Difference between revisions of "Ether" - New World Encyclopedia
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'''Ether''' is the general name for a class of [[chemical compound]]s which contain an ether [[functional group|group]] — an [[oxygen]] [[atom]] connected to two (substituted) [[alkyl]] groups. A typical example is the [[solvent]] and [[anesthetic]] [[diethyl ether]], commonly referred to simply as "ether," (ethoxyethane, CH<sub>3</sub>-CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>3</sub>). | '''Ether''' is the general name for a class of [[chemical compound]]s which contain an ether [[functional group|group]] — an [[oxygen]] [[atom]] connected to two (substituted) [[alkyl]] groups. A typical example is the [[solvent]] and [[anesthetic]] [[diethyl ether]], commonly referred to simply as "ether," (ethoxyethane, CH<sub>3</sub>-CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>3</sub>). | ||
| − | == | + | == Nomenclature == |
| − | + | === Trivial names and IUPAC names === | |
| + | |||
| + | The traditional approach has been to name the two alkyl groups attached to the oxygen atom (of the ether) and to append ''"ether"'' at the end. Examples are "ethyl methyl ether" and "diethyl ether." These are called "[[trivial name]]s." | ||
| + | |||
| + | In the [[IUPAC nomenclature]] system, ethers are named using the general formula ''"alkoxyalkane"''. For example, CH<sub>3</sub>-CH<sub>2</sub>-O-CH<sub>3</sub> is [[methoxyethane]]. If the ether is part of a more complex molecule, it is described as an alkoxy substituent, so -OCH<sub>3</sub> would be considered a ''"[[methoxy]]-"'' group. | ||
| + | |||
| + | === Primary, secondary, and tertiary ethers === | ||
| + | |||
| + | The ether may be classified as a ''"primary ether"'', ''"secondary ether"'', or ''"tertiary ether"'', depending on the substituents on the carbon atoms next to the ether oxygen. For example, diethyl ether, CH<sub>3</sub>-CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>3</sub>, is called a primary ether because each carbon atom attached to the ether oxygen atom is directly linked to only one other carbon atom. An example of a ''secondary ether'' is [[diisopropyl ether]], (CH<sub>3</sub>)<sub>2</sub>CH-O-CH(CH<sub>3</sub>)<sub>2</sub>, in which each carbon atom attached to the ether oxygen atom is directly linked to two other carbon atoms. An example of a ''tertiary ether'' is [[di-tert-butyl ether]], (CH<sub>3</sub>)<sub>3</sub>C-O-C(CH<sub>3</sub>)<sub>3</sub>, in which each carbon atom attached to the ether oxygen atom is directly linked to three other carbon atoms. | ||
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| + | <center> | ||
| + | |||
| + | [[Image:Dimethylether chemical structure.png|40px|Dimethyl ether]] | ||
| + | |||
| + | [[Image:Diethylether chemical structure.png|72px|A primary ether (diethyl ether)]] | ||
| − | + | [[Image:Diisopropyl ether chemical structure.png|71px|A secondary ether (diisopropyl ether)]] | |
| − | + | [[Image:Di-tert-butyl ether chemical structure.png|72px|A tertiary ether (di-''tert''-butyl ether)]] | |
| − | + | <br/> | |
| + | ''Top to bottom:'' Dimethyl ether; a primary ether (diethyl ether); a secondary ether (diisopropyl ether); and a tertiary ether (di-''tert''-butyl ether). | ||
| + | </center> | ||
| − | == | + | === Polyethers === |
| − | + | Polyethers are compounds with more than one ether group. The term is generally used when referring to [[polymer]]s such as [[polyethylene glycol]] and [[polypropylene glycol]]. It is also used for low molecular weight compounds such as the [[crown ether]]s. | |
== Compounds with similar structures == | == Compounds with similar structures == | ||
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** Thionoesters R'-C(=S)-O-R | ** Thionoesters R'-C(=S)-O-R | ||
| − | == | + | == Physical properties == |
| − | + | Ether molecules cannot form [[hydrogen bond]]s among each other, resulting in a relatively low [[boiling point]] comparable to that of the analogous [[alcohol]]s. However, the differences in the boiling points of the ethers and their isometric alcohols become smaller as the carbon chains become longer, as the [[hydrophobic]] nature of the carbon chain becomes more predominant over the presence of hydrogen bonding. | |
