Advanced Refinement Techniques

by D.Gold

The translucent amber oil produced by charcoal filtering the ether phase of the extraction and isomerizing the cannabidiol present to THC contains, in most cases, between thirty and sixty per cent THC. Utilizing rather complex and exacting techniques of modern chemistry, it is possible to further refine this oil. Fractional distillation of the oil will yield a product which is up to twice as strong as the ether phase, and can be converted into nearly pure THC. Totally pure THC, a thin transparent oil, can be produced by chemically isolating the pure cannabidiol and then isomerizing it to THC. This is a very complex chemical operation and requires much sophisticated equipment and chemicals. These advanced laboratory techniques are probably beyond the reach of the starting alchemist but are important in the sense that they lead to the production of the THC of highest purity.

Fractional Distillation

Fractional distillation of the oil requires that the oil be heated to a high temperature under a reduced pressure created by a vacuum pump. This causes the THC and related cannabinoid substances to vaporize. The vapors are condensed back into an oil on contact with a cooled surface.

The desired fraction is collected by selecting the appropriate temperature and pressure for the distillation. Many of the impurities do not vaporize and are left behind in the flask used for heating the oil. The following is a description of a laboratory method for refinement of crude red oil and purified red oil from the basic extract. The work was done by Roger Adams in 1940 and appears on page 198 of volume 62 of the Journal of the American Chemistry Society.

Wild hemp, grown in Minnesota during the season of 1938, was used in the following experiments. The hemp plants were cut after flowering had begun but before seed had set in the female tops; they were stored in a room for six weeks to dry out. A fan was used for circulation and no molding was evident. One-third of the dry hemp plants amounted to stems. These were held and shaken to remove the leafy part of the plant. This clean marijuana was extracted with 95% pure ethyl alcohol. The methods of extraction are described below. Four twenty-gallon crocks, each with a capacity of 23 pounds of material, were arranged for countercurrent extraction. Each crock held 61 liters of solvent, of which 40 were withdrawn at each transfer, with 20 liters being retained by the cannabis. After the process had become uniform, the extract of crock #4 at each transfer held approximately 2 gm of solids per 100 cc. Transfers were made once or twice a day as necessary. The most concentrated extract obtained in this manner was passed to a concentrator, where most of the solvent was flashed off under vacuum. Never was the temperature raised above 50°C. The evaporation was carried out at 30°C. The concentrated solution contained 23.1 gm of solids per 100 cc 95% ethanol, and each 1 cc represented 4.13 gm of hemp.

The red oil from these extracts was obtained by the following methods: ethanolic extract was poured into a 1-liter Claisen flask with a short, wide neck and filled with glass wool until the flask was twothirds full. The temperature of the bath was

raised gradually from 90° to 140°C as the pressure was diminished slightly. The distilled ethanol was discarded, and the flask was again filled to two-thirds capacity. This process was repeated until 1600 cc of extract had been added and the alcohol removed. The temperature was then raised to 200°C, and when the last traces of ethanol ceased, the bath was lowered to 180°C and the pressure reduced to 30 mm. Care was necessary to prevent the liquid from foaming over. The temperature was raised gradually to 200°C until distillation ceased.

The bath was then cooled to 170°C and the pressure reduced to 2-5 mm. The residual product was then distilled. Much care was necessary to keep the bath at the lowest temperature at which the oil distilled evenly, since there was a marked tendency to foam. The material distilled at between 100° and 220°C (3 mm) with the bath temperature at 170—310°C. Yield 180—200 gm crude red oil.

This product was dissolved in 500 cc 30—60°C b.p. petroleum ether and extracted several times with water. The ether layer was distilled and the residue fractionated through a good column having an outside heating unit. The first fraction boiled at 115—120°C and gave a yield of 70—80 gm. The second fraction distilled at 150—175°C, yielding 25—30 gm. The material remaining in the flask was removed by dissolving in ethanol and filtering from the glass wool. The ethanol was evaporated and the product distilled from a 250 cc flask, b.p. 175—195°C (2 mm). Bath temperature was 220—270°C. Yield 90—110 gm purified red oil.

Chromatography

An advanced separation method known as chromatography may be used to remove non-active elements from the product. This involves filling a tube with a material which retains unwanted constituents of the oil. The oil is dissolved in a solvent and passed through the material. Chromatography of the hexane extract of hashish in the following formula (hexane is a solvent with

properties similar to petroleum ether) removed unwanted constituents of the oil amounting to 49% of its weight. The chromatographed extract obtained was almost totally composed of cannabinoid

elements. Alter conversion of the nonactive elements of the oil, the resultant extract will be nearly all THC. The process following is derived from the Lloydia Journal of Natural Products, page 456, vol. 33, no.4.

Isolating the cannabinoids from hashish

The National Institute of Mental Health supplied 13 kg of confiscated hashish, origin unknown. The hashish was extracted in a stainless-steel pot, using 95% ethyl alcohol at 50°C, and was stirred for five hours. A second and third extraction were then completed using 32 liters for 24 hours and 20 liters for 72 hours, respectively. The combined hexane extracts were washed with 5 liters of 50% aqueous ethanol. The solvent was then removed in vacuum at 40° C to provide a 22.9% recovery, or 3056 gm. This is shown by gas-liquid chromatography to contain 29.5% cannabidiol, 8.2% cannabinol, and 5.8% Δ9 THC. Florisil (30.5 kg) and methanol (2%) in hexane were used to chromatograph this oil. The resulting dark oil contained 50% cannabidiol, 20% cannabinol, 15% Δ9-THC,

and 15% unidentified components. Although using Florisil (40:1) provided essentially pure cannabidiol by gas-liquid chromatography, the product could not be induced to crystallize. Crystallized

cannabidiol is obtained by using the following modified procedure of Roger Adams.

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.

Conversion of Pure Cannabidiol to Pure THC

The crystalline prisms of cannabidiol are converted to pure THC utilizing a formula of Roger Adams found on page 2211 of volume 63 of the Journal of the American Chemistry Society. The following is a description of a method for producing pure THC.

Isomerizing the cannabidiol with sulfuric acid

One drop of 100% sulfuric acid was added to a mixture of 1.94 gm crystalline cannabidiol in 35 cc cyclohexane. After refluxing for one hour, the alkaline beam test was negative. The solution was

decanted from the sulfuric acid, then was washed twice with aqueous 5% bicarbonate solution and twice with water. It was then evaporated. This residue was distilled under reduced pressure to yield pure THC with a rotation range of 259° to 269°.