Isomerization of CBD to THC using citric acid
Please be safe, at least pretend you are a professional chemist when doing the experiment, wear glasses and gloves, and have a fire extinguisher handy
It is important to note that this process is designed to use readily available materials and reagents and to convert CBD to THC as efficiently as possible, both in terms of yield and time efficiency, and is not comparable to professional laboratory techniques.
Reagents.
Citric acid
CBD
Distilled water
Sodium bicarbonate or sodium carbonate
Non-polar solvent
Equipment:
Small flask (do not fill a boiling flask more than half full)
small leibig condenser (200mm will be fine)
Small pump for condenser, aquarium pump can be
Small tube to fit the condenser fitting
Small bucket to put the pump into
Heat source suitable for your flask, preferably a heating jacket with magnetic stirring
PH test strips
A scale accurate to the gram
Dispensing funnel
Isomerization.
Determine your batch size and then determine how much water you want to use. You can go as low as 1gr H2O:1gr CBD, but you can also use more water to make the mechanics a little easier. For 1g batches I usually use 5g of water, for 5g batches I usually use 10g of water.
Add the desired amount of distilled water to the boiling flask using a small stirring bar. To do this, add at least 15% by weight of water to anhydrous citric acid, food grade. (So 1g of water will contain 0.15g of citric acid, it does not matter how much CBD you use). Attach the reflux condenser to the flask and secure it with metal clips and tube clamps. Fill the condenser and leave the aquarium pump running continuously. Turn on stirring to ~75 rpm, heat to ~120C, and bring the solution to a boil. Reflux for anywhere from 4 to 12 hours, depending on the CBD/D8/D9 mix you want. The longer the reaction runs, the more D8 you get and the less D9 you get. I prefer about 8 hours. You can run small batch tests to see what reflow times will yield the product you like. If you want 100% D8, run the reaction for 10-12 hours or until the test is negative.
Post-treatment.
Neutralization: Once the allotted time is up, turn off the heat source and allow the solution to cool to room temperature. Remember, your target is insoluble in water and is a solid at room temperature. After cooling, your flask should have large chunks of solid product floating on top of the water and clumped against the flask walls. You neutralize the citric acid with some sodium bicarbonate (3 moles of sodium bicarbonate to 1 mole of citric acid). You can add the bicarbonate directly to your solution and test the pH, or prepare a concentrated bicarbonate solution and add it to your flask, it makes little difference. Test with pH paper to confirm ~7 pH (does not need to be exact, 6-8 is fine).
Extraction.
Next, in this flask, add a portion of NPS. you will need to experiment to see exactly the smallest amount you can use, but your target molecule is readily soluble in DCM or EtOAc at room temperature. for a 5 g batch, I usually use ~20-30 mL of DCM. spin the NPS and you will see that your product has dissolved. Separate the aqueous phase and discard (I do this in a separatory funnel). Wash the NPS with an equal amount of dH2O (20ml of NPS with 20ml of dH2O) to remove any impurities physically trapped/entrapped in the product. Re-separate. If the organic phase becomes cloudy, it has absorbed some water. Dry with MgSO4 until the solution is clarified again. Decant or filter to remove MgSO4.
Isolate the product.
Your product is now dissolved in the NPS. Ideally, you can extract and recycle this NPS, thus significantly reducing the cost and environmental impact. If this is not an option, you can simply heat your solution to allow the NPS to evaporate. Perform this operation in a well ventilated area