| − | + | Ethers are slightly polar as the C - O - C bond angle in the functional group is about 110 degrees, and the C - O dipole does not cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters or [[amide]]s of comparable structure. However, the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible, causing the solubility of alcohols (for instance, butan-1-ol) and ethers (ethoxyethane) to be quite dissimilar. | |
| − | [[ | + | Cyclic ethers such as tetrahydrofuran and 1,4-dioxane are totally miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to [[aliphatic]] ethers. |
| − | [[ | + | Ethers can act as [[Lewis base]]s. For instance, diethyl ether forms a complex with [[boron]] compounds, such as [[boron trifluoride]] diethyl etherate (BF<sub>3</sub><sup>.</sup>OEt<sub>2</sub>). Ethers also coordinate to magnesium in [[Grignard reagent]]s (RMgBr). |
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== Organic reactions == | == Organic reactions == | ||
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== External links == | == External links == | ||
| − | * [http://www.cem.msu.edu/~reusch/VirtualText/intro1.htm#info Virtual Textbook of Organic Chemistry.] Retrieved April 12, 2007. | + | * [http://www.cem.msu.edu/~reusch/VirtualText/intro1.htm#info Virtual Textbook of Organic Chemistry.] ''Department of Chemistry, Michigan State University''. Retrieved April 12, 2007. |
| − | * [http://www.ilpi.com/msds/ref/ether.html Ether | + | * [http://www.ilpi.com/msds/ref/ether.html Ether.] ''ILPI.com''. Retrieved April 12, 2007. |
{{Functional Groups}} | {{Functional Groups}} | ||
Revision as of 03:38, 10 June 2007
- This article is about a general class of chemical compounds. For other uses, see Aether.
Ether is the general name for a class of chemical compounds which contain an ether group — an oxygen atom connected to two (substituted) alkyl groups. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether," (ethoxyethane, CH3-CH2-O-CH2-CH3).
Nomenclature
Trivial names and IUPAC names
The traditional approach has been to name the two alkyl groups attached to the oxygen atom (of the ether) and to append "ether" at the end. Examples are "ethyl methyl ether" and "diethyl ether." These are called "trivial names."
In the IUPAC nomenclature system, ethers are named using the general formula "alkoxyalkane". For example, CH3-CH2-O-CH3 is methoxyethane. If the ether is part of a more complex molecule, it is described as an alkoxy substituent, so -OCH3 would be considered a "methoxy-" group.
Primary, secondary, and tertiary ethers
The ether may be classified as a "primary ether", "secondary ether", or "tertiary ether", depending on the substituents on the carbon atoms next to the ether oxygen. For example, diethyl ether, CH3-CH2-O-CH2-CH3, is called a primary ether because each carbon atom attached to the ether oxygen atom is directly linked to only one other carbon atom. An example of a secondary ether is diisopropyl ether, (CH3)2CH-O-CH(CH3)2, in which each carbon atom attached to the ether oxygen atom is directly linked to two other carbon atoms. An example of a tertiary ether is di-tert-butyl ether, (CH3)3C-O-C(CH3)3, in which each carbon atom attached to the ether oxygen atom is directly linked to three other carbon atoms.
Top to bottom: Dimethyl ether; a primary ether (diethyl ether); a secondary ether (diisopropyl ether); and a tertiary ether (di-tert-butyl ether).
Polyethers
Polyethers are compounds with more than one ether group. The term is generally used when referring to polymers such as polyethylene glycol and polypropylene glycol. It is also used for low molecular weight compounds such as the crown ethers.
Compounds with similar structures
Ethers are not to be confused with other classes of compounds with the same general structure R-O-R'. Some examples are given below.
- Aromatic compounds like furan, where an oxygen atom is part of the aromatic system.
- Compounds where a carbon atom next to the oxygen is connected to oxygen, nitrogen, or sulfur:
- Esters R'-C(=O)-O-R
- Acetals R'-CH(-O-R)-O-R
- Aminals R'-CH(-NH-R)-O-R
- Anhydrides R'-C(=O)-O-C(=O)-R
- Thionoesters R'-C(=S)-O-R
Physical properties
Ether molecules cannot form hydrogen bonds among each other, resulting in a relatively low boiling point comparable to that of the analogous alcohols. However, the differences in the boiling points of the ethers and their isometric alcohols become smaller as the carbon chains become longer, as the hydrophobic nature of the carbon chain becomes more predominant over the presence of hydrogen bonding.
Ethers are slightly polar as the C - O - C bond angle in the functional group is about 110 degrees, and the C - O dipole does not cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters or amides of comparable structure. However, the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible, causing the solubility of alcohols (for instance, butan-1-ol) and ethers (ethoxyethane) to be quite dissimilar.
Cyclic ethers such as tetrahydrofuran and 1,4-dioxane are totally miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to aliphatic ethers.
Ethers can act as Lewis bases. For instance, diethyl ether forms a complex with boron compounds, such as boron trifluoride diethyl etherate (BF3.OEt2). Ethers also coordinate to magnesium in Grignard reagents (RMgBr).
Organic reactions
Synthesis
Ethers can be prepared in the laboratory in several different ways.
- Intermolecular Dehydration of alcohols:
- R-OH + R-OH → R-O-R + H2O
- This direct reaction requires drastic conditions (heating to 140 degrees Celsius and an acid catalyst, usually concentrated sulphuric acid). Effective for making symmetrical ethers, but not as useful for synthesising asymmetrical ethers because the reaction will yield a mixture of ethers, making it usually not applicable:
- 3R-OH + 3R'-OH → R-O-R + R'-O-R + R'-O-R' + 3H2O
- Conditions must also be controlled to avoid overheating to 170 degrees which will cause intramolecular dehydration,a reaction that yields alkenes. In addition, the alcohol must be in excess.
- R-CH2-CH2(OH) → R-CH=CH2 + H2O
- Such conditions can destroy the delicate structures of some functional groups. There exist several milder methods to produce ethers.
- Nucleophilic displacement of alkyl halides by alkoxides
- R-O- + R-X → R-O-R + X-
- This reaction is called the Williamson ether synthesis. It involves treatment of a parent alcohol with a strong base to form the alkoxide anion followed by addition of an appropriate aliphatic compound bearing a suitable leaving group (R-X). Suitable leaving groups (X) include iodide, bromide, or sulfonates. This method does not work if R is aromatic like in bromobenzene (Br-C6H5), however, if the leaving group is separated by at least one carbon from the benzene, the reaction should procede (as in Br-CH2-C6H5). Likewise, this method only gives the best yields for primary carbons, as secondary and tertiary carbons will undergo E2 elimination on exposure to the basic alkoxide anion used in the reaction due to steric hindrance from the large alkyl groups. Aryl ethers can be prepared in the Ullmann condensation.
- Nucleophilic Displacement of Alkyl halides by phenoxides
- As mentioned above, when one of the R groups in the target ether is aromatic, the R-X cannot be used to react with the alcohol. However, phenols can be used to replace the alcohol, while maintaining the alkyl halide. Since phenols are acidic, they readily react with a strong base like sodium hydroxide to form phenoxide ions. The phenoxide ion will then substitute the -X group in the alkyl halide, forming an ether with an aryl group attached to it.
- HO-C6H5 + OH- → O--C6H5
- O--C6H5 + R-X → R-O-C6H5
- Electrophilic addition of alcohols to alkenes.
- R2C=CR2 + R-OH → R2CH-C(-O-R)-R2
- Acid catalysis is required for this reaction. Tetrahydropyranyl ethers are used as protective groups for alcohols.
Cyclic ethers which are also known as epoxides can be prepared:
- By the oxidation of alkenes with a peroxyacid such as m-CPBA.
- By the base intramolecular nuclephilic substitution of a halohydrin.
Reactions
Ethers in general are of very low chemical reactivity. Organic reactions are:
- Ethers are hydrolyzed only under drastic conditions like heating with boron tribromide or boiling in hydrobromic acid. Lower mineral acids containing a halogen, such as hydrochloric acid will cleave ethers, but very slowly. Hydrobromic acid and hydroiodic acid are the only two that do so at an appreciable rate. Certain aryl ethers can be cleaved by aluminium chloride.
- Nucleophilic displacement.
- Epoxides, or cyclic ethers in three-membered rings, are highly susceptible to nucleophilic attack and are reactive in this fashion.
- Peroxide formation.
- Primary and secondary ethers with a CH group next to the ether oxygen easily form highly explosive organic peroxides (e.g. diethyl ether peroxide) in the presence of oxygen, light, and metal and aldehyde impurities. For this reason ethers like diethyl ether and THF are usually avoided as solvents in industrial processes.
Important ethers
|
Ethylene oxide | The smallest cyclic ether. |
|
|
Dimethyl ether | An aerosol spray propellant. |
|
|
Diethyl ether | A common low boiling solvent. |
|
Dimethoxyethane (DME) | A high boiling solvent: |
|
Dioxane | A cyclic ether and high boiling solvent. |
|
Tetrahydrofuran (THF) | A cyclic ether, one of the most polar simple ethers that is used as a solvent. |
|
Anisole (methoxybenzene) | An aryl ether and a major constituent of the essential oil of anise seed. |
| Chemical structure of 18-crown-6 | Crown ethers | Cyclic polyethers that are used as phase transfer catalysts. |
|
Polyethylene glycol (PEG) | A linear polyether, e.g. used in cosmetics: |
Similar terms, dissimilar meanings
Mythology:
- Aether (mythology): In Greek mythology, aether (or ether) was the personification of the "upper sky," space, and heaven.
Early science and philosophy:
- Aether (classical element): In ancient and medieval science, aether (or ether) was thought of as a substance that filled the region of the universe above the terrestrial sphere. Aristotle considered it to be the fifth element, distinct from Air, Fire, Earth, and Water.
- Luminiferous aether (or luminiferous ether): This term, meaning "light-bearing ether," was postulated to exist in outer space as the medium for the propagation of light. From the early twentieth century, scientific theories have been formulated without the concept of this type of ether.
- Etheric plane: It was thought of as a finer grade of matter—in addition to solids, liquids, and gases—that permeates the subatomic structure of the Earth and its atmosphere.
- Etheric body: A sort of life-force body or aura that constitutes the "blueprint" of the physical body and sustains the physical body.
Modern chemistry:
- Petroleum ether: This term is used for a low-boiling mixture of hydrocarbons, although chemically it does not contain any ether.
- Thioether: This is the general term for analogs of ethers in which the oxygen atom (that characterizes an ether) is replaced by a sulfur atom.
See also
ReferencesISBN links support NWE through referral fees
- Daley, Richard F., and Sally J. Daley. 2005. Organic Chemistry. OChem4Free.com. Retrieved April 12, 2007.
- McMurry, John. 2004. Organic Chemistry. 6th ed. Belmont, CA: Brooks/Cole. ISBN 0534420052.
- Morrison, Robert T., and Robert N. Boyd. 1992. Organic Chemistry. 6th ed. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-643669-2.
- Solomons, T.W. Graham, and Fryhle, Craig B. 2004. Organic Chemistry. 8th ed. Hoboken, NJ: John Wiley. ISBN 0471417998.
External links
- Virtual Textbook of Organic Chemistry. Department of Chemistry, Michigan State University. Retrieved April 12, 2007.
- Ether. ILPI.com. Retrieved April 12, 2007.
| Functional groups |
|---|
| Chemical class: Alcohol • Aldehyde • Alkane • Alkene • Alkyne • Amide • Amine • Azo compound • Benzene derivative • Carboxylic acid • Cyanate • Ester • Ether • Haloalkane • Imine • Isocyanide • Isocyanate • Ketone • Nitrile • Nitro compound • Nitroso compound • Peroxide • Phosphoric acid • Pyridine derivative • Sulfone • Sulfonic acid • Sulfoxide • Thioether • Thiol • Toluene derivative |
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