Azulenes: A Clear Sign of Cannabis Oil Contamination

Figure 1: Azulene, aromatic and yet polar.

Figure 2: Azulene distillate. Photo credit: Illuminated Extractors.

Figure 3: Blue and green azulene fractions. Photo credit: Joel Reiss of NUG.

Figure 4: Guaiol is converted to guaiazulene.

As the licensed cannabis market continues to evolve, companies continue to innovate and consumer demand grows for cutting-edge, best-in-class products. But in this era of rapid progression, there is an essential factor that production facilities and research and development laboratories should prioritize: recognizing and avoiding vectors of contamination. Fortunately, there are clear-cut methods to recognizing the signs of certain types of contamination so companies can minimize risk and maximize their production of pure, clean cannabis.

While most contaminants of cannabis oil are confirmed only through analytical testing there is one type of contamination that can be easily identified through visual inspection. Azulenes are a class of compounds that display an intense blue to green color and their presence can be easily observed during the distillation of cannabis oil.  Careful collection of the distilled fractions is required to prevent these compounds from contaminating the main cannabinoid fraction. There is little though that can be done to prevent this “smurf blood” from ruining both the appearance and the smell of the sesquiterpene or heads fraction. What’s of even greater concern though is the strong correlation between the appearance of azulenes and the presence of Δ⁹-tetrahydrocannabinol (THC) isomerization products, namely Δ⁸-THC and Δ¹⁰-THC, in the distilled cannabinoid fraction. Δ⁸-THC and Δ¹⁰-THC are known to be significantly weaker agonists at the CB1 receptor compared to Δ⁹-THC, so the conversion to these isomers means a less psychoactive product. However, to understand why azulenes are linked to isomerized THC distillate we first need to know what exactly these azulene compounds are and where they are coming from.

What Are Azulenes?

Azulenes are hydrocarbon molecules that have in their base structure a seven-membered ring fused at two adjacent carbons to a five-membered ring (see Figure 1). Both of these rings are aromatic and yet the electron density is unequal between these two rings such that the seven-membered ring is relatively more cationic, and the five-membered ring is more anionic. This means that azulene compounds are both aromatic and at the same time also polar. This extremely uncommon set of circumstances is the cause for yet another unique attribute of azulenes: their intense color, which is a highly unusual attribute for simple aromatic hydrocarbons to possess. The colors of azulenes, ranging from deep blues to greens, are determined by the electronic effects of the substituents that are attached to the base bicyclic structure (see Figures 2 and 3). Considering the intense colors that azulenes produce, even trace amounts of these oxidized terpenes are quite noticeable when being distilled over. (See upper right for Figure 1, Figure 2, and Figure 3, click to enlarge.)

How Are Azulenes Produced?

Azulenes are created through the dehydrogenation of certain terpenes that similarly possess a seven-membered, five-membered bicyclic structure. Through the loss of hydrogens, terpenes such as cedrane, cedrol, gurjunene, and guaiol will acquire the aromatically stabilized azulene system (see Figure 4). This reaction typically requires elevated temperatures plus the presence of an acidic species. Wet activated carbon, sulfur, residual acids from clays, as well as many nonneutral ionic species (such as sodium metabisulfite) are all examples which, when combined with heating during decarboxylation or distillation of cannabis oil, create azulenes. These same contaminants also react with Δ⁹-THC to create the aforementioned isomerization products as well as oxidation products, all of which contribute to a net reduction in the psychoactive potency of the distillate. (See upper right for Figure 4, click to enlarge.)

Preventing Azulenes

So, how can we prevent these reactants from wreaking havoc in our precious products of distillation? Aside from not introducing them in the first place, the only other choice is to remove them prior to any heating processes. To remove fine solids like activated carbon and sulfur one must dissolve the oil in an appropriate polar solvent and then perform gentle gravity filtration of the solution. For acids and other dissolved ionic species, the oil can be dissolved in a nonpolar solvent, placed in a separatory funnel or reactor, and then neutralized by washing first with water, then with dilute sodium bicarbonate solution, and finally with two more water washes. Do these steps correctly and you’ll liberate your distillates from the oppression of isomerized cannabinoids and gross terpene fractions!

Conclusion

There are a multitude of contaminants that when combined with heat can cause significant damage to cannabis oil distillates. But the silver lining is that they are easy to notice and address thanks to the intense blue-green colors that are produced. After gaining a better understanding of the causes and implications of encountering azulenes, one can then identify potential causal agents and take steps going forward to intervene and remove them before any further damage is caused to future batches.

About the Author

Matt Finley is the Chief Chemist for NUG, a vertically integrated California-licensed cannabis company. NUG operates the highest volume cannabis extraction facility in California, producing the majority of concentrates, vapes and other infused cannabis products sold in California under the NUG label and other leading brands. Direct correspondence to: matt@nug.com

How to Cite this Article

M. Finley, Cannabis Science and Technology3(4), 52–53 (2020).