The solubility of the cannabinoids found in cannabis allow for them to be extracted with various organic solvents to create concentrated cannabis products. The solvents employed in cannabis processing, primarily hydrocarbons and alcohol, extract cannabinoids from cannabis plant material, while removing particulates, waxes, lipids, fats, and other dissolved impurities.
Regulation requires cannabis samples to fail quality assurance testing for residual solvents if any compound in the table below exceeds its corresponding limit.
Below is the ICH Class, GHS Classification, Exposure Limit, and Boiling Points of each solvent used in Cannabis extraction:
Acetone is a commonly used solvent that is colorless, highly flammable, and easily evaporated. Acetone has a pungent, irritating, floral odor that is reminiscent of cucumber and can be toxic in high doses. Acetone is readily soluble in a number of solvents, including water and ethanol. Acetone is found in many everyday products, such as fingernail polish. Acetone is also commonly used for laboratory cleaning.
Benzene is a liquid aromatic hydrocarbon that naturally occurs in crude oil and is responsible for the distinct, sweet, aromatic smell of gasoline. In addition to being found in gasoline, trace amounts of benzene are found in cigarette smoke. Benzene is volatile, highly flammable, and toxic. The ICH has classified benzene as a Class 1 solvent because it is a known carcinogen and environmental hazard. Despite its toxicity, benzene is used to produce various dyes, detergents, explosives, pesticides, synthetic rubbers, plastics, and pharmaceuticals. However, benzene is a banned ingredient for products intended for use in the home.
Butane is a colorless gas that has many applications. Butane is regularly used in the synthesis of butane hash oil. Cannabinoids are extracted from plant material with butane gas, and afterwards the butane gas is evaporated from the product. Impurities, such as the presence of pentane and isopentane, can arise in concentrated cannabis products if poor quality butane is used for extraction.
Isobutane, an isomer of butane, is a hydrocarbon that has many industrial uses. Isobutane is well-known in the petrochemical industry, where it is used to synthesize chemicals on a massive scale. For example, isobutane is used in the production process of high-density polyethylene (HDPE), the class 2 plastic of the ASTM International's Resin Identification Coding System. Additionally, isobutane is soluble in ethanol, ether, and chloroform. Commercially, isobutane is a common constituent of blended fuels, such as in fuel canisters used for camping. Isobutane is also contained in aerosol cans, refrigerators, and foam products. Isobutane is a colorless gas that is transported under pressure as a liquefied gas. It should also be noted that isobutane is easily ignited, and if isobutane tanks are exposed to prolonged or intense heat, then they may rupture and violently explode.
Chloroform is a common laboratory solvent that has a strong, ethereal odor. Chloroform can be used to produce certain cannabis isolates and has been used in the extraction of THC in Chinese hemp. It should be noted that chloroform is listed under California's Proposition 65 as a chemical that is known to cause cancer or reproductive toxicity.
Cyclohexane is a clear, colorless liquid that is predominantly used as an extraction solvent. Cyclohexane is insoluble in water, exudes vapors that are heavier than air, and has a sweet odor that is similar to gasoline. Cyclohexane is also used in certain industrial and commercial non-pesticidal agricultural chemicals.
Dichloromethane, also known as methylene chloride, is a clear, chlorinated liquid hydrocarbon that is primarily used in manufacturing, pharmaceutical, and food technology industries as a solvent. Dichloromethane is nonflammable, but it is volatile and its vapors act as a narcotic in high concentrations. When heated, dichloromethane emits fumes that are highly toxic. Dichloromethane is listed under California's Proposition 65 as a chemical that is known to cause cancer or reproductive toxicity. Dichloromethane can also be used to distill color additives and as a solvent to prepare hops and decaffeinated coffee, but it is currently seldom used because there is concern for solvent residue remaining in the final products.
Ethanol, or ethyl alcohol, is commonly used in the extraction of cannabinoids from cannabis. Ethanol for extraction purposes generally refers to purified ethanol, containing no more than one percent water, which is not intended for consumption. Purified ethanol often contains trace amounts of benzene, which is used to remove water. The ethanol can then be evaporated in an oven, a heated vacuum, a water bath, or any other chosen method. Ethanol is listed under California's Proposition 65 as a chemical that is known to cause cancer or reproductive toxicity. Ethanol can also be used as a co-solvent in CO2 extractions. Industrially, ethanol is used in paints, mouthwashes, perfumes, and deodorants and more than 1 billion pounds of ethanol are produced every year.
Ethyl acetate is a clear liquid, less dense than water, that has a fruity odor. Ethyl acetate is primarily used as a solvent to produce hop extracts or decaffeinated tea and coffee. Ethyl acetate is also used to manufacture artificial fruit essences.
