Earlier, we discussed unknown compounds found in cannabis oil after other processes such as distillation and even decarboxylation. Don’t worry though, those unwanted side reactions can be limited with simple techniques.

Let’s #AskAnExpert how THCa and CBDa change after they are distilled and what happens to their acid groups after an acidic cannabinoid is decarboxylated.

What are distillation and decarboxylation?

We more recently reported on the production of Delta-8-THC from other active cannabinoids. The cannabis plant, on the other hand, only produces acidic cannabinoids, such as THCa.

Active cannabinoids are normally formed from acidic ones through a process known as decarboxylation. That is when the acid group falls off of the THCa molecule and leaves behind active THC, for example. But, heat is always required for this reaction.

Short path distillation apparatuses are commonly employed for cannabis oil.

Our earlier report on the production of Delta-8-THC more specifically discussed isomerization. Distillation of cannabinoids alone, however, can also cause accidental isomerization of THC and CBD.

A recommended alternative to distillation is oftentimes the decarboxylation of pure cannabinoid fractions. Yet, the number of side reactions that occur after decarboxylation compared to distillation depends on the finer points of the process. (1, 2)

CLN’s resident scientist, Dr. Markus Roggen, released a study in Chem Archive with his colleagues in November 2020 that detailed THCa and CBD-acid decarboxylation. Dr. Roggen received a Ph.D. in organic chemistry, so naturally, the paper dives deep into the technical ins and outs of the process. Their study includes an explanation as to why THCa takes far less time to decarboxylate than CBDa.

“…the hydrogen plucks the hole…”

THC acid changes after it is decarboxylated for specific amounts of time
Infrared Spectrometry can be used to perfect decarboxylation strategies and produce active and golden cannabis oil.

Decarboxylation and distillation, similarities, and differences

I called Dr. Roggen for a pedestrian explanation from an expert on the nuances of cannabinoid decarboxylation. He is also the founder of CBDV (Delic Labs) a research lab licensed by Health Canada to study cannabis and psilocybin.

Can you explain how general decarboxylation differs from distillation?

So, it’s a different processing step aside from distillation. In both cases, decarboxylation and distillation, you use heat. So, from that aspect, a lot of the same things can happen, such as isomerization.

There is one big difference between decarboxylation and distillation, which is that distillation is generally done under vacuum, or reduced pressure. So, you suck out all of the air from the system. There is nothing in the gas-phase above the THC [or CBD] and other compounds in the oil because there is no gas-phase – it’s a vacuum.

Decarboxylation is not done under vacuum, or, at least, not a very good vacuum. Therefore, you still have oxygen in the atmosphere. So, that is definitely quite important because now, we not only have heat, we have oxygen. And, that can cause other reactions. So, having oxygen [in the system] oxidizes THC, and that is when THC turns into CBN (cannabinol).

Dr. Markus Roggen

You previously mentioned the use of a CO2 environment during decarboxylation to limit unwarranted side reactions.

CBN is the oxidized form of THC, which means you need oxygen in the system to go from THC to CBN. So, therefore, under decarboxylation that can happen. Therefore, you should do decarboxylation under CO2 or nitrogen.

CO2 is often cheaper and more available in production sites. But, nitrogen would be the classic set-up you would do it under. And if you want to be really sensei, then you would do it under argon. But, that is what research centers do because [argon] is expensive. 

Dr. Markus Roggen

THCa decarboxylation
The decarboxylation of THC typically requires heat. During this process, the H (hydrogen) breaks the bond between the THC and the acid group. THC gives off pure CO2 after it decarboxylates.

So, in a perfect environment – and skipping on protonation – how does THCa change after it is decarboxylated?

Actually, the acid recombines into THC and CO2. The acid group on THCa is COOH, and carbon dioxide is COO, or CO2. So, we are actually left with one H. But, that H is needed to pluck the hole where the COOH group was initially. 

So, if you can think of it that way, then THC-acid has a COOH group and the H plucks the hole. So, there is no acid anymore.

Dr. Roggen

Thank you, Dr. Roggen. End of the phone call.

Decarboxylation and distillation will both cause Delta-9-THC to degrade into CBN as well as isomerize to Delta-8-THC. (1, 2) However, distillation does this due to the heat involved. Decarboxylation’s problem, on the other hand, is the number of other gasses in the associated atmosphere. The environment, not the acid group itself, affects the decarboxylation of THC or CBD.

To learn more details on the outcome after THCa is decarboxylated, and how to further avoid a molecular change in the wrong direction, we recommend the study Dr. Roggen conducted with his colleagues. You will also learn what molecule will speed up the reaction

Let us know in the comments if you knew how THC acid changes after decarboxylation in the comments. And, are you interested in learning about the different causes behind side reactions in distillates, such as how residual fire retardant can encourage Delta-10-THC?

Photo of CBN formulation courtesy of Dr. Roggen.


  1. He, Weiying; Foth, Paul J.; Roggen, Markus; Sammis, Glenn M.; Kennepohl, Pierre (2020): Why Is THCA Decarboxylation Faster than CBDA? an in Silico Perspective. ChemRxiv. Preprint. https://doi.org/10.26434/chemrxiv.12909887.v1 Copy citation
  2. Katrina J. Holly, Jeffrey B. Williams, M.Sc., and Kirk W. Hering, Ph.D. Nov 2020. Degradants Formed During Phytocannabinoid Processing. Cayman Chemical.

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