| 词条 | Free base |
| 释义 |
Free base (freebase, free-base) is the conjugate base (deprotonated) form of an amine, as opposed to its conjugate acid (protonated) form. The amine is often an alkaloid, such as nicotine, cocaine, morphine, and ephedrine, or derivatives thereof. PropertiesSome alkaloids are more stable as ionic salts than as free base. The salts usually exhibit greater water solubility. Common counterions include chloride, bromide, sulfate, phosphate, nitrate, acetate, oxalate, citrate, and tartrate. Ammonium salts formed from the acid-base reaction with hydrochloric acid are known as hydrochlorides. For example, compare the free base hydroxylamine (NH2OH) with the salt hydroxylamine hydrochloride (NH3OH+ Cl−). Freebasing is a more efficient method of self-administering alkaloids via the smoking route. For example, cocaine hydrochloride decomposes at the high temperatures necessary for smoking. Free base cocaine, in which the cocaine alkaloid is "freed" from the hydrochloride salt, has a melting point of 98 ℃ and is volatile at temperatures above 90 ℃, therefore providing an active drug for smoking. After inhalation the alkaloid is absorbed into the blood stream and rapidly transported throughout the body. However, since blood is buffered with carbonate at physiological pH (near 7.4), free-base amines will be rapidly converted back into their acid form. In fact, 94.19% of cocaine will exist as the acid form under equilibrium at pH=7.4, calculated using the Henderson-Hasselbalch equation[1]{{Better source|reason=per WP:CIRCULAR|date=March 2018}} assuming a pKa of 8.61[2]. A small portion (5.81%) of cocaine will remain as free-base and pass through the blood-brain barrier; according to Le Chatelier's principle[3]{{Better source|reason=per WP:CIRCULAR|date=March 2018}} the acid form of cocaine will be continually converted to free-base as the base form is continually removed across the blood-brain barrier. Extraction kits for converting the hydrochloride to the base are commercially available.[4] Freebasing also tends to remove water-soluble impurities and adulterants such as sugars (lactose, sucrose, glucose, mannitol, inositol), which are often added to street cocaine. Cocaine freebase is only slightly soluble in water (1 in 600 of water) as compared to the high solubility of cocaine hydrochloride (1 in 0.5 of water).[5]PreparationCocaine freebase ("white tornado")[6] is prepared from cocaine hydrochloride by extracting the cocaine with an alkaline solution (sodium hydroxide or ammonia) and adding a non-polar solvent such as diethyl ether or benzene. The mixture separates into two layers, the top solvent layer containing the dissolved cocaine. The solvent is then evaporated leaving almost pure cocaine crystals, white and crumbly like feta cheese. A solution of cocaine hydrochloride can also be heated ("cooked") in a pan with baking soda added until a solid "rock" is formed, pieces of which can be smoked directly (crack cocaine).[7] HistoryThe smoking of cocaine base first appeared in the United States in 1974 and was mostly confined to the state of California. The first hospital admission for a problem related to free-basing was in 1975, the year in which extraction kits and smoking accessories became commercially available. In 1978, distribution of these accessories or paraphernalia spread from California throughout the United States. In 1979, only 1% of cocaine-related hospital admissions involved the use of free base, but by 1982 this figure had increased to 7%.[8] OtherIn South America, coca leaves are traditionally chewed with a quantity of an alkaline lime substance ("llipta") typically derived from the ashes remaining after burning plants, shells or limestone.[9] In South America, coca paste, also known as cocaine base or basuco and, therefore, often confused with cocaine freebase in North America, is relatively inexpensive and is widely used by low-income populations.[5] References1. ^Henderson–Hasselbalch equation 2. ^{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/cocaine#section=pKa|title=Cocaine|first=|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov}} 3. ^Le Chatelier's principle 4. ^{{citation | editor=John Grabowski | author=Marian W. Fischman | chapter=The Behavioral Pharmacology of Cocaine in Humans | title=Cocaine: Pharmacology, Effects, and Treatment of Abuse | series=NIDA Research Monograph | volume=50 | pages=72–91 | year=1984 | publisher=U.S. Dept. of Health and Human Services | url=http://archives.drugabuse.gov/pdf/monographs/50.pdf}} 5. ^1 {{citation | editor1=Nicholas J. Kozel | editor2=Edgar H. Adams | author=Ronald K. Siegel | contribution=New Patterns of Cocaine Use: Changing Doses and Routes | title=Cocaine Use in America: Epidemiologic and Clinical Perspectives | series=NIDA Research Monograph | volume=61 | year=1985 | publisher=U.S. Dept. of Health and Human Services | pages=204–222 | url=http://archives.drugabuse.gov/pdf/monographs/61.pdf}} 6. ^{{citation | author=Tom Dalzell | entry=white tornado | title=The Routledge Dictionary of Modern American Slang and Unconventional English | publisher=Routledge | year=2009 | pages=1052a | isbn=978-0-415-37182-7}} 7. ^{{citation | author=VV Pillay | title=Modern Medical Toxicology | edition=4th | year=2013 | publisher=Jaypee | isbn=978-93-5025-965-8 | pages=553–554}} 8. ^{{citation | editor=A. Arif | title=Adverse health consequences of cocaine abuse | publisher=World Health Organization | year=1987 | url=http://apps.who.int/iris/bitstream/10665/37270/1/9241561076.pdf}} 9. ^{{citation | editor1=Robert C. Petersen | editor2=Richard C. Stillman | author=Robert C. Petersen | contribution=History of Cocaine | title=Cocaine: 1977 | series=NIDA Research Monograph | volume=13 | year=1977 | publisher=U.S. Dept. of Health and Human Services | pages=17–34 | url=http://archives.drugabuse.gov/pdf/monographs/13.pdf}} 3 : Alkaloids|Bases (chemistry)|Drug culture |
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