Cannabis Alchemy

by D.Gold

Isolation of Pure Cannabidiol

If completely clear THC (a clear, thin, colorless oil) is desired, it is necessary first to isolate pure cannabidiol from the chromatographed oil by converting it to cannabidiol-bis-3,5-dinitrobenzoate. This is then converted back into pure cannabidiol, which is now in the form of white crystalline prisms. The process for this operation is found on pages 456 and 457 of the Lloydia volume previously mentioned, and a description of it follows.

Cannabidiol-bis-3,5-dinitrobenzoate is made by rapidly adding 300 gm fresh 3,5- dinitrobenzoyl chloride (m.p. 68—69°C) to a mechanically stirred solution of a chromatographed hashish extract in dry pyridine at 0° under nitrogen. The mixture was stirred for 15 minutes, then warmed in a 60°C hot water bath for 30 minutes. This mixture was then poured into a mixture of 200 gm of ice and 300 ml concentrated hydrochloric acid and extracted with ethyl acetate (750 ml). The precipitate was filtered and washed with another 750 ml ethyl acetate. The aqueous phase was separated and washed with 500 ml ethyl acetate. The combined organic phases were washed with aqueous sodium bicarbonate (2 x 200 ml) followed by 300 ml distilled water and dried over CaSO4. The solvent was removed in vacuum to yield 340 gm of a dark oil. This was purified by crystallization from 1800 ml ethyl ether, yielding 194 gm of off-white powdered cannabidiol-bis-3,5-dinitrobenzoate melting at 97—101°C.

Pure cannabidiol is made by adding 220 ml of liquid ammonia to a solution of 288 gm cannabidiol-bis-3,5dinitrobenzoate in anhydrous toluene (400 ml) at -70°C in a Parr bomb. The sealed apparatus was mechanically stirred. During five hours the pressure built to 110 psi and the temperature rose to 20°C. The ammonia fumes were released overnight. The product was dissolved in heptane (400 ml) and insoluble 3,5-dinitrobenzamide was removed by filtration. The precipate was washed twice with 150 ml heptane. The heptane solutions were combined and washed with boiling water (5 x 200 ml) and the solvent removed in vacuum to yield 120 gm of a dark oil. Chromatography on 180 gm of this product on 3400 gm of Florisil and elution with 30% chloroform in hexane yielded oily cannabidiol (140 gm).

Crystallization from 30—60° petroleum ether yielded 99.2 gm white prisms, and recrystallization gave 94.8 gm pure cannabidiol.