Azulene, Acidic Distillation, The Mystery Blue

Hello! I frequent the Future 4200 forums in search of answers that often come up in my work. I am a laboratory tech in an extraction lab associated with a dispensary. We do extraction with different solvents different ways and my responsibilities involve much of the vacuum distillation used to procure high concentration delta 9 distillate.

Some time ago we produced a less than satisfactory green shatter. In the effort not to let the material go to waste we made several attempts to clean it up, get rid of the funky color and associated smell. Try as we might, no effort to remove both the color and the smell was successful and the wack shatter was consigned to distillation to try and capture the cannabinoids away from whatever contaminant was producing such unappealing properties.

That distillation run was not only one of the highest purity distillations the company has achieved but also primarily delta 8 thc (99.2% total cannabinoids, 86.5% delta 8, 11.3% delta 9). Now the name of the game has been to reobtain and refine the SOP for consistency and in these trials a peculiar trend has arisen. When delta 8 was recovered during distillation the heads leading up to the 150+ vapor temp range always contained a strikingly blue fraction. When delta 8 was not present (or present only in a tiny concentration, say <8% total) the blue heads were notably absent. Some of the material used for positive runs was already old, darkened distillate itself (routinely tested above 92% d9 with terps already removed) so the likelihood of a blue terpene existing there in concentration is slim.

The key seems to be the presence of an acidic environment in the boiling flask during distillation. I have observed extensively others using bleaching earth, clays and Lewis acids for isomerizing both CBD and d9-THC into d8-THC however we have measured marked success using even a strong Bronsted-Lowry acid in low concentrations placed directly in the boiling flask during vacuum distillation.

What I am mostly interested in is the chemical processes that are occurring to produce these results.
The inclusion of a strong acid is clearly enough to alter the position of the double bond in the cannabinoid molecule but it is not behaving in a purely catalytic fashion. The resulting distillate and residue in the flask both respond negatively for the presence of acid when treated with a sodium bicarbonate solution. The ratio of d9 and d8 can vary, CBN and CBC come and go in varying amounts between tests. The residue in the boiling flask after distillation has a characteristic sulfurous odor that sulfuric acid lacks, suggesting the presence of detectable by-products.

I’ve heard mention of HHC being produced via the hydrogenation of the phenolic double bonds, and that HHC can sometimes produce a false positive as CBC by various testing agencies. Is it possible that the reaction of sulfuric acid with some cannabinoid or terpene is producing hydrogen gas and hydrogenating other molecules under high heat and vacuum?

If azulene or chamazulene are present due to an acidic reaction then what is the most likely reagent that is interacting with the acid to produce a bright blue fraction?

I have searched for others discussing the matter but most seem to be curious in how to prevent or dispose of these oddly colored heads. I seek to understand and better characterize just what is going on. Anybody with experience or insight into the matter would be greatly appreciated for coming forward.


Send me the weird colored heads- as soon as im set up with a flash system I am planning on trying to isolate them to their constituients. Azulene is super neat stuff.


A little of the isolated blue fraction spotted on a paper towel to show the color. It is a liquid that lacks much viscosity, common in the accumulated terps that come before cannabinoids.

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Two terpenoids, vetivazulene and guaiazulene, feature the azulene skeleton and are found in nature as constituents of pigments. Maybe these are your blue compounds?

Or maybe mono- or di-terpenes are combining/cyclizing due to the acid?


Some potentially valuable info:

I often get a blue fraction in my wf external condenser. Based on the color I was sure there was at least some azulene content. Had it tested, absolutely zero azulene. Quite an interesting array of terpenes and degradation products, though.

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Here’s what it was. I’m too lazy to post the azulene standard as well, but, it peaks at 16.


Thanks for sharing @ExTek90 very interesting for sure!

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Sulfur might be dehydrogenating the “terpene-type compounds”

Search patent US2734931A

I had run a bunch of material that had sulfur
Burns while growing.
I go directly to sp after evaporating room temp extraction etho.
When I used t41 at 10% I would get that amazing blue,where with out t41 I would see that milk,waxy darkish green.
Material that had not used sulfur while growing ,no blue.
I hope this helps.great thread guys.


Do you by any chance have the mass spec of the “azulene” peak?

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This is the standard.


Did you just run GC, or did you also do MS?

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The analytical lab I use did this, not I. Afaik this is all they did to identify compounds. It was also tested for cannabinoids, which came back at 2% Delta-9 THC.

Edited for D9.


∆8 or ∆9?


I suspect its some form of oxidation product that happens in acidic conditions. Our lab partner, that has all our GCMS data, is going to let me comb the MS for what I believe is the source of the blue color, which is a highly substituted azulene; one that resembles the terpinoid azulenes (Vetivazulene and Guaiazulene).

I will PM you, if i figure anything significant out.


It most likely is, most of my runs are slightly acidic (which I’m convinced is due to CO2 extraction.)


Pfff I am cleaning up a batch of co2 extracted European cbd strain (4%)
Extracted by a facility owned and run by the polish government
Damn cbd 32% thc etc 4 % riddeled with fats and waxes and to top it of chlorophyll
All fats and waxes take 12/15% of cannabinoids content so redisolve and winterize again a real nightmare
And worse of all PH of 2/3 sour like a motha fu &;: !
I wich I knew of a base to neutralize
Instead off LLE

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Fair warning I haven’t tried this on cannabis, but I did adjust pH in a cGMP laboratory that produced pharma grade biological.

That being said, you can try a non-nucleophilic organic bases such as DBU. I dont know of any food grade ones, but I am sure they are out there.

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Sorry to ask but what does dbu stand for :grin:


You can look at the Wikipedia page for a optimal candidate. Hopefully this helps.