Method for preparing high-purity cannabidiol
A method for preparing high-purity cannabidiol is characterized in that: the leaves of cannabis and top portions of the plant which account for about one-fifth of the whole plant are used as extraction sites; a technology of combined macroporous adsorption resin chromatography and polyamide chromatography is used for purification; and a mixed solvent system is used for crystallization purification so as to ensure that the yield is improved to the maximum extent under the premise of obtaining a high-purity product. The product obtained from this method contains high-purity CBD; the method has a high yield and is a simple process, and thus easy to industrialize.
1. A method for preparing high-purity cannabidiol, comprising the following steps:
(1) a solvent extraction including extracted sites of cannabis sun-dried and pulverized into a coarse powder, and extracted three times with 95% ethanol as a solvent, wherein each time the amount of the solvent is 10-20 times the amount of the powder; the extracts are combined and filtered, and dealcoholized under reduced pressure at 50° C. to 70° C. until a solution which remains is slightly cloudy, and then the solution is cooled to room temperature;
(2) a combined use of macroporous adsorption resin chromatography and polyamide chromatography including:
a first step of column chromatography using a macroporous adsorption resin as a chromatographic medium, and a column loading of 3-10 g hemp stems and leaves/mL resin; firstly, the column is eluted with 5-10 column volumes of 45-55% ethanol to wash away most highly-polar impurities and then eluted with 3-5 column volumes of 80-95% ethanol to elute cannabidiol; an eluent rich in the cannabidiol is collected, and dealcoholized under reduced pressure at 50° C. to 70° C. until a solution is slightly cloudy, and then cooled to room temperature;
a second step of column chromatography using a polyamide adsorption resin as a chromatographic medium, and a column loading is 30-50 mg CBD/mL resin; firstly, the column is eluted with 3-5 column volumes of 30-50% ethanol to wash away impurities and then eluted with 3-5 column volumes of 50-80% ethanol to elute cannabidiol; an eluent rich in the cannabidiol is collected, and concentrated under reduced pressure at 50° C. to 70° C. to obtain a thick paste; and
(3) a crystallization purification of mixed solvent including the thick paste dissolved in a mixed solvent system to prepare a saturated solution of CBD, and the solution is allowed to stand to obtain colorless or pale yellow crystals, which are filtered and dried to obtain high-purity CBD crystals.
2. The method for preparing high-purity cannabidiol of claim 1 , wherein the extracted sites are the leaves of cannabis and top portions of the plant which account for about one-fifth of the whole plant.
3. The method for preparing high-purity cannabidiol of claim 1 , wherein macroporous adsorption resin chromatography and polyimide chromatography are used in combination, wherein the macroporous adsorption resin as employed comprises, but is not limited to, HPD-417, HPD-450, AB-8, ADS-17, D-101, DM-130, LSA-7, and LSA-10.
4. The method for preparing high-purity cannabidiol of claim 1 , wherein a mixed solvent system is used as a crystallization solvent for purification, and the mixed solvent system is composed of A (cyclohexane or n-hexane) and B (ethanol or methanol) in a ratio of (1-5):1 (V/V).