Alkaloid

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Alkaloids are naturally occurring organic bases found mainly in plants and fungi. Chemical structures of alkaloids vary highly, but they can be grouped in a number of groups with similar molecular structures. Alkaloids are very biochemically active substances: they display a wide range of properties which may include neurotoxicity, medicinal or psychoactive properties. Most well-known psychoactive drugs are either alkaloids (morphine, cocaine, ephedrine) or semi-synthetic derivatives of alkaloids displaying similar properties (heroin, amphetamine and their derivates). For this reason, a significant part of alkaloid chemistry is a prime interest of cooks, and the entire area of amateur alkaloid study is often derided as cookery.

Common properties

All alkaloids display basic properties, and this is the source of their very name (Greek for "similar to alkali"). Some alkaloids are amphoteric, but most are weakly basic without any acidic properties. They are nearly universally bitter in taste. Alkaloids form salts with acids; these salts tend to be soluble in water, while freebase alkaloids are sparsely soluble, if soluble at all, though some alkaloids like nicotine are very soluble in water. Freebase alkaloids, though, tend to be soluble in nonpolar organic solvents such as hydrocarbons (hexane, toluene) and halocarbons (dichloromethane, chloroform).

These properties allow for acid-base extraction of alkaloids from plant matter or other mixtures. If an alkaloid is found in salt form, bases such as sodium hydroxide are used to treat the matter, and a hydrocarbon or chloroform solvent is used to extract the freebase. Then the solution is shaken with an aqueous solution of hydrochloric acid to extract the alkaloid as a hydrochloride salt. The procedure is repeated several times, and finally, to extract the freebase in solid form, the aqueous solution is treated with alkali and the resulting precipitate filtered out. If the alkaloid is found in freebase form in the mixture, the procedure starts with hydrochloric acid treatment.

Most alkaloids become unstable on heating and decompose, but some, such as caffeine and strychnine, can sublimate without decomposing. This method can be used to separate these alkaloids from others.

Semi-synthetic alkaloid derivatives display the same properties as natural alkaloids, which allow extracting them using the same procedure.

Projects

Handling

Safety

All alkaloids are very biologically active substances, with many of them being toxic. Some, such as nicotine and strychnine, are very potent toxins. Others are illegal drugs, and experimenting with them may lead to trouble with the law.

Storage

Alkaloids should be kept in small quantities in closed containers, in dark well ventilated areas. Alkaloids in salt form are much more stable, though they too will degrade over time.

Disposal

Alkaloids are biodegradable, so disposing them into the soil or down the drain is always an option. They can also be destroyed by strong oxidizers such as Fenton's reagent, though this is only required if the alkaloids are hazardous to organisms.

References

Relevant Sciencemadness threads