Conversion of CBD (Cannabidiol) to THC with Anhydrous Aluminum Chloride under Various Conditions
There are several different methods for converting CBD to THC in various solvents and under different conditions. Many studies contradict each other in their data, yielding results different from those described or perhaps not detailed enough. In this case, we have examined a method for converting CBD using a Lewis acid catalyst (in this instance, aluminum chloride) under various temperature conditions with minimal equipment (one might call it kitchen synthesis).Reagents:
Cannabidiol (CBD) - 30g
Dichloromethane (DCM) - 150ml
Anhydrous Aluminum Chloride (AlCl3) - ~3g
Soda bicarb - ~6g
Sodium Chloride - in excess
Water - in excess
Ice
Equipment:
Magnetic stirrer
Beakers
Pyrex
Syringes
Reaction 1. Conversion of CBD to THC with anhydrous aluminum chloride at room temperature
1. To a beaker equipped with a magnetic stir bar and placed on a magnetic stirrer, we add 10g of cannabidiol (CBD) isolate (in powder form) and 50ml of dichloromethane (DCM). The CBD should dissolve instantly. Begin stirring, adjusting the speed to a stable rotation of the magnet in the center of the beaker.
2. Add 0.9g of anhydrous aluminum chloride in a single portion. If you do not have analytical scales, you can use approximately 1g of aluminum chloride, this will not cause a major issue. However, you must account for the amount when quenching the reaction. The reaction mixture quickly changes to a reddish color. Start a timer for 15 minutes with constant stirring. After this time, the mixture darkens slightly.
3. While the reaction mixture is stirring, prepare a sodium bicarbonate solution. You can use regular baking soda. The soda solution in water is necessary for rapidly quenching the reaction, to stop the conversion and avoid obtaining byproducts during product isolation. The amount of soda is calculated based on the amount of aluminum chloride used, as I mentioned above. In any case, we use a slight excess, for example, 2g of soda. This amount will be acceptable for both a precise calculation and for 1g of aluminum chloride. Dissolve 2g of soda in 50ml of water, place a magnetic stir bar in the beaker, and set it on the magnetic stirrer after the 15 minutes of the main reaction.
4. Add our reaction mixture containing CBD to the stirred soda solution. It is crucial to add it in this specific order to prevent the product from being degraded. Add it in small portions, but quickly, so that the mixtures have time to react, but we don’t lose too much time and avoid further conversion. During the mixing process, the mixture should start to thicken, but our magnetic stirrer will handle it. After complete mixing, stir for another up to 5 minutes and then pour in pure water (the volume is not critical, you can use 100ml or more) to separate the DCM layer containing the product as the lower layer.
5. We separate the upper wash water by decantation or using a syringe and add brine (saturated solution of sodium chloride), repeating the procedure of stirring and brine separation. You can repeat the washing operation with clean water to remove residual salt.
6. We completely separate the extracted lower layer from the water and place it in a heat-resistant dish (Pyrex) with hot tap water or water heated in a kettle. The main thing is that the water temperature should be above the boiling point of DCM or hotter to evaporate any residual water if it was poorly removed. While stirring and maintaining the water temperature, the DCM gradually evaporates, leaving a thick oil.
7. Continue evaporating the DCM until the smell completely disappears and the oil becomes transparent (this is easily visible when held up to the light). You can further ensure consumer health by repeating the procedure, adding anhydrous alcohol (e.g., isopropanol) and repeating the evaporation to extract any micro-residues of DCM. Be sure to note that the presence of transparency indicates the end of distillation. The oil will be slightly liquid, so let it cool before inverting the beaker.
Reaction 2. Conversion of CBD to THC with anhydrous aluminum chloride under heating
1. Repeat all the steps, analogous to the conversion at room temperature, but fill the Pyrex with water no hotter than 40 *C. Allow some time for the mixture to heat up while stirring, then add the anhydrous aluminum chloride, and set the timer for 15 minutes.
2. Wash analogously with solutions of soda (sodium bicarbonate), sodium chloride (brine), and water. As you can see in the photo, the mixture has a more saturated reddish color during washing, which is a bad sign. Nevertheless, repeat all steps until the complete distillation of DCM and obtaining a transparent oil.
Reaction 3. Conversion of CBD to THC with anhydrous aluminum chloride under cooling
1. Repeat the steps used in Reaction 1, but fill the Pyrex with ice, and pour brine over the ice (a sodium chloride solution retains a low temperature better). You don’t have to use ice, you can prepare chilled brine in advance in the freezer or cool the CBD solution in DCM without aluminum in the freezer. The required temperature is 0 *C or lower. During the conversion under cooling, we observe that the reaction mixture does not darken as much as it does at room temperature, and especially not as much as it does under heating. This is a good sign.
2. After 15 minutes, we wash with a solution of soda and salt as in the previous syntheses, and separate the lower layer containing DCM for evaporation. The photo shows that our mixture and extract have a much lighter color.
3. Distill the DCM in a dish with hot water while stirring until completely transparent. The photo shows some bubbles related to intense stirring in a narrow beaker, but in person, it looks acceptable – the oil from the cooling method is the purest and most transparent.
UPD:
Reaction 4. Conversion of CBD to THC with a catalytic amount of anhydrous aluminum chloride under cooling
1. Similar to Reaction 3, we employ cooling, but add a catalytic amount of anhydrous aluminum chloride, approximately 0.3g. The reaction mixture remains lighter in color during the conversion process, yet visually, the reaction proceeds just as quickly.
2. Wash the reaction mixture similarly to previous reactions, using a soda solution, water, and a sodium chloride solution sequentially. If the aqueous and organic layers separate poorly, you can add a little more DCM and use slight warming to better separate from emulsions.
3. Evaporate the DCM on a water bath until the smell completely disappears and it thickens.
Results of CBD to THC Conversions
The oil yield from all conversions is approximately the same (quantitative) relative to CBD. Losses can mainly occur during careless separation of the oil from water. In some cases, you can use additional portions of DCM for better extraction, but distillation will take longer.
Visually, the color and purity are better for the conversion done under cooling, but in my opinion, the room temperature method can also be used. The heating method is not recommended, the oil quickly began to oxidize when exposed to air. Regarding air oxidation, THC is very susceptible to it, so after preparing batches, it is best to find a tightly sealed container or store it under vacuum.
UPD:
Using the method with cooling and a catalytic amount of anhydrous aluminum chloride (0.3g per 10g of CBD) yielded the purest and most transparent THC oil of all the tested conditions, based on visual parameters. Special thanks to CristalKing for asking about the reagent proportions.
To fully understand the product quality, analytical methods are, of course, necessary. I believe that some technical cannabis steeped in the resulting oils using IPA will help conduct this analysis. Alternatively, using a vape with a temperature range from 160 to 220 *C, with triethyl citrate (TEC) as a carrier for vaporization. I would be glad if someone would join me in conducting analyses using the methods mentioned above. Perhaps the heating conditions are not optimal, but the most interesting effect will result due to the mixture of isomers.
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