactory sense, and try again. If you come up with a blend that is really you, you can order the ingredients to make your personal perfume. Perfumery-the science and art of odor-has found its place in our modern world. Today the science goes far beyond the perfume counter, as most industries consume perfumed materials (plastics, synthetic textiles, rubber goods, paper products, inks, paints, soaps, and foods, to name a few). Perfume truly contributes greatly in many ways to our enjoyment of a pleasant world. Literature Clted 1. Chriniani,R. P~ifumrry& KindredArr: Baird: Philadelphia. 1877; pp 2 M 4 2. Wimmer.C.P.J.Chrm.Educ. 1960.37.434.
~~
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8. Bu&. J.J. Voaue 1983,May,306. 9. Plummor. B. Frapiance:Dover: New York. 1975.
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