Freebase or free base refers to the pure basic form of an amine, as opposed to its salt form. The amine is usually an alkaloid natural product. Free base is commonly used in organic chemistry and pharmaceuticals to describe the deprotonated amine form of a compound.
Most alkaloids are unstable in their pure form and exist instead in ionic salt form. The salts usually exhibit greater water solubility. Common counterions include chloride, bromide, acetate, oxalate and, in case of chiral amines, tartarate. Because of the ubiquity of chloride salts, formed from the reaction of the amine with hydrochloric acid, these amine derivatives are known as the hydrochlorides. For example, compare the free base hydroxylamine (NH2OH) with hydroxylamine hydrochloride (NH3OH+ Cl-).
The term "freebasing" means converting an ionic form into free base. It can refer to deprotonating the hydrochloride salt form of cocaine to free base form. The process provides for some merits of acid-base extraction. The free base is preferred for smoking because the evaporation point of the free base is further apart from the burning point compared to the hydrochloride salt, making the salt form more prone to destruction by pyrolysis. Some of the active drug is lost in the deprotonation process.
Freebasing can also refer to the consumption by smoking of free base cocaine (crack cocaine) or heroin. Freebasing became popular in the United States during the 1980s, mainly because of the fear of diseases such as HIV and viral hepatitis, since users did not have to share hypodermic needles.