Ethylbenzene is a pungent, aromatic chemical that is used as a solvent and in the production of other chemicals. In particular, ethylbenzene is used to produce styrene, a chemical that is in turn used to make latex, synthetic rubber, and plastic. Ethylbenzene is also used in the production of certain inks, insecticides, and paints. The EPA has classified ethylbenzene as a substance that is not known to cause carcinogenicity, because there is only limited information regarding the carcinogenic effects of ethylbenzene. Interestingly, ethylbenzene will float on water, because it is both less dense than water and insoluble in water.
Heptane is a colorless alkane hydrocarbon that can be used as a non-polar solvent. Heptane is liquid at room temperature, making it more desirable for transportation and storage than a compressed gas. Heptane smells like gasoline, and similarly to ethylbenzene, it will float on water because it is both insoluble in and less dense than water.
Hexane is a hydrocarbon that is mainly used as a solvent in the extraction of edible oils from various seed and vegetable crops. Hexane is also used in the extraction of cannabinoids from cannabis. Hexane can also be used to defat cannabis plant material before extraction with other solvents. Additionally, hexane is commonly used to extract oil from seeds in other crops, such as soybeans, peanuts, and corn. The EPA has not classified hexane as a carcinogen, because there is only limited information available regarding its carcinogenic effects. Certain low temperature thermometers may contain hexane, and hexane is also used in the production of many commercial grade glues, varnishes, and inks.
Isopropanol, or isopropyl alcohol, is a clear, colorless liquid with a strong, sharp aroma that is often used as a disinfectant due to its potent antibacterial properties. Interestingly, the disinfecting chemical mechanism of isopropanol is unknown. Isopropanol can also be used as a solvent, a topical antiseptic, and to produce acetone.
Methanol is a clear, colorless liquid that is commonly used in laboratories as an extraction solvent. Methanol also has many industrial uses, such as in the production of certain inks, resins, adhesives, and dyes. Methanol is also used in the pharmaceutical industry to produce vitamins, hormones, and various other compounds. Methanol is listed under California's Proposition 65 as a chemical that is known to cause cancer or reproductive toxicity. Methanol is poisonous and ingestion is toxic and may cause blindness. Accidental ingestion is the primary cause of methanol poisoning, so it is important to keep cannabis products and drinks free from methanol contamination.
Pentane is a hydrocarbon that can be used as a specialty solvent in the extraction of cannabinoids from cannabis. Pentane is also a component of some fuels and found in alcoholic beverages and hop oil. Pentane is clear, colorless, and a liquid at room temperature. Other properties of pentane are very similar to those of butane and hexane. Like butane and hexane, pentane is also less dense than water and insoluble in water, so it will float on water.
Propane is a hydrocarbon gas that can be used to extract cannabinoids from cannabis. Propane is a by-product of natural gas processing and gasoline refining and is not produced for its own sake. Propane is often used as a propellant and fuel for engines, barbecues, and central heating. Of the propane used in the U.S., approximately 44 percent is used in the petrochemical industry, approximately 43 percent is used commercially, and the remaining 13 percent is used for various purposes, such as in crop drying, weed control, and food aeration.
Toluene, formerly known as toluol, is an aromatic hydrocarbon that is frequently used as an industrial solvent. Toluene is insoluble in water and is listed under California's Proposition 65 as a chemical that is known to cause cancer or reproductive toxicity. Industrially, toluene is added to gasoline to improve octane ratings and in the production of nylon, cosmetic nail products, and plastic. Toluene can also be used to produce benzene.
Xylene, one of the top 30 chemicals produced in the United States, is a synthetic chemical produced from petroleum. m-Xylene is a colorless, highly flammable, aromatic hydrocarbon. m-Xylene, like o-Xylene and p-Xylene, is an isomer of dimethylbenzene and is one of the compounds known collectively as xylenes. m-Xylene is naturally found in crude oil and coal tar. m-Xylene is also produced to a small extent during forest fires. The m stands for meta, and indicates the compounds structure. Xylene is found in a wide array of products, such as cleaning agents, paints, paint thinners, lacquers, varnishes, rust preventives, cigarettes, and solvents used primarily in the printing, rubber, and leather industries. Xylene is used in the production of synthetic fibers, which are used in clothing, containers, and vacuum packaging.
Crude oil, or petroleum, is approximately 1% m-xylene, and small amounts of m-xylene can be found in jet fuel, as well as gasoline. Xylene is not exceedingly toxic and the primary concern is for potential narcotic effects. Vapors from a variety of products can produce exposure to m-xylene, such as from paint fumes and cigarette smoke, especially in buildings with poor ventilation.
It should be noted that m-xylene does not mix well with water, mixes well with alcohol, and evaporates and burns easily. Aside from contact during use as a solvent, the primary cause of exposure to m-xylene is from automobile exhaust. Contact with shellac nail polish can also leave products with trace amounts of m-xylene. m-Xylene is rapidly absorbed through skin contact and when inhaled. It should also be noted that m-xylene is fat-soluble.