Ether (anesthetic)

Diethyl ether, also known as ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor. It is the most common member of a class of chemical compounds known generically as ethers. It is an isomer of butanol. Diethyl ether has the formula CH3-CH2-O-CH2-CH3. It is used as a common solvent and has been used as a general anesthetic. Ether is sparingly soluble in water (6.9 g/100 mL). The diffusion of diethyl ether in air is 0.918*10^-5 m2/s (298K 101.325 kPa).

History
Alchemist Raymundus Lullus is credited with discovering the compound in 1275 AD, although there is no contemporary evidence of this. It was first synthesized in 1540 by Valerius Cordus, who called it "oil of sweet vitriol" (oleum dulcis vitrioli)—the name was because it was originally discovered by distilling a mixture of ethanol and sulfuric acid (then known as oil of vitriol)—and noted some of its medicinal properties. At about the same time, Theophrastus Bombastus von Hohenheim, better known as Paracelsus, discovered ether's analgesic properties. The name ether was given to the substance in 1730 by August Siegmund Frobenius.

Metabolism
A putative cytochrome P450 enzyme is believed to metabolize diethyl ether.

Diethyl ether inhibits alcohol dehydrogenase, and thus slows down the metabolism of ethanol. It also inhibits metabolism of other drugs requiring oxidative metabolism.

Applications
Diethyl ether is a common laboratory solvent. It has limited solubility in water, thus it is commonly used for liquid-liquid extraction. Being less dense than water, the ether layer is usually on top. Diethyl ether is a common solvent for the Grignard reaction, and for many other reactions involving organometallic reagents. It is particularly important as a solvent in the production of cellulose plastics such as cellulose acetate. Diethyl ether has a high cetane number of 85 - 96 and is used as a starting fluid for diesel and gasoline engines because of its high volatility and low autoignition temperature. For the same reason it is also used as a component of the fuel mixture for carbureted compression ignition model engines.

Anesthetic use
William T.G. Morton participated in the first public demonstration of ether anesthesia on October 16, 1846 at the Ether Dome in Boston, Massachusetts. However, Crawford Williamson Long, M.D., is now known to have demonstrated its use privately as a general anesthetic in surgery to officials in Georgia, as early as March 30, 1842.

Ether was sometimes used in place of chloroform because it had a higher therapeutic index, a larger difference between the recommended dosage and a toxic overdose. Ether is still the preferred anesthetic in some developing nations due to its high therapeutic index (~1.5-2.2) and low price.

Because of its associations with Boston, the use of ether became known as the "Yankee Dodge."

Today, ether is rarely used. The use of flammable ether waned as nonflammable anesthetic agents such as halothane became available. Additionally, ether had many undesirable side effects, such as postanesthetic nausea and vomiting. Modern anesthetic agents, such as methyl propyl ether (Neothyl) and methoxyflurane (Penthrane) reduce these side effects.

Ether may be used to anesthetize ticks before removing them from an animal or a person's body. The anesthesia relaxes the tick and prevents it from maintaining its mouthpart under the skin.

Recreational use
The anesthetic effects of ether have made it a recreational drug, although not a popular one. Diethyl ether is not as toxic as other solvents used as recreational drugs, such as ethanol.

Ether, mixed with ethanol, was marketed in the 19th century as a cure-all and recreational drug, during one of Western society's temperance movements. At the time, it was considered improper for women to consume alcoholic beverages at social functions, and sometimes ether-containing drugs would be consumed instead. A cough medicine called Hoffmann's Drops was marketed at the time as one of these drugs, and contained both ether and alcohol in its capsules. Ether tends to be difficult to consume alone, and thus was often mixed with drugs like ethanol for recreational use. Ether may also be used as an inhalant.

Due to its immiscibility with water and the fact that non-polar organic compounds are highly soluble in it, ether is also used in the production of freebase cocaine, and is listed as a Table II precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.

Production
Diethyl ether is rarely prepared in laboratories because of the hazards involved and the easy availability to legitimate labs. Most diethyl ether is produced as a byproduct of the vapor-phase hydration of ethylene to make ethanol. This process uses solid-supported phosphoric acid catalysts and can be adjusted to make more ether if the need arises. Vapor-phase dehydration of ethanol over some alumina catalysts can give diethyl ether yields of up to 95%.

Diethyl ether can be prepared both in laboratories and on an industrial scale by the acid ether synthesis. Ethanol is mixed with a strong acid, typically sulfuric acid, H2SO4. The acid dissociates producing hydrogen ions, H+. A hydrogen ion protonates the electronegative oxygen atom of the ethanol, giving the ethanol molecule a positive charge:


 * CH3CH2OH + H+ → CH3CH2OH2+

A nucleophilic oxygen atom of unprotonated ethanol displaces a water molecule from the protonated (electrophilic) ethanol molecule, producing water, a hydrogen ion and diethyl ether.


 * CH3CH2OH2+ + CH3CH2OH → H2O + H+ + CH3CH2OCH2CH3

This reaction must be carried out at temperatures lower than 150°C in order to ensure that an elimination product (ethylene) is not product of the reaction. At higher temperatures, ethanol will dehydrate to form ethylene. The reaction to make diethyl ether is reversible, so eventually an equilibrium between reactants and products is achieved. Getting a good yield of ether requires that ether be distilled out of the reaction mixture before it reverts to ethanol, taking advantage of Le Chatelier's principle.

Another reaction that can be used for the preparation of ethers is the Williamson ether synthesis, in which an alkoxide (produced by dissolving an alkali metal in the alcohol to be used) performs a nucleophilic substitution upon an alkyl halide.

Safety
Diethyl ether is prone to peroxide formation, and can form explosive diethyl ether peroxide. Ether peroxides are higher boiling and are contact explosives when dry. Diethyl ether is typically supplied with trace amounts of the antioxidant BHT (2,6-di-tert-butyl-4-methylphenol), which reduces the formation of peroxides. Storage over NaOH precipitates the intermediate ether hydroperoxides. Water and peroxides can be removed by either distillation from sodium and benzophenone, or by passing through a column of activated alumina.

Ether is an extremely flammable material. Open flames and even electrically heated devices should be avoided when using ether since it is easily ignited by a flame or spark. The autoignition temperature of ether is only 170°C (338°F), so it can be ignited by a hot surface without a flame or spark. The most common practice in chemical labs is to use steam (thus limiting the temperature to 100°C (212°F) when ether must be heated or distilled.

Cultural references
Recreational use of diethyl ether was portrayed in the film Fear and Loathing in Las Vegas, based on the book of the same name by Hunter S. Thompson who described its effects to that of a "town drunk in some early Irish novel", and portrayed in the novel The Cider House Rules by John Irving and in the film adaptation of the same name. An example of ether being used as a drug in the 19th century is to be found in Italo Svevo's novel Senilità (1898). One of the main characters, Amalia, a reticent spinster in her early thirties, becomes addicted to ether, falls into delirium and dies.