SANDALWOOD

Odor profile: A classic oriental woody note, milky, soft, sturdy, rich, with a green top note and a satisfying lingering scent. The best quality used to be the Mysore sandalwood variety from India, nowadays greatly reduced to the point of extinction from perfumery due to shortage of the natural material (the species is protected from harvesting because it's an endangered species). Australian sandalwood and New Caledonian sandalwood are different species with a harsher odor profile.

Sandalwood is one of the many primordial incense materials that mankind has known. Ramayana, an ancient Indian epic poem, written in IV century BCE, addresses the burning of fragrant slivers some 4,000 years ago. Its timber and essential oil (with 6% yield from the dry matter) are acquired from Indian sandalwood (lat. Santalum album), an evergreen tropical tree. Interestingly, sandalwood is a parasite: its seeds attach to the roots of other plants and nibble on the juices of their host. The oil is extracted from trees that are at least 30-40 years old, but the high worldly demand for sandalwood oil has led to the huge amounts of oil produced specifically in India (from 200 to 5,000 tons per year, according to different estimates).

The species is now recognized as "vulnerable" and is legislatively protected from over-exploitation: since 2004 Indian sandalwood has been listed on the IUCN Red List, and the Indian government has placed a ban on the export of sandalwood materials. At this moment, the essential oil of Australian sandalwood is available as an alternative (lat. S. spicatum (R.Br.) A.DC). There is also African sandalwood (lat. Osyris tenuifolia Engl.) and the so-called "American sandalwood", or sea torchwood (lat. Amyris balsamifera), which belongs to the genus of flowering plants in the Citrusfamily (lat. Rutacea). Botanically speaking, sea torchwood and true sandalwood have nothing in common, and their essential oils are chemically different. But the scent of these materials is somewhat alike, and given the fact that the torchwood oil is 6 times cheaper, one can imagine it is quite often used to falsify the sandalwood oil.

 

Essential components of sandalwood essential oil are sesquiterpene ethers, (+)-cis-α-santanol and (-)-cis-β-santanol, which are present in the amount of 65-72% (up to 90% according to other sources). These two substances (and mostly β-isomer) are responsible for the woody and creamy nuances of the "noble timber" scent, characteristic for sandalwood. Many experience it as specifically animalic and slightly urinal. The presence of eugenol, isoeugenol, and 6-methoxy eugenol tinctures the sandalwood oil with fumose, a "smoke-dried" aspect, while several carbonyl compounds (para-methyl acetophenone and its relatives) add flowery undertones.

 

The α-Santalol structure was first deduced in 1910 by the German chemist Friedrich Wilhelm Semmler, while Leopold Ružička described the structure of β-santalol a quarter of a century later. The scientists have more than once tried to develop protocols of the synthesis and to acquire these substances in vitro, but even today this problem remains unsolved (the best we have today is the 11-stage synthesis).

 

The first attempts to synthesize sandalwood odorants date back to the war time. This happened in German labs: German chemists acquired 4-camphyl cyclohexanol, the first synthetic odorant with the scent of sandalwood. This idea was picked up by Soviet scientists (the first notion of synthetic sandalwood odorants was delivered by military intelligence, as the first official publication about these compounds dates back to 1947), who recomposed the synthesis of this matter in VNIISNDV (the All-Russian Scientific and Research Institute of Synthetic and Natural Fragrance Compounds), and called the resulting substance santalidol. In 1956 the first pilot batch appeared, and since 1957, Soviet santalidol has been put out in masse editions, with its production amounting to 30 tons per year by the year 1975.

Santalidol is actually a mixture of several compounds with very similar chemical structures. Such materials are present in the palette of many manufacturers (see Sandela, Sandela NP by Givaudan, Indisan, Sandiff by IFF, Santalex by Berge), but due to the different synthesis protocols, the percentage ratio of the components and the resulting smell of these substances varies slightly. The descriptions sometimes feature the formula of one single component, which can lead to confusion. The extensive use of santalidol started, quite typically for that time, long before its composition and structure were described, which happened only a decade later as a result of the profitable collaboration of Soviet, American, and Swiss scientists: by the year 1964 the molecular structure of santalidol had been finally deduced, as well as the dependence of the scent from the structure of the matter.

I want you to fix your eyes on this phrase since it is extremely important: chemists that work with fragrant substances, as well as all synthetic chemists in general, do exactly this: they trace a connection between the structure and the property, in our case between the structure and the scent. Scientists are looking for the methods of analysis, which could possibly help to determine whether the substance possesses the sought-for scent or whether the structure of a sought-for molecule could be built on the basis of computations and the rationale. Owing to the painstaking work process and tens or even hundreds of described synthetic substances, we can sometimes formulate a couple of empirical laws that have a certain predictive validity. Using the example of sandalwood odorants, you can retrace the history of such empirical laws in the last 40 years.

 

It often happens that a presence of one seemingly unimportant detail can radically change the scent. Take a look at the formula of a substance that was manufactured in the Soviet Union under the name of Cedrol (not to be confused with the real cedrol, one of the components of cedarwood essential oil): an additional methyl group in the cyclohexane ring leads to the complete loss of the creamy-sandalwood character: that is why "cedrol" possesses a dry, woody cedar scent.

Among the materials that are synthesized nowadays one can find something similar to the mythic santalidol, too: see Mysore Acetate made by Symrise, also called Sandelione and Melozol Acetate, and Fleursandol, or Methyl Sandal. Quite rarely, one may encounter substances with a rather surprising structure for a sandalwood odorant - for example, Osyrol, Decalinyl Formate(or Santalozone), and Santalol, the latter being an ether with four conjugated double bonds, that can be found in organic sandalwood oil. Most of the contemporary sandalwood odorants (with javanol among them) are derived from the campholene aldehyde, the one with a cyclopentene ring.

Below you can see a photo of a real page from the lab journal of Jacques Vaillant, a synthetic chemist, who studied substances possessing the scent of sandalwood in the 70s. Here, one can count 45 entities, with an approximately similar amount of formulas on the following pages. Each structure requires at least a week of work (starting with the substance purification leading to the synthesis and description of the new substance), hence this page displays the result of the daily labor of a chemist for almost a year. Can you guess how many substances really possess the scent of sandalwood? All these substances smell differently - there is peach, cedar, lemongrass, rosewood, camphor, even mown grass. But just one of them really smells like sandalwood.

 

The quest for synthetic substances smelling like sandalwood has been quite prolific, so today we have quite a number of terpinyl cyclohexanol sandalwood odorants, with their cumulative production volume reaching 1,000 tons per year.

The first substance among those with a similar structure was Sandacore, which can be found under a huge number of trade names: Sandelice (Cognis, Penta), Sandal Mysore Core (KAO), Santalaire (De Laire), Madrol (Dragoco, сейчас Symrise), Sandaxol (DRT), Santaliff (IFF), Hindinol (Takasago), Sandafleur (ACS), Sandaxol (Vigon). Partial hydrogenizing turns it into Brahmanol (Dragoco, Symrise), a compound with a more intense scent. Homologous to Sandacore, Bacdanol, a compound with a tail ethyl group, possesses a similar scent that lasts a bit longer, and is also known as Sanjinol (IFF), Bangalol, Balinol (BASF), Sandranol (Dragoco, Symrise), Sandolen (Symrise), Dartanol(Firmenich), Sanderol (DRT).

 

The next group consists of the secondary alcohols, with Sandalore (made by Givaudan, also known as Santal Pentanol), Polysantol(made by Firmenich, also known Santal Pentenolor Santol Pentenol, Megasantol, Aquisantol, Nirvanol, Mysantol, and Supersantol), and Ebanol (synchesized at Givaudan, also known Sandal Pentenol) among them. These compounds possess a stronger and more realistic scent than the aforementioned relatives of Sandacore. At the end of the last century, Firmenich introduced Firsnatol, an even more powerful and substantive odorant. I would also like to mention, that not only alcohols smell like sandalwood, but carbonyl compounds do, too - see the ketone called Sandex (Givaudan).

 

Finally, we can come closer to our man of the hour. In 1997, Givaudan chemists Jerzy Bajgrowicz and Georg Frater discovered a new and extremely fragrant sandalwood odorant which was later called Javanol. The odor threshold of Javanol is 0,02 ppt (or 0,02 nanogram/Liter), which is 400 times less than its closest analogue, Pashminol (Givaudan). Javanol possesses a distinctive tropical fruity nuance resembling tropical fruits and grapefruit, and an impressively fresh, flowery, cologne-metallic aspect.

Thanks to its standalone technical properties (lasting power, substantiality, and diffusivity), its unique organoleptic profile, and the capability to make interesting combinations with other fragrant compounds, Javanol won the perfumers' affection, notwithstanding the variety of similar materials on the market. The pacesetter in the range of javanol-based fragrances is Orto Parisi Bergamask: perfumer Alessandro Gualtieri uses this compound profusely, for example, see his recently launched Seminalis. The use of Javanol is not limited to mono-sandalwood fragrances (like the before mentioned Escentric 04 or, say, Comme Des Garçons Wonderwood);this contemporary and compelling material can be found in fragrances of almost any kind.

 

By Mat Yudov