Tikalon Blog by Dev Gualtieri

Synthetic Fragrances

September 3, 2018

A chemical laboratory will have a background fragrance that identifies what work is done in it. For safety reasons, such laboratories are well ventilated, but the human nose is capable of detecting minute quantities of substances in the air. It's easy to identify an inorganic chemistry laboratory, principally because of the sulfur and nitrate odors. An organic chemistry laboratory is very easy to identify, since organic compounds have an "organic" fragrance, and they have a high volatility.

For a period of several months, my laboratory had the pleasant scent of lilac. I was doing a novel electroplating, not from an aqueous solution, but from an alcohol. Although I was getting some encouraging results, my process needed some optimization, so I decided to try different mixtures of alcohols. The alcohol, α-terpineol, has a pleasant lilac fragrance, so it's a common additive to soaps and perfumes. It's also an alcohol with a much higher molecular weight (154.25 grams/mol) than that of the simple alcohols, methanol (32.04) and ethanol (46.07), so it was a good modifier for my electroplating bath.

There's definitely a resemblance. Α-terpineol and a lilac flower. Lilac is an Asterid Eudicot Angiosperm of the Order Lamiales, Family Oleaceae, and Genus Syringa. Olive, jasmine, and forsythia are also members of the Oleaceae Family. Left image, an α-terpineol ball-and-stick model (Carbon=black, Oxygen=red, and hydrogen=white) by Ben Mills and Jynto; right image, lilac flowers and leaves, by Jjron. Both images via Wikimedia Commons. (Click for larger image.)

As I wrote in an earlier article (Smell, October 23, 2013), our sense of smell is more properly termed olfaction, and it's one of the five traditional senses of man. The others are taste, sight, hearing and touch. Man's sensitivity to sexual pheromones is much less than that of many animals, but pheromones do affect our mate choice. We try to game the system through use of perfumes. The 2016 fragrance materials market was estimated to have been nearly fifty billion dollars.

The way to a man's heart is through his nose?

Most men will admit that the scent of a certain perfume will bring back memories of a girlfriend. Marcel Proust's "À la recherche du temps perdu" ("Remembrance of Things Past") contains a scene, known as the "episode of the madeleine," in which the taste of a cake triggers a childhood memory.

(Portion of an advertisement for Evening in Paris perfume that appeared in an 1889 issue of Ladies' Home Journal, via Wikimedia Commons, but sourced from the Internet Archive.)

Can there be too much of a good thing? The 1980s saw the rise of "monster-scented" perfumes whose provenance can be traced to Chanel No. 5. These fragrances are called monsters, since you smell them not just on the woman, but everywhere she's been in the last few hours. There are anecdotes about gas chromatographs in chemical laboratories giving extra peaks when certain female technicians were in the area. In that decade, I could always tell when a certain female chemist was in the building. Fortunately, the scent of her monster perfume was quite pleasant.

The monsters of the 1980s were Yves Saint Laurent's Opium and Poison by Christian Dior. Even their names invoke their monster status. The scent trail left by these monsters is termed sillage, which is the French word for the water wake left by a passing ship. The ship might have vanished over the horizon, but its wake is still visible. Note the similarity of the word, tillage, the making of furrows in soil for planting, to sillage, the analogous furrowing of the sea.

The most abundant natural fragrances are floral. Interestingly, while prehistoric man used flowers in burials,[1] there is no evidence that our prehistoric ancestors adorned themselves with flowers. However, in historical times, floral perfumery was well established, reaching a culmination with the 1927 introduction of Arpège, a perfume that contains about 60 floral components. The ancient Greeks had developed a perfume industry at least as far back as the 4th century BC.

Theophrastus (c. 371 - c. 287 BC) described the perfumer's art in a short treatise on odors, not surprisingly entitled, On Odors. This is usually placed as an appendix to his Enquiry into Plants (Περι φυτων ιστορια, Historia Plantarum).[2-3] On Odors discusses the oil extraction of fragrant compounds.

"Now the composition and preparation of perfumes aim entirely, one may say, at making the odours last. That is why men make oil the vehicle of them, since it keeps a very long time and also is most convenient for use. By nature indeed oil is not at all well suited to take in an odour, because of its close and greasy character: and of particular oils this is specially true of the most viscous, such as almond-oil, while sesame-oil and olive-oil are the least receptive of all." [2]

Nature provides us with a multitude of fragrance sources, as listed on the Wikipedia Perfume Page. Along with flowers, there are the fruits, leaves, and twigs of plants; plant resins, of which frankincense and myrrh are examples; bulbs and roots, such as ginger; seeds such as coriander, anise, and nutmeg; tree bark, such as sandalwood, cedar, and pine; animal musk, and the cetacean secretion, ambergris.

Patchouli and (sandlewood) incense, pogostemon cablin and santalum album plants

Pogostemon cablin and santalum album plants, the sources of the patchouli and sandalwood fragrances. Patchouli has a strong scent, and it's been used in perfumes for centuries. Sandlewood was a common fragrance for incense in the youth culture of the 1960s and 1970s. The verse, "she comes in incense and patchouli...," was part of the The 1976 song, Year of the Cat, by Al Stewart. (left image, a pogostemon cablin plant at the Old Botanical Garden of Göttingen University, and right image, a santalum album plant by Krish Dulal, both from Wikimedia Commons.)

While steeping roses and other natural materials in a pot of solvent was the sole method of perfume manufacture in antiquity, most of today's fragrances are produced synthetically. Fragrance chemists start with a chemical analysis of natural fragrances as an aid in producing the same chemical compounds or some functional analogs. The International Fragrance Association lists 3,999 chemicals used by its members in 2015.[4]

As I wrote in an earlier article (Terpene, May 15, 2017), most natural odorants are a class of chemicals called terpenes. There are thousands of terpenes to be found in natural and synthetic fragrances, with the smaller terpene molecules being more strongly fragrant. The higher molecular weight terpenes have lower volatility, and this makes their scents more tenacious.

The five principal fragrance terpenes are geraniol-nerol, linalool, citronellol, citronellal and citral. These, and derived compounds such as their esters and alcohols, are widely used. They are used, also, as reagents for synthesis of other terpenes. The following table lists some important terpene-derived chemicals.[5] Wikipedia's Aroma Compound Page lists many more fragrance chemicals.

Material	Odor
Geraniol-nerol	Rose
linalool	Floral, wood
citronellol, citronellal and citral	Rose
Dihydromyrcenol	Citrus, floral
Hydroxycitronellal	Lily of the valley
(Methyl)ionones	Violet
Linalyl acetate	Lavender
Borneol/isoborneol and acetate	Pine
α-Terpineol and acetate	Lilac
Amberlyn®	Ambergris
Carvone	Spearmint
Menthol	Mint
Acetylated cedarwood	Cedar

Fragrance categories are an arbitrary construct, and each person will interpret a fragrance in relation to his past experience. That's why an Internet search will yield many different lists of fragrance categories. I've compiled my list of eight categories into the chart shown below. In my choice of eight, I've followed in the tradition of the Eightfold Way organization of hadrons that led to the development of the quark model.

My synthesis of the "eightfold way of fragrance."

The categories are Floral, Fruity, Citrus, Vegetable/Green, Woody, Spicy, Oriental, and Fresh/Oceanic.

Decades ago, my wife has a bottle of the floral fragrance, Lancome Trésor. Yves Saint Laurent Opium, mentioned above, would go into the oriental category. Britney Spears Believe is a woody scent. Sea-breeze scented Calone, also known as the "watermelon ketone," is a member of the fresh/oceanic category.

(Created using Inkscape. Click for larger image.)

Catherine Maxwell, professor of Victorian literature at Queen Mary University of London, has written an enlightening and entertaining article about synthetic fragrances in a recent issue of Aeon Magazine.[6] While the natural is preferred over the artificial in things such as gemstones, Victorian culture preferred synthetic fragrances to natural fragrances.

Of course, cost is one factor in this. Such sources of natural fragrances as jasmine are relatively rare, they are expensive to cultivate, and their fragrance is hard to extract. More importantly, the quality of natural materials is affected by soil quality and the weather, while synthetics are uniform from batch to batch. Modern perfumes might use natural substances, but they're augmented with about 80% synthetics since those chemicals give them qualities beyond those of the natural materials.[6] In fact, hydroxycitronellal, a synthetic lily-of-the-valley fragrance developed in 1905, is a better lily-of-the-valley fragrance than the flower.[6]

Maxwell also presents the history of synthetic musk.[6] The original source of musk is an abdominal gland of the male musk deer, and it's obtained by killing the animal. While natural musk was always difficult to obtain, the musk deer became an endangered and protected species in 1979. Albert Baur found a synthetic alternative to musk in 1888; interestingly, his "nitro-musk" was a derivative of TNT that he found while doing research on explosives.[6]

Baur subsequently developed other nitro-musks, such as musk ketone and musk ambrette. The later was a component of Chanel No 5. Patents on synthetic musk made a fortune for Baur, but his synthetics have been replaced in recent times by safer and more stable synthetics.[6] Patented synthetics are still a source of income for many fragrance companies, which might patent three or four synthetics in a year.[6]

Synthetic Fragrances

References: