# Conversion of CBD to THC

Conversion of cannabidiol (CBD) to tetrahydrocannabinol (THC) can occur through a ring-closing reaction. This cyclization can be acid-catalyzed or brought about by heating.

## Known methods

Phytocannabinoids exist like precursors to their pharmacologically active counterparts. At least three independent methods have successfully converted CBD to THC.
* Despite the CBD and THC having the same molecular weight, multiple analytical methods are able to differentiate them.
* "on the recovery of both THC (86.7−90.0%) and CBD (92.3−95.6%). The slightly lower recovery of THC can be explained by the fact that THC is less polar than CBD and more likely to remain in the nonpolar sunflower oil."

### By heat

CBD heated to 175, or 250–300 °C may partially be converted into THC. Even at room temperature, trace amounts of THC can be formed as a contaminant in CBD stored for long periods in the presence of moisture and carbon dioxide in the air, with storage under inert gas required to maintain analytically pure CBD.
* Heat is required to decarboxylate the non-psychoactive phytocannabinoid THCA to its psychoactive form, THC. Likewise, CBDA turns into CBD.
* From hemp plant material in an oven, cannabinoid concentration plots (time/temp) show THC:
* STP 0 minutes 0.20mg/g
* 140-160C 20 minutes 0.27mg/g
* 140-160C 60 minutes 0.05-0.15mg/g
* 120C 45 minutes 0.27mg/g
* 120C 90 minutes 0.20mg/g
* 100C 90 minutes 0.25mg/g
* 80C 120 minutes 0.24mg/g
Multiple oxidation products form during degradation in the presence of oxygen, a process known as thermolysis In contrast, the absence of oxygen leads to a process called pyrolysis which significantly reduces the loss.
* "...the boiling point for THC has been determined at 157 °C, and the boiling point range for CBD sits between 160 and 180 °C."

### With acid

CBD converts to various isomers of THC with catalysts in acidic environments. A wide variety of acids can be used, though different conditions result in varying yield and formation of characteristic impurities.
* Catalytic acid solution in 5 minutes in a microwave oven with a 40% THC (Δ9-THC) and 35% Δ-8-Tetrahydrocannabinol yield.
* Adding protons until the CBD sterically-hindered alcohol functional group cyclises to the pyran ring of THC.
* Lewis acids. - a continuous rather than batch implementation with similar materials
* Gaoni and Mechoulam also described a method for converting CBD to Δ9-THC comprising refluxing a mixture of CBD in ethanol containing 0.05% hydrogen chloride for 2 hours. Percentage yield of Δ9-THC (Δ1-THC) was 2%. Using boron trifluoride, the yield was 70% although purity was not given.

### With zeolite

Methods have been claimed for converting CBD to a mixture of Δ8-THC and Δ9-THC using "Zeolites selected from the group consisting of analcime, chabazite, clinoptilolite, erionite, mordenite, phillipsite, and ferrierite."

## Purification
### Δ-8-Tetrahydrocannabinol to THC

When CBD is treated with acid, Δ-8-Tetrahydrocannabinol may form as an impurity. Nevertheless, Δ-8-Tetrahydrocannabinol can be isolated and subsequently converted into THC.
* Δ-8-Tetrahydrocannabinol, which can be converted to THC by addition of HCl followed by dehydrochlorination.
* Treatment of the purified Δ8 -THC under Lucas' reagent gives the chloro compound. Following treatment with potassium tert-amylate, the desired (-)-6a,10 a-trans-Δ9 -tetrahydrocannabinol is yeilded. The Mechoulam and Petrzilka methods require three steps and involve at least two careful chromatographic separations to obtain (-)-6a,10 a-trans-Δ9 -tetrahydrocannabinol of high purity.

## In vivo
### Oral

There is a debated hypothesis that oral CBD could be metabolized into THC under acidic conditions in the stomach and then absorbed into the bloodstream. However, neither THC nor any of its active metabolites have been detected in blood in animals or humans after ingesting CBD. There is no direct evidence of the conversion of CBD to THC in the human gut; both CBD and THC are excreted unchanged within human feces.

## History

The conversion of CBD to THC by an acid based cyclization reaction was first patented by Roger Adams in the 1940s.