Alexis St-Gelais, M. Sc., Chimiste – Popularization
Essential oils are worth quite a lot of money. It so happens that, in order to boost profits, unscrupulous people alter oils in various ways. This “Adulterants and you” series is there to introduce you to some of the adulterations we encounter. This is because not all of them are necessarily obvious, nor bear the same level of risk for the final consumer.
Today, we will take a look at that nice bottle (figure 1) I have just received from Vigon International, a fragrance ingredients retailer. It contains isobornyl cyclohexanol, a compound which I have seen plenty of times in the courses of my analyzes.
|Figure 1. Today’s suspect is isobornyl cyclohexanol.|
What Is It?
The term “compound” was in fact confounding in the previous sentence: isobornyl cyclohexanol, also called sandal hexanol, is by no means a single compound. It is in fact a mixture of stereoisomers (molecules that have a similar basic structure but differ in their 3D arrangement) and molecular rearrangements of the structure shown in figure 2. It is likely that each producer of that ingredient sells in fact its own “signature” blend, which may have an impact on its final organoleptic, since each isomer may have a different scent, or even bear no smell at all.
|Figure 2. Structure of the main isomers of isobornyl cyclohexanol. The wobbly lines indicate undefined stereochemistry, or, in other words, that the 3D arrangement of the molecule at this place can change.|
It can be obtained by reacting guaiacol and camphene, two easily and cheaply accessible molecular building blocks , and then reducing the guaiacol part of the molecule. Isobornyl cyclohexanol is a clear and extremely thick liquid, stuck in position and not moving at any visible pace. It is also pretty sticky, but dissolves easily in solvents and essential oils. As I am writing these lines, Vigon sells it for $140/kg, a price that readily drops for larger quantities. This is really cheap compared to essential oils prices.
What Does it Do as an Adulterant?
It smells! We have observed this compound in many sandalwood (Santalum sp.) and vetiver (Vetiveria zizanoides) essential oils, that could or not contain any trace of the original plant constituents. The mixture has a woody scent similar to that of those oils. As part of a mixture with other synthetics or natural ingredients, it thus can mimic a genuine oil, or complement a dull-scented batch. It seems to be quite a common sight on the market, as we have seen it regularly.
From a broader point of view, the use of isobornyl cyclohexanol should not be too harshly frowned upon. Indeed, Santalum species are under heavy pressure for oil and wood production, and the use of a synthetic equivalent to replace the oil is not always a bad idea. Of course, this does not apply to aromatherapy, where the genuine oil must be used.
Is It Dangerous?
Likely not so much at the concentrations of oils anyone should be using. The pure isobornyl cyclohexanol is a skin and eye irritant, but keep in mind that any genuine essential oil can also be – once again, essential oils, whether pure or adulterated, should not be taken orally, not put near the eyes or other sensitive parts of the body without proper dilution. Under a dilute form, isobornyl cyclohexanol is used in fragrant preparations.
How Do we Detect it?
The composition of the mixture obtained depends on the reaction conditions, and since no particular fractionation of the reaction product is made, all by-products are kept. This gives rise to a complex profile in GC analysis (figure 3). This peaks “blob” clashes with the usual vetiver/sandalwood GC profiles, making them much more complex to analyze, but adulterations are in general quite easy to suspect.
|Figure 3. Vigon’s isobornyl cyclohexanol signature in gas chromatography using our regular essential oil analysis method.|
The trickiest part is proving it by GC-MS. Common databases do not include isobornyl cyclohexanol signatures. In our case, we previously could identify the mixture from a colleague’s custom database. We have just this week gone a step further with Vigon’s sample, building our own MS database for upcoming suspicious samples.
Bottom of the Line
Isobornyl cyclohexanol is a synthetic fragrant ingredient used to mimic sandalwood and vetiver woody notes. It shows as a group of irregular peaks on the GC profile, leading to their identification given that the testing lab is aware of their possible existence.
 Sell, C. S. Ingredients for the Modern Perfumery Industry. In The Chemistry of Fragrances; Pybus, D. H.; Sell, C. S., Eds.; Royal Society of Chemistry: Cambridge (UK), 1999; p. 